ABILITY OF LACTIC ACID BACTERIA TO BREAKDOWN SOYBEAN PROTEINS

AGUIRRE L.; SAVOY DE GIORI G.; KAUL P.; GARRO M.S.

San Miguel de Tucumán. Tucumán

Simposio; III Simposio Internacional de Bacterias Lácticas; 2009

CERELA-CONICET

Soybean is rich in several proteins (40-50%) most of which contribute to nutrition and good health. Recently, interest in the composition of soy and its fermented products has grown since potential anti-carcinogens, antioxidant, and other therapeutic agents have been reported. In soy hydrolysate and soy-fermented foods, the proteins are only partly hydrolyzed because of the inability of most proteases to cleave glycoproteins, phosphoproteins, or domains that contain a high number of disulfide bridges. The loss of the native protein conformation during heat treatment increase accessibility of the enzyme to cleavage sites. The action of proteolytic lactic acid bacteria (LAB) enzymes is well known on different substrates such as casein. However, this effect on soy proteins has not been studied in detail. The aim of this work was to evaluate the action of the proteolytic system of LAB on thermal treated soybean proteins. Native soy protein isolate (SPI) and denatured SPI (boiling SPI for 10 min) were evaluated as different protein sources. SPI was obtained from defatted soy flour. Concentrated cell suspensions of Lactobacillus paracasei subsp. paracasei CRL207, L. delbruecki subsp. lactis CRL581 or L. helveticus CRL1062 grown in a chemically defined medium were used. The cell: protein mixture (2:1 ratio) was incubated at 37ºC for 24 h taking samples at different periods. The hydrolysis of SPI and denatured SPI was evaluated by the o-phtaldialdehide (OPA) test, SDS-PAGE and the released peptides were analyzed using RP-HPLC. Denatured SPI was hydrolyzed 52% by the strain CRL 207, the a- and a-´ subunits of the b-conglycinin were the preferred substrates, and the basic subunit of the glycinin was the less degraded. The strains CRL 581 and CRL 1062 showed the lowest proteolytic activity (26 and 18% degradation, respectively) on the denatured SPI. The release of smaller peptides than the basic subunit of glycinin was observed for the strains CRL 207 and CRL 1062 after 12 h of incubation. Thermal processing changed the structure of soybean proteins and enhanced protein hydrolysis by LAB more than 50%. The RP-HPLC profiles obtained with the LAB strains showed the release of hydrophilic and hydrophobic peptides. The proteolytic enzymes from L. paracasei subsp. paracasei CRL207 showed the highest activity on native and denatured SPI. Thus, LAB able to release peptides from different soy protein matrix may constitute an interesting source of health benefitial peptides.