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冷冻食品保质期试验.pdf

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Shelf Life Testing:
;Bg @ D/A`0Procedures and Prediction Methods for Frozen食品伙伴个性空间I W a)?-F"rF
Foods食品伙伴个性空间(| K{] O5Z{
Bin Fu
+c;FS/MN0Kellogg's Battle Creek MI食品伙伴个性空间+j F)]9Ll;h8@&Wfz
Theodore P. Labuza
C6X#e0Qg;I)[h0Dept. of Food Science & Nutrition, University of Minnesota食品伙伴个性空间*jheo.nHt
1334 Eckles Ave., St. Paul, MN 55108
Al#QZyy02
&s.c-d_Sj\,C!Y019.1 Introduction
BQu~5S'L_W M0The shelf life of a food can be defined as the time period within which the food is safe
s_Ai!Ok0to consume and/or has an acceptable quality to consumers. Just like any other food,食品伙伴个性空间v.F.f C%qj rU8W
frozen foods deteriorate during storage by different modes or mechanisms, as食品伙伴个性空间"Ey$Q*|7z2}1i;| Rx
summarized in Table 1. Microbes usually are not a problem since they cannot grow at
FJ6[.M a!qT0freezing temperatures unless subjected to extensive temperature abuse above the
q bf*??.Z\#G0freezing point. Enzymes are a big concern for frozen foods, which can cause flavor
o$IlM N+i%DF9dvD0change (lipoxygenase) in non-blanched fruits and vegetables and accelerated食品伙伴个性空间YUQy9viM
deterioration reactions in meat and poultry (enzymes released from disrupted
qj.?w,G L*BN0membranes during precooking). Cell damage or protein and starch interactions during
,hG3aJ/TY;`0freezing cause drip and mushiness upon thawing. Discoloration could occur by nonenzymatic
0Q2j*r8e,P L8v?&l#W;R I0browning, bleaching, and freezer burn. Vitamin C loss is often a major
(? @ ~$nsP0concern for frozen vegetables. Physical changes, such as package ice formation,
#e Xa*Kl-H}S UD$k0moisture loss, emulsion destabilization, recrystallization of sugars and ice of frozen
.iOZL"E0desserts are often accelerated by fluctuating temperatures.食品伙伴个性空间6H"[(LQ3D
For any specific frozen product, which mode determines its shelf life, depends
f1opKeK%_#]*p!v;\0on the product characteristics (raw materials, ingredients, formulation), pre-freezing
dez9W(?S ]0treatment, freezing process, packaging film and processes, and of course storage食品伙伴个性空间Hl@&w knP
conditions. All of the quality deterioration and potential hazards are usually食品伙伴个性空间fg@#Td0D k
exaggerated or complicated by a fluctuating time-temperature environment (e.g.食品伙伴个性空间*TGA5d0kZ,bct K#^
freeze/thaw cycle) during storage. On the other hand, the shelf life of a frozen food食品伙伴个性空间9R|a3I5i&s-F?[ Ij;P
can be extended through ingredient selection, process modification and change of
7YKh(c{8t0package or storage conditions, as discussed in Section 3 of this book.
Bc-Imj![P1F4z.v0This chapter will focus on shelf life testing of frozen foods for product
j{XqP,B0development and market practices. Shelf life testing consists basically of selecting the
x_B_c(O0quality characteristics which deteriorate most rapidly in time and the mathematical
+BXU-p9D]W+@0modeling of the change. Table 19.1 can be used as a reference for the selection of
w [ b(L#k+}:T0quality characteristics, which depends on the specific product and usually requires
~L7WQ i0tG0professional judgment. Mathematical modeling of quality deterioration will be食品伙伴个性空间:zv9z/e8U#xx
discussed next.食品伙伴个性空间2OA'`T'gz&I,?$VT
3食品伙伴个性空间*W'xg$F+T
Table 19.1 Deterioration modes of frozen foods
S*z"IL$u F4rz0Frozen Foods Deterioration Modes食品伙伴个性空间bI D.w9H
Frozen meats, poultry and seafood Rancidity食品伙伴个性空间7]-PbqpQn:l
Toughening (protein denaturation)
$UT;]M%[+KO P0Discoloration食品伙伴个性空间C$gG6|#M:UpU
Desiccation (freezer burn)
$R7}8J?#G e;A3MH M!N0Frozen fruits and vegetables Loss of nutrients (vitamins)食品伙伴个性空间+W!k(Lo-H ~
Loss of texture (temperature abuse)
q%v(U'c*vg%d%}-B5SP0Loss of flavor (lipoxygenase, peroxidase)食品伙伴个性空间\4f{7]9oz?U
Loss of tissue moisture (forming package ice)
*wvp$VoBk,I!l&k0Discoloration食品伙伴个性空间B8rjyAfpEcJ
Frozen concentrated juices Loss of nutrients (vitamins)
JVwU U:K"m0Loss of flavor食品伙伴个性空间8K%b*](XC&D"XS|
Loss of cloudiness
:Xv ~$Pt3X;S ?A0Discoloration食品伙伴个性空间0G(hJ GV7Ok
Yeast growth (upon temperature abuse)食品伙伴个性空间1g)ot1?^!x
Frozen dairy products食品伙伴个性空间-VT _T2n*v4i#k
(ice cream, yogurt, etc.)
1u M!H!f%kR5QzP^0Iciness (recrystallization of ice crystals)
e7\F/|AC0Sandiness (lactose crystallization)食品伙伴个性空间%tE-Y*a t \1HkO
Loss of flavor
v J|#sv^2]^ g0Disruption of emulsion system食品伙伴个性空间2~t*q ?%Z'r9K*D5hs
Frozen convenience foods Rancidity in meat portions
7M L|w I | q0Weeping and curdling of sauces
w!q1M`4}8m"K0Loss of flavor
n e6k!AS&F0Discoloration
w&S3[d5D0Package ice食品伙伴个性空间M7X:z,y U0p'}&aL)S Q
Frozen bakery products (raw dough,食品伙伴个性空间W$R?2W Q;W?F
bread, croissants)食品伙伴个性空间uX~.j_QX0EOf
Burst can (upon temperature abuse) (dough)食品伙伴个性空间:ZS;Q4[-i)x F5?
Loss of fermentation capability (dough)食品伙伴个性空间@&y\ ?r&I^
Staling (becoming leathery)
g s,j2T`B0Loss of fresh aroma
%L2?9Cfz4W!d-m%]s019.2 Modeling of quality deterioration
7|L Iw7VU019.2.1 Basic equation食品伙伴个性空间o|-E6_9?0aO%P
A frozen food starts to degrade once it is produced (Figure 19.1). The rate and
FblM9O[0the degree of degradation depends on both the composition and the environmental食品伙伴个性空间OVi_gC
conditions during storage and distribution. In general, the loss of food quality or shelf食品伙伴个性空间 wdv:Wi3g.rure
life is evaluated by measuring a characteristic quality index, "A". The change of quality
dN.o0^n+T*]\0index A with time (dA/dt) can usually be represented by the following kinetic equation:食品伙伴个性空间^#a!Mr[ Jj
- dA/dt = k An (19.1)食品伙伴个性空间_su5gM&["{5q"Bi z
where k is called a rate constant depending on temperature, product and packaging食品伙伴个性空间)b0y9OZ&D#Hs*iQ
characteristics; n is a power factor called reaction order which defines whether the rate食品伙伴个性空间L4nQlB8@
4
AOX+Sg!r4qs0of change is dependent on the amount of A present. If environmental factors are held食品伙伴个性空间b/tK u\ _+i
constant, n also determines the shape of deterioration curve.
my2q:d[_0e0Ao
|gu,G\d0A a
/I+H:o1q ^QT:V%k0b食品伙伴个性空间(Y-GBUo)M$b
c食品伙伴个性空间 ^#b)k(P1Q-Ht%a!p.d
t
4kq/~r,?$n7Y0d
a7NHMo#w0e食品伙伴个性空间o(c0jo]#bA
Figure 19.1 Quality deterioration curves: a) linear; b) exponential;
A*^6w)H{e;nl0c) hyperbolic; d) quadratic; e) complex.食品伙伴个性空间"Y+I*lLvTR#@7p
19.2.2 Zero and first order kinetics
zp'aA2V.Wd:t*]0Equation 19.1 can also be written as:食品伙伴个性空间u1_ P}G0H8bs
f(A) = k t (19.2)食品伙伴个性空间 PLt Je
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-oTAMA8tA3uR
depends on the value of n. When n is equal to zero it is called zero order reaction
A I*G4t0{b0_E*U};Ez#U0kinetics, which implies that the rate of loss of quality is constant under constant食品伙伴个性空间E"l n7i#cW{/j lJq$s
environmental conditions (curve (a) in Fig. 19.1). If n is equal to one it is called first
0G4?~#K dt'{9F]u3bPa%J0order reaction kinetics, which results in an exponential decrease in rate of loss as食品伙伴个性空间B!my7eI"bn#J
quality decreases (curve (b) in Fig. 19.1, which becomes a straight line if plotted on a
}PmPl:bC8Tq0semi-log plot). These quality functions can be expressed as follows:食品伙伴个性空间7MeS*X%ag0b
f(A) = Ao - A = kzt zero order (19.3a)食品伙伴个性空间D?-IEV
f(A) = ln Ao - ln A = kft first order (19.3b)食品伙伴个性空间!l-KwN1K&} HCkN
5
+f] cG"]2{0where Ao is the initial quality value. If Ae corresponds to the quality value at the end of食品伙伴个性空间l Z.oJ$_Cj3SS
shelf life, the shelf life (q) of the food is inversely proportional to the rate食品伙伴个性空间 {t;T L$q ZI
constant:
5lZ ld/u?,b0q = (Ao - Ae) / kz zero order (19.4a)食品伙伴个性空间0K4ll%T3sC5A
q = ln (Ao/Ae) / kf first order (19.4b)
^ d8Q6ZI w]E0It should be noted that most chemical reactions leading to quality loss in frozen食品伙伴个性空间k~(\;]/c\.~,J
food systems are much more complex. However, the reaction kinetics can be食品伙伴个性空间+AYnC7L4a
simplified into either pseudo-zero order or pseudo-first order kinetics. In the case of
|D{.T/e0complex reaction kinetics with respect to reactants, an intermediate or a final product
4t r!{k(r y7fwh0(e.g. peroxides or hexanal in lipid oxidation ) could be used as a quality index. There
#b;y[H.U0are few cases where neither zero nor first order kinetics apply. Curve (c) in Fig. 19.1食品伙伴个性空间i%b;Wt)c)c
shows the degradation curve for a 2nd order reaction (with single reactant), which also
`3I5Eg$w0shows a straight on a semi-log paper. A fractional order should be used to describe食品伙伴个性空间+Q3_aUnNC ce
the curve (d) in Fig. 19.1.食品伙伴个性空间'v | G(fww*O'v&t
Sometimes, there is an induction period or lag time before the quality食品伙伴个性空间[ ? }!\&aaQ3S
deterioration begins (e.g. browning pigment formation in the Maillard reaction or a食品伙伴个性空间2N9GYi`(|jF
microbial growth lag phase, as shown in curve (e) in Fig. 19.1. The length of the lag
pu8r"EV2C vM6Cl0depends on many factors, but temperature is a predominant factor. Given this,
nnj` @ K0modeling of both the induction or lag period and deterioration phase are necessary for
"PgC$OwRRy |)N F0accurate prediction of quality loss or shelf life remaining. An example of such work has食品伙伴个性空间-DMrJUF-\`+H{
been demonstrated by Fu et al. (1991) for the growth of bacteria in milk.食品伙伴个性空间@Q5^0{!mz^
In certain circumstances (e.g. A represents a sensory hedonic score), a nonkinetic食品伙伴个性空间4f#CW Y;o w"a
approach, e.g. a statistical data fitting technique can also be used to describe食品伙伴个性空间fo6Eb(m:if8m_
the deterioration curves. Varsanyi and Somogyi (1983) found that the change in
$t}@{l+S)IPn3t0quality characteristics as a function of time could be approximately described with
KS}t2I7eaj0linear, quadratic and hyperbolic functions and that storage temperature and packing
)Lt2{0y5br0conditions affected the shape of the deterioration curves. However, the parameters食品伙伴个性空间j8H lZ1?Nc&g$Q_r
determined by data fitting are difficult to use for prediction under variable storage食品伙伴个性空间H0c6`T^7j!t
conditions except for the linear curve.食品伙伴个性空间9iGH#D'o+{D4Fot9?
