99D-13 |
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C. T. PRUITT1, O. Anggraeni1, and P. D. Courtney. (1) Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 Propionibacteria metabolize lactate into propionate, acetate, and CO2, contributing to the characteristic flavor and eyes in Swiss cheese. Propionibacteria growth is encouraged during early ripening (20-24°C). Elastic texture allows proper eye formation. The cheese is then cooled (4-10°C) for further ripening. Reduced elasticity during late ripening can result in splits if CO2 production continues during ripening, storage or distribution. Amino acids naturally present in cheese may serve as compatible solutes, promoting cold tolerance during ripening. The present study investigated cold tolerance of dairy P. freudenreichii strains and the effects of amino acid compatible solute uptake. Forty-three different P. freudenreichii strains isolated from commercial starter cultures or cheeses were grown in complex medium (CM) at 4, 10, 22, and 30°C. Selected strains were also grown in chemically defined medium (CDM), and monitored spectrophotometrically. Transport of glycine betaine, proline, and glutamate was evaluated using 14C-labeled amino acids at the same temperatures. Dairy propionibacteria vary in growth rate at low temperatures in CM, with some strains not growing or growing slowly at lower temperatures. Four strains differing in growth abilities at low temperatures were selected for further studies in CDM containing glycine betaine, proline, or glutamate. Growth of cold tolerant strains was improved at 22, 10 and 4°C by all amino acids. Growth of cold sensitive strains was not improved at 10°C and 4°C by any amino acids. The degree of proline and glutamate import was greater for cold sensitive strains; whereas, the degree of glycine betaine import was greater for cold tolerant strains. The most sensitive strain was unable to uptake glycine betaine at any temperature. Generally, rate of uptake decreased with decreasing temperature for all strains. Dairy propionibacteria vary in cold tolerance. Glycine betaine import correlated positively with cold tolerance. Results have implications in reducing split defect occurrence in Swiss cheese.
Session 99D, Food Microbiology: General
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