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冷冻食品保质期试验.pdf

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Shelf Life Testing:
O-zsNv1PX*j*E0Procedures and Prediction Methods for Frozen食品伙伴个性空间,J[.wf0C
Foods食品伙伴个性空间 M"R3_s(Dpv
Bin Fu
'`Ay-nM3u.gj0Kellogg's Battle Creek MI
.K;\K }JB Ne`h(lRg0Theodore P. Labuza
c7ad/B+RRZ L0Dept. of Food Science & Nutrition, University of Minnesota
8c5} tk0|SS;L01334 Eckles Ave., St. Paul, MN 55108食品伙伴个性空间 {)e ]|%q
2
hj!s^Yv(_019.1 Introduction
L5Tq7o+U4fb/R u0The 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r.|f%?2Su$y
to consume and/or has an acceptable quality to consumers. Just like any other food,
*o x~(W7@0frozen foods deteriorate during storage by different modes or mechanisms, as食品伙伴个性空间/F#o(W m^0Bn d
summarized in Table 1. Microbes usually are not a problem since they cannot grow at食品伙伴个性空间1re mg"K?2vGZ
freezing temperatures unless subjected to extensive temperature abuse above the
Iwj2~kJ |7Y'`0freezing point. Enzymes are a big concern for frozen foods, which can cause flavor食品伙伴个性空间G5t5mz2s+| Eh{ V
change (lipoxygenase) in non-blanched fruits and vegetables and accelerated
rP@D/n`J0deterioration reactions in meat and poultry (enzymes released from disrupted食品伙伴个性空间}.qS3b#J
membranes during precooking). Cell damage or protein and starch interactions during
*V RHSwf(B3H0freezing cause drip and mushiness upon thawing. Discoloration could occur by nonenzymatic食品伙伴个性空间UNR!{ZfAR]
browning, bleaching, and freezer burn. Vitamin C loss is often a major
^'VcwXh3n;I0concern for frozen vegetables. Physical changes, such as package ice formation,食品伙伴个性空间(Mvn.lu
moisture loss, emulsion destabilization, recrystallization of sugars and ice of frozen食品伙伴个性空间 Y[dA#KU#UGi
desserts are often accelerated by fluctuating temperatures.
b$DaEjhxf(E\0For any specific frozen product, which mode determines its shelf life, depends
'Z5hf(bb0on the product characteristics (raw materials, ingredients, formulation), pre-freezing食品伙伴个性空间8D,|6u(M0N3\2z;Q
treatment, freezing process, packaging film and processes, and of course storage食品伙伴个性空间}J6l\lx;e
conditions. All of the quality deterioration and potential hazards are usually
j4_ HV-k|t7G0exaggerated or complicated by a fluctuating time-temperature environment (e.g.食品伙伴个性空间t7~7I Fw_v6y%`
freeze/thaw cycle) during storage. On the other hand, the shelf life of a frozen food
1Zw`+qbZ5^0can be extended through ingredient selection, process modification and change of食品伙伴个性空间'F$R"K~]S U
package or storage conditions, as discussed in Section 3 of this book.
wL~+e7c3w/m R5[0This chapter will focus on shelf life testing of frozen foods for product食品伙伴个性空间 HZ+YU}
development and market practices. Shelf life testing consists basically of selecting the食品伙伴个性空间~ AV'Mu
quality characteristics which deteriorate most rapidly in time and the mathematical食品伙伴个性空间6y6Ue;p CJ
modeling of the change. Table 19.1 can be used as a reference for the selection of
)a"W3r4mUm0quality characteristics, which depends on the specific product and usually requires
reKon-Q9}0professional judgment. Mathematical modeling of quality deterioration will be食品伙伴个性空间8X,hJ_;\/L,Nx4m wi
discussed next.
N%fAi-K^&e03食品伙伴个性空间OtN6LVlG_\
Table 19.1 Deterioration modes of frozen foods
.V? ~4[YMV-M0Frozen Foods Deterioration Modes
'b8b8JM%K.TH0Frozen meats, poultry and seafood Rancidity
3lBKm4f wU(U0Toughening (protein denaturation)食品伙伴个性空间$ws7A:g'E;A
Discoloration食品伙伴个性空间$\*|l7~c
Desiccation (freezer burn)
e;| H)YTQ%h0Frozen fruits and vegetables Loss of nutrients (vitamins)食品伙伴个性空间V5CM3{b
Loss of texture (temperature abuse)
K7qk@1bBC#`Q%P\0Loss of flavor (lipoxygenase, peroxidase)食品伙伴个性空间8]`o `rdG
Loss of tissue moisture (forming package ice)食品伙伴个性空间o+~6ZSPm3te'T~C
Discoloration
3\5J\La0N} JYG0Frozen concentrated juices Loss of nutrients (vitamins)
%S#PWw)_'o3N$n iF0Loss of flavor食品伙伴个性空间0tZ+_(h ~"YZ[
Loss of cloudiness食品伙伴个性空间5R(i DH&d;H1a3P.DM
Discoloration食品伙伴个性空间8f%R&xh&|4OjIY;S
Yeast growth (upon temperature abuse)食品伙伴个性空间"?]H9rxmP
Frozen dairy products食品伙伴个性空间1|B Z$p3[
(ice cream, yogurt, etc.)
Sc X#[z#Lg#v.W0Iciness (recrystallization of ice crystals)
/EP9x-L*x` f0Vkq1H0Sandiness (lactose crystallization)食品伙伴个性空间([(q#Ynk fNj
Loss of flavor食品伙伴个性空间)pnG-Y D ?{
Disruption of emulsion system
k k3v [q)y0Frozen convenience foods Rancidity in meat portions食品伙伴个性空间5^nEEI3OQ5xp7DJ+Y
Weeping and curdling of sauces
.n:W!{h4D#E2q3H)h@A}0Loss of flavor食品伙伴个性空间2Q ]2a:m(R+mx
Discoloration
O~![Tx w&~+k0Package ice
.SDjlI#}.p$}E+I0Frozen bakery products (raw dough,
.Ha+F q_ [1y4L0bread, croissants)食品伙伴个性空间"qQ1e$F PB dH8lF
Burst can (upon temperature abuse) (dough)食品伙伴个性空间?(N"za:w sU5SVXh
Loss of fermentation capability (dough)食品伙伴个性空间2Iupj/ek%\
Staling (becoming leathery)食品伙伴个性空间 {kP!F rO j
Loss of fresh aroma
%~"hvJE019.2 Modeling of quality deterioration
jOg$r5vD5y(O9|019.2.1 Basic equation
#}`1aR"b0A frozen food starts to degrade once it is produced (Figure 19.1). The rate and食品伙伴个性空间Y:k[WJY(\
the degree of degradation depends on both the composition and the environmental
K]([V}x,fhb`0conditions during storage and distribution. In general, the loss of food quality or shelf食品伙伴个性空间T$F;Z7Ye*GEO9hA6b(d
life is evaluated by measuring a characteristic quality index, "A". The change of quality
!W&f(N1ii zTY0index A with time (dA/dt) can usually be represented by the following kinetic equation:
p3s+M r"`'r,K0- dA/dt = k An (19.1)食品伙伴个性空间'HxU4gK,zP6D
where k is called a rate constant depending on temperature, product and packaging
/N[X6h*OJ0characteristics; n is a power factor called reaction order which defines whether the rate
0\2}]J.adp04
'O/oU [ o+|C j2P0of change is dependent on the amount of A present. If environmental factors are held
-VuvZ5x~Bk&p0constant, n also determines the shape of deterioration curve.
F.Q*LqV0Ao食品伙伴个性空间9Fk})Mir-{r
A a食品伙伴个性空间EB ]4CwHCPo
b食品伙伴个性空间G5g:bw#h\7P cS6Q
c
6v0XW!re-y S^0t
5s!J/feQ!?:w2N{0d食品伙伴个性空间ac)}4rd ts
e食品伙伴个性空间_d|.n Re \
Figure 19.1 Quality deterioration curves: a) linear; b) exponential;
y4rNiS+R%OBy0c) hyperbolic; d) quadratic; e) complex.食品伙伴个性空间0Kn(j!k&iCB0FJ]
19.2.2 Zero and first order kinetics食品伙伴个性空间8]mXtJ6YW Ug
Equation 19.1 can also be written as:食品伙伴个性空间!s4gE mm!M Q5j
f(A) = k t (19.2)
:D ]7Y*@ R o sA3L0where f(A) is the quality function, k and t are the same as above. The form of f(A)食品伙伴个性空间W/`;d1n/J2t-J&J
depends on the value of n. When n is equal to zero it is called zero order reaction食品伙伴个性空间 ^ ol&}JG`Xdl Q'bo
kinetics, which implies that the rate of loss of quality is constant under constant
w(n-P)C y6b0environmental conditions (curve (a) in Fig. 19.1). If n is equal to one it is called first食品伙伴个性空间/xRVU t/_Z.NgI
order reaction kinetics, which results in an exponential decrease in rate of loss as
~B*f2Q K f-\%r0quality decreases (curve (b) in Fig. 19.1, which becomes a straight line if plotted on a
-L E#u;i#N6E9em0semi-log plot). These quality functions can be expressed as follows:食品伙伴个性空间1I([Q7L3rX0R&~ s"|
f(A) = Ao - A = kzt zero order (19.3a)
-oE9vn+O6@0f(A) = ln Ao - ln A = kft first order (19.3b)食品伙伴个性空间(s l5UbA8}
5食品伙伴个性空间z%a$_6e;qG
where Ao is the initial quality value. If Ae corresponds to the quality value at the end of
lGar-i@!b"]0shelf life, the shelf life (q) of the food is inversely proportional to the rate
[F-yqK_.[0constant:
T']JmeG0q = (Ao - Ae) / kz zero order (19.4a)
'g P&g3{WYpF0q = ln (Ao/Ae) / kf first order (19.4b)
Rk S"^;]0It should be noted that most chemical reactions leading to quality loss in frozen食品伙伴个性空间~{h0c*~sc\
food systems are much more complex. However, the reaction kinetics can be食品伙伴个性空间&}.I+~/J7t1c+gy[
simplified into either pseudo-zero order or pseudo-first order kinetics. In the case of
,lK&Fp8YCv6u0complex reaction kinetics with respect to reactants, an intermediate or a final product食品伙伴个性空间a?H%t dr({9k/I
(e.g. peroxides or hexanal in lipid oxidation ) could be used as a quality index. There
2\"q"?1VD7VJ.x0are few cases where neither zero nor first order kinetics apply. Curve (c) in Fig. 19.1
&W4`^}7G:\T0shows the degradation curve for a 2nd order reaction (with single reactant), which also食品伙伴个性空间9S}8qTl!D%Y jN
shows a straight on a semi-log paper. A fractional order should be used to describe
C7E:N:SvIk9d0the curve (d) in Fig. 19.1.食品伙伴个性空间)QhXh.{5gkI
Sometimes, there is an induction period or lag time before the quality食品伙伴个性空间)Y6]6N1P G'yF:L}4i7{$I
deterioration begins (e.g. browning pigment formation in the Maillard reaction or a食品伙伴个性空间vi)Lj&Sos
microbial growth lag phase, as shown in curve (e) in Fig. 19.1. The length of the lag食品伙伴个性空间L6E4w0k^
depends on many factors, but temperature is a predominant factor. Given this,食品伙伴个性空间O6u A$yq*r
modeling of both the induction or lag period and deterioration phase are necessary for食品伙伴个性空间!?!`\'\LH7P
accurate prediction of quality loss or shelf life remaining. An example of such work has
.@Pl#kv Zj0been demonstrated by Fu et al. (1991) for the growth of bacteria in milk.
