Quality of cow milk plain set yoghurt as affected by ultrafiltration process

Abstract

The aim of the study was to investigate the effect of ultrafiltration (UF) process on quality of cow milk plain set yoghurt. Direct UF of cow skim milk and highly concentrated UF cow skim milk retentate addition were used to adjust the total solids (TS) of yoghurt milk, at two different UF concentration levels (UFCLs). Ultrafiltered (approximately to 1.5 and 2 fold) cow skim milk/ equivalent 5 fold UF skim milk retentate added cow skim milk were standardized to 3.3% fat and 13.8% TS. Yoghurts were prepared by inoculating with 2% yoghurt culture (Lactobacillus delbrueckii subsp. bulgaricus: Streptococcus thermophilus) and analyzed for chemical composition, spontaneous whey syneresis, water holding capacity, textural and sensory attributes. Protein, lactose and ash percentages of yoghurt prepared from direct UF milk were 5.27±0.04, 4.20±0.03 and 0.82±0.02, whereas, in yoghurt prepared from retentate added milk were 5.18±0.02, 4.28±0.03 and 0.84±0.01, respectively at 1.5 fold UFCL, which had optimum quality product. The values were not significantly different in yoghurt made by direct UF concentrated milk compared to retentate added milk. Further, it was observed that protein percentage increased and lactose content progressively decreased significantly (p<0.05) in yoghurt with increase in UF concentration/ UF retentate addition with similar TS in yoghurt milk. None of the quality parameters tested showed significant difference with UF process so that both procedures would be recommended at 1.5 fold UFCL to produce good quality yoghurt with enhanced protein content without addition of stabilizers