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冷冻食品保质期试验.pdf

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Shelf Life Testing:
{q]o#B+II)Z3I[0Procedures and Prediction Methods for Frozen食品伙伴个性空间`&H-m \1|0]\"`
Foods
-K CVLw,i#mf:{A0Bin Fu食品伙伴个性空间,xY@$o;R ? C r
Kellogg's Battle Creek MI食品伙伴个性空间NqJR-V BF1U'] H
Theodore P. Labuza
-NfQ"t)I0Dept. of Food Science & Nutrition, University of Minnesota食品伙伴个性空间S{*]vHvz
1334 Eckles Ave., St. Paul, MN 55108食品伙伴个性空间 ]x@L(hn
2食品伙伴个性空间h'k)~q1`n:r!QX
19.1 Introduction食品伙伴个性空间la'a;Nf K
The shelf life of a food can be defined as the time period within which the food is safe食品伙伴个性空间2];z0Xq7K
to consume and/or has an acceptable quality to consumers. Just like any other food,
"Jp(gpo:k7P)@"M7Q0frozen foods deteriorate during storage by different modes or mechanisms, as食品伙伴个性空间/xF.O6K$O h
summarized in Table 1. Microbes usually are not a problem since they cannot grow at食品伙伴个性空间P[6B co
freezing temperatures unless subjected to extensive temperature abuse above the食品伙伴个性空间vS c/O4wm y H
freezing point. Enzymes are a big concern for frozen foods, which can cause flavor
yd5Q6c1r#|0change (lipoxygenase) in non-blanched fruits and vegetables and accelerated
zKv-B$j;_0deterioration reactions in meat and poultry (enzymes released from disrupted食品伙伴个性空间 y$Fd C%UR f
membranes during precooking). Cell damage or protein and starch interactions during食品伙伴个性空间&e*d([;WJc@
freezing cause drip and mushiness upon thawing. Discoloration could occur by nonenzymatic
_b(`2`;b \y/j0browning, bleaching, and freezer burn. Vitamin C loss is often a major
KJdF/q-k0concern for frozen vegetables. Physical changes, such as package ice formation,
p;FP_4o o0moisture loss, emulsion destabilization, recrystallization of sugars and ice of frozen
+xjV EO-IV9X0desserts are often accelerated by fluctuating temperatures.食品伙伴个性空间6Gc8[ly;Y#EZT$m
For any specific frozen product, which mode determines its shelf life, depends食品伙伴个性空间N;Yx A.r
on the product characteristics (raw materials, ingredients, formulation), pre-freezing食品伙伴个性空间d'zc Ul#M8|l
treatment, freezing process, packaging film and processes, and of course storage
L1^|%c _*U rIJ0conditions. All of the quality deterioration and potential hazards are usually
Ntx}i0exaggerated or complicated by a fluctuating time-temperature environment (e.g.食品伙伴个性空间N,f-q4rZ3M^&H
freeze/thaw cycle) during storage. On the other hand, the shelf life of a frozen food食品伙伴个性空间XDY&A/i Y1l
can be extended through ingredient selection, process modification and change of
EO7H#e)`X0package or storage conditions, as discussed in Section 3 of this book.
Rc}r8@{~0This chapter will focus on shelf life testing of frozen foods for product食品伙伴个性空间x)Ii},|nk"\
development and market practices. Shelf life testing consists basically of selecting the食品伙伴个性空间%x4sA5rR j)~
quality characteristics which deteriorate most rapidly in time and the mathematical食品伙伴个性空间r;JC;|"q$zy
modeling of the change. Table 19.1 can be used as a reference for the selection of食品伙伴个性空间Ge7n$\Yp
quality characteristics, which depends on the specific product and usually requires食品伙伴个性空间.f6I z9uE
professional judgment. Mathematical modeling of quality deterioration will be
.E*Cq-Z.z0discussed next.食品伙伴个性空间1kw8Z7M2C?
3
oEty"c|/Xm0Table 19.1 Deterioration modes of frozen foods
5YT-DPnsX3['bw0Frozen Foods Deterioration Modes
B k5R IL!\9Fm,l0Frozen meats, poultry and seafood Rancidity食品伙伴个性空间r5~*pd9MEx|*~(Y
Toughening (protein denaturation)
-bR's$CvR6c0Discoloration
q mFc0Z \0Desiccation (freezer burn)
/D/@B4_,?+TF[1I?4D7B0Frozen fruits and vegetables Loss of nutrients (vitamins)食品伙伴个性空间gE S$H%D6k
Loss of texture (temperature abuse)食品伙伴个性空间3xN n&Ysh6Q$S
Loss of flavor (lipoxygenase, peroxidase)食品伙伴个性空间!Y?YX!wqR
Loss of tissue moisture (forming package ice)
A[6i r)EK7i0Discoloration
|vp"t1I0Frozen concentrated juices Loss of nutrients (vitamins)食品伙伴个性空间'~C+k'Q.B qv K
Loss of flavor
z| XvL\'H'SD0aU0Loss of cloudiness
x8rhH(e0Discoloration
EQ$pe2u[B:tq~0Yeast growth (upon temperature abuse)食品伙伴个性空间^;j8['F E p
Frozen dairy products食品伙伴个性空间0g!d6b6ccXT
(ice cream, yogurt, etc.)
[td%s+dn0Iciness (recrystallization of ice crystals)
KQH8iB;m|y0Sandiness (lactose crystallization)
)yH3VN;k+t"R!M,y[0Loss of flavor食品伙伴个性空间G&K8e(qK m
Disruption of emulsion system
&L1d;g"\Nu)L6D0Frozen convenience foods Rancidity in meat portions食品伙伴个性空间 my,d4RH U3G
Weeping and curdling of sauces
:o Us A?*W1p0Loss of flavor
t+e8m pVG0Discoloration食品伙伴个性空间3r"uES6we
Package ice食品伙伴个性空间g+}/r!q}/L-R'M
Frozen bakery products (raw dough,食品伙伴个性空间Cr%N1E!F:A-s
bread, croissants)食品伙伴个性空间R A5}1~Jb/C1N
Burst can (upon temperature abuse) (dough)
]gp)s/w0Loss of fermentation capability (dough)食品伙伴个性空间x4N*^'MP8v0Qc1bX?SR
Staling (becoming leathery)食品伙伴个性空间cqX&AU!]5O/rQ
Loss of fresh aroma食品伙伴个性空间ED I;EnR-nx}/Z
19.2 Modeling of quality deterioration
!eQ0_'F&E@v019.2.1 Basic equation
P"Uo1Js#D0A frozen food starts to degrade once it is produced (Figure 19.1). The rate and食品伙伴个性空间L#d(FP%i
the degree of degradation depends on both the composition and the environmental
y-b,P0D B5d0conditions during storage and distribution. In general, the loss of food quality or shelf食品伙伴个性空间7p8L1u$lgX
life is evaluated by measuring a characteristic quality index, "A". The change of quality食品伙伴个性空间w+Yv p5NO0GP5K4f*p9P+V
index A with time (dA/dt) can usually be represented by the following kinetic equation:
4H\gi2o\7R0- dA/dt = k An (19.1)食品伙伴个性空间-L~(I ur[:Ee$Y e
where k is called a rate constant depending on temperature, product and packaging食品伙伴个性空间 jOA i6J1`
characteristics; n is a power factor called reaction order which defines whether the rate食品伙伴个性空间-{c p*f#u!x3p
4食品伙伴个性空间Q_Ul%bfa
of change is dependent on the amount of A present. If environmental factors are held
M0yLjwi?2IW/Q6J b0constant, n also determines the shape of deterioration curve.食品伙伴个性空间1[~$L:IPu&h^2s
Ao食品伙伴个性空间\w Q ~4S uUT
A a
4j2O Ln%^3Y-J y g#A0b
K Z I:F4] P W g v}0c
XU:e6VQ!u_0t食品伙伴个性空间f$[/nT(x?8p
d
OK*{*l&eR0e食品伙伴个性空间ucd;jm&J E
Figure 19.1 Quality deterioration curves: a) linear; b) exponential;食品伙伴个性空间sm;A1r"U!oG
c) hyperbolic; d) quadratic; e) complex.
'IUANA%JI1[I.[019.2.2 Zero and first order kinetics
XnS$C.?R+e`H6i0Equation 19.1 can also be written as:
\6C ZYsW0f(A) = k t (19.2)
e5D9o"HL4N \0where f(A) is the quality function, k and t are the same as above. The form of f(A)
-cc7hyeT.w4yO*I0depends on the value of n. When n is equal to zero it is called zero order reaction食品伙伴个性空间(^\^'S3f/Qv)G!a
kinetics, which implies that the rate of loss of quality is constant under constant
_"xk@2B0environmental conditions (curve (a) in Fig. 19.1). If n is equal to one it is called first
Pw%F&K+H0Q/x I&Ag%l0order reaction kinetics, which results in an exponential decrease in rate of loss as食品伙伴个性空间c8];~ aj
quality decreases (curve (b) in Fig. 19.1, which becomes a straight line if plotted on a食品伙伴个性空间 @nC1N9E}2Z x
semi-log plot). These quality functions can be expressed as follows:食品伙伴个性空间/?Gg.R0Mt I
f(A) = Ao - A = kzt zero order (19.3a)食品伙伴个性空间1fA8P3c6w|b,f
f(A) = ln Ao - ln A = kft first order (19.3b)食品伙伴个性空间5Nu_;|0eK v,^D!j
5食品伙伴个性空间"Bue3Ht wp9u(M`Y
where Ao is the initial quality value. If Ae corresponds to the quality value at the end of食品伙伴个性空间;F1R@9z4FA#HN4G7oy)m
shelf life, the shelf life (q) of the food is inversely proportional to the rate
mJL7T;svl'y0constant:食品伙伴个性空间rr cRO9@,Zv
q = (Ao - Ae) / kz zero order (19.4a)食品伙伴个性空间Q!I/L \,w"J,|$tv
q = ln (Ao/Ae) / kf first order (19.4b)食品伙伴个性空间+^cF+I `5KD6Sw
It should be noted that most chemical reactions leading to quality loss in frozen
X F6EE,o0food systems are much more complex. However, the reaction kinetics can be食品伙伴个性空间.Y[mRo v
simplified into either pseudo-zero order or pseudo-first order kinetics. In the case of
q\ly7b-}K0complex reaction kinetics with respect to reactants, an intermediate or a final product
t%z8R#P{0(e.g. peroxides or hexanal in lipid oxidation ) could be used as a quality index. There食品伙伴个性空间5xU6y'bt_,y6g
are few cases where neither zero nor first order kinetics apply. Curve (c) in Fig. 19.1
)FVI6n vH/v._wkp0shows the degradation curve for a 2nd order reaction (with single reactant), which also
.Gv5o|jj8J0shows a straight on a semi-log paper. A fractional order should be used to describe食品伙伴个性空间&{*wxWe)k:].Q$V|:u
the curve (d) in Fig. 19.1.食品伙伴个性空间*In][#l e&S
Sometimes, there is an induction period or lag time before the quality食品伙伴个性空间+W)cZ~oY I
deterioration begins (e.g. browning pigment formation in the Maillard reaction or a
%D L(U pY p/k0microbial growth lag phase, as shown in curve (e) in Fig. 19.1. The length of the lag
J QF#AFn.H%~^f[V0depends on many factors, but temperature is a predominant factor. Given this,
*KA |e0MH7nsp0modeling of both the induction or lag period and deterioration phase are necessary for食品伙伴个性空间)Y ]R So,v&L+h](R
accurate prediction of quality loss or shelf life remaining. An example of such work has食品伙伴个性空间e0]RTC
been demonstrated by Fu et al. (1991) for the growth of bacteria in milk.食品伙伴个性空间A)g#j)ir[
In certain circumstances (e.g. A represents a sensory hedonic score), a nonkinetic
-g`k5q|2U0approach, e.g. a statistical data fitting technique can also be used to describe食品伙伴个性空间Q:c*R:t,rqN
the deterioration curves. Varsanyi and Somogyi (1983) found that the change in食品伙伴个性空间'J!P/K^Gf w r
quality characteristics as a function of time could be approximately described with
]a7])H/}z0linear, quadratic and hyperbolic functions and that storage temperature and packing
b qM+@:M I!QwL0conditions affected the shape of the deterioration curves. However, the parameters食品伙伴个性空间rS G'xurG)c8`x
determined by data fitting are difficult to use for prediction under variable storage
"Sk,L6Qi*cP;dQ8d%@0conditions except for the linear curve.