4z M0J9hH0o0In certain circumstances (e.g. A represents a sensory hedonic score), a nonkinetic食品伙伴个性空间Tmq H:V8_Fm d
approach, e.g. a statistical data fitting technique can also be used to describe
Kf(qT2Kn0the deterioration curves. Varsanyi and Somogyi (1983) found that the change in食品伙伴个性空间.N-M X:wK'H#V5KY'j
quality characteristics as a function of time could be approximately described with食品伙伴个性空间%~.v!U-do
linear, quadratic and hyperbolic functions and that storage temperature and packing
,h4W.W*Q:I"xa0conditions affected the shape of the deterioration curves. However, the parameters
fyx'FCvfU)Hg0determined by data fitting are difficult to use for prediction under variable storage
^8W4X3f8Z z8\\yp0conditions except for the linear curve.
?%c:Nk\019.2.3 Temperature dependence of deterioration rate
2X C.D0D5}Z019.2.3.1 Arrhenius kinetics
,IS'v7t0p)Q6i0Once a frozen product is made and packaged and starts its journey from the食品伙伴个性空间!]@3B!La+P [
manufacturer's plant to warehouse, distribution center, retail store and finally
(]pP @6?tf?,j.dC N06食品伙伴个性空间3W9hW f"V
consumer's freezer, the rate of quality loss is primarily temperature dependent食品伙伴个性空间5P5Oj*d8L&bL}
(Zaritzky, 1982). The Arrhenius relationship is often used to describe the temperature食品伙伴个性空间1By&?c$z EPu'r"PR
dependence of deterioration rate where for either zero or first order:食品伙伴个性空间 k X(D"c0ti K
k = ko exp (-Ea/RT) (19.5a)
i+fHL/E+ZST-E%W0or ln k = ln ko - Ea/(RT) (19.5b)
NK*j x X9T c-Wd0where ko is a pre-exponential factor; Ea is an activation energy in cal/mol; R is the gas食品伙伴个性空间1q yLej'j9}
constant in cal/mol K and equal to 1.986; T is an absolute temperature in K (273 + °C).
2ciY6}J3|$r0Thus, a plot of the rate constant on semi-log paper as a function of reciprocal absolute
Ks1d7v8T J7C x0temperature (1/T) gives a straight line as shown as Fig. 19.2. The activation energy is食品伙伴个性空间hR+@2GI2`XH_i
determined from the slope of the line (divided by the gas constant R). A steeper slope食品伙伴个性空间` lu8CPo
means the reaction is more temperature sensitive, i.e., a small change in T produces
,lMN%W/l \'i_0are large change in rate.食品伙伴个性空间]&|~,~g&R [
Figure 19.2 Arrhenius plot食品伙伴个性空间7vI1H*Td M"V
ln k食品伙伴个性空间 `,j&bv(Sm(j
1/T食品伙伴个性空间!B1sr%@Y M
slope = -Ea/R
!~ B f|:G.` @'q0Thus, by studying a deterioration process and measuring the rate of loss at two食品伙伴个性空间$mrDv-eq
or three temperatures (higher than storage temperature), one could then extrapolate食品伙伴个性空间.M,S7uXT&};w-Df
on an Arrhenius plot with a straight line to predict the deterioration rate at the desired
/`S~1lH:X qy0storage temperature. This is the basis for accelerated shelf life testing (ASLT), which食品伙伴个性空间d r4bQ&mt5?0P-DC
will be discussed later. One should note however that in some cases a straight line
hnQ2f#B:^0will not ensue for a variety of reasons, especially if a phase change occurs (Labuza食品伙伴个性空间2rS5p:^N#j&^;x Z
7食品伙伴个性空间QI5i \G
and Riboh, 1982). Thus for frozen foods, extrapolation from temperatures above 0¥C食品伙伴个性空间:Y(P&mcc IS
are meaningless for shelf life prediction.
!M6O1v z)S nQ7? k019.2.3.2 WLF kinetics食品伙伴个性空间RgD1J/Q&o{:L
Besides the Arrhenius equation, another popular equation at least in the more recent食品伙伴个性空间KR-W [A&qN
food literature, is the Williams Landau Ferry (WLF) model (Williams et al., 1955). Its
sf] Y@oP0original form was based on the variation of the viscosity in the temperature range
O4S+\#j:`"fEt4q0above Tg as addressed in Chapter 3. When the rate constant at Tg' is substituted for Tg
!H?w7Y7P*U @ S0(Tg' is the Tg of a maximally freeze-concentrated system), the WLF model can be
zi\e:bF0written as follows:食品伙伴个性空间!G I]E'R5M9QS
log (kT/kg) = C1(T-Tg')/[(C2+(T-Tg')] (19.6a)
Zn"d DTL0or [log (kT/kg)]-1 = (C2/C1)/(T-Tg') + 1/C1 (19.6b)
\-N2o7n'?h}U0where C1 and C2 are constants. Thus a plot of [log (kT/kg)]-1 vs. (T-Tg)-1 will be a食品伙伴个性空间{qr![,mVm5_S2~]
straight 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K@Q.j"m
seen this is a two parameter temperature dependent model as is the Arrhenius
w*g^%j:EIA5ai0equation.
!De5~-Fc|,l6a#l2i6_0Frozen foods stored below Tg' are stable to ice recrystallization and other食品伙伴个性空间8z@!x3aG8C7`q
physical changes. Levine and Slade (1988) postulated that stability is related to the食品伙伴个性空间#i:^~&{)ZLv
temperature difference between storage temperature and Tg'. This cryostabilization of
:aX)E+hw%~p*@'F$l5F%d0foods assumes stability below Tg' and rapid decrease of stability above Tg' according
M fw2R*u`R"go0to the WLF relationship, exhibiting an increase in reaction rate, much higher than食品伙伴个性空间 y O;R/I*F1u*~
expected from the Arrhenius kinetics. However, this may not be true since the rate of食品伙伴个性空间W,kvM3Tu2F
chemical reactions can be expected to be influenced by temperature increase in a
?E2mq4t0complex way: (i) an increase of the rate constant, resulting from both the viscosity食品伙伴个性空间I-Yl0y@:g^
decrease and the increased molecular mobility (Fennema 1996); (ii) a decrease of the
#qI j:U/Qh0reaction rate as a consequence of the increasing dilution of the reactants Roos et al.
}bB.N5R%Y0(1996). For these reasons, it seems that the WLF model over predicts the temperature食品伙伴个性空间n9qkFl%c7L-Dt_ b
effect of rate constant (Simatos et al., 1989). As noted by Nelson and Labuza (1994),
M#NE@ P [0because of the small temperature range over which foods are stored, e.g., about D30°C
H5{Be%OoQ4PSP0for dry foods and D20°C for frozen foods, both the Arrhenius and the WLF model give食品伙伴个性空间y*Z8LD:N!L FvG
good correlations as long as one does not use the universal coefficients suggested by食品伙伴个性空间6A;R*qRsQ8?
Slade and Levine (1991). In fact as shown by Nelson and Labuza (1994), their use of食品伙伴个性空间_Q ` _}|
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 u6Y[S PLd@
is not proof that the Arrhenius relationship does not apply, WLF was assumed because食品伙伴个性空间l ?0MU1`+k
the rate was negligible below -10°C which was the measured Tg. But as seen in
8Iml Z"g5[08食品伙伴个性空间r Bc [T,d
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^v+N L!J!i
challenge in applying the WLF model for stability or shelf life prediction is that (1) Tg is食品伙伴个性空间n/g*sD"GKH,Z
not known; (2) Tg is difficult to determine; and (3) the universal coefficients of Levine食品伙伴个性空间'e.@t'jmo mki
and Slade (1986) are not applicable.
8tW8k)m!~ vy00 50 100 150 200 250食品伙伴个性空间 W5p x)k-y
0
F i&di2cJ01食品伙伴个性空间4~4kZ$d2~$BZxj#q.u
2
a4{ y4N[7NDC03
-q QmE2Y0z04食品伙伴个性空间4P/T_h}_'IA"t ]
5
;u/o] ZT d#u0-3.5
2y'Z4g `k1~0-5.5食品伙伴个性空间:OM| u+Vi/g'\"k
-8.5
(m#Cbq }^ OY0-13
9QY\&n~5vSe X0-19
NZqO2g#|.e~0Time (hours)食品伙伴个性空间I"]h-GR&{z@f
Relative absorbance食品伙伴个性空间)Aiq*dn(k
Temperature (°C)
h5^nX1u@ s00.0037 0.0038 0.0039
L#g J"D lm,X0-4
emLr^{0-3
'K:PM!~G*? J0m0-2
7{#c] KS~)c1G!f0-1食品伙伴个性空间A|wUKo|#S
0
&f`?n5QYrP,j01/T (K-1)食品伙伴个性空间1C%v,` ];K-Rp7R$Q
ln(k)
Xg*T/`4Qo0y = 79.497 - 2.1621E+4x R2 = 0.999食品伙伴个性空间!d*iF~,B9S$K
Figure 19.3 Hydrolysis of maltodextrin in the frozen state (Lim and Reid; 1991)
3nip O%M0a. Rate as a function of temperature (Note Tg is -10 ¡C)
)C Z0f iYM(j PE5kx0b. Arrhenius plot食品伙伴个性空间pJ7ah+W w
19.2.3.4 Shelf life model
:jv \2j;O3M&q4W0Most published data related to quality deterioration do not give rates or rate constants
7h0D!P)M'WVc;j/F G0but rather are in the form of an overall shelf life (end-point analysis) as a function of
1ZZ5XE4h1NP*HV0storage temperature. Since the temperature range used is usually quite narrow, the食品伙伴个性空间[[;v)JI%}\"gZl
following exponential relationship exists between shelf life and storage temperature:食品伙伴个性空间 IWsG5o/@C;e
q = exp(-bT+c) (19.7a)食品伙伴个性空间yUJ OlTa }
or ln q = -bT+c (19.7b)
`e#W&X:@:q0where 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1Tfd5F7]l'?j5v ~
and c is the intercept or reference temperature as shown as Fig. 19.4. Practically, this食品伙伴个性空间_ }p1fu-d_
is used frequently for shelf life determination and prediction due to its simplicity and食品伙伴个性空间Pgn(A8f:Z)yq1K
straightforwardness.
!r1T9e{l*f09
f%|(`o oq z9b1hsfu0Figure 19.4 Shelf life plot
%f0`"[\5h8c7s7x0ln q食品伙伴个性空间t)G-ITW(z5H*A%Iw
T
r-A8`.tQ6]&A8D/f019.2.3.4 Q10 or q10
,_~[t4|-@A(j0The Q10 approach is also often used for estimation of the temperature acceleration of
9i HTl4c-s0shelf life, which is defined as :食品伙伴个性空间+r G0U?E:fO
Q10 = rate @ T1+10 °C / rate @ T1 (19.8a)食品伙伴个性空间+LEi&l(b
Q10 = shelf life @T1 / shelf life @T1+10 °C (19.8b)
|g?rJ#j:G0Q10 = (q10)1.8 (19.8c)
%l#_n*m1rsJ;N0where 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1{o!W(V%rkx#`!U
used, which in fact is more often used than Q10 in the frozen food literature.
'D|(_6lbn O9k0The magnitude of Q10 depends on the food system, the temperature and the
E9l+E{P0absolute range. Q10 values from 2 up to 20 have been found for frozen foods (Labuza,
O+U-wc:s(Dw01982) Labuza and Schmidl, 1985. Q10 can be shown to be related to the Arrhenius
'mC^,r)yiA0equation and the shelf life model through the following expression:食品伙伴个性空间`Um x a7n&CT&G/k(@
Q10 = exp [10 Ea/(R T (T+10)] (19.9a)
k C s |pu.v`6r~?0Q10 = exp (10 b) (19.9b)
"t4F)B/^)Lk0Thus Q10 is not constant but depends on Ea and the absolute temperature T.
T xk N|U)a0Some data gleaned from July (1989) and Labuza (1982) is shown in Table 19.2.
