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

very small, allowing us to treat it as an irreversible reaction. In most cases the
concentration of the reactant that primarily affects overall quality is limiting, the
concentrations of the other species being relatively in large excess so that their change with
time is negligible (Labuza, 1984). That allows the quality loss rate equation to be
expressed in terms of specific reactants, as:
r = -d[Α]
dt = k f ' [Α] α (6)
where α is an apparent or pseudo order of the reaction of compoment A and k f ' is the
apparent rate constant. Another case that can lead to a rate equation similar to equation (6)
is when the reactants in reaction (2) are in stoichiometric ratios (Hills, 1977). Then from
equation (3) we have:
r= k f
∏
i
m [A i ] n i = k f
⎝
⎜ ⎛
m
∏
i
µ i
ni
⎠ ⎟⎞
⎡A 1⎤ ∑ n i
⎣n 1 ⎦
(7)
or
r = -d[A]
dt = k f ' [A] α (8)
where A = A 1 and α = Σn i, an overall reaction order.
Based on the aforementioned analysis and recognizing the complexity of food
systems, food degradation and shelf life loss is in practice represented by the loss of
desirable quality factors A (e.g. nutrients, characteristic flavors) or the formation of
undesirable factors B ( e.g. off flavors, discoloration). The rates of loss of A and of
formation of B are expressed as in eq. (6), namely:
7