Storage Effect on Chemical and Rheological Qualities of Synthetic and Naturally Flavored Yoghurt

Abstract

Fresh cow’s milk was obtained from White Fulani cows and clarified, homogenized and pasteurized at 80oC for 3 minutes. Sucrose (5%) was then added as sweetener. The milk was thereafter cooled to 420C for inoculation. Commercial freeze-dried starter culture was added to 12 litres of the milk. Reconstituted commercial strawberry flavour (T₁), fruit juices (coconut (T₂), orange (T₃) and pineapple (T₄₎ were then added at 200ml into 1 litre each of the inoculated milk. The inoculated and flavoured milk was incubated at 43oC for 14 hours in an incubator. Each flavoured yoghurt produced was replicated thrice, and 250ml of each product was refrigerated for storage periods of 1, 7 and 14 days. The yoghurt for each of the storage periods was then subjected to chemical and rheological evaluations. The completely randomized design in a 4x3 factorial arrangement was adopted. The results of the analysis indicated that storage period had significant (p<0.05) effect on the parameters investigated. Storage period had significant (p<0.05) effect on Total Titratable Acidity (TTA), pH, viscosity, and free fatty acid (FFA). However, there was no significant (p>0.05) difference in the Peroxide value (PV). The storage and treatment effect showed that T₂ had the highest values of pH (5.00) at day 7, viscosity (4.73dPas) at day 14 and TTA of 0.05mg/100g. However, T₃ and T₄ had the highest FFA (17.72mg/100g) at day 14 respectively. It was generally observed that viscosity, pH of the yoghurt samples improved with storage period, the FFA also increased with storage time.