Enzymatic deglycosylation of soy proteins as a method to increase the efficiency of their hydrolysis

Objectives. Soy protein hydrolysates are now widely used in the food industry, fish farming, poultry farming, livestock farming, as well as in medical preparations. The most effective method for their production is enzymatic hydrolysis. However, even with optimal proteolysis parameters, it is not always possible to achieve the required degree of hydrolysis. For this reason, various technological approaches are used to more intensively break down soy proteins, including the addition of enzyme preparations and pretreatment of the protein substrate. β-Conglycinin, one of the main soy proteins, is a glycoprotein whose carbohydrate portion consists primarily of mannose residues. We hypothesize that deglycosylation of β-conglycinin by an enzyme preparation with mannanase activity as a pretreatment of the soy substrate will lead to change in the structure of its protein portion due to the destruction of the carbohydrate component to increase the accessibility of peptide bonds to proteolytic enzymes. Thus, the work sets out to study the effect of enzymatic deglycosylation on the efficiency of soy protein hydrolysis.

Methods. Deglycosylation of β-conglycinin, hydrolysis of polysaccharides and lipids were performed by the Complex-concentrate enzyme preparation (Ferment, Republic of Belarus). Protein hydrolysis was carried out by the Protozyme C330 enzyme preparation (Ferment, Republic of Belarus). The formation of reducing sugars was confirmed by the Miller method. The degree of protein hydrolysis was determined by the pH-stat method. The molecular weight distribution of peptide fractions was analyzed by low-pressure liquid gel chromatography on a column with Sephadex^® G-50 Medium. Computer processing of the elution profile of peptide fractions was performed in the OriginPro 8.5.1 program using the Gauss function.

Results. It is established that the treatment of soy flour by the Complex-concentrate enzyme preparation (enzyme-substrate ratio 1 : 40, hydromodule 1 : 10) promotes the breakdown of both free oligo- and polysaccharides, as well as the carbohydrate component β-conglycinin. Proteolysis by the Protozyme C330 enzyme preparation (enzyme-substrate ratio 1 : 20, pH 7.5, 50°C, 3.5 h) carried out following 20 h of deglycosylation results in a product with a degree of hydrolysis of 56.3%. The content of low-molecular-weight peptides in soy hydrolysate is 83.9%. Proteolysis without enzymatic destruction of the carbohydrate part of β-conglycinin is shown to be characterized by a degree of hydrolysis of 9.2%.

Conclusions. A pretreatment approach involving deglycosylation of enzymatic β-conglycinin can be used to significantly increase the degree of hydrolysis of soy proteins.

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