Modelling the stability of lycopene-rich by-products of tomato processing

Tomato by-products were produced by puree manufacturing from heat-stabilised fruits and raw fruits to simulate both conventional and innovative processing technologies. By-products were freeze-dried, ground and stored in five relative humidity environments in the range 11-75%, for 4 months at 30 degrees C. The aims were: (a) to investigate the effect of heating applied during tomato processing on by-product hygroscopicity and stability, (b) to find out the optimal water activity (a(w)) range for by-product stability. Hygroscopicity was studied by applying the Guggenheim-Anderson-de Boer (GAB) model. By-product stability was studied by evaluating the kinetics of lycopene, beta-carotene rutin and chlorogenic acid degradation and the changes in Hunters colourimetric parameters during storage. By-products obtained from heat-stabilised fruit and raw fruits had the same hygroscopicity, with an average estimated n(sm) value of 0.080 +/- 0.013 kg water/kg dry solids corresponding to the mean a(w) of 0.44 and the confidence interval of 0.31 < a(w) < 0.51 (on the 95% probability level). During storage, in both by-products the rate constant for lycopene degradation was maximum at the a(w) level of 0.17 (half-life time was 38 d); it then decreased by more than threefold with increasing the a(w) level up to 0.75 (half-life time was 138 d). beta-Carotene degradation rates had the same order of magnitude as those of lycopene and decreased with increasing the a(w) level an the heat-treated by-product. However beta-carotene degradation was accelerated at a(w) levels >= 0.56 in the by-product obtained from raw fruits suggesting the involvement of lipoxygenase. Chlorogenic acid and rutin were more stable than the carotenoids and showed an opposite dependence of their stability on the a(w) level, being significantly degraded only at the highest a(w) level. The degradation of these phenolics was higher in the by-product obtained from raw fruits, indicating the likely involvement of polyphenol oxidase. The colour difference Delta E represented the sum of different degradation processes, indicating that for maximum stability, i.e. minimal Delta E variation, a dehydration level corresponding to 0.22 <= a(w) <= 0.56, has to be achieved and then maintained by preventing moisture exchanges with both environment and other food components. (C) 2010 Elsevier Ltd All rights reserved.