L#|k:R4gTF.f010食品伙伴个性空间+m eui}7V
Table 19.2
$c)E5r(@"j X0Estimate of the Q食品伙伴个性空间~&bSv5k@8[
10食品伙伴个性空间#R^T5p#U(REY
for shelf life of selected frozen foods食品伙伴个性空间xm1mCU q'l
Days of HQL
B)wi:a6z1ar0I te m - 10°C - 20°C Q 1 0
uZ1[Xs'cl!H&?Y0pork sausage 20 120 4
_5s,`~iW/x`0pork 50 400 8
B#kqu4l0beef 60 200 3.3食品伙伴个性空间O|NNN)d-LV
ground hamburger 250 800 3.2食品伙伴个性空间qNPP{p,^$K
fried hamburger 35 250 7食品伙伴个性空间Y} m8@g:a2W!Rx
raw poultry 200 700 3.5
(DcX|(I3Z0fried poultry 25 700 3.2食品伙伴个性空间3k2y6R[G h
fatty fish 7 60 9
+E bB bF,SDe019.2.3.5 Other models食品伙伴个性空间sA(kKy'u4JM
The following models have also been proposed to describe the temperature
|)I X0i&[U0reQ*m0dependence of the rate constant (Kwolek and Bookwalter, 1971) for frozen systems:
8Ut&wHt [t.l{:E_&?0kT = a + b T (19.10a)食品伙伴个性空间&T2rm/I3{mCO
kT = a Tb (19.10b)
2J&W6?!Y*v tx+S$H0kT = a / (b - T) (19.10c)食品伙伴个性空间R jN3g2{n%m
where a, and b are constants. In most cases, Equation 19.10c fits data better.
*q"@ho#n"m U0However, all these have very limited practical application.食品伙伴个性空间 sS^3y(lOy-g8cA(?/XT
19.2.4 Time-temperature tolerance食品伙伴个性空间yQeG`~
Frozen foods are often exposed to a variable temperature environment, e.g. during
g I*fRU*y:AA2{0distribution or due to freezing/defrosting cycle in retail or home freezers. In general, the
E$q6t ~Uc p V0value of the quality function, f(A), at time t under changing environmental conditions
c0ImAZ+|s5t0can be estimated from:
Fp1t"LpO5b-O0f(A) = ò k[T(t)] dt (19.11)
V2d1t){-kC0where 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6Q(t5SQ)E$y
reaction order as discussed previously. If an effective temperature, Teff, is defined as食品伙伴个性空间4{s9{Cu)g&]e0D
11食品伙伴个性空间2g(] d1d;x_:MZ
that constant temperature exposure which causes the same quality change as the
%LU;| u~ z`|g xzpl0variable temperature condition, as proposed by Schwimmer et al. (1955), then食品伙伴个性空间0rT7|0M lpP
f(A) = keff t (19.12)
bE `0L V g'_0The rate constant at that defined temperature is termed the effective rate constant, i.e.食品伙伴个性空间I]i[H
keff. To estimate the quality change under variable temperature conditions, one食品伙伴个性空间 Eqjov^
needs to either solve for f(A) numerically or know the value of Teff or keff that
!v+]kaS,YT"V0corresponds to the variable conditions.食品伙伴个性空间 X(A8e o x
The numerical approach for a randomly variable temperature history is食品伙伴个性空间$n.K.mIZ$_-P
essentially the same as the Time/Temperature/Tolerance (TTT) approach initiated by
N^~{-k(G0Van Arsdel et al. (1969) and derived empirically in the 1960's for the prediction of shelf食品伙伴个性空间0_~Z'p%Wd+`)v
life of frozen foods (July, 1984). It is assumed that the temperature history of the食品伙伴个性空间 u o9thPA]
product is known. Thus the fraction of shelf life consumed, fcon, was calculated as the食品伙伴个性空间IIC:e?oH[
sum of the times at each temperature interval, ti, divided by the shelf life at that食品伙伴个性空间d v&B0L(y"En
temperature, qi:食品伙伴个性空间9AK9LH^ wz
fcon = S (ti / qi) (19.13)
_'dj$_:~#N0Thus the remaining shelf life at a reference temperature is equivalent to (1-fcon)*q.
Bg/z+x,z*a L [0Equation 19.13 assumes that the rule of additivity is valid for frozen foods (July,
q9rCxML01984), which means that the loss of remaining storage life or quality can be calculated食品伙伴个性空间Q*Mg)s5lD
from knowledge of the prior time-temperature episodes the product has been exposed食品伙伴个性空间/~9_(Su tj/{:A@V
to. This also implies that the prior sequence of the time-temperature episodes is of no
%W!V.jh3}y;X]0importance except to calculate the amount of quality remaining up to that time, i.e.食品伙伴个性空间.Gi!X7n `O&mt
there is no history effect. If the rule of additivity is valid with reasonable accuracy, the
7LXHM,_0use of time-temperature integrators (TTI) should provide reliable results with respect to
EW-yKEI&V0prediction of shelf life remaining, which will be discussed later.食品伙伴个性空间4Mx2aSZ8HX
However, there are some cases where the total effect of various temperature食品伙伴个性空间d8C)h,FzV8YfPh
experiences may not be independent of the order in which they occur or of the nature食品伙伴个性空间K g-b5M+GS
of temperature history. For example, widely fluctuating temperatures may cause食品伙伴个性空间!`1q0S:M"pt]Dw;b"k"~
freezer burn or in-package desiccation, which is not additive (July, 1984). Where the食品伙伴个性空间~ S(l4F;tu"R.|U+I
colloidal nature of a product is affected, the effect of time-temperature history may not食品伙伴个性空间$Y k6u^s1yX
be additive either, especially with a freeze/thaw cycles. This is also true when growth
x [&W6r9_Tm+D0of microorganisms occurs (Fu et al., 1991). Certain chemical reactions, enzymatic as
V/f-IS5d n0well as nonenzymatic, could even proceed more rapidly at temperatures below
lc7d$\`1g S012
D~2rq&oubZ[0freezing. This is called a negative effect of temperature (Singh and Wang, 1977),食品伙伴个性空间 g M;KAS I*ZHZ
which could be caused by one or more of the following factors: (1) a freeze食品伙伴个性空间_7Eg4f7B%wo&WX
concentration effect; (2) the catalytic effect of ice crystals; (3) a greater mobility of食品伙伴个性空间wD:I0z,udO Yz
protons 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7~1CG qxR3[
favorable orientation of reactants in the partially frozen state; (6) a salting in or out of
`]P.M8a-E/Z@f0proteins; (7) decrease in dielectric constant; and (8) the development of antioxidants at食品伙伴个性空间K` ?+^7gR
higher temperatures. As has been shown by Fennema (1975), the freeze
xBU;ex0concentration effect can cause rates of chemical reactions to increase dramatically just
6O*Z EH&f[ {0below the freezing point (Figure 19.5), e.g. ascorbic acid loss at -3°C can be faster
U3z8yBa`X0than at higher temperatures this one should not use data in the -4°C to 0°C range or
/tW:W8KMj0above as part of an accelerated shelf life test to predict rates at lower temperatures.
"w| ~;]0d#v A2S0Fennema (1975), showed that the time to 50% loss of vitamin C in broccoli was 44
7@E V t5V H C4T0days at -5°C, 120 days at -2°C and 162 days at +2°C. This concentration effect is食品伙伴个性空间S/Q'B `-bS\T4I}/i
evident in the shelf life plot of frozen strawberries as shown in Fig. 19.6 using the data食品伙伴个性空间 J0D)V Mz*N7f1b&B/F^7U
of Guadagni (1968). If the data collected only at 25 and 30°F (-3.9°C and -1.1°C) are食品伙伴个性空间5zI(` \.krt.qZ
used, the predicted shelf life at 0°F (-17.8°C) is over 27 years, if data are collected at
Q1JcW0g6J)~0only 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_;]V$U"^ ~
below 20¥F extrapolated to the true expected shelf life is about 280 days.
(|%Q.nfP\h0Figure 19.5 Rate of chemical reaction as a function of temperature食品伙伴个性空间O _HTo;x,U
above and below the freezing point of a food.食品伙伴个性空间,@6OETr$A5vG\)Q
13食品伙伴个性空间2X-RP$Rvqe@AD
Figure 19.6. Shelf life plot of frozen strawberries showing the食品伙伴个性空间8JX%o%L_4Z^@j
influence of the freeze concentration effect just below the freezing
v.ZM$yV4u)T:j0point on prediction of shelf life at 0¡F . Data from Guadagni (1968).
o$i7[0^/Te v2D Nuf0Each line represents a regression through a different selected set of食品伙伴个性空间m/W|+X5n9b
temperatures.食品伙伴个性空间_/OJTi:BA
The response ratio of the food to changes in environmental temperature (RT) is
a,rq)P*P4D7r0dependent on the fluctuating temperature conditions as well as the heat transfer食品伙伴个性空间Z0lR"Z3`+Z,[4A!`q
properties of the food as well as the package (Cairnes and Gordon, 1976; Dagerskog,食品伙伴个性空间8y"KF^d_JJ6V
1974). In the analysis of food shelf life, an inherent assumption is made that the food
7c]x_r5bK0is responding instantaneously to the environmental temperature changes, i.e., RT = 1.
?[gj&Vvx0This may be acceptable if a surface deterioration process is the deterministic factor for食品伙伴个性空间6b.D AP#fD D
shelf life, e.g. mold growth in some foods. Freeze-defrost cycles generally can be食品伙伴个性空间;`+H3A'{S
considered as sinusoidal oscillations. The amplitude of the effect is reduced inside the食品伙伴个性空间JL|hQ+I7a'Yu
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a6V&CE;bn4v
the ambient variation the smaller the RT, and hence the smaller the amplitude of the
*R G+u;es4_o0cyclic temperature variation in the package. Zuritz and Sastry (1986) also studied the
~7HHCb N0effect of packaging materials on temperature fluctuations for frozen ice cream and
~F jl;Rp0found that packaging materials coupled with a layer of stagnant air were effective
2M k zHxX0barriers against thermal fluctuations.
n?#N"Y [019.2.5 Hazard function食品伙伴个性空间E1`-{C4S?"U
14
J0iN.z r0After the product is produced, it may fail at any point in time in accordance with its life食品伙伴个性空间 sV)f Ddk t
distribution (Nelson, 1972). The hazard function h(t) of a distribution is defined for t ³ 0食品伙伴个性空间4V[@M0w!C0m
by:食品伙伴个性空间BI0|3S|
h(t) = f(t)/[1-F(t)] (19.14)
1B+Tk%q.f0where f(t) is a probability density function and F(t) is a cumulative distribution function.食品伙伴个性空间4xkS tcf2A
The h(t) is the conditional probability of failure at time t, given that failure has not食品伙伴个性空间5Mm@S;H'l
occurred before ..食品伙伴个性空间~WlI ~)T-yR
The behavīor of a hazard function for studying the shelf life of food products can
]+K$v |w yh-nd0be easily understood by examining the "bathtub" shaped curve in Fig. 19.7. Note that
U7g?X$RX4bY ~0at time to, a frozen food product begins its journey to many distribution outlets for
z C`6F'q0consumption. During the time between to and t1, early failures may occur owing to a
t$mf6u/aa-v|0failure in the process itself, faulty packaging, extreme initial product abuse, and many食品伙伴个性空间8W$D:]&Vjk _L/N} d:@
other environmental stresses to which the product is subjected. Early failure should not食品伙伴个性空间tg;}u.T$S
be taken as a true failure relative to the shelf life of the product unless it represents the
#p xn [ @ De t0normal condition. From t1 to t2 one can expect, barring chance major temperature食品伙伴个性空间f*{ZPka9e{ J
fluctuations, no failures. This interval represents the true period of the product's
Cs]f$i/t X0l,E0stability. The failure rate is almost constant and small during this time. The hazard or
"kn^9Fh7q0failure rate increases from time t2 to the termination point t3, owing to the true
%V&\1Zub h"r6v]'H0deteriorative changes occurring within the product. The concept of hazard function is食品伙伴个性空间#B!]CwFr5hBVl
important in the analysis and interpretation of the failure times of a product.食品伙伴个性空间 e7J{6a1Ga"c9m;a m
Time
)kwT5ke j%sC0to t1 t2 t3
U.ILOY \0Early
P9E1ShZ(W5Z W0failure
*@a~uKy(R/D0Period of product stability食品伙伴个性空间$`'B(F j1u;N"D5L3E h
Failure due to食品伙伴个性空间7~A uO ?
