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冷冻食品保质期试验.pdf

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Shelf Life Testing:
Z7t-p(|xi*Q0Procedures and Prediction Methods for Frozen
7l5u~D$w&? I0Foods食品伙伴个性空间H.}*AQ0@8V"h
Bin Fu食品伙伴个性空间*D#HAism V$WO.?6v
Kellogg's Battle Creek MI食品伙伴个性空间ha1wk:n;[M @+Z M}
Theodore P. Labuza食品伙伴个性空间/F)W\r:f(w
Dept. of Food Science & Nutrition, University of Minnesota食品伙伴个性空间"D6@(z ~5@5@z_
1334 Eckles Ave., St. Paul, MN 55108食品伙伴个性空间5Q a7nW4tMkb ^+D
2
i)k9z0\h p4A\5V+SP2bY019.1 Introduction
^ `qlIQz0The 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 Pe*Z J;v
to consume and/or has an acceptable quality to consumers. Just like any other food,食品伙伴个性空间j1W)G"e8Rw&b.~t5L
frozen foods deteriorate during storage by different modes or mechanisms, as
)b(MG6V]9i]2x*M'f0T ^0summarized in Table 1. Microbes usually are not a problem since they cannot grow at食品伙伴个性空间f M+k{\7g3]6M+@
freezing temperatures unless subjected to extensive temperature abuse above the
Rh {Jc7x+c'w XbX,_0freezing point. Enzymes are a big concern for frozen foods, which can cause flavor食品伙伴个性空间)^1m]Y1N\!__ks7~
change (lipoxygenase) in non-blanched fruits and vegetables and accelerated
!}4@ vN2HY0deterioration reactions in meat and poultry (enzymes released from disrupted食品伙伴个性空间Xo'a LlLMQU+b
membranes during precooking). Cell damage or protein and starch interactions during
T`|fZ)I]0freezing cause drip and mushiness upon thawing. Discoloration could occur by nonenzymatic食品伙伴个性空间~~_`R#T8P
browning, bleaching, and freezer burn. Vitamin C loss is often a major食品伙伴个性空间6B] @7gOcyL
concern for frozen vegetables. Physical changes, such as package ice formation,
)D |1mA(l~:Z i0moisture loss, emulsion destabilization, recrystallization of sugars and ice of frozen食品伙伴个性空间%L$n x5xk)c-B4U*R
desserts are often accelerated by fluctuating temperatures.食品伙伴个性空间J tDL7j
For any specific frozen product, which mode determines its shelf life, depends
wR#[vKTG@/zv0s U0on the product characteristics (raw materials, ingredients, formulation), pre-freezing食品伙伴个性空间K:[%uv%Xh3N3a~@AU
treatment, freezing process, packaging film and processes, and of course storage
f$Dx.|4O0conditions. All of the quality deterioration and potential hazards are usually
Gqq'J N2cp3D0O0exaggerated or complicated by a fluctuating time-temperature environment (e.g.
'X K ].u1x d.?2m} _0freeze/thaw cycle) during storage. On the other hand, the shelf life of a frozen food
*Hn[#{ B(x#U;~P"r{(^0can be extended through ingredient selection, process modification and change of食品伙伴个性空间8S"f|%s8EeaW
package or storage conditions, as discussed in Section 3 of this book.
%f8W*pk I0This chapter will focus on shelf life testing of frozen foods for product食品伙伴个性空间:wMmrh_h!A
development and market practices. Shelf life testing consists basically of selecting the食品伙伴个性空间b o,B1spN(W
quality characteristics which deteriorate most rapidly in time and the mathematical
'u;_ X,Q$NOAvf0M0modeling of the change. Table 19.1 can be used as a reference for the selection of
PZW*Z+od0quality characteristics, which depends on the specific product and usually requires
]mm.\;Z2Z;\a0professional judgment. Mathematical modeling of quality deterioration will be
h&k H/\ e4y+k3X2c,i0discussed next.食品伙伴个性空间BSk(} Vq2J,Z
3食品伙伴个性空间2Z}%O F!hQ2dm&Q
Table 19.1 Deterioration modes of frozen foods食品伙伴个性空间+yJ1k7]5mr
Frozen Foods Deterioration Modes食品伙伴个性空间`E*?u!G:R;|V,T
Frozen meats, poultry and seafood Rancidity
)?\(bfb$kr9\0Toughening (protein denaturation)食品伙伴个性空间 n Q t|i
Discoloration食品伙伴个性空间/N6@vI [Z [
Desiccation (freezer burn)
6m3s2snYf N*D?2w0Frozen fruits and vegetables Loss of nutrients (vitamins)
2U E*L$Z ^:[zf?0Loss of texture (temperature abuse)食品伙伴个性空间u Kx1c.E*d
Loss of flavor (lipoxygenase, peroxidase)
0x7s O FQ,v8x#dO0Loss of tissue moisture (forming package ice)
+cY l$}1X5D k/m(hV }0Discoloration食品伙伴个性空间&H;wS/^!i$Q+|!o
Frozen concentrated juices Loss of nutrients (vitamins)食品伙伴个性空间:FiT#Nf f R
Loss of flavor食品伙伴个性空间)dNC Z ]#{1I
Loss of cloudiness
dcZ9q's~%f;W&}1V3?u0Discoloration
ev$lX:w NY9B.B0Yeast growth (upon temperature abuse)食品伙伴个性空间){b2F f(J
Frozen dairy products
)Tt} UQ9h ZQ0(ice cream, yogurt, etc.)
cd4f[%Y2X0Iciness (recrystallization of ice crystals)
|4lh$o] Z+Z0Sandiness (lactose crystallization)
A%I ]b D+w+e;S?0Loss of flavor
3~M!Px$WBv0Disruption of emulsion system食品伙伴个性空间2N,Lw%U)}i/^e
Frozen convenience foods Rancidity in meat portions食品伙伴个性空间6AV(l"^q5J
Weeping and curdling of sauces食品伙伴个性空间rY2RS(b%|;E@O
Loss of flavor
0xx2xcC*n O{0Discoloration食品伙伴个性空间C D'N G6h.E,B t
Package ice
Y^ j%K Ka,F3]0Frozen bakery products (raw dough,
&V)|2Vs;pZ]0bread, croissants)食品伙伴个性空间n6K-@ W:T/UY/e._y
Burst can (upon temperature abuse) (dough)食品伙伴个性空间a1p[ E6Lo
Loss of fermentation capability (dough)
4|9Bgy'z0Staling (becoming leathery)
q#Tj2a sz:d7sZ0Loss of fresh aroma
b:w O]W+G2e#B019.2 Modeling of quality deterioration食品伙伴个性空间_o m,Y V
19.2.1 Basic equation
@is$yPg!bx0j(P0A frozen food starts to degrade once it is produced (Figure 19.1). The rate and食品伙伴个性空间"X)J%}{XL(H
the degree of degradation depends on both the composition and the environmental
ex"Ca$i*tu0conditions during storage and distribution. In general, the loss of food quality or shelf食品伙伴个性空间1od]4?z0i$l%M
life is evaluated by measuring a characteristic quality index, "A". The change of quality食品伙伴个性空间UZd r7v4X
index A with time (dA/dt) can usually be represented by the following kinetic equation:
(g:Z9{}FF0- dA/dt = k An (19.1)
`? w4{+Es%{"S*rH5G0where k is called a rate constant depending on temperature, product and packaging
s!hT|e5oV'SVn0characteristics; n is a power factor called reaction order which defines whether the rate
3RB^&~:N Ra04
c n^4~%O2["o0of change is dependent on the amount of A present. If environmental factors are held
0q#n"dM@DF0constant, n also determines the shape of deterioration curve.食品伙伴个性空间&e]~1Wq
Ao
(G;d6b+Nh4@+a.uZ0A a食品伙伴个性空间#~Uc:O$iH.evar0l p
b
E`${jA F)@Q0c食品伙伴个性空间cK9Oz5q,u
t
(ac g[Oy3Q pI0d
n`#i S'^6R]b,Wr0e食品伙伴个性空间R;R)W,U`c
Figure 19.1 Quality deterioration curves: a) linear; b) exponential;食品伙伴个性空间UG_ Z aZ
c) hyperbolic; d) quadratic; e) complex.食品伙伴个性空间CN/@ s8u!y3C9V
19.2.2 Zero and first order kinetics
f[U5KE)Rv k D0Equation 19.1 can also be written as:
Yg!c/z jm}0f(A) = k t (19.2)食品伙伴个性空间t!E%O2ut t2|bR
where 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 `9aH4j8M.~
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;xt([m&Mx
kinetics, which implies that the rate of loss of quality is constant under constant食品伙伴个性空间h I!ZPgA6F]
environmental conditions (curve (a) in Fig. 19.1). If n is equal to one it is called first
v*u{e;gx0order reaction kinetics, which results in an exponential decrease in rate of loss as
(C'C*U.fri7Mj9i0quality decreases (curve (b) in Fig. 19.1, which becomes a straight line if plotted on a食品伙伴个性空间 mo3D({,Q [4jC[3T0H
semi-log plot). These quality functions can be expressed as follows:
@1o?Miv0f(A) = Ao - A = kzt zero order (19.3a)食品伙伴个性空间g"p*`0C;h/\j(x@#{3v
f(A) = ln Ao - ln A = kft first order (19.3b)食品伙伴个性空间vm+hT_1a zR
5
uY%P(k'[Y0where Ao is the initial quality value. If Ae corresponds to the quality value at the end of
+d$x6k9I.B&C](aYrr0shelf life, the shelf life (q) of the food is inversely proportional to the rate
^*K.qe|Ja0constant:食品伙伴个性空间4h2Y8fR;l!t-Rl2F
q = (Ao - Ae) / kz zero order (19.4a)食品伙伴个性空间4_V$@g1V
q = ln (Ao/Ae) / kf first order (19.4b)
3c)Y/E)c(BD+E0It should be noted that most chemical reactions leading to quality loss in frozen食品伙伴个性空间.z!_f+O%KAx8Z
food systems are much more complex. However, the reaction kinetics can be食品伙伴个性空间1y0M5F%ZM*kFx:ty5[
simplified into either pseudo-zero order or pseudo-first order kinetics. In the case of食品伙伴个性空间s Lk`2O(c j
complex reaction kinetics with respect to reactants, an intermediate or a final product
3NY%H,l;?s/o0(e.g. peroxides or hexanal in lipid oxidation ) could be used as a quality index. There食品伙伴个性空间l;u1H N)P6pD
are few cases where neither zero nor first order kinetics apply. Curve (c) in Fig. 19.1
c1M S}Rr#u-`e$n0shows the degradation curve for a 2nd order reaction (with single reactant), which also食品伙伴个性空间lyy2]a%p`
shows a straight on a semi-log paper. A fractional order should be used to describe
5q YO0ZK~e4M0the curve (d) in Fig. 19.1.
h2yD"PlB6[0Sometimes, there is an induction period or lag time before the quality
5l!ac2m!S0deterioration begins (e.g. browning pigment formation in the Maillard reaction or a食品伙伴个性空间K%kt1?b
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8eRgL,^%}D
depends on many factors, but temperature is a predominant factor. Given this,食品伙伴个性空间"~u2`E]{l6Dq
modeling of both the induction or lag period and deterioration phase are necessary for
1\|5vqd c0accurate prediction of quality loss or shelf life remaining. An example of such work has
{r8rDTK0been demonstrated by Fu et al. (1991) for the growth of bacteria in milk.
