Slide 1

Ong, Law - Hygrothermal Properties of FVFs

Reaction rate as a function of temperature and moisture content can be used to pre-
dict the extent of the deterioration of important nutritive factors during processing.
Generally, first order reaction is assumed for most food deteriorations (Equation 2.1)
unless the rate is too slow and zero order reaction has to be used (Labuza and Tannen-
baum, 1972).

k[A]

dt

d[A]=

(2.1)
where [A] (mol dm-3) is the concentration of the interested quality parameter and k
(s-1) is the temperature dependant rate constant which can be described by Arrhenius
equation (Equation 2.2). Details of quality parameters and quality attributes can be re-
ferred to Chapter 6.

E/RT

k k 0 e a

= −

(2.2)^
where k 0 (s-1) is the absolute rate constant, Ea (J mol-1) is the activation energy, R
(8.314 J mol-1 K-1) is the gas constant and T(K) is the absolute temperature. Table

2. 1Table 2.1 shows the typical activation energies for some deteriorative reactions oc-
   cur in food materials compiled by Labuza and Tannenbaum (1972). Integrated first or-
   der reaction rate in Equation 2.1 yields,

ln[A]=−kt+ln[A] (^0) (2.3)
A plot of ln[A] versus t gives a straight line with a slope of –k. Useful information can
be extracted from Equation 2.3, for instance, half life of the nutrient at a particular tem-
perature which is given by,

k

ln( 2 )

t 1 / 2 =

(2.4)

Table 2.1. Typical activation energies for some deteriorative reactions in food

Reaction Ea (kJ mol-1)

Diffusion controlled 0-34

Enzyme reactions 42 - 63

Hydrolysis 63

Lipid oxidation 42-105

Non-enzymatic browning 105-209

Spore destruction 251-335

Vegetative cell destruction 209-628

Protein denaturation 335-502

Ascorbic acid 42-126