Total inactivation of lipoxygenase in whole soya bean by pulsed light and the effect of pulsed light on the chemical properties of soya milk produced from the treated soya beans

AbstractThe inactivation of lipoxygenase (LOX) in the whole soya bean prevents lipid oxidation that produces an off‐flavour of soya food. The inactivation of lipoxygenase in the whole soya bean by pulsed light (PL) was examined with three distances (5, 7 and 9 cm) from thePLstrobe and for different durations. Soya bean was treated withPLwith and without ice surrounding the soya bean sample tray for limiting the rise in sample temperature. Results show that without ice surrounding the sample tray, the lowestLOXresidual activity was 4.7%, 0.4% and 0.0% for 80‐s duration at 5 cm distance from thePLstrobe, 110 s at 7 cm from the strobe and 150 s at 9 cm from the strobe, respectively; the soya bean temperature after treatment was 109.6, 116.3 and 114.8 °C, respectively. The instantaneous temperatures of the soya bean core measured duringPLoperating were above 100 °C. The lipoxygenase band was disappeared after longestPLtreatments of each distance compared with theLOXband control as assessed by electrophoresis. The pulsed light had no negative effect on peroxide value of produced soya milk. However,PLreduced significantly the total solid amount and changed the colour of the produced soya milk. The residual activity with sample cooling by ice during treatment was 79.0%, 98.8% and 95.7%, with sample temperatures of 81.7, 91.2 and 66.9 °C, respectively. This study indicates thatPLillumination could fully inactivateLOXin whole soya beans, with the photo‐thermal effect ofPLas the main factor responsible for the inactivation ofLOX.