Effects of culture concentration and inoculation temperature on physicochemical, microbial and organoleptic properties of yoghurt

Abstract

A study on the effects of culture concentration (2.5 g/l, 5.0 g/l and 10.0 g/l) and inoculation temperature (25°C and 45°C) on physicochemical, microbial and organoleptic properties of yoghurt produced from three base materials (whole cow milk, WCM, powdered milk, PM, and soymilk, SM) was conducted in a nested experimental design. The two inoculation temperatures were nested within the three inoculation concentrations in each of the three base materials and replicated three times to form 54 experimental units. The shortest coagulation times were recorded on WCM (52 min) and PM (60 min) inoculated with 10.0 g/l at both temperatures (25°C and 45°C). The result also showed a significant (P<0.001) difference in titratable acidity of the yoghurts (ranging from 1.31% to 2.52%), pH (4.49 to 5.38) and total solids (12.4% to 17.1%). Total protein (2.55% to 3.09%) and ash (0.48% to 0.85%) also differed (P<0.01). The total microbial load differed significantly (P<0.01) with the highest values of 0.93 x 10⁸ and 0.85 x 10⁸ cfu/ml recorded on whole cow milk yoghurt (WCMY) and powdered milk yoghurt (PMY) respectively, and the lowest value of 0.52 x 10⁸ recorded on soymilk yoghurt (SMY). A significant difference (P<0.05) in taste and colour of PMY produced with 2.5 g/l inoculant at 25°C and 45°C incubation temperatures was obtained. It was concluded that yoghurt with an acceptable quality could be produced with the three inoculation concentrations even at low incubation temperature. Also, PMY and WCMY produced with low concentrations of inoculant at both temperatures were preferred to SMY by the consumers.

Keywords: culture concentration, inoculation, yoghurt, physiochemical properties

Nigerian Food Journal Vol. 23 2005: 156-165