Characterization of thermophilic rod and coccus starter strains used in mozzarella cheese manufacture Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g445cg956

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  • The present investigation was undertaken to characterize a number of strains of Lactobacillus bulgaricus and Streptococcus thermophilus intended for use by a commercial starter supply company. Thorough characterization of each culture was required in order to combine compatible strains so that their usefulness in Mozzarella cheese manufacture would be maximized. In this regard, cocci were assayed for formate and carbon dioxide production, rods for proteolysis, and both types for salt and phosphate tolerance as well as rate of acid production. In addition, certain combinations of cocci and rods were assayed as mixtures for these characteristics. Analyses of the various strains of lactobacilli and S. thermophilus were performed. Proteolysis, as determined by the Church method, for the rods (L. bulgaricus , L. helveticus and L. lactis ) varied from as low as 11.3 to as high as 34.7 mM when incubated for six hours. Proteolysis analyses for S. thermophilus also revealed a wide range of values from a low of 18.5 to a high of 46.4 mM. However, when strains were incubated for 16 hours, rods were shown to be nearly twice as proteolytic as cocci. When mixed cultures were tested for proteolysis, results were dependent on strain synergism. Values ranged from a low of 5.1 mM to 70.5 mM in mixed cultures. Various strains of S. thermophilus and mixed cultures were assayed for formate production. The S. thermophilus strain values were from a low of 4.2 to as high as 20.3 mg/L. Formate production in mixed cultures varied from traces of formate in one culture to quantities two and a half times that produced by the single S. thermophilus strains tested. Carbon dioxide production for the rods (L. bulgaricus , L. helveticus , and L. lactis ) varied from as low as 0 μl to as high as 376 μl when incubated for six hours at 44 °C. Carbon dioxide production for S. thermophilus ranged from 5 μl to 1259 μl. Also, S. thermophilus strains produced significantly more carbon dioxide than rod cultures, with only three exceptions. All mixtures were weak producers of carbon dioxide. Nine of 19 L. bulgaricus strains were stimulated by 0.1% phosphate ion and one strain showed stimulation at 0.3% phosphate ion. Thirteen of 19 strains were severely inhibited by 0.5% phosphate. Three of 10 L. helveticus strains were stimulated by 0.1% phosphate and another three strains were unaffected. All strains were inhibited by 0.5% phosphate. Two L. lactis strains showed stimulation at 0.1% phosphate, but inhibition at 0.3% and 0.5%. Acid production by strains of S. thermophilus was inhibited in 11 of 13 cases at 0.1% phosphate. The two strains not inhibited were slightly stimulated by 0.1% and 0.3% phosphate and unaffected by 0.5% phosphate. The mixed cultures of L. bulgaricus CR 14/ S. thermophilus 2 and L. bulgaricus Ql S. thermophilus 2 were not inhibited by 0.1% phosphate, but inhibition occurred at higher concentrations. Mixed cultures of L. bulgaricus C, E/ S. thermophilus 7, 12 and L. bulgaricus C, G/ S. thermophilus 4, 12 were stimulated by all three concentrations of phosphate salts tested. Sodium chloride produced toxic effects on the rods at concentrations ranging from 2.5% to 3.0%, and acid production was stimulated 7 of 32 strains by low salt concentrations(0.5%). In general, cocci were more sensitive to NaCl, with 6 of 13 strains showing sensitivity at 0.5%. Sensitivity to salt was a more gradual effect in the cocci as revealed by a gradual reduction in rate of acid production as NaCl concentrations increased. Mixed cultures were more tolerant to NaCl with no inhibition occurring at concentrations of 1.0%. Culture L. bulgaricus C, GIS. thermophilus 4, 7 were stimulated at concentrations through 1.5%. The synergistic properties of the mixed strains increased NaCl tolerance.
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