K5e ^T6E019.2.3 Temperature dependence of deterioration rate
"K:V8h C%m6i\J019.2.3.1 Arrhenius kinetics食品伙伴个性空间eE/s X S?)Hb/}
Once a frozen product is made and packaged and starts its journey from the食品伙伴个性空间 ?m#oz?Zgo8{,P
manufacturer's plant to warehouse, distribution center, retail store and finally食品伙伴个性空间rl+h1IV/{ IH2I;k
6
T)] t+h&GR-`{0consumer's freezer, the rate of quality loss is primarily temperature dependent食品伙伴个性空间6[q]Z4T9~f
(Zaritzky, 1982). The Arrhenius relationship is often used to describe the temperature食品伙伴个性空间T$m}b};H(G
dependence of deterioration rate where for either zero or first order:
:BDG[ `O^0j0z&c$U0k = ko exp (-Ea/RT) (19.5a)
9Iww!HODX/qy:N0or ln k = ln ko - Ea/(RT) (19.5b)食品伙伴个性空间o)i$}0w)hbaH%w
where ko is a pre-exponential factor; Ea is an activation energy in cal/mol; R is the gas食品伙伴个性空间EAi[x*M\
constant in cal/mol K and equal to 1.986; T is an absolute temperature in K (273 + °C).食品伙伴个性空间/C|E"{wWr
Thus, a plot of the rate constant on semi-log paper as a function of reciprocal absolute食品伙伴个性空间'dzNoW
temperature (1/T) gives a straight line as shown as Fig. 19.2. The activation energy is
[m }4n5_`0determined from the slope of the line (divided by the gas constant R). A steeper slope食品伙伴个性空间'`b.w Z6t1Sw9N
means the reaction is more temperature sensitive, i.e., a small change in T produces
]P1Qf7|RZW0are large change in rate.食品伙伴个性空间#u:eK5lN!q`3I W8V5U
Figure 19.2 Arrhenius plot
1Pw y| D)CY'ii`X0ln k
t8YW&th#mk;~01/T
7B,cs(fr5w k(t%b-c [0slope = -Ea/R食品伙伴个性空间us3k-z9v!O0C1z](N*G0j:ga
Thus, by studying a deterioration process and measuring the rate of loss at two食品伙伴个性空间 M,U#chD4e)v)N X
or three temperatures (higher than storage temperature), one could then extrapolate
%K*B SqN6f Jd@6^0on an Arrhenius plot with a straight line to predict the deterioration rate at the desired食品伙伴个性空间Na"`6MQy(A
storage temperature. This is the basis for accelerated shelf life testing (ASLT), which食品伙伴个性空间 cQ1w3e#MO9@ ]_8c
will be discussed later. One should note however that in some cases a straight line食品伙伴个性空间.{/mXx*~_#{&J
will not ensue for a variety of reasons, especially if a phase change occurs (Labuza食品伙伴个性空间qr9P0y F S
7食品伙伴个性空间7tM6c7]x|.`?BM r&@
and Riboh, 1982). Thus for frozen foods, extrapolation from temperatures above 0¥C食品伙伴个性空间a[.H p z!R
are meaningless for shelf life prediction.
2G'_V ?&T8j019.2.3.2 WLF kinetics食品伙伴个性空间C_/K.S#@s:q:_
Besides the Arrhenius equation, another popular equation at least in the more recent食品伙伴个性空间5\Q#M h%G M5xO
food literature, is the Williams Landau Ferry (WLF) model (Williams et al., 1955). Its食品伙伴个性空间)vSoD*P]@.JR
original form was based on the variation of the viscosity in the temperature range
uG Pj6~6q mB-Vo0above Tg as addressed in Chapter 3. When the rate constant at Tg' is substituted for Tg食品伙伴个性空间 }a*k&Bc:[&jqQ~N;H
(Tg' is the Tg of a maximally freeze-concentrated system), the WLF model can be
9@#H { |'kvh"c:W2D0written as follows:食品伙伴个性空间CTY'e qM
log (kT/kg) = C1(T-Tg')/[(C2+(T-Tg')] (19.6a)
6Lx1E@!`N!k_4HG'x0or [log (kT/kg)]-1 = (C2/C1)/(T-Tg') + 1/C1 (19.6b)食品伙伴个性空间+zX;f7@Qi
where C1 and C2 are constants. Thus a plot of [log (kT/kg)]-1 vs. (T-Tg)-1 will be a
5Kw7~&j)e;Y`|$s0straight line with the slope equal to C2/C1 and the intercept equal to 1/C1. As can be食品伙伴个性空间 _6gvT}2`
seen this is a two parameter temperature dependent model as is the Arrhenius食品伙伴个性空间R \ ` H1l vz(rR0u
equation.
.y:Q yKo y[4D0Frozen foods stored below Tg' are stable to ice recrystallization and other食品伙伴个性空间4[ OZb'a!n
physical changes. Levine and Slade (1988) postulated that stability is related to the
0l)r}_:eKi0temperature difference between storage temperature and Tg'. This cryostabilization of食品伙伴个性空间 Bz%I)ieZ4|
foods assumes stability below Tg' and rapid decrease of stability above Tg' according食品伙伴个性空间}"hR~Y!_l
to the WLF relationship, exhibiting an increase in reaction rate, much higher than食品伙伴个性空间"t+O3V2ie3B4N
expected from the Arrhenius kinetics. However, this may not be true since the rate of
,Z4YzA+m&S0chemical reactions can be expected to be influenced by temperature increase in a
3S HghT9J3[0complex way: (i) an increase of the rate constant, resulting from both the viscosity
K"u;F,qvF?0decrease and the increased molecular mobility (Fennema 1996); (ii) a decrease of the
1L5G:jC"YU\;Q0reaction rate as a consequence of the increasing dilution of the reactants Roos et al.
$T~zwL)Ey0(1996). For these reasons, it seems that the WLF model over predicts the temperature
g[G$@_ iKEic0effect of rate constant (Simatos et al., 1989). As noted by Nelson and Labuza (1994),食品伙伴个性空间 uA}zu)O?6LIE4~
because of the small temperature range over which foods are stored, e.g., about D30°C
W(aZU C3m0for dry foods and D20°C for frozen foods, both the Arrhenius and the WLF model give食品伙伴个性空间#C)~9`?Kz [2dR I
good correlations as long as one does not use the universal coefficients suggested by
Y9qH;F"`!nWT6?E0Slade and Levine (1991). In fact as shown by Nelson and Labuza (1994), their use of食品伙伴个性空间#q z,df'A{ }VF
the Lim and Reid (1991) data for enzymatic activity in the frozen state as shown in 19.3食品伙伴个性空间@;K"\3hMm!CD1i+B
is not proof that the Arrhenius relationship does not apply, WLF was assumed because
5[o ?'kS~qA:aR0the rate was negligible below -10°C which was the measured Tg. But as seen in食品伙伴个性空间(l _G5b\}Na!s gb
8食品伙伴个性空间|~:O h~}?
Figure 19.3b if the data is plotted as Arrhenius plot an r2 of 0.999 ensues. The食品伙伴个性空间lGJ(_` j-M_M:P ?3FY
challenge in applying the WLF model for stability or shelf life prediction is that (1) Tg is
6s:z5T1_v6k5A0LG'b0not known; (2) Tg is difficult to determine; and (3) the universal coefficients of Levine食品伙伴个性空间(P u%Z4q]Sa"TgAw
and Slade (1986) are not applicable.
5bnH f/e8xp00 50 100 150 200 250食品伙伴个性空间5Q)O3kmKp
0
\:O5JI?m,\ k5q01
t2UmUr.\02
3s_+EW(e4B03
g%IHc}04
q3S"A,AW7_ yzJ05
{F ^2i"wj)z!AEK0-3.5食品伙伴个性空间&}Su `5z
-5.5
+H?9Dm-\"I0-8.5
Q1o8lT_.v;z"v#JP0-13食品伙伴个性空间yQ8wx*XArc1x:|
-19
:Y/T@!D4Dij"c0Time (hours)食品伙伴个性空间&}5x'LTCp,y*_:C4}
Relative absorbance食品伙伴个性空间 L6dl3b'lR:p_O n
Temperature (°C)
g/p,B:t(r r1fC/s9k00.0037 0.0038 0.0039
Rd4YSh#c6y0-4食品伙伴个性空间\iW:OVE"z(j!]6d
-3
`!F7Ba(n-h8M0-2
fi*s*fw)RK4h|0-1食品伙伴个性空间 SLfIMPH
0
"p(sDD+j6J/~01/T (K-1)
&qn#K4rk rzk$C0ln(k)
"g/e-w"JKiE u0y = 79.497 - 2.1621E+4x R2 = 0.999
o2J*~-T.LO0Figure 19.3 Hydrolysis of maltodextrin in the frozen state (Lim and Reid; 1991)
Q m'O6M-O0a. Rate as a function of temperature (Note Tg is -10 ¡C)食品伙伴个性空间i0Y$ZW_ ^ k
b. Arrhenius plot
fK+c `g)e019.2.3.4 Shelf life model
g R Nx(|qk0Most published data related to quality deterioration do not give rates or rate constants食品伙伴个性空间 p/K%~5Hx p:ym!^
but rather are in the form of an overall shelf life (end-point analysis) as a function of
2~%i\-m5Y[0storage temperature. Since the temperature range used is usually quite narrow, the
9i%A h1T]X:e7D0following exponential relationship exists between shelf life and storage temperature:食品伙伴个性空间2E$kT$g'o FbI
q = exp(-bT+c) (19.7a)
5?&jm+G4yI k0or ln q = -bT+c (19.7b)食品伙伴个性空间hCN:gnYF+B
where q is shelf life at temperature T in °C, b is the slope of the semilog plot of q vs T食品伙伴个性空间#] m [ W^H Q+u y
and c is the intercept or reference temperature as shown as Fig. 19.4. Practically, this
6^? W0\+x3M,s7g0is used frequently for shelf life determination and prediction due to its simplicity and食品伙伴个性空间p9Jw'fY-L%X
straightforwardness.
w.zz:[7`09
FC"HL)p x0Figure 19.4 Shelf life plot
b3v)p]Z#`.v c0ln q食品伙伴个性空间 FG;m~X6p n oc
T
JuLe'S`$C@019.2.3.4 Q10 or q10食品伙伴个性空间1|p1O ^1V
The Q10 approach is also often used for estimation of the temperature acceleration of
~bH*X2^2l g0shelf life, which is defined as :
+S+Q]A/?\/{0\5Y0Q10 = rate @ T1+10 °C / rate @ T1 (19.8a)食品伙伴个性空间-U~6^ R cWN
Q10 = shelf life @T1 / shelf life @T1+10 °C (19.8b)
!@FZ bP kd0Q10 = (q10)1.8 (19.8c)食品伙伴个性空间$L!J7v]2b-baY3V
where T1 is temperature in °C. If the temperature unit is in °F, then the term q10 is食品伙伴个性空间^;NmGVc
used, which in fact is more often used than Q10 in the frozen food literature.
J.y[-}D8q6W-t0The magnitude of Q10 depends on the food system, the temperature and the
cOX3C^&a0absolute range. Q10 values from 2 up to 20 have been found for frozen foods (Labuza,
,Q0t Gn@ygu01982) Labuza and Schmidl, 1985. Q10 can be shown to be related to the Arrhenius食品伙伴个性空间cj!D;q#E8B!_1|,c
equation and the shelf life model through the following expression:
BSt8|&aYpa0Q10 = exp [10 Ea/(R T (T+10)] (19.9a)
3W5`]'n9GD$C(io#Q0Q10 = exp (10 b) (19.9b)
M~!qD{1B0Thus Q10 is not constant but depends on Ea and the absolute temperature T.
a*lb;et4^B0Some data gleaned from July (1989) and Labuza (1982) is shown in Table 19.2.食品伙伴个性空间nV.w%S%?b'\/PX
10
7ia.q7DG3jF W0Table 19.2
EX&@G!L0a,t#]B6]i0Estimate of the Q食品伙伴个性空间0\%SSK ]WHZ
10
I&Dy.B5^;EX Z0for shelf life of selected frozen foods食品伙伴个性空间?L/H%X7}l(\ j
Days of HQL食品伙伴个性空间 ?5q T-bhF
I te m - 10°C - 20°C Q 1 0
s(~Q/o,yp[ Po0pork sausage 20 120 4食品伙伴个性空间A+p{;@-O3E'I
pork 50 400 8食品伙伴个性空间:E7c tih5O*XC
beef 60 200 3.3
[p3l'F+JV0ground hamburger 250 800 3.2
y GPD2]Na0fried hamburger 35 250 7
"z#v,g1wT9|0raw poultry 200 700 3.5食品伙伴个性空间 wn?6{3IQ6P3]
fried poultry 25 700 3.2食品伙伴个性空间B/YB nGbIQ!OI {
fatty fish 7 60 9
!W!dI[Q!R.rtz [019.2.3.5 Other models
Z!M+g9f^@[Z)S,\0The following models have also been proposed to describe the temperature食品伙伴个性空间Hx}R!fK#s5@4Y
dependence of the rate constant (Kwolek and Bookwalter, 1971) for frozen systems:
@*UtVt*X3@0kT = a + b T (19.10a)
BU8W9D ]3T0kT = a Tb (19.10b)食品伙伴个性空间? Q+R }uj9o+U
kT = a / (b - T) (19.10c)
$S4y'i$qj+M&W9V0where a, and b are constants. In most cases, Equation 19.10c fits data better.
