Optimization Of Production Techniques And Evaluation Of Nutritional Value Of Grey Sufu

Grey sufu is one of the most popular traditional snacks in China. It is classified as afermented-tofu product. Soybean with high quality is used for grey sufu manufacturing. Withthe gradual development and expansion of grey sufu market, the awareness of safeconsumption of grey sufu has increased among consumers and the industry of beanprocessing. The unsafe factors regarding grey sufu include raw materials, strains, pickling,soaking solution preparation, additives, containers, package, processing environment,pathogens, and gene modification. Among these factors, most of them are closely related tothe processing of grey sufu. In addition to safety issue, the nutritional value of grey sufu hasalso attracted much attention of consumers.In my thesis, the diversity of bacteria strains in commercial soaking solution was analyzedand discussed. First, most of the strains were separated and purified from the commercialsoaking solution for further observation and identification. The strains obtained were subjectto biochemical identification and safety evaluation for consumption. The safe and suitablestrains were selected for future grey sufu preparation with removal of hazardous bacterialstrains. The results showed that soaking solution used in grey sufu preparation contains avariety of microorganisms of which most are lactic acid bacteria, Bacillus spp, Psuedomonas, andunknown vibrios. Lactobacillus brevis, stick lactobacillus distorted subspecies, and L.plantarμm were the major three lactic acid bacteria in soaking solution, while Bacillus sppincluded B. megateriμm, B. circulans. Among them, L. plantarμm, Psuedomonas, B. circulans,and stick lactobacillus distorted subspecies were examined to be harmless strains used ingrey sufu manufacturing. Based on the results, the safe production processing of grey sufuwith fermentation was investigated, specially focusing on the amount of ferrous sulfate. Thecoloring effect of0%and1.5%ferrous sulfate even higher concentration on grey sufu did notindicate significant difference between each other on the fifth day fermentation. Therefore,the mount of ferrous sulfate cannot be added.In addition to safety issue regarding grey sufu consμmption, the nutritional value of sufu wasevaluated in my thesis. The pH and crude protein content of grey sufu during fermentationwere determined. The overall tendency of grey sufu pH during fermentation was slight increase towards fermentation time, rising from6.7at0day to7.1on5thday. The crudeprotein content of grey sufu was decreased from38.2%at0day to32.8%on5thday. Thecomposition and content of free amino acids (FAA) and total amino acids (TAA) in grey sufubefore and after processing were detected by amino acid analyzer. The content of FAA wasshown to increase during fermentation, showing the effect of fermentation in improving greysufu protein bioactivity. Based on the figures of crude protein content and total amino acids,the composition of essential amino acids (EAA) containing in grey sufu proteins wascalculated and compared to two high-quality animal proteins-eggs and milk. Generally, thecontents of EAAs (except methionine, cysteine, and valine) in grey sufu were close to that ineggs and milk. Some EAAs in grey sufu even had higher amount than eggs and milk.