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Processing and Bioavailability (WG2) page 42
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2. Heat damage and antioxidant power
When evaluating the effects of heat treatments on the antioxidant activity of tomato
products, the formation of Maillard reaction products must also be considered. HMF and
furosine (ε-N-(2-furoyl-methyl-L-lysine) formation in heat-treated tomato products has been
studied by Hydalgo et al. (1999). In this study, HMF and furosine reaction kinetics were
examined in four tomato products with differing dry matter content (from 10.2 to 34.5%) over
a temperature range of 80-120°C. The reactions followed a pseudo-zero order kinetics; Ea
values were 139.9 kJ/mol for HMF and 93.9 kJ/mol for furosine formation. Furosine
concentration was also determined in many commercial products (detecting values from 43 to
140 for tomato pulp, from 93 to 132 for tomato sauce, and from 220 to 468mg/100 g protein
for tomato paste) and during the industrial production of tomato pulp and paste (Hydalgo et
al., 1998). This study led to the conclusion that furosine can represent a sensitive heat damage
index in tomato products. The interest in Maillard reaction products is due to their activity as
pro-oxidant and antioxidant compounds.
Anese et al. (1999) studied the antioxidant properties of tomato juice as affected by
heating (70° or 95°C for up to 50 h). The antioxidant activity was measured as peroxyl radical
quenching and oxygen scavenging activity. A decrease in the antioxidant potential was found
for short heat treatments; this decrease was ascribed to both degradation of natural antioxidant
components (such as ascorbic acid) and the formation of early Maillard reaction products with
pro-oxidant properties. However, prolonged heating caused a recovery of the initial
antioxidant activity and then an increase in the overall antioxidant activity. This was ascribed
to the formation of melanoidins, which exert antioxidant activity during the advanced steps of
the Maillard reaction.