INFLUENCE OF TOTAL SOLUBLE CONTENT, STARTER CULTURE AND TIME PERIOD ON RHEOLOGICAL BEHAVIOUR OF CULTURED BUTTERMILK

Abstract

Casein gels are part of the dairy products, hard or soft products, as cheese and yogurt, cultured buttermilk, and their rheological behaviour can be measured by various instrumental techniques. For this study we used three types of milk (7.5%, 10%, and 12.5% respectively TSS) and starter culture (Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris) in different concentrations (2 g/100 l, 3 g/100 l, 4 g/100 l). The rheological properties of the cultured buttermilk obtained from milk were investigated by a Brookfield RV Pro II+ viscometer at different shear rates, during the time period keeping (from the 1^st day – the obtaining day, till the 20^th  day – the last day when the product is good for human consumption). The samples with the highest TSS (total soluble content) present the highest viscosity, while the samples with 7.5% TSS content present the smallest viscosity. During the rheological tests, the samples with 3 g/100 l starter culture presented the best rheological properties (the samples had the highest viscosity), while the samples with 4 g/100 l had the smallest viscosity due to the proteolysis generated by the starter culture activity. The flow index behaviour was influenced more by the TSS content rather than by the starter culture dose.  It can be seen that the change in the apparent viscosity was not linear with solids concentration, where a 5% (from 7.5% to 12.5%) increase in the solids concentration led to triplicate in the apparent viscosity.