WH0I-KUk!Y.l8J B,f0In certain circumstances (e.g. A represents a sensory hedonic score), a nonkinetic
M)x W0ny!^'p(ub]8i0approach, e.g. a statistical data fitting technique can also be used to describe
(M3r/[ XC u cSp0the deterioration curves. Varsanyi and Somogyi (1983) found that the change in食品伙伴个性空间 i*ns[q
quality characteristics as a function of time could be approximately described with食品伙伴个性空间Qp/@%T8fx
linear, quadratic and hyperbolic functions and that storage temperature and packing
/rYV T.lxy6}D0conditions affected the shape of the deterioration curves. However, the parameters食品伙伴个性空间 Z({1u e"?c$nU;N|K-f
determined by data fitting are difficult to use for prediction under variable storage食品伙伴个性空间h%I1?q _0y
conditions except for the linear curve.食品伙伴个性空间6y;^:~#M"TE9h
19.2.3 Temperature dependence of deterioration rate食品伙伴个性空间x a2`.vY4D6{$V*]
19.2.3.1 Arrhenius kinetics
,r%?"d6mC;H{0Once a frozen product is made and packaged and starts its journey from the
j(_]]7H7l(d'N/d0manufacturer's plant to warehouse, distribution center, retail store and finally
j3~!q1YL SV06
^4yJ:L1v#u`W-``0consumer's freezer, the rate of quality loss is primarily temperature dependent
-P3B ^ Bv'b3m)`,x0(Zaritzky, 1982). The Arrhenius relationship is often used to describe the temperature食品伙伴个性空间6D\2t8|*FE7d}
dependence of deterioration rate where for either zero or first order:食品伙伴个性空间4B Dy~ tgQ'KV
k = ko exp (-Ea/RT) (19.5a)食品伙伴个性空间L$ys f_*R
or ln k = ln ko - Ea/(RT) (19.5b)
7f)cO2q:K7Chz@0where ko is a pre-exponential factor; Ea is an activation energy in cal/mol; R is the gas
7X4J dNM(h?+OLa6b0constant in cal/mol K and equal to 1.986; T is an absolute temperature in K (273 + °C).
_Ix.UX7C`0Thus, a plot of the rate constant on semi-log paper as a function of reciprocal absolute
OL,V!svk0temperature (1/T) gives a straight line as shown as Fig. 19.2. The activation energy is食品伙伴个性空间^\)l+BY o
determined from the slope of the line (divided by the gas constant R). A steeper slope食品伙伴个性空间\i s-a'G#y(~s
means the reaction is more temperature sensitive, i.e., a small change in T produces食品伙伴个性空间.tul]q9^#W%M*Jt
are large change in rate.食品伙伴个性空间3yu.oK)n}|p*]
Figure 19.2 Arrhenius plot
xZ5HcX/bp)dX:D0ln k食品伙伴个性空间quw| B"D _
1/T食品伙伴个性空间 V@ mZx2cKM
slope = -Ea/R食品伙伴个性空间p"q g q? {`
Thus, by studying a deterioration process and measuring the rate of loss at two食品伙伴个性空间 M VGcs[ pN1n*F
or three temperatures (higher than storage temperature), one could then extrapolate
;nL,F n1}"A0j0on an Arrhenius plot with a straight line to predict the deterioration rate at the desired
6U'W(i+z0bL?D-n-O0storage temperature. This is the basis for accelerated shelf life testing (ASLT), which食品伙伴个性空间sq p {]s{
will be discussed later. One should note however that in some cases a straight line食品伙伴个性空间5oS6KO8bm JDq
will not ensue for a variety of reasons, especially if a phase change occurs (Labuza食品伙伴个性空间t*mtLyV
7食品伙伴个性空间L qL{:i"op
and Riboh, 1982). Thus for frozen foods, extrapolation from temperatures above 0¥C食品伙伴个性空间 b r.fU8wdb
are meaningless for shelf life prediction.
\ d9v/l%f#E019.2.3.2 WLF kinetics食品伙伴个性空间*h2k|Zu1h3L
Besides the Arrhenius equation, another popular equation at least in the more recent
7o^w(UQUxR'P0food literature, is the Williams Landau Ferry (WLF) model (Williams et al., 1955). Its
dx7D \/C:`EQYD S0original form was based on the variation of the viscosity in the temperature range食品伙伴个性空间r#qy#uiU
above Tg as addressed in Chapter 3. When the rate constant at Tg' is substituted for Tg
(@ qn6C7r,D#u9b2?0(Tg' is the Tg of a maximally freeze-concentrated system), the WLF model can be
|K:iIH@0written as follows:食品伙伴个性空间v+c;\ZHX
log (kT/kg) = C1(T-Tg')/[(C2+(T-Tg')] (19.6a)食品伙伴个性空间6W'f n+~8qVP
or [log (kT/kg)]-1 = (C2/C1)/(T-Tg') + 1/C1 (19.6b)
`"t0Yt{x2e9S [,W9y#A0where C1 and C2 are constants. Thus a plot of [log (kT/kg)]-1 vs. (T-Tg)-1 will be a
#d'_:?+O C ?M"I0straight line with the slope equal to C2/C1 and the intercept equal to 1/C1. As can be
PLR3X&fJ'H r.o0seen this is a two parameter temperature dependent model as is the Arrhenius
p:WG:QQ;W(l!q9V0equation.食品伙伴个性空间8O7ZHp2T(G
Frozen foods stored below Tg' are stable to ice recrystallization and other食品伙伴个性空间 wljd5\]sY
physical changes. Levine and Slade (1988) postulated that stability is related to the
.K jj#N*EQ[|4e7Wa0temperature difference between storage temperature and Tg'. This cryostabilization of食品伙伴个性空间;V3R3b3n8tiaz#\ d
foods assumes stability below Tg' and rapid decrease of stability above Tg' according
/Hx9x#U0](X0to the WLF relationship, exhibiting an increase in reaction rate, much higher than食品伙伴个性空间z5jTrp.F y'P
expected from the Arrhenius kinetics. However, this may not be true since the rate of
A0Bwm \%sRF0chemical reactions can be expected to be influenced by temperature increase in a食品伙伴个性空间w_LB:x
complex way: (i) an increase of the rate constant, resulting from both the viscosity
8I*~-p;\,na0decrease and the increased molecular mobility (Fennema 1996); (ii) a decrease of the食品伙伴个性空间`'{pY_)A5@5H
reaction rate as a consequence of the increasing dilution of the reactants Roos et al.
h4HlJ8l@0(1996). For these reasons, it seems that the WLF model over predicts the temperature
`(Y3Ng-_-h,o0effect of rate constant (Simatos et al., 1989). As noted by Nelson and Labuza (1994),食品伙伴个性空间bZ"f0_0}
because of the small temperature range over which foods are stored, e.g., about D30°C
8i@1D7V];Eyqa0for dry foods and D20°C for frozen foods, both the Arrhenius and the WLF model give食品伙伴个性空间pO)`I(Db
good correlations as long as one does not use the universal coefficients suggested by食品伙伴个性空间 tN#M M Rx
Slade and Levine (1991). In fact as shown by Nelson and Labuza (1994), their use of
4l4Z4LC l1h0the Lim and Reid (1991) data for enzymatic activity in the frozen state as shown in 19.3
1in6X9L'O7X1QK#f+\a0is not proof that the Arrhenius relationship does not apply, WLF was assumed because
`,y+P&{@,oPP0the rate was negligible below -10°C which was the measured Tg. But as seen in食品伙伴个性空间C0a1A-p.x#M9yg
8
v%_%MM4DkZ~;x0Figure 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T\ jf-nE/V
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nv5k C!G{UL$CU
not known; (2) Tg is difficult to determine; and (3) the universal coefficients of Levine食品伙伴个性空间N(}0f~ESWvEK
and Slade (1986) are not applicable.
p]z-N4\B2l6eO00 50 100 150 200 250食品伙伴个性空间MK5e_:e2tQ&Z+y-k
0
;Y Ge#i&m6?'E i01食品伙伴个性空间"L;P-|;@ Z
2食品伙伴个性空间&d4i#D UJBMS
3
I9^0n,P&a5R-V04
jZS-TA+zi Pcgr05食品伙伴个性空间"] M5k X1qu$eE,xv c
-3.5食品伙伴个性空间,Y(inML m#F4q
-5.5
)p];b7F Y0-8.5
r EBhGU)@{0-13
Gr Dw6Oj/W r.Kg0-19
cW8W,m3ZQq0Time (hours)
SQS:QI|M1^0Relative absorbance
WQW`e}8L6?0Temperature (°C)
{6p` B&q#v00.0037 0.0038 0.0039食品伙伴个性空间*O s"^k5t8Z6ve k_
-4食品伙伴个性空间3OHEb8K-D ] _d V
-3食品伙伴个性空间xbzzXHA
-2
/EvbO(HK Y0-1
NA;LD3fT00
8s }_9n? Mc5`3M01/T (K-1)
.T[,}/b euKe0ln(k)
6U Y;AV-H(E"v-Kc.b0y = 79.497 - 2.1621E+4x R2 = 0.999食品伙伴个性空间p"owqK [
Figure 19.3 Hydrolysis of maltodextrin in the frozen state (Lim and Reid; 1991)
4n-T lA|4G0a. Rate as a function of temperature (Note Tg is -10 ¡C)
W.Itz&Y3^e%Q1wCp0b. Arrhenius plot食品伙伴个性空间J"Qg[C T3R
19.2.3.4 Shelf life model食品伙伴个性空间cYlU'Vh.]KM
Most published data related to quality deterioration do not give rates or rate constants
9G*^'x6[evX0but rather are in the form of an overall shelf life (end-point analysis) as a function of
%yj'I~+LA0storage temperature. Since the temperature range used is usually quite narrow, the食品伙伴个性空间3F6EVW8G b1e9~K bO
following exponential relationship exists between shelf life and storage temperature:食品伙伴个性空间.rT'qg2^6xR
q = exp(-bT+c) (19.7a)
o?hr1DI s0or ln q = -bT+c (19.7b)食品伙伴个性空间0cLY.W/M-]jx6Z
where q is shelf life at temperature T in °C, b is the slope of the semilog plot of q vs T
h+B/b%V`2Ui0and c is the intercept or reference temperature as shown as Fig. 19.4. Practically, this
7v wo:UI$]-o$q0is used frequently for shelf life determination and prediction due to its simplicity and
F@)i,U6sG\v0straightforwardness.
vipw v w]@1l09食品伙伴个性空间 lI7S5p3BFp"`!O
Figure 19.4 Shelf life plot
FXf!S,t1^^8q0ln q食品伙伴个性空间"\a Fss%E }s
T
%xw4zM-~019.2.3.4 Q10 or q10
LhLY(|^j:h0The Q10 approach is also often used for estimation of the temperature acceleration of
;K3};f3cU0shelf life, which is defined as :食品伙伴个性空间:G:LU7S"I Xa
Q10 = rate @ T1+10 °C / rate @ T1 (19.8a)食品伙伴个性空间)YR1|Sb+]v^
Q10 = shelf life @T1 / shelf life @T1+10 °C (19.8b)食品伙伴个性空间1C~ Bg.N!Z3`
Q10 = (q10)1.8 (19.8c)
~:VU Pw/\:} Js0where 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vF"T4v3p-~ j c
used, which in fact is more often used than Q10 in the frozen food literature.食品伙伴个性空间Tq4N/DK5e bB
The magnitude of Q10 depends on the food system, the temperature and the
hM&k \I(t0absolute range. Q10 values from 2 up to 20 have been found for frozen foods (Labuza,
^$}^HOlenG01982) Labuza and Schmidl, 1985. Q10 can be shown to be related to the Arrhenius
+Z$XB;U/ZBc,f C0equation and the shelf life model through the following expression:
4X3i*sF'|m I6PZ W0Q10 = exp [10 Ea/(R T (T+10)] (19.9a)食品伙伴个性空间 NWe?*rd ~D
Q10 = exp (10 b) (19.9b)食品伙伴个性空间Q9k'I%u6bG ~B
Thus Q10 is not constant but depends on Ea and the absolute temperature T.食品伙伴个性空间\fGJQ|&zL)Ls-W+v
Some data gleaned from July (1989) and Labuza (1982) is shown in Table 19.2.
