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A. TSIOULPAS, M. Lewis, and A. Grandison. School of Food Biosciences, Univ. of Reading, Whiteknights, PO Box 226, Reading, RG6 6AP, United Kingdom Casein micelle stability has a major impact on milk functionality in many processes including rennetability, emulsification, foaming, and heat treatment. The stability can vary throughout the year due to seasonal, lactational, nutritional, and mineral effects. It is of vital importance to study the changes in milk properties in order to determine milk suitability for various dairy applications. The aim of the study was to investigate the role of season, stage of lactation, and mineral composition on casein micelle structure and stability of individual milk samples of two herds. Fresian and Jersey milk samples were collected every week from the university farm. Casein micelle stability was determined by the ethanol test and the rennet clotting time test. Average size, size distribution of casein micelles, and zeta potential were analyzed using a ZetaMaster. Major minerals were determined by analytical methods and the ionic calcium using a 634-pH/Calcium analyzer. The results revealed that milk stability was affected by the different lactation stages, indicating that it was highest in the late stage. Ionized calcium was found to be a good determinant of milk stability and exhibited a good correlation to ethanol stability. Mineral composition was generally higher at early lactation, at which milk stability was lowest. Further, the Jersey milk was found to be less stable than the Fresians, making it more suitable for processes requiring coagulation. This study is of vital importance for understanding how different factors affect milk stability and how the optimum stability can be achieved for various dairy processes. No such work has been performed in the past, which looked at how all the factors influence stability of individual milk samples at natural pH.
Session 31, Dairy Foods: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |