| Yogurt is a cultured dairy product, made by fermentation of heated milk with lactic acid bacteria, which converts lactose into lactic acid resulting in a reduction in pH. As yogurt is a complex system, there are many different types of interactions, such as, colloidal calcium phosphate (CCP) bridging, hydrophobic and electrostatic interactions and hydrogen bonds, which, collectively, have a strong influence on the physical and rheological properties of yogurt. Furthermore, yogurts are dynamic in nature, and can undergo rearrangement at any level (particle, cluster or strand) before, during or after gelation. Insight into the mechanism of the aggregation process during the acidification of milk and understanding structure-function relationships are important for understanding the factors that influence the final texture of acid milk gels. The properties of yogurt gels are influenced by both milk composition, such as dry matter fortification, and processing conditions, including incubation temperature, inoculum level, rate of pH change and fermentation time. The main objective of this study was, to better understand the molecular interactions that influence the properties of acid milk gels; the concepts of casein micelle integrity, internal micellar structure and particle rearrangements will be considered during gel formation. An overall hypothesis is that casein-casein interactions and the internal micellar integrity modifies the nature of interactions and rearrangements of caseins in gel network, which play a critical role in controlling the textural attributes of yogurt. Thus, by studying the rheological, physical properties and microstructure using fundamental techniques, we can begin to understand the physicochemical basis for the physical properties of yogurts. The impact of fortification with milk protein, preacidification pH, fermentation time, incubation temperature and stirring temperature, were investigated by determining the rheological, physical and microstructural properties of yogurts in order to elucidate the role of the different interaction forces in the formation and structure of acid skim milk gels. |