Iwmj~ k3z7IC t010食品伙伴个性空间'|a0rZ Hi3l
Table 19.2食品伙伴个性空间 ] n&vR&[+qZQ;~4K2y9\
Estimate of the Q
!iz J3w i7_/}0~*f010食品伙伴个性空间3@r k+B id
for shelf life of selected frozen foods食品伙伴个性空间#h4v)L|RN
Days of HQL食品伙伴个性空间*S/B ~`yBJ~
I te m - 10°C - 20°C Q 1 0
MQ{4T"z[nEY0pork sausage 20 120 4食品伙伴个性空间_.u|X.o&s0h)@*P
pork 50 400 8
ZO-nQo6[0beef 60 200 3.3食品伙伴个性空间8`9|+?+N)L
ground hamburger 250 800 3.2
tX4k9UT _0fried hamburger 35 250 7食品伙伴个性空间nD4p"_W{2z"V5g
raw poultry 200 700 3.5食品伙伴个性空间$h'Oi7@ks;k
fried poultry 25 700 3.2食品伙伴个性空间B3ea.r&i~ `i8[
fatty fish 7 60 9食品伙伴个性空间%u0q5R+U x7Ffn%O#nB
19.2.3.5 Other models
9X!J st4U]8s0The following models have also been proposed to describe the temperature
0W-N_'?*V(dvHC0dependence of the rate constant (Kwolek and Bookwalter, 1971) for frozen systems:食品伙伴个性空间7xh)`pz@zj]
kT = a + b T (19.10a)食品伙伴个性空间[?1THC.LL_ w"[2a.e
kT = a Tb (19.10b)
!Sd7Em#`0kT = a / (b - T) (19.10c)
5Y;tw#^y,~4y/l1A0where a, and b are constants. In most cases, Equation 19.10c fits data better.
} Wy7X4@ZD2L0However, all these have very limited practical application.
BOnk2WK*_019.2.4 Time-temperature tolerance食品伙伴个性空间e VG? {1u:_ y
Frozen foods are often exposed to a variable temperature environment, e.g. during食品伙伴个性空间:P [;|.s9]7t:^r(]
distribution or due to freezing/defrosting cycle in retail or home freezers. In general, the食品伙伴个性空间C8]eF-d
value of the quality function, f(A), at time t under changing environmental conditions食品伙伴个性空间"pBP3c?;mm
can be estimated from:
6P9|A`EAU0f(A) = ò k[T(t)] dt (19.11)
8_HRE$kyz0where T(t) is the temperature as a function of time. The form of f(A) depends on the
;iir_4sZy,D0reaction order as discussed previously. If an effective temperature, Teff, is defined as食品伙伴个性空间P!G1]7oz0w/S
11
#a~Z5[HTl Pe0that constant temperature exposure which causes the same quality change as the
T4v,iO-Bf8M0variable temperature condition, as proposed by Schwimmer et al. (1955), then食品伙伴个性空间9x~I u:`!^
f(A) = keff t (19.12)食品伙伴个性空间Wo n1h&w
The rate constant at that defined temperature is termed the effective rate constant, i.e.
6A-O8D u|$A3p2E@+pJ0keff. To estimate the quality change under variable temperature conditions, one食品伙伴个性空间K],bgK w
needs to either solve for f(A) numerically or know the value of Teff or keff that食品伙伴个性空间Ngugv
corresponds to the variable conditions.食品伙伴个性空间6?|^9PIn6Y
The numerical approach for a randomly variable temperature history is食品伙伴个性空间[)vuM(fk
essentially the same as the Time/Temperature/Tolerance (TTT) approach initiated by食品伙伴个性空间B%f'd x w+e2Nm
Van Arsdel et al. (1969) and derived empirically in the 1960's for the prediction of shelf食品伙伴个性空间 gA#I*K]fcH
life of frozen foods (July, 1984). It is assumed that the temperature history of the食品伙伴个性空间,y+Y;r2[I X
product is known. Thus the fraction of shelf life consumed, fcon, was calculated as the食品伙伴个性空间 ] S;WgJ4c?7s'k&?
sum of the times at each temperature interval, ti, divided by the shelf life at that食品伙伴个性空间2T/dthB:H
temperature, qi:食品伙伴个性空间!p!t#f {/R7pj'X'L5@
fcon = S (ti / qi) (19.13)
edi:Z9h]!z0Thus the remaining shelf life at a reference temperature is equivalent to (1-fcon)*q.
F(ls3Hb8Q@8p0Equation 19.13 assumes that the rule of additivity is valid for frozen foods (July,
Fh1a&cb]01984), which means that the loss of remaining storage life or quality can be calculated
Q;sl#j]'i8q0from knowledge of the prior time-temperature episodes the product has been exposed食品伙伴个性空间$r0}a\}S,p
to. This also implies that the prior sequence of the time-temperature episodes is of no
PU9m8o K X0importance except to calculate the amount of quality remaining up to that time, i.e.
2y*Dd{*Y5l$S0there is no history effect. If the rule of additivity is valid with reasonable accuracy, the
@YNrV}0use of time-temperature integrators (TTI) should provide reliable results with respect to
:B]D2B7y R#L9_z0prediction of shelf life remaining, which will be discussed later.
f$u/gP ]L0However, there are some cases where the total effect of various temperature食品伙伴个性空间(n8w:W6w#q
experiences may not be independent of the order in which they occur or of the nature食品伙伴个性空间Uq8`7YmdL d_6k
of temperature history. For example, widely fluctuating temperatures may cause
[l$]*f#N0freezer burn or in-package desiccation, which is not additive (July, 1984). Where the食品伙伴个性空间 n$bn@ R
colloidal nature of a product is affected, the effect of time-temperature history may not食品伙伴个性空间RBih:Bg%D
be additive either, especially with a freeze/thaw cycles. This is also true when growth食品伙伴个性空间#KM-c6R G
of microorganisms occurs (Fu et al., 1991). Certain chemical reactions, enzymatic as
O;X o&\A}y5T0well as nonenzymatic, could even proceed more rapidly at temperatures below食品伙伴个性空间T2gNlY2H!N e
12食品伙伴个性空间^FNj:V
freezing. This is called a negative effect of temperature (Singh and Wang, 1977),食品伙伴个性空间O2Gk a&sM c@
which could be caused by one or more of the following factors: (1) a freeze
\!t+{M#cKv L e0]0concentration effect; (2) the catalytic effect of ice crystals; (3) a greater mobility of食品伙伴个性空间6w2BjXi~
protons in ice than in water; (4) a change in pH, up or down with freezing; (5) a
p8kIOHW9a0favorable orientation of reactants in the partially frozen state; (6) a salting in or out of食品伙伴个性空间S,P4ayF
proteins; (7) decrease in dielectric constant; and (8) the development of antioxidants at
,Xg'y0d_J\#D$v0higher temperatures. As has been shown by Fennema (1975), the freeze食品伙伴个性空间(^ a8R8aIB W3\#j
concentration effect can cause rates of chemical reactions to increase dramatically just食品伙伴个性空间Fk|R-]$U,hS1x
below 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7Ep)G)z5~$uz.V!a
than at higher temperatures this one should not use data in the -4°C to 0°C range or
-HAf o8c/F2}3o8YMZ0above as part of an accelerated shelf life test to predict rates at lower temperatures.食品伙伴个性空间"~p6[Q hN;ro
Fennema (1975), showed that the time to 50% loss of vitamin C in broccoli was 44食品伙伴个性空间3{P U7v1^9?Yc(x.Dx]
days at -5°C, 120 days at -2°C and 162 days at +2°C. This concentration effect is
5]X+T S+_%|D{Qw0evident in the shelf life plot of frozen strawberries as shown in Fig. 19.6 using the data
(zD? {.k#]Jn T/w)n0of Guadagni (1968). If the data collected only at 25 and 30°F (-3.9°C and -1.1°C) are食品伙伴个性空间k"Ubd"v7e
used, the predicted shelf life at 0°F (-17.8°C) is over 27 years, if data are collected at
(d:N0~-Bu0only 20 and 25°F (-6.7 and 3.9°C), the shelf life predicted at 0°F is 40 days while data
[$Ia aR/M N0below 20¥F extrapolated to the true expected shelf life is about 280 days.
w(`SZ%U+Qy,Ja0Figure 19.5 Rate of chemical reaction as a function of temperature食品伙伴个性空间BtZ RG^
above and below the freezing point of a food.食品伙伴个性空间)}:PD Q4O;m+Y
13食品伙伴个性空间 aT w#x9o)xp.E{E
Figure 19.6. Shelf life plot of frozen strawberries showing the食品伙伴个性空间'y6MD1b-T mr+A/K0W%u,D!k
influence of the freeze concentration effect just below the freezing食品伙伴个性空间,u$~.f L ?,{
point on prediction of shelf life at 0¡F . Data from Guadagni (1968).
3hcg6VL d is(JIX.T(\0Each line represents a regression through a different selected set of
y3y[ DboNA0temperatures.食品伙伴个性空间/?6^7x!Ag"j
The response ratio of the food to changes in environmental temperature (RT) is
#H.c^ _ s0dependent on the fluctuating temperature conditions as well as the heat transfer食品伙伴个性空间b0H-hV.F9i
properties of the food as well as the package (Cairnes and Gordon, 1976; Dagerskog,食品伙伴个性空间d s{#m*O5I
1974). In the analysis of food shelf life, an inherent assumption is made that the food食品伙伴个性空间 n-Js2a^
is responding instantaneously to the environmental temperature changes, i.e., RT = 1.
#M5{` sKs0This may be acceptable if a surface deterioration process is the deterministic factor for食品伙伴个性空间:c+h KD#]
shelf life, e.g. mold growth in some foods. Freeze-defrost cycles generally can be
1Vc8r$i#I!U3B0considered as sinusoidal oscillations. The amplitude of the effect is reduced inside the食品伙伴个性空间 `)a)]j)j7A
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*zf:PL5W`
the ambient variation the smaller the RT, and hence the smaller the amplitude of the食品伙伴个性空间KL-rp k$[(B1|
cyclic temperature variation in the package. Zuritz and Sastry (1986) also studied the
e){3@NM z9@@B6b0effect of packaging materials on temperature fluctuations for frozen ice cream and
8O R8i'Y)d x'T?0found that packaging materials coupled with a layer of stagnant air were effective食品伙伴个性空间$a1o]YWJrh9{
barriers against thermal fluctuations.
2iH,j J M019.2.5 Hazard function食品伙伴个性空间.c)zi*w/no4e
14
d'Hz V;T/M@M0After 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)]G\(D3Uy8l
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:nr^'| R4^.G&F5vI
by:食品伙伴个性空间K)m+E!P4y
h(t) = f(t)/[1-F(t)] (19.14)
^Ez8n7cQ sB0where f(t) is a probability density function and F(t) is a cumulative distribution function.食品伙伴个性空间'P7VRUL$\},N
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2T_gIf3v)d`-x
occurred before ..食品伙伴个性空间 k!D7jaL dr'V`
The behavīor of a hazard function for studying the shelf life of food products can
YcB"B]R1{ A)E0be easily understood by examining the "bathtub" shaped curve in Fig. 19.7. Note that
-c3q1m5f JO*_0at time to, a frozen food product begins its journey to many distribution outlets for
db9f&W9K1^0consumption. During the time between to and t1, early failures may occur owing to a
5IY-wg|5@LZ#R0failure in the process itself, faulty packaging, extreme initial product abuse, and many食品伙伴个性空间?q1AE0p
other environmental stresses to which the product is subjected. Early failure should not
b7|iV;BN\%m0be taken as a true failure relative to the shelf life of the product unless it represents the
x w n%~E8WYc3W-w0normal condition. From t1 to t2 one can expect, barring chance major temperature食品伙伴个性空间9RWJk)Q d k'rb
fluctuations, no failures. This interval represents the true period of the product's食品伙伴个性空间q%E C2cE,?9T{
stability. The failure rate is almost constant and small during this time. The hazard or食品伙伴个性空间 Nlv`R#qF
failure rate increases from time t2 to the termination point t3, owing to the true
u9E3S'QG#FS$U;n0deteriorative changes occurring within the product. The concept of hazard function is食品伙伴个性空间9H9E f D@2x
important in the analysis and interpretation of the failure times of a product.
