Protease technology for obtaining a soy pulp extract enriched in bioactive compounds: isoflavones and peptides

Abstract

This work presents a new bioprocess process for the extraction of bioactive components from soy pulp by-product (okara) using an enzymatic technology that was compared to a conventional water extraction. Okara is rich in fiber, fat, protein, and bioactive compounds such as isoflavones but its low solubility hampers the use in food and fertilizer industry. After the enzymatic attack with endoproteases half of the original insoluble proteins were converted into soluble peptides. Linked to this process occured the solubilization of isoflavones trapped in the insoluble protein matrix. We were able to extract up to 62.5% of the total isoflavones content, specially aglycones, the more bioactive isoflavone forms, whose values rose 9.12 times. This was probably due to the increased solubilization and interconversion from the original isoflavones. In conclusion, our process resulted in the formulation of a new functional product rich in aglycones and bioactive peptides with higher antioxidant potency than the original source. Therefore, we propose that the enzymatic extraction of okara bioactive compounds is an advantageous tool to replace conventional extraction.

Keywords: Antioxidant; Bioactive peptides; Enzymatic extraction; Food chemistry; Food science; Isoflavone; Okara; Subtilisin.

Fig. 1

Chromatography profile of the soluble protein content of okara according to its molecular weight using a Superdex Peptide 10/300GL column.

Fig. 2

A. Solubility of okara at different pH values after subtilisin treatment or using water as negative control. B. Soluble protein (mg/g of dry okara) extracted after subtilisin treatment at different pH values or using water as negative control. Bars with different letters are significantly different (p < 0.001).

Fig. 3

Linear relationship between soluble proteins and isoflavones extracted from okara.

Fig. 4

Reducing activity of okara extracts at different pH values, with or without subtilisin treatment using the FRAP method. Bars with different letters are significantly different (p < 0.001).