Abstract: To study the effect of different prebiotics on the free amino acids and flavor of yogurt, the contents of basic nutrients such as protein, fat and non-fat milk solids were measured in yogurts with added xylooligosaccharide, oligomeric isomaltose, galacto-oligosaccharide, or sucrose (as a control) using a milk composition analyzer, and free amino acids were determined by electronic tongue and high performance liquid chromatography-mass spectrometry. Furthermore, a comprehensive evaluation was carried out based on taste activity value and amino acid score using principal component analysis and correlation analysis. The results showed that the contents of protein, fat, total solids and non-fat milk solids in all yogurts with added prebiotics were in line with the national standards. There was little difference in all flavor attributes except for sour taste, and the sour taste intensity of various yogurts was ranked in the following order: xylooligosaccharide < galacto-oligosaccharide < oligo-isomaltose < control. In total, 17 free amino acids were detected in the three prebiotic yogurts, and the content of total free amino acids in the yoghurt with added xylooligosaccharide was about 119.31 mg/g, which was significantly higher than in those added with the other probiotics and the control group. The content of total free amino acids in the control group was 112.49 mg/g, which was significantly higher than that (79.48 mg/g) in the yogurt with added galacto-oligosaccharide, but was not significantly different from that (108.93 mg/g) in the yogurt with added oligo-isomaltose. The contents of sweet, umami and bitter amino acids in the yogurt with added xylooligosaccharide was significantly higher than those in the control group and the other prebiotic addition groups. The contents of sweet and bitter amino acids in the control group were higher than those in the yogurt with added oligomeric isomaltose or galacto-oligosaccharide. The content of each class of taste-active amino acids was the lowest in the yogurt with added galacto-oligosaccharide. For the four yogurts, amino acid scores were mostly higher than the amino acid standard pattern values. On the whole, not all prebiotics had a positive effect on yoghurt fermentation. The yoghurt with added xylooligosaccharide had the highest free amino acid content and good flavor. This study will provide reference for regulating the basic nutrient composition and flavor of industrial produced prebiotic yogurt.

Key words: yogurt; prebiotics; free amino acids; flavor