GL2n8lZ#I0However, all these have very limited practical application.
$I-s%XaxI9Og?@`019.2.4 Time-temperature tolerance食品伙伴个性空间;Nm3H}4t.B
Frozen foods are often exposed to a variable temperature environment, e.g. during食品伙伴个性空间I\'xh.fFz{F
distribution or due to freezing/defrosting cycle in retail or home freezers. In general, the
x}D:_ ?y:zC a'F0value of the quality function, f(A), at time t under changing environmental conditions
Xr'|W2V0can be estimated from:食品伙伴个性空间u s u1B3Bm8{D_+p
f(A) = ò k[T(t)] dt (19.11)食品伙伴个性空间X$`p#li0Xs
where T(t) is the temperature as a function of time. The form of f(A) depends on the食品伙伴个性空间,E!k.Fqz}
reaction order as discussed previously. If an effective temperature, Teff, is defined as
"N3n8{*eA_LS011
c~/Pe&F ~ HX0that constant temperature exposure which causes the same quality change as the
1S,P? {"y&i Ht&c&HH0variable temperature condition, as proposed by Schwimmer et al. (1955), then
*J0A Tp!G~ i:u4B0f(A) = keff t (19.12)食品伙伴个性空间Rh4N`aj7h
The rate constant at that defined temperature is termed the effective rate constant, i.e.食品伙伴个性空间 F8~E[N'B(K
keff. To estimate the quality change under variable temperature conditions, one食品伙伴个性空间OU.@1FBgr\c
needs to either solve for f(A) numerically or know the value of Teff or keff that
L@:i1oHC(F:U0corresponds to the variable conditions.食品伙伴个性空间W9` __g
The numerical approach for a randomly variable temperature history is
8x A6])of*`0essentially the same as the Time/Temperature/Tolerance (TTT) approach initiated by
0@N0r7e,o8K.G0Van Arsdel et al. (1969) and derived empirically in the 1960's for the prediction of shelf食品伙伴个性空间}}7O!KR
life of frozen foods (July, 1984). It is assumed that the temperature history of the食品伙伴个性空间G(L~6a8H
product is known. Thus the fraction of shelf life consumed, fcon, was calculated as the
$NZl?2{TG/b0sum of the times at each temperature interval, ti, divided by the shelf life at that食品伙伴个性空间FrN'[(r,b5D
temperature, qi:
"z?1J*y!v[;]0fcon = S (ti / qi) (19.13)
^}1B]U,_$h9Q0Thus the remaining shelf life at a reference temperature is equivalent to (1-fcon)*q.食品伙伴个性空间;ao%j%y8y
Equation 19.13 assumes that the rule of additivity is valid for frozen foods (July,食品伙伴个性空间Yu^*T%O%WL/Z"s
1984), which means that the loss of remaining storage life or quality can be calculated
#@,{/vOm0from knowledge of the prior time-temperature episodes the product has been exposed食品伙伴个性空间:L Z:LUin
to. This also implies that the prior sequence of the time-temperature episodes is of no食品伙伴个性空间IR? a8D
importance except to calculate the amount of quality remaining up to that time, i.e.食品伙伴个性空间.L!BBft*r` KV
there is no history effect. If the rule of additivity is valid with reasonable accuracy, the
l? d/r:P2u0use of time-temperature integrators (TTI) should provide reliable results with respect to
+o [ t1m$CqLf0prediction of shelf life remaining, which will be discussed later.食品伙伴个性空间7~@"oh,e"JW`
However, there are some cases where the total effect of various temperature食品伙伴个性空间@j;Ha.I*{'DP*FE8Z
experiences may not be independent of the order in which they occur or of the nature食品伙伴个性空间^5Xo4@v:s2@
of temperature history. For example, widely fluctuating temperatures may cause
I%q:rH0Z0freezer burn or in-package desiccation, which is not additive (July, 1984). Where the
Z!kV#h![2C q P0colloidal nature of a product is affected, the effect of time-temperature history may not
d0|~#eH s ^0be additive either, especially with a freeze/thaw cycles. This is also true when growth食品伙伴个性空间2Q ^8]su Cw1cm
of microorganisms occurs (Fu et al., 1991). Certain chemical reactions, enzymatic as食品伙伴个性空间 Jc_\l
well as nonenzymatic, could even proceed more rapidly at temperatures below食品伙伴个性空间(nHz7| k6GjHn5D
12
SuA3~z$v7`5o*@{}E0freezing. This is called a negative effect of temperature (Singh and Wang, 1977),
6R'P dp_x0which could be caused by one or more of the following factors: (1) a freeze
Aaf3cW0concentration effect; (2) the catalytic effect of ice crystals; (3) a greater mobility of
4|/g1C4io2j;D `8B(I0protons in ice than in water; (4) a change in pH, up or down with freezing; (5) a食品伙伴个性空间/V5J.z2a6g%I'M;Y
favorable orientation of reactants in the partially frozen state; (6) a salting in or out of
w x UC mS0proteins; (7) decrease in dielectric constant; and (8) the development of antioxidants at食品伙伴个性空间p"Ibq)w*t9W\Th%g2k
higher temperatures. As has been shown by Fennema (1975), the freeze
OQl9cOU*p4y0concentration effect can cause rates of chemical reactions to increase dramatically just
n'q zL*d0below the freezing point (Figure 19.5), e.g. ascorbic acid loss at -3°C can be faster食品伙伴个性空间d(N3C7q&H }`5d~C
than at higher temperatures this one should not use data in the -4°C to 0°C range or
9q{)DB"or0above as part of an accelerated shelf life test to predict rates at lower temperatures.食品伙伴个性空间T-h!a(k%PC
Fennema (1975), showed that the time to 50% loss of vitamin C in broccoli was 44
2G&D~2^&u:X{!\ Q0days at -5°C, 120 days at -2°C and 162 days at +2°C. This concentration effect is
a[ ] @#t0evident in the shelf life plot of frozen strawberries as shown in Fig. 19.6 using the data
})Ce'b9m[4aY(z]0of Guadagni (1968). If the data collected only at 25 and 30°F (-3.9°C and -1.1°C) are
u/]&X~.G O1X(Y0used, the predicted shelf life at 0°F (-17.8°C) is over 27 years, if data are collected at食品伙伴个性空间PMAq%Z
only 20 and 25°F (-6.7 and 3.9°C), the shelf life predicted at 0°F is 40 days while data食品伙伴个性空间-m b$X2_gh
below 20¥F extrapolated to the true expected shelf life is about 280 days.食品伙伴个性空间)_S2gg"RL
Figure 19.5 Rate of chemical reaction as a function of temperature
I_:U \*Towox0above and below the freezing point of a food.
'U'C5g3gr L0z013
g_kB~/s{%p0Figure 19.6. Shelf life plot of frozen strawberries showing the
pqj^+W4z0influence of the freeze concentration effect just below the freezing
Y/C#RZ,Ee0point on prediction of shelf life at 0¡F . Data from Guadagni (1968).
,| r rZ ^3f0Each line represents a regression through a different selected set of食品伙伴个性空间R_&D%j^+Q f
temperatures.食品伙伴个性空间6F+m5sV-{.[
The response ratio of the food to changes in environmental temperature (RT) is食品伙伴个性空间-TtS&p&xq&xjsA
dependent on the fluctuating temperature conditions as well as the heat transfer食品伙伴个性空间IdiQhmNA1x-W
properties of the food as well as the package (Cairnes and Gordon, 1976; Dagerskog,
SW&L7y;`k]3u01974). In the analysis of food shelf life, an inherent assumption is made that the food
6Vl-L5tk%skk0is responding instantaneously to the environmental temperature changes, i.e., RT = 1.食品伙伴个性空间K.Ifbi
This may be acceptable if a surface deterioration process is the deterministic factor for
6fBq/yys ? L9v,x#TX0shelf life, e.g. mold growth in some foods. Freeze-defrost cycles generally can be食品伙伴个性空间1s0P;GE,q(e1h
considered as sinusoidal oscillations. The amplitude of the effect is reduced inside the食品伙伴个性空间F?8o${Ze"A
package by some factor thus RT. < 1. It can be expected that the shorter the period of食品伙伴个性空间;xCbh \j:nQ1@
the ambient variation the smaller the RT, and hence the smaller the amplitude of the食品伙伴个性空间+Uu%RN2K O2j4\
cyclic temperature variation in the package. Zuritz and Sastry (1986) also studied the食品伙伴个性空间m1\)w0j8e,L
effect of packaging materials on temperature fluctuations for frozen ice cream and食品伙伴个性空间U W"rP HNA7i`5t5]
found that packaging materials coupled with a layer of stagnant air were effective
w)v7SIFe z7F0barriers against thermal fluctuations.
6}u,x]#^||$jf019.2.5 Hazard function
}u~6K,qyq3J*~014
s?#v!Z~]c e0After the product is produced, it may fail at any point in time in accordance with its life
"\FQ.K R5nk*j0distribution (Nelson, 1972). The hazard function h(t) of a distribution is defined for t ³ 0
6m$D+@ E*Y4p mz0by:
0X|/}+C wg%I1n0h(t) = f(t)/[1-F(t)] (19.14)
vyW)Y}rMu:c0where f(t) is a probability density function and F(t) is a cumulative distribution function.食品伙伴个性空间2w5W`)eR;|@]m0P9h.J
The h(t) is the conditional probability of failure at time t, given that failure has not
K\ b YH0occurred before ..食品伙伴个性空间jME uDH Vd
The behavīor of a hazard function for studying the shelf life of food products can食品伙伴个性空间r5k7E i1d
be easily understood by examining the "bathtub" shaped curve in Fig. 19.7. Note that
*So.Dc]0at time to, a frozen food product begins its journey to many distribution outlets for食品伙伴个性空间vh#b n(L
consumption. During the time between to and t1, early failures may occur owing to a食品伙伴个性空间5m&{jj(qu
failure in the process itself, faulty packaging, extreme initial product abuse, and many
0{'c/U{3sZ0other environmental stresses to which the product is subjected. Early failure should not
*|$DZW!dp6K_/c0be taken as a true failure relative to the shelf life of the product unless it represents the食品伙伴个性空间}UQT7W
normal condition. From t1 to t2 one can expect, barring chance major temperature食品伙伴个性空间r] { t _uN-[_
fluctuations, no failures. This interval represents the true period of the product's
I9}]a;T3z z$H9a)T0stability. The failure rate is almost constant and small during this time. The hazard or
HNpf)maw#y3b0failure rate increases from time t2 to the termination point t3, owing to the true
l7^0sb;V/Z7}0deteriorative changes occurring within the product. The concept of hazard function is食品伙伴个性空间(s!{n-~Q5\
important in the analysis and interpretation of the failure times of a product.食品伙伴个性空间-s%I^~Z%]Y*Q3@e
Time
?n-I;\t F%I0to t1 t2 t3
et8H _,ANV0Early食品伙伴个性空间t4_*Q.os0\%d K
failure
cn'O4y|%@Vv/Yc0Period of product stability
X)]m H;i }@&~0Failure due to食品伙伴个性空间1Y8|*PN:K]T
product食品伙伴个性空间A;QE)qiZ
deterioration
\eVw ^H0Figure 19.7 Failure rate as a function of time食品伙伴个性空间|N(`$p5~"R
15
.}CxG PHi!I0A fundamental assumption underlying statistical analysis of shelf life testing is
M!X(lf ^w(e,k.j)d@#i0that the shelf life distribution of a food product belongs to a family of probability食品伙伴个性空间1rN2M6R a:RDh4m\
distributions and that observations are statistically independent. Parameters of a shelf
3C{4I E5P(b0life distribution are estimated by use of shelf life testing experimental data. Once the
$XC]7J [0parameters of a shelf life model have been estimated, it can be used to predict the食品伙伴个性空间*^3y!CD:v8\e
probabilities of various events, such as future failures (Nelson, 1972). Five statistical食品伙伴个性空间y{6r]:v&W#Q%s"Y gz
models, normal, log normal, exponential, Weibull and extreme-value distributions食品伙伴个性空间S3oG I2`+L6yX4v
were tested for a few food products (Gacula and Kubala, 1975; Labuza and Schmidl,食品伙伴个性空间)Y)F*t,T$Xz v|{X
1988) and it was found that the Weibull distribution fits best, which will be
?~i hk4e0demonstrated later.