product
S \5nhe q0deterioration食品伙伴个性空间hD W,t#}*G}c {
Figure 19.7 Failure rate as a function of time食品伙伴个性空间gv!R i Ur
15
i;a n4^'du5po _#L r0A fundamental assumption underlying statistical analysis of shelf life testing is食品伙伴个性空间E+@M Vc"j&K M
that the shelf life distribution of a food product belongs to a family of probability食品伙伴个性空间(nr4n;]R(D
distributions and that observations are statistically independent. Parameters of a shelf食品伙伴个性空间9x/ON\BB z^4hYS
life distribution are estimated by use of shelf life testing experimental data. Once the
*@:f \0c } \|*y0parameters of a shelf life model have been estimated, it can be used to predict the
]tv9z)Iy9S3e"g0probabilities of various events, such as future failures (Nelson, 1972). Five statistical食品伙伴个性空间{0D^XW1uD(P
models, normal, log normal, exponential, Weibull and extreme-value distributions
~,PN'Lz+bt0were tested for a few food products (Gacula and Kubala, 1975; Labuza and Schmidl,
E-C/vxu01988) and it was found that the Weibull distribution fits best, which will be食品伙伴个性空间y/o\|"e'LD
demonstrated later.食品伙伴个性空间 b;D1\tE y$oe
19.3 Shelf life testing — overall aspects
Wp"y2^!n ~&^019.3.1 Purpose食品伙伴个性空间 A0SlO)B$c$|3d
In the development of any new food product including reformulating, change of
.N,TuW+x~@/j0packaging or storage/distribution condition (to penetrate into a new market), one食品伙伴个性空间s"p?o2LP
important aspect is the knowledge of shelf life. The shelf life of a food product is vital to
cm"SL~;f0its success in the marketplace. This life must at least exceed the minimum distribution食品伙伴个性空间L[ jF| n
time required from the processor to the consumer. Shelf life testing can assess
!ZqMW2i V%d%o0problems that the product has in the development stage, following a "fail small fail食品伙伴个性空间$a Z'Bs"XhUy%I)Q
early" philosophy, thereby eliminating large disasters later. Marketing/brand managers食品伙伴个性空间9c'\hz!E
also need reliable shelf life data to position the products and to establish the brand.
4Y!_k M:]Hk qQw0Periodic determination of shelf life help to provide assurance that the product remains食品伙伴个性空间%tm2U A/L1Ir
consistent over time with respect to quality.
(x,A#nT7}F-\ai0Different shelf life testing strategies are necessary at different stages, as食品伙伴个性空间t!O*jq`wr k Ad
illustrated in Fig. 19.8. If the objective is to identify whether pathogens and spoilage
7`*w/j7f|EA0microbes will grow in the case of temperature abuse, then a challenge study is
j,_CBL3C0necessary. If the objective is to quickly estimate the approximate shelf life of the
5~j'}kS8@d [0product then an ASLT can be used, as long as the proper temperature range is
-o [;_)n0xC5p`0chosen. A confirmatory shelf life test may be conducted at the last stage with食品伙伴个性空间_+T mF
simulated distribution chain conditions, although in today’s R & D environment, this食品伙伴个性空间(y4t ?!S/e
may be skipped.
N.s t4@'d*yj O016食品伙伴个性空间&L-{-Rq^WI
Product concept食品伙伴个性空间B)y"y k)I:v#Ns({Br
Prototype development食品伙伴个性空间9U6g-J)Wq
Pilot line testing
:ZN%V fV1C.y0Scale-up line trial食品伙伴个性空间Xp)GS8ni
Full line production
:HKxoJV H0Marketplace
&cS P6{|~;S Gl0General stability information
lp!Cjsd0Challenge Study食品伙伴个性空间%W B.v` n@-_ D"r
Accelerated shelf life testing食品伙伴个性空间O!D"[%o ~-j
Confirmatory storage study
,I OI8op{6j7n0On-going shelf life monitoring
`CIRT0Q0}2I {0Figure 19.8 Shelf life testing strategy at different product development stages食品伙伴个性空间tVLWRO
19.3.2 Shelf life criteria
|$G ^,c'x/hH0The criterion for the end of shelf life may be variable depending on the definition of
g p(JlCM'_0product quality grade, so the shelf life of a product may also be variable. The shelf life食品伙伴个性空间JqRv;]
of most perishable and semiperishable foods is almost solely based on sensory食品伙伴个性空间3z0Z"Ft5d7Hc!]2y
quality. For example, fresh meat degrades mainly by bacterial activity and rapid食品伙伴个性空间JS$M(w(q
chemical oxidations that cause an off-flavor development and loss of color. This is
7?(T0M"_DZ9a0readily recognizable by consumers. In contrast, many longer shelf-life foods including食品伙伴个性空间}~)fw O[
most frozen foods degrade mainly by slow chemical reactions such as loss of
y_;Fs.\/~P0nutritional value. For example, the vitamin C content of some frozen fruits and食品伙伴个性空间M1n:B7E9rY
vegetables, may fall below the required standard as listed on the label before sensory
~0^:hY.\ ?-iH%?0quality becomes inadequate.
v$qp7\]+c3o(U0x0The criteria for shelf life may also vary depending on the sensitivity of the
P%J%{(N'xk"k9I,m#M0consumer. For consumers, taste, odor, and appearance are the most obvious criteria;
FyP)Y"DR&I~+B ?0in academia and in the industry, sensory evaluation correlated with instrumental
$I8[x^'iB ?s0measurements of a given quality index (e.g., vitamin C level) are usually conducted. In
nd/j#K@-?J0general, the criteria level corresponding to the end of shelf life of a product depends食品伙伴个性空间Oi xstg:`
17食品伙伴个性空间ti4Dxh-~Gk
on: (i) any legal requirement, e.g. zero tolerance for botulinum toxin; (ii) consumer食品伙伴个性空间 AEzs+u"n&N
preferences or marketing requirements; and (iii) cost. In essence, the end of shelf life食品伙伴个性空间*~'A$Xz)cjx oy
depends on the percentage of consumers a company is willing to displease. If 100%食品伙伴个性空间&h+f7T*qgX.Y
acceptance is required then high cost ingredients and absolute control of distribution
!G&j)L2FA Y uiB ?0up to point of consumption is necessary, otherwise there will always be some people
J9A8A4|f!Y!f0who will get foods beyond shelf life. The aim is to keep this as small as possible.食品伙伴个性空间7\G Q,o uh;F:B%f
19.3.2.1 Just noticeable difference (JND)
#g+OOOw5d!Ek!I9G0Sensory (organoleptic) examination of foods was a general procedure used by the食品伙伴个性空间~C]!mrR#C,St
human race to evaluate wholesomeness of foods long before the discovery of食品伙伴个性空间?a%y(qPT#M7Q
microorganisms. Sensory evaluation of foods by scientific methods can be used to食品伙伴个性空间Cd&cbM+zC
evaluate such attributes as taste, odor, body, texture, color and appearance. Changes
$qgb fCa#]b0in these attributes may be brought out by microbial or non-microbial actions, usually食品伙伴个性空间 ?wK3F*~&q6|
the latter for frozen foods.
b u r}.^ O0xN0The methods used to evaluate sensory shelf life data include difference testing食品伙伴个性空间?hb%fCx'T
and hedonic scoring. Difference testing can involve paired comparisons, duo-trio食品伙伴个性空间%APjwD N%A8y^
tests, or triangle tests. The paired comparison procedure determines the time when a
0s/{ ht T{SkU0measurable difference in quality occurs between two test samples at a certain level of食品伙伴个性空间 w2m4urjW2H [u
probability. When applied to frozen foods, this method is often referred to as the Just
f D!FBa c0?]0Noticeable Difference (JND) test or High Quality Life (HQL) test (July, 1984), which is食品伙伴个性空间N@ENk(sGK0?9w
usually based on flavor changes. Duo-trio testing compares two unknowns to an食品伙伴个性空间j%E*H4?|
unabused control sample and asks the question of whether either of the unknowns are食品伙伴个性空间Z~O0H;[
the same as or different from the identified control. Triangle testing determines the one
C6I#Z6P3[}$|3S0different product among three test samples presented randomly to a set of judges (at
p OK+C']/YS+Q4X]0least 10). Probability plots are used to predict shelf life at a given probability level.食品伙伴个性空间/}}ljL"R2i P V3_#H
The difference method can result in finding a difference when none really exists (Type食品伙伴个性空间AQ[,L PT(W
I error), or not finding one when indeed there is a true difference (Type II error).食品伙伴个性空间AE,l.}v$|W/i6F kg
Labuza and Schmidl (1988) have discussed this topic more thoroughly in relationship食品伙伴个性空间'~[&}m8f$V^V2ML
to shelf life testing, which is not commonly found in sensory textbooks. Table 19.3
'[%n }9\"Mh NVu\0shows some data from Guadagni (1968) for HQL of frozen foods.
h+uT Yg018
0J"`4ney7I"S;i c0Table 19.3
Yq6[,nR:pi#e0Days of High Quality Life for fruits and vegetable (from Guadagni 1968)
$D+LHcj1Co0P roduct T yp e 0 °F 1 0°F 2 0°F食品伙伴个性空间U?5l,z|+MP$kd
apples pie filling 360 250 60
q8V2w#[(NK au2BJa0blueberries pie filling 175 77 18食品伙伴个性空间\R8s8U{z QS
cherries pie filling 490 260 60
I"W!Gwp@B0peaches retail syrup 360 45 6食品伙伴个性空间`SI7e?
blackberries bulk, no sugar 630 280 50
&FM'X@^'U,y `l0raspberriesbulk, no sugar 720 315 70
CZ$Q E-B0I)o'z5E0retail, syrup 720 110 18
2N!}.R'|E0strawberries bulk, sugar 630 90 18
!w2F{%^LB1fi-|U0retail 360 60 10
Zkuox0green beans retail 296 94 30食品伙伴个性空间U M&A;D6`8D4~7V T9|Ay
cauliflower retail 291 61 13食品伙伴个性空间_q4Y8[(s4_ r zS
peas retail 305 90 27食品伙伴个性空间9{4d|w%@ L` s6in
spinach retail 187 57 23食品伙伴个性空间-oH:?\tm-[|
corn retail 720 360
~qcD;?,m^!V0corn on cob retail 275 150
aT4g @m6ot0q019.3.2.2 Hedonic scoring
,r O @$[k r^(t0Hedonic scoring — which indicates acceptance on a numerical scale, e.g. a 1-9 point
*{$Y!oS d#pu V0scale labeled from "dislike extremely" to "like extremely", is typically used for shelf-life食品伙伴个性空间n5dl6_2~9?
evaluation. The test can be designed to not only evaluate the overall acceptance of the食品伙伴个性空间0{ Xk {Hyd#p8d
product, but that of specific characteristics such as flavor, texture, appearance,
`NF)l {"M0aftertaste, etc. Trained panels can also use this technique on a line scale, which can
.UE}rMgE0be converted to numerical equivalents.
h2D7y[(X8l0If the hedonic method is used to evaluate shelf life, one can simply use the食品伙伴个性空间 ][ k qwn
score as quality index A and plot the score vs. storage time, run a linear regression,食品伙伴个性空间0a f!X wcn!y#lZ
and choose the end of shelf life as the time when the progressed value drops below a食品伙伴个性空间S(e]_E7|
pre-set level (Waltzeko and Labuza, 1976; Gacula, 1975). The shelf life determined in食品伙伴个性空间)_?V?.G H#W ID
this way is called the practical shelf life (PSL) for frozen foods (July, 1984), and is食品伙伴个性空间r6Ot E [gfn
longer than the HQL or JND. The use of hedonic rating scales may be of limited use in食品伙伴个性空间 hT%u%I-\
shelf life testing, yet it is probably the most used method. Many food companies use a
XO B rzG6f1{0loss in hedonic score equal to D=0.5 for HQL and D=1.5 for PSL as the end of shelf life食品伙伴个性空间9nw3e}q*ZW&u$u
19
/gDv^2^z%a9t0(Labuza, 1982). Objective measurements and professional judgment are often
2~C1c!BvL{4rG0required to determine the end point. Data in Table 19.4 from an report published by食品伙伴个性空间*uS6td7YH
the former Refrigerated and Frozen Foods Institute (1973) Unfortunately there were no食品伙伴个性空间3q-Nz)tExc&A
methods 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 d3DbF soe,CV/c
HQL value. This in itself suggests that the HQL methods can be used to shorten shelf
7E(g'H'u:]Bp/g zG0life testing times.
p6H^E#hRV(O0Table 19.4
Y)P h5yV3n;J+?0Relationship between practical shelf life (PSL)食品伙伴个性空间[Is#Ow'M
and High Quality Life for frozen foods.
