Antiradical activity in soy protein hydrolysed by action of lactic acid bacteria

AGUIRRE, L.; HEBERT, E.M.; GARRO, M.; SAVOY DE GIORI, G.

San Miguel de Tucumán

Simposio; II SIMPOSIO INTERNACIONAL DE BACTERIAS LACTICAS. Tucumán; 2006

CERELA-CONICET

Soy proteins are widely used as functional or nutritional ingredients in a variety of food products. Enzymatic modifications with different proteases or microorganisms have been used to improve the functional properties and to obtain peptides with biological activities. In the last years, there has been increasing interest in the food industry for "natural antioxidants" as replacements for artificial ones. In this context, the search has been directed towards antioxidant peptides from natural sources. The objective of this work was to obtain protein hydrolysates with antioxidant activities using enzymatic action of lactic acid bacteria (LAB). As protein sources, we evaluated i) isolated proteins from soy (APS) obtained in the laboratory and ii) commercial soymilk (aqueous extract from soy, EAS). These studies were performed using concentrated cell suspensions of Lactobacillus (L.) paracasei subsp. paracasei (L. paracasei) CRL 207, L. delbruecki subsp. lactis CRL 581 and L. helveticus CRL 1062 that were obtained from cultures grown in chemically defined medium, incubated at the optimal temperature until exponential phase. The protein substrate and cellular suspensions, in phosphate buffer (0,1 M, pH 7,0) (2:1 ratio), were incubated during 6 h at 30 or 37ºC, depending on the microorganism used, and samples were taking at different times. The proteolytic activity was determined by using sodium dodecyl sulfate polyacrilamide gel electrophoresis (SDS-PAGE) and the released peptides were analyzed using high pressure liquid chromatography (HPLC). The antiradical activity was evaluated using the method containing 2,2-diphenyl-1-picrylhyrazyl (DPPH). All strains were able to hydrolyze soy proteins, independently of the protein source. The profiles resulting from the proteolytic action of the LAB, evaluated by HPLC, showed an increase in peptides of hydrophilic and hydrophobic nature. L. paracasei CRL 207 was able to release hydrophobic peptides with potential activity from APS during 6 h incubation. Antiradical activity determination in the hydrolysates indicated that these presented the greatest reactivity (59,6%) with respect to the other samples. These were comparable with the activity of a commercially used antioxidant (2,6-di-tert-butyl-4-metylphenol, BHT 10mM). LAB capable of releasing peptides with antioxidant activities from soy proteins constitutes an interesting biotechnological alternative for the design of novel functional foods.