19.2.3 Temperature dependence of deterioration rate食品伙伴个性空间:\RnhZ#P
19.2.3.1 Arrhenius kinetics
T"G&dL#mZ7EV;DU0Once a frozen product is made and packaged and starts its journey from the
L nf M_'~w0manufacturer's plant to warehouse, distribution center, retail store and finally
0J0[xd8d}06食品伙伴个性空间yA/BH9OT
consumer's freezer, the rate of quality loss is primarily temperature dependent食品伙伴个性空间-?` W"]~N#B L Mc
(Zaritzky, 1982). The Arrhenius relationship is often used to describe the temperature
3~2Cs'W ~_|,W1W0dependence of deterioration rate where for either zero or first order:食品伙伴个性空间[AT-E/d+}c/Q1p m
k = ko exp (-Ea/RT) (19.5a)食品伙伴个性空间2Z `3zC5me^%@Y
or ln k = ln ko - Ea/(RT) (19.5b)食品伙伴个性空间TI0?9^r_z]
where ko is a pre-exponential factor; Ea is an activation energy in cal/mol; R is the gas
o*X%L1y0f0constant in cal/mol K and equal to 1.986; T is an absolute temperature in K (273 + °C).食品伙伴个性空间y'c.T;y@"v Mv
Thus, a plot of the rate constant on semi-log paper as a function of reciprocal absolute食品伙伴个性空间]1GxHSFX'bD\4e{
temperature (1/T) gives a straight line as shown as Fig. 19.2. The activation energy is
hoLV4iLQz0determined from the slope of the line (divided by the gas constant R). A steeper slope食品伙伴个性空间'^4h _{5^#rL,C
means the reaction is more temperature sensitive, i.e., a small change in T produces食品伙伴个性空间I9L H)[P1u5xR T
are large change in rate.
(W$nai4n"LKG(w W0Figure 19.2 Arrhenius plot食品伙伴个性空间\fR H,Wt*C
ln k食品伙伴个性空间0z;u PU5o H
1/T食品伙伴个性空间 rl p3c+gI
slope = -Ea/R食品伙伴个性空间Y/C6?{@k Z
Thus, by studying a deterioration process and measuring the rate of loss at two
!m _5?1K/W dWX0or three temperatures (higher than storage temperature), one could then extrapolate食品伙伴个性空间.KgQ)ye[CP[I
on an Arrhenius plot with a straight line to predict the deterioration rate at the desired
)k'|x Y#f/I,J0storage temperature. This is the basis for accelerated shelf life testing (ASLT), which食品伙伴个性空间B'k;l:bCo
will be discussed later. One should note however that in some cases a straight line
q7J0G4eq.B-foy1m0will not ensue for a variety of reasons, especially if a phase change occurs (Labuza食品伙伴个性空间:l/b4Xm5y@2I2wY9R
7食品伙伴个性空间t!A9s)vW`W^kZ4i
and Riboh, 1982). Thus for frozen foods, extrapolation from temperatures above 0¥C食品伙伴个性空间b"Q%HMxp*]Q m
are meaningless for shelf life prediction.食品伙伴个性空间u2^oM fB#F4@)j
19.2.3.2 WLF kinetics食品伙伴个性空间tA4];L_en He;m&d
Besides the Arrhenius equation, another popular equation at least in the more recent
OD1FfcE0food literature, is the Williams Landau Ferry (WLF) model (Williams et al., 1955). Its食品伙伴个性空间!p8NrHE.P.Vk
original form was based on the variation of the viscosity in the temperature range食品伙伴个性空间k J6Q'rwv3Q
above Tg as addressed in Chapter 3. When the rate constant at Tg' is substituted for Tg
!r)n nW m0M+f6n0(Tg' is the Tg of a maximally freeze-concentrated system), the WLF model can be
0@*rE)D3Q\+@#]5bz f(h4I0written as follows:
pn(Q$p W0log (kT/kg) = C1(T-Tg')/[(C2+(T-Tg')] (19.6a)食品伙伴个性空间8m9NR)r.R%r2up
or [log (kT/kg)]-1 = (C2/C1)/(T-Tg') + 1/C1 (19.6b)食品伙伴个性空间5LObWQ,L
where C1 and C2 are constants. Thus a plot of [log (kT/kg)]-1 vs. (T-Tg)-1 will be a
%E-k y Sb&\'u0^*|0straight line with the slope equal to C2/C1 and the intercept equal to 1/C1. As can be
F W7yD0N de#ng0seen this is a two parameter temperature dependent model as is the Arrhenius
9^*^"^n1R!s{u0equation.
I5Z l7}g#j0Frozen foods stored below Tg' are stable to ice recrystallization and other
b:y^4u8]tc0physical changes. Levine and Slade (1988) postulated that stability is related to the
b;@$ef)ZS0temperature difference between storage temperature and Tg'. This cryostabilization of食品伙伴个性空间/ev%|4l?
foods assumes stability below Tg' and rapid decrease of stability above Tg' according食品伙伴个性空间g~ j"r}JW nSUhw
to the WLF relationship, exhibiting an increase in reaction rate, much higher than
YD ~ I4R*c0expected from the Arrhenius kinetics. However, this may not be true since the rate of食品伙伴个性空间6xf'`,p}b!X
chemical reactions can be expected to be influenced by temperature increase in a食品伙伴个性空间2T2x(G(?3nFW'Ps3m
complex way: (i) an increase of the rate constant, resulting from both the viscosity
2B`VT$pdcRx0decrease and the increased molecular mobility (Fennema 1996); (ii) a decrease of the食品伙伴个性空间9O]O5uR)U B
reaction rate as a consequence of the increasing dilution of the reactants Roos et al.食品伙伴个性空间/qoG7@/`
(1996). For these reasons, it seems that the WLF model over predicts the temperature食品伙伴个性空间!T.Pl[ v[Z
effect of rate constant (Simatos et al., 1989). As noted by Nelson and Labuza (1994),
-| g`0`UoO0because of the small temperature range over which foods are stored, e.g., about D30°C食品伙伴个性空间G6dw,V| ~cdS!a o
for dry foods and D20°C for frozen foods, both the Arrhenius and the WLF model give
KWk7|w^0good correlations as long as one does not use the universal coefficients suggested by食品伙伴个性空间uT6?L%OL
Slade and Levine (1991). In fact as shown by Nelson and Labuza (1994), their use of
6QWO/R,T!NFj0the Lim and Reid (1991) data for enzymatic activity in the frozen state as shown in 19.3
i!s1x%Nc0E1q;rg0is not proof that the Arrhenius relationship does not apply, WLF was assumed because食品伙伴个性空间D`&Im hd4loD:j
the rate was negligible below -10°C which was the measured Tg. But as seen in
H{M_ bvoF U K,r08
?Q3f ]K-~l"D%_0Figure 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dM!]\5?3c&x
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,g5PU ~s.b*i._
not known; (2) Tg is difficult to determine; and (3) the universal coefficients of Levine食品伙伴个性空间J6n9C*dk*lcP V
and Slade (1986) are not applicable.
%vP;[m(dL00 50 100 150 200 250
6\ g:_4YY00食品伙伴个性空间y?*_,hT:tX#c)f&L
1
*f:pK/m4^02
+_y9S{G^W03食品伙伴个性空间TKtIp|A-e f
4食品伙伴个性空间u)KrhS$d/s(w
5
&c:nqeX,K'f0-3.5食品伙伴个性空间|;wC|+pJ:urA
-5.5食品伙伴个性空间*a"`&e9c{W
-8.5
9f|:C*@zwa0-13食品伙伴个性空间6nfC Ti `0{k
-19食品伙伴个性空间/LYJh[p
Time (hours)食品伙伴个性空间a/X3w-niT mC
Relative absorbance食品伙伴个性空间R~g+A*i [1Ay T
Temperature (°C)
d5uO T)f.xL00.0037 0.0038 0.0039食品伙伴个性空间:yWWDd'] M
-4食品伙伴个性空间e3L$M%]b'}"E._ i
-3
w8qrrS@3z n6c|_0-2食品伙伴个性空间SxOkAu
-1食品伙伴个性空间-@&[5w h wd5o'x
0
qi{fb4H [T*s|1g01/T (K-1)食品伙伴个性空间'\su&RQ3@/P/r
ln(k)
s|v%?"M^Y1o0y = 79.497 - 2.1621E+4x R2 = 0.999食品伙伴个性空间Q\:K7X W^A'n:A
Figure 19.3 Hydrolysis of maltodextrin in the frozen state (Lim and Reid; 1991)食品伙伴个性空间j&C[$_/v
a. Rate as a function of temperature (Note Tg is -10 ¡C)
5j z*_"U\3\0a~,?,n0b. Arrhenius plot食品伙伴个性空间!qq/D8zxdSM
19.2.3.4 Shelf life model
bq1S1`rC$B3x0Most published data related to quality deterioration do not give rates or rate constants食品伙伴个性空间 K#poD^t0M{
but rather are in the form of an overall shelf life (end-point analysis) as a function of食品伙伴个性空间`2C| Z6n y
storage temperature. Since the temperature range used is usually quite narrow, the食品伙伴个性空间Hr(dhY t1}
following exponential relationship exists between shelf life and storage temperature:
'i {4O6df;K ?(MK0q = exp(-bT+c) (19.7a)
,f%TzP5D'^ g0or ln q = -bT+c (19.7b)
7k oK NOg/g0where q is shelf life at temperature T in °C, b is the slope of the semilog plot of q vs T
+WR2wis0and c is the intercept or reference temperature as shown as Fig. 19.4. Practically, this食品伙伴个性空间#N7GD2~Pw%\
is used frequently for shelf life determination and prediction due to its simplicity and食品伙伴个性空间!ce R*I.rS$c.W
straightforwardness.
o+h(VO*I09食品伙伴个性空间 P4q7]`2jY+\ZW
Figure 19.4 Shelf life plot食品伙伴个性空间 N,c3OL+E)r2[
ln q
g7^;Q o;?? z8mz)`0T食品伙伴个性空间 u3}-u1Kf${
19.2.3.4 Q10 or q10
)n)U3Gmf-e}:{6p0The Q10 approach is also often used for estimation of the temperature acceleration of食品伙伴个性空间+]"CyoNj
shelf life, which is defined as :
Ap2Oin ^@L U7~|v0Q10 = rate @ T1+10 °C / rate @ T1 (19.8a)
f(M#U1Vs(@ awa0Q10 = shelf life @T1 / shelf life @T1+10 °C (19.8b)
~}4} v(n'U0Q10 = (q10)1.8 (19.8c)食品伙伴个性空间7o)`O:Yd[ Vq
where T1 is temperature in °C. If the temperature unit is in °F, then the term q10 is
(to_1d5pxmqv0used, which in fact is more often used than Q10 in the frozen food literature.食品伙伴个性空间6uYv)`9t/n7C8Q!HA
The magnitude of Q10 depends on the food system, the temperature and the食品伙伴个性空间 Ag VqB3p~
absolute range. Q10 values from 2 up to 20 have been found for frozen foods (Labuza,食品伙伴个性空间,z,jrh+cR
1982) Labuza and Schmidl, 1985. Q10 can be shown to be related to the Arrhenius
!Ii1zoG q0equation and the shelf life model through the following expression:
9jg*nP L2C-z0Q10 = exp [10 Ea/(R T (T+10)] (19.9a)
4@ed+D5~I$`0Q10 = exp (10 b) (19.9b)
&T1Q:H)S7{~!c3w0Thus Q10 is not constant but depends on Ea and the absolute temperature T.