&FNC?8{Ou;J U)n0Time
D8vKNo4g6o0to t1 t2 t3食品伙伴个性空间4aLK!K'fr b9lL
Early
3XV.f*l8w(I*\0failure
f~!Y1_-Xf1Bj0Period of product stability食品伙伴个性空间Cq$wBn
Failure due to
5B+{hN8Yah?0product
?8B2bi3f*sU}A0deterioration
$[*^$Dt*j/PV*HS0Figure 19.7 Failure rate as a function of time
0l9] I5v `7RW\015
1_1J[ He ~&WC0A fundamental assumption underlying statistical analysis of shelf life testing is食品伙伴个性空间m,VR'`.]L&@.g!h
that the shelf life distribution of a food product belongs to a family of probability食品伙伴个性空间,]qfe:u
distributions and that observations are statistically independent. Parameters of a shelf
!?0I"Sn+D1WM/aj0life distribution are estimated by use of shelf life testing experimental data. Once the
WIK5~3F+N] uHtD0parameters of a shelf life model have been estimated, it can be used to predict the食品伙伴个性空间_ySW4HQ
probabilities of various events, such as future failures (Nelson, 1972). Five statistical食品伙伴个性空间%l9}wp2tt3X&K
models, normal, log normal, exponential, Weibull and extreme-value distributions
,s#| V-M!w0Q0were tested for a few food products (Gacula and Kubala, 1975; Labuza and Schmidl,
[ ~!E B-T G6\N+v ^*^ q01988) and it was found that the Weibull distribution fits best, which will be
JDP'o'nSb;U0demonstrated later.食品伙伴个性空间rJb8S)z;{
19.3 Shelf life testing — overall aspects
Gn.ySUl6M5Q019.3.1 Purpose食品伙伴个性空间!ZI4^)L&Q`"x9^6Y
In the development of any new food product including reformulating, change of食品伙伴个性空间 hWPaj-V.B b?S
packaging or storage/distribution condition (to penetrate into a new market), one
crbzm!|&e2Xb2T0important aspect is the knowledge of shelf life. The shelf life of a food product is vital to
W3}3t r)N#i0its success in the marketplace. This life must at least exceed the minimum distribution
.y,vE p ]%is q:on D0time required from the processor to the consumer. Shelf life testing can assess食品伙伴个性空间"qGbLV
problems that the product has in the development stage, following a "fail small fail
!q%Vi0Dd(LJ:JFV0early" philosophy, thereby eliminating large disasters later. Marketing/brand managers
@Pe3hW"v%o0also need reliable shelf life data to position the products and to establish the brand.食品伙伴个性空间0`n'x,a4a8p
Periodic determination of shelf life help to provide assurance that the product remains
(M7~}Rc.v0consistent over time with respect to quality.
ch}.Nc*j0Different shelf life testing strategies are necessary at different stages, as
bCOZ1S4r7MHE0illustrated in Fig. 19.8. If the objective is to identify whether pathogens and spoilage食品伙伴个性空间D Hg"cPb&|/C
microbes will grow in the case of temperature abuse, then a challenge study is食品伙伴个性空间 tBS;|+h;UL+\
necessary. If the objective is to quickly estimate the approximate shelf life of the食品伙伴个性空间}S4c:r#U6Q"hV
product then an ASLT can be used, as long as the proper temperature range is
;n i3H _M0chosen. A confirmatory shelf life test may be conducted at the last stage with食品伙伴个性空间9TE!n ^}Xxw
simulated distribution chain conditions, although in today’s R & D environment, this食品伙伴个性空间8@ E4?0i3h9w_
may be skipped.食品伙伴个性空间h"eqTlMEe
16食品伙伴个性空间C Xg0}q d
Product concept食品伙伴个性空间.HL*b8_3O$j u
Prototype development食品伙伴个性空间 @!r]c7C*\v8@i#\3?
Pilot line testing
7c`r4Hx0Scale-up line trial食品伙伴个性空间C#y:j+W$h6?
Full line production食品伙伴个性空间z }t!Tx!gvcf/E
Marketplace
o9c&Zn6K2aabv8x0General stability information
2|E7AU v0Challenge Study
!j(kn+dg8}c0Accelerated shelf life testing食品伙伴个性空间%CMZ7ylBwkY
Confirmatory storage study食品伙伴个性空间IreV9dB
On-going shelf life monitoring
2C*v3m,vX`RI0Figure 19.8 Shelf life testing strategy at different product development stages
^3~}:Q:tKjL019.3.2 Shelf life criteria
Q a wpF[|0The criterion for the end of shelf life may be variable depending on the definition of食品伙伴个性空间{(g/{_n8`j4q
product quality grade, so the shelf life of a product may also be variable. The shelf life食品伙伴个性空间$a0t"I7]0enk
of most perishable and semiperishable foods is almost solely based on sensory食品伙伴个性空间;a&RDv"pl w N
quality. For example, fresh meat degrades mainly by bacterial activity and rapid食品伙伴个性空间,onc)GtX(C1j
chemical oxidations that cause an off-flavor development and loss of color. This is
H:LgUF I0readily recognizable by consumers. In contrast, many longer shelf-life foods including
7v"?8t_2Q:nTlZ`0most frozen foods degrade mainly by slow chemical reactions such as loss of
Y ?S] { jO0nutritional value. For example, the vitamin C content of some frozen fruits and
L,u3j2]1XM4Q4O0vegetables, may fall below the required standard as listed on the label before sensory食品伙伴个性空间a$L)I9|p!QxBYS
quality becomes inadequate.
Mipl&x1\%NN0The criteria for shelf life may also vary depending on the sensitivity of the
{G$r+WD)e_y|0consumer. For consumers, taste, odor, and appearance are the most obvious criteria;食品伙伴个性空间2\i4N9o%TwL
in academia and in the industry, sensory evaluation correlated with instrumental
[3C+S8~*\T,]0measurements of a given quality index (e.g., vitamin C level) are usually conducted. In
d'R c1J8_q8Ro0general, the criteria level corresponding to the end of shelf life of a product depends食品伙伴个性空间inW6Q!f1h)\%U
17食品伙伴个性空间0{6T,o ~#N+L]o
on: (i) any legal requirement, e.g. zero tolerance for botulinum toxin; (ii) consumer食品伙伴个性空间 pLxRy4C%Y
preferences or marketing requirements; and (iii) cost. In essence, the end of shelf life食品伙伴个性空间D4w9R7G Y n(S
depends on the percentage of consumers a company is willing to displease. If 100%食品伙伴个性空间Rj[d0f v7V a
acceptance is required then high cost ingredients and absolute control of distribution食品伙伴个性空间6l U K5kMc}c(M
up to point of consumption is necessary, otherwise there will always be some people食品伙伴个性空间/F0}i ] fm6~
who will get foods beyond shelf life. The aim is to keep this as small as possible.
FlA4o~%od019.3.2.1 Just noticeable difference (JND)
+\_N9~AlH,qe0Sensory (organoleptic) examination of foods was a general procedure used by the食品伙伴个性空间2eC@ F6UO"{ O7a;r#x
human race to evaluate wholesomeness of foods long before the discovery of
z0{S_T0v)C0microorganisms. Sensory evaluation of foods by scientific methods can be used to
/k3R;d9K2T5b?*p0evaluate such attributes as taste, odor, body, texture, color and appearance. Changes食品伙伴个性空间3G)h)m^%X@
in these attributes may be brought out by microbial or non-microbial actions, usually
0Ai4UPL fwI'?0the latter for frozen foods.
%X_9f%Ab@j U0z5j0The methods used to evaluate sensory shelf life data include difference testing
I'L i e$`%Z0and hedonic scoring. Difference testing can involve paired comparisons, duo-trio食品伙伴个性空间U7_$dh]Lf?#f!RpK
tests, or triangle tests. The paired comparison procedure determines the time when a食品伙伴个性空间}8`#zr)\'m"|
measurable difference in quality occurs between two test samples at a certain level of
F(h x!M}4} v0probability. When applied to frozen foods, this method is often referred to as the Just
7S|a$_N3oh0Noticeable Difference (JND) test or High Quality Life (HQL) test (July, 1984), which is食品伙伴个性空间u%NW5gL2OiFp
usually based on flavor changes. Duo-trio testing compares two unknowns to an食品伙伴个性空间3e Dg a9oUUh Dn
unabused control sample and asks the question of whether either of the unknowns are
6`[c:sl;RA N0the same as or different from the identified control. Triangle testing determines the one
z7HM m(D+\*V&bH!Z0different product among three test samples presented randomly to a set of judges (at
9o+}9C?gkfY7@M0least 10). Probability plots are used to predict shelf life at a given probability level.食品伙伴个性空间icD I:K8]e
The difference method can result in finding a difference when none really exists (Type
mmc+P3V'l.G1e0I error), or not finding one when indeed there is a true difference (Type II error).食品伙伴个性空间kJ^7aq&^
Labuza and Schmidl (1988) have discussed this topic more thoroughly in relationship
.? i7S_8\){[0to shelf life testing, which is not commonly found in sensory textbooks. Table 19.3
H1^(Cwv|*E0shows some data from Guadagni (1968) for HQL of frozen foods.食品伙伴个性空间S&?{`2K'z8M| N
18
2{"I ^$wkG/_~!J0Table 19.3食品伙伴个性空间D9i0M/V@OgQ8E
Days of High Quality Life for fruits and vegetable (from Guadagni 1968)食品伙伴个性空间!\'yl4jpp+OjY5M!z
P roduct T yp e 0 °F 1 0°F 2 0°F
t.Z4zU,dX0apples pie filling 360 250 60食品伙伴个性空间JQ+g*| Q(i"C+M
blueberries pie filling 175 77 18
+k0G"@y-t9l @0cherries pie filling 490 260 60食品伙伴个性空间"i2k7UI3bN0@
peaches retail syrup 360 45 6
,V,I+`C'`dj0blackberries bulk, no sugar 630 280 50食品伙伴个性空间4ul#]5v Mr j k1S
raspberriesbulk, no sugar 720 315 70
;tF?n r-\*^/Q G/S0retail, syrup 720 110 18食品伙伴个性空间XM{*hC3Hc
strawberries bulk, sugar 630 90 18食品伙伴个性空间M ].lP2u9Jt'?%u#w
retail 360 60 10
#~(L|SJ~'b9\0green beans retail 296 94 30
Zh)T]5[ _0cauliflower retail 291 61 13
H@:@kv\5K-A9[0peas retail 305 90 27
$VfZ8rgCy y#u0spinach retail 187 57 23食品伙伴个性空间H c-I`%S0^^N
corn retail 720 360食品伙伴个性空间U?L1Q U
corn on cob retail 275 150
&aI[ }%nga019.3.2.2 Hedonic scoring
e s9O^OUF0Hedonic scoring — which indicates acceptance on a numerical scale, e.g. a 1-9 point
bt$[K*Z0scale labeled from "dislike extremely" to "like extremely", is typically used for shelf-life
0qpe&uCr|9mvu0evaluation. The test can be designed to not only evaluate the overall acceptance of the
8\i)yE/g$`f x0product, but that of specific characteristics such as flavor, texture, appearance,食品伙伴个性空间@EA,Z*fn\
aftertaste, etc. Trained panels can also use this technique on a line scale, which can食品伙伴个性空间 bbMC NNv
be converted to numerical equivalents.食品伙伴个性空间plTnX IR#m'M Y
If the hedonic method is used to evaluate shelf life, one can simply use the
+C:_\`$h'H+W M0score as quality index A and plot the score vs. storage time, run a linear regression,
NU!hy4R3SC0and choose the end of shelf life as the time when the progressed value drops below a
MF^I!M6RX0pre-set level (Waltzeko and Labuza, 1976; Gacula, 1975). The shelf life determined in食品伙伴个性空间P9B;xUK
this way is called the practical shelf life (PSL) for frozen foods (July, 1984), and is食品伙伴个性空间 w0c W5nP-X!kn
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 a+lv}5x Jr)b9KV
shelf life testing, yet it is probably the most used method. Many food companies use a食品伙伴个性空间RHmoR4gH
