Study On The Specifics Spoilage Organisms In Tofu And Shelf Life Predictive Model

Tofu is accepted by people because it contains rich proteins,fat acids and microelements.However,the growth of contaminated microorganism which leads to the spoilage product has been become the great barrier for producer during production, transportation and preservation,and the food safety is the most attention problem for consumer.Presently,it is an effective measure of mathematics model to improve the inspect level of safety,because it can predict the shelf life of tofu.But it has no research in the tofu. In this research,we first obtained four dominant strains from spoiling tofu by traditional isolation technology and determined their species based on the characteristics of morphology,physiology,biochemistry and the 16S rDNA,Then we studied the microbial effect on the quality in order to find out the main spoilage organisms and establish the scientific quality predictive model.The aim is to provide a theory basis and technique for the inspection of quality and safety during the production,transportation and preservation of tofu.The contents and results are as follows:1 Isolation and identification of the main spoilage microorganisms in tofu during storageFour spoilage bacteria strains named FM-1,FM-2,FM-3 and FM-4 separated from four different tofu samples.Based on the characteristics of morphology,physiology, biochemistry and the 16S rDNA phylogenetic tree constructed with MEGA3.1,strain FM-1 was identified as a strain of Empedobacter,strains FM-2 and FM-3 were two strains of Kurthia gibsonii,strain FM-4 was a strain of Bacillus cereus.2 Microbial effect on the change of tofu quality and the determination of the specifics spoilage microorganismsThe four dominant microorganisms which were isolated from tofu were inoculated to the surface of tofu in order to study the microbial effect on the tofu spoilage quality.All samples were packed and preserved at 25℃and taken on 0,4,8,12,16,20,24 hours to analysis the sensory value and the changes of different indices.The result indicted that the microorganisms had significant effect on tofu spoilage quality,the microbial counts were not consistent with the tofu spoilage extent.With the apparent and character,the results from microbiological behaviors analysis,we determined FM-1,FM-2,FM-3 were the specifics spoilage microorganisms of tofu.The average numbers of FM-1,FM-2,FM-3 were 6.3×10⁷cfu/g,1.38×10⁷cfu/g and 10⁸cfu/g at the end of shelf life,respectively.3 Construction of Microbial Growth Kinetics Prediction Model of Kurthia in Tofu and shelf life predictionThe tofu was inoculated by the specific spoilage organism kurthia,then the sample was stored at 4℃,12℃,20℃and 30℃.A series of experiments had been carried out to develop and validate the growth kinetics model of kurthia for predicting the microbial quality and remaining shelf life of tofu stored in different temperature.The results from microbiological behaviors analysis showed that the kinetics models of specific spoilage organism had been developed and the growth of dynamics of this organism under 4-30℃could be well described by a Gompertz type model.And four growth models were established in tofu.The temperature dependence of Kurthia kinetic parameters-μ_max (maximum specific growth rate) and Lag phase were modeled using Belehradek(square root) model.The correlation coefficient showed could finely describe the influence of temperature on growth.Validation of built kinetic models was carried out by comparing with experimental development of kurthia grown on tofu at 8℃and 25℃.Bias and accuracy factors were used as comparison indices which were 1.04,1.02 and 1.20,1.18 respectively.The results derived from validation showed that the developed models could finely predict the growth kinetic of Kurthia at 4-30℃.The predicted model of shelf life was SL=lag-[(8.6-N₀) /(μ_max^*2.718)]^* {ln[-ln(7.14-N₀)/(8.6-N₀)]-1 },Basic errors between predicted shelf life and real shelf life were -3.47%å'Œ4.89%at 8℃and 25℃respectively,it suggested microbial growth models established in our research were valuable for rapid and realistic prediction of the microbial quality and remaining shelf life of tofu stored from 4℃to 30℃.