E,| u B mrN9{}0Some data gleaned from July (1989) and Labuza (1982) is shown in Table 19.2.
bSeU.ik5n3}c010
&{o9zC"[;r6cP0Table 19.2食品伙伴个性空间 Eu2Ye+lv/\!c0x,G
Estimate of the Q
$|yi+j{ HdRd'X2Z010
F-}2J0U \,M0for shelf life of selected frozen foods食品伙伴个性空间 er8s tqMw)q \
Days of HQL
tblRchX^0I te m - 10°C - 20°C Q 1 0
eAp)dr-ny}I$G!W?M0pork sausage 20 120 4
F gmpY ?/nS\:ru]0pork 50 400 8食品伙伴个性空间nU6x/Wk\$\8UO
beef 60 200 3.3
7{3~~0V#{SJ0ground hamburger 250 800 3.2食品伙伴个性空间9|l4LK @'X bW5|E
fried hamburger 35 250 7食品伙伴个性空间 K1E]UA7x)@e3? v
raw poultry 200 700 3.5
:?+X IsjA P0fried poultry 25 700 3.2食品伙伴个性空间L\ rd+q N
fatty fish 7 60 9食品伙伴个性空间QdNl@ L-YU'tE
19.2.3.5 Other models食品伙伴个性空间|%@OTe*Ci.[5E
The following models have also been proposed to describe the temperature
"kcmk6B6e;C)W5T"G V(|0dependence of the rate constant (Kwolek and Bookwalter, 1971) for frozen systems:食品伙伴个性空间n8\|8z+a4uR)Rh
kT = a + b T (19.10a)食品伙伴个性空间 cUO)U$K X
kT = a Tb (19.10b)食品伙伴个性空间E|X!T&X_W,x.j
kT = a / (b - T) (19.10c)
J]uJ1f?kBs0where a, and b are constants. In most cases, Equation 19.10c fits data better.食品伙伴个性空间"~ O{0J z#QB
However, all these have very limited practical application.
\D` N4X019.2.4 Time-temperature tolerance
(b2Z7Vv S0Frozen foods are often exposed to a variable temperature environment, e.g. during
@#w#ZK*`_0distribution or due to freezing/defrosting cycle in retail or home freezers. In general, the食品伙伴个性空间1q4J:jX9n0h`L
value of the quality function, f(A), at time t under changing environmental conditions
1O&q,p-Y Bh)eUD"p0j0can be estimated from:食品伙伴个性空间-v1W&GY_.^K'{
f(A) = ò k[T(t)] dt (19.11)
&?Em8t*u v)k,Bu5m0where T(t) is the temperature as a function of time. The form of f(A) depends on the食品伙伴个性空间:O5y!mF1ZBb
reaction order as discussed previously. If an effective temperature, Teff, is defined as食品伙伴个性空间] s/DA1qi%gz!r
11
7K]:\6I&] k z:g0that constant temperature exposure which causes the same quality change as the食品伙伴个性空间K3u\0s@}V
variable temperature condition, as proposed by Schwimmer et al. (1955), then食品伙伴个性空间!K!l,n,zy,SK
f(A) = keff t (19.12)食品伙伴个性空间*}](I#cG"^"N7X%c a'd5Pu
The rate constant at that defined temperature is termed the effective rate constant, i.e.食品伙伴个性空间M MQl5]
keff. To estimate the quality change under variable temperature conditions, one食品伙伴个性空间5NXcxMM
needs to either solve for f(A) numerically or know the value of Teff or keff that
.Jd6U)m0WJG0corresponds to the variable conditions.
&{/U3GK1l:W)La0The numerical approach for a randomly variable temperature history is食品伙伴个性空间 ],bs NM$|
essentially the same as the Time/Temperature/Tolerance (TTT) approach initiated by
$lOM f)^9x3B:Ds0Van Arsdel et al. (1969) and derived empirically in the 1960's for the prediction of shelf
uo9bys[n0life of frozen foods (July, 1984). It is assumed that the temperature history of the
7U:eR0X\1R;of-|:ei0product is known. Thus the fraction of shelf life consumed, fcon, was calculated as the食品伙伴个性空间$v~kf#x)c2k%v^K
sum of the times at each temperature interval, ti, divided by the shelf life at that
Ro ~@9gy$J0temperature, qi:
un5N J]:aS3k aO0fcon = S (ti / qi) (19.13)食品伙伴个性空间,{T9V vW.z {\ L
Thus the remaining shelf life at a reference temperature is equivalent to (1-fcon)*q.
.Nt/k'ulx @7B#T0Equation 19.13 assumes that the rule of additivity is valid for frozen foods (July,
G3y}FA$]+^(kIR01984), which means that the loss of remaining storage life or quality can be calculated
+al~,lnFG0from knowledge of the prior time-temperature episodes the product has been exposed
sU1wL9e.p9Ou0to. This also implies that the prior sequence of the time-temperature episodes is of no食品伙伴个性空间3_MK_E
importance except to calculate the amount of quality remaining up to that time, i.e.
#v$Q t#bX q Q$z t0there is no history effect. If the rule of additivity is valid with reasonable accuracy, the食品伙伴个性空间!\'fZ&N$[f5ww4M
use of time-temperature integrators (TTI) should provide reliable results with respect to
o {OSc;p/hf0D nd0prediction of shelf life remaining, which will be discussed later.食品伙伴个性空间q&yf$e'^y+Qd
However, there are some cases where the total effect of various temperature食品伙伴个性空间lGr1KCF
experiences may not be independent of the order in which they occur or of the nature
#RPf? z I}2\0of temperature history. For example, widely fluctuating temperatures may cause
9z/E*K5cK!Rm0freezer burn or in-package desiccation, which is not additive (July, 1984). Where the
hns9V3a)M,o-ma0colloidal nature of a product is affected, the effect of time-temperature history may not
Pnyo5VoK&b0be additive either, especially with a freeze/thaw cycles. This is also true when growth
b;d&v+~ x7l7[6wT0of microorganisms occurs (Fu et al., 1991). Certain chemical reactions, enzymatic as食品伙伴个性空间A3N?I+We
well as nonenzymatic, could even proceed more rapidly at temperatures below食品伙伴个性空间k G/p%f)ywj.Oi
12食品伙伴个性空间@f {&RyZ:{7I
freezing. This is called a negative effect of temperature (Singh and Wang, 1977),
3AO*V5}8M+l I(A@)c0which could be caused by one or more of the following factors: (1) a freeze食品伙伴个性空间?K f RtX{i*C$\
concentration effect; (2) the catalytic effect of ice crystals; (3) a greater mobility of食品伙伴个性空间"yHCF6]j9{$zd
protons in ice than in water; (4) a change in pH, up or down with freezing; (5) a
-^`t!Y!D`.h ?0favorable orientation of reactants in the partially frozen state; (6) a salting in or out of食品伙伴个性空间&^"K? n)[
proteins; (7) decrease in dielectric constant; and (8) the development of antioxidants at食品伙伴个性空间:E~*DB @$lk"y
higher temperatures. As has been shown by Fennema (1975), the freeze食品伙伴个性空间4{ [{jx#D
concentration effect can cause rates of chemical reactions to increase dramatically just
b+W)Kl!_.fV V!?!p0|0below the freezing point (Figure 19.5), e.g. ascorbic acid loss at -3°C can be faster
xs x{1f OE(R/K0than at higher temperatures this one should not use data in the -4°C to 0°C range or食品伙伴个性空间(k6gk5e,S
above as part of an accelerated shelf life test to predict rates at lower temperatures.
n.R8y owCT0Fennema (1975), showed that the time to 50% loss of vitamin C in broccoli was 44食品伙伴个性空间$G)[U8cza2Zb)A
days 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XG8`jQw ?
evident in the shelf life plot of frozen strawberries as shown in Fig. 19.6 using the data
K{#F;Pi D0of Guadagni (1968). If the data collected only at 25 and 30°F (-3.9°C and -1.1°C) are
4|KY)q pG0used, the predicted shelf life at 0°F (-17.8°C) is over 27 years, if data are collected at食品伙伴个性空间s9n;O#M'}? J
only 20 and 25°F (-6.7 and 3.9°C), the shelf life predicted at 0°F is 40 days while data食品伙伴个性空间~h5as&^1}R]u
below 20¥F extrapolated to the true expected shelf life is about 280 days.
\4X&ne1v3`0Figure 19.5 Rate of chemical reaction as a function of temperature食品伙伴个性空间p{KqqW$r&R[5_.Z
above and below the freezing point of a food.
4w]+PP@ T013
;p7^?0g }w-@7] [K0Figure 19.6. Shelf life plot of frozen strawberries showing the食品伙伴个性空间+Y C yD^0M*O:sN
influence of the freeze concentration effect just below the freezing
rzv?x)T9`G0point on prediction of shelf life at 0¡F . Data from Guadagni (1968).食品伙伴个性空间&h?vA;Zt,]S
Each line represents a regression through a different selected set of
uZ'_4kJ1u#D1?&Y0temperatures.食品伙伴个性空间(Z8t&ly(D@H:E
The response ratio of the food to changes in environmental temperature (RT) is
dmY%Ju!`0S0dependent on the fluctuating temperature conditions as well as the heat transfer
oMe \.p4o0properties of the food as well as the package (Cairnes and Gordon, 1976; Dagerskog,食品伙伴个性空间A3x?_D(er8~-M
1974). In the analysis of food shelf life, an inherent assumption is made that the food食品伙伴个性空间J,Qf4Jr)a(Z)p
is responding instantaneously to the environmental temperature changes, i.e., RT = 1.食品伙伴个性空间t~mq(Mo&Ot8kT kl|
This may be acceptable if a surface deterioration process is the deterministic factor for食品伙伴个性空间]Fl3CVYA9^
shelf life, e.g. mold growth in some foods. Freeze-defrost cycles generally can be
C9Gxt7R-JGO2U0considered as sinusoidal oscillations. The amplitude of the effect is reduced inside the食品伙伴个性空间bm.p*uDg-{K
package by some factor thus RT. < 1. It can be expected that the shorter the period of
fd.]T,^ |0the ambient variation the smaller the RT, and hence the smaller the amplitude of the食品伙伴个性空间+h:J5fR@2I$\
cyclic temperature variation in the package. Zuritz and Sastry (1986) also studied the
qG8{&G]X0effect of packaging materials on temperature fluctuations for frozen ice cream and
q i&jEE;z"\0found that packaging materials coupled with a layer of stagnant air were effective食品伙伴个性空间0Njk I O-E6ycA(DZ
barriers against thermal fluctuations.食品伙伴个性空间{qJN d X)D
19.2.5 Hazard function
t!I8Th@'G014食品伙伴个性空间;w L1|ub%lS6V
After the product is produced, it may fail at any point in time in accordance with its life
|seon8y0distribution (Nelson, 1972). The hazard function h(t) of a distribution is defined for t ³ 0食品伙伴个性空间3] i5VB6q*g.S1IX,B
by:
dw P!m8qpe!F0h(t) = f(t)/[1-F(t)] (19.14)
ZJVr:CXZ9[F7K0where f(t) is a probability density function and F(t) is a cumulative distribution function.
dB+x2e%v O0The h(t) is the conditional probability of failure at time t, given that failure has not食品伙伴个性空间6E%E6]"a V
occurred before ..