loss in hedonic score equal to D=0.5 for HQL and D=1.5 for PSL as the end of shelf life
"_ZT_/BOZ4WF+d019
:Gw'MJE"wy0(Labuza, 1982). Objective measurements and professional judgment are often食品伙伴个性空间 fB{l6OEs
required to determine the end point. Data in Table 19.4 from an report published by
C,\5I2i3t/| ?)p.En0the former Refrigerated and Frozen Foods Institute (1973) Unfortunately there were no
i1T(w3b k&[t0methods 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@`| Pf
HQL value. This in itself suggests that the HQL methods can be used to shorten shelf
4]1m/M+L]_0life testing times.食品伙伴个性空间is|/on rP)`W+? e.cs
Table 19.4食品伙伴个性空间sr$^"\:T!H
Relationship between practical shelf life (PSL)
G&Gb1`6Z0and High Quality Life for frozen foods.食品伙伴个性空间gI)FK"A(Nt1b
F rozen Food P SL/HQL Rati o食品伙伴个性空间*],x1zX x7KgZ
lean meat 1.9 - 2
C)\2PZG#t#H0fatty meat 2.0-2.4
9hd j*t j&\]0lean fish 1.9-2.2
t x(d6d}G0fatty fish 2.4-2.7
h[O-n#O\9Mu0precooked foods 2.8-3.0
M}1t p8E0fruit 2.8-3.1食品伙伴个性空间.l3}v0A.^SW"H_
vegetables 3.1-3.5
"iJS z ca'm019.3.2.3 Instrumental analysis
s_)b7}i1|f(S0h0}6r-SH0Chemical or instrumental analysis, such as moisture, nutrient loss, free-fatty acids or食品伙伴个性空间p:FWvWU~
color measurement that closely correlate to sensory attributes, can supplement食品伙伴个性空间6}VA#rW9XX8N#d
sensory techniques. They are usually less expensive and less time-consuming than食品伙伴个性空间WOqPR?*s\
sensory approaches. A correlation between a physical or chemical test can increase食品伙伴个性空间C'F4h\Wu)l
the confidence level of the sensory results. For example, the following constituents or
{)G7D l0?D`$G o t0properties can be considered for monitoring chemical changes of pizza quality during食品伙伴个性空间 Z'`rb;LEb
frozen storage: total free fatty acids, specific volatile free fatty acids by HPLC,
+cN L?-M&A"l0`Q0peroxides, oxidative volatiles (e.g., hexanal) by GC, spice volatiles by GC, lysine, color
:^ oie [H(n5^f0(decrease in red color or increase in brown), in addition to sensory evaluation of taste食品伙伴个性空间)H TY7vg9P
and flavor (Labuza, 1986). Most sensory experts agree that analytical methods should食品伙伴个性空间/x^:}$e!{sI
complement the sensory tests. Vice versa, the endpoint determined by objective
f@-t6P3{0measurements should be confirmed by sensory techniques as well.食品伙伴个性空间-P"US0d6P G+a"h!X
20
%v8xcX#Wlks A+wJ019.3.2.4 Weibull Hazard analysis食品伙伴个性空间Sj${SV
The Weibull Hazard procedure requires one to first make an estimation of the time to食品伙伴个性空间^rx)w'v jr
the end of shelf life. This becomes the initial estimated time limit for the study. The time
2LJ&h~M,PD z0limit is then divided into several segments at which points panelists grade the product.食品伙伴个性空间{e~,n ik
Additional panelists are added at a constant number for each subsequent time period
s4T5d f%b4KL0to maximize the number of testers near the end of the test. The panelist is asked to食品伙伴个性空间:EJ7`0s8x _&nN t
grade the food as good (acceptable) or bad (unacceptable), i.e. no ranking on a食品伙伴个性空间z$\^L k"EwC-PS
hedonic score. When the product is identified as unacceptable by 50% of the食品伙伴个性空间W%`3KJ8]Es/X
panelists, the number of testers for the next period is increased by the number of failed
RnB9G:} f*v0samples plus the constant number. The interval between sample times is also食品伙伴个性空间t)SF/@0b J&~r,f9K
shortened as the end of shelf life gets closer. The test ends when no more samples or食品伙伴个性空间\ @`&gBY+I{XF
panelists are available. The scores are ranked and the cumulative hazard calculated.食品伙伴个性空间$W&^;[ [?d%Y
The critical probability of failure Pc, can then be calculated from the following equation:
1t/K)\oxG0Pc = 100 (1 - exp(-å(H/100))) (19.15)食品伙伴个性空间"ql]o,xZ T$i
where H is the hazard value equal to 100/Rank. Choosing Pc = 50%, corresponds to食品伙伴个性空间ve5ciQ#@z
an accumulated hazard value of 69.3%.
To.YV-]W`V0The relationship between the logarithm of storage time (log t) and the logarithm食品伙伴个性空间]a3esK
of hazard value (log H) is linear:食品伙伴个性空间AJp8s UON
log t = (1/b) log H + log a (19.16)食品伙伴个性空间)v7j&g Dk4M:I:w-O
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2X8Ew3I3~ ^ _
be determined based on the desired probability level allowed for product failure. The食品伙伴个性空间7y[.{BVh/sA
lower this probability, the shorter the shelf life. This plot then allows one to make a
i,}#p`5V,x&z!_"FY8I@0management decision with respect to the probability of displeasing a certain fraction of
#[:pvX7ZJ9g-z ]0consumers. It is hoped that the distribution time is such that greater than 99 percent of食品伙伴个性空间*S'A#Ro:\ N'K'xk
the product is consumed before the end of shelf life based on displeasing less than食品伙伴个性空间UdY[ y ku5d;E
X% of consumers where X is the economic value. An detailed example was given by
0pD"E t(vV+h)N/B0Labuza and Schmidl (1988). It should be noted that this process can also be used for
p+j b!~`G;^i0simple analytical tests such as plate counts or vitamin C. In these cases the number of食品伙伴个性空间5N0?;pYT?
panelists are replaced with the number of samples tested. Some criterion such as 20%
D(c kf4B(J0vitamin C loss is used as the negative response. Figure 19.9 shows an example of食品伙伴个性空间y8g"D4p"{ ULJ
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u'g-XX~[ ?
21
.t&?^"@i1gfp/r0found at Pc = 50% from the graph. From this graph then, if 95% of the food were
M+Cx+UmJMw&RW&c0distributed and consumed in 3 weeks, only 1% of the consumers would be displeased食品伙伴个性空间X7zJ0CW"z
.01 .1 1 10 100 1000
%VyZ3{&n;D+d01
)AY2O1i+c'~!K010
y/bBx2HH*j0100食品伙伴个性空间/}#iK*dvC}
Cumulative hazard (%)
'A(IK$e7s+UW,p0Shelf life (wk)
W5sk:VCP.Cx$m0Probability (%)
LX*{Y;M(q#wjb+I00.01 0.1 1 10 50 99.99食品伙伴个性空间&GJc6o{Q'V:jq
Figure 19.9 An example of Weibull plot for a frozen food.食品伙伴个性空间)IHi8Pv3?
A shelf life of 16 wk was determined at Pc = 50%.
(E/t~N6v.x]6hM0(or 0.95% of the product is out of compliance). If the rest were held and consumed at
LW%Q$S]K010.5 weeks, 50% of those eating it would have out of quality food or another 0.5 x 5%食品伙伴个性空间-m3{3A3y2@/y8Y
= 2.5% of product. Thus in this distribution model about 3.5% of the product is食品伙伴个性空间}0a]q}"hE[:E
unacceptable. To improve on this, the product must either move faster or one must食品伙伴个性空间*\#?`(^"i WX%|@
distribute it at a lower temperature. Wittinger and Smith (1986) used this approach to
9L"n7oz2Q H0determine sensory shelf life of ice cream based on iciness and found a shelf life of 5食品伙伴个性空间9G`IG$c$|;z
weeks at 0°F (-15.5) which fits the general data for iciness in ice cream as shown in食品伙伴个性空间sA3aoY` Q
Figure 19.10 (Labuza, 1982). It should be noted that this gives a Q10 of about 12.
b5R] AOg-?.k.W022
J*O*t}!^,[z0.1
~E2I.G9X01食品伙伴个性空间!Z;{Hxe&}4`TDW
10食品伙伴个性空间LR w(r*f8h3?
100
;g%C3w GVs*@"r/g0Temperature °C食品伙伴个性空间%zB9X Z:^(kF2yx
1食品伙伴个性空间j;ig\:T?
10
}%|]RsF.Z[V0B'`L0100
:\,g:E| l [4LOa9a3T_0-30 -20 -10 0
+R2O_K%qAv:P00.1食品伙伴个性空间 x$B.L)R-V#I
weeks
)AD3E;o-w|3P0Figure 19.10 Shelf life plot for ice cream based on icyness食品伙伴个性空间B3nJF s4rt
perception from data of Labuza (1992)
x7D D ]LZDJ`019.3.3 General procedures食品伙伴个性空间!a9eCam v2H
Shelf life testing experiments are designed to measure the average shelf-life of a
%pz3Dw3l9_~1ZI0product under given conditions. General procedures for shelf life testing of foods were食品伙伴个性空间\&G+fxXWq
proposed by Labuza and Schmidl (1985), which include:
5G!Awv(PPvb7K0Step 1: Develop testing protocol — The protocol should consist of: i) specific
-V__O7h0objective; ii) detailed test design in terms of product, package, and storage condition;
,Ack$z`;v9X0iii) execution procedures in terms of time, space and resource availability; iv) cost食品伙伴个性空间w"h9R:s!f
estimation.
,s[/{4i$]0Step 2: Identify key quality indicator — Any previous shelf life data and kinetic食品伙伴个性空间}z0T G]Dmu"\ f
parameters of food deterioration available in the literature (Labuza, 1982; Man and
2Nd]h4yhUT l([0Jones, 1994) or the distribution turnover time of a similar or a competitive product in
'g"o^uV9],l0the market place, if any, would be very helpful in this preliminary identification or in食品伙伴个性空间'u^ M2cGC ~v$^
determining the shelf life requirement.食品伙伴个性空间}bM*R`n4r/@
Step 3: Estimate product sample and control needs — The number of samples
aF I Y(H5I6FU*t;hU0and controls required should be based on the detailed experimental design. If
OE;M,M.R'U;W0sufficient product is available, extra samples should be placed into each storage
[2|uHx Z8Jx+D!~023食品伙伴个性空间's@ C.Z2d:l\H{B
condition. Now and then it may be necessary to recheck a sample, especially if a value
j,M$nG~T)K0is not in line with other data. It would be disastrous to be out of sample before failure
#R*u7g*JV6[)f K0has occurred or the predetermined termination of the test is reached. Extra controls食品伙伴个性空间Ad:r6wKG!r;s+SM
should also be prepared and stored. When the samples are placed into storage食品伙伴个性空间&|}0as:CzNq
rooms, they should be positioned so that the complete package is exposed to the
`?.h,l8Ra f0external atmosphere, unless otherwise specified. The specific location of the test食品伙伴个性空间3G!|l @`'} KL4W0@L1f
sample should be recorded. Temperature controllers should be checked for accuracy,
i%k\OU{3fK;` D0periodically. In addition, removal of all unused samples from the storage room to make食品伙伴个性空间 u9n6T~9xx
space for future studies is a must.
A9e-~!_,g0]2o)B0There are various thoughts when it comes to using a control product. Some食品伙伴个性空间_Z-qV p
sensory experts prefer an actual physical control; others are satisfied to just use the食品伙伴个性空间p*f#?%U$r6Q
numbers obtained in the zero time evaluation. There are three alternatives when using
*gD#\kC2R0a physical example as a control: (i) making the control from scratch each time using食品伙伴个性空间1[7dq5S!OcKo0ik4F
the same ingredients, procedures, etc.; (ii) deep-freezing the control (e.g. pizza held at食品伙伴个性空间&C ]e3Z*P/G
-70 °C) and accepting that it might have changed slightly, but minimally compared to
5Ru$D I9G_md3o0the product in shelf life; (iii) using a fresh batch of product which may not be identical.
