Inactivation of Pichia membranaefaciens in Soybean Paste by Dual-Frequency and Moderate Thermosonication

Dual-frequency and moderate thermosonication (TS, 300 + 300 W, 20 + 40 kHz, 25~60 °C) was employed to inactivate <i>Pichia membranifaciens</i> in soybean paste. The aim was to evaluate the effect of TS on the inactivation of <i>P. membranaefaciens</i> and on the quality of soybean paste. The Weibull model fitted the survival data of <i>P. membranaefaciens</i> in thermosonicated soybean paste well and a decrease of 5 log of <i>P. membranaefaciens</i> in soybean paste was obtained at TS_50°C, TS_55°C, TS_60°C, and T_65°C for 15.41, 7.49, 2.27, and 18.61 min. Scanning electron microscope observation revealed TS_50°C damaged the cell structure, leading to the leakage of intracellular contents. The physicochemical properties of soybean paste treated by TS were more retained than in paste treated by heat. The GC-MS analysis indicated that the flavor components had increased after TS treatment, especially at TS_50°C. In conclusion, TS can inactive <i>P. membranaefaciens</i> in soybean paste without causing significant changes in its physicochemical and flavor qualities.