异常大豆油浸腐乳中未知白色晶体的研究

Study on Unknown White Crystals in Abnormal Fermented Bean Curd Soaked in Soybean Oil

油浸腐乳是由豆腐坯经接种发酵、加盐腌制并添加油脂制备而成。一般腐乳中添加的油脂为大豆油,如果腐乳中出现不明结晶物则严重影响其品质。对异常油浸腐乳中未知白色晶体进行了分析,研究结晶形成原因。结果表明:该白色晶体在显微镜下观察具有不规则形态,加热至40℃时可熔化。异常油浸腐乳中的油脂酸价达到正常商品一级大豆油酸价的240倍以上,为123.34mg/g。通过薄层色谱定性分析发现异常油浸腐乳中油脂的甘三酯含量很低,而游离脂肪酸含量和甘二酯及甘一酯含量很高;且腐乳中提取的固体脂的游离脂肪酸中的棕榈酸(C16∶0)和硬脂酸(C18∶0)含量远高于液体油,分别为24.72%和12.52%,远远大于国标。由此推断,该白色晶体为饱和游离脂肪酸聚合形成的结晶物,可能是腐乳中的脂肪酶(来自毛霉)水解油脂所致。

Fermented bean curd soaked in oil is prepared by inoculation fermentation,salt pickling and oil addition.Normally,the oil added to the bean curd is soybean oil.The presence of unknown crystals in the fermented bean curd can affect its’quality.In this paper,the unknown white crystals in the abnormal fermented bean curd soaked in oil were analyzed in order to obtain the reasons for crystals formation.The results showed that the shape of the white crystals was irregular by microscope,and it can be melted when heated to 40℃.The acid value of the oil in the abnormal fermented bean curd was 123.3 mg/g,which was 240 times that of the first grade soybean oil.After qualitative analysis by thin-layer chromatography,the content of triglyceride in the oil of the abnormal fermented bean curd was very low.However,the contents of free fatty acid,monoglyceride and diacylglycerol were very high.The contents of palmitic acid(C16∶0)and stearic acid(C18∶0)in the free fatty acids of the solid fat extracted from the fermented bean curd(24.72%and 12.52%)were great higher than those of the liquid oil,which were also great higher than those of the national standard"GBT 1535-2017 soybean oil".Therefore,the white crystals could be formed by the polymerization of saturated free fatty acids,which might be ascribed the hydrolysis of fat by the lipase from Mucor in the bean curd.