牦牛脱脂乳白霉菌软质奶酪后发酵期发酵特性的研究

Study on fermentation characteristics of white mold cheese of Yak skim milk during fermentation

以共和县倒淌河牦牛乳为原料,采用水分、p H值、乳酸菌计数、微量凯式定氮法、扫描电镜、顶空固相微萃取-气相色谱-质谱联用（SPME-GC-MS）等测定方法,对牦牛脱脂乳白霉菌软质奶酪后发酵期理化指标、微观结构、发酵成熟时间及其风味物质进行了研究。结果显示：牦牛脱脂乳软质奶酪的杀菌温度控制在65℃,杀菌时间为30min,乳酸菌发酵剂添加量为1%,氯化钙添加量为0.02%,凝乳酶添加量为0.003%;凝乳温度31℃~33℃,成熟条件为：温度20℃、湿度80%。随着成熟时间的增加,奶酪的水分由86%减少至47%;p H值由5.2降低到4.0;乳酸菌数量先增加到6.8 lg,后减少到6.1 lg;蛋白质水解指数第8d达到最高值27.3%,由此确定奶酪成熟时间为7~8d;对达到成熟的软质奶酪的微观结构进行了观察后显示了一个类似海绵的网状结构均匀分布在奶酪体系中,其中酪蛋白彼此聚集结合,并且没有明确的方向,蛋白质降解程度加大,蛋白质结构壁上出现更小的孔眼,且结构变得粗糙,进而判定了牦牛脱脂乳软质奶酪的发酵成熟时间;成熟奶酪主要风味物质有双乙酰、2-呋喃甲醇、3-羟基-2-丁酮等。

Yak milk from Daotang river, Gonghe County is as raw material, physicochemical indicators, micro structure, fermentation ripening time and flavor of white mold soft cheese of Yak skim milk were studied during the later fermentation by the using of determination moisture, p H, lactic acid bacteria count, trace kay type nitrogen determination method, scanning electron microscopy（SEM）,headspace solid phase micro extraction gas chromatography-mass spectrometry（SPME/GC-MS） determination method. The results showed that sterilization temperature control of yak skim milk soft cheese is in 65 ℃, sterilization time is 30 min, addition of lactic acid bacteria starter of 1%, addition of calcium chloride of 0.02%, addition of rennet of 0.003%. The coagulation temperature is from 31 ℃ to 33 ℃,The mature conditions is that temperature of 20 ℃, humidity of 80%. With the passing of mature time, cheese moisture decreased from 86% to 47%; the p H value decreased from 5.2 to 4; the number of lactic acid bacteria increased to 6.8 lg, then reduced to 6.1.lg.The protein hydrolysis index reached the highest value of 27.3% at eighth days, the cheese maturity time is from 7 to 8 days. The microstructure of mature soft cheese was observed. It shows a similar sponge reticular structure of the evenly distributed in cheese system, casein gathered, no clear direction, protein degradation increasing, the protein structure walls appear smaller hole, and structure become rough. Then fermentation ripening time of cheese is determind. The main flavor substance of mature cheese is diacetyl,2-furfurylalkoho, 3-hydroxy-2-butanone, etc.