Methods for food shelf life determination and prediction - Oxidation in Foods and Beverages and Antioxidant Applications - page 209

excessive levels of rancidity, which are not relevant to normal storage
conditions. For instance, Kaya et al. (1993) evidenced an overestimation of the
induction periods at room temperature when performing the tests at
temperatures >100 ëC. In addition, a kinetic study of olive oil triacylglycerol
oxidation indicates that the Arrhenius equation could be employed to describe
the temperature dependence of primary and secondary oxidation product
formation only between 25 and 75 ëC (Gomes-Alonso et al., 2004). According
to Frankel (2005), the more polyunsaturated the oils, the lower the temperatures
that should be used to test their oxidative stability; for instance, vegetable oils
should be tested at temperatures lower than 60 ëC while fish oils only below
40 ëC. Beside the rancidity level reached in ASLT, the eventual thermal
degradation of minor compounds with pro- or antioxidant activity could
become critical since they can modify the temperature dependence of the
overall oxidation rate of lipids.
Additional and even more intricate complications arise in multi-component
foods, in which lipids, carbohydrates and proteins could react at high
temperatures producing new compounds. The latter could affect the oxidation
rate by acting as pro- or antioxidants, e.g., Maillard reaction products. Moreover,
it is evident that the successful application of the Arrhenius model is that food is
able to withstand the increase in temperature without leading to dramatic
development of phenomena other than oxidative reactions responsible for
product unacceptability at usual storage temperatures. For instance, at high tem-
perature, pigment bleaching upon oxidation can be masked by the concomitant
Fig. 9.5 Temperature and water activity combination discriminating conditions
associated to the prevalence of carotenoid oxidation or non-enzymatic browning in
tomato derivatives.