Study On Sterilization Of Seasoned Crayfish (Procambarus Clarkii) By Superheated Steam

Procambarus clarkii is an important aquaculture shrimp with huge yield and best-selling marke in China.Crayfish products are popular with consumers because of their safety,hygiene,unique taste and simple pretreatment.However,the industrial sterilization technology of crayfish could not effectively inactivate the microorganisms of products,resulting in short shelf life of products,which restricted the development of crayfish processing industry.It is necessary to explore a new sterilization technology,which could effectively inactivate the microorganisms of crayfish,ensure the quality of products and prolong shelf life.In this paper,crayfish was used as raw material and superheated steam was used as sterilization method.Firstly,the dominant spoilage bacteria of crayfish were isolated and identified.Then,the inactivation effect of superheated steam on dominant spoilage bacteria of crayfish was studied.Furthermore,the effects of superheated steam sterilization on the quality of seasoned crayfish were investigated.Finally,the quality changes of the products during refrigeration were analyzed.The purpose of this paper was to demonstrate the potential and prospect of the application of superheated steam in the processing of seasoned crayfish,to provide new selection and technical reference for crayfish sterilization technology and to extend shelf life of crayfish products.The main research contents were as follows:1.The dominant spoilage bacteria of crayfish products which reached the end of storage after pasteurization were cultured by aerobic plate culture,and the dominant spoilage bacteria were separated.Then the morphological characteristics of spoilage bacteria were observed by microscopy.Finally the dominant spoilage bacteria were identified by 16S r DNA molecular sequence analysis and phylogenetic tree construction.The results showed that the dominant spoilage bacteria of crayfish meat at the end of storage were identified as Bacillus pumilus,Bacillus subtilis,Bacillus cereus and Lysinibacillus macroides.2.The effect of superheated steam treatment parameters such as temperature,flow rate and time on the 4 colonies of dominant spoilage bacteria isolated was investigated.Inactivation kinetics of the dominant spoilage bacteria by superheated steam was fitted by using Weibull model.The sterilization mechanism of superheated steam were explained by analyzing the values of conductivity and ultraviolet absorption,and observing the microbial morphology of the bacteria.The results showed that in the initial stage of superheated steam sterilization,the survival rate of dominant spoilage bacteria decreased rapidly,and with the prolongation of sterilization time,the decline rate became slow,and finally tended to be stable.Superheated steam can completely sterilize the dominant spoilage bacteria of crayfish.Increasing of superheated steam temperature and flow rate can achieve better inactivation effect on spoilage bacteria from crayfish.Inactivation kinetics curve of 4 colonies of the dominant spoilage bacteria by superheated steam were well fitted by Weibull model(R~2?0.935).After superheated steam treatment,the conductivity and UV absorbance of bacterial suspension increased rapidly,and the observation of the microbial morphology of the bacteria showed that the bacterial of the cell membrane was seriously damaged,resulting in the change of bacterial morphology,the outflow of intracellular substances and the death of bacteria.3.The effects of superheated steam treatment parameters on sensory score,color,texture,volatile odor and initial colony count of crayfish during sterilization during sterilization were studied.the superheated steam sterilization process was optimized by response surface methodology.The sensory score and the total number of initial colonies were used as the response values.The results showed that superheated steam treatment could maintain the texture and volatile odor of crayfish before sterilization,improve the color and sensory score of products,and reduce the total number of initial colonies of products compared with boiled crayfish and pasteurized crayfish.The optimal superheated steam sterilization process of crayfish was obtained by response surface methodology:superheated steam flow 29 m~3/h,superheated steam temperature 230?,and treatment time 303 s.Under these conditions,the sensory score of the product was 3.521 points,and the total number of colonies was 39.42 cfu/g.4.The seasoned crayfish products were sterilized by superheated steam and pasteurization respectively,and then stored at 4?or 10?.Sensory evaluation,total bacterial count,total volatile base nitrogen,peroxide value and volatile odor were measured.The results showed that,compared with pasteurization,superheated steam sterilization could effectively inactivate the microorganisms of crayfish,reduce the initial total colonies of crayfish,slow down the increase of total colonies and TVN-B content during storage,prolong the storage days reaching the end point of sensory score,and slow down the change of volatile odor of crayfish.According to the quality changes of crayfish during storage,The shelf life of steam group was up to 48 d at 4?and 27 d at 10?,which was extended by 24 d and 15 d compered with the pasteurized group,respectively.Superheated steam treatment can effectively prolong the shelf life of crayfish products.