Bioproduction of novel proteases and process flavours from agro-industrial wastes

Abstract

The bioproduction of promising compounds from wastes, which are found in abundance as byproducts during food processing, receives a global interest. The present study aimed at using waste of cabbage leaves and rice bran as potential substrates for the production of proteolytic bacteria and process flavours. Two newly protease producing bacteria strains, isolated from cabbage leaves powder and defatted rice bran, were identified as Bacillus velezensis and Bacillus siamensis, respectively. The optimum activity of the partial purified proteases from these two bacteria was attained at 30 min, 50°C and pH 7. Cabbage leaves and rice bran protein concentrate were hydrolyzed, separately, by a mixture of the two purified proteases, at optimum conditions. The two hydrolysates, supplemented and unsupplemented with the appropriate flavour precursors (amino acids), were used, separately, as substrates for the biogeneration of the desired flavours by Corybacterium glutamicum incubated for 9 days. The highest degree of hydrolysis of cabbage leaves waste and rice bran hydrolysates were 30.6 % and 17.8 %, respectively. The higher intensity of beef-like aroma of cabbage leaves hydrolysate supplemented with cysteine and thiamine compared to that unsupplemented was attributed to its high content of the most potent odorants of beef aroma. In the same context, the higher score of nutty-like aroma of rice bran hydrolysate supplemented with lysine and threonine compared to the unsupplemented hydrolysate was mainly correlated to its high content of pyrazines, the key odorant of nutty aroma. The results revealed that the ability of Corybacterium glutamicum for biosynthesis of the desired aroma is mainly dependent on the composition of the substrates.