Study On Spoilage Bacteria Diversity And Quality Changes In Boxed Tofu

Tofu is an important non-fermented soybean product.Because of high nutrition and easy to digest and absorb,it is a popular food in the Oriental world and western world.In addition,there is a Chinese proverb:“Tofu is meat without bones”is well known in the western world.Tofu is polluted by microorganisms in the raw materials and processing environment during the processing.Also,because of the rich nutrition and high moisture in tofu,growth and reproduction of microorganisms is rapid.This ultimately leads tofu corruption and even causes food poisoning.Therefore,research and control of spoilage bacteria of tofu is a major issue in the tofu storage and circulation.In addition,it is of great significance to study the relationship between the diversity of spoilage bacteria in tofu and the factors of environments or origin.In this paper,the relationship between the origin of tofu and spoilage bacteria diversity was analyzed by traditional culture and PCR-DGGE.Then,spoilage bacteria diversity changes were tested in commercial tofu and homemade boxed tofu by different temperature in storage and transportation.Finally,quality?pH,sensory evaluation,texture profile analysis and colony count?were analyzed under different temperature.The results showed:1)There is high correlation between spoilage bacteria diversity and soybean origin?Shenzhen,Guangzhou and Foshan respectively?.There is different spoilage strains in different distribution,but less correlated with tofu type.Tofu is spoilaged by Bacillus under room temperature.The main spoilage strains are as follow:Bacillus subtilis,Bacillus pumilus,Bacillus megatherium,Bacillus firmus,Bacillus thermoamylovorans.2)Comparing with the control group,the similarity coefficient of spoilage bacteria diversity of tofu stored under different temperatures are all less than 0.5.This result shows that even under 4?,spoilage bacteria diversity of tofu would change greatly.W ith the increase of storage temperature?4-25??,diversity of spoilage bacteria increased gradually.The order of spoilage bacteria diversity under different temperatures as follow:25?>15?>4?.Due to different processing technology,spoilage bacteria diversity of GDL tofu affected by temperature is minimum in 3 kinds of commercial tofu?hard tofu,soft tofu and GDL tofu respectively?3)4?storage and transportation has little effect on the diversity of bacteria in boxed tofu,mainly because of the low temperature bacteria Pseudomonas.25?storage and transportation effects diversity of bacteria greatly because of the Clostridium perfringens,Bacillus firmus and Bacillus subtilis.Temperature sensitive period of boxed tofu is from 2^nd day to 6^th day because of Bacillus.During this period,the higher temperature,the greater the variation of spoilage bacteria diversity is.4)6 combinations of storage and transportation temperature are as follow:treatment 1:transportation under 25?,storage under 4?;treatment 2:transportation under 25?,storage under 15?;treatment 3:transportation under 25?,storage under 25?;treatment 4:transportation under 4?,storage under 4?;treatment 5:transportation under 4?,storage under 15?;treatment 6:transportation under 4?,storage under 25?).Studying on the total number of colonies,the order of 6 treatment is 4>1>5>2>6>3;studying on the pH,the worst is treatment 3 and 6;while studying on the sensory quality and texture characteristics,treatment 4 is greater than other treatments.There is no significant difference in other treatments while treatment 3 is worst.The sensory quality of 6 treatments were all not accpeted after day 8.