Quality of Plain Set Yoghurt as affected by Levels of Ultrafiltration Concentration of Milk and Inoculum of Yoghurt Culture

Abstract

Quality of plain set yoghurt was investigated by varying levels of ultrafiltration concentration of cow skim milk (1-without ultrafiltration, 1.5 and 2 folds) and inoculum (2, 2.5 and 3%) of yoghurt culture (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus 1:1). Titratable acidity development and pH reduction were significantly faster during incubation of yoghurt with increasing ultrafiltration concentration level and inoculum level. Increased ultrafiltration concentration level decreased spontaneous whey syneresis, but increased water holding capacity and firmness of the product significantly. Body & texture and overall acceptability scores were significantly better in yoghurts prepared from 1.5 fold concentrated milk irrespective of the inoculum level studied. Inoculum level did not show any significant effect on the quality of yoghurt, but higher inoculum level decreased the incubation period significantly. Optimized product was obtained with 1.5 fold concentrated skim milk standardized to 3.3% fat and incubated with 2% inoculum level in about five and a half hour of incubation. Optimized product had 13.60±0.02% total solids, 3.31±0.01% fat, 5.27±0.04% protein, 4.20±0.03% lactose and 0.82±0.02% ash. Whey syneresis, water holding capacity and firmness in optimized product were nil, 63.49% and 1.89 N, respectively. Thus, high quality plain yoghurt could be prepared by employing ultrafiltration, without addition of stabilizers, which is otherwise widely used commercially for the manufacture of yoghurt to control its wheying off and body.