E#e#Tl\c$w0O,jn0F rozen Food P SL/HQL Rati o食品伙伴个性空间,}3cS/}ND7{ zF4E
lean meat 1.9 - 2食品伙伴个性空间n8XA+d8^P:e*c
fatty meat 2.0-2.4
EpY,c1~@O0lean fish 1.9-2.2
M.ena0D'K{!N o [^g0fatty fish 2.4-2.7
8f^;n/E9OiU6g0precooked foods 2.8-3.0
Aj%c NL!~0fruit 2.8-3.1
N$Y;Vxh}3L0vegetables 3.1-3.5
j(Jl4Y.@.V+z019.3.2.3 Instrumental analysis食品伙伴个性空间+_w'G u @1D9y
Chemical or instrumental analysis, such as moisture, nutrient loss, free-fatty acids or
9n#v!|{1P$zt6_E4I9A0color measurement that closely correlate to sensory attributes, can supplement
B Nix_~Ax0sensory techniques. They are usually less expensive and less time-consuming than
Soo/i+HA0sensory approaches. A correlation between a physical or chemical test can increase食品伙伴个性空间/?1xs]d,Y#X;X,Y-p
the confidence level of the sensory results. For example, the following constituents or食品伙伴个性空间*P+w[ { {P)m7@
properties can be considered for monitoring chemical changes of pizza quality during
:A@8{\7c\ |0frozen storage: total free fatty acids, specific volatile free fatty acids by HPLC,
Wm6NLbvV x)S!G0peroxides, oxidative volatiles (e.g., hexanal) by GC, spice volatiles by GC, lysine, color
HO&hL{;a%a0(decrease in red color or increase in brown), in addition to sensory evaluation of taste
w/xR3q4?Y+pb0and flavor (Labuza, 1986). Most sensory experts agree that analytical methods should食品伙伴个性空间'{&W{PPN
complement the sensory tests. Vice versa, the endpoint determined by objective食品伙伴个性空间c)S?lpO
measurements should be confirmed by sensory techniques as well.食品伙伴个性空间M,oo8n${!xg
20
A w I4f ZVX019.3.2.4 Weibull Hazard analysis食品伙伴个性空间S2SAuma
The Weibull Hazard procedure requires one to first make an estimation of the time to
`)Vxh[.SEk5j0the end of shelf life. This becomes the initial estimated time limit for the study. The time食品伙伴个性空间q-[)t'xW(jy&~_ \
limit is then divided into several segments at which points panelists grade the product.食品伙伴个性空间{d x Fu,C7s
Additional panelists are added at a constant number for each subsequent time period
@ ^e u;p6E*P0to maximize the number of testers near the end of the test. The panelist is asked to食品伙伴个性空间~)SVL%|PF[,|_
grade the food as good (acceptable) or bad (unacceptable), i.e. no ranking on a食品伙伴个性空间4b/EY3oa4x|d&O
hedonic score. When the product is identified as unacceptable by 50% of the
"F2jb [s ^9k._(I0panelists, the number of testers for the next period is increased by the number of failed食品伙伴个性空间%__8N E#KE
samples plus the constant number. The interval between sample times is also食品伙伴个性空间\"I8?:v;x'n
shortened as the end of shelf life gets closer. The test ends when no more samples or
|Ru]cP0panelists are available. The scores are ranked and the cumulative hazard calculated.食品伙伴个性空间9n-h }cIAP5tX R
The critical probability of failure Pc, can then be calculated from the following equation:
i BS],T,mPq M0Pc = 100 (1 - exp(-å(H/100))) (19.15)食品伙伴个性空间+A'IR.I1uu.r
where H is the hazard value equal to 100/Rank. Choosing Pc = 50%, corresponds to
|z.Q _-GH^$ahJ0an accumulated hazard value of 69.3%.食品伙伴个性空间'Yc']/@q*l|S5v0C
The relationship between the logarithm of storage time (log t) and the logarithm
L fv:e eD'?0of hazard value (log H) is linear:
.v/X;iI vPTG0log t = (1/b) log H + log a (19.16)食品伙伴个性空间6^'z `%wcu
where b is the shape parameter and a is the scale parameter. The shelf life can then食品伙伴个性空间?Lg;k+T];mM
be determined based on the desired probability level allowed for product failure. The
{;v]'A L(z5Q"Y0lower this probability, the shorter the shelf life. This plot then allows one to make a食品伙伴个性空间O7I:D7WT ?y
management decision with respect to the probability of displeasing a certain fraction of食品伙伴个性空间|c9VV u ~KDXV
consumers. It is hoped that the distribution time is such that greater than 99 percent of食品伙伴个性空间2j)L0b;H@QP
the product is consumed before the end of shelf life based on displeasing less than
8orX,uE0X% of consumers where X is the economic value. An detailed example was given by食品伙伴个性空间L!\ ?BGP;M5R
Labuza and Schmidl (1988). It should be noted that this process can also be used for食品伙伴个性空间(E6C]-i6k'O$V
simple analytical tests such as plate counts or vitamin C. In these cases the number of
1c Vnh#])z7b0panelists are replaced with the number of samples tested. Some criterion such as 20%食品伙伴个性空间0XW}3V"YBRa
vitamin C loss is used as the negative response. Figure 19.9 shows an example of食品伙伴个性空间?2},j-_5bt5x5X+f6L
Weibull plot for a frozen food based on assumed data. A shelf life of 16 months is食品伙伴个性空间D1@1H)nTO-A
21食品伙伴个性空间5`v6OdNH x1k qC
found at Pc = 50% from the graph. From this graph then, if 95% of the food were
G0{@T9G8r*GR5g$}0distributed and consumed in 3 weeks, only 1% of the consumers would be displeased食品伙伴个性空间#Bg4S7_Gb
.01 .1 1 10 100 1000
K6xI#UmPJ[9S01食品伙伴个性空间({L?0Z[v
10
7dWC K*|7z2[0100
U.D'}(xoZjB eY0Cumulative hazard (%)食品伙伴个性空间(VKY5`#W{GA
Shelf life (wk)
6J*m&N0x-C8YQa"ij0Probability (%)
2Z4A!y z+h00.01 0.1 1 10 50 99.99食品伙伴个性空间L{f)WKc
Figure 19.9 An example of Weibull plot for a frozen food.
Oh|q[a0A shelf life of 16 wk was determined at Pc = 50%.食品伙伴个性空间u(w3afS"X9@P(u
(or 0.95% of the product is out of compliance). If the rest were held and consumed at
)U*~$Tm]uh1^x010.5 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 Kro'J-?,@|(i k9N
= 2.5% of product. Thus in this distribution model about 3.5% of the product is食品伙伴个性空间IFNY,| Sj _(}
unacceptable. To improve on this, the product must either move faster or one must
o[:X9z)X hq"r%QC0distribute it at a lower temperature. Wittinger and Smith (1986) used this approach to食品伙伴个性空间(wh c"o^
determine sensory shelf life of ice cream based on iciness and found a shelf life of 5
+T(U7|wy I0weeks at 0°F (-15.5) which fits the general data for iciness in ice cream as shown in食品伙伴个性空间)K7U bQW2c$` Tw
Figure 19.10 (Labuza, 1982). It should be noted that this gives a Q10 of about 12.食品伙伴个性空间k?)X2rr:H
22
6U0oGX8F I0.1食品伙伴个性空间!n_6u4f1qc
1
a5Ub iO"\3s{ N010
D(g8K:]*p7g ?;[0100
NF7a|-p0Temperature °C食品伙伴个性空间M1BBE8od^)b
1
L;[]s#r5deY010
;` Y*y[;JG&D0100
c7Hc G,s!w(^e'V0-30 -20 -10 0食品伙伴个性空间K"K o(pP
0.1食品伙伴个性空间 Qg?(a1r
weeks
|AvYwV N@-u Y0Figure 19.10 Shelf life plot for ice cream based on icyness
6qH"j `Cw f5Sh0perception from data of Labuza (1992)食品伙伴个性空间O/]f o6Q? W
19.3.3 General procedures
h ^~3I5Q,V0Shelf life testing experiments are designed to measure the average shelf-life of a
5q M8\~2@!uG0product under given conditions. General procedures for shelf life testing of foods were
ZE1?Ky1R"q0proposed by Labuza and Schmidl (1985), which include:食品伙伴个性空间$kAcC(k%F:?o
Step 1: Develop testing protocol — The protocol should consist of: i) specific食品伙伴个性空间5u ZgV$J~jY b#l5U
objective; ii) detailed test design in terms of product, package, and storage condition;
G.uI(I a0N(n:_0iii) execution procedures in terms of time, space and resource availability; iv) cost食品伙伴个性空间pKI_P6xU;TBT
estimation.食品伙伴个性空间Pt?&U#vN](^4?V
Step 2: Identify key quality indicator — Any previous shelf life data and kinetic食品伙伴个性空间d%tm$j3G1Q
parameters of food deterioration available in the literature (Labuza, 1982; Man and
VfX\c#P*J2`0Jones, 1994) or the distribution turnover time of a similar or a competitive product in
By7NE1V6ON0the market place, if any, would be very helpful in this preliminary identification or in
Y!q-@\`@PN:d0determining the shelf life requirement.
4Xx3P7?ytFa/Q0Step 3: Estimate product sample and control needs — The number of samples
t1J3P3p vN^0and controls required should be based on the detailed experimental design. If食品伙伴个性空间lpN$Q9E{\
sufficient product is available, extra samples should be placed into each storage食品伙伴个性空间m#\:aCK_XZ
23
([3?#d]8M!hz \0condition. Now and then it may be necessary to recheck a sample, especially if a value食品伙伴个性空间kVm5])M lW
is not in line with other data. It would be disastrous to be out of sample before failure
l+K0I*e+F&GRg5QChS0has occurred or the predetermined termination of the test is reached. Extra controls
6gO7Lzz0should also be prepared and stored. When the samples are placed into storage
-f.Y6uk4@q {!v;s(J0rooms, they should be positioned so that the complete package is exposed to the食品伙伴个性空间a#~9hYl/ad
external atmosphere, unless otherwise specified. The specific location of the test食品伙伴个性空间(s8g!Z7@~
sample should be recorded. Temperature controllers should be checked for accuracy,食品伙伴个性空间4P5w6v{,EW LF
periodically. In addition, removal of all unused samples from the storage room to make
M _EDiJ'ux-P[.Ts0space for future studies is a must.食品伙伴个性空间3xU%F/a(@8G!bo
There are various thoughts when it comes to using a control product. Some食品伙伴个性空间 D3mt PQm5[ms0Q;Os
sensory experts prefer an actual physical control; others are satisfied to just use the食品伙伴个性空间-S)dqDR
numbers obtained in the zero time evaluation. There are three alternatives when using
3O!@ | @t+`0a physical example as a control: (i) making the control from scratch each time using食品伙伴个性空间?'L/e f&a*y
the same ingredients, procedures, etc.; (ii) deep-freezing the control (e.g. pizza held at食品伙伴个性空间6S9xhlpz.`k)maL
-70 °C) and accepting that it might have changed slightly, but minimally compared to
#g:_5qwx0the product in shelf life; (iii) using a fresh batch of product which may not be identical.