`0AZi ~/g(oF0The behavīor of a hazard function for studying the shelf life of food products can食品伙伴个性空间(H qr tW$x]
be easily understood by examining the "bathtub" shaped curve in Fig. 19.7. Note that食品伙伴个性空间VR-irr KS j9R0r
at time to, a frozen food product begins its journey to many distribution outlets for
hs$jcW`)v$hH0consumption. During the time between to and t1, early failures may occur owing to a食品伙伴个性空间+pG2f4hK
failure in the process itself, faulty packaging, extreme initial product abuse, and many
k] rqp3C VF0other environmental stresses to which the product is subjected. Early failure should not
:^'_,s2c z*Z0be taken as a true failure relative to the shelf life of the product unless it represents the食品伙伴个性空间.awd;dsK'Lve3_
normal condition. From t1 to t2 one can expect, barring chance major temperature食品伙伴个性空间z ?0G5B*J-x
fluctuations, no failures. This interval represents the true period of the product's食品伙伴个性空间+AN;sO rV
stability. The failure rate is almost constant and small during this time. The hazard or
Dj/H6N)``'fqf0failure rate increases from time t2 to the termination point t3, owing to the true食品伙伴个性空间(_3}u+DL
deteriorative changes occurring within the product. The concept of hazard function is食品伙伴个性空间:XVI0hz"kQ
important in the analysis and interpretation of the failure times of a product.食品伙伴个性空间4X0tZt"SC ~
Time
r!l/O[!os0to t1 t2 t3食品伙伴个性空间MU,N L\W(e.p R5Q
Early食品伙伴个性空间esx |1WF F%r
failure
/S]2~:W'{eP3f0Period of product stability
K,KW'@Ko0Failure due to
1vw;r3?'xMS0product
6RF-EP'~ rs^0deterioration
9e5RL6L(U1J+d6z/Tq0Figure 19.7 Failure rate as a function of time食品伙伴个性空间 {Vg;IQ'M)M%P0i
15
Y;DW*?pJS0A fundamental assumption underlying statistical analysis of shelf life testing is食品伙伴个性空间7v3PQz'P
that the shelf life distribution of a food product belongs to a family of probability食品伙伴个性空间R)`C|H!['mcOy
distributions and that observations are statistically independent. Parameters of a shelf食品伙伴个性空间dZtx t)~_
life distribution are estimated by use of shelf life testing experimental data. Once the
PB KS:^Ob0parameters of a shelf life model have been estimated, it can be used to predict the食品伙伴个性空间,H"m2@C|
probabilities of various events, such as future failures (Nelson, 1972). Five statistical
FXW{;|2dY4Y0models, normal, log normal, exponential, Weibull and extreme-value distributions
J*T VhK X1Z*sm0were tested for a few food products (Gacula and Kubala, 1975; Labuza and Schmidl,食品伙伴个性空间m,v~ x"OA/s
1988) and it was found that the Weibull distribution fits best, which will be食品伙伴个性空间e NXEO(Ro
demonstrated later.
g$rK)k DM019.3 Shelf life testing — overall aspects食品伙伴个性空间+F#[7{ s7z#uV
19.3.1 Purpose食品伙伴个性空间]*t-t`,vP
In the development of any new food product including reformulating, change of
IZQ&g9]K6_'I U R0packaging or storage/distribution condition (to penetrate into a new market), one食品伙伴个性空间-Q3@ D$@VII-d
important aspect is the knowledge of shelf life. The shelf life of a food product is vital to
Ir-lKx Q%x0its success in the marketplace. This life must at least exceed the minimum distribution
O+wKinP^0time required from the processor to the consumer. Shelf life testing can assess食品伙伴个性空间 c6M9P'WPM
problems that the product has in the development stage, following a "fail small fail食品伙伴个性空间0J:~?5OD9M
early" philosophy, thereby eliminating large disasters later. Marketing/brand managers
:[Q,TZ+{0also need reliable shelf life data to position the products and to establish the brand.食品伙伴个性空间G$Sa0eq0s
Periodic determination of shelf life help to provide assurance that the product remains食品伙伴个性空间V,[p(zaLW AH
consistent over time with respect to quality.
#sD6`?ItuV0Different shelf life testing strategies are necessary at different stages, as
7]i+y,I_ uoK#v2C0illustrated in Fig. 19.8. If the objective is to identify whether pathogens and spoilage食品伙伴个性空间9G!_LF5r8fu
microbes will grow in the case of temperature abuse, then a challenge study is
G5IOfA!|I0necessary. If the objective is to quickly estimate the approximate shelf life of the食品伙伴个性空间 je1Ps&IM~/r*c;?
product then an ASLT can be used, as long as the proper temperature range is
L)_1dxI*R7F0chosen. A confirmatory shelf life test may be conducted at the last stage with
!bi+w.`[(U'S2S+x*q0simulated distribution chain conditions, although in today’s R & D environment, this
bM(]'u[M0may be skipped.
B(^5\7qU ~CSQ?016食品伙伴个性空间g"[/`.h K`4W
Product concept食品伙伴个性空间X g-s0e?4h%U
Prototype development食品伙伴个性空间lp'fxH?:d
Pilot line testing食品伙伴个性空间nY6FhQm
Scale-up line trial食品伙伴个性空间yA^nL,[
Full line production食品伙伴个性空间9k:s4R8Uu;j ~'Q0[4e/_
Marketplace
4?|F4z0fr:~fU0General stability information食品伙伴个性空间*uZ6@/MTh*V8e Q OxT
Challenge Study食品伙伴个性空间-A&[9e3o P+a5h
Accelerated shelf life testing
~X~jq0Confirmatory storage study食品伙伴个性空间0M&^A A m"_
On-going shelf life monitoring食品伙伴个性空间 Ht eI5`Ox5a
Figure 19.8 Shelf life testing strategy at different product development stages食品伙伴个性空间hXo:i)d|L
19.3.2 Shelf life criteria食品伙伴个性空间W"R(dv9n
The criterion for the end of shelf life may be variable depending on the definition of
!{lW @;Y1N#D*K3v0product quality grade, so the shelf life of a product may also be variable. The shelf life
^"UxA9J(z,{,] `8W g0of most perishable and semiperishable foods is almost solely based on sensory
$n)g3xA5h2h9c5IM0quality. For example, fresh meat degrades mainly by bacterial activity and rapid食品伙伴个性空间SPCeKW
chemical oxidations that cause an off-flavor development and loss of color. This is
SYX#Q2~AO.[\0readily recognizable by consumers. In contrast, many longer shelf-life foods including
CG+k$NuK0most frozen foods degrade mainly by slow chemical reactions such as loss of
"mF hek,r0nutritional value. For example, the vitamin C content of some frozen fruits and食品伙伴个性空间z~_z&Qy5p
vegetables, may fall below the required standard as listed on the label before sensory食品伙伴个性空间3jf] DYC;O.H,i+]
quality becomes inadequate.食品伙伴个性空间B&K.dexHj4y]
The criteria for shelf life may also vary depending on the sensitivity of the
#?8lx"Q-ne*h0consumer. For consumers, taste, odor, and appearance are the most obvious criteria;
)_x+q|{YoDQ0in academia and in the industry, sensory evaluation correlated with instrumental食品伙伴个性空间2llkg;ORFT
measurements of a given quality index (e.g., vitamin C level) are usually conducted. In
i,R%K7g6Y![ E$B*[LR0general, the criteria level corresponding to the end of shelf life of a product depends
"l.kd(nARj017食品伙伴个性空间{Dhp4o](]
on: (i) any legal requirement, e.g. zero tolerance for botulinum toxin; (ii) consumer食品伙伴个性空间yz h.P4y |n
preferences or marketing requirements; and (iii) cost. In essence, the end of shelf life
u3?W;W_/T5mt0depends on the percentage of consumers a company is willing to displease. If 100%食品伙伴个性空间8[%X4o5[x#kk C%N
acceptance is required then high cost ingredients and absolute control of distribution
U~2~ r'P c7C$l|}z0up to point of consumption is necessary, otherwise there will always be some people
1]-h8[zv`0`8L&_6Hf+`0who will get foods beyond shelf life. The aim is to keep this as small as possible.食品伙伴个性空间g VNb;Fk
19.3.2.1 Just noticeable difference (JND)
{7A \zQY0Sensory (organoleptic) examination of foods was a general procedure used by the
%I:\2B b0WTN0human race to evaluate wholesomeness of foods long before the discovery of食品伙伴个性空间,V$z%IRYf v
microorganisms. Sensory evaluation of foods by scientific methods can be used to
t[s"J-]klkq0evaluate such attributes as taste, odor, body, texture, color and appearance. Changes食品伙伴个性空间 _%i0f+l8g/dT
in these attributes may be brought out by microbial or non-microbial actions, usually食品伙伴个性空间8j)B8H f i
the latter for frozen foods.食品伙伴个性空间P0Ro#q3l1tr2s |
The methods used to evaluate sensory shelf life data include difference testing食品伙伴个性空间H'B8tZ3h6@?3`7n5s
and hedonic scoring. Difference testing can involve paired comparisons, duo-trio
9d l:V'st6zl0tests, or triangle tests. The paired comparison procedure determines the time when a
:J6l i_'_d6oN0measurable difference in quality occurs between two test samples at a certain level of
m1lc.P vls!Q"?U0probability. When applied to frozen foods, this method is often referred to as the Just
9O#p H8r} n q W U6G0Noticeable Difference (JND) test or High Quality Life (HQL) test (July, 1984), which is食品伙伴个性空间 ?_ {%yRkq
usually based on flavor changes. Duo-trio testing compares two unknowns to an
,N${pj!n0unabused control sample and asks the question of whether either of the unknowns are
!e#KFE*S&w'C0the same as or different from the identified control. Triangle testing determines the one食品伙伴个性空间A'Q fY3B
different product among three test samples presented randomly to a set of judges (at食品伙伴个性空间bye h0B1l0A}Yf
least 10). Probability plots are used to predict shelf life at a given probability level.食品伙伴个性空间1\ Kz6F4GOx
The difference method can result in finding a difference when none really exists (Type
*H%N"~W?6r;x0I error), or not finding one when indeed there is a true difference (Type II error).
9x,?(T)J%RH0Labuza and Schmidl (1988) have discussed this topic more thoroughly in relationship食品伙伴个性空间~:xV'D}*E.b_4P$G
to shelf life testing, which is not commonly found in sensory textbooks. Table 19.3食品伙伴个性空间8eq;Xi0_#U1k
shows some data from Guadagni (1968) for HQL of frozen foods.食品伙伴个性空间&[(Si6q6lF
18食品伙伴个性空间W Psb[(X
Table 19.3食品伙伴个性空间5[ \By|/Qu TYZ4B
Days of High Quality Life for fruits and vegetable (from Guadagni 1968)
:Qd f+VX0P roduct T yp e 0 °F 1 0°F 2 0°F
6MZi!kfF0apples pie filling 360 250 60食品伙伴个性空间e.yz"Ql#p1I
blueberries pie filling 175 77 18
)Y$s"V&S,E0cherries pie filling 490 260 60食品伙伴个性空间a%w K$y6M`gNp
peaches retail syrup 360 45 6
f}%c S,na%t0blackberries bulk, no sugar 630 280 50
O bu\yZ9o5O1q"`0raspberriesbulk, no sugar 720 315 70食品伙伴个性空间)emuT:yY;A4B7xj
retail, syrup 720 110 18
4h3`IC{/]$VA,g0strawberries bulk, sugar 630 90 18
0z"b&w\(yt0retail 360 60 10食品伙伴个性空间 qp)W8D)@ A5ziD
green beans retail 296 94 30
cs-S2R)s_'Lg0cauliflower retail 291 61 13食品伙伴个性空间6t2O+uW(@#w
peas retail 305 90 27食品伙伴个性空间6u!v8JY[z-Hb
spinach retail 187 57 23食品伙伴个性空间W4W2[Ml
corn retail 720 360
c X:R H ` L,l&X2U*mAE0corn on cob retail 275 150
:K| eZ5nq019.3.2.2 Hedonic scoring
}5d[G0Ew ~0Hedonic scoring — which indicates acceptance on a numerical scale, e.g. a 1-9 point食品伙伴个性空间8t,~1B-V agiL@
scale labeled from "dislike extremely" to "like extremely", is typically used for shelf-life
B e-X^1@-u`u4C0evaluation. The test can be designed to not only evaluate the overall acceptance of the食品伙伴个性空间Eoq4T~y
product, but that of specific characteristics such as flavor, texture, appearance,
B n;z @cT0aftertaste, etc. Trained panels can also use this technique on a line scale, which can
P'q6At&oe7u8n0be converted to numerical equivalents.
X'[B,l)K _0If the hedonic method is used to evaluate shelf life, one can simply use the食品伙伴个性空间j#l-i'?.V
score as quality index A and plot the score vs. storage time, run a linear regression,食品伙伴个性空间![%gAWD4}6sFc
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 ai.s4PJ G
pre-set level (Waltzeko and Labuza, 1976; Gacula, 1975). The shelf life determined in
w&z5L mw%O/Q"n_ f0this way is called the practical shelf life (PSL) for frozen foods (July, 1984), and is
FSb2~y#k0longer 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-R6vhO(?%X lA3C
shelf life testing, yet it is probably the most used method. Many food companies use a
@0JT ED0loss 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U-GBm(Jh flo
19
d:LP;Yo b Jg0(Labuza, 1982). Objective measurements and professional judgment are often
7n*F1Ku U3| @0required to determine the end point. Data in Table 19.4 from an report published by
y"[q \.B"j*yh0the former Refrigerated and Frozen Foods Institute (1973) Unfortunately there were no
3u9F~he}Hi~'w0methods given, but the data suggests that the PSL is about 2 to 3 times longer than the
,pD0oZ-ZT0HQL value. This in itself suggests that the HQL methods can be used to shorten shelf食品伙伴个性空间Y-dl A%yTV a0i._
life testing times.食品伙伴个性空间"}'s(}!H4k8ikt[ J
Table 19.4
jt`-BO%Bf?4cM0Relationship between practical shelf life (PSL)
7V6t{V.b)]_w6?0and High Quality Life for frozen foods.
