Quality assessment of pear juice under ultrasound and commercial pasteurization processing conditions.

Microbial and enzymatic inactivation in fresh pear juice were studied under conventional and ultrasound-pasteurizations. The ultrasound-pasteurization conditions were 25, 45 and 65 °C for 10 min using a 750 W probe sonicator (frequency 20 kHz and amplitude 70%) while conventional pasteurization conditions were 65 °C for 10 min and 95 °C for 2 min. Complete inactivation of enzymes (peroxidase, pectinmethylesterase and polyphenol oxidase) and microbes (total plate count, yeast and mould) were observed in conventional pasteurization at 95 °C but this treatment also showed highest losses of ascorbic acid, total phenols, flavonoids and antioxidant capacity. Ultrasound-pasteurization at 65 °C for 10 min showed the best results in retention of ascorbic acid and other phenolic compounds with significant reduction in enzyme activities and complete inactivation of microbes. Values of pH, acidity and °Brix showed no significant changes under conventional or ultrasound-pasteurization treatments. The findings of the present study indicate that pasteurization at low temperatures in combination with ultrasound can successfully be employed for commercial processing of pear juice with improved quality. [ABSTRACT FROM AUTHOR]