There is an increasing demand for dairy products, but the presence of food-spoilage bacteria seriously affects the development of the dairy industry. Bacteriocins are considered to be a potential antibacterial or antibiofilm agent that can be applied as a preservative. In this study, bacteriocin BM173 was successfully expressed in the Escherichia coli expression system and purified by a 2-step method. Furthermore, it exhibited a broad-spectrum antibacterial activity, high thermal stability (121°C, 20 min), and broad pH stability (pH 3-11). Moreover, the minimum inhibitory concentration values of BM173 against E. coli ATCC 25922 and Staphylococcus aureus ATCC 25923 were 14.8 μg/mL and 29.6 μg/mL, respectively. Growth and time-kill curves showed that BM173 exhibited antibacterial and bactericidal activity. The results of scanning electron microscopy and transmission electron microscopy demonstrated that BM173 increased membrane permeability, facilitated pore formation, and even promoted cell lysis. The disruption of cell membrane integrity was further verified by propidium iodide uptake and lactic dehydrogenase release. In addition, BM173 exhibited high efficiency in inhibiting biofilm formation. Therefore, BM173 has promising potential as a preservative used in the dairy industry.

Koumiss is a type of famous fermented mare milk and considered an important nutritious beverage in central Asian countries. However, the production of koumiss cannot meet public demand in the market due to availability of mare milk. In the present study, 52 lactic acid bacteria and 20 yeast strains from traditional homemade Kazakhstan koumiss were isolated and identified. The isolates were used in a trial that included fermented cow milk, and the flavor profiles, color, and taste to determine their contribution in the co-fermentation of cow milk. Based on the sensory evaluation, KZLAB13 and KZY10 strains were selected as the best cofermentation combinations. The optimal fermentation conditions were confirmed as the ratio of the starter culture 2.4:1.6 % (vol/vol) KZLAB13 strain to KZY10 strain and a temperature of 36°C for 16 h using response surface methodology. After evaluating the quality of the optimized cow-milk koumiss compared with the Kazakhstan koumiss, results suggested that cow milk fermented by these 2 strains possessed a promising taste, flavor, and physicochemical and rheological properties. Altogether, our results showed that cow milk fermented with a combination of KZLAB13 and KZY10 strains can simulate the taste, flavor, and quality of traditional koumiss. Our study provided a novel alternative to mare-milk koumiss and could be used in dairy programs to fulfill the needs of people.

Chinese yam with damaged outer skin can be easily oxidized and infected by spoilage fungi. To find preservatives in the storage of the Chinese yam, Aspergillus niger 103 was isolated, identified, and determined as the dominant spoilage fungus in Chinese yam according to Kochs postulates. Then, the strain was used as a model to screen antifungal agents and study antifungal mechanisms in this study. We found that cinnamon essential oil was the best antifungal agent, and the minimum concentration against Aspergillus niger 103 was 25μg/mL. The storage life of Chinese yam could significantly extend by 27.66 days by spraying with cinnamon essential oil (25μg/mL). To further explore the antifungal mechanism of cinnamon essential oil against Aspergillus niger 103, alkaline phosphatase activity and electrolyte content in the fungal solution were measured. The alkaline phosphatase activity and electrolyte content of the fungal solution with cinnamon essential oil were significantly increased than those without cinnamon essential oil, which showed that the cinnamon essential oil could destroy the integrity of the cell wall and cell membrane of Aspergillus niger 103, and disrupted cellular homeostasis of Aspergillus niger 103.