Production and In vitro evaluation of bioactive peptides resulting from hydrolysis of soybean meal through autoclave and bio-fermentation process

Soybean meal is widely used in animal feed production due to its high protein content and relatively good amino acid pattern balance. However, soybean meal contains several anti-nutritional agents that can affect the digestion and absorption of nutrients. To overcome these limitations, pre-processing of soybean meal through fermentation can be an optimal solution to eliminate anti-nutritional agents and improve the digestibility of nutrients. During fermentation, proteolytic enzymes produced by the microbial population hydrolyze proteins into free peptides and amino acids. This study aimed to produce bioactive peptides from soybean meal by fermentation by Bacillus subtilis, Bacillus licheniformis, Aspergillus oryzea, and hydrolysis by autoclave. Also, isolated and hydrolyzed protein sources were evaluated under in vitro conditions.

Soybean meal was first ground and then its protein was extracted through alkaline extraction and acid precipitation. Microorganisms were cultured in a specific culture medium and after growing in the liquid culture medium, they were added to the isolated protein and the fermentation hydrolysis process was performed on the isolated protein. The autoclave was used to perform the hydrolysis process by autoclave. The isolated and hydrolyzed protein sources were evaluated according to the standard methods to determine the nutritional value such as the amount of crude protein, organic matter, ash, dry matter, and ether extract. In vitro gas production test was performed to assessed effects of hydrolysis methods and hydrolysis extent on biological functionality of protein sources. To use ruminal fluid to perform the gas production test under in vitro conditions, three adult Holstein bulls with ruminal fistula were used. Finally, the data that were obtained from laboratory evaluation were statistically analyzed using a completely randomized design statistical model and the data were analyzed by SAS 9.4 software and GLM PROC command, and the means were compared by Tukey test method at the statistical level of 0.05.

The results of production and evaluation of isolated and hydrolyzed protein sources showed that during hydrolysis, minor changes were made in the chemical composition, but all four hydrolysis treatments increased the production of low molecular weight peptides. Also, it was found that the production of bioactive peptides from soybean meal by different methods has different efficiencies. The highest amount of low molecular weight peptides was produced by Bacillus licheniformis (0.483 μg / ml). Also, autoclave treatment led to the breaking of weak chemical bonds and increased production of small peptides. Also, the results of in vitro gas production method showed that hydrolysis of soybean meal by using A. oryzea increased the amount of gas production and the fermentable part (159.09 and 210.52, respectively).

The general results of the study showed that hydrolysis of soybean meal through bio-fermentation and hydrolysis by autoclave increased the production of bioactive peptides and Bacillus licheniformis produced the highest amount of peptides. Also, Aspergillus oryzea treatment compared to other treatments showed the greatest improvement in the amount of gas production and fermentable part.