Combined effects of different concentrations of starter culture and incubation temperatures on physicochemical, microbial and sensory features of stirred yogurt produced from Sheep’s milk

Subject Areas : Food Microbial Contamination

Golsa  Mehrabadiyan ¹ (Department of Food Science and Technology, Varamin-Pishva Branch, Islamic Azad University, Varamin, Iran.)
Ali Reza  Shahab Lavasani ² (Innovative Technologies in Functional Food Production Research Center, Varamin-Pishva Branch, Islamic Azad University, Varamin, Iran.)
Sara  Movahed ³ (Department of Food Science and Technology, Varamin-Pishva Branch, Islamic Azad University, Varamin, Iran)

Received: 2017-09-09 Accepted : 2018-06-12 Published : 2018-05-22

Keywords: incubation temperature, physicochemical properties, Stirred yogurt, Starter culture, Sheep&rsquo, s milk,

Abstract :

Yogurt gels are a type of soft solid. Streptococcus thermophilus and Lactobacillus bulgaricus are yogurt starter cultures widely used in the dairy industry. Co-culture of these bacteria leads to higher biomass yield than their separate single strain culture. Incubation temperature also affected some physicochemical and sensory features of yogurt, so the aim of this work is to determined physicochemical and sensory features of yogurt containing different concentrations starter and different incubation temperatures made from sheep’s milk. The preparation of all treatments(T) as follows, Yogurt produced from: 2% starter culture and incubation temperature 42˚C ,T(A);  1% starter culture and incubation temperature 37˚C,T(B); 1% starter culture and incubation temperature 42˚C,T(C: as a Control); 2% starter culture and incubation temperature 37ᵒC, T(D); 3% starter culture and incubation temperature 42˚C, T(E) and 3% starter culture and incubation temperature 37˚C,T(F).the results indicated that fat%, dry matter% and moisture% did not change during 22 days of storage period and parallel to drop of pH, acidity (Dornic scale) continuously increased. The protein content of treatments B,C; continuously increased during 22 days storage period. The starter culture bacterial counts of yogurt  showed that both Streptococcus thermophilus and Lactobacillus bulgaricus decreased during storage period. Sensory evaluation was performed for two features (flavor and texture). The scores for these features decreased during storage period but scores that allocated for treatment D were highly similar to control sample. According to above mentioned, it was concluded that treatment D was more similar to treatment C as a control sample.