Microbial Control And Quality Improvement In The Production Of Natural Salted Casings

The natural salted casings are casing products that can be used to make sausages after processing steps such as cleaning and curing of large and small intestines of pigs,cows,sheep,etc,which have the advantages of good air permeability and strong pressure resistance.Although salt curing can reduce the water activity（a_w）of casings to guarantee the safety of food,quality deterioration caused by microbial multiplication can still occur in the actual production,transportation and storage.In addition,due to the differences in individual animals and intestinal parts,the caliber and thickness of the salted casings are jagged,so the quality characteristics of the casings such as elasticity and rigidity are easily destroyed.Most casings processing enterprises still adopt manual operation,and it is difficult to control the strength of the manual cleaning and scraping process,which will aggravate the breakage of the casings.At present,although the casing processing enterprises have established a mature process system,the rules for change of quality index of the casings in each section during processing are unclear.And the effect of the key section on the microbes and quality characteristics of the casings are still uncertain,which needs to be further studied.Therefore,the natural salted casings were taken as the research object in this paper.Firstly,the key section was determined based on the analysis of the change laws of the key quality indicators of the casings in different sections in the processing.Then the changes of microorganisms were analyzed before and after the key section to identify specific key microorganisms.Finally,antibacterial agents for key microorganisms were screened,and quality of casings was improved based on modifiers.This study provides a theoretical basis for microbial control and quality improvement in the subsequent processing of natural salted casings,which has certain practical significance for improving the quality of casings,such as safety of microorganisms and the characteristics of machinery.1.In order to explore the change laws of key quality indexes of natural salted casings in the processing of raw materials,watering,scraping,rehydration,curing and finished products,the basic components,tensile properties and physical and chemical properties of natural salted casings were measured.The results showed that after salt curing,the moisture content of casings decreased by 14.67%,the water activity decreased by 0.191,the concentration of chloride increased by 13.19%,the elongation at break decreased by 5.977%,the tensile strength decreased by 1.85 MPa,the swelling ratio decreased by 8.53%,the water absorption ratio increased by 25.54%,and the brightness also decreased.Therefore,it is determined that the key section in the processing is the salt curing.2.In order to further explore the changes of microorganisms before and after salt curing,the changes of the number of microorganisms and the structure of microbial flora were measured and analyzed.The results showed that after salt curing,the total number of colonies,the colony number of staphylococcus,halophile,psychrophiles and lactic acid bacteria in the casings was reduced by 2.89 lg CFU/g,2.34 lg CFU/g,1.83 lg CFU/g,2.04 lg CFU/g,and 1.24lg CFU/g,respectively.Meanwhile,the relative abundances of Pseudoalteromonas,Halomonas,Psychrobacter and Salinivibrio in the casings were changed significantly before and after salt curing.3.In order to control specific key microorganisms,the effects of the treatment by antibacterial agents ultrasonic-assisted immersion on the number of microorganisms,tensile properties,physicochemical properties and structure of the casings were investigated.The results showed that 0.4%citric acid,0.03%tea polyphenols,0.04%nisin or 0.4%chitosan oligosaccharide made the number of halophile decreased by 0.96 lg CFU/g,0.52 lg CFU/g,0.49lg CFU/g and 0.66 lg CFU/g,respectively.And the number of psychrophiles was reduced by0.95 lg CFU/g,0.70 lg CFU/g,0.66 lg CFU/and 0.60 lg CFU/g,respectively.Then,the changes of the total number of colonies of the casings after the treatment by compound antibacterial agents ultrasonic-assisted dipping were measured,and the formula of the optimal compound antibacterial agent was:0.27%citric acid,0.01%tea polyphenols and 0.013%nisin.Under this condition,the total number of colonies was decreased by 44.8%compared with the blank control group.4.In order to improve the quality of casings,the effects of salt curing by compound phosphate,dipping treatments（atmospheric pressure and vacuum）of surfactant soybean lecithin and soybean oil or glycerin on the quality were investigated.And the basic composition,tensile properties,physicochemical properties,thermal stability and air permeability of casings were measured based on the key section.The results showed that the water content of casings processed with soybean lecithin and soybean oil,soybean lecithin and glycerin was increased by 8.3%and 8.2%compared to the blank control group,respectively.And the elongation at break of the casings after treatment was increased significantly,from 94.9%in the blank control group to 107.9%and 113.7%,respectively.The water vapour transmission rate and oxygen permeance ratio of the casings processed with soybean lecithin and soybean oil decreased by23.08%and 17.06%compared to the blank control,but the oil permeability coefficient was increased.Besides,the thermostability of casings treated by soybean lecithin and soybean oil vacuum impregnation was improved.Under the low-field NMR,the value of T₂₂ of casings processed with soybean lecithin and soybean oil,soybean lecithin and glycerin was decreased significantly,while the value of A₂₂ increased considerably.