In this study, four prebiotics including inulin, fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and yeast β-glucan were added singly (inulin) or in different combinations (inulin + FOS + GOS and inulin + FOS + GOS + yeast β-glucan) to fermented milk containing Bifidobacterium animalis subsp. lactis PB200. The titratable acidity, pH, whey syneresis and total viable count of the fermented milk were measured during storage periods. Moreover, the rheological and textural properties were measured. The aim was to clarify the effect of different prebiotic combinations on the yogurt system in order to obtain the optimal probiotic combination. Compared with the control group with no prebiotic added, the addition of prebiotics significantly delayed the post-acidification, and promoted the growth of B. animalis subsp. lactis PB200. Besides, the titratable acidity of fermented milk added with inulin, FOS, GOS and β-glucan was the lowest , and the titratable acidity increased slowly and whey syneresis was less with the extension of storage time. The addition of all four prebiotics could maintain a higher viable count of B. animalis subsp. lactis PB200. The results of rheological and textural analysis showed that yogurt added with all four prebiotics had higher gel strength, hardness, cohesiveness, gumminess, adhesiveness and springiness, showing better texture. In summary, the addition of inulin, FOS, GOS and β-glucan resulted in better quality of probiotic fermented milk with B. animalis subsp. lactis PB200.

In this study, the effect of thermal modifications (25, 75, 85 and 95 ℃ for 15 min) on the structure and digestibility of milk protein concentrate (MPC70) was evaluated. Results shows that the free sulfhydryl content and surface hydrophobicity increased significantly with temperature up to 95 ℃, reaching the highest value of 42 μmol/L and 1 008, respectively. The contents of α-helix and β-turns decreased, while the contents of β-sheet and random coil increased. sodium dodecyl sulfate polyacrylamide gel electrophoresis after simulating gastrointestinal revealed that a certain degree of heat treatment enhanced the digestibility of milk proteins, which may be attributed to structural changes.

The effect of chitooligoosaccharide on the fermentation and sensory properties of yogurt was investigated. The fermentation progress was assessed by measuring pH value, titratable acidity, lactic acid bacteria counts and rheological properties. The sensory quality was evaluated by flavor, taste, texture, and color. Results showed that the addition of 50 mg/mL chitooligosaccharide did not cause any significant difference in titratable acidity compared with the control group (P > 0.05). When chitooligosaccharide addition was lower than 100 mg/mL, there was no significant difference (P > 0.05) in pH value or sensory quality scores in comparison with the control group. Additionally, at the same fermentation time, lower titratable acidity and lactic acid bacteria counts and higher pH value were observed with increasing addition of chitooligosaccharide (P < 0.05). Chitooligosaccharide addition in the range of 0–100 mg/mL had no detrimental effect on the fermentation characterstics or quality of yoghurt and improved the flavor. Hence chitooligosaacharide can be used in the production of yogurt.

The dipeptidyl peptidase-Ⅳ (DPP-Ⅳ) inhibitory activity and physicochemical properties of yak milk casein hydrolysates produced with alcalase, papain and trypsin were investigated. The effect of hydrolysis periods and different proteases on the DPP-Ⅳ inhibitory activity of yak milk casein hydrolysates was assessed by DPP-Ⅳ inhibitory rate. The physicochemical properties of yak milk casein hydrolysates were evaluated by degree of hydrolysis, trichloroacetic acidnitrogen soluble index (TCA-NSI), solubility and ash content. Results showed that the DPP-Ⅳ inhibitory activity of yak milk casein hydrolysate obtained with papain was significantly higher than that of those obtained with alcalase or trypsin at the same hydrolysis period (P < 0.05). The yak milk casein hydrolysate obtained after 0.50 h hydrolysis with papain displayed the highest DPP-Ⅳ inhibitory activity (with inhibitory rate of (53.95 ± 1.57) %), higher extent of hydrolysis degree, and the lowest ash content. The results suggest that peptides with DPP-Ⅳ inhibitory activity can be generated from yak milk casein. The yak milk casein hydrolysate produced by papain may be used as a functional dairy ingredient to develop functional foods.