酸奶在储藏过程中酸度、pH值、细菌的变化

CHANGES OF ACIDITY,PH VALUE AND BACTERIA COUNT OF YOGURT DURING STORAGE

将酸奶储藏在不同温度条件下,通过测得其酸度、pH值和乳酸菌活菌数,得出使酸奶的品质变化最小、货架期较长的最佳储藏条件和酸奶的最佳饮用期.先将同批酸奶分别置于常温、4℃和-18℃下,在储藏期不同时间点进行观察,测定其pH值、酸度,观察其感官变化.采用平板菌落计数法计算活菌数.研究表明,常温储藏5 d的酸奶菌含量最高达到4.6×108cfu/mL,酸度为85.7°T,pH=4.08,有少量乳清析出,口感适宜;4℃储藏13 d的酸奶菌含量最高达到4.6×108cfu/mL,酸度为85.5°T,pH=4.05,口感适宜;-18℃储藏19 d的酸奶菌含量最高达到4.5×108cfu/mL,酸度为85.5°T,pH=4.06,但组织结构已发生改变.故4℃储藏的酸奶13 d内饮用最好.

In the paper,we measured the acidity,the pH value and the viable count of Lactobacillus of yogurt stored at different temperatures to determine optimal storage conditions and the peak drinking period of yogurt.Firstly,we respectively stored the yogurt samples of the same batch at the normal temperature,4 ℃ and-18 ℃;then,we observed the sensory changes and measured the pH value and the acidity at different time points;finally,we calculated the viable count by plate count method.The study showed that the amount of lactic acid bacteria in the yogurt stored at normal temperature for 5 days was up to 4.6×10^8 cfu/mL,the acidity 85.7 °T,and pH 4.08,and the yogurt had a small amount of milk serum separated out and had a good taste;the amount of lactic acid bacteria in the yogurt stored at 4 ℃ for 13 days was up to 4.6×10^8 cfu/mL,the acidity 85.5 °T,and pH 4.05,and the yogurt had a good taste;and the amount of lactic acid bacteria in the yogurt stored at-18 ℃ for 19 days was up to 4.5×10^8 cfu/mL,the acidity 85.5 °T,and pH 4.06,but the tissue structure changed.So,the yogurt stored at 4 ℃ for 13 days was in the peak drinking period.