,aS StIM hs?019.3 Shelf life testing — overall aspects食品伙伴个性空间r&a9U!x(V%mG
19.3.1 Purpose食品伙伴个性空间 _Q \-]G*nm$SX
In the development of any new food product including reformulating, change of
+u o/lC9n2@'CE0packaging or storage/distribution condition (to penetrate into a new market), one
K,X1wS;]/W0important aspect is the knowledge of shelf life. The shelf life of a food product is vital to
%~ lh oP3W0its success in the marketplace. This life must at least exceed the minimum distribution
4}'H8\%w(Zt$t0time required from the processor to the consumer. Shelf life testing can assess
wt^'_4P0problems that the product has in the development stage, following a "fail small fail
&^|f/MY N1ha0early" philosophy, thereby eliminating large disasters later. Marketing/brand managers
F PGt2i!N0also need reliable shelf life data to position the products and to establish the brand.
Xs4A5RX~ {-yLd0Periodic determination of shelf life help to provide assurance that the product remains
G/l"@ O#kGu0consistent over time with respect to quality.
v]0X6p RO0Different shelf life testing strategies are necessary at different stages, as食品伙伴个性空间pV?J$R~ZJ
illustrated in Fig. 19.8. If the objective is to identify whether pathogens and spoilage食品伙伴个性空间P1@,\p;p af7s~q g#YX
microbes will grow in the case of temperature abuse, then a challenge study is
P3R/W$reC'xA0necessary. If the objective is to quickly estimate the approximate shelf life of the
+X%A+_5z,["e0J0product then an ASLT can be used, as long as the proper temperature range is食品伙伴个性空间 cy H0]$ut,zZ0~
chosen. A confirmatory shelf life test may be conducted at the last stage with
J.H H+RT V"]/t0simulated distribution chain conditions, although in today’s R & D environment, this
"t9K$SGK*}:K$b;T0may be skipped.
,FiU ~^#{ cxJ016食品伙伴个性空间6N+K(TNV;K2c+d
Product concept
"Z0r;A2rM K0Prototype development
/m;R8GC8T b0Pilot line testing
fq&~W%{C1V7e4~"T0Scale-up line trial
K t.q0h[*f0s0Full line production
js2k7B'E k;I}0Marketplace
+C]_2uq4~;Z5KA0General stability information
.L%n6T;g5n u0Challenge Study食品伙伴个性空间a"]&rZhT+kVJ0z
Accelerated shelf life testing
/fc,I1t$u }+G0Confirmatory storage study食品伙伴个性空间a`w ^JPQ*~
On-going shelf life monitoring食品伙伴个性空间~)sF)E}Kt.},Au
Figure 19.8 Shelf life testing strategy at different product development stages
Q4q L q8?5w-?019.3.2 Shelf life criteria
g_JX!AF)T;CR8]0The criterion for the end of shelf life may be variable depending on the definition of
} b8Ih.q:? R0product quality grade, so the shelf life of a product may also be variable. The shelf life食品伙伴个性空间K;ED:X w(K
of most perishable and semiperishable foods is almost solely based on sensory食品伙伴个性空间 dk+s:^Q#Z
quality. For example, fresh meat degrades mainly by bacterial activity and rapid
@4|#Yn9B0chemical oxidations that cause an off-flavor development and loss of color. This is
"@Ty^6u`h/~.|;g0readily recognizable by consumers. In contrast, many longer shelf-life foods including食品伙伴个性空间0@(arfm-c!L{A#i;h
most frozen foods degrade mainly by slow chemical reactions such as loss of食品伙伴个性空间%f2ch,yG;V2Y7^gpM
nutritional value. For example, the vitamin C content of some frozen fruits and食品伙伴个性空间0u6Lb&?\m;C
vegetables, may fall below the required standard as listed on the label before sensory食品伙伴个性空间.k]+H5hy Vf
quality becomes inadequate.食品伙伴个性空间0Kv{S2G&Y
The criteria for shelf life may also vary depending on the sensitivity of the食品伙伴个性空间4N'by i)R~5L
consumer. For consumers, taste, odor, and appearance are the most obvious criteria;
ID/F2r0o0in academia and in the industry, sensory evaluation correlated with instrumental食品伙伴个性空间H)mlJ0JM4H'z
measurements of a given quality index (e.g., vitamin C level) are usually conducted. In食品伙伴个性空间Q4`"vd c.c_3KK
general, the criteria level corresponding to the end of shelf life of a product depends
YenYq017食品伙伴个性空间"W`X$D}"|+G
on: (i) any legal requirement, e.g. zero tolerance for botulinum toxin; (ii) consumer
p*{{&T p7PE"n@W0preferences or marketing requirements; and (iii) cost. In essence, the end of shelf life
4C2BG\:tl2M0depends on the percentage of consumers a company is willing to displease. If 100%食品伙伴个性空间+T#HBnI6d,X
acceptance is required then high cost ingredients and absolute control of distribution食品伙伴个性空间P0H.~ wC#a
up to point of consumption is necessary, otherwise there will always be some people食品伙伴个性空间:[["P7DF:ec~ },DW
who will get foods beyond shelf life. The aim is to keep this as small as possible.
RT&sM;E yw7| x[aH019.3.2.1 Just noticeable difference (JND)
G;pjAyS0Sensory (organoleptic) examination of foods was a general procedure used by the食品伙伴个性空间3e5?N4cM&wqb_4k
human race to evaluate wholesomeness of foods long before the discovery of
3TL'Og.z.]F3`5Y0microorganisms. Sensory evaluation of foods by scientific methods can be used to食品伙伴个性空间8Yp)]$m,P X
evaluate such attributes as taste, odor, body, texture, color and appearance. Changes食品伙伴个性空间xSSMm
in these attributes may be brought out by microbial or non-microbial actions, usually
Dn ix$~zu0the latter for frozen foods.食品伙伴个性空间/F4~ m1e8q
The methods used to evaluate sensory shelf life data include difference testing食品伙伴个性空间 \,IujyR6\GhG
and hedonic scoring. Difference testing can involve paired comparisons, duo-trio食品伙伴个性空间#c{+aBU3bC
tests, or triangle tests. The paired comparison procedure determines the time when a食品伙伴个性空间!h po v[i
measurable difference in quality occurs between two test samples at a certain level of食品伙伴个性空间7`(J cc*@ J+tS
probability. When applied to frozen foods, this method is often referred to as the Just食品伙伴个性空间'r$z~bT4N8{F
Noticeable Difference (JND) test or High Quality Life (HQL) test (July, 1984), which is
b aQ,t"Cyz0s5n5c0usually based on flavor changes. Duo-trio testing compares two unknowns to an食品伙伴个性空间 UMh8c#X%e[X
unabused control sample and asks the question of whether either of the unknowns are
Rz e+i5|]:L9`I0the same as or different from the identified control. Triangle testing determines the one
rcD6u J+[#lQ0I4A!}0different product among three test samples presented randomly to a set of judges (at
#Lmb;T_V$|0least 10). Probability plots are used to predict shelf life at a given probability level.食品伙伴个性空间c.Fsl7c'bBz[
The difference method can result in finding a difference when none really exists (Type食品伙伴个性空间x8Za%D a d
I error), or not finding one when indeed there is a true difference (Type II error).
%gUW\&d%}Y0J$s0Labuza and Schmidl (1988) have discussed this topic more thoroughly in relationship食品伙伴个性空间 lb2M C_
to shelf life testing, which is not commonly found in sensory textbooks. Table 19.3
4P Ro%g4Ug0shows some data from Guadagni (1968) for HQL of frozen foods.
.^K~P0o#oex018
P2j^.h H6j0Le2a!D0Table 19.3
Dm'v0`8Pu8?0Days of High Quality Life for fruits and vegetable (from Guadagni 1968)食品伙伴个性空间 ]i*O4bxC v
P roduct T yp e 0 °F 1 0°F 2 0°F食品伙伴个性空间4o2ZO?i@D
apples pie filling 360 250 60
lc[;|(L0blueberries pie filling 175 77 18食品伙伴个性空间i:[2X*A%E
cherries pie filling 490 260 60
i$^Mv?0peaches retail syrup 360 45 6
ef"O#s'ANB2j X0blackberries bulk, no sugar 630 280 50食品伙伴个性空间{].{#Z4rU7Jr
raspberriesbulk, no sugar 720 315 70
|X y*o*g^ p0retail, syrup 720 110 18食品伙伴个性空间raB M5V0](n!e3Z
strawberries bulk, sugar 630 90 18
#}%|iT8v@\)o)~0retail 360 60 10食品伙伴个性空间"MNz(j!d5O
green beans retail 296 94 30食品伙伴个性空间 O,g7kZt0F-I
cauliflower retail 291 61 13
o j)]V2j7j0peas retail 305 90 27
j$? [ z F5[/c(C0spinach retail 187 57 23食品伙伴个性空间a9A,n!v6\i
corn retail 720 360食品伙伴个性空间,vOcF|FwwY
corn on cob retail 275 150食品伙伴个性空间$c.O*b ~9T\ f$gl~
19.3.2.2 Hedonic scoring食品伙伴个性空间,fwl FPk2H3{ A-x
Hedonic scoring — which indicates acceptance on a numerical scale, e.g. a 1-9 point
8b)o{7_6E a"NJ0scale labeled from "dislike extremely" to "like extremely", is typically used for shelf-life食品伙伴个性空间n @-l2["} x#G5K.r
evaluation. The test can be designed to not only evaluate the overall acceptance of the食品伙伴个性空间%H}s9|l ]dL
product, but that of specific characteristics such as flavor, texture, appearance,食品伙伴个性空间KsDhx&J N+T@5F
aftertaste, etc. Trained panels can also use this technique on a line scale, which can
tvg\ q\1s0be converted to numerical equivalents.
QL n6M+CKDi R0If the hedonic method is used to evaluate shelf life, one can simply use the食品伙伴个性空间XS#_9^2| t$TmcX\ ?
score as quality index A and plot the score vs. storage time, run a linear regression,
C G(|c?0Z op0and choose the end of shelf life as the time when the progressed value drops below a
ovx(l[0pre-set level (Waltzeko and Labuza, 1976; Gacula, 1975). The shelf life determined in
SsW/{{ v-y7nv @0this way is called the practical shelf life (PSL) for frozen foods (July, 1984), and is食品伙伴个性空间 PNd8j"StF
longer than the HQL or JND. The use of hedonic rating scales may be of limited use in
3Yl7S `-A0shelf life testing, yet it is probably the most used method. Many food companies use a
y4_B9D L E0loss in hedonic score equal to D=0.5 for HQL and D=1.5 for PSL as the end of shelf life食品伙伴个性空间%R v5P0d']/Y A
19食品伙伴个性空间&] ?%[R,T SKg2V Z$XrX
(Labuza, 1982). Objective measurements and professional judgment are often
lkoG m/J Rkr0required to determine the end point. Data in Table 19.4 from an report published by食品伙伴个性空间Hi.S.l`_\
the former Refrigerated and Frozen Foods Institute (1973) Unfortunately there were no
MaX(?%? e t"}bw"|y0methods given, but the data suggests that the PSL is about 2 to 3 times longer than the食品伙伴个性空间o:v!J0m7|/vQz
HQL value. This in itself suggests that the HQL methods can be used to shorten shelf
)iBIEVr$yLv J!M-t0life testing times.
