Study of rheological, physical and microstructural changes during rennet-induced gelation and their impact on cheese yield and texture

The hypothesis underpinning this research is that the strength and nature of casein interactions during rennet gel formation continue to modulate the properties of curd during rest of the cheesemaking process and would also influence cheese textural properties during ripening.; Gelation is one of the most critical stages during cheesemaking. The storage modulus of rennet-induced gels, increased with an increase in milk solids non-fat content, gelation temperature and a decrease in gelation pH. Loss tangent value of gels increased with an increase in gelation temperature and a reduction in milk solids non-fat content. The yield stress value of gels increased with an increase in milk solids non-fat and a decrease in gelation pH; yield strain was positively affected by gelation pH.; Gelation parameters, such as, the value of storage modulus at cutting and yield stress at cutting were positively associated with cheese yield and, the yield strain at cutting was significantly negatively associated with fat recovery in cheese. The cutting properties of rennet-induced gels influenced cheese yield, e.g. a more brittle gel had higher fat losses probably because it shattered more during gel cutting cycle. The functional properties of cheese during ripening were affected by the amount of insoluble Ca remaining in cheese and proteolysis. Degree of flow, maximum in loss tangent and storage modulus value at 80°C were used as measures of cheese meltability. High insoluble Ca levels during ripening were observed in cheese made with high milk solids non-fat content and high gelation pH values, while pH 4.6 soluble nitrogen levels during ripening were lower in cheese made from gels that had high milk solids non-fat content. Degree of flow of cheese during heating increased when there was an increase in pH 4.6 soluble nitrogen and a decrease in the insoluble Ca content.; It can be concluded that modifications in the gelation stage of cheesemaking continued to have a lasting impact on subsequent stages of cheese manufacture and on cheese properties during ripening. With the increased use of higher solids milk in the dairy industry, adjustments in the gelation conditions could help in controlling cheese texture, physical characteristics and cheese yield properties.