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

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.