• Effect of Milk Composition on the Quality of Fresh Fermented Dairy Products

      Wilkinson, M.G.; Guinee, Timothy P.; Fenelon, Mark (Teagasc, 2000-09-01)
      The rheology of yogurts or fresh fermented products generally describes and measures the texture of the product and includes such terms as viscosity and firmness of the gel while syneresis refers to the tendency of the yogurt to whey-off during storage. The importance of rheology and susceptibility to syneresis of fermented milk products is that they both have major impacts on consumer perceptions of the final product quality. Indeed, variation in the quality of yogurt products can lead the consumer to experience either an over-thin watery or an over-thick stodgy texture or a product which has a high level of free whey. It is obvious that the seasonal milk supply in Ireland compounds the particular difficulties associated with achieving a consistency in the quality of yogurts or other fresh fermented products. Importantly, both the rheology and syneresis of yogurts are markedly influenced by milk composition, processing treatments and the addition of hydrocolloids. Therefore, this project was undertaken so as to develop a laboratory fermented milks model system which allows the evaluation of the effects of variation of milk components, individually or in combination, on the rheological and syneretic properties of fermented milk products such as yogurt. In particular, the effects of varying total protein, casein-to-whey protein ratio, and fat content were studied as these variations reflect both the differences in milk composition due to lactational/seasonal effects and those due to process variations such as milk heat treatment.
    • Improving the Quality of Low Fat Cheddar Cheese

      Guinee, Timothy P.; Fenelon, Mark; O'Kennedy, Brendan; Mulholland, E. (Teagasc, 1999-02-01)
      The aims of this study were to elucidate the contribution of fat to cheese biochemistry and texture and to improve the texture and flavour of half-fat Cheddar cheese by modifications in make procedure, the addition of a fat mimetic, and/or the use of novel starter cultures/bacterial culture adjuncts. The main conclusions were as follows: A 'Moorepark Process' has been established for the production of half-fat Cheddar cheese with improved sensory acceptability. The flavour and texture of half-fat (17% w/w) Cheddar was improved by modification of the cheesemaking procedure and/or ripening conditions and through the use of novel starter cultures and/or bacterial culture adjuncts. Extensive databases have been compiled on: the effects of fat on the compositional, microbiological, biochemical, rheological and sensory properties of, and the yield of, Cheddar cheese. the compositional, biochemical and sensory characteristics of commercial Cheddar cheeses of different fat levels, available on the Irish and UK markets. Reduction in the fat level of Cheddar cheese resulted in a marked deterioration both in texture and flavour due to: increases in cheese hardness and fracture stress, indicating that the cheese became more elastic, tough and less amenable to mastication. a higher ratio of secondary-to-primary proteolysis a reduction in the level of primary proteolysis and an increase in the concentration of hydrophobic peptides which are conducive to bitterness.