1J haI#Oi4k0Step 4: Select proper package materials and package size — This is largely
%v|._] N0dependent on shelf life requirements, packaging costs and availability, and consumer
anl,b,O"WP0information. Factors such as vacuum packaging, nitrogen flushing, or use of食品伙伴个性空间_ F,[Wh
antioxidants are often considered in combination with packaging materials.食品伙伴个性空间LT)i9\*O|(k:_
Step 5: Choose storage conditions — Storage conditions are chosen based
)P&j q"EL0bUa0on the type of shelf life testing. For example, the intended commercial食品伙伴个性空间@(T:uC'ZnF1C%S
storage/distribution temperature range should be used in confirmatory shelf life testing.食品伙伴个性空间 F)T f'~.c2Bka
Elevated temperatures are often used in accelerated shelf life testing to obtain data for
t0I[5S8Z0prediction of shelf life at lower temperature or for prediction of shelf life under variable食品伙伴个性空间9z{:_e.qYl5{
time-temperature distributions. Humidity control and/or monitoring is less important for食品伙伴个性空间)}5m6U;dt1l"u5YS.s`"e
frozen foods as compared to other foods (e.g., snacks, cakes, pies, and pastries).食品伙伴个性空间2M%\6v,h5I1i
Light in the room should be properly controlled depending on the package.食品伙伴个性空间Y*B b1P6lGI8b@
Step 6: Estimate sampling frequency and duration of testing — The sampling
Kd(`jdu0frequency is generally an estimation based upon experience from prior studies with食品伙伴个性空间9x e*v:P"`Sf}2VC9s
similar foods. However, once one knows an interval at one temperature, then the食品伙伴个性空间.U`:w7o:bdx
intervals at other temperatures can be estimated using a Q10 value i.e., if the Q10 is 3
B)\^x[+|bzG;D0then for a 10°C lower temperature the sampling times can be 3 times longer. If the
6|F9\y6Dv@:y0interval between sampling is too long, the risk of under- or over-estimating shelf life
Y PI8X^ v;}_!?+X0increases. The more analyses that are completed, the more accurate will be the shelf食品伙伴个性空间+cG(A(n m]
life determination.食品伙伴个性空间oiY0Mz xG|-q
24食品伙伴个性空间 ?+k3w4`"n"v;dIc
The question as to when one should end the experiment must be based on
;H?U~yE0some pre-set criteria for failure. One criterion could be the minimum shelf life食品伙伴个性空间 {] ^z3eaT
requirement driven by product category, distribution chain, and the benchmark's食品伙伴个性空间1^/E"k)G+~{7p @
product stability. If there is an accompanying sensory test, the end time can be based食品伙伴个性空间 A@o,kH6o G
on some organoleptic inferior quality criteria from which one then can get a microbial食品伙伴个性空间4u&N` d gDq$P3{)A%d
or chemical index limit. For frozen products, several weeks to months are usually
cH7eZK0needed. If the shelf life can be estimated with any accuracy, the test intervals can be
1^ fIn Es-QkL0lengthened and clustered around the expected failure period. Most of the experts only
g)o!p+Q ^5`u0require about six evaluations to provide reliable results.
L+ZGB2Dg'n(_&y+X0Step 7: Schedule for execution — Before scheduling the starting date for a shelf食品伙伴个性空间8|A(b4r,E p
life test, one must check for the availability of ingredients, packaging materials, and食品伙伴个性空间Bi \H;N/^
storage space, and the time and resource available in the pilot plant or in the
H a^d,Q'}0processing plant to prepare the samples. One should also check for the time and食品伙伴个性空间z/U*nf Z
resources available in the microbial lab, the analytical lab and/or the sensory support食品伙伴个性空间bLhu [O[+g LU
staff throughout the test period. A copy of the test request and schedule should be食品伙伴个性空间:V&}"@4}%d+`
sent in advance to those who will be doing the work. The courtesy of providing those食品伙伴个性空间IN%Z v&F_
involved with this advance information always pays dividends. Holidays should be食品伙伴个性空间 J&h+|V;JMK+Gy
marked on the scheduling calendar, since scheduling too many evaluations near食品伙伴个性空间 z(b3i3W6nmP H(Q0E/rH
major holidays or Friday afternoon is not recommended. However, once scheduled,
I0dB w7nK1k7_q0sample observations on weekends and holidays should not be skipped over, since食品伙伴个性空间5h drN2Z
important data points could be missed.
,p'\-P A7`#c;V)ns0Step 8: Take sample and evaluate quality — Samples should be taken and
SU/E@3eh0evaluated following pre-determined schedules. Sampling plans should be
)Alwc"Zf%Qe6Ui0administratively and economically feasible, taking into account the heterogeneity of食品伙伴个性空间0cHUfE@6VJ
the food. Maxcy and Wallen (1983) pointed out the problem of heterogeneity of
#d]_]Q Q5B0samples in shelf life prediction. Multiple subsamples (³ 3) should be done for nonhomogenous
l.Y B'o v:z*MP0samples. A single package is usually used as an experimental unit.
.E"[:g1bm7[V&Sk0Replication of 3 or 4 units are desired for each measurement. For frozen foods, a
:C{$y~`d&J9Z'n$@0thawing process is often involved in the sampling procedure. Proper thawing or食品伙伴个性空间O(o8m.K*U?+EZ
microwave heating is critical to the product quality. All samples should be thawed or食品伙伴个性空间4d$hZubg
microwaved in the same way to minimize any biases.
oS1l/Ob@8R0The intended analyses should be based on the specific mode of deterioration,
[z?$B+X(H0which was discussed earlier. Whatever the choice, the tests should be reasonable and
6bh)hK&I H5]u!F0logical. The key is to make sure that one is measuring the right thing. If the wrong食品伙伴个性空间D ?? K2M$R(C*V
quality factor is measured, the test starts out a failure. Unfortunately, in many cases this食品伙伴个性空间&ON V$d%O4W9S-Q!VO
cannot be established initially, so sensory evaluation is a must in almost all shelf life
C l$L J[_&Z.w025
P2t.Dy+~5Af0tests. Key sensory evaluation techniques for frozen foods have been discussed
0e]Rk;?0before.
u2t QPFTO0At the time of each pull, one unit of the sample should be evaluated (informally食品伙伴个性空间%[*R3[xW3Z4N9j
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R.s5?&yKg
addition to the final tasting prior to a consumer sensory test. This is necessary since it
(W wdWISe%rM7Q~0helps the developer know approximately how the product is doing during the progress
2C&PO?W!o"~~*Z0of the shelf-life, helping to avoid any surprises in the results. Control samples may
.Y/W(L,E Ou0need to be prepared fresh.食品伙伴个性空间(|YI#?U)BAi:^'C v
Step 9: Analyze data — Shelf life is the predicted day at which the stored食品伙伴个性空间.d]"Ot6QOir
product (test pull) is X% less than the control at day zero (Reference). The data should食品伙伴个性空间F%H!},K-i!th
be plotted and regressed to determine that point using the proper model (zero or first).
Qt.K`3gO7d9U0All too often the data are not analyzed until the experiment is over and then the食品伙伴个性空间m OM*Yt
scientist finds that nothing can be concluded because of lack of points or a poor fit or
\3V%^)E? j\$v;aR0some surprises. Statistical curve fitting should be consistent with the chosen model食品伙伴个性空间uR6ArhkH ^1|
based on a theoretical mechanism. The amount of change and number of data points
Gw8^*j0BkM \%y0are related to the coefficient of variation (CV) of the test. A weighting factor may be
L,pN.ilJ,\3Kj0used in estimating the rate constant and its statistical limits. When the data for an
5@ yI Z O0xc SAu3qt0attribute does not fit the regression model well (adjusted R2 of < 0.8), scientific食品伙伴个性空间 J:O(Pp6N pYe
judgment should be used to decide whether the data are applicable.食品伙伴个性空间F P1e/|B^
When in doubt, a rerun on retention samples might help understand or clarify
T/g)n!n4|]0the results. Error analysis could be performed before experiments are run by first食品伙伴个性空间~0nJA'p'e)C
finding inherent errors in time, temperature, and quality index measurements, then食品伙伴个性空间q/M%W.A7?3r:bg#o]
calculating an expected standard deviation for the plot being used to determine a rate
R9nN/Csk`7|0constant. If the experimental data have a standard deviation much higher than the
MS{9^&M*eL/Rb;Q0expected value, either the functional form of the rate expression is incorrect or the data
#u|%xpZw0contain errors from unanticipated sources.
+L?gq:OuC T2g0Step 10: Prepare shelf life report — Depending on the type of shelf life食品伙伴个性空间EjkvF^ T
determination, the results should either throw light on the technical viability of the食品伙伴个性空间/E \ bRS-OXwB
product or provide answers to the questions about the maximum safe shelf life as well
R9Wi0J4}3a.h*u0as the maximum quality shelf life of the product. Before a shelf life is finally set, factors食品伙伴个性空间)s'o aZO!S9Q$~m1Xfj
in the scale-up of shelf life data will need to be taken into consideration. Based on食品伙伴个性空间,Yd0kEkg?
results from ASLT, the provisional shelf life will be set for the product. There is no食品伙伴个性空间/l yhrLc4n
government regulation which defines the product end point except for that related to
,o v Cb.a3Q#sq0nutrient levels (vitamin C and vitamin A) in 21 CFR 101.9(g)(1)(ii) which states that for
+[0h+_5wC0A.k0the vitamins listed, the analysis level cannot be below 80% of the label value if it is a食品伙伴个性空间+h:}:fNdR
natural food with no added nutrients or cannot be below 100% (21 CFR 101.9(g)(1)(i))
1u/[ i \AO+n.~026
$L*o'hm!ba+O V;RXI0if the product has any added vitamin or nutrient whether or not it is the nutrient under食品伙伴个性空间8o'H8MC+iS/z
test. Thus one must base the label value on some predicted initial variability and
&_$N2U9n1m9K| ka-m0some predicted loss during distribution and storage. The FDA usually takes samples at
*S#[ilC0the supermarket level (where they can purchase them) for compliance testing, not from食品伙伴个性空间`4_6`!Xhi*zi*G.Sv
the end of the process line so distribution losses must be factored in.食品伙伴个性空间 Ub;x9d/T
The end point of shelf life is thus dependent on your corporate objectives and
_+PQ@!BR0how much risk the company is willing to take with the brand. No shelf life test is
1TVQ^ C"~0completed until a termination summary has been written. All termination summaries
_)q;YY_(H!W.o9x x0should include the objective of the test, product descrīption, package descrīption,
"lR @3IKoL6^4_0conditions and length of storage, methods of evaluation, results (in the form of graphs,食品伙伴个性空间V[b%k@G$Ro
shelf life plots and Q10 values) and conclusions. Termination summaries should食品伙伴个性空间8tCSI4C.p1\&_8C
become a permanent record in the company library for future reference and preferably食品伙伴个性空间;K#XbR"Sl
indexed well on a computer data base for later retrieval when needed. The final shelf食品伙伴个性空间ysk^ `4v
life should also be set to give a clear margin of safety. In any case, the shelf life of a食品伙伴个性空间`*D'a$DA5L)T
new product, particularly of the high risk category, should be set based on data that
t8d3E:M{DPk0relate to the worst case manufacturing and storage scenario. The shelf life can then食品伙伴个性空间hlu/Z j'WLW&Hk
be reviewed and if necessary re-set in the light of further experience in manufacturing
dI rKjH0and control after the product has been launched.
