Effect of Temperature and Total Solid Contents on the Apparent Viscosity of Coconut Milk Yoghurts

摘要

Procedures for the preparation and rheological characterisation of coconut milk yoghurts are described. Coconut milk was fortified with soymilk, 50:50 (v/v/) percent (coconut milk:soymilk), Nonfat dry milk, 60:40 (coconut milk:Nonfat dry milk), while whole coconut milk served as control. Milk preparations were homogenized, heated to 40, 60 and 80 deg C for 30 mins, inoculated with Streptococcus thermophilus and Lactobacillus bulgaricus and incubated at 43 deg C to attain pH 4.6. Rheological properties of yoghurts were studied at temperatures ranging from 10 - 80 deg C. All samples exhibited a pseudo plastic behaviour and described by a power law model. The effect of temperature on apparent viscosity was explained by a polynomial equation and gave a better fit than the Arrhenius relationship. The consistency coefficient exhibits strong dependence on temperature for which the activation energy of flow ranged from 4.57-6.47kJ/mol. The flow behaviour index was low and nearly constant (approx 0.78) up to 40 deg C and then decreased with further increase in temperature.