Inactivation of lipoxygenase in soybean by radio frequency treatment

Polyunsaturated fatty acids are oxidised to generate beany flavour under catalysis of lipoxygenase (LOX). Using conventional thermal treatment to inactivate LOX lead to a serious nutritional and functional loss in soybean products due to the prolonged exposure to the high-temperature environment. Radio frequency (RF) is a different type of heating technology that sample is heated inside and outside at the same time with deep penetration. RF treatment was proposed to process soybean to rapidly inactivate LOX while remaining the quality and functional properties of soybean product. The results showed that the inactivation rate of LOX subjected to RF treatment for 210 s was 94.30%, as compared with 3.08% under conventional thermal treatment (110 degrees C) for the same duration. Functional properties of soybean protein isolate (SPI) after RF treatment were much higher than that of SPI with conventional thermal treatment. Analysis of the volatile compounds of soy milk indicated that the relative concentration of hexanal decreased from 521 to 116 mu g L-1 and that of 1-hexanol decreased from 271 to 6.99 mu g L-1. Therefore, RF treatment could better improve the sensory properties of soy milk.