Cv2T t1k,i^G\L0Table 19.4
c`qV*Oc_0Relationship between practical shelf life (PSL)
;JU X+oS\0YX0q4^0and High Quality Life for frozen foods.食品伙伴个性空间DGprM/m*A
F rozen Food P SL/HQL Rati o
1s3O&P7j"oAYxe~0lean meat 1.9 - 2食品伙伴个性空间L6Hm-}p*ps1Q
fatty meat 2.0-2.4
v E'Sg0I^ sU"Q;sH0lean fish 1.9-2.2食品伙伴个性空间}y9kGn$]n.H
fatty fish 2.4-2.7
&M1~3ij)`P\6U&[0precooked foods 2.8-3.0食品伙伴个性空间S:L'wc m+B W
fruit 2.8-3.1
W@g.nP0vegetables 3.1-3.5食品伙伴个性空间)CL5W&K!N qF
19.3.2.3 Instrumental analysis食品伙伴个性空间LQAFn?Y
Chemical or instrumental analysis, such as moisture, nutrient loss, free-fatty acids or食品伙伴个性空间5r3r8JP'L
color measurement that closely correlate to sensory attributes, can supplement食品伙伴个性空间r.k:JY!o
sensory techniques. They are usually less expensive and less time-consuming than
#k(PB6a qT,B0sensory approaches. A correlation between a physical or chemical test can increase
0^&? tWe9u Mk0the confidence level of the sensory results. For example, the following constituents or食品伙伴个性空间b-n#w5BW b
properties can be considered for monitoring chemical changes of pizza quality during食品伙伴个性空间Chd%`g"k!z
frozen storage: total free fatty acids, specific volatile free fatty acids by HPLC,食品伙伴个性空间'c3eyI\0@@'jnxsIy
peroxides, oxidative volatiles (e.g., hexanal) by GC, spice volatiles by GC, lysine, color
]Yc\.Y^etE0(decrease in red color or increase in brown), in addition to sensory evaluation of taste
YUCX5x7seo0and flavor (Labuza, 1986). Most sensory experts agree that analytical methods should食品伙伴个性空间#g.l*Ve*T2t G
complement the sensory tests. Vice versa, the endpoint determined by objective食品伙伴个性空间(|Jh t2No
measurements should be confirmed by sensory techniques as well.食品伙伴个性空间1jL MF]h%]]s(o
20
_9O/|Xv}c$M019.3.2.4 Weibull Hazard analysis
"fR`!J$u:V,E%QwM0The Weibull Hazard procedure requires one to first make an estimation of the time to食品伙伴个性空间 Y`7zs7P1S| Sl
the end of shelf life. This becomes the initial estimated time limit for the study. The time食品伙伴个性空间0YR)a h&LVN7n
limit is then divided into several segments at which points panelists grade the product.
W%gGL `z5X!R3{0Additional panelists are added at a constant number for each subsequent time period食品伙伴个性空间4@!m-Qn_j iBe*f;Y
to maximize the number of testers near the end of the test. The panelist is asked to
o f"irq5Z'^A MxgD0grade the food as good (acceptable) or bad (unacceptable), i.e. no ranking on a
Oaax_O e'Q0hedonic score. When the product is identified as unacceptable by 50% of the
I-tn5OY?r0panelists, the number of testers for the next period is increased by the number of failed食品伙伴个性空间U+g7oD0TE2z7c{v
samples plus the constant number. The interval between sample times is also食品伙伴个性空间9E?&z'Mv(t](kZ
shortened as the end of shelf life gets closer. The test ends when no more samples or
!f({ [+}/^4[0panelists are available. The scores are ranked and the cumulative hazard calculated.食品伙伴个性空间%]jT9_c$Ppi
The critical probability of failure Pc, can then be calculated from the following equation:
a&j4it#u&S[%R:R0Pc = 100 (1 - exp(-å(H/100))) (19.15)
(Q9@o ]jCr0where H is the hazard value equal to 100/Rank. Choosing Pc = 50%, corresponds to
'~Ew4?AYtjf#[0an accumulated hazard value of 69.3%.
GNCAB3c0The relationship between the logarithm of storage time (log t) and the logarithm
4P%Vt K3gU)c.o4n0of hazard value (log H) is linear:
;V@"g _:\r0log t = (1/b) log H + log a (19.16)
zu1oP@@NG.z0where b is the shape parameter and a is the scale parameter. The shelf life can then食品伙伴个性空间3t9AL;tF7w~
be determined based on the desired probability level allowed for product failure. The
1_qT$S:D0lower this probability, the shorter the shelf life. This plot then allows one to make a
4c?*Rsl0management decision with respect to the probability of displeasing a certain fraction of食品伙伴个性空间 Yc&B4M8L'QS
consumers. It is hoped that the distribution time is such that greater than 99 percent of
zj#G1li)Mr _aR0the product is consumed before the end of shelf life based on displeasing less than食品伙伴个性空间0y'LZ,W*|{5S
X% of consumers where X is the economic value. An detailed example was given by
7^;^|+yW-? c0`;jQ0Cc0Labuza and Schmidl (1988). It should be noted that this process can also be used for食品伙伴个性空间Xt,l#u#Q3N0e"B`b
simple analytical tests such as plate counts or vitamin C. In these cases the number of
P!a3Au*S/R0R0panelists are replaced with the number of samples tested. Some criterion such as 20%
.Q!jR%Qg0vitamin C loss is used as the negative response. Figure 19.9 shows an example of食品伙伴个性空间 xa h4N.Ux
Weibull plot for a frozen food based on assumed data. A shelf life of 16 months is
_BOM(\{.sZ1U/o021食品伙伴个性空间P ox,|&zr;gq p
found at Pc = 50% from the graph. From this graph then, if 95% of the food were
0up7p:h4GP/o0distributed and consumed in 3 weeks, only 1% of the consumers would be displeased
{wu3GN1f0m9C0.01 .1 1 10 100 1000食品伙伴个性空间9~FE*s.EZ RF
1食品伙伴个性空间\ H:|Of
10食品伙伴个性空间2{n*\&h'gClF{0?
100
'z7cr)Q6H0Cumulative hazard (%)食品伙伴个性空间#K$R ^f!k&X7m#S u(E
Shelf life (wk)食品伙伴个性空间]6Ic1g4m3t
Probability (%)食品伙伴个性空间!b?%|!n&p
0.01 0.1 1 10 50 99.99食品伙伴个性空间 ~bT [#W'QNa[K
Figure 19.9 An example of Weibull plot for a frozen food.食品伙伴个性空间W,F bC G'R
A shelf life of 16 wk was determined at Pc = 50%.
5_h{2W&Q(u6G0(or 0.95% of the product is out of compliance). If the rest were held and consumed at食品伙伴个性空间$YY$u-iU;PH4~
10.5 weeks, 50% of those eating it would have out of quality food or another 0.5 x 5%食品伙伴个性空间P$j#N [] D]w0v Q)p Q
= 2.5% of product. Thus in this distribution model about 3.5% of the product is
Ub1U(|Gmj0unacceptable. To improve on this, the product must either move faster or one must食品伙伴个性空间XV;D\C-k*p O
distribute it at a lower temperature. Wittinger and Smith (1986) used this approach to
'_ E4S"Vm0determine sensory shelf life of ice cream based on iciness and found a shelf life of 5食品伙伴个性空间?:S6F&fm M6y&X
weeks at 0°F (-15.5) which fits the general data for iciness in ice cream as shown in
#c[]f7LS0Figure 19.10 (Labuza, 1982). It should be noted that this gives a Q10 of about 12.食品伙伴个性空间D ~5x"d{
22
t8o*S(iV0.1食品伙伴个性空间kwR^9]+]
1食品伙伴个性空间-z \[#|;}qf6Vp
10
?n`?_6X^0100食品伙伴个性空间]-q*JSyO}5eo
Temperature °C食品伙伴个性空间 KO ok'g ?H
1食品伙伴个性空间)buT,E3CL
10
y^Z9_Xt0100食品伙伴个性空间zdm)`C3sn3Q bd;V
-30 -20 -10 0
+^"T0wl5leU.O.H }00.1食品伙伴个性空间J)B J"e*l3mHx m,W,h
weeks食品伙伴个性空间8N(T.@3S+H)gH
Figure 19.10 Shelf life plot for ice cream based on icyness食品伙伴个性空间.@3gV;~QR
perception from data of Labuza (1992)食品伙伴个性空间[oB.K/TLY1GB
19.3.3 General procedures
I?[*fE tR VGR+J0Shelf life testing experiments are designed to measure the average shelf-life of a食品伙伴个性空间? L2ek1Fg[bw9C#L
product under given conditions. General procedures for shelf life testing of foods were食品伙伴个性空间)~3P i y i1Q
proposed by Labuza and Schmidl (1985), which include:
o"RlS v/t'k$l5}\0Step 1: Develop testing protocol — The protocol should consist of: i) specific食品伙伴个性空间VP \V9S$@Bj&F
objective; ii) detailed test design in terms of product, package, and storage condition;食品伙伴个性空间tu$ftu(p;MiR
iii) execution procedures in terms of time, space and resource availability; iv) cost食品伙伴个性空间[ `n,Eg,B)A
estimation.
czZCEOo0Step 2: Identify key quality indicator — Any previous shelf life data and kinetic
7n Vn+{v |"Cz5^0parameters of food deterioration available in the literature (Labuza, 1982; Man and
@ B0@+`'L0p&y0Jones, 1994) or the distribution turnover time of a similar or a competitive product in
FKc)o7A7rw+_0the market place, if any, would be very helpful in this preliminary identification or in
;has8^{0determining the shelf life requirement.食品伙伴个性空间q,eMUOy(o
Step 3: Estimate product sample and control needs — The number of samples
%T(|3do:Qv hMJE0and controls required should be based on the detailed experimental design. If食品伙伴个性空间b2C-y/q1|+hlB$J+A
sufficient product is available, extra samples should be placed into each storage
|2^;gN4R ~+v023
H;HP*Y g5`7L`$F6rA A0condition. Now and then it may be necessary to recheck a sample, especially if a value食品伙伴个性空间%L/u];?hg4we F
is not in line with other data. It would be disastrous to be out of sample before failure食品伙伴个性空间M(c(`;Vr1cM7\ r
has occurred or the predetermined termination of the test is reached. Extra controls食品伙伴个性空间-T9G%D(AI~g+m
should also be prepared and stored. When the samples are placed into storage
.?Gl_z*}K0rooms, they should be positioned so that the complete package is exposed to the
rs2B(eN2`*m+[0external atmosphere, unless otherwise specified. The specific location of the test
0xZ @7J Ka;pQ0sample should be recorded. Temperature controllers should be checked for accuracy,
'd#X?vk-W0periodically. In addition, removal of all unused samples from the storage room to make
_q0N8v3R(a2q0space for future studies is a must.
&v"M\0s Q A%KMV s0There are various thoughts when it comes to using a control product. Some
%i+D2x/o;e0b`tF c0sensory experts prefer an actual physical control; others are satisfied to just use the食品伙伴个性空间Ws^o)a[|
numbers obtained in the zero time evaluation. There are three alternatives when using
D;^r6E:}#{u1B6YBH0a physical example as a control: (i) making the control from scratch each time using食品伙伴个性空间 iy FrF&Z,y1Jc
the same ingredients, procedures, etc.; (ii) deep-freezing the control (e.g. pizza held at
_&g9iQ0S7}%kh0-70 °C) and accepting that it might have changed slightly, but minimally compared to食品伙伴个性空间NH~U7^?`,@
the product in shelf life; (iii) using a fresh batch of product which may not be identical.食品伙伴个性空间/i8wyv"Q S E$t
Step 4: Select proper package materials and package size — This is largely
(K,_ i)M+l0dependent on shelf life requirements, packaging costs and availability, and consumer食品伙伴个性空间2RNNHTw
information. Factors such as vacuum packaging, nitrogen flushing, or use of食品伙伴个性空间0c}e.\Y"F)VO X~4w K
antioxidants are often considered in combination with packaging materials.
"ga YL\ L3c)E(?@0Step 5: Choose storage conditions — Storage conditions are chosen based
8eZ w n&a9Un}X0on the type of shelf life testing. For example, the intended commercial食品伙伴个性空间 Vz j-Q&o(Au/W
storage/distribution temperature range should be used in confirmatory shelf life testing.食品伙伴个性空间qE yWFI-T?X p
Elevated temperatures are often used in accelerated shelf life testing to obtain data for
taf/?av G0prediction of shelf life at lower temperature or for prediction of shelf life under variable
Y~E5o(`,s0time-temperature distributions. Humidity control and/or monitoring is less important for
pu_5s3L G:nT-zR I0frozen foods as compared to other foods (e.g., snacks, cakes, pies, and pastries).
u(K | F7}]OV'S0Light in the room should be properly controlled depending on the package.
