Abstract

Enzymatic hydrolysis is an agro-processing aid that can be utilized in order to improve nutritional quality of protein extracts from many sources. In this study, protein extracts from ungerminated and/or germinated local Egyptian soybean and lupin flours were hydrolyzed using the enzyme papain. The hydrolysis processes were carried out for 2 h and aliquots were withdrawn at different time intervals. We have analysed the protein hydrolysate after 30 min hydrolysis as an example of a partially hydrolyzed protein, and after 120 min as an example of greatly hydrolyzed protein. The hydrolysate (2 h treatment at 80°C and pH 7.4) from both soybean and lupin flour contained significantly decreased trypsin inhibitor activity and urease activity, and a reduced phytate content, which improved the overall protein quality. Hydrolysis caused almost complete inactivation of urease in all soybean and lupin samples regardless if the seeds were germinated or not. High protein content, nitrogen solubility and in vitro protein digestibility was shown after hydrolysis. Total protein content (in g/100 g extract) increased in hydrolyzed samples from 48.1 to 51-60 for soybean (dependent on pre-treatment) and from 36.8 to 39.9-48.6 for lupin. Total essential amino acid content was also increased in papain hydrolyzed samples, compared to that in raw and germinated legumes. More specifically, the amount of lysine, sulphur amino acids, histidine, and to a certain extent isoleucine and threonine increased in samples from both legume species. All soybean samples exhibited antioxidant activity while in lupin samples, only those subjected to hydrolysis showed activity. Generally, it was clearly observed that the longer the duration of enzymatic hydrolysis (within the time frame of the experiment), the higher the improvement of the nutritional quality.

Key words: Lupin, soybean, germination, enzymatic hydrolysis, papain, protein extract, nutritive value.

Abbreviation

Abbreviations: AOA, Antioxidant activity; EAA, essential amino acids; TIA, trypsin inhibitor activity; and UA urease activity.