The effect of ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms

The application of power ultrasound during immersion freezing significantly (P < 0.05) affected freezing rate of mushrooms. Ultrasound at 0.39 W cm -2 (20 kHz) reduced nucleation time by 24%, 53% and 34% in Lentinulaedodes, Agaricusbisporus and Pleurotuseryngii respectively. Drip losses during the thawing process were found to be 10% less compared to control samples. Whiteness index increased when ultrasound intensity was higher than 0.27 W cm-2 (20 kHz) in L. edodes and P. eryngii whereas, ultrasound at 0.39 W cm-2 (20 kHz) showed the highest chroma value with lower yellowness and browning indices. Ultrasound at 0.39 W cm-2 (20 kHz) resulted in the highest textural hardness values in all the three mushroom varieties. Polyphenol oxidase and peroxidase enzyme activities were also significantly (P < 0.05) reduced with the increase in ultrasound power during ultrasound-assisted freezing (UAF). These results indicated that UAF can be a suitable technology for industrial freezing of mushroom.