Effects of ultrasound combined with mild heat and potassium sorbate on Pichia membranaefaciens and the quality of soy sauce

The aim of this study was to investigate the effects of ultrasound (US) combined with mild heat (T) and potassium sorbate (PS) on Pichia membranaefaciens in soy sauce and the quality of soy sauce. The maximum reduction of P. membranaefaciens was 5.34 ± 0.15 log after thermoultrasound (TS, 300 W, 10/3 s, 20 + 40 kHz, 60°C) + PS (0.1 mg/mL) treatment for 20 min. Physicochemical properties, including pH and total acid of soy sauce, did not change significantly after TS + PS treatment. Electronic nose analysis showed changes in the flavour of soy sauce after different treatments. A total of 122 and 125 volatile compounds were detected by SPME-GCMS before and after TS + PS treatment respectively. T₉₀ (soy sauce processed at 90°C) treatment decreased the content of the flavour compounds greatly, while TS + PS decreased the content of the flavour compounds slightly in soy sauce. TS + PS treatment inactivated P. membranaefaciens effectively in soy sauce and maintained and partially improved the sensory and flavour characteristics of soy sauce, which indicates that this combination technology has potential application in the commercial processing of soy sauce.