ILm)mr6z i7nB0Step 6: Estimate sampling frequency and duration of testing — The sampling食品伙伴个性空间_eSaF.I#F$~-D
frequency is generally an estimation based upon experience from prior studies with
9p5{&Q(P@mP4N(g8n?$}0similar foods. However, once one knows an interval at one temperature, then the
4G{B)xJ#z/v0intervals at other temperatures can be estimated using a Q10 value i.e., if the Q10 is 3
B8grw{}0tU(\0then for a 10°C lower temperature the sampling times can be 3 times longer. If the
|_x}#k5W0interval between sampling is too long, the risk of under- or over-estimating shelf life
3w4{)Y!b7UT8O b+|0increases. The more analyses that are completed, the more accurate will be the shelf
/SF1N o7Xj z;?0life determination.食品伙伴个性空间-s-?0mml"g
24食品伙伴个性空间BP(pB&s(o(V Y
The question as to when one should end the experiment must be based on食品伙伴个性空间E&S7X)Y-~a0S']D
some pre-set criteria for failure. One criterion could be the minimum shelf life
-B%pt8J6f"L R:v ^o0requirement driven by product category, distribution chain, and the benchmark's食品伙伴个性空间U j b`wnM
product stability. If there is an accompanying sensory test, the end time can be based
x&B.~YrAb5D0on some organoleptic inferior quality criteria from which one then can get a microbial
C"^2M\fE(bI/K)@7a0or chemical index limit. For frozen products, several weeks to months are usually
L9u$tS-x0needed. If the shelf life can be estimated with any accuracy, the test intervals can be食品伙伴个性空间/C7U[!B ]){N$Obs
lengthened and clustered around the expected failure period. Most of the experts only
8`9F:C-rzDQT6U(A-G%U0require about six evaluations to provide reliable results.
'@~Rcs0Step 7: Schedule for execution — Before scheduling the starting date for a shelf
U0S0O W&Q XsfU0life test, one must check for the availability of ingredients, packaging materials, and食品伙伴个性空间/kwY^ D"dP:x0J k$qM*v
storage space, and the time and resource available in the pilot plant or in the
;X$VQ"X!C%PI0processing plant to prepare the samples. One should also check for the time and
h*Pa@!Y0Q/Bd)nb0resources available in the microbial lab, the analytical lab and/or the sensory support食品伙伴个性空间Et!E|-K'P%d ^
staff throughout the test period. A copy of the test request and schedule should be
&}/s9DwF.rDZ3`a0sent in advance to those who will be doing the work. The courtesy of providing those食品伙伴个性空间GBOS H R:U9O)C
involved with this advance information always pays dividends. Holidays should be
u^8Z W+Mh(e4s0marked on the scheduling calendar, since scheduling too many evaluations near食品伙伴个性空间%^MQC,~N
major holidays or Friday afternoon is not recommended. However, once scheduled,
rA{(^:R0sample observations on weekends and holidays should not be skipped over, since食品伙伴个性空间:J:c!~vPI\&F
important data points could be missed.食品伙伴个性空间-K/x\0_0zD
Step 8: Take sample and evaluate quality — Samples should be taken and
X)c M'h*C/EOD0evaluated following pre-determined schedules. Sampling plans should be
O!sy/~tTh0administratively and economically feasible, taking into account the heterogeneity of
%W3KK;\Pc |y0the food. Maxcy and Wallen (1983) pointed out the problem of heterogeneity of
dQ$D'DBNA5t t0samples in shelf life prediction. Multiple subsamples (³ 3) should be done for nonhomogenous
3zc V$k8}1RZ0samples. A single package is usually used as an experimental unit.食品伙伴个性空间LJ2F.u4z"pbZ!o
Replication of 3 or 4 units are desired for each measurement. For frozen foods, a
?3_s d?T)M2Q0thawing process is often involved in the sampling procedure. Proper thawing or
S sqBjM0microwave heating is critical to the product quality. All samples should be thawed or食品伙伴个性空间2iaoy.K\$s`8A.C
microwaved in the same way to minimize any biases.食品伙伴个性空间 x[2G5K3~0X3yI;JT\
The intended analyses should be based on the specific mode of deterioration,
VG)E*N(cF5rZqr v0which was discussed earlier. Whatever the choice, the tests should be reasonable and食品伙伴个性空间!GNe[]Xm
logical. The key is to make sure that one is measuring the right thing. If the wrong食品伙伴个性空间UMO7b[jM
quality factor is measured, the test starts out a failure. Unfortunately, in many cases this食品伙伴个性空间$u p+@s^#qb6C0I{
cannot be established initially, so sensory evaluation is a must in almost all shelf life食品伙伴个性空间Q jqDX/F-Dk
25食品伙伴个性空间V$N-n _A
tests. Key sensory evaluation techniques for frozen foods have been discussed
~T+xI0^ Oy'Us0before.
vLpbAXv5Q)X0At the time of each pull, one unit of the sample should be evaluated (informally食品伙伴个性空间Kg4Y _{pD6a
by a minimum of 2-3 people) for changes in flavor and texture. This should be done in食品伙伴个性空间OzWh&F R&i vS
addition to the final tasting prior to a consumer sensory test. This is necessary since it
[,Z1jxSh\0helps the developer know approximately how the product is doing during the progress食品伙伴个性空间 JVAFDe5^YK
of the shelf-life, helping to avoid any surprises in the results. Control samples may
d ~Z.n8}0need to be prepared fresh.食品伙伴个性空间k qz l"y0x
Step 9: Analyze data — Shelf life is the predicted day at which the stored
(?`H&VdL0product (test pull) is X% less than the control at day zero (Reference). The data should食品伙伴个性空间|6a2FO`5{ P
be plotted and regressed to determine that point using the proper model (zero or first).食品伙伴个性空间G4O2K,d?R!h4S:`V
All too often the data are not analyzed until the experiment is over and then the食品伙伴个性空间,Lt/i$~*kj$jN
scientist finds that nothing can be concluded because of lack of points or a poor fit or
rT8Z ?]Z0some surprises. Statistical curve fitting should be consistent with the chosen model
TIh0s;A0based on a theoretical mechanism. The amount of change and number of data points
M H2YH`c0are related to the coefficient of variation (CV) of the test. A weighting factor may be食品伙伴个性空间 E U"H%k @k3BiV&C4`
used in estimating the rate constant and its statistical limits. When the data for an
w.V%t$J7|D0attribute does not fit the regression model well (adjusted R2 of < 0.8), scientific食品伙伴个性空间 K8Z `7l a xH3P
judgment should be used to decide whether the data are applicable.
xvoL%I0When in doubt, a rerun on retention samples might help understand or clarify
.S)M)y#M;\0the results. Error analysis could be performed before experiments are run by first
F4C J Wv"D0finding inherent errors in time, temperature, and quality index measurements, then食品伙伴个性空间3K%_NF,JF
calculating an expected standard deviation for the plot being used to determine a rate
GtVoM:FU0constant. If the experimental data have a standard deviation much higher than the食品伙伴个性空间+Y/F+s'N,U#H
expected value, either the functional form of the rate expression is incorrect or the data食品伙伴个性空间f3F+x2k7Py!]
contain errors from unanticipated sources.食品伙伴个性空间0q*~])B;x Mk
Step 10: Prepare shelf life report — Depending on the type of shelf life食品伙伴个性空间Vo ]T&O Dy+y
determination, the results should either throw light on the technical viability of the食品伙伴个性空间 |g K&?'w*afa
product or provide answers to the questions about the maximum safe shelf life as well
Hk[G9B0as the maximum quality shelf life of the product. Before a shelf life is finally set, factors
3\g$g'p rW?0in the scale-up of shelf life data will need to be taken into consideration. Based on食品伙伴个性空间8rIaV.ZN0X6Wvs h
results from ASLT, the provisional shelf life will be set for the product. There is no
@uno7WYKhbw0government regulation which defines the product end point except for that related to食品伙伴个性空间$RDM3P${;N;V
nutrient levels (vitamin C and vitamin A) in 21 CFR 101.9(g)(1)(ii) which states that for
t Z.@gu P0the vitamins listed, the analysis level cannot be below 80% of the label value if it is a
G%M L(By|4I0natural food with no added nutrients or cannot be below 100% (21 CFR 101.9(g)(1)(i))
;Ri,Q6y ^026食品伙伴个性空间&S{!f?)T^/v0p
if the product has any added vitamin or nutrient whether or not it is the nutrient under食品伙伴个性空间al6G)Z7ls"j~
test. Thus one must base the label value on some predicted initial variability and食品伙伴个性空间ijwsT
some predicted loss during distribution and storage. The FDA usually takes samples at食品伙伴个性空间Q T5[I#E#OP@
the supermarket level (where they can purchase them) for compliance testing, not from
n{okJ6ET`%r0the end of the process line so distribution losses must be factored in.食品伙伴个性空间G y,gdF)Om6`D
The end point of shelf life is thus dependent on your corporate objectives and食品伙伴个性空间\3J h6V0[5G
how much risk the company is willing to take with the brand. No shelf life test is
MH%PMf1G!Z0completed until a termination summary has been written. All termination summaries
eZ H U)o CF-n9x0should include the objective of the test, product descrīption, package descrīption,食品伙伴个性空间6F!V"o%Gq
conditions and length of storage, methods of evaluation, results (in the form of graphs,
|!~\E u0shelf life plots and Q10 values) and conclusions. Termination summaries should食品伙伴个性空间x pq Nl'K
become a permanent record in the company library for future reference and preferably食品伙伴个性空间7`M K2v!{
indexed well on a computer data base for later retrieval when needed. The final shelf
6~Y![3~){8c0life should also be set to give a clear margin of safety. In any case, the shelf life of a食品伙伴个性空间|(e1B H3s DCd
new product, particularly of the high risk category, should be set based on data that食品伙伴个性空间;g Qf`9b `5^_
relate to the worst case manufacturing and storage scenario. The shelf life can then
%ST h@ R]F"}0be reviewed and if necessary re-set in the light of further experience in manufacturing食品伙伴个性空间5E_D(~r#zq Wb7jy7r
and control after the product has been launched.食品伙伴个性空间U3F v%}.K[9{R
Step 11: Implementation — One should get top management’s approval of the
T3Q G/H-\'UL2mzZ0test results so that they can be implemented. Management must believe and support食品伙伴个性空间SP `I9b1D6X;d
those test results. It is important for production, sales, distribution, purchasing and食品伙伴个性空间s;joh VZ!X+B
quality control to work together to be sure that the production is properly handled from食品伙伴个性空间1Md:~^3@"R*a
the time of manufacture until this product is consumed.
