Phage-insensitive Streptococcus cremoris starter strains were selected by assaying cheese whey against potential starter strains. Six strains were selected and characterized for continual use in cheesemaking. Upon phage-infection, strains were removed from the blend. Cheesemaking continued with remaining strains. A phage-insensitive, fast-acid-producing mutant of the infected strain was isolated and characterized. This mutant, similar to the parent, was returned to the strain mixture. Multiple-blend starters were also used in cottage cheese and cultured buttermilk manufacture. Individual strains were used as antigens for a rapid detection test for lactic-streptococcal agglutinins in cheese milk. When sedimentation was encountered, agglutinin-sensitive strains were identified and replaced instead of an entire culture blend. Phage-insensitive mutants were compared to their respective parent strains. Traits examined included acid-producing activity, optimum temperature, generation time, proteolysis, phosphate and NaCl tolerance, phage adsorption, agglutination, morphology, and induction. Mutant strains showed variations in individual characteristics, but no general pattern of variation was observed. Bulk starters, prepared by growing then freezing individual strains in a commercial internal-pH-control medium (PHASE 4), were stored for 3 mo with and without glycerol. Strains varied in storage survival at -20 C. Glycerol enhanced cell viability and activity at -20 C. Storage in PHASE 4 at -40 C and -80 C preserved activity and viability without glycerol. Unfrozen PHASE 4 cultures retained original activity and viability after 1 mo refrigerated storage. Frozen and refrigerated PHASE 4 starters have been used in Cheddar and cottage cheese manufacture for more than 1 yr. Exclusive use of defined-strain cultures resulted in significant manufacturing and economic improvements including elimination of culture rotations and starter failure from phage infection, no ripening period, greater cheese uniformity, predictable starter activity, standardized manufacture, and improved cheese quality. Grade-A cheese production was increased by almost 10%. This technology enabled some factories to increase cheese yields by adding whey cream to cheese milk. The combined improvements, based on defined-strain technology, have enabled factories to increase production—some by nearly 50%. To date, more than 150 million lb of Cheddar cheese have been manufactured with defined-strain cultures. / Graduation date: 1983

Please read the abstract in the front section of this document / Dissertation (M Inst Agrar (Food processing))--University of Pretoria, 2005. / Food Science / unrestricted

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It has been reported recently that extracts of filbert nuts demonstrate considerable proteolytic activity on a non-fat milk solids substrate. The addition of these extracts to cheddar cheese, in an attempt to enhance the rate of ripening, has been suggested. In these experiments, the extracts of two varieties of filbert nuts, i.e. Du Chilly and Barcelona, were added to cheddar cheese samples at the milling stage of manufacture. The rate of proteolysis, in the cheese samples, was determined quantitatively by the increase in soluble protein content over a three month period. At the termination of these experiments a taste evaluation was performed on all cheese samples. A statistical analysis on the results of the soluble protein analyses showed that the proteolysis in the treated cheese samples was significantly greater than the proteolytic breakdown in the control samples. A defatted extract of Barcelona variety of filbert nuts was the most effective treatment of enhancing the proteolysis in the cheese samples. The results of the taste tests showed that no significant improvement in the flavor of the cheese resulted from the addition of filbert extracts. / Graduation date: 1951

