Enzymatic modification as a tool to improve the functional properties of heat-processed soy flour

BACKGROUND: There are a number of antinutritional factors present in soybeans that exert a negative impact
on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are protease
inhibitors and lectins. Protease inhibitors show antinutritional effect and moreover the digestibility of the protein
is limited by the presence of these antinutrients. The aims of the present study are (1) to study the effect of
autoclaving on the trypsin inhibitor inactivation, nitrogen solubility and protein digestibility of defatted soy flour
and (2) to study the effect of enzymatic modification on the functional properties of autoclaved soy flour.
RESULTS: The solubility of the soy flour decreased with increase in autoclaving time. Partial hydrolysis of the
autoclaved soy flour increased its acid solubility (pH 4.5) from 17% to 56% over a control value of 24% without
affecting its functional properties. Inactivation of trypsin inhibitors improved the protein digestibility of soy flour
from 25% to 95%. Particle size analysis of the autoclaved flour indicated the formation of soy protein aggregates,
which resulted in poor solubility. The enzymatic modification of autoclaved soy flour resulted in its property as a
good emulsifying agent with an emulsion capacity of 118 ± 4mL.
CONCLUSION: Enzymatic modification of the heat-processed soy flour increased its solubility and other
functional attributes. The increased acid solubility would be advantageous in the utilization of soy proteins
in acidic foods. Thus the autoclaved and partially modified soy flour is a potential source for specific functional
foods.