X"M~ctDe Ol"k/n0F rozen Food P SL/HQL Rati o食品伙伴个性空间ya0f4vl&IG r@
lean meat 1.9 - 2
vo-s^kh(n0fatty meat 2.0-2.4食品伙伴个性空间M3^woIP0^0ee&q6T:y
lean fish 1.9-2.2
['v;R?w(]0fatty fish 2.4-2.7食品伙伴个性空间@~O7S1J G
precooked foods 2.8-3.0
K ~^$U!f|4K4PF\V0fruit 2.8-3.1
k8R\.tw aS0vegetables 3.1-3.5食品伙伴个性空间 ~bB/xuiI8U)`
19.3.2.3 Instrumental analysis食品伙伴个性空间k? Nrt/D:H
Chemical or instrumental analysis, such as moisture, nutrient loss, free-fatty acids or
Z Iu S@N Q0color measurement that closely correlate to sensory attributes, can supplement
?r_J/kVR0sensory techniques. They are usually less expensive and less time-consuming than
5T? j@L`]"hp? j0sensory approaches. A correlation between a physical or chemical test can increase
j.B7i-`9e M#h0the confidence level of the sensory results. For example, the following constituents or食品伙伴个性空间nA k)V$}v
properties can be considered for monitoring chemical changes of pizza quality during
S[qk|-fH0frozen storage: total free fatty acids, specific volatile free fatty acids by HPLC,食品伙伴个性空间O yW [(c$Qr
peroxides, oxidative volatiles (e.g., hexanal) by GC, spice volatiles by GC, lysine, color食品伙伴个性空间1q#C3OkO
(decrease in red color or increase in brown), in addition to sensory evaluation of taste
T \J/w*_$r$Z9f0and flavor (Labuza, 1986). Most sensory experts agree that analytical methods should
2R1t i4d0f0c~+q0complement the sensory tests. Vice versa, the endpoint determined by objective
,K.nk+f0}hUN0measurements should be confirmed by sensory techniques as well.
5LFn%v/at,\T%e2a#b020
Hss^}7?af019.3.2.4 Weibull Hazard analysis
bUuf pU_0The Weibull Hazard procedure requires one to first make an estimation of the time to食品伙伴个性空间;cD.GKc"~Rs6U
the end of shelf life. This becomes the initial estimated time limit for the study. The time食品伙伴个性空间RSr|1AN T
limit is then divided into several segments at which points panelists grade the product.
4z)a+i]4[Bmj6J0Additional panelists are added at a constant number for each subsequent time period
2C3a TZ5rnE0to maximize the number of testers near the end of the test. The panelist is asked to食品伙伴个性空间 \)lC4nebh2u0vb v
grade the food as good (acceptable) or bad (unacceptable), i.e. no ranking on a
^ g-PXW6e JRvI7h0hedonic score. When the product is identified as unacceptable by 50% of the食品伙伴个性空间4@@ w+`hZj:@ J
panelists, the number of testers for the next period is increased by the number of failed食品伙伴个性空间 E@#p3~I
samples plus the constant number. The interval between sample times is also食品伙伴个性空间 S`9C4E*^1CT`m w4_
shortened as the end of shelf life gets closer. The test ends when no more samples or
C2H+QS$xB Y3Z8C7nY0panelists are available. The scores are ranked and the cumulative hazard calculated.
P:x3D*\-KZ0The critical probability of failure Pc, can then be calculated from the following equation:食品伙伴个性空间(S&?g3xCE
Pc = 100 (1 - exp(-å(H/100))) (19.15)
1{ [~"j[P?0where H is the hazard value equal to 100/Rank. Choosing Pc = 50%, corresponds to
0X.Bp{XO2Rb"x0an accumulated hazard value of 69.3%.食品伙伴个性空间w | Y:O YmP)s
The relationship between the logarithm of storage time (log t) and the logarithm食品伙伴个性空间6]*@@3F8EfI l)`7^_D
of hazard value (log H) is linear:
aH%e0B(o7\.D2~-fr2I0log t = (1/b) log H + log a (19.16)食品伙伴个性空间G1kk?G.~lF
where b is the shape parameter and a is the scale parameter. The shelf life can then
#L h N:}XWXGI;x.P0be determined based on the desired probability level allowed for product failure. The食品伙伴个性空间5u Z|-?/Cm
lower this probability, the shorter the shelf life. This plot then allows one to make a食品伙伴个性空间d0{ C Gr(E)j%^Y!v
management decision with respect to the probability of displeasing a certain fraction of食品伙伴个性空间){Z {U K$vf}
consumers. It is hoped that the distribution time is such that greater than 99 percent of
Uhd [Wp7Rp(s0the product is consumed before the end of shelf life based on displeasing less than食品伙伴个性空间ku1g3C&J+A
X% of consumers where X is the economic value. An detailed example was given by
Mrv6AM`*D0Labuza and Schmidl (1988). It should be noted that this process can also be used for食品伙伴个性空间5gS!e];S+RGf%U K/A:Zg
simple analytical tests such as plate counts or vitamin C. In these cases the number of食品伙伴个性空间d_|Me3}8l.IX
panelists are replaced with the number of samples tested. Some criterion such as 20%食品伙伴个性空间9R3~"m2V{ FCU|
vitamin C loss is used as the negative response. Figure 19.9 shows an example of
i'Y_DU R-z K4r0Weibull plot for a frozen food based on assumed data. A shelf life of 16 months is食品伙伴个性空间%|+p@1q3U.S/Q` vM
21
9_3M'JoT.S"FqF'_0found at Pc = 50% from the graph. From this graph then, if 95% of the food were
] P%A r z)mkzbA0distributed and consumed in 3 weeks, only 1% of the consumers would be displeased食品伙伴个性空间k-G.n\Uay
.01 .1 1 10 100 1000食品伙伴个性空间j$btj$~({ Z'^
1食品伙伴个性空间 nsr~ W-d3T)?2fN
10
-LA_L1N]"vT!E0100
9L _g/@ O0Cumulative hazard (%)食品伙伴个性空间l7A | y5`.CJ
Shelf life (wk)
f3DPB"_ R&L0Probability (%)食品伙伴个性空间8`[;|1H6[XX D
0.01 0.1 1 10 50 99.99食品伙伴个性空间lq4Gkr
Figure 19.9 An example of Weibull plot for a frozen food.
t.P#?.M!OPH0A shelf life of 16 wk was determined at Pc = 50%.
.\0Mh7S @F \5O7D)[0(or 0.95% of the product is out of compliance). If the rest were held and consumed at
'yJ5N wM"z/Gu010.5 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0Dr&h Au/]/BU
= 2.5% of product. Thus in this distribution model about 3.5% of the product is食品伙伴个性空间6Pd,?*O%~4j+h}8~1Q'U
unacceptable. To improve on this, the product must either move faster or one must食品伙伴个性空间fDD8f-k:Fp2p,A_
distribute it at a lower temperature. Wittinger and Smith (1986) used this approach to食品伙伴个性空间3{pk D/q,i p _ H%R
determine sensory shelf life of ice cream based on iciness and found a shelf life of 5
/WN+Wf9`0@2by3V0weeks at 0°F (-15.5) which fits the general data for iciness in ice cream as shown in
|3z(Xt.PF8|1H#c u0Figure 19.10 (Labuza, 1982). It should be noted that this gives a Q10 of about 12.食品伙伴个性空间6~ l5~"T;Sw1`5na.u
22
_Y*aoR0.1食品伙伴个性空间xSJM-[Q
1
2[b \ gm({010
M @o;V+V.o D0100
8f4`/Dl$F"]0Temperature °C食品伙伴个性空间x$](V aVkIK-^ed
1食品伙伴个性空间N\XQ5[1_U
10
:bVzz#JW7sqB0100
c0a6~eeED ws0-30 -20 -10 0
C jwf&Y@ G+Z:_00.1
1dR'p"Cr P2]0weeks
XQS7v/y5sb0Figure 19.10 Shelf life plot for ice cream based on icyness食品伙伴个性空间9C}*}6q` zgC-AsP
perception from data of Labuza (1992)食品伙伴个性空间&o(M(hM hvz v5s?
19.3.3 General procedures
`3o,G+b bui3i0Shelf life testing experiments are designed to measure the average shelf-life of a食品伙伴个性空间8T\t8^D C [8p0o
product under given conditions. General procedures for shelf life testing of foods were食品伙伴个性空间u9dUi bf5_
proposed by Labuza and Schmidl (1985), which include:食品伙伴个性空间%TC3?M y
Step 1: Develop testing protocol — The protocol should consist of: i) specific
R!V+{5B/rd1Bb,v0objective; ii) detailed test design in terms of product, package, and storage condition;食品伙伴个性空间,{,l9|nDV zL7S)J\
iii) execution procedures in terms of time, space and resource availability; iv) cost食品伙伴个性空间1{R&WYjV)K B,jU
estimation.
_l0W4p I]%H0Step 2: Identify key quality indicator — Any previous shelf life data and kinetic食品伙伴个性空间}%bH\(GtL4h
parameters of food deterioration available in the literature (Labuza, 1982; Man and
2o)s^ `Q&g T/l0Jones, 1994) or the distribution turnover time of a similar or a competitive product in食品伙伴个性空间-Sn/z:m'u @ h
the market place, if any, would be very helpful in this preliminary identification or in食品伙伴个性空间P(mb h;y
determining the shelf life requirement.
2OX)PV$G(P` {0Step 3: Estimate product sample and control needs — The number of samples食品伙伴个性空间iEmlV6t N1l
and controls required should be based on the detailed experimental design. If食品伙伴个性空间&H%Y"g!e m|.t
sufficient product is available, extra samples should be placed into each storage食品伙伴个性空间 O#`2uq*I;Hk4U;p
23
qS6K _Ye[ o0condition. Now and then it may be necessary to recheck a sample, especially if a value
Fe2@u+]A"}0is not in line with other data. It would be disastrous to be out of sample before failure
&|ERM(f8{|Z0has occurred or the predetermined termination of the test is reached. Extra controls
'L:F B;\t$q+ME:}d5O0should also be prepared and stored. When the samples are placed into storage
+y-_:r8V.Y?'qq0rooms, they should be positioned so that the complete package is exposed to the食品伙伴个性空间Z3K5j2gxP)^I
external atmosphere, unless otherwise specified. The specific location of the test
2l3T{h(Ai nKk0sample should be recorded. Temperature controllers should be checked for accuracy,食品伙伴个性空间5K4s(~dH0dW@8^D\
periodically. In addition, removal of all unused samples from the storage room to make食品伙伴个性空间k|'F R1`/ixdi
space for future studies is a must.食品伙伴个性空间gM:f5IU_w
There are various thoughts when it comes to using a control product. Some食品伙伴个性空间!L D*m PV5\w9HL
sensory experts prefer an actual physical control; others are satisfied to just use the食品伙伴个性空间$S5R7z4|(}a/eJ4ri
numbers obtained in the zero time evaluation. There are three alternatives when using
2J*gu0\/r0a physical example as a control: (i) making the control from scratch each time using食品伙伴个性空间2viM MU,B3f
the same ingredients, procedures, etc.; (ii) deep-freezing the control (e.g. pizza held at
I/|&n S1V\:us-P0-70 °C) and accepting that it might have changed slightly, but minimally compared to食品伙伴个性空间)Jw8|*N+|-|&pl
the product in shelf life; (iii) using a fresh batch of product which may not be identical.食品伙伴个性空间-`[(] E7F-o!d`
Step 4: Select proper package materials and package size — This is largely
wO"n%Y1@'r6V*UR)S0_U0dependent on shelf life requirements, packaging costs and availability, and consumer食品伙伴个性空间N T4DC,mDml/Ki"?%J
information. Factors such as vacuum packaging, nitrogen flushing, or use of
kh p ]g Z n]-S0antioxidants are often considered in combination with packaging materials.