1}U0SYur9]iw0Step 4: Select proper package materials and package size — This is largely食品伙伴个性空间P/N0t{ h+|1t0N
dependent on shelf life requirements, packaging costs and availability, and consumer
1zt0Jh]B-i/i0information. Factors such as vacuum packaging, nitrogen flushing, or use of食品伙伴个性空间rEv,Yl$P.[
antioxidants are often considered in combination with packaging materials.
n7mqxQ'g9dH h0Step 5: Choose storage conditions — Storage conditions are chosen based食品伙伴个性空间4C jm7v|Xj~a*kDo
on the type of shelf life testing. For example, the intended commercial
;iu7TO0FZ\o'G0storage/distribution temperature range should be used in confirmatory shelf life testing.食品伙伴个性空间O*q'B1|x GU%D#|T
Elevated temperatures are often used in accelerated shelf life testing to obtain data for食品伙伴个性空间0LRq3bUu|_ b H2i:S
prediction of shelf life at lower temperature or for prediction of shelf life under variable
t+OM1e*D8@7P0time-temperature distributions. Humidity control and/or monitoring is less important for食品伙伴个性空间%c&h[:`c_7B
frozen foods as compared to other foods (e.g., snacks, cakes, pies, and pastries).食品伙伴个性空间*Y\z8LE^
Light in the room should be properly controlled depending on the package.食品伙伴个性空间0s n.\z3Z/bN%C+a`+X0z
Step 6: Estimate sampling frequency and duration of testing — The sampling
/wCZ&YkM-_0frequency is generally an estimation based upon experience from prior studies with
9Im,b%S7z0similar foods. However, once one knows an interval at one temperature, then the食品伙伴个性空间3E})m)M$U9S G u)s]
intervals at other temperatures can be estimated using a Q10 value i.e., if the Q10 is 3
5t@qW Y,q5f3i+w0then for a 10°C lower temperature the sampling times can be 3 times longer. If the
WEl0C.~0interval between sampling is too long, the risk of under- or over-estimating shelf life
8N+H5fP;A g$r;Y0increases. The more analyses that are completed, the more accurate will be the shelf
j`a~%B@i0life determination.
hj.i T,^/XR024食品伙伴个性空间B;qJ I y*k
The question as to when one should end the experiment must be based on
+Nj1K(MUb,HPdj0some pre-set criteria for failure. One criterion could be the minimum shelf life食品伙伴个性空间 Q~xh2C"N vS
requirement driven by product category, distribution chain, and the benchmark's食品伙伴个性空间)Kvd/TvoF
product stability. If there is an accompanying sensory test, the end time can be based食品伙伴个性空间9IGxc Jd
on some organoleptic inferior quality criteria from which one then can get a microbial食品伙伴个性空间;Y5H ?f;z c|!a
or chemical index limit. For frozen products, several weeks to months are usually食品伙伴个性空间mWk$B)k?:X#F~
needed. If the shelf life can be estimated with any accuracy, the test intervals can be
5[3D ^pW2~ H0lengthened and clustered around the expected failure period. Most of the experts only
s L _e r+`0require about six evaluations to provide reliable results.食品伙伴个性空间sn#neH0`jG]e/U
Step 7: Schedule for execution — Before scheduling the starting date for a shelf食品伙伴个性空间 F:x4]1@ Mt.T] U
life test, one must check for the availability of ingredients, packaging materials, and食品伙伴个性空间iWf:JT,K
storage space, and the time and resource available in the pilot plant or in the
4PSeXA)Dld4M0processing plant to prepare the samples. One should also check for the time and
W{F)Kv?yi0resources available in the microbial lab, the analytical lab and/or the sensory support食品伙伴个性空间3Xc ~0G$_%T{`
staff throughout the test period. A copy of the test request and schedule should be食品伙伴个性空间v7kK7}(W;h
sent in advance to those who will be doing the work. The courtesy of providing those
Z9e)v:u2C j0involved with this advance information always pays dividends. Holidays should be
/~uV,YaVTJ1g0marked on the scheduling calendar, since scheduling too many evaluations near食品伙伴个性空间"S3bqf-X/vO'm
major holidays or Friday afternoon is not recommended. However, once scheduled,
G*g"|Dd0sample observations on weekends and holidays should not be skipped over, since食品伙伴个性空间1y{ q4_{3k}
important data points could be missed.食品伙伴个性空间S"b"SH,x#fu
Step 8: Take sample and evaluate quality — Samples should be taken and
k X-xg@d EU0evaluated following pre-determined schedules. Sampling plans should be食品伙伴个性空间M7Y)NP A}
administratively and economically feasible, taking into account the heterogeneity of食品伙伴个性空间/PU8q+v)q9I(`? @
the food. Maxcy and Wallen (1983) pointed out the problem of heterogeneity of食品伙伴个性空间@1J}6[ Q4G3n
samples in shelf life prediction. Multiple subsamples (³ 3) should be done for nonhomogenous食品伙伴个性空间q,F!Jh%U+r5N|$`/?
samples. A single package is usually used as an experimental unit.
F \"Y+NGE0Replication of 3 or 4 units are desired for each measurement. For frozen foods, a食品伙伴个性空间$dl8]~$l#B6|%{B+I
thawing process is often involved in the sampling procedure. Proper thawing or
mW-@$m5@ [g0microwave heating is critical to the product quality. All samples should be thawed or
$o`%B Vi/bV7l0microwaved in the same way to minimize any biases.
US9G'{uQ oM0The intended analyses should be based on the specific mode of deterioration,食品伙伴个性空间WB x:fB&H/Ma#Qn
which was discussed earlier. Whatever the choice, the tests should be reasonable and食品伙伴个性空间])GR.}klbi#\1c
logical. The key is to make sure that one is measuring the right thing. If the wrong食品伙伴个性空间5~(q/] e a8@mc
quality factor is measured, the test starts out a failure. Unfortunately, in many cases this
CKS&I%uB#R},Ga0cannot be established initially, so sensory evaluation is a must in almost all shelf life
e.C{i~025
,g2`1~'RK)EJ0tests. Key sensory evaluation techniques for frozen foods have been discussed食品伙伴个性空间~ T v^)\r ^&Y
before.食品伙伴个性空间2SkT2O%_-tq2P r
At the time of each pull, one unit of the sample should be evaluated (informally
.Nk;F8[o| C6`!p0by a minimum of 2-3 people) for changes in flavor and texture. This should be done in
D(y5?E-m;Uvr0addition to the final tasting prior to a consumer sensory test. This is necessary since it食品伙伴个性空间*@z/fp(V#i }ux
helps the developer know approximately how the product is doing during the progress
!IgW8F[?T ~:D0of the shelf-life, helping to avoid any surprises in the results. Control samples may
dr,P}q3Q,b:[0need to be prepared fresh.
-L3C Lc9u@9I0Step 9: Analyze data — Shelf life is the predicted day at which the stored
yB$gWSOV0product (test pull) is X% less than the control at day zero (Reference). The data should
Z5|bdg0BW#F3X0be plotted and regressed to determine that point using the proper model (zero or first).食品伙伴个性空间C,C#{ W%F0kMV&c6q
All too often the data are not analyzed until the experiment is over and then the
"e0Q&C"v e3w9I;y Bnj0scientist finds that nothing can be concluded because of lack of points or a poor fit or食品伙伴个性空间k Z T:A-S
some surprises. Statistical curve fitting should be consistent with the chosen model食品伙伴个性空间l(UwLB vUn8a8t
based on a theoretical mechanism. The amount of change and number of data points
w7z&|3cx7SSs y:K0are related to the coefficient of variation (CV) of the test. A weighting factor may be食品伙伴个性空间.CyDLSX-oml
used in estimating the rate constant and its statistical limits. When the data for an
nX3r2?WURfG(e0attribute does not fit the regression model well (adjusted R2 of < 0.8), scientific食品伙伴个性空间KH\ ?UT
judgment should be used to decide whether the data are applicable.
%u7|~1^ L~0When in doubt, a rerun on retention samples might help understand or clarify
Az5WG$F0the results. Error analysis could be performed before experiments are run by first食品伙伴个性空间&R]k1U5u
finding inherent errors in time, temperature, and quality index measurements, then食品伙伴个性空间0l0_$L~Y2?
calculating an expected standard deviation for the plot being used to determine a rate
)fB}+Pi,`0constant. If the experimental data have a standard deviation much higher than the食品伙伴个性空间?PIoRN
expected value, either the functional form of the rate expression is incorrect or the data
pBloC2js"o@:Xg0contain errors from unanticipated sources.
5oV'p z%I0Zo0Step 10: Prepare shelf life report — Depending on the type of shelf life食品伙伴个性空间0v#Y*y6y$p5qi c
determination, the results should either throw light on the technical viability of the
KD/R/o6V0product or provide answers to the questions about the maximum safe shelf life as well
g Q fO r0as the maximum quality shelf life of the product. Before a shelf life is finally set, factors
(E#b f-fG0in the scale-up of shelf life data will need to be taken into consideration. Based on食品伙伴个性空间 e.XZ!i/W1m@ol
results from ASLT, the provisional shelf life will be set for the product. There is no
@x^CjZA1gv0government regulation which defines the product end point except for that related to
B'Q*bIco2{~ [)^0nutrient levels (vitamin C and vitamin A) in 21 CFR 101.9(g)(1)(ii) which states that for食品伙伴个性空间nee"s8j#bNr.\ a
the vitamins listed, the analysis level cannot be below 80% of the label value if it is a
2m-P6zWJ~7R'q0natural food with no added nutrients or cannot be below 100% (21 CFR 101.9(g)(1)(i))食品伙伴个性空间"}Ql5gP6x#_hHXZ
26
DEZa9Fj&S1wM0if the product has any added vitamin or nutrient whether or not it is the nutrient under
(EU C2Sc7~~D0test. Thus one must base the label value on some predicted initial variability and食品伙伴个性空间W W A0dfBE
some predicted loss during distribution and storage. The FDA usually takes samples at
{DN.yIj0the supermarket level (where they can purchase them) for compliance testing, not from食品伙伴个性空间5~j%V/@:f _+b-[ ^
the end of the process line so distribution losses must be factored in.
3JA x/uuV Ew[0The end point of shelf life is thus dependent on your corporate objectives and食品伙伴个性空间'vmiOe_bl5je-td
how much risk the company is willing to take with the brand. No shelf life test is食品伙伴个性空间O5?Ow3V
completed until a termination summary has been written. All termination summaries
e;zX(r9Md7A v_0should include the objective of the test, product descrīption, package descrīption,食品伙伴个性空间M;A+U3KeW!YTL@
conditions and length of storage, methods of evaluation, results (in the form of graphs,
2Q6e)@,x)R|2|'X0shelf life plots and Q10 values) and conclusions. Termination summaries should
|CIiy p0become a permanent record in the company library for future reference and preferably食品伙伴个性空间2zCR| G KS0C
indexed well on a computer data base for later retrieval when needed. The final shelf
lyK1Bz$yb7UR0life 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!B.la5M_}#Y'Y2]
new product, particularly of the high risk category, should be set based on data that
:^\)Ap0BZY:A&E/wV0relate to the worst case manufacturing and storage scenario. The shelf life can then食品伙伴个性空间 xf]RFn V,d7X
be reviewed and if necessary re-set in the light of further experience in manufacturing
U)M$HC^0and control after the product has been launched.
n"wu p+f0Step 11: Implementation — One should get top management’s approval of the食品伙伴个性空间hJR2M/X2M5F+O1U8J
test results so that they can be implemented. Management must believe and support
4W#Z;H)t1cB!w(\0those test results. It is important for production, sales, distribution, purchasing and
8Z2g4Q ZRy/g#cs Fu T0quality control to work together to be sure that the production is properly handled from食品伙伴个性空间V8F3r&n5N3LVR4Z4E
the time of manufacture until this product is consumed.食品伙伴个性空间'cSq2\0G:?5@
19.4 Challenge study食品伙伴个性空间@YF8Y}1RAU
19.4.1 Basis
l#vB}Ka0Freezing reduces the microbial population of foods but considerable numbers usually食品伙伴个性空间 Uw3u%M W.UW8A%y
survive even prolonged frozen storage. A challenge study is often used in the
7R]*|Scv.e t2T0laboratory to study the factors and factor interactions as they affect the shelf life of the
B{mS'j0product. Such simulated experiments enable the researcher to better control the study.
