MODULATING THE GEL PROPERTIES OF SOY GLYCININ BY CROSSLINKING WITH TYROSINASE

Soy proteins have been widely applied in food products due to their high nutritional value and their ability to improve texture as gelation agents. The ability of gel formation of soy proteins or their fractions, induced by heat was widely investigated as well as by chemical means such as addition of formaldehyde. A biological approach was also evaluated and it was shown that soy crosslinking using microbial transglutaminase led to the formation of cold-set gels. However, there is a constant need for novel enzymes that offer new pathways for effective and specific biocatalysis of reactions that can modulate food functionality. This work is aimed at improving the functionality of soy proteins and their gel properties in order to facilitate their diverse applications in foods. To this end, we utilized tyrosinase from Bacillus megaterium (TyrBm). We investigated the crosslinking ability of TyrBm on glycinin-rich fractions by SDS-PAGE and demonstrated the formation of high-molecular weight fractions. The crosslinked protein was later used for gel preparation upon heating at 95°C (10% glycinin). Dynamic oscillation measurements show that the gelation point of the crosslinked glycinin occured at lower temperature compared with the native glycinin gel, and with higher modulus values. The textural characteristic of the gels was analyzed according to texture profile analysis (TPA) using a Texture Analyzer in the compression mode. The TPA curves suggest that the crosslinked gel was firmer (Hardness at 75% compression) and less resilient than the native glycinin gel (4-fold), whereas the native glycinin gel showed larger springiness values (2-fold). As the gels differ in their properties, they may be used for different food applications.