Effects of isolation, enzymatic hydrolysis, heating, hydratation and Maillard reaction on the antioxidant capacity of cereal and legume proteins

The antioxidant capacity of maize proteins, wheat gluten, pea protein isolates and hydrolysates and melanoproteins (MRPs) was evaluated as a radical scavenging activity against ABTS (22-azino-bis/3-ethil-benothiazoline-6-sulfonic acid) reagent by the direct procedure. In addition, the effect of high temperature and water during thermal treatments on changes of the antioxidant capacity of proteins was investigated. The concentration of total cysteine, free sulfhydryl groups (-SH) and disulfide bonds (-S-S) were determined using Ellman's reagent, 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) and disodium 2-nitro-5-thiosulfobenzoate (NTSB2-). Wheat gluten, as the most complex protein, had higher concentration of disulfide bonds (4537 nmol/mg) and total cysteine (93.88 nmol/mg) compared to other tested proteins and showed the highest ABTS radical scavenging activity (74.39 mmol Trolox/kg). The antioxidative capacity of tested proteins was correlated negatively with free -SH group concentration and positively with total cysteine and -S-S bond concentration indicating a high effect of physical structure of a protein on its antioxidative properties. The antioxidant activity of melanoproteins formed in pea protein isolate/glucose model system during heating was threefold higher than that of initial pea protein. However, the highest amount of furosine was also formed in this model system under the same heating conditions. (C) 2012 Elsevier Ltd. All rights reserved.