8s+ZV aq/l)K5B0Step 5: Choose storage conditions — Storage conditions are chosen based食品伙伴个性空间r4Y$z^ d:oy%b
on the type of shelf life testing. For example, the intended commercial
/@3|#muwC0storage/distribution temperature range should be used in confirmatory shelf life testing.
v,{`(_*ZmoJL0Elevated temperatures are often used in accelerated shelf life testing to obtain data for
p K| M#OwF$QW+AX0prediction of shelf life at lower temperature or for prediction of shelf life under variable食品伙伴个性空间aE o Y4H a(k d
time-temperature distributions. Humidity control and/or monitoring is less important for食品伙伴个性空间Gbx.Wa)m$N!q
frozen foods as compared to other foods (e.g., snacks, cakes, pies, and pastries).食品伙伴个性空间1r(c5oJs\a
Light in the room should be properly controlled depending on the package.食品伙伴个性空间btN @q}4c%K)z7A
Step 6: Estimate sampling frequency and duration of testing — The sampling食品伙伴个性空间V8Vva5Y)A4m
frequency is generally an estimation based upon experience from prior studies with
-\&Y u:TP0similar foods. However, once one knows an interval at one temperature, then the
N$YO$CX{H9V0intervals at other temperatures can be estimated using a Q10 value i.e., if the Q10 is 3
'~l.Iy!@2f$J0then for a 10°C lower temperature the sampling times can be 3 times longer. If the
R"qGeCmH8}X0interval between sampling is too long, the risk of under- or over-estimating shelf life
J.O GuND;l_M(J0increases. The more analyses that are completed, the more accurate will be the shelf食品伙伴个性空间7j&c^Ojy/e6a\.g
life determination.食品伙伴个性空间 NG8o|En
24食品伙伴个性空间%f/S(?"u+@xg~Y#~
The question as to when one should end the experiment must be based on
cJz'XTle0some pre-set criteria for failure. One criterion could be the minimum shelf life
b8pK-]h0requirement driven by product category, distribution chain, and the benchmark's
t#z/{ W:n0product stability. If there is an accompanying sensory test, the end time can be based
7Y2^$_)KG*Zs0on some organoleptic inferior quality criteria from which one then can get a microbial
"z1`ex!X%XHMZ0or chemical index limit. For frozen products, several weeks to months are usually
2S!x?;uA6{X0needed. If the shelf life can be estimated with any accuracy, the test intervals can be
$W3n2[l%wR;v0lengthened and clustered around the expected failure period. Most of the experts only食品伙伴个性空间jZDpzti
require about six evaluations to provide reliable results.
haAnI0Step 7: Schedule for execution — Before scheduling the starting date for a shelf食品伙伴个性空间 J5t;ZgMr
life test, one must check for the availability of ingredients, packaging materials, and食品伙伴个性空间 z&b6e$z.[
storage space, and the time and resource available in the pilot plant or in the
(v oa2O6J0processing plant to prepare the samples. One should also check for the time and食品伙伴个性空间4\R#j!N%fOS9R
resources available in the microbial lab, the analytical lab and/or the sensory support
4?)j Q7h\q0staff throughout the test period. A copy of the test request and schedule should be
;Pg u4j!}0sent in advance to those who will be doing the work. The courtesy of providing those食品伙伴个性空间[_"VJ;@
involved with this advance information always pays dividends. Holidays should be食品伙伴个性空间Mj p.@)Ho1P
marked on the scheduling calendar, since scheduling too many evaluations near
*J0KY:{6J5Qt#N0major holidays or Friday afternoon is not recommended. However, once scheduled,
i NX"j }?7e+\0sample observations on weekends and holidays should not be skipped over, since
t"SF#^4bl0important data points could be missed.
w\YtrgM3S0Step 8: Take sample and evaluate quality — Samples should be taken and
%d*HZ ~\vYf;v+|9BO0evaluated following pre-determined schedules. Sampling plans should be
oD5p*u Dv ]0administratively and economically feasible, taking into account the heterogeneity of
-p X"F1V2f1F7x7gO'u0the food. Maxcy and Wallen (1983) pointed out the problem of heterogeneity of食品伙伴个性空间z q9goNo3EV y
samples in shelf life prediction. Multiple subsamples (³ 3) should be done for nonhomogenous食品伙伴个性空间yF f |s6DMP5f
samples. A single package is usually used as an experimental unit.
]7b%XSG0Replication of 3 or 4 units are desired for each measurement. For frozen foods, a
~ xg4m'`*axM0thawing process is often involved in the sampling procedure. Proper thawing or
9_E_ ~X(O(PE R#_0microwave heating is critical to the product quality. All samples should be thawed or食品伙伴个性空间"^6Z;D/KM X
microwaved in the same way to minimize any biases.
L+sQC}&bX`&f0The intended analyses should be based on the specific mode of deterioration,
n(m Xj"V1Ky0which was discussed earlier. Whatever the choice, the tests should be reasonable and食品伙伴个性空间oq|;j^;z?1|Z
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;k#Xp$z:T#{5N
quality factor is measured, the test starts out a failure. Unfortunately, in many cases this
d vO1SO;?T0cannot be established initially, so sensory evaluation is a must in almost all shelf life
k0|Y*`rO m025
!d$D6yc%T0tests. Key sensory evaluation techniques for frozen foods have been discussed食品伙伴个性空间 \!?,_.SU
before.食品伙伴个性空间 ~2Ug6x&n9I/j!P
At the time of each pull, one unit of the sample should be evaluated (informally
3F,V$VK]x0by a minimum of 2-3 people) for changes in flavor and texture. This should be done in
QP+Xa0a4^0f\)\S0addition to the final tasting prior to a consumer sensory test. This is necessary since it
j r1|-neT0helps the developer know approximately how the product is doing during the progress
?No c |0of the shelf-life, helping to avoid any surprises in the results. Control samples may食品伙伴个性空间o"ja yz gwI4Y
need to be prepared fresh.
r!J8O+[yU:~"N0Step 9: Analyze data — Shelf life is the predicted day at which the stored
RQ I l*^B:hDqN0product (test pull) is X% less than the control at day zero (Reference). The data should
&{U0Bod4il)]0be plotted and regressed to determine that point using the proper model (zero or first).食品伙伴个性空间P%Z@9\7b&W3y%n#c
All too often the data are not analyzed until the experiment is over and then the
)@"n[,cNH{0scientist finds that nothing can be concluded because of lack of points or a poor fit or
,Q-A:q!w1O%]5L0some surprises. Statistical curve fitting should be consistent with the chosen model食品伙伴个性空间"I B*Wd9CQ
based on a theoretical mechanism. The amount of change and number of data points
J;G'N%OUx P9g i8h8p0are related to the coefficient of variation (CV) of the test. A weighting factor may be食品伙伴个性空间mD;GA"N
used in estimating the rate constant and its statistical limits. When the data for an食品伙伴个性空间 Kuy l8^;h~
attribute does not fit the regression model well (adjusted R2 of < 0.8), scientific食品伙伴个性空间.xc[bAC
judgment should be used to decide whether the data are applicable.
_6[ e-y)I4[8] DC7D8m"lI0When in doubt, a rerun on retention samples might help understand or clarify食品伙伴个性空间@%f[pZB:m,j
the results. Error analysis could be performed before experiments are run by first食品伙伴个性空间+tgU3c^l'b$E
finding inherent errors in time, temperature, and quality index measurements, then
h?e"Vw"URP0calculating an expected standard deviation for the plot being used to determine a rate
Y,ux7up v0constant. If the experimental data have a standard deviation much higher than the食品伙伴个性空间m0hP9r+XJ
expected value, either the functional form of the rate expression is incorrect or the data食品伙伴个性空间0s't9d%j ]&G
contain errors from unanticipated sources.食品伙伴个性空间t~!j9rF0`-q
Step 10: Prepare shelf life report — Depending on the type of shelf life
y:CvWiq L B P0determination, the results should either throw light on the technical viability of the
6@)Id0i,M`A0product or provide answers to the questions about the maximum safe shelf life as well食品伙伴个性空间 ~_d:Q0VV^
as the maximum quality shelf life of the product. Before a shelf life is finally set, factors
] \`U)p;z7oA0in the scale-up of shelf life data will need to be taken into consideration. Based on食品伙伴个性空间I$U&e-j)f!MPT)U
results from ASLT, the provisional shelf life will be set for the product. There is no
2ci!E.W(|R0government regulation which defines the product end point except for that related to食品伙伴个性空间*Yns9Z P$}s}%|
nutrient levels (vitamin C and vitamin A) in 21 CFR 101.9(g)(1)(ii) which states that for
6ts m*^1~w1_e0the vitamins listed, the analysis level cannot be below 80% of the label value if it is a
BF5_:}ee |!ZX3k9O0natural food with no added nutrients or cannot be below 100% (21 CFR 101.9(g)(1)(i))食品伙伴个性空间 Q{4I(`%\V6S%Xy#U
26食品伙伴个性空间Y~ mY5\2Ewiy
if the product has any added vitamin or nutrient whether or not it is the nutrient under
*y xn$F"uJ9IC.X0test. Thus one must base the label value on some predicted initial variability and食品伙伴个性空间9gG%y YWJn0NO
some predicted loss during distribution and storage. The FDA usually takes samples at
C8z~UT E5rP+[0the supermarket level (where they can purchase them) for compliance testing, not from食品伙伴个性空间?(\ [Ii"N2|
the end of the process line so distribution losses must be factored in.食品伙伴个性空间Ct:Q#Kp
The end point of shelf life is thus dependent on your corporate objectives and食品伙伴个性空间_a8P#TfM2y E
how much risk the company is willing to take with the brand. No shelf life test is
&J5p6A7Akb0completed until a termination summary has been written. All termination summaries食品伙伴个性空间&r%~$w.g^
should include the objective of the test, product descrīption, package descrīption,
O!TE6cc6e!ao5g0conditions and length of storage, methods of evaluation, results (in the form of graphs,食品伙伴个性空间_ b2d Kup
shelf life plots and Q10 values) and conclusions. Termination summaries should食品伙伴个性空间"RyWa'_*Ip
become a permanent record in the company library for future reference and preferably
P e)Ag*Z1\on0indexed well on a computer data base for later retrieval when needed. The final shelf食品伙伴个性空间1Mj$@,B@[6dC+o`a0c
life should also be set to give a clear margin of safety. In any case, the shelf life of a
KiEt[nA v0new product, particularly of the high risk category, should be set based on data that食品伙伴个性空间+W$UjiK)G&C3r
relate to the worst case manufacturing and storage scenario. The shelf life can then食品伙伴个性空间 K&]^yg v&N7_
be reviewed and if necessary re-set in the light of further experience in manufacturing
Afv/i4t^t0and control after the product has been launched.食品伙伴个性空间%lj T6U U~)m
Step 11: Implementation — One should get top management’s approval of the食品伙伴个性空间6H5{ \W;Qn5K/W,h/J
test results so that they can be implemented. Management must believe and support
/t|?},T$@;J F0those test results. It is important for production, sales, distribution, purchasing and
)w} Mx z0quality control to work together to be sure that the production is properly handled from食品伙伴个性空间`5Q9s.Lx j&E {3S
the time of manufacture until this product is consumed.食品伙伴个性空间7o vW aeer
19.4 Challenge study
0_0q`8Ugj ] HZ*n2o019.4.1 Basis食品伙伴个性空间)?;_'H~@j5s
Freezing reduces the microbial population of foods but considerable numbers usually食品伙伴个性空间N1~g b.Fl'd
survive even prolonged frozen storage. A challenge study is often used in the食品伙伴个性空间y UKG8c/Dr
laboratory to study the factors and factor interactions as they affect the shelf life of the
hpN%?&pU:C0product. Such simulated experiments enable the researcher to better control the study.食品伙伴个性空间 v:h2xh ~^K
A challenge study is necessary for frozen foods for two reasons: (i) to predict microbial
y%zPvLjF!^`0growth and potential risk of the product upon temperature abuse in a distribution
]q(i4@6R0A&nm0chain; and (ii) to assess the relative stability and the relative risk of different formula,
5g[5J$h2E1_C0different processes or different packaging materials, which is a must in new product食品伙伴个性空间3@O"a E,hD d^)u
development. A challenge study may also be considered as a preliminary shelf life
(C1b,c2W,K(_0determination in terms of microbiological safety. It is often used in the early stage of
J:e:f#^4tRQl027
RkD$x)wX"o0development since if microbial safety is a concern at this stage, then reformulating can
u;Xj}pZ`y6I,zo0be done quickly.食品伙伴个性空间 wM+U,H-kG
19.4.2 Microbial abuse procedures
Zz(} K E0Step 1: Identify barriers — A composition/ingredient analysis should be done to食品伙伴个性空间W{(H })sv9xT*D
identify any barrier(s) against spoilage microbes and pathogens in case of食品伙伴个性空间'|8]0i!G"Z u;~k
temperature abuse.食品伙伴个性空间3X ?S h r4Q
Step 2: Choose types of organisms/strains and inoculation level — One食品伙伴个性空间j_HY,\OM P4lKo
principle is to use an organism or a strain that has been isolated previously from the食品伙伴个性空间;yx#o+pq;l-T
product or similar foods which is responsible for spoilage or risk. The more isolates in
U-\-U Z6i9J\ V0the study, the greater is the confidence in the accuracy of the shelf life assessment. An
9P m9^Nr?-X&WQZ([0inoculation level must also be determined, which is generally much higher than the食品伙伴个性空间$m:SFd;W&}+c?
