Pressure Inactivation of Yeasts, Molds, and Pectinesterase in Satsuma Mandarin Juice: Effects of Juice Concentration, pH, and Organic Acids, and Comparison with Heat Sanitation

Abstract

Satsuma mandarin juice, the concentrated juice and the acid-free juice were prepared and treated with pressures of 1000–6000 bar after mixing with organic acids, various yeasts and molds, or pectinesterase, to study the effects of pressure on inactivation of microorganisms and the enzyme. The effects of heat treatment were also studied in similar conditions. As results, the inactivation effect of pressure on microorganisms and the enzyme was decreased by increasing juice concentration. Pressure-induced inactivation of microorganisms was not affected by either juice pH (between 2.5 and 4.5) or kinds of organic acids (citric, tartaric, lactic, or acetic acid). With 9 species of yeasts and molds tested, pressurization at 3500 bar for 30 min or at 4000 bar for 5 min was required to reduce them to 1/105 or below 1/105. Microorganisms resistant to heat tend to be highly resistant to pressure. Although no complete inactivation of pectinesterase was attained after pressurization at 3000 or 4000 bar for 10 min, the partly inactivated enzyme did not recover under ordinary conditions of storage and transportation.