%g,K@cPH\0A challenge study is necessary for frozen foods for two reasons: (i) to predict microbial食品伙伴个性空间 yxC_&_md
growth and potential risk of the product upon temperature abuse in a distribution食品伙伴个性空间'[e [T+p W0E
chain; and (ii) to assess the relative stability and the relative risk of different formula,食品伙伴个性空间L:d@,O9Tg P7P)x
different processes or different packaging materials, which is a must in new product食品伙伴个性空间4Jt-I+P$I4^_:X)Aw L
development. A challenge study may also be considered as a preliminary shelf life食品伙伴个性空间;Mwo`{"B)`,j
determination in terms of microbiological safety. It is often used in the early stage of食品伙伴个性空间9J'o:ykf[:j
27食品伙伴个性空间FCs~xZ,}
development since if microbial safety is a concern at this stage, then reformulating can食品伙伴个性空间@W&pW QG"`
be done quickly.食品伙伴个性空间 c Z5@MR*bM
19.4.2 Microbial abuse procedures
@,_"W T-RCDY0Step 1: Identify barriers — A composition/ingredient analysis should be done to
!k\:yX:e0identify any barrier(s) against spoilage microbes and pathogens in case of食品伙伴个性空间 f"q'_vV0lA
temperature abuse.
O$d9Wz2a Q%S0Step 2: Choose types of organisms/strains and inoculation level — One食品伙伴个性空间I4Z%Eyh y1ZH
principle is to use an organism or a strain that has been isolated previously from the食品伙伴个性空间.bs)k6?:Uq-gk
product or similar foods which is responsible for spoilage or risk. The more isolates in食品伙伴个性空间`IgG-\5M^ p%\%^"U
the study, the greater is the confidence in the accuracy of the shelf life assessment. An食品伙伴个性空间8c:MTq!p,wJ
inoculation level must also be determined, which is generally much higher than the食品伙伴个性空间*jH(cex#G-fY?w
normal contamination level in a product. If the average contamination level for a
4vPh"j&l-q C5h&[0particular product is known, then the inoculation level should be as close to that level
`,T0H {j#^0as possible. Sometimes several inoculation levels are used.食品伙伴个性空间9Y7S(W$u:X(K)e V&u
Step 3: Determine temperature abuse conditions — After inoculation, products
p K]M(~0should be packaged using the desired commercial packaging conditions, and食品伙伴个性空间l,t.qq7q6}DgL.A
subjected to temperature abuse. Factorial design and response surface methodology
a$Q[6b;UljKH0are often used in designing a challenge study. A typical temperature abuse condition食品伙伴个性空间Bm1W~ y
used by some food companies is provided in Table 19.5. It starts out with five sets of食品伙伴个性空间SXD$J`.Q7Z0E
test packages placed at -18 °C to begin the cycle. At the end of the first 24 hr, one set食品伙伴个性空间RJe-C4J
of packages is removed and tested for microbiological indicators to establish a zerotime食品伙伴个性空间B kc*v1?s,[B
level. All the other packages are kept at -18 °C for the next 20 hr, then removed
cSa9Q*kWP6N0and abused by placing them at 38 °C for 4 hr. Another set of packages is then食品伙伴个性空间.]lyc4W:Z0Z
removed for microbiological testing, and the cycle is repeated for the remaining
9u,B(nQ0w/\s0F;v0packages, i.e. they are all returned to -18 °C for at least 20 hr, then abused at 38 °C
[^m0?O3cI0for 4 hr. This procedure is repeated so that one set goes through at least four freezethaw食品伙伴个性空间1R6MrDnH&[vV(v
cycles. If there is no significant increase in spoilage organisms or pathogenic
Gl4HS x"X p8ew0organisms after the fourth cycle, the food is deemed safe microbiologically.食品伙伴个性空间,G2{2sM;d^4qw y7|T y
28食品伙伴个性空间N:nx+n'r ay
Table 19.5 A typical temperature abuse test sequence for microbial challenge食品伙伴个性空间:AJ*I5\#^2Ej[+D
studies
R/C } v2t4@0Day Abuse temperature cycle Number of package sets
2] Kv3B;lS `0J h0remaining
W"k?4yc+e!}1_01 24 hr at -18 °C 5
)[TT.q]$@1[yu!~02 20 hr at -18 °C
R1hVM!j;h bcP04 hr at 38 °C食品伙伴个性空间-B~\S'k+{8T
4
pb-zL}|+~)o03 20 hr at -18 °C食品伙伴个性空间 neR#{AQ]X
4 hr at 38 °C食品伙伴个性空间;JuWz-w#w/l\
3食品伙伴个性空间}"iA3nU(ao;nP:o#B
4 20 hr at -18 °C食品伙伴个性空间1l(]#P6_h7ksqg_,c#v
4 hr at 38 °C食品伙伴个性空间 Y ^9HwF"Km"xV6|
2
s*A:d%dA05 20 hr at -18 °C食品伙伴个性空间9N V5Cx%A-{(s
4 hr at 38 °C
:Z3o9f#Tc wnJ01食品伙伴个性空间Bze.o\kaw"h
Source: Labuza and Schmidl (1985)
Q8~ wp$k0Step 4: Do microbial survival analysis — This is to find out if there are any食品伙伴个性空间Cu*v?C[6l
microbial growth upon temperature abuse or if the inoculated microbes survived the
;s$B([+L[;n+Q.v)D0]h0process. Appropriate detection and enumeration techniques should be used.食品伙伴个性空间B,jx1R ^o
19.4.3 Applicability食品伙伴个性空间*B9m;}IT m!ov,\
The use of inoculated pack studies conducted by independent laboratories allows a
4W7h8}xw3J?]0food processor to assess the relative risks that can occur under conditions of
`K F)T5N o0temperature abuse of the food product in question. Taking frozen pizza as an
}K]X&?3_tj0example, both the cheese and sausage, if naturally fermented, will have high total食品伙伴个性空间_F|.cw Z+i
counts of bacteria. Since the product is usually partially pre-baked and then frozen, the食品伙伴个性空间W9Vu\3o,I8r
numbers of vegetative microorganisms will decrease until thawing occurs.食品伙伴个性空间NTbkP4zF
Unfortunately, pathogens such as Staphylococcus aureus will not be totally食品伙伴个性空间&EG0iTnB3k w
inactivated by these treatments. If the product is abused during distribution so食品伙伴个性空间W`C*sw hP8Ss$Yj
severally that the temperature near the surface reaches about 7 °C, pathogens may食品伙伴个性空间 m3`oC8Y]}s5W
grow. A challenge study with Staphylococcus aureus will verify the microbial safety食品伙伴个性空间@ Z,mT H2_*PW
of the product.
'?VX)h4^l0It should be noted that inoculated pack studies with pathogens should not be
)q2H tW;l2x/C0conducted in food industry laboratories that are located close to the food processing食品伙伴个性空间7b,J!|B#O
facilities because of the possible transfer of pathogens to food products. No sensory食品伙伴个性空间.?7mu.M;hx q9z fW
29食品伙伴个性空间WO4a#z2fH4e
panel can be applied to evaluate the inoculated samples other than visual
(K/q)Q0vZ.J0observation.
+SCHw?r0k_019.5 Accelerated shelf life testing
h%]8Dypu9V8gb019.5.1 Basis食品伙伴个性空间9{?'c)w3l0t&H6]*X
During product development, preliminary shelf life knowledge is often needed in食品伙伴个性空间6b*P}p-zI6D
addition to microbiological safety. Shelf life testing experiments at this stage are often
7]:C{/a{I0accelerated to evaluate the effects of various formulation and processing parameters
3w k lJ6A2|dV0on shelf life stability of the product being developed periodically since one can not食品伙伴个性空间Tl&J`v2xL1G;t
afford the relatively long shelf life period for a frozen food stored under normal freezing食品伙伴个性空间2T0N[_!q5`nZ7G
conditions. In addition, temperature fluctuations may occur in distribution and retail食品伙伴个性空间(stt \m*rI!F GO;G*b
holding for frozen storage. Thus kinetic studies at several temperatures within that
QKUoR/bQ*@l*k0range are necessary to predict its shelf life. Accelerated shelf life testing conducted at食品伙伴个性空间5R8N S*zw3N/I
elevated isothermal temperatures and/or with freeze/thaw cycles for frozen products
__ F6ij7|-a:^2RQ0have been used extensively for several decades by industry and government
F/g,T6V8VP3L0agencies (Labuza and Schmidl, 1985). The Arrhenius relation and the Q10 approach
?6Mhhy0are used to extrapolate the results to the expected lower storage temperature.食品伙伴个性空间D5D&y?-hCgze
Acceleration factors other than temperature have also been studied for some other
;eQ6^\5S7`:Cg0deterioration modes, such as moisture gain or loss and lipid oxidation (Labuza, 1984),食品伙伴个性空间(br J~,y#lj0]4U@v
but rarely done for frozen foods.食品伙伴个性空间q0uoq0P%d
19.5.2 Unique procedures食品伙伴个性空间X r-nS9SPZ
Step 1: Clarify test objectives — In general there are two occasions where
e] q!Ip7s0ASLT applies: i) estimate approximate shelf life quickly during development stage; ii)食品伙伴个性空间t6A@5B] vk,G
collect kinetic parameters for actual shelf life prediction as in the marketplace, which is
hW'o;R!~H$O[?7T^0conducted generally near the launch phase.食品伙伴个性空间 iQz2H9S/Z+_2D
Step 2: Select accelerating temperature conditions — Suggested isothermal
aHZ5upI0accelerating conditions for frozen foods are -15, -10, and -5 °C with a control stored at食品伙伴个性空间R.@d9X/B&s8}
< -40 °C (Labuza and Schmidl, 1985). The inherent assumption is that the
}L};WY,xu0deterioration mechanism is the same across the temperature range although as noted
u3KS:[C4MH G{C/i0earlier, there is concern about how close to freezing one can go.食品伙伴个性空间s+mpL*Rq2_
Moisture migration from the food into the surrounding air with resulting食品伙伴个性空间kQ5ql] VB
desiccation of the food and ice crystal formation in the package is a major mode of
,coga+U@0deterioration of frozen foods under fluctuation temperature conditions. Cycling食品伙伴个性空间f V)?%l3NW1p;D/\.\T
temperature storage is used to test for this, i.e. from 0 °F or 10 °F up to 20 °F with one食品伙伴个性空间"b+EXv2wbp"e
day at each temperature and then repeated several times. A freeze-thaw cycling study
9iOnkc"a ?(nF0is also needed to determine its effect on sensory quality. Usually, the high temperature食品伙伴个性空间$QK8a'_We%K x
30食品伙伴个性空间'H$w(b-n%Cn8QZ
can be much lower than that used in a microbial challenge study unless microbial食品伙伴个性空间6ZM/m h _+T:d
survival is still a concern. Typically, cycling temperature/time can be three to five 24
,@TG~'s5H0hour cycles between -18 °C and -7 °C, or between - 18 °C and 7 °C, depending on
\3I){%P`E3dm H@0the product.食品伙伴个性空间@~(NCqT4W
Step 3: Estimate testing time and sampling frequency— Testing times are食品伙伴个性空间Y(o7G lrgj VJ
dependent on a desired shelf life at target storage conditions. For example, given that
/\&Rt1z!i6f.}"]0a shelf life of 12 months at -18 °C is desired, a shelf life plot can be constructed. Figure食品伙伴个性空间)w q\|P;mI
19.11 indicates the test time at -4 °C that equates to 12 months at -18 °C for various食品伙伴个性空间vR,GgA](?\ r
Q10 values. Sampling times at -4 °C should thus be 1 wk, 2 wk, 1 month, 3 months, and
tT3@BH2z6d04.5 -5 months. Most published results suggest that Q10 values for vitamin C loss and食品伙伴个性空间qm3i(b[c;D'C.N
quality loss in frozen vegetables range from 2 to 20 and that the shelf life of vegetables食品伙伴个性空间U$Zk|g"Kx+t:u
is only 6-8 months at -18 °C (Labuza, 1982). Considering these Q10 values, a product食品伙伴个性空间 a/`Qkg/]5t#n
that does not retain good quality for 4.5 months at -4 °C may not retain good quality for
Vq\%miSM Ct)H012 months at -18 °C. This also suggests the sampling frequency shown in Table 19.6.食品伙伴个性空间$RX [_+W/k
All simple tests should be conducted at each sampling time, while sensory testing
Z/A*i'n*I'w0should be concentrated mainly toward the end of the test sequence with a few near the
j%S!L0~)b1MI0beginning.