!y/T3vW0w lGo0Step 11: Implementation — One should get top management’s approval of the
l b R wVB!iu["S0test results so that they can be implemented. Management must believe and support
P!~&j.[0[4B0]@'r0those test results. It is important for production, sales, distribution, purchasing and
H3^$e%DD} KQ:u0quality control to work together to be sure that the production is properly handled from
5m7i3JD [Q0the time of manufacture until this product is consumed.
r.sm)X)vG z:I0Hj019.4 Challenge study
+i].B0U ^%P]8A3`019.4.1 Basis
'b P4?/mZ;R#r0Freezing reduces the microbial population of foods but considerable numbers usually
k Zx[iW'j%L*Z3nS0survive even prolonged frozen storage. A challenge study is often used in the食品伙伴个性空间 W%rzy]2R4i_aY
laboratory to study the factors and factor interactions as they affect the shelf life of the食品伙伴个性空间D2u*[%xtS
product. Such simulated experiments enable the researcher to better control the study.食品伙伴个性空间 i?(z7^0p H
A challenge study is necessary for frozen foods for two reasons: (i) to predict microbial
2v"dj JZ|0growth and potential risk of the product upon temperature abuse in a distribution
m|C!w8i]`6^ f0chain; and (ii) to assess the relative stability and the relative risk of different formula,食品伙伴个性空间z$I0h"B @bf W,]4dD
different processes or different packaging materials, which is a must in new product
9UR3u Y c'YC|_0development. A challenge study may also be considered as a preliminary shelf life
(Q)J2nb+@!lw5{M0determination in terms of microbiological safety. It is often used in the early stage of食品伙伴个性空间8i-oh!F(Wy+G)q
27
2O _:gC._:x6{Ey0development since if microbial safety is a concern at this stage, then reformulating can食品伙伴个性空间g^8aVN#PF"H
be done quickly.食品伙伴个性空间,q9[ PmYk
19.4.2 Microbial abuse procedures
\`[%j9u0Step 1: Identify barriers — A composition/ingredient analysis should be done to
yuC._ h9Z3^2E0e0identify any barrier(s) against spoilage microbes and pathogens in case of食品伙伴个性空间;fy#q7W T-f qXe
temperature abuse.食品伙伴个性空间p$HG1C*s6x3Prz
Step 2: Choose types of organisms/strains and inoculation level — One食品伙伴个性空间&} @)n"Mg ]/o
principle is to use an organism or a strain that has been isolated previously from the
S n,sc_ P0product or similar foods which is responsible for spoilage or risk. The more isolates in
Ag V.W%S$V0the study, the greater is the confidence in the accuracy of the shelf life assessment. An
7U;USxa?0inoculation level must also be determined, which is generally much higher than the
)r4\0\_}C;d!~"eI0normal contamination level in a product. If the average contamination level for a食品伙伴个性空间0t3Q1h*Jkl(s,^
particular product is known, then the inoculation level should be as close to that level食品伙伴个性空间:yMX.s#kxE
as possible. Sometimes several inoculation levels are used.食品伙伴个性空间|qp"?2xgk#hT
Step 3: Determine temperature abuse conditions — After inoculation, products
%^Al o ga'q0should be packaged using the desired commercial packaging conditions, and
*i4S~5^a8QmD0subjected to temperature abuse. Factorial design and response surface methodology食品伙伴个性空间i4R]4nd!JW
are often used in designing a challenge study. A typical temperature abuse condition
5l"?G@'W0used by some food companies is provided in Table 19.5. It starts out with five sets of食品伙伴个性空间:e(R#iS#kpx
test packages placed at -18 °C to begin the cycle. At the end of the first 24 hr, one set
O5dp^kqu0of packages is removed and tested for microbiological indicators to establish a zerotime食品伙伴个性空间[n-u)r Bs N$g
level. All the other packages are kept at -18 °C for the next 20 hr, then removed
hH-{x5I0and abused by placing them at 38 °C for 4 hr. Another set of packages is then食品伙伴个性空间3EE"Tsa(^
removed for microbiological testing, and the cycle is repeated for the remaining
8\I6f/n&`bK0packages, i.e. they are all returned to -18 °C for at least 20 hr, then abused at 38 °C食品伙伴个性空间3GW:?7U9By FxD:E${Z
for 4 hr. This procedure is repeated so that one set goes through at least four freezethaw
D%IE)q J'h6CK0cycles. If there is no significant increase in spoilage organisms or pathogenic
'k$qNPgW4? R0organisms after the fourth cycle, the food is deemed safe microbiologically.食品伙伴个性空间q.D`l!C)s3W*k
28食品伙伴个性空间%P6H5[5h1^u;f
Table 19.5 A typical temperature abuse test sequence for microbial challenge
]RZ%\l'G!@0studies食品伙伴个性空间n0S3K8@{%f:G W
Day Abuse temperature cycle Number of package sets食品伙伴个性空间kg(W`v?(@
remaining
)|B Pt^2v01 24 hr at -18 °C 5
Cht"CkG02 20 hr at -18 °C
dr$U)Wl$p.WUz04 hr at 38 °C
E7MrM7F!?N!\U^-o04食品伙伴个性空间?k&~So+I^hH$GKZ
3 20 hr at -18 °C食品伙伴个性空间:QN!SC;sQ
4 hr at 38 °C食品伙伴个性空间#avy9s-|T:m#W{6w
3食品伙伴个性空间+Oq@\`hC
4 20 hr at -18 °C食品伙伴个性空间cl!FS5X @$lTu0b8I
4 hr at 38 °C
(\ h1O2PdH ]W'x;|02
w4r^ sw05 20 hr at -18 °C食品伙伴个性空间9q2e&Kx[ir]
4 hr at 38 °C食品伙伴个性空间3S&F4V x z
1
8n1oG/V.UEw0Source: Labuza and Schmidl (1985)食品伙伴个性空间jz k&n@Oz U9V4|M
Step 4: Do microbial survival analysis — This is to find out if there are any食品伙伴个性空间I7y3T#_#n8]z/`?
microbial growth upon temperature abuse or if the inoculated microbes survived the食品伙伴个性空间Z9CE|k+v Q){g
process. Appropriate detection and enumeration techniques should be used.食品伙伴个性空间q*Ps8~k K5D
19.4.3 Applicability
\\|OJ0The use of inoculated pack studies conducted by independent laboratories allows a食品伙伴个性空间#_l%UoSR hi
food processor to assess the relative risks that can occur under conditions of
yLL%YAml(w0temperature abuse of the food product in question. Taking frozen pizza as an
1T p A-b!vU'?g0example, both the cheese and sausage, if naturally fermented, will have high total
x:v.@ {UG ivd d0counts of bacteria. Since the product is usually partially pre-baked and then frozen, the食品伙伴个性空间h7D z2_"J
numbers of vegetative microorganisms will decrease until thawing occurs.食品伙伴个性空间S U%q!nN*D
Unfortunately, pathogens such as Staphylococcus aureus will not be totally
1\h%v7q }0inactivated by these treatments. If the product is abused during distribution so食品伙伴个性空间 c }sC&| A8o
severally that the temperature near the surface reaches about 7 °C, pathogens may食品伙伴个性空间 FY:fD-y
grow. A challenge study with Staphylococcus aureus will verify the microbial safety食品伙伴个性空间1y!J#H%|\8DO
of the product.食品伙伴个性空间J_gX%n
It should be noted that inoculated pack studies with pathogens should not be食品伙伴个性空间$nbH i+viA
conducted in food industry laboratories that are located close to the food processing食品伙伴个性空间$|2hC~xC2A-q/g
facilities because of the possible transfer of pathogens to food products. No sensory
'p0}Yz2Dx:Q029食品伙伴个性空间V5E9F\l Wx^
panel can be applied to evaluate the inoculated samples other than visual
/pq+oq,Ey w/J0observation.
9@/B3~'y+n019.5 Accelerated shelf life testing食品伙伴个性空间6^-VNTzMj
19.5.1 Basis食品伙伴个性空间 o,k\0{#w
During product development, preliminary shelf life knowledge is often needed in
|/seY|0N)b%qs}?0addition to microbiological safety. Shelf life testing experiments at this stage are often
2B^[3jH2Y0accelerated to evaluate the effects of various formulation and processing parameters
_5NE$bcE[0on shelf life stability of the product being developed periodically since one can not
/D$g(lQ'^%[0afford the relatively long shelf life period for a frozen food stored under normal freezing
L E)g/?9n@F U~0conditions. In addition, temperature fluctuations may occur in distribution and retail食品伙伴个性空间t"SL:@R;o
holding for frozen storage. Thus kinetic studies at several temperatures within that
kV h8AzAQg4K0range are necessary to predict its shelf life. Accelerated shelf life testing conducted at
X M ?7sIkP0elevated isothermal temperatures and/or with freeze/thaw cycles for frozen products食品伙伴个性空间a6q9W Ncl/V
have been used extensively for several decades by industry and government食品伙伴个性空间%qD0RgWdap
agencies (Labuza and Schmidl, 1985). The Arrhenius relation and the Q10 approach
5k*YN7m*yK0are used to extrapolate the results to the expected lower storage temperature.
yfn j\s0Acceleration factors other than temperature have also been studied for some other食品伙伴个性空间[ ~4M,G3^5V?u
deterioration modes, such as moisture gain or loss and lipid oxidation (Labuza, 1984),
,D*f4i*pTj0V0but rarely done for frozen foods.食品伙伴个性空间"AoF lXE_3y g8b {
19.5.2 Unique procedures
6?G"j K B\e0Step 1: Clarify test objectives — In general there are two occasions where食品伙伴个性空间 D*B3OW'p ] f
ASLT applies: i) estimate approximate shelf life quickly during development stage; ii)
;lhdPW1|WcZ5W0collect kinetic parameters for actual shelf life prediction as in the marketplace, which is食品伙伴个性空间z!aH9GE X
conducted generally near the launch phase.食品伙伴个性空间e,J^'wR-{8_ F6w"?6{6j
Step 2: Select accelerating temperature conditions — Suggested isothermal
Bt C p&~c mY2{&p` C3P3_0accelerating conditions for frozen foods are -15, -10, and -5 °C with a control stored at食品伙伴个性空间3L&m4K)\8H
< -40 °C (Labuza and Schmidl, 1985). The inherent assumption is that the
rq+dK-Pr[;jZ0deterioration mechanism is the same across the temperature range although as noted食品伙伴个性空间G;D7`zv+N
earlier, there is concern about how close to freezing one can go.
6o)X'WSxy |0Moisture migration from the food into the surrounding air with resulting
m!Vv9mW/L%l0desiccation of the food and ice crystal formation in the package is a major mode of食品伙伴个性空间IBs5^R I#},y
deterioration of frozen foods under fluctuation temperature conditions. Cycling
s4D[6h N4x8M7\0temperature storage is used to test for this, i.e. from 0 °F or 10 °F up to 20 °F with one
3j2uu$\up9a1F!B2t0day at each temperature and then repeated several times. A freeze-thaw cycling study食品伙伴个性空间d:K mat:M M I E
is also needed to determine its effect on sensory quality. Usually, the high temperature
'?f#nQ?gH In1D3T030食品伙伴个性空间7B3hj:pyl"hr;C
can be much lower than that used in a microbial challenge study unless microbial
/jC rg eUR0survival is still a concern. Typically, cycling temperature/time can be three to five 24食品伙伴个性空间 k#ge'n1RL-h
hour cycles between -18 °C and -7 °C, or between - 18 °C and 7 °C, depending on
UV"hx H `0the product.食品伙伴个性空间n$e`9IsR,FnI6x/E7C
Step 3: Estimate testing time and sampling frequency— Testing times are
l!RMW L0dependent on a desired shelf life at target storage conditions. For example, given that
],P*z[Pe$z T(VS0a 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3@dq$Q"A9b
19.11 indicates the test time at -4 °C that equates to 12 months at -18 °C for various食品伙伴个性空间Wr.BKA)? Q
Q10 values. Sampling times at -4 °C should thus be 1 wk, 2 wk, 1 month, 3 months, and
FP#hiSJ,X_6m9d-O04.5 -5 months. Most published results suggest that Q10 values for vitamin C loss and食品伙伴个性空间PlP1cM O
quality loss in frozen vegetables range from 2 to 20 and that the shelf life of vegetables食品伙伴个性空间j3us+}!]}M
is only 6-8 months at -18 °C (Labuza, 1982). Considering these Q10 values, a product
~2H\ I-V&`6r0?~0that does not retain good quality for 4.5 months at -4 °C may not retain good quality for
D8K0V:{hE/R.kET012 months at -18 °C. This also suggests the sampling frequency shown in Table 19.6.