e'E|fNZ0CW019.4 Challenge study
Wx&s DJ019.4.1 Basis食品伙伴个性空间F`-Uni I
Freezing reduces the microbial population of foods but considerable numbers usually
z u3t ^%Q.ALlMBIW0survive even prolonged frozen storage. A challenge study is often used in the食品伙伴个性空间g Gt)aM7Q
laboratory to study the factors and factor interactions as they affect the shelf life of the食品伙伴个性空间Q#Zn%f.j6Z1[,k,B-a
product. Such simulated experiments enable the researcher to better control the study.食品伙伴个性空间/gy8L"tzsd9N
A challenge study is necessary for frozen foods for two reasons: (i) to predict microbial食品伙伴个性空间f6f0J&v:\;c
growth and potential risk of the product upon temperature abuse in a distribution
gd6c1jB0chain; and (ii) to assess the relative stability and the relative risk of different formula,
Nk1h,I,T,?gj8b6F0different processes or different packaging materials, which is a must in new product
OID"Q.i:\}q+TN1d0development. A challenge study may also be considered as a preliminary shelf life食品伙伴个性空间]*Y)\]+kR
determination in terms of microbiological safety. It is often used in the early stage of食品伙伴个性空间!L&?~7R6nQV!ko
27食品伙伴个性空间.G.?.rHg!h
development since if microbial safety is a concern at this stage, then reformulating can食品伙伴个性空间-fMF$S$c1r*\
be done quickly.食品伙伴个性空间9~Y sXqo5xg
19.4.2 Microbial abuse procedures食品伙伴个性空间SM-zIK'Z&k(^
Step 1: Identify barriers — A composition/ingredient analysis should be done to
&V0C*ZWy F(A/_{F0identify any barrier(s) against spoilage microbes and pathogens in case of食品伙伴个性空间 eP"y8M5ioEg
temperature abuse.食品伙伴个性空间7N^-[A)T,R
Step 2: Choose types of organisms/strains and inoculation level — One
,sb~3kW:x0Z0principle is to use an organism or a strain that has been isolated previously from the食品伙伴个性空间e5v_G.DXO
product or similar foods which is responsible for spoilage or risk. The more isolates in
$G Wj9T0~Gr!Z4v#H0the study, the greater is the confidence in the accuracy of the shelf life assessment. An食品伙伴个性空间p Qq nGX#t9HD!y]/g
inoculation level must also be determined, which is generally much higher than the
P_ N_S b,M0normal contamination level in a product. If the average contamination level for a食品伙伴个性空间 O.T'QP r5Jcb
particular product is known, then the inoculation level should be as close to that level
a4e Tb2Ikg0as possible. Sometimes several inoculation levels are used.食品伙伴个性空间6v0t%?'I F0am;v d/~:^
Step 3: Determine temperature abuse conditions — After inoculation, products食品伙伴个性空间,ttiHd9h
should be packaged using the desired commercial packaging conditions, and食品伙伴个性空间q9S^g,|xe,A Bk
subjected to temperature abuse. Factorial design and response surface methodology食品伙伴个性空间'i(t'R` D*d|
are often used in designing a challenge study. A typical temperature abuse condition食品伙伴个性空间AV[!LF7nz2UK
used by some food companies is provided in Table 19.5. It starts out with five sets of
*z5Q x8@1m$vu0test packages placed at -18 °C to begin the cycle. At the end of the first 24 hr, one set
[3@Tj+LPE0of packages is removed and tested for microbiological indicators to establish a zerotime食品伙伴个性空间&m*I\.Ycx
level. All the other packages are kept at -18 °C for the next 20 hr, then removed
W6{R)Dov0and abused by placing them at 38 °C for 4 hr. Another set of packages is then
UFe`f@D0removed for microbiological testing, and the cycle is repeated for the remaining
3y u m9X`4o`*]D0packages, i.e. they are all returned to -18 °C for at least 20 hr, then abused at 38 °C
H!d EKCr[0for 4 hr. This procedure is repeated so that one set goes through at least four freezethaw食品伙伴个性空间1U9o.B6oc_eE)Sr
cycles. If there is no significant increase in spoilage organisms or pathogenic食品伙伴个性空间 ]]5V&b I(TD:i1qw
organisms after the fourth cycle, the food is deemed safe microbiologically.食品伙伴个性空间xR o @$v E
28
2G8APn a;v&kv#m0Table 19.5 A typical temperature abuse test sequence for microbial challenge食品伙伴个性空间2G+Dq5xE1qzyK
studies食品伙伴个性空间)kI d:J{
Day Abuse temperature cycle Number of package sets食品伙伴个性空间-{A`I6`
remaining食品伙伴个性空间t.A+?M;A6YF9z
1 24 hr at -18 °C 5食品伙伴个性空间0_;n+]X k"t:vl
2 20 hr at -18 °C
5?T j{l9N#st(zvb%G04 hr at 38 °C食品伙伴个性空间#mF SZ;UV0eL
4食品伙伴个性空间/{gI*{fl2D
3 20 hr at -18 °C
g)bLJC |H04 hr at 38 °C
` ~!SVO;SL#xa/T}03食品伙伴个性空间TW3cc9i:f
4 20 hr at -18 °C
L9kbr5ZcT04 hr at 38 °C食品伙伴个性空间S ^|%B.g4N"@u8C3\:|
2食品伙伴个性空间$T1Z4_+~!W ~ U
5 20 hr at -18 °C食品伙伴个性空间)p U n+s,_O*s
4 hr at 38 °C食品伙伴个性空间B_,p:r%U%[
1
%YxX4U5X+i/_(f0Source: Labuza and Schmidl (1985)
;w'`4a WAK0Step 4: Do microbial survival analysis — This is to find out if there are any
@#h2U9DNK0microbial growth upon temperature abuse or if the inoculated microbes survived the
6Ad6xW+B%u0process. Appropriate detection and enumeration techniques should be used.
)VKBZw gP7I019.4.3 Applicability食品伙伴个性空间@7tS I$\m
The use of inoculated pack studies conducted by independent laboratories allows a
\2FWV2~j$kan"\9P5hW0food processor to assess the relative risks that can occur under conditions of食品伙伴个性空间'C:i3X6[+ip
temperature abuse of the food product in question. Taking frozen pizza as an食品伙伴个性空间9cw|#y ~A p T5W
example, both the cheese and sausage, if naturally fermented, will have high total
McKi~0counts of bacteria. Since the product is usually partially pre-baked and then frozen, the
4qtz$Kg3JLY0numbers of vegetative microorganisms will decrease until thawing occurs.
T#vCNS_3V2m0Unfortunately, pathogens such as Staphylococcus aureus will not be totally
6L[4sVDt Y"H0inactivated by these treatments. If the product is abused during distribution so
+` Qq"H2T5uz8FP0severally that the temperature near the surface reaches about 7 °C, pathogens may
B Bx8g!F](v [ED8O0grow. A challenge study with Staphylococcus aureus will verify the microbial safety
:JW g,R6b0of the product.食品伙伴个性空间:gfd2Gq N q
It should be noted that inoculated pack studies with pathogens should not be食品伙伴个性空间2q!k4aCx-Ch~+o5X
conducted in food industry laboratories that are located close to the food processing食品伙伴个性空间G"`+D.^jb,[
facilities because of the possible transfer of pathogens to food products. No sensory食品伙伴个性空间%|'Y6{1D8i3[&_e1p'A;d
29
j\5d"Ve~I:YQ0panel can be applied to evaluate the inoculated samples other than visual
I%sq;b,k0S3C0observation.食品伙伴个性空间 GE4@1k\U)F
19.5 Accelerated shelf life testing
-r/O#SLW1_(}:E019.5.1 Basis
yU[-D Q0During product development, preliminary shelf life knowledge is often needed in食品伙伴个性空间u7H[5Km*da6o iv
addition to microbiological safety. Shelf life testing experiments at this stage are often
'v!Kt2avK;hy Tm0accelerated to evaluate the effects of various formulation and processing parameters
,iE.T6^@Z@ A0on shelf life stability of the product being developed periodically since one can not
L D'G&tHZ^.isj0afford the relatively long shelf life period for a frozen food stored under normal freezing
,].{(O1n;y;x]0conditions. In addition, temperature fluctuations may occur in distribution and retail
c.K%|/cJ9Dw/v5zi9na0holding for frozen storage. Thus kinetic studies at several temperatures within that
&_$w,XC'g2n0\d0range are necessary to predict its shelf life. Accelerated shelf life testing conducted at食品伙伴个性空间 voi-Q6Q^yz\y
elevated isothermal temperatures and/or with freeze/thaw cycles for frozen products食品伙伴个性空间4^)G#?&I t:} T}t:j1W
have been used extensively for several decades by industry and government食品伙伴个性空间#`u\ }2\+F
agencies (Labuza and Schmidl, 1985). The Arrhenius relation and the Q10 approach食品伙伴个性空间S4y[8]8T$|7f"b5u
are used to extrapolate the results to the expected lower storage temperature.食品伙伴个性空间Y(ev5uuc;s
Acceleration factors other than temperature have also been studied for some other食品伙伴个性空间H*_/\ gQ
deterioration modes, such as moisture gain or loss and lipid oxidation (Labuza, 1984),
&pmHaV!fD"k0but rarely done for frozen foods.食品伙伴个性空间f_R| s6L}/N
19.5.2 Unique procedures
oa7yt Y!Y*n]0Step 1: Clarify test objectives — In general there are two occasions where
J2AB-lm ~_0ASLT applies: i) estimate approximate shelf life quickly during development stage; ii)
!Tt `6GpEM0collect kinetic parameters for actual shelf life prediction as in the marketplace, which is
r"m3` k]'d0conducted generally near the launch phase.食品伙伴个性空间8n'?7ZsVr
Step 2: Select accelerating temperature conditions — Suggested isothermal
{#h;k z}!j0T0accelerating conditions for frozen foods are -15, -10, and -5 °C with a control stored at食品伙伴个性空间 v3p;f7`'p rX$QN1G
< -40 °C (Labuza and Schmidl, 1985). The inherent assumption is that the食品伙伴个性空间yt g Lx+B
deterioration mechanism is the same across the temperature range although as noted
'?6K1{c-F0earlier, there is concern about how close to freezing one can go.
CC^;?PT6n(K0Moisture migration from the food into the surrounding air with resulting
'Gq/kO!THaN0desiccation of the food and ice crystal formation in the package is a major mode of食品伙伴个性空间.IhJ;} NXh7U
deterioration of frozen foods under fluctuation temperature conditions. Cycling
Fu1tt^ G)l0temperature storage is used to test for this, i.e. from 0 °F or 10 °F up to 20 °F with one
'Q6sx3]Qz p1Z0day at each temperature and then repeated several times. A freeze-thaw cycling study
a5?d/BvW0is also needed to determine its effect on sensory quality. Usually, the high temperature食品伙伴个性空间1d7@3Q8?7K
30食品伙伴个性空间1YSxuy#e|!b&A{'M
can be much lower than that used in a microbial challenge study unless microbial食品伙伴个性空间$^8r*lk6zK*cdf
survival is still a concern. Typically, cycling temperature/time can be three to five 24食品伙伴个性空间%H\0d5E }a&R.X
hour cycles between -18 °C and -7 °C, or between - 18 °C and 7 °C, depending on
~Lt'r w7c5I0the product.食品伙伴个性空间'N0x'B @p%toOe z
Step 3: Estimate testing time and sampling frequency— Testing times are
~,j]1zIc:q n.\0dependent on a desired shelf life at target storage conditions. For example, given that食品伙伴个性空间JY;xA5q'h8j)_!T
a shelf life of 12 months at -18 °C is desired, a shelf life plot can be constructed. Figure食品伙伴个性空间8}2yDe,w&Z
19.11 indicates the test time at -4 °C that equates to 12 months at -18 °C for various食品伙伴个性空间 uu~)g$RZr
Q10 values. Sampling times at -4 °C should thus be 1 wk, 2 wk, 1 month, 3 months, and食品伙伴个性空间7_5Ik2V a4]RbNO
4.5 -5 months. Most published results suggest that Q10 values for vitamin C loss and食品伙伴个性空间E;Uy6E ZC)F9z0aT
quality loss in frozen vegetables range from 2 to 20 and that the shelf life of vegetables
7G }E\r0is only 6-8 months at -18 °C (Labuza, 1982). Considering these Q10 values, a product
.e}dt1U+?r0that does not retain good quality for 4.5 months at -4 °C may not retain good quality for
!JHF/vFbr3~B012 months at -18 °C. This also suggests the sampling frequency shown in Table 19.6.食品伙伴个性空间6h:k|O1_:bcV4p W#`
All simple tests should be conducted at each sampling time, while sensory testing
u_#r}|QwVwk0should be concentrated mainly toward the end of the test sequence with a few near the
"o!_LT8B8Eqps&\"a0beginning.
3a*K.s?Fq!K00 5 10 15 20 25 30食品伙伴个性空间%^!{9_;bR;G qN\
.1
Qvf_)t01
-Z$|4EoJ010食品伙伴个性空间1M)dc0L c
100食品伙伴个性空间:C3S w Q+ne
T (°F)食品伙伴个性空间tRMr)C
Shelf life 12 mo at 0食品伙伴个性空间j*aWY3L&a5XZ]m
ASLT at 25 °F食品伙伴个性空间C?3f(THA MZ
4.5 mo食品伙伴个性空间2]6PQ{4u |
1.2 mo食品伙伴个性空间)pM"^)`EYd
14 days食品伙伴个性空间BMZ6N d7zW
6 days食品伙伴个性空间 B_Y+iD!`V gA {i
Q10=2
%g1_-IgQ)H4tx:H l0Q10=5食品伙伴个性空间0Z];F2rUdJ P1y g
Q10=10食品伙伴个性空间$o0N|.YC'c"Z E
Q10=20
/l[J7q9w7|"cr0Figure 19.11 Shelf life testing times at 25 °F equivalent to 12 mo at 0 °F食品伙伴个性空间&|S1n*H-G6G
for various Q10 values.食品伙伴个性空间;w6|.l"q%w t7}
Table 19.6 Sampling frequency for frozen pizza ASLT
T0]4dG;c-~%@ N5o T031
C*`J8d{"`&j3c fl0Temperature (°C) Sampling times (wk)食品伙伴个性空间h'V\(V$p-j4t1Z
- 4 1, 2*, 3, 4, 5, 8, 12, 14, 16*, 20*食品伙伴个性空间,\U'dWZ
- 7 2, 4*, 10, 15*, 20*食品伙伴个性空间*W9Fa\i i
- 10 4*, 10, 15*, 20*食品伙伴个性空间6gPf2g%P_)Im
* Sensory test times Source: Labuza (1986)食品伙伴个性空间H"C[n*sllJO
Step 4: Determine end point — Figure 19.12 shows a comparison of times to食品伙伴个性空间-]$bd9S&j3E8M3u oK
various levels for the loss of vitamin C in frozen spinach as a function of temperature
m |2C)urYpi#D0(Kramer, 1974). The dotted line represents the 80/80 rule, i.e., from a legal standpoint,食品伙伴个性空间v B[0?+c9r"^\
for natural products, 80% of the tested sample must have no more than a loss of 20%
C2c{'F5\ K,| H0(i.e. 80% of the label value). Consumer sensory testing will not always give such a食品伙伴个性空间 E;w^9Jte%eQ
clear shelf-life result since different shelf life times can result using different quality食品伙伴个性空间[0lEf{9k
attributes. Often professional judgment has to be made to decide what factor to use as食品伙伴个性空间 @S d{ {@:v#oG
the base for the end of shelf-life of the product. When shelf life is unacceptably short,食品伙伴个性空间/w-LdpS[V)S+w
adjustments should be made to the food, its environment, packaging, process and食品伙伴个性空间dc$]U^6uO[+b4^
hygienic conditions, until a suitable extension of shelf life can be achieved. For some食品伙伴个性空间%l!_"I:{p5j;z!H
products, the test results may demonstrate that the target shelf life is not attainable. At
,H9C6j$v-y;P:v5I#d0this point, the question of whether to launch the new product with a shorter shelf life or食品伙伴个性空间"o9XZ%N|d~4})m
to abandon the entire project becomes a marketing decision.