*Q(_7q[aI8m+Ma8a00 5 10 15 20 25 30食品伙伴个性空间'j*M5q*A"~ Smn
.1
Ew&XK*s:z!a8|9QA01食品伙伴个性空间iQzU+{H1h&^Hh2k
10食品伙伴个性空间D[;S;xJ._,d
100食品伙伴个性空间w]D+aiP
T (°F)食品伙伴个性空间 N9G'X}~5Z
Shelf life 12 mo at 0食品伙伴个性空间:j3EdN@['|Qp
ASLT at 25 °F食品伙伴个性空间+rGz4yA,b{
4.5 mo食品伙伴个性空间xS!Je] R
1.2 mo
w0[-}@:l1O4R._D014 days
3{/I9q*@l06 days
S6Fk-Y3{3R9v,J0Q10=2食品伙伴个性空间 W:w3QEn*Mx:a
Q10=5食品伙伴个性空间Ns5a2y-j-Q1[Km9r
Q10=10食品伙伴个性空间EL r~7l8g
Q10=20食品伙伴个性空间^%[;Z y Gb;EX
Figure 19.11 Shelf life testing times at 25 °F equivalent to 12 mo at 0 °F食品伙伴个性空间l5Ss*DU#q#U
for various Q10 values.
M9Y,ZE?8J*d+il%P5i0Table 19.6 Sampling frequency for frozen pizza ASLT
P'm)\G-h)a031食品伙伴个性空间`j(A Ccd
Temperature (°C) Sampling times (wk)
%H!Wy6}7c0sb&@-z4w0- 4 1, 2*, 3, 4, 5, 8, 12, 14, 16*, 20*
]oyCGCu0- 7 2, 4*, 10, 15*, 20*食品伙伴个性空间']/fHc#UF;S
- 10 4*, 10, 15*, 20*食品伙伴个性空间;~r$r-~ Q@4yY
* Sensory test times Source: Labuza (1986)食品伙伴个性空间| Q7w&cDr y+n;@
Step 4: Determine end point — Figure 19.12 shows a comparison of times to
-F%y;KP`W6SUA0various levels for the loss of vitamin C in frozen spinach as a function of temperature食品伙伴个性空间7@px)m v#R+Z!{.e*g
(Kramer, 1974). The dotted line represents the 80/80 rule, i.e., from a legal standpoint,
"o9~V:f Jm} p1U9o0for natural products, 80% of the tested sample must have no more than a loss of 20%食品伙伴个性空间 S ZV:Zk
(i.e. 80% of the label value). Consumer sensory testing will not always give such a食品伙伴个性空间+}7e#N9O*dK P
clear shelf-life result since different shelf life times can result using different quality食品伙伴个性空间p^\\ Q ahPs
attributes. Often professional judgment has to be made to decide what factor to use as食品伙伴个性空间J9MhJn V(S
the base for the end of shelf-life of the product. When shelf life is unacceptably short,
_A-CWj@eX0adjustments should be made to the food, its environment, packaging, process and食品伙伴个性空间:A3v1A;g2M3y
hygienic conditions, until a suitable extension of shelf life can be achieved. For some食品伙伴个性空间/z)h Q#A i
products, the test results may demonstrate that the target shelf life is not attainable. At
3k:ra$_Z~ h c r0this point, the question of whether to launch the new product with a shorter shelf life or食品伙伴个性空间"m-PI/Q Oo r:i
to abandon the entire project becomes a marketing decision.食品伙伴个性空间&C4q1P5xmN:F
-20 -10 0 1 0食品伙伴个性空间QswpX#kO
1
FDfV]010食品伙伴个性空间L3{R)j-ft
100
2b[iw EWw0Storage Temperature (°F)
5Ju {(@&p(K3O G&D1`0Shelf life (mo)食品伙伴个性空间:|7G9R!@$L x|6gt'mTt
Figure 19.12食品伙伴个性空间!? n,Om8B.S"J
Shelf life of frozen spinach as a function of vitamin loss level
1[hO)D(r*C050% loss食品伙伴个性空间0NI5n/W7hE:L
25% loss食品伙伴个性空间 Rl c5YzB
10% loss食品伙伴个性空间+@_ z@ddq7p1{
Quality (80/80 rule)
9pLJ3qR;Gw4?8[r032
-KmiS}:J2ad5H0Step 5: Estimate kinetic parameters — From each test storage condition,食品伙伴个性空间nV8U-Xr-Mz
estimation of k or q is needed to make the appropriate shelf life plot. From this one can
q|v9yQ7Cua0then estimate the potential shelf life and confidence interval for the storage condition.
} bRd2wo lI#x;v!s6\0Then parameters for the Arrhenius relation and the shelf life plot are determined by
:FoZI Iv0linear regression, which are used for shelf life prediction.
T J| iY0Step 6: Extrapolate to normal freezing storage condition — The most useful食品伙伴个性空间:Eu4F j;^
shelf life information is obtained for product kept at its intended storage temperature,食品伙伴个性空间X/Gde0\Ol
which is about -18°C for retail frozen products and -23°C for distribution of frozen食品伙伴个性空间 U"x9@ J[-S*{{LlWg
foods. Figure 19.13 demonstrates how the shelf life plot is used for extrapolation. It is
l'e!Fq I,Y#wN0always a good practice to compare a model's prediction against actual experimental
.@c$Dc/oB`c0results because of the potential for errors from using the higher temperature data as
.S0OG.h5^;P2o ePI%l0noted earlier besides the other errors suggested by Labuza and Riboh (1982). In食品伙伴个性空间?#EgLK3KeR1]
addition, the existence of a glass transition at a temperature between the test食品伙伴个性空间wQii%q,@a
temperature and the prediction temperature would lead to error as shown by Nelson食品伙伴个性空间.y([ Z5Nz P d]*m s
and Labuza (1994). In the case of frozen foods, most likely the error would be an食品伙伴个性空间5c/\(@5C9Ct%R,_'R
under prediction of the shelf life.食品伙伴个性空间hoJ*c5A
ln Q食品伙伴个性空间^}` A5Ak [
T
VM6@DKq.A/Qo[0T1
%`u:Lv'h}um@+U0T2食品伙伴个性空间A7| |~.o4\e
T3
T(ld/au\0Ts (commercial storage temperature)食品伙伴个性空间1qSgn P@:j
Figure 19.13 Extrapolation from ASLT食品伙伴个性空间.jI8@Fr;m i jB
Step 7: Predict quality loss for a fluctuating time-temperature distribution — The
/Dap Z I*hCD0prediction is based on two assumptions: (1) that there is no history effect from the食品伙伴个性空间`2x_;[7x
time-temperature variation and (2) that the key deterioration mode does not change as食品伙伴个性空间,s,]L.MnPI} Y8~1E
a function of temperature. The frozen spinach data shown in Figure 19.12 is used in食品伙伴个性空间 V(bU;\(M h
the following example in Table 19.7 for a time-temperature distribution. The line
&q'C'o2Mo*tk.zH7pA033
*?J Spf(h:u0equivalent 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H\gw\6Bz2F
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食品伙伴个性空间Z'C0H1rMa
each temperature of exposure, the time on the 80/80 line is the time for 20% loss, thus
A$GN _B(u0at -10°F, the 20% loss (equivalent to 100% shelf life) time is 16.5 months. Thus for 6食品伙伴个性空间:oaZE S5S.?Z
months storage at -10°F, there is 6/16.5 or 36.3% of the shelf life lost and the amount食品伙伴个性空间brs7Y9S9xX%A
left is 36 - 6.36 x 7.2 = 33.4 mg.食品伙伴个性空间9DD4]/Bz2z ~\Y
Table 19.7 Estimation of quality remaining of frozen spinach after exposed to a
Jxpb0? O0variable time-temperature history with Ao = 36 mg/100g spinach.
[~J5Q-l`U5vF0Temperature
.F'Dg1GO5K%J3z"}0(°F)食品伙伴个性空间,kX0}9xpS y
Time t食品伙伴个性空间tOl;d^~!P
(months)
/\.Hf#zPjL_;O%D0q shelf life
.YU7r v5EE.@)A~0(months)
(d7} |5LG9Ykx0fcon食品伙伴个性空间t`3f[4Mz6D8Z+w
(t/q )
u/UA(UE(N*Q5_z0Sfcon Aremaining食品伙伴个性空间#e0GH q)c$cwN;^
(mg/100g)食品伙伴个性空间]Q6] eT3yV2R
-10 6 16.5 0.363 0.363 33.4食品伙伴个性空间CVZyj |"I8I~
+3 1 4.5 0.256 0.619 31.5食品伙伴个性空间X~t ja1{o M
+12 0.25 1.6 0.156 0.775 30.4
a&@`Y!y4O0Since 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(UB T-Q \+Dp
still acceptable at the end of the set of three different time/temperature exposures. In
2r+e~Q O|0fact, the shelf life left @ 5 °F = (1-0.775) x 3.3 = 0.74 months = 22 days.
Bz3B0vo e?g:eQ019.5.3 Applicability
)]Qb1w n7MZ8P1mp0Because of relatively long shelf life for frozen foods and the unique feature of freezing,
(f7j Q4C8wcL1u-s0{:\+e0the degree of temperature elevation is largely limited. Prediction of actual shelf life食品伙伴个性空间Y O,r]b*g
from ASLT may be severely limited except in very simple food systems. Frozen foods食品伙伴个性空间a&Z&Yw!Iy#g2q
such as frozen pizzas, may present problems with moisture migration. The moisture食品伙伴个性空间lY`h-^ H&T
may diffuse from the pizza sauce which has a higher aw into the crust containing a
~o3X0K)EB)| cb;]0lower aw, creating a pizza crust that is limp and soggy. Product development scientists食品伙伴个性空间S7IZD}\#Q
should only use the results as a guideline and must use as many storage conditions食品伙伴个性空间k6FBtx$JlML
as possible to minimize prediction errors.食品伙伴个性空间G1D M+Z/Y-?$i }!bKV
34食品伙伴个性空间Fm"X9m.~ W'x
ASLT is just a quick method, which can not replace the normal storage tests食品伙伴个性空间 ` eJuR/xv W{
discussed next. Once it is verified that the extrapolation may be wrong, i.e., too large
W)P1S/X+G0an error, then a careful look should be taken at the deterioration mode, the experiment食品伙伴个性空间"],I({5u+K
design and procedure, the data collected and the model developed. If the食品伙伴个性空间,h`)iyC
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is over predicted, then reformulating may be necessary. If the shelf life prediction食品伙伴个性空间Q b8f A(zi-uS*r
indicates that the product meets the stability expectation, then the product has a
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experimental test batches to pilot plant and then to full scale production. Experience
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much use for large-scale production (Graf and Saguy, 1991). Scale-up not only affects
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microbial growth and chemical reactions leading to deterioration, scale-up may食品伙伴个性空间+BdQ5PB"Wd

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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
;p0O5eq,OHI5q9_P食品论坛;食品社区全是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!
kul
r2pG        q!Pspace.foodmate.net
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.
-g
gBB-s(M4l1_'h3@space.foodmate.net
  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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