Assessment of the Quality of Yoghurt Produced From Cow Milk Using Natural and Artificial Starter Culture as a Function of Storage Time

Abstract

Yoghurt is globally regarded as a functional food which combines unique nutritional values with promotion of good health, heart functions, and natural immune defense in humans. This study aimed to assess the quality of yoghurt produced from cow milk using natural and artificial starter culture and determine its physicochemical properties, antioxidant and mineral composition using the standard storage time (28 days). Fresh milk was collected from cow farms at National Animal Production Research Institute (NAPRI), Ahmadu Bello University, Zaria, it was kept in an ice box immediately to protect it from fermentation. A 1000 mL milk sample was boiled, cooled, poured to a small bowl and a tea spoon of the lemon juicy was added to it, it was kept for 20 Hrs in a warm place to thicken. The sample was heated to 63 °C for 30 minutes to destroy unwanted microorganisms and provide a cleaner medium in which the desired organism can grow. It was immersed in a basin of cold water to stabilize it to about 42^oC. The pasteurized milk samples was then mixed with 2.5% of a mixed starter culture (2:1 of Lactobacillus bulgaricus and Streptococcus thermophilus) and stirred cautiously until the pH reached 4.7. It was then left to coagulate for 3 hours at 42 ^oC. Some physicochemical parameters were comparatively determined. The findings revealed that, yoghurts produced from cow milk using natural starters has the highest Total solids TS (13.95 %),  Ash TAC (0.69 %), Oil (5.3 %), Protein (3.31 %), pH 4.96, and Lactic Acid (1.07 %) at day1.  It also exhibited higher phenol content (0.125 g/L), phosphomolybdate (0.082 g/L) and Tannins (0.082 g/L). It also content higher % of macro nutrient (P: 0.234 g/L, K: 1.050 g/L, Na: 1.450 g/L, Zn: 0.101 g/L and Ca s0.697 g/L). On the other hand, the one with artificial starter culture had higher Vitamin C (7.56 g/L) at storage time (28) days. It was concluded that, yoghurts produced from natural starter culture content higher % of some macro nutrient. While the one from artificial starter culture exhibited better storage capability and stability of shelf life.