Raw milk samples were processed using four frozen-thawed temperatures: cryogenic (-20～-16 ℃) freezing-homeothermic(20～25 ℃) thawing(CFHT),cryogenic freezing-refrigeration (2～4 ℃) thawing (CFRT), ultracryogenic (-80～-76 ℃) freezing-homeothermic thawing (UFHT) and ultracryogenic freezing-refrigeration thawing (UFRT). The changes of acidity, color and nutritional composition of the frozen-thawed milk on day 1, 3, 5, 7, 14, 21, 28 were detected. The results showed that the milk acidities demonstrated increased trend in the storage period, but were all below the upper limit of the national food safety standard. Significantly decreased L* values of 1.08%～3.73% (P<0.05) were observed after milk frozen-thawing except for the UFRT group on day 1, and UFRT treatment showed the minimun effect on milk color. The fat contents in the frozen-thrawed milk were 1.47%～4.66% lower than that of the fresh milk(P<0.05), while the milk protein loss rates in the four processed samples reached 1.40%～4.09%. In general, UFRT was the best frozen-thawing method for maintaining the quality of raw milk, while CFHT also showed small influence on the physicochemical properties and nutritional composition of raw milk and can be applied when economic issue is considered. Our finding provides theoretical support and technical reference for the frozen storage and subsequent production and processing of surplus raw material milk.

Transglutaminase (TG) of 1, 2, 3 U/g protein were added to goat milk and incubated at 40 ℃ for 2 h to prepare set goat milk yogurt. The effects of TG addition on the quality of set goat milk yogurt stored for 1, 7, 14 and 21 d were studied, including acidity, texture properties, water holding capacity, lactobacillus number, flavor substance contents and sensory characteristics. The results of physical and chemical properties showed that TG addition did not influence the acidity and elasticity of the yogurt compared with the control sample during storage, while the hardness, viscosity and water holding capacity of the TG treated yogurt were significantly improved. Meanwhile, TG addition was able to inhibit the formation of acetaldehyde and diacetyl in set goat milk yogurt, but had no effect on the growth of Lactobacillus bulgaricus and Streptococcus thermophilu. The results of microscopic structure of set goat milk yogurt showed that TG treatment was beneficial for the formation of a densified three-dimensional network structure, and could enhance the sensory characteristics and mouthfeel of the set goat milk yogurt. Our finding confirmed that TG addition had positive effects on the quality of set goat milk yogurt during storage.

The formula for yogurt powder containing Epimedii Folium was developed using fuzzy comprehensive evaluation and orthogonal test. The key techniques for manufacturing yogurt powder containing Epimedii Folium were discussed, and the sensory quality and functional factors of the manufactured yogurt powder were analyzed. The optimal formula for yogurt powder was as follows: dilution of Epimedii Folium extract, 20%; granulated sugar, 20%; and citric acid, 0.35%. Dilution of Epimedii Folium extract was the most important factor affecting sensory quality of yogurt powder, followed by granulated sugar and citric acid. The content of total flavonoids in yogurt powder was 1.48 mg/g determined by ultraviolet spectrophotometric method, and the contents of icariin, epimedin A, epimedin B and epimedin C were quantified to be 34.5, 79.1, 81.7 and 116.0 μg/g, respectively, using high performance liquid chromatography. Both Lactobacillus bulgaricus and Streptococcus thermophilus were found in yogurt powder with a total probiotic bacteria number of 6.2×106 CFU/g. The optimized yogurt powder containing Epimedii Folium demonstrated high sensory quality as well as a considerable number of flavonoids and probiotic bacteria, thus providing a material basis for its health benefits.