Study On The Quality Of Cooked Sausage, Establishment Of Mathematical Model And Mechanism Of C. Sporogenes Inhibition Affected By Nitrite

As one of western meat products with low temperature heated, cooked sausage isamong the favorite processed meat products in the market due to its unique flavor and taste.In the manufacturing of cooked sausages, nitrate and/or nitrite are commonly added to thesausage mince, which are used to stabilize the pink curing color, enhance the flavor andtexture, acting as an antioxidant and a microbiological preservative, especially againstClostridium botulinum. However, the principal concern with the use of nitrite in cured meatproducts is the eventual formation of carcinogenic N-nitrosamines with secondary amines,and excessive additions of nitrite into the food may cause toxicity to people. In addition, C.botulinum is an anaerobe which produces an extremely powerful neurotoxin. Its growth infoods often results in the production of sufficient toxin to cause severe illness or even death.Thus it is imperative that the safety of all foods is ensured with respect to this bacterium. Inorder to solve these two problems according to the safety of food additives andmicroorganisms, studies on the quality of cooked sausage, establishment of mathematicalmodel and mechanism of C. sporogenes inhibition affected by nitrite were investigated. C.sporogenes used in this research is considered to be a non-toxingenic equivalent ofproteolytic C. botulinum, and it also causes food spoilage. Therefore, results of this thesiswould be theoretical references to further research of nitrite substitutes and N-nitrosaminereduction, and could be applied into practice to ensure food safety with respect to C.botulinum control. The contents and results of each chapter are as follows:1) Effects of different nitrite contents on the quality of cured pork during curingtime.The variations of the quality of cured pork with different nitrite additions (0, 50, 100and 150 mg·kg^-1) at 0-4℃during 0-48 h were investigated. It indicated that the color,texture and freshness of cured pork were affected significantly by nitrite. First, CIE a^*value of cured pork was found to be positively correlated to sensory score, chromogenicrate, myoglobin content, with Pearson correlation parameters 0.91, 0.92 and 0.72,respectively. Second, the results of Texture Profile Analysis (TPA) showed that hardness,adhesiveness, springiness and chewiness of cured pork increased, cohesiveness and resilience decreased, as the curing time increasing. The correlation analysis betweenchemical contents and TPA attributes indicated moisture was positively correlated toadhesiveness, resilience and springiness, nitrite negatively to springiness, and collagennegatively to resilience. Third, it demonstrated that TBA and TVBN values were decreasingwith nitrite added during cured time.2) Effects of different nitrite contents on the quality of cooked sausage duringcold storage.A study to determine the effect of sodium nitrite on the quality of cooked pork sausageduring 0-21 days at 0-4℃storage was demonstrated. Cooked sausages like frankfurter-typewere prepared at 4 levels of sodium nitrite (0, 50, 100, 150 mg·kg^-1) added during curing. Itindicated cooked sausages produced with nitrite addition were more acceptable for sensoryevaluation than those without nitrite addition, according to their color, texture, aroma/flavorand taste. Furthermore, TPA attributes of cooked sausage changed due to different nitriteadditions, then a principal component analysis (PCA) based on the correlation of nitriteresidues and TPA parameters were applied for reducing variables. It indicated that principalcomponent 1 (PC 1) accounted for 65.09% represented by hardness, springiness,cohesiveness, adhesiveness and resilience, and principal component 2 (PC 2) accounted for16.46% mainly related to chewiness. The volatile flavor compounds of cooked sausages at10 d cold storage were extracted by solid phase microextraction (SPME), and thenidentified by gas chromatography/mass spectrometry (GC/MS). New ten volatile flavorcompounds from cooked sausages with different nitrite additions were ethanol, 1-butanol,2-hexen-1-ol,(E)-, 2-hepten-1-ol,(E)-, 2-octen-1-ol,(E)-, menthol, butanal,3-methyl-,hexanoic acid, pinene and 4-nitrophthalamide, as a result of enhancing the cured-meatflavor of cooked sausage. In addition, color and water holding capacity (WHC) were notaffected significantly by nitrite addition (P＜0.05).3) Establishment and validation of bacteria inhibition model from nitrite incooked sausage.In this study, bacteria strains Escherichia coli, Staphylococcus aureus and Clostridiumsporogenes were inoculated for 1.5×10³-1.5×10⁴ CFU·g^-1 respectively into cooked sausageprepared at 4 levels of sodium nitrite (0, 50, 100 and 150 mg·kg^-1) added during curing. Thegrowth curves of certain bacteria generated within 0-30 d cold storage were fitted bymodified Gompertz and Baranyi function. From the statistical comparison, Banranyifunction was finally chosen as the better one to estimate two growth parameters (growthrate, GR; lag-time, LT). Furthermore, BÄ›lehrádek or Ratkowsky function of root-squarewas applied for the fitting bacteria inhibition from nitrite in cooked sausage. The highestenduring concentrations of nitrite were lower than 400, 200 and 190 mg·kg^-1, respectively. Then, goodness for fitting of the established model was evaluated by validation of marketsamples and evaluation of mathematical parameters. It were found that the standard error ofprediction (%SEP), root-mean-squares error (RMSE), bias factor (B_f) and accuracy factor(A_f) were within acceptable range, and bacteria inhibition model provides a useful andaccurate method for predicting and controlling the spoilage and pathogen microorganisms.4) Inactivation modeling on the thermal resistance of Clostridium sporogenesspores under different conditions.The effects of temperature (101-121℃), pH value (5.5-6.5) and concentrations ofsodium chloride (2-6%) on the heat resistance of C. sporogenes spores in laboratoryconditions were investigated. The inactivation curves of spores reduction from 10¹⁰CFU·mL^-1 to 10⁵ CFU·mL^-1 were fitted by Weibull frequency distribution model, and theprimary prediction equations were obtained with R²ï¼ž0.90. Moreover, the inactivationparametersδand p of Weibull equations were modeled using a quadratic polynomialequation of response surface model (RSM). Mathematical validation demonstrated lowerstandard error of prediction (%SEP) and Root-Mean-Squares Error (RMSE),acceptancerange of Accuracy factor (A_f) and Bias factor (B_f) obtained by RSM, RSM thus provides auseful and accurate method of predicting the effect of experimental conditions on the heatresistance of C. sporogenes spores.5) Effects of nitrite on the cell structure, protein expression and Fe-S activity of C.sporogenes.From the cell and protein aspect, some mechanism of nitrite inhibition of C.sporogenes, as equivalent of proteolytic C. botulinum, was investigated in this chapter.Different nitrite concentrations (0, 100, 200, 300, 400 and 500 mg·L^-1) were added intoculture medium of C. sporogenes at lag phase of growing. It indicated that the cell yields ofC. sporogenes decreased significantly with nitrite concentrations increased (P＜0.05).Moreover, the cell structures were destroyed seriously from the observations ofTransmission Electron Microscope (TEM) after nitrite addition for about 20 h. On the otherhand, the protein concentration and expression were influenced by nitrite addition to someextent. It also showed that the activity of ferredoxin (Fd) and pyruvate-ferredoxinoxidoreductase (PFO) were inhibited significantly by nitrite, and PFO activity decreasedfrom 1.447 to 0.753 U·mL^-1 while nitrite concentration increased from 0 to 500 mg·L^-1. Inconclusion, Fe-S protein inhibition of anaerobic bacteria would be the main mechanism ofnitrite in the food.