Okara is a protein-rich byproduct from soymilk production. It has little market value, so it is usually used as animal feed or discarded. The growing consumption of soy-based products has lead to the search for more sustainable soy processing with greater profits. Soymilk obtention includes a step of grinding in cold or hot water in which the cell walls are broken. However, some cells are not damaged. Enzymatic-assisted pretreatment (EAP) could improve protein extraction by breaking these cells. The aim of this work was to evaluate the effect of the grinding type and the EAP on the extraction yield, thermal behavior and protein solubility of concentrates obtained from okara.

The okara used was from hammer (water at 90ºC) (HO) and disc milling (water at 20°C) (DO). PCD-T and PCH-T protein concentrates were obtained by extracting proteins from DO and HO by solubilization at pH 8.0 and subsequent precipitation at pH 4.5 (traditional method). Also, an EAP with Viscozyme was made prior to extraction at pH 8.0, obtaining PCD-E and PCH-E. Protein content was determined by the Kjeldahl method (Nx6.25) and thermal behavior was determined by DSC for HO and DO and their protein concentrates. The protein solubility of the concentrates was quantified by the BCA method (pH range: 2.5-11.5).

The heat-treated samples (hammer mill) showed lower extractability. There was a significant increase in extraction yield in the EAP samples (17 times for HO and 3 times for DO). The thermal profiles of HO, PCH-E and PCH-T did not present the characteristic endothermic peaks of soy proteins, which indicates that the thermal treatment probably denatured them. The protein solubility presented the typical U-shape with a minimum at pH 4.5.

Disc milling leads to better protein yields and less protein denaturation. The EAP increased the yield. These results encourage the use of this byproduct to obtain protein concentrates that could be utilized in nutrition and as functional ingredients.