ANTIOXIDANT CAPACITIES OF RICE PROTEIN HYDROLYZED BY DIFFERENTS ENZYMES

During enzymatic hydrolysis of protein, the large complex structure protein molecules are broken down into smaller sized peptides and specific amino acids. This type of protein structure modification has an effect on its physicochemical and functional properties, with applications in the food and pharmaceutical industry. The aim of this study was to investigate the antioxidant capacity of protein hydrolysates of rice and possible applications in the food industry processing. In this work, two enzymes, Alcalase and Flavourzyme were used to obtain hydrolysates with different degree of hydrolysis (1%, 2%, 4%, 8% and 10%). The degree of hydrolysis (DH, %), defined as the percent ratio of the number of peptide bonds broken to the total numbers of bonds per unit weight, was determined using the pH-stat method. The antioxidant capacity of the protein hydrolysates of rice was evaluated by the ability to donate hydrogen to the stable free radical DPPH and ferric reducing antioxidant power (FRAP). A positive correlation was observed between antioxidant capacity and degree of hydrolysis, in which the higher DH provided a higher antioxidant capacity to the hydrolysates. For the hydrolysates obtained by Alcalase, the ability to reduce the ferric ion to ferrous in FRAP reagent increased from 644.24 ± 2.92 to 967.27 ± 4.72 µmol Trolox equivalents (TE)/g protein with DH. On the other hand, for Flavourzyme, this variation was 85.15 ± 0.85 to 156.21 ± 1.07 µmol TE/g protein. For the free radical DPPH scavenging activity, the results increased from 793.05 ± 1.92 to 958.61 ± 4.8 and 436.94 ± 0.96 to 516.94 ± 2.55 µmol TE/g protein with DH for Alcalase and Flavouzyme, respectively. For the intact protein, the antioxidant capacities by FRAP and DPPH were 46.67 ± 2.29 and 377.5 ± 3.33, respectively. Although the DH values were the same for both enzymes, the results clearly indicated that the type of enzyme had a significant role for antioxidant capacity. Both proteases contain catalytic sites that provide different substrate specificity to cleave distinct peptide bonds with different properties. Alcalase is an endopeptidase and has a range of specificity of peptide bonds for hydrolysis. Already Flavourzyme is a mixture of endoprotease, aminopeptidases and peptidylpeptidases. This study suggests that protein hydrolysates of rice are good sources of natural antioxidants that can be used as food supplement, additives for conservation or in the pharmaceutical industry.

Financial support: National Council for Scientific and Technological Development (CNPq).