normal contamination level in a product. If the average contamination level for a食品伙伴个性空间$T;["uiC$MC y u8e
particular product is known, then the inoculation level should be as close to that level食品伙伴个性空间3\2mN']w2zU
as possible. Sometimes several inoculation levels are used.食品伙伴个性空间e)BVr!o
Step 3: Determine temperature abuse conditions — After inoculation, products食品伙伴个性空间`!eeWkxw
should be packaged using the desired commercial packaging conditions, and食品伙伴个性空间;]-x2blV@_#r XM
subjected to temperature abuse. Factorial design and response surface methodology
~i?-D6^p m TtH0are often used in designing a challenge study. A typical temperature abuse condition
K-q.Xq(]I.WF7t0used by some food companies is provided in Table 19.5. It starts out with five sets of
WY(Rrr0test packages placed at -18 °C to begin the cycle. At the end of the first 24 hr, one set
BFbP\z_0of packages is removed and tested for microbiological indicators to establish a zerotime
:au Ox!m)NT:mk U0level. All the other packages are kept at -18 °C for the next 20 hr, then removed
$x+vnLXT0and abused by placing them at 38 °C for 4 hr. Another set of packages is then
V\?"W \!ji*E0removed for microbiological testing, and the cycle is repeated for the remaining
0q9oz(u4CAF0packages, i.e. they are all returned to -18 °C for at least 20 hr, then abused at 38 °C食品伙伴个性空间^M y;[o!\6[(q X#L-h-z
for 4 hr. This procedure is repeated so that one set goes through at least four freezethaw
X)v.i1r"G9]:a4_ I*N0cycles. If there is no significant increase in spoilage organisms or pathogenic食品伙伴个性空间?rg.s}SX
organisms after the fourth cycle, the food is deemed safe microbiologically.
vEGdBAZE;yu028食品伙伴个性空间m\D2R-B }A/nV
Table 19.5 A typical temperature abuse test sequence for microbial challenge食品伙伴个性空间i6m%|J~y)X
studies
7RwR%t0{!z6r'~-Mo0Day Abuse temperature cycle Number of package sets食品伙伴个性空间)bP7X5a/ma
remaining食品伙伴个性空间njNb)Y'l!K@
1 24 hr at -18 °C 5食品伙伴个性空间 `._e)R,B%uso0U
2 20 hr at -18 °C食品伙伴个性空间(}"w{*TA}
4 hr at 38 °C食品伙伴个性空间R I9kfm2LX Jt w
4
y{Y`)J!DT03 20 hr at -18 °C
f\@7e,@ Y"YNV04 hr at 38 °C
Iv;R.[*HP!h03食品伙伴个性空间T2Ax Lh
4 20 hr at -18 °C食品伙伴个性空间AARiA6x9V$a*]
4 hr at 38 °C
~'i_(~2_c02食品伙伴个性空间h*m5LBj4CRs
5 20 hr at -18 °C食品伙伴个性空间,wI#H0I4yX
4 hr at 38 °C
XcR U ~/N\'b#I'd7zd01
j%B_x$UKU1N1w/r0Source: Labuza and Schmidl (1985)食品伙伴个性空间*@:Y"DOLh
Step 4: Do microbial survival analysis — This is to find out if there are any
!C ^1Ao_$f"n+LP;M0microbial growth upon temperature abuse or if the inoculated microbes survived the
3c%c7y:f7e0process. Appropriate detection and enumeration techniques should be used.食品伙伴个性空间 OQ l!o8W
19.4.3 Applicability食品伙伴个性空间,K{6Z4Q1L|0IG5?
The use of inoculated pack studies conducted by independent laboratories allows a食品伙伴个性空间p&n@4\5M#s%VS
food processor to assess the relative risks that can occur under conditions of
#f6o)TqUajy+Z:T0temperature abuse of the food product in question. Taking frozen pizza as an食品伙伴个性空间c Jyh(j:S p` R M
example, both the cheese and sausage, if naturally fermented, will have high total食品伙伴个性空间"OXM8P `:A?/i'g$n d
counts of bacteria. Since the product is usually partially pre-baked and then frozen, the食品伙伴个性空间Oj#W%^d | u
numbers of vegetative microorganisms will decrease until thawing occurs.
)y D!rUA r&YbZ0Unfortunately, pathogens such as Staphylococcus aureus will not be totally食品伙伴个性空间[I&ljMk
inactivated by these treatments. If the product is abused during distribution so食品伙伴个性空间cicg7QP-X#]'u.m
severally that the temperature near the surface reaches about 7 °C, pathogens may
#P'Fy9?? Z0grow. A challenge study with Staphylococcus aureus will verify the microbial safety
6Zdj:?)A a5V2u*{}0of the product.
F:~:CEc0It should be noted that inoculated pack studies with pathogens should not be食品伙伴个性空间}6l0cq[
conducted in food industry laboratories that are located close to the food processing食品伙伴个性空间Uq'L*c P4M U
facilities because of the possible transfer of pathogens to food products. No sensory
"c(|)c0wZp ^[[029食品伙伴个性空间aQcQ~
panel can be applied to evaluate the inoculated samples other than visual食品伙伴个性空间*TR V Y;Zi5b`
observation.
_;v @4}],l4x019.5 Accelerated shelf life testing食品伙伴个性空间-_9I2f6`;{"T6P
19.5.1 Basis
)|S7i%n6qx5~0During product development, preliminary shelf life knowledge is often needed in食品伙伴个性空间RUw L/]G,p
addition to microbiological safety. Shelf life testing experiments at this stage are often食品伙伴个性空间Nb#T-Lu w |
accelerated to evaluate the effects of various formulation and processing parameters
xJ`u^ _ j/B$V0on shelf life stability of the product being developed periodically since one can not
'?#C*xR(wc'G$d3_0afford the relatively long shelf life period for a frozen food stored under normal freezing食品伙伴个性空间 Nw\-pGU
conditions. In addition, temperature fluctuations may occur in distribution and retail
rdNe\&Bw7x` Y0holding for frozen storage. Thus kinetic studies at several temperatures within that
M:A+x6|%Zu8x,hd4j0range are necessary to predict its shelf life. Accelerated shelf life testing conducted at
Z Q?}s sX-Y%wN0elevated isothermal temperatures and/or with freeze/thaw cycles for frozen products食品伙伴个性空间H?7h:}:p)[sr[
have been used extensively for several decades by industry and government
;?6JD0p2R T x0agencies (Labuza and Schmidl, 1985). The Arrhenius relation and the Q10 approach食品伙伴个性空间 L#aMc4Q mZ|;QT
are used to extrapolate the results to the expected lower storage temperature.食品伙伴个性空间6j#bJnU zFj ^
Acceleration factors other than temperature have also been studied for some other
M gi#|k C1_?a0deterioration modes, such as moisture gain or loss and lipid oxidation (Labuza, 1984),
tE/C `4Prmu}0but rarely done for frozen foods.食品伙伴个性空间Y/U WB0t{I3O7_/k
19.5.2 Unique procedures
;X%e%cvu1i:mL0Step 1: Clarify test objectives — In general there are two occasions where食品伙伴个性空间&\1gA y4XuGd g'q
ASLT applies: i) estimate approximate shelf life quickly during development stage; ii)食品伙伴个性空间3_{:Q \f``m"V
collect kinetic parameters for actual shelf life prediction as in the marketplace, which is
,CLc[}(X`4k0conducted generally near the launch phase.
h"t o6w}0Step 2: Select accelerating temperature conditions — Suggested isothermal食品伙伴个性空间{C0x0Hkx
accelerating conditions for frozen foods are -15, -10, and -5 °C with a control stored at
ZZy_#M0< -40 °C (Labuza and Schmidl, 1985). The inherent assumption is that the
0F'pM-o dq.g5|6M0deterioration mechanism is the same across the temperature range although as noted食品伙伴个性空间 I m"r__
earlier, there is concern about how close to freezing one can go.食品伙伴个性空间d(Z4Oh-_/ol
Moisture migration from the food into the surrounding air with resulting
V+My;|+]&K0lRI1G0desiccation of the food and ice crystal formation in the package is a major mode of食品伙伴个性空间:CSFlmWU'X
deterioration of frozen foods under fluctuation temperature conditions. Cycling
|0t7qU#J XY%c2t7@G0temperature 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"[v w~4P8A7b)z*Y
day at each temperature and then repeated several times. A freeze-thaw cycling study
4BCePZ @b/K/q~:T VI0is also needed to determine its effect on sensory quality. Usually, the high temperature
:WF p(z1Ur030食品伙伴个性空间c?7C/e Q.c E
can be much lower than that used in a microbial challenge study unless microbial食品伙伴个性空间 v4b}ZN4l'dAs#J ^
survival is still a concern. Typically, cycling temperature/time can be three to five 24
-[(QTp6MfK0hour cycles between -18 °C and -7 °C, or between - 18 °C and 7 °C, depending on
IU2f&M$[ lj8U8OT0the product.
h{i ~}i0Step 3: Estimate testing time and sampling frequency— Testing times are食品伙伴个性空间x0EDS*Kg%C.z
dependent on a desired shelf life at target storage conditions. For example, given that
3`_I Ftr1o:Oo0a shelf life of 12 months at -18 °C is desired, a shelf life plot can be constructed. Figure
I$b!E!@0yD2J t8U019.11 indicates the test time at -4 °C that equates to 12 months at -18 °C for various食品伙伴个性空间 [{/m%a?i[
Q10 values. Sampling times at -4 °C should thus be 1 wk, 2 wk, 1 month, 3 months, and食品伙伴个性空间*|yOP-^ F
4.5 -5 months. Most published results suggest that Q10 values for vitamin C loss and食品伙伴个性空间'u,Li!pI#Wn v mln(c j
quality loss in frozen vegetables range from 2 to 20 and that the shelf life of vegetables食品伙伴个性空间a,sC-H/s U5z ^#D
is only 6-8 months at -18 °C (Labuza, 1982). Considering these Q10 values, a product
-}Lbq`G:oh0that does not retain good quality for 4.5 months at -4 °C may not retain good quality for食品伙伴个性空间[;iOU m-f
12 months at -18 °C. This also suggests the sampling frequency shown in Table 19.6.食品伙伴个性空间$G2kR:nQ@z
All simple tests should be conducted at each sampling time, while sensory testing食品伙伴个性空间9\&I1I)Tq
should be concentrated mainly toward the end of the test sequence with a few near the食品伙伴个性空间.wFS#j'iQ1_3C2q"O
beginning.食品伙伴个性空间A9T&@-q7PMnn(_
0 5 10 15 20 25 30
cGD@9v ^Lu0.1
#L%ae#_nj}01食品伙伴个性空间*^@efQG*V
10
fLW;pw`,QD{/}0100食品伙伴个性空间+C"E(N(uO F
T (°F)食品伙伴个性空间KvOa {+vK H
Shelf life 12 mo at 0食品伙伴个性空间W,V"DC a1rws
ASLT at 25 °F食品伙伴个性空间D(a5?ly9h`2_L
4.5 mo
W [da1S01.2 mo
N+A1EE$j,] Q5f/bs D014 days食品伙伴个性空间jMg+r}m
6 days
;`"~ u/dW;Y0]0Q10=2食品伙伴个性空间G8@I ^/\\0?
