76C-28 |
Effect of high pressure throttling on the survival of Saccharomyces cerevisiae and Bacillus megaterium in single strength and concentrated orange juice |
V. AREEKUL, Department of Food Science and Technology, The University of Georgia, 2010 Food Science Building, Cedar Street, The University of Georgia, Athens, GA 30602 and R. T. Toledo, Department of Food Science and Technology, The University of Goergia, 2010 Food Science Building, Cedar Street, The University of Georgia, Athens, GA 30602. Fruit juice concentrates would be cheaper to process and store than single strength juices. High pressure processes can be made more cost effective if volume is reduced by concentration, e.g. reverse osmosis before processing. Yeasts spoil juices while aciduric bacteria may survive minimal pasteurization treatments. High pressure throttling (HPT) could pasteurize juices without adverse effects on flavor. However the effects of high osmotic pressures on microbicidal effectiveness of a HPT process is not known. HPT inactivation of cells of Saccharomyces cerevisiae and Bacillus megaterium on single strength (SSOJ) and concentrated orange juice (COJ) were studied. Twenty four hour actively growing suspensions of S. cerevisiae and B. megaterium ATCC 14581 were inoculated into SSOJ (11 Brix) and COJ (45 Brix). The mixes were introduced into a HPT system that consists of a Stansted pressure intensifier (Stansted Fluid Power LTD., Essex, UK) and a throttling valve to instantaneously reduce pressure to atmospheric. The processed juices were immediately cooled after exiting the throttling valve by collecting in bottles immersed in ice water. Survivors were enumerated by pour plating. Yeast inactivation increased exponentially with operating pressure while B. megaterium increased linearly. Temperature rise was 39 and 60 oC, respectively at 68 and 204 MPa for SSOJ while COJ rise was 34 and 64 oC respectively. Inactivation of S. cerevisiae was 6.6 log in SSOJ at 204 MPa and 0 oC initial temperature, but was only 2.1 log in COJ. B. megaterium was more resistant than yeast with only 0.8 log and 0.3 log inactivated at 204 MPa in SSOJ and COJ, respectively at 204 MPa. Increased osmotic pressure increases resistance of microorganisms to HPT inactivation, therefore treatment of fruit juice concentrates will require more severe conditions than single strength juices.
Session 76C, Fruit & Vegetable Product: Fresh Fruits and Vegetables
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