The tendency for certain single- and mixed-strain lactic starter cultures to develop a fruity and/or fermented off-flavor in ripening Cheddar cheese was traced to certain strains of Streptococcus lactis in the starter. A very intense fruity and/or fermented flavor developed in experimental cheeses when one particular S. lactis strain was used as a component microorganism in the starter culture. Contrary to previous implications, strains of Streptococcus diacetilactis did not produce a fruity and/or fermented flavor in experimental cheeses made with starter cultures containing these organisms. Mixed-strain cultures of Streptococcus cremoris were used to produce control cheeses, which did not develop the fruity and/or fermented flavor defect. The starter culture and treatment of the cheese milk were the only variables used in the cheesemaking trials. Results obtained indicate that the specific species and/or strain of lactic streptococci contained in the starter culture affect the flavor score and type of flavor in the resultant cheese, independent of the temperature of the heat treatment or hydrogen peroxide-catalase treatment of cheese milk. There were no apparent correlations between "normal" and "defective" starter cultures for the level of proteolytic activity or production of acetaldehyde or diacetyl to the development of fruity and/or fermented off-flavor in cheeses. Existing procedures for the quantification of acetaldehyde, diacetyl and volatile esters were adapted and modified for determining the concentration of these compounds in cheese curd and ripened cheese. The method of slurry preparation, type of diluent and the pH were factors found to affect the recovery rate for acetaldehyde from cheese. The relative flavor preference for typical experimental cheeses was determined with the aid of a flavor panel. A sample of fermented- unclean cheese received the lowest hedonic flavor score, whereas the flavor score of a slight fruity and/or fermented sample compared favorably with that of the reference sample. / Graduation date: 1967

Strains of Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris with potential use in the food industry which had been previously isolated from nature using 16S rRNA probes were characterized for unique identifying traits and for attributes important for potential use in cheese manufacture. Strains of Lc. cremoris which showed desirable characteristics for cheesemaking were selected for Cheddar cheese making trials where they were used first as single strains then in combination. Biochemical testing included lithium chloride sensitivity using Alsan medium. Strains of Lc. cremoris showed greater sensitivity to lithium chloride than Lc. lactis. strains. however sensitivity was generally indicated by reduced colony size rather than absence of growth as predicted for Lc. cremoris. strains. Strains of both Lc. lactis and Lc. cremoris produced blue colonies on Alsan medium indicating citrate utilization. Citrate utilization could not be confirmed by other traditional methods. Carbohydrate utilization using API 50 test kits revealed no pattern which could definitively differentiate strains of Lc. lactis from Lc. cremoris. It was found that all strains fermented galactose, D-glucose. D-fructose. D-mannose. N-acetyl glucosamine and lactose. Regardless of genotype. strains which were shown to be phenotypically Lc. lactis generally fermented additional carbohydrates. whereas Lc. cremoris phenotype strains did not. Only one probe-isolated strain of Lc. lactis fermented D-xylose. Tests to identify potential Cheddar cheese starter strains were performed on all environmental isolates. All strains which were phenotypically identified as Lc. lactis were rejected as potential starters because they railed to coagulate milk after 15 to 18 hours or they developed undesirable flavors in milk. Nine of twenty strains that were both phenotypically and genotypically Lc. cremoris were identified as having good potential for use as Cheddar cheese starter cultures. Four strains (MS-9, MS-23, MS-24, MS-51) were selected for Cheddar cheesemaking trials. Twenty small vats of cheese were made using each of the four strains individually then in every possible combination. In each case the experimental strains showed good functional characteristics with no sensitivity to bacteriophage present in the manufacturing environment. Five commercial scale cheese trials (53,500 lbs of milk) with automated equipment were also undertaken. Each strain was used first individually then in combination. Starter activity in the automated system using the experimental strains was sufficient to allow a 14% reduction in starter usage and still obtain good acid development. Flavor development of the cheese was monitored for one year of aging. Single strains varied in flavor development, with bitter notes being the most prominent off flavor detected. For some strains the bitter flavor was transitory and varied in intensity. Cheese produced from the four combined strains never developed the bitter defect, indicating that proteolysis of the combined strains was sufficient to degrade the bitter peptides as they were produced. / Graduation date: 1999

Call number: LD2668 .T4 1960 K55

Call number: LD2668 .T4 1963 V76 / Master of Science

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. / Graduation date: 1993

Please read the abstract in the section, 00front of this document / Dissertation (MSc (Agric) Food Science and Technology)--University of Pretoria, 2008. / Food Science / MSc / Unrestricted