This study explored the impact of ultra-high pressure jet (UHPJ) treatment on the quality of fresh skimmed milk. After UHPJ treatment at pressures ranging from 100 to 300 MPa, the changes in the color, odor and overall flavor of skimmed milk were detected by using electronic eye, electronic nose and sensory evaluation. The results showed that the main color number of skimmed milk was white 4095, constituting 46.80%–53.83%. A total of 42 volatile flavor components such as esters, ketones, and aldehydes were detected by electronic nose. The majority of the flavor components exhibited milky, fruity, roasted, and grassy aromas. Principal component analysis (PCA) revealed that the flavor of samples treated at 300 MPa differed greatly from that of other treated samples. Sensory evaluation indicated that among the flavor attributes evaluated, milky aroma and sweetness were prominent, and there were considerable differences between different samples in terms of sweetness, peptone-like, rusty, burnt and bland flavors. Samples treated at 250 and 300 MPa generated sulfide compounds such as dimethyl sulfide that significantly enhanced the burnt and peptone-like flavors of skimmed milk. In conclusion, UHPJ treatment with 200 MPa can better retain the flavor components in skimmed milk and consequently maintain the flavor of raw milk.

The impact of adding polysaccharides extracted from liquid-cultured mycelia of Inonotus obliquus into yak yogurt on its sensory evaluation score and titratable acidity was investigated to determine the optimal addition amount of the polysaccharides. The process parameters for producing yak yogurt with added Inonotus obliquus polysaccharides were optimized, and the quality of the yogurt prepared under optimized conditions was evaluated and compared with that of yogurt without added Inonotus obliquus polysaccharides as a control. The results showed that addition of 0.4% Inonotus obliquus polysaccharides to yak yogurt led to the highest sensory score together with a moderate acidity. Using orthogonal array design, the optimal process conditions were determined as follows: ratio of Streptococcus thermophilus G2 to Lactobacillus paracasei L9, 1:1; fermentation time, 14 h; temperature, 38 ℃; and sucrose concentration, 8 g/100 mL. Compared with the control, the as-prepared yogurt increased the number of viable lactic acid bacteria, titratable acidity and water-holding capacity by 34.1%, 11.0% and 16.8% respectively, and the pH value decreased accordingly. Addition of Inonotus obliquus polysaccharides into yak yogurt improved its firmness and viscosity as well as flavor.

Molecular biology studies have confirmed that bioactive polysaccharides are naturally occurring polymers that have a variety of physiological and biochemical functions. The water-complexing ability, high viscosity, antioxidant and anti-aging properties of bioactive polysaccharides lay the foundation for their application in the fields of food, and the use of bioactive polysaccharides as a bioactive ingredient in functional foods has become a current research focus. Fermented milk has good flavor and probiotic properties, but it also has the disadvantages of short shelf life, poor curd quality, and general probiotic performance. How to improve the quality of fermented milk is a current major challenge. This article focuses on recent progress in the application of different types of bioactive polysaccharides in fermented milk, and reviews the effects and mechanisms of action of bioactive polysaccharides on the physicochemical, gel and probiotic properties of fermented milk. Furthermore, it discusses future prospects for the application of bioactive polysaccharides in fermented milk. This review is expected to provide a reference for exploring the functions of bioactive polysaccharides and improving the quality of fermented milk.