6_*s"`-?{8kW0-20 -10 0 1 0食品伙伴个性空间x![(@Z#k3u^N1X]HD
1食品伙伴个性空间*HIEhOc(e
10
K9RO}N;`,z0100食品伙伴个性空间+fo'K%qr~
Storage Temperature (°F)食品伙伴个性空间$zS&T:K*l |c
Shelf life (mo)
Hm/b4`:Vzy YB0Figure 19.12
6P#TU7`5W(C&R0Shelf life of frozen spinach as a function of vitamin loss level
"n+WQ0a c'e(]J m050% loss食品伙伴个性空间U&y5niN pX
25% loss
Xv}5V_Lu|!@010% loss
|0MqQ@0Quality (80/80 rule)
Sf9@g;C-nf6R032
pf/m7a{ c0Step 5: Estimate kinetic parameters — From each test storage condition,
)I6hnQ7O!K|0estimation of k or q is needed to make the appropriate shelf life plot. From this one can食品伙伴个性空间 W ?,`#cd
then estimate the potential shelf life and confidence interval for the storage condition.食品伙伴个性空间qO$?du,|a'X
Then parameters for the Arrhenius relation and the shelf life plot are determined by
HLol L l0linear regression, which are used for shelf life prediction.食品伙伴个性空间3\M g%R/| Ej
Step 6: Extrapolate to normal freezing storage condition — The most useful
!E-GmUh0shelf life information is obtained for product kept at its intended storage temperature,
:C sl!z?c~^0which is about -18°C for retail frozen products and -23°C for distribution of frozen食品伙伴个性空间"j$r A Np7KT n
foods. Figure 19.13 demonstrates how the shelf life plot is used for extrapolation. It is食品伙伴个性空间Kn_x8M
always a good practice to compare a model's prediction against actual experimental
Q`{2e"x ?0nM0results because of the potential for errors from using the higher temperature data as
$@ ?$igo[O[)At0noted earlier besides the other errors suggested by Labuza and Riboh (1982). In
^KNTp:dP'Vx2F Z0addition, the existence of a glass transition at a temperature between the test
!R!T1|d ~.^Cq\q0temperature and the prediction temperature would lead to error as shown by Nelson
@:tU(p Z-~|/Fi0and Labuza (1994). In the case of frozen foods, most likely the error would be an食品伙伴个性空间Yk_k"_:A
under prediction of the shelf life.食品伙伴个性空间7M,`CI+o"\P
ln Q食品伙伴个性空间*DIR)u8yE
T
-{h)wZN?p1n&q0T1食品伙伴个性空间V|Y4W9G
T2
O1ZjEn6V4v0T3食品伙伴个性空间tCRw6rHDY
Ts (commercial storage temperature)
9x!eTA] NwNy-]4sigure 19.13 Extrapolation from ASLT
1L8Z:iz2y:nD'_,lz0Step 7: Predict quality loss for a fluctuating time-temperature distribution — The食品伙伴个性空间b/Nc_r:J
prediction is based on two assumptions: (1) that there is no history effect from the食品伙伴个性空间"AS!L'l#Vl D_t
time-temperature variation and (2) that the key deterioration mode does not change as食品伙伴个性空间 Q8u3H-T"Gl[)]
a function of temperature. The frozen spinach data shown in Figure 19.12 is used in食品伙伴个性空间5m-x9hR6}&q!\/[#W
the following example in Table 19.7 for a time-temperature distribution. The line食品伙伴个性空间h5g&n`U~J
33食品伙伴个性空间B_,x%d:H j#L R&L.J
equivalent to 20% loss is set as the end of shelf life limit i.e., if Ao = 36 mg/100 g then A
)t"jo+Z JR0at the end of shelf life is 0.8 x 36 or 28.8 mg or 7.2 mg of vitamin C can be lost. For
m"AIt7Ma4v)|)_0each temperature of exposure, the time on the 80/80 line is the time for 20% loss, thus
s-W dgY!lYd:e$bj0at -10°F, the 20% loss (equivalent to 100% shelf life) time is 16.5 months. Thus for 6食品伙伴个性空间;d:{2Q:AbQSm A
months storage at -10°F, there is 6/16.5 or 36.3% of the shelf life lost and the amount
0SGiF tB(?A0left is 36 - 6.36 x 7.2 = 33.4 mg.
B}d%R%rieI l`0Table 19.7 Estimation of quality remaining of frozen spinach after exposed to a
2N3DI'nt0variable time-temperature history with Ao = 36 mg/100g spinach.食品伙伴个性空间qgaYjIj;h'Xj
Temperature
#Ex9tX0f(C4Cq0(°F)
&L:sB%~ Au\#ET vE0Time t
Q,QQO*[8Imi0(months)食品伙伴个性空间^1a9l%Hl.V
q shelf life
9D1p7R9^)i6F(f h7R2eU0(months)
%{/TyZy0fcon食品伙伴个性空间m x$J8]T CE;C^Eli
(t/q )食品伙伴个性空间 }2O*j~L _LX
Sfcon Aremaining食品伙伴个性空间-D?4i^ iX4`,y{
(mg/100g)
"]kX7x$UG0-10 6 16.5 0.363 0.363 33.4食品伙伴个性空间 l&P&OT"p c)qL
+3 1 4.5 0.256 0.619 31.5
@,R {Y+h3k)[JV#L0+12 0.25 1.6 0.156 0.775 30.4食品伙伴个性空间 LL%s)^(U/A:d1A$j
Since as noted 80% of Ao is equal to 28.8 mg/100g at end of shelf life, this product is食品伙伴个性空间;j] k8K}sN |
still acceptable at the end of the set of three different time/temperature exposures. In
+?e2vY_q z0fact, the shelf life left @ 5 °F = (1-0.775) x 3.3 = 0.74 months = 22 days.食品伙伴个性空间g$FwU1Eg h
19.5.3 Applicability
3w"T5E^os1G6m/Cm0Because of relatively long shelf life for frozen foods and the unique feature of freezing,
u8ZW^ A1YO0the degree of temperature elevation is largely limited. Prediction of actual shelf life食品伙伴个性空间Z8Nn$vz8Dk1y
from ASLT may be severely limited except in very simple food systems. Frozen foods食品伙伴个性空间6~f U~1C)G-}
such as frozen pizzas, may present problems with moisture migration. The moisture
-p0e|?;@0may diffuse from the pizza sauce which has a higher aw into the crust containing a食品伙伴个性空间A'jx$AV2jp\@
lower aw, creating a pizza crust that is limp and soggy. Product development scientists
xmxsu$f/tw0should only use the results as a guideline and must use as many storage conditions
Wjq&leB+f'xAG0as possible to minimize prediction errors.食品伙伴个性空间9LJNDVw W^
34
l1bu,}w'd%i0ASLT is just a quick method, which can not replace the normal storage tests
I+W$b \"mKa,r@1N.l6w0discussed next. Once it is verified that the extrapolation may be wrong, i.e., too large食品伙伴个性空间(~AA^Z"` TL F
an error, then a careful look should be taken at the deterioration mode, the experiment食品伙伴个性空间6yA.])c$kb
design and procedure, the data collected and the model developed. If the
*vxYGs,bPCOG0extrapolation under predicts the true shelf life, then it becomes an economic concern, it食品伙伴个性空间s-s2Z~b:W
is over predicted, then reformulating may be necessary. If the shelf life prediction
K@0S(W9FZ{F0indicates that the product meets the stability expectation, then the product has a食品伙伴个性空间lP ? h2DK7mKm
chance of performing satisfactorily in the marketplace.食品伙伴个性空间&M/N^ KtT+Y
19.6 Confirmatory storage study食品伙伴个性空间2Q:ce.Q9JX~ ~(XYE5v
19.6.1 Basis
%{"P7})w6R \.O zp0The difference in potential shelf life should be considered when scaling up from食品伙伴个性空间,_b @'g$X6[koNv
experimental test batches to pilot plant and then to full scale production. Experience
f:P:?;_N1z |0has shown that results of small-scale experiments in the laboratory may not be of食品伙伴个性空间G.pq@FG!Y7p
much use for large-scale production (Graf and Saguy, 1991). Scale-up not only affects食品伙伴个性空间U6\i9Jgj KD`7jU8Zb"T
the processability and quality of a food product, but it often alters its shelf life.
"d"?tE9VL6`0Depending on the mode of failure and the food scientist's approach to inhibiting
Z%f'CX`2m1r0microbial growth and chemical reactions leading to deterioration, scale-up may
$X.X5Wj4\0

TAG:

sunny leesunny 发布于2007-12-01 11:26:42
冷冻食品保质期试验.pdf
冷冻食品保质期试验.pdf

冷冻食品保质期试验.pdf
(2007-12-01 11:26:42, Size: 193 KB, Downloads: 185)

xldu发布于2007-12-04 13:25:24
正好想跟大家请教一个问题,食品的保质期是如何人确定的?
璇玑之 爱乐爱乐 发布于2007-12-04 13:40:14
晕就一个字space.foodmate.net/Nju        y_
_:};?4{

全是E文
洞庭码头 oliver2008twist 发布于2008-03-20 11:34:03
Very good book ,Thank you
chenfenna的个人空间 chenfenna 发布于2008-09-11 08:19:29
有点难度!
/qtK(a
W}u*tQ食品论坛,食品行业社区,关注食品安全、食品技术、食品质量、检测技术等
请哪位高人翻译翻译,就太感谢了!
XRH2004的个人空间 XRH2004 发布于2009-04-14 20:36:56
冷冻食品保质期
请高人能否把他翻译成中文
sunjm0320发布于2009-04-21 09:44:09
这个很有用的,谢谢啊!
wtao-0678发布于2009-04-26 11:32:36
英文的,看不懂啊,那位大虾给翻译翻译就更好了
麦香豆发布于2009-04-27 10:53:41
神呀!E文专业地!!
KX-T7665发布于2009-06-29 12:04:49
回复 1# leesunny 的帖子
正想找有關資料,謝謝
food86发布于2009-06-29 13:19:00
只能认识单个单个的词,那位高手翻译一下啊
clyde-chen的个人空间 clyde-chen 发布于2009-07-20 10:49:57
下载学习中,谢谢楼主!
食品专业户发布于2009-07-23 16:33:34
正好想跟大家请教一个问题,食品的保质期是如何人确定的?
论道-竹叶青 论道-竹叶青 发布于2009-07-23 22:22:16
楼主太抬举我的水平了!
heiniuzxf发布于2009-07-24 08:32:04
有需要翻译资料的找我:heiniuzxf@126.com
binggan1217发布于2009-07-24 09:18:26
下载学习中,谢谢楼主!
junshengwang67发布于2009-07-24 10:31:13
保质期有以下确定方法:1.国家法律法规规定.'z%~!J,A/X
  2.实验室确定的数据.3.经验数据.
spzhr发布于2009-07-24 16:45:34
好资料,谢谢楼主,就是看不懂英文
unwakenman发布于2009-10-10 17:03:04
英文就是更难准确理解
joseph612的个人空间 joseph612 发布于2010-06-15 11:29:17
谢谢分享,下载了好好研究!
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