Effect of different vegetable oils on the qualities, flavors and fermentation characteristics of probiotic yoghurt

The objectives of this study were to evaluate the texture characteristics, volatile flavor compounds and sensory quality of yoghurt after adding four kinds of vegetable oil to fermentation process of skim yogurt. Bifidobacterium, Lactobacillus bulgaricus and Streptococcus thermophilus were used as starter and the p H values, titratable acidity, water holding capacity, texture analysis and sensory evaluation were determined. Volatile flavor compounds in yogurt were detected using solid phase micro-extraction ( HS-SPME) combined with gas chromatography mass spectrometry hyphenated technique ( GC-MS) after ripening and at 24, 48 or 96 h.The results showed that the addition of soybean oil, peanut oil and walnut oil could significantly reduce the yoghurt p H values ( p < 0.01) . In addition, the addition of soybean oil and peanut oil could significantly increase titratable acidity values ( p < 0.05) and the addition of walnut oil and grape seed oil could significantly improve the water holding capacity ( p < 0.05) , but the addition of four kinds of vegetable oils could significantly reduce the firmness and consistency ( p <0.05) , while the cohesiveness and index of viscosity were improved. Meanwhile, the relative contents of volatile flavor compounds in yogurt changed and some vegetable oil components were identified with the extension of the ripening time of yoghurt.Sensory evaluation results showed that added vegetable oil did not significant influence the color of the yogurt ( p >0.05) , but affected smell, taste and texture significantly ( p < 0.05) .This study provides useful information for the development of new products which rich in unsaturated fatty acids.