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UBC Theses and Dissertations

Assessment of bacteriophage-insensitive culture bacteria for cheddar cheese making and subsequent discriminant analysis for objective flavour evaluation Amantea, Gerald Fiore


The first part of this two-part study deals with six defined strains of bacteriophage-insensitive Streptococcus cremoris used over a period of 10 months to produce more than 2 million kg of Cheddar cheese on continuous cheesemaking equipment. Flavour development in this cheese was less than that in cheese made with conventional bulk starter. Proteolysis and Theological properties were examined. Pattern recognition techniques were used to analyze the multivariate data. Texture was affected by the mechanical process, moisture content and yield point. Casein proteolysis, age, culture type and firmness were the most discriminating variables affecting maturity. In part two, it is well recognized that a minimum maturation period is required before Cheddar cheese is acceptable to the consumer. This is a lengthy and costly procedure in which quality is based on subjective evaluation. Classically, trained graders and sensory panels have performed this duty, but because of the variable, subjective and time consuming nature or organoleptic methods, a simple, more objective and reliable method for accurately assessing cheese flavour is proposed. Sensory evaluations by trained graders were done on more than 60 commercially produced cheese samples, and water soluble fractions prepared from all samples. A ternary gradient system was used to elute the non-volatile flavour components from an Adsorbosphere C₈ reverse phase column. A new mapping simplex optimization technique was applied to the HPLC profiles to optimize separation of the multi-component mixture. More than 45 peaks were obtained using an initial solvent volume ratio of 44.6:0:55.4 of trifluoroacetic acid (0.1%), acetonitrile and water. Over 56.6 min the ratio was changed to 0:36.6:63.4 at a flow-rate of 0.97 mi/min. The optimized gradient system was superior to previous isocratic separations and the elution patterns differed for the various categories of cheese. Statistical pattern recognition techniques - principal component analysis and stepwise linear discriminant analysis - were used to interpret the HPLC profiles. Cheese samples were correctly classified according to their discriminant functions into groups. The technique differentiated between first grade and downgraded samples and was capable of assessing cheese flavour quality at an early age.

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