the handbook of food engineering practice crc press chapter 10 ...

plot will give a relatively straight line in a shelf life plot, i.e. Q 10 and b are functions of
temperature:
ln Q 10 = 10 b = E A
R
10
T (T+10) (31)
The variation of Q 10 with temperature for reactions of different activation energies is
shown in Table 3.
Table 3. Q 10 dependence on E A and temperature.
E A Q 10 Q 10 Q 10 Reactions in E A range
kJ/mol at 4°C at 21°C at 35°C
50 2.13 1.96 1.85 Enzymic, hydrolytic
100 4.54 3.84 3.41 Nutrient loss, lipid oxidation
150 9.66 7.52 6.30 Non enzymatic browning
Similarly to Q 10 the term Q A is sometimes used. The definition of Q A is the
same as Q 10 with 10 °C replaced by A °C :
A/10
Q A = Q 10
(32)
Another term used for temperature dependence of microbial inactivation
kinetics in canning and sometimes of food quality loss (Hayakawa, 1973) is the z-value.
The value of z is the temperature change that causes a 10-fold change in the reaction rate
constant. As in the case of Q 10 , z depends on the reference temperature. It is related to b
and E A by the following equation
z =
ln 10
b
=
(ln 10) R T2
E A
(33)
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