High hydrostatic pressure effect on Saccharomyces cerevisiae, Escherichia coli and Listeria innocua in pear nectar
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An isostatic pressure system was used for processing fresh-prepared pear nectar, inoculated with Saccharomyces cerevisiae, Escherichia coli and Listeria innocua, at selected pressures (0 to 241MPa), and times (2s, and 0 to 15min). The come up time (time to reach the working pressure) had an important microbial inactivation effect in view of the fact that the initial counts of 6.0×105, 1.02×107 and 2.4×107cfu/mL were reduced to 2.4×105, 6.3×105 and 2.2×107cfu/mL, for S.cerevisiae, E. coli and L.innocua, respectively, in nectar. Decimal reduction time values, in the range of 2.0-35.3, 0.6-20.6 and 9.2-588.2min, were calculated from the first order kinetics modeling of S.cerevisiae, E. coli, and L. innocua survivors, respectively. zp values of 120.5, 92.6 and 75.2MPa were obtained for the three types of microorganisms, respectively. PRACTICAL APPLICATIONS: The application of high hydrostatic pressure may deliver a "cold pasteurized" pear nectar. This "cold pasteurization" may inactivate microorganisms and enzymes as thermal pasteurization does; however, high hydrostatic pressure does not generate unwanted chemical compounds that may change the nectar fresh sensory characteristics. Thus, a fresh-like fruit product, free from chemicals and with high quality and sensory characteristics, could be offered to consumers. © 2011 Wiley Periodicals, Inc.