Methods for food shelf life determination and prediction - Oxidation in Foods and Beverages and Antioxidant Applications - page 216

Fig. 9.10 Bleaching rate constants (k) of a saffron-containing beverage stored at 20 ëC
under increasing light intensity (L). Results of linear regression analysis are also shown
(Manzocco et al., 2008 with permission).

light the food is exposed to rather than to the environmental temperature. In this
regard, Fig. 9.10 shows the light dependence at 20 ëC of colour fading of a
saffron-containing beverage upon pigment oxidation under increasing light
conditions.
It is thus evident that light can speed up the oxidation rate of photosensitive
foods thus strongly affecting their shelf life. At constant temperature, a linear
relation between bleaching rate (k L ) and light intensity (L) was obtained:
k L mLn

9:10

where m and n are experimental parameters. Light could thus be easily used as a
non-conventional accelerating factor in shelf life testing by measuring bleaching
rate under increasing light intensity and then extrapolating the rate to the milder
conditions usually experienced by the product on the retail shelves.
It is also possible to integrate into a single model the effect of both light and
temperature:

ÿ pLq
R

ÿ T ÿ 1
T ref

k L mLne 9:11

where p and q are experimentally determined parameters. Such a model, which
was validated for a saffron-containing beverage (Manzocco et al., 2008), is
particularly useful and versatile since it allows the prediction of the bleaching
rate at any combination of temperature and light intensity within the
experimental range considered. In fact, if the beverage is stored in the dark
(L 0) at increasing temperatures, the model is brought back to the Arrhenius
equation. By contrast, if the beverage is stored at room temperature under
increasing light intensity, the model returns to equation 9.10.