Kinetics of Enzymatic Browning of Minimally Processed Iceberg Salad

Abstract

Iceberg lettuce (Lactuca sativa L.) is a highly perishable product and it is considered one of the most popular minimally processed vegetables. Commercially available iceberg lettuce has a short shelf-life of 7 days at 7°C. Enzymatic browning is one of the main factors affecting product shelf life when oxygen is present in the packaging system. For this purpose, the aim of this work was (i) to investigate the decay kinetics of minimally processed iceberg salad following polyphenols and browning index evolution at different temperature (4°C, 8°C, 12°C); (ii) to evaluate the effect of salicylic acid on enzymatic browning. Minimally processed iceberg samples were stored at 4°C, 8°C, 12°C in air for 14 days. Samples treated with salicylic acid were stored at 8°C for 14 days. Polyphenols and browning index were evaluated by spectrophotometric analysis. The kinetics constant and activation energy (Ea) has been calculated by non-linear regression. The enzymatic browning was well described by a pseudo first order kinetic. The kinetic constant at reference temperature (8°C) was 0.00948 h^-1 for polyphenols decay and 0.0184 h^-1 for browning index. Ea for polyphenols and browning index were 83.21 kJ/mol and 63.49 kJ/mol, respectively. Salicylic acid showed a significant effect on enzymatic browning kinetic by delaying the evolution of the reaction during the first days of storage.
Keywords: lettuce; oxidation kinetics; salicylic acid; storage temperature; polyphenols; quality