This study aimed to compare the effect of different ratios of Streptococcus thermophilus to Lactobacillus bulgaricus (3 : 1, 1 : 1, and 1 : 3) under the various stressful temperatures (37 and 45°C) on the fatty acid profiles quality of Kermanshahi roghan (yogurt by-product) and sour cream to obtain a formula for producing a kind of animal fat healthier than milk and cream. Stresses such as fermentation play an important role in bacterial behavior and consequently in food quality. Our findings presented a significant difference between roghan and sour cream fatty acid levels only at 37°C. Furthermore, starter culture 3 : 1 was the best starter for producing products with a higher quality of fatty acid profile at 37°C, and a 1 : 1 S. thermophilus to L. bulgaricus ratio was optimal at 45°C. It seems that bacteria adapt to harsh growth conditions by changing the fatty acid profiles, and these changes warrant consideration in the production of a kind of animal fat with the best fatty acid profiles. In conclusion, the roghan fatty acid profile is more suitable than sour cream only at 37°C.

The objective of the study reported in this Research Communication was to investigate the effect of fermentation temperature (37 and 45 °C) and different ratios of Streptococcus thermophilus to Lactobacillus bulgaricus (3 : 1, 1 : 1 and 1 : 3) on Kermanshahi roghan and yoghurt fatty acid profiles (FAP) in order to obtain a product with optimized fatty acid profiles. Kermanshahi roghan is a yoghurt by-product in western Iran (Kermanshah). The results revealed that incubation temperature at 37 °C as compared to 45 °C had a better effect on fatty acid profiles of roghan and yoghurt. Furthermore, the results showed that fatty acid profile of roghan is better than yoghurt at two experimental temperatures. On the other hand, the roghan products made by equal ratio of S. thermophilus and L. bulgaricus (1 : 1) had the best quality of fatty acid profiles. Although a lower incubation temperature increases incubation time, our finding suggests that inoculation ratio 1 : 1 at 37 °C as compared to 45 °C can affect the quality of roghan and yoghurt fatty acid profiles.