Q10=5食品伙伴个性空间,L)U| {v b
Q10=10
f*H*L8r*@0Q10=20食品伙伴个性空间0H:dq m!g
Figure 19.11 Shelf life testing times at 25 °F equivalent to 12 mo at 0 °F
u6a*u;K+A0for various Q10 values.食品伙伴个性空间}\fXF
Table 19.6 Sampling frequency for frozen pizza ASLT
b-\0AP1W031
tug-Ps%u0Temperature (°C) Sampling times (wk)食品伙伴个性空间 b\ azS;I
- 4 1, 2*, 3, 4, 5, 8, 12, 14, 16*, 20*
9I+GE#M X@h)p+M0- 7 2, 4*, 10, 15*, 20*食品伙伴个性空间!P+uq}P@+@\:t
- 10 4*, 10, 15*, 20*
%B%iSkU?t)f0* Sensory test times Source: Labuza (1986)食品伙伴个性空间/qh)Az0F5c3T
Step 4: Determine end point — Figure 19.12 shows a comparison of times to食品伙伴个性空间x6G{JV#fc4U&v-f9D$a
various levels for the loss of vitamin C in frozen spinach as a function of temperature
0K/tT SG ]-d#]0(Kramer, 1974). The dotted line represents the 80/80 rule, i.e., from a legal standpoint,
tsz @*p,C6|_m0for natural products, 80% of the tested sample must have no more than a loss of 20%
k;k/I1Ii'\8r0(i.e. 80% of the label value). Consumer sensory testing will not always give such a
7{h\a&~P0clear shelf-life result since different shelf life times can result using different quality食品伙伴个性空间5{%K*TCS+dI+\
attributes. Often professional judgment has to be made to decide what factor to use as食品伙伴个性空间4Ho{(@ H2U0r v9msR"Z
the base for the end of shelf-life of the product. When shelf life is unacceptably short,食品伙伴个性空间C(v$[`bS Y6a
adjustments should be made to the food, its environment, packaging, process and
T8M/P#f'?H)z0hygienic conditions, until a suitable extension of shelf life can be achieved. For some食品伙伴个性空间8a9~yI P,u
products, the test results may demonstrate that the target shelf life is not attainable. At
:w p/m*kf q2?-z0this point, the question of whether to launch the new product with a shorter shelf life or食品伙伴个性空间W @ O({gT.t*{8s
to abandon the entire project becomes a marketing decision.食品伙伴个性空间8Jb;iP5TTG;v
-20 -10 0 1 0食品伙伴个性空间K l`L4m'X$g_
1食品伙伴个性空间M9}5n U%tx}C!~Q8T
10食品伙伴个性空间:B zy6E9ss,O
100
H[mp j~cF0Storage Temperature (°F)食品伙伴个性空间bg7CETxoK-u
Shelf life (mo)食品伙伴个性空间.K+rdd9F{i
Figure 19.12食品伙伴个性空间)P"@IA"M
Shelf life of frozen spinach as a function of vitamin loss level食品伙伴个性空间b`Bwt.VI
50% loss
+uNt.e`K025% loss
IExn m3R010% loss食品伙伴个性空间TC)CJ/Hf h y
Quality (80/80 rule)食品伙伴个性空间.^u_F-T9b
32食品伙伴个性空间K |z-up%JM2t'Y
Step 5: Estimate kinetic parameters — From each test storage condition,食品伙伴个性空间4m|%f IO)LOi;f
estimation of k or q is needed to make the appropriate shelf life plot. From this one can
#GvNJ'_){0z0then estimate the potential shelf life and confidence interval for the storage condition.食品伙伴个性空间 nOgw Z ad v+UN
Then parameters for the Arrhenius relation and the shelf life plot are determined by食品伙伴个性空间J2iu!^$Q4dy
linear regression, which are used for shelf life prediction.食品伙伴个性空间 Yh_h*zU
Step 6: Extrapolate to normal freezing storage condition — The most useful
6fj#i#o)l!}LV0l0shelf life information is obtained for product kept at its intended storage temperature,食品伙伴个性空间.b#B] ~iDKo
which is about -18°C for retail frozen products and -23°C for distribution of frozen食品伙伴个性空间e2C9~ }axs
foods. Figure 19.13 demonstrates how the shelf life plot is used for extrapolation. It is
rvzk9H8QifV0always a good practice to compare a model's prediction against actual experimental
7I3MZfd"X8S+T0results because of the potential for errors from using the higher temperature data as食品伙伴个性空间4G"x"UA|
noted earlier besides the other errors suggested by Labuza and Riboh (1982). In
-r1b7lP C4Wx,YO0addition, the existence of a glass transition at a temperature between the test
{6D3[wN!Q ]4~0temperature and the prediction temperature would lead to error as shown by Nelson
hf#LV6J1d pd0and Labuza (1994). In the case of frozen foods, most likely the error would be an食品伙伴个性空间P nm T%~*P9|
under prediction of the shelf life.食品伙伴个性空间A^9u4Re6C|$@%T\ Yr
ln Q食品伙伴个性空间}PvJSD"{ bdtc:@
T食品伙伴个性空间HRX C({'j,u
T1食品伙伴个性空间(M`^M(r6e
T2食品伙伴个性空间P+U(nF.Rt
T3食品伙伴个性空间n u5L^^*c E9H"?
Ts (commercial storage temperature)
bD9dCm:{E,M0Figure 19.13 Extrapolation from ASLT食品伙伴个性空间;y oX4tB*`
Step 7: Predict quality loss for a fluctuating time-temperature distribution — The食品伙伴个性空间*^ B? ~9sU ev
prediction is based on two assumptions: (1) that there is no history effect from the食品伙伴个性空间1t.n\ O'F-q e+U
time-temperature variation and (2) that the key deterioration mode does not change as食品伙伴个性空间9W8I/E2_1mB1x b Q)e q
a function of temperature. The frozen spinach data shown in Figure 19.12 is used in食品伙伴个性空间.Q(W%e%s` `5QuM
the following example in Table 19.7 for a time-temperature distribution. The line食品伙伴个性空间%?2^.K[.d#q!zR6PO
33
/|;ch.c$|$W4Y5ReY0equivalent 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wrVBM3j;s.@
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
f)OG%[ ME+J0each temperature of exposure, the time on the 80/80 line is the time for 20% loss, thus食品伙伴个性空间aP&{xbdb
at -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9V9rOw3^d`8e8wws
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Xs3] K&Gt iy
left is 36 - 6.36 x 7.2 = 33.4 mg.
c$MPsH u,u6@7D0Table 19.7 Estimation of quality remaining of frozen spinach after exposed to a食品伙伴个性空间gtp2lHh"x9Wh^
variable time-temperature history with Ao = 36 mg/100g spinach.
6W9K^i"Fo:x0Temperature食品伙伴个性空间-ytrkSJ)x
(°F)
-{QfH7_ Wy0Time t食品伙伴个性空间;N*ba*` q6}'x
(months)
xe ^bZWW0q shelf life食品伙伴个性空间 Z!L#wUo1g
(months)食品伙伴个性空间V'f X(R2aT.P.^2A
fcon
6b5a8G}e(A8Mv0(t/q )食品伙伴个性空间:N^E%G thFV$}5V
Sfcon Aremaining食品伙伴个性空间)Kc4O j$_*gx1L
(mg/100g)
-sTFuBBm0-10 6 16.5 0.363 0.363 33.4
!h H4O%gVg4}PX0+3 1 4.5 0.256 0.619 31.5
_j5k,M/Q3D0+12 0.25 1.6 0.156 0.775 30.4食品伙伴个性空间3hJivA(Tw
Since as noted 80% of Ao is equal to 28.8 mg/100g at end of shelf life, this product is
4N!a/Z:g wh0still acceptable at the end of the set of three different time/temperature exposures. In食品伙伴个性空间E9sEx ~ U
fact, the shelf life left @ 5 °F = (1-0.775) x 3.3 = 0.74 months = 22 days.食品伙伴个性空间 XNsI mP\
19.5.3 Applicability食品伙伴个性空间Da9n AZW+O AZ)`t9y
Because of relatively long shelf life for frozen foods and the unique feature of freezing,食品伙伴个性空间c&^}#l.GT8@/C
the degree of temperature elevation is largely limited. Prediction of actual shelf life食品伙伴个性空间+lY,M9[&Y{ MB
from ASLT may be severely limited except in very simple food systems. Frozen foods食品伙伴个性空间7@xox;^
such as frozen pizzas, may present problems with moisture migration. The moisture食品伙伴个性空间0G{bw;BJ#hc
may diffuse from the pizza sauce which has a higher aw into the crust containing a食品伙伴个性空间l,R-y)\,n O iAd
lower aw, creating a pizza crust that is limp and soggy. Product development scientists食品伙伴个性空间&|$J0C6G&t
should only use the results as a guideline and must use as many storage conditions
L,`"R6L/}0as possible to minimize prediction errors.
7Z ODqW`,Ke u7H mu034
L [6j G+A KN&{0ASLT is just a quick method, which can not replace the normal storage tests
&DPn0ekNd vE&P0discussed next. Once it is verified that the extrapolation may be wrong, i.e., too large食品伙伴个性空间-|^,Q GZ O%T%E
an error, then a careful look should be taken at the deterioration mode, the experiment
tj-VkAd2v C7U0design and procedure, the data collected and the model developed. If the
&e(}/pf%E8{|C0extrapolation under predicts the true shelf life, then it becomes an economic concern, it
N8OMc&x0is over predicted, then reformulating may be necessary. If the shelf life prediction
1z~k(P2R+\YG"r }%Ee0indicates that the product meets the stability expectation, then the product has a食品伙伴个性空间NU(X ]%SMDm
chance of performing satisfactorily in the marketplace.食品伙伴个性空间$Z(d6rD"F'Wk
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experimental test batches to pilot plant and then to full scale production. Experience食品伙伴个性空间n,P:Ed/g-K
has shown that results of small-scale experiments in the laboratory may not be of食品伙伴个性空间[R}J*Y,y
much use for large-scale production (Graf and Saguy, 1991). Scale-up not only affects
3[:cH&d[Bf0the processability and quality of a food product, but it often alters its shelf life.
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microbial growth and chemical reactions leading to deterioration, scale-up may食品伙伴个性空间,z%Iw+`*`

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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space.foodmate.net2@9Q9Piv Z
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!
DmW&K(W:u#dw
lyn
请哪位高人翻译翻译,就太感谢了!
XRH2004的个人空间 XRH2004 发布于2009-04-14 20:36:56
冷冻食品保质期
请高人能否把他翻译成中文
sunjm0320发布于2009-04-21 09:44:09
这个很有用的,谢谢啊!
wtao-0678发布于2009-04-26 11:32:36
英文的,看不懂啊,那位大虾给翻译翻译就更好了
麦香豆发布于2009-04-27 10:53:41
神呀!E文专业地!!
KX-T7665发布于2009-06-29 12:04:49
回复 1# leesunny 的帖子
正想找有關資料,謝謝
food86发布于2009-06-29 13:19:00
只能认识单个单个的词,那位高手翻译一下啊
clyde-chen的个人空间 clyde-chen 发布于2009-07-20 10:49:57
下载学习中,谢谢楼主!
食品专业户发布于2009-07-23 16:33:34
正好想跟大家请教一个问题,食品的保质期是如何人确定的?
论道-竹叶青 论道-竹叶青 发布于2009-07-23 22:22:16
楼主太抬举我的水平了!
heiniuzxf发布于2009-07-24 08:32:04
有需要翻译资料的找我:heiniuzxf@126.com
binggan1217发布于2009-07-24 09:18:26
下载学习中,谢谢楼主!
junshengwang67发布于2009-07-24 10:31:13
保质期有以下确定方法:1.国家法律法规规定.
z+L*W_ hGU  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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