@zV/za7x$?6G0All simple tests should be conducted at each sampling time, while sensory testing
0] ^9c8N*~G0should be concentrated mainly toward the end of the test sequence with a few near the
4i1c'[(\E/G\;?~0beginning.
'H;YW6dd9Ly.q I00 5 10 15 20 25 30
l7_-f C+}N0.1食品伙伴个性空间 w*Y;v@h5We|+U|
1
&vH4i_nZ#i010
r*N$c&b&^l5F {0100食品伙伴个性空间'DMY9dd,Lm/v [
T (°F)食品伙伴个性空间p!M2@&k e5mw
Shelf life 12 mo at 0食品伙伴个性空间[9zW5H n xQ
ASLT at 25 °F食品伙伴个性空间6vQ I3OhS Yo]V
4.5 mo食品伙伴个性空间&b;e-AOXa#EI3t
1.2 mo食品伙伴个性空间%d |B F*y'_
14 days
cS'pu3Zl$Yr x06 days
s9LtvT6x4W(X4eAuj0Q10=2食品伙伴个性空间8W6N'n)IX7K
Q10=5
~;D JRz@#_S o0Q10=10食品伙伴个性空间 hO2])A F$S!l]t5u-D
Q10=20食品伙伴个性空间e!o#H9cB d c&B
Figure 19.11 Shelf life testing times at 25 °F equivalent to 12 mo at 0 °F食品伙伴个性空间cFR4O3xbfB
for various Q10 values.食品伙伴个性空间2~5hZx0E.q X
Table 19.6 Sampling frequency for frozen pizza ASLT食品伙伴个性空间K%[bv_k9b
31食品伙伴个性空间eFQ.Rv6hT j{ I
Temperature (°C) Sampling times (wk)
MLm jRU8OD*c0- 4 1, 2*, 3, 4, 5, 8, 12, 14, 16*, 20*
-{c g} bx,s0- 7 2, 4*, 10, 15*, 20*
:bd}8c%Od\$l9TI0- 10 4*, 10, 15*, 20*
e$nPdW:{0* Sensory test times Source: Labuza (1986)
&}u4Y`{0Step 4: Determine end point — Figure 19.12 shows a comparison of times to食品伙伴个性空间#fb6i#SV"t)jsr
various levels for the loss of vitamin C in frozen spinach as a function of temperature
-@Q@|*W4K0(Kramer, 1974). The dotted line represents the 80/80 rule, i.e., from a legal standpoint,
K#u,H)L6R i0for natural products, 80% of the tested sample must have no more than a loss of 20%食品伙伴个性空间Y*N bp|Xp
(i.e. 80% of the label value). Consumer sensory testing will not always give such a
XK8c JI;hfx3Tpt0clear shelf-life result since different shelf life times can result using different quality
o&t#WWJ/wA0g0attributes. Often professional judgment has to be made to decide what factor to use as
HM'z,EF E#|$G&k0the base for the end of shelf-life of the product. When shelf life is unacceptably short,
$K|.Sp"XWV0adjustments should be made to the food, its environment, packaging, process and
+?#Dg ^ et+T0hygienic conditions, until a suitable extension of shelf life can be achieved. For some食品伙伴个性空间M_ y{w
products, the test results may demonstrate that the target shelf life is not attainable. At
&bJO:HI]-s U(E0this point, the question of whether to launch the new product with a shorter shelf life or
9N^5]kc]JAv/];P*@0to abandon the entire project becomes a marketing decision.食品伙伴个性空间s:oZ!Rq"A
-20 -10 0 1 0食品伙伴个性空间 jfq'}ES
1
7k0}@nK;m)bA010
gLBjp'` S1}$i0100食品伙伴个性空间)D9Lt0pu\
Storage Temperature (°F)食品伙伴个性空间&m,Z0g,`X.goI.e(B
Shelf life (mo)食品伙伴个性空间7_U2b{'R6E,w
Figure 19.12食品伙伴个性空间%x ob1u"f"G#M
Shelf life of frozen spinach as a function of vitamin loss level食品伙伴个性空间cH-w]T q[$se F8M
50% loss食品伙伴个性空间Xnf E3I:av
25% loss
Ti|"`|G3S010% loss
_8| ntfc!^0Quality (80/80 rule)食品伙伴个性空间x.B~'X3X
32食品伙伴个性空间 }A,b"a/F%|M
Step 5: Estimate kinetic parameters — From each test storage condition,食品伙伴个性空间hF%\ xq6xg9KK2D
estimation of k or q is needed to make the appropriate shelf life plot. From this one can食品伙伴个性空间/kg;JY$Jrv$I
then estimate the potential shelf life and confidence interval for the storage condition.
8wL a WT-X p?0Then parameters for the Arrhenius relation and the shelf life plot are determined by
F2b m3d8x#u%uZ6J0linear regression, which are used for shelf life prediction.
y!q5njk&Ok%q5q0Step 6: Extrapolate to normal freezing storage condition — The most useful
_AuC8H:t0shelf life information is obtained for product kept at its intended storage temperature,食品伙伴个性空间b~@6O Nt
which is about -18°C for retail frozen products and -23°C for distribution of frozen食品伙伴个性空间%O%UD%dM#f;Zq9C
foods. Figure 19.13 demonstrates how the shelf life plot is used for extrapolation. It is
1?c`Wqc0always a good practice to compare a model's prediction against actual experimental食品伙伴个性空间|j9\8J%|`f
results because of the potential for errors from using the higher temperature data as食品伙伴个性空间"fk$M)D7i3l)fFDL
noted earlier besides the other errors suggested by Labuza and Riboh (1982). In食品伙伴个性空间N1|/S.w"L9\7bQ5Z
addition, the existence of a glass transition at a temperature between the test食品伙伴个性空间9hqNS{)U.c
temperature and the prediction temperature would lead to error as shown by Nelson
x1ame*yNg0and Labuza (1994). In the case of frozen foods, most likely the error would be an
w7F1H&~Sgg$x0under prediction of the shelf life.食品伙伴个性空间 `7L |*p,uq9P+@
ln Q食品伙伴个性空间N3is.b*bC*S
T
!^ rIf4ch,kM0T1
[%H`Ua(FnG0T2食品伙伴个性空间F6I1M w[.lG
T3
%v3F4T,z9d!Qw^ ?0Ts (commercial storage temperature)食品伙伴个性空间|,c,X3V-OS d
Figure 19.13 Extrapolation from ASLT
Sy8` O"w1Ns(a1|0Step 7: Predict quality loss for a fluctuating time-temperature distribution — The食品伙伴个性空间YEW4H }a5H
prediction is based on two assumptions: (1) that there is no history effect from the食品伙伴个性空间 z-e*c"QV*y3W
time-temperature variation and (2) that the key deterioration mode does not change as食品伙伴个性空间u}9aE[qXzo5W
a function of temperature. The frozen spinach data shown in Figure 19.12 is used in
+j7m"t@a*bN6M7G0the following example in Table 19.7 for a time-temperature distribution. The line食品伙伴个性空间gHY t-]bvM,r\f
33
7sA2@$o Qs-uI\5I0equivalent to 20% loss is set as the end of shelf life limit i.e., if Ao = 36 mg/100 g then A食品伙伴个性空间K%wE IK
at 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
/NYK}\T _0each temperature of exposure, the time on the 80/80 line is the time for 20% loss, thus
$G/fP0Y4S5rf0at -10°F, the 20% loss (equivalent to 100% shelf life) time is 16.5 months. Thus for 6
a`7_Y&y7LQ@0months storage at -10°F, there is 6/16.5 or 36.3% of the shelf life lost and the amount
,D W3{"B/Y([ U0left is 36 - 6.36 x 7.2 = 33.4 mg.食品伙伴个性空间`.uB1{U[[)U
Table 19.7 Estimation of quality remaining of frozen spinach after exposed to a
jwh]%w3mBR4L0variable time-temperature history with Ao = 36 mg/100g spinach.食品伙伴个性空间ez*i \QmAF7N
Temperature
1tm?:D1N_0(°F)
L"M)Y*Y6\0Time t食品伙伴个性空间#P-D#RE ]
(months)
v0plN7d0q shelf life
#hBp L.Ur/Dk0(months)
7lg.W Lg'x~ {?*`0fcon
.v!@"w5q(d A(O0(t/q )
:] pU1jDH2fy0Sfcon Aremaining
(XcXb/qZ ]g2?0(mg/100g)
_!]Q0~7];YO%dM0p0-10 6 16.5 0.363 0.363 33.4食品伙伴个性空间 Q,~)X z | M5s `
+3 1 4.5 0.256 0.619 31.5
~p ^B3p8J!Q0+12 0.25 1.6 0.156 0.775 30.4食品伙伴个性空间;` mXD*?4w&I
Since as noted 80% of Ao is equal to 28.8 mg/100g at end of shelf life, this product is
6U+y:PZvgV1\0still acceptable at the end of the set of three different time/temperature exposures. In食品伙伴个性空间.e MSH$]`'[eE
fact, the shelf life left @ 5 °F = (1-0.775) x 3.3 = 0.74 months = 22 days.
{Km i6z019.5.3 Applicability
5F9[(W jeK;W0Because of relatively long shelf life for frozen foods and the unique feature of freezing,食品伙伴个性空间wxIZ#q`;p1N5YC
the degree of temperature elevation is largely limited. Prediction of actual shelf life
)~nE;[ L#Y0from ASLT may be severely limited except in very simple food systems. Frozen foods食品伙伴个性空间u z1i-r]Ev(s
such as frozen pizzas, may present problems with moisture migration. The moisture食品伙伴个性空间8X8l1?k J v
may diffuse from the pizza sauce which has a higher aw into the crust containing a食品伙伴个性空间UHn#e wb
lower aw, creating a pizza crust that is limp and soggy. Product development scientists
4? `5_.M9C4D Sd4q0should only use the results as a guideline and must use as many storage conditions食品伙伴个性空间0Eq9b{SWx4^*^$u8BO
as possible to minimize prediction errors.食品伙伴个性空间e;o0cA(r/n9U7KVk#c
34食品伙伴个性空间pAi*}B)k@
ASLT is just a quick method, which can not replace the normal storage tests
%m`0TMR0discussed next. Once it is verified that the extrapolation may be wrong, i.e., too large
L+iQ[1Yyl_I S0an error, then a careful look should be taken at the deterioration mode, the experiment食品伙伴个性空间_ wl}{UAQ
design and procedure, the data collected and the model developed. If the
[vIGe_2r`&x/dA0extrapolation under predicts the true shelf life, then it becomes an economic concern, it
,@4Z4{ ~r.AV)]?0is over predicted, then reformulating may be necessary. If the shelf life prediction
xGv'Wc1]0indicates that the product meets the stability expectation, then the product has a
8A:}] dQ"]Eqv0chance of performing satisfactorily in the marketplace.
,_(X_(S}6La EYG019.6 Confirmatory storage study食品伙伴个性空间HYkIm[
19.6.1 Basis食品伙伴个性空间%ZT.QcEW
The difference in potential shelf life should be considered when scaling up from
/rP_5A.NL0experimental test batches to pilot plant and then to full scale production. Experience食品伙伴个性空间s!k"Ds[R
has shown that results of small-scale experiments in the laboratory may not be of食品伙伴个性空间]%|o [V1P(B N2| {
much use for large-scale production (Graf and Saguy, 1991). Scale-up not only affects食品伙伴个性空间A)@U?9G8E
the processability and quality of a food product, but it often alters its shelf life.
2x}A._-XG\g0Depending on the mode of failure and the food scientist's approach to inhibiting食品伙伴个性空间f,rR6|8hx
microbial growth and chemical reactions leading to deterioration, scale-up may
,] N1V,_U2MD FK0

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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-x$Q9N-U2F
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!
e(Ki0BwO'aBX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.
Wi^@5boc"[  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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