Screening of frozen-thawed conditions for keeping nutritive compositions and physicochemical characteristics of goat milk.

Frozen milk can help producers overcome the seasonality of goat milk production, low goat production and short lactation periods, and avoid discarding milk during some special periods. We investigated effects of combination between freezing (cryogenic refrigerator of -16 to -20°C or ultra-cryogenic refrigerator of -76 to -80°C) and thawing (homeothermy of 20 to 25°C or refrigeration of 2 to 4°C) on nutritive compositions and physicochemical characteristics of raw goat milk during storage period (80 d). Compared with fresh goat milk, the frozen-thawed milk decreased contents of fat, protein, and lactose, as well as surface tension and stability coefficient, whereas increased effective diameter and polydispersity index. The average values of color values (L*, a*, and b*) in 4 group samples changed from 83.01 to 82.25, -1.40 to -1.54, 3.51 to 3.81, respectively, and the ΔE of most samples did not exceed 2. In contrast to the other 3 frozen-thawed treatments, goat milk treated with ultra-cryogenic freezing-homeothermic thawing (UFHT) possessed higher fat (5.20 g/100 g), smaller effective particle diameter (0.32 µm), and the lowest polydispersity index value (0.26). The color and confocal laser scanning microscopy images of UFHT were similar to those of fresh goat milk, illustrating UFHT was the optimal approach to maintain the natural quality of goat milk. Our finding provides a theoretical basis for producers to freeze surplus milk.

Quality characteristics of goat milk powder produced by freeze drying followed by UV-C radiation sterilization.

Goat milk was directly freeze-dried into milk powder after freezing and then sterilized using UV-C radiation to produce low-dose, medium-dose and high-dose UV-C radiation sterilized freeze-dried goat milk powder (LGP, MGP and HGP). UV-C sterilization effectively reduced the total bacteria count and coliform bacteria in the goat milk powder while preserving the active proteins, and maintaining the color unchanged. Additionally, LGP, MGP, and HGP all exhibited a moisture content below 5 g/100 g and water activity below 0.5. Upon reconstitution, the milk powder formed uniform and stable emulsion. During accelerated storage tests, the increased Aw did not compromise the microbial quality of milk powder, and there were no significant changes in active proteins as confirmed via SDS-PAGE results. Furthermore, the color parameters (a*, b* and ΔE) showed a strong correlation with hydroxymethyl furfural levels.

Screening of lactic acid bacteria with the ability to reduce goaty flavor related fatty acids in goat milk.

In this study, we conducted sensory evaluation and gas chromatography-mass spectrometry analysis on fermented goat milk samples prepared by 12 strains of lactic acid bacteria (LAB) isolated from goat milk to screen for strains with the ability to reduce the goaty flavor. The bacterial counts of fermented goat milk was 7.07-9.01 log CFU/mL. The electronic nose distinguished fresh goat milk (FGM) and fermented goat milk, and the electronic tongue results showed that Leuconostoc citreum 1, 4, 20, 22, 32, and 57, Latilactobacillus curvatus 144 and 147 imparted fermented goat milk a taste different from FGM. Overall, Leuconostoc citreum 57, Leuconostoc citreum 126, Latilactobacillus curvatus 142, Latilactobacillus curvatus 143, and Latilactobacillus curvatus 147 were screened with the ability to improve the flavor of goat milk. They gave fermented goat milk a goat flavor score lower than or equal to FGM. And the fermented goat milk samples 57, 126, 142, 143, and 147 contained 25, 22, 15, 24, and 17 volatile flavor compounds, respectively, with a greater variety and content of ketones and aldehydes and lower levels of hexanoic acid, octanoic acid, and decanoic acid than FGM. However, the pH and WHC results indicated that the application of these strains as secondary cultures is necessary. Our finding provides basic research data to improve the flavor of goat milk products.

Goat milk fermented with combined lactic acid bacterium alter microbial community structures and levels of the targeted short-chain fatty acids in the large intestine of mice.

The present study investigated effects of the fermented goat milk (FGM) produced with a combination of Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (SL) and with another one of SL as well as Bifidobacterium animalis subsp. lactis (SLB) on the internal environment in the large intestine of mice. Both the richness and the diversity of microbiota was the most abundant in SL group. SL, SLB and the control groups were clustered into three independent groups. At the phylum level, Firmicutes was the most abundant in all the groups, and Deferribacteres in SLB group was more abundant than in SL group. SL and SLB increased the proportions of 6 and 5 genera, respectively. Firmicutes was positively correlated with all the significantly different species but negative to Actinobacteria at the phylum level. SL and SLB both significantly decreased the levels of butyric and valeric acids. Either SL or SLB can significantly improve the structures of microbiota, and both of them significantly decreased the levels of butyric and valeric acids in the large intestine of mice. Certain microbiota negatively related to the levels of butyric and valeric acids. FGM produced with SL or SLB can effectively alter the microbialflora and the levels of SCFA in the large intestine of mice.