Study On Bacterial Flora Analysis And Quality Control Technologies Of Pickled Raw Bullacta Exarata

In this paper,The pickled raw Bullacta exarata was chosen as the research object.The microbial community structure of pickled raw B.exarata under different storage temperatures were analyzed.The sterilization effect of ultrasound,NaClO and H2O2 treatment on B.exarata pretreatment was compared,and the best sterilization condition of B.exarata pretreatment was selected.Natural chemicals(tea polyphenols,Nisin,?-polylysine,chitosan and lysozyme)were selected to determine the optimum concentration range,and the optimum pressure for Ultra-high pressure(UHP)were determined.L9(34)orthogonal optimization test were applied to optimize the optimal formula of natural chemicals.Application and effects of the combination of natural chemicals and UHP treatment on pickled raw B.exarata products were evaluated from several aspects.The main contents and results are as follows:1.The pickled raw B.exarata stored at 4 and-20? for 45 days were chosen as the research object,16S rDNA,V1-V3,V3-V4 regions were sequenced by using Illumina MiSeq high-throughput sequencing technique,and OTU clustering,alpha diversity and species classification were performed.The results showed that:(1)Compared with the samples stored at 4?,the samples stored at-20? had more diverse flora;(2)Dominant flora with relative abundance greater than 1%,the samples stored at 4 ?,was Psychrobacter,and the samples stored at-20? were Legionella?Aestuariispira?Mycoplasma?Marinifilum?Anaplasma?Salinispira?Methylophaga and Burkholderia.2.Different concentrations of NaCIO(50,100,150,200 mg.L-1),H2O2(0.5,1,1.5,2 g.L-1)and ultrasonic(150,200,250,300 W)were used to treat the B.exarata for 2.5,5,7.5 and 10 min.The total viable count(TVC)was used as the detection index to screen out the best bacteria reduction method and treatment conditions for B.exarata.Results:all the three bacteria reduction treatments had significant(P<0.05)effect on the bacteria reduction of B.exarata.The optimal sterilization conditions for B.exarata were 50 mg.L-1 NaClO for 7.5 min immersion;1.5 g.L-1 H2O2 for 10 min treatment;200 W ultrasonic treatment for 5 min.Considering the bacteriostatic effect and safety,the optimal sterilization condition on B.exarata is the treatment with 200 W ultrasonic for 5 min.3.The combined effect of natural chemicals(tea polyphenols,nisin,?-polylysine,chitosan and lysozyme)and/or ultra-high pressure(UHP,100 MPa,300 MPa,500 MPa)on quality of pickled raw B.exarata were investigated.The changes of sensory,total viable count(TVC),pH,total volatile base nitrogen(TVB-N)content and thiobarbituric acid reactive substance(TBARs)value of B.exarata were evaluated during storage at(4± 1)?.The results showed that:(1)the application of all these natural chemicals or UHP could significantly(P<0.05)inhibit the increase in bacterial total viable count(TVC).However,the sensory quality,especially texture,was significantly(P<0.05)decreased after the UHP treatment,and the sensory score of samples measured immediately after 500 MPa treatment was decreased 1.41 points compared with the control.(2)The results of L9(34)orthogonal optimization test indicated that the combination treatments have a synergistic effect.Taken preservation effect and the amount of chemicals applied into consideration,the optimal combination was A1B1C1D1(0.05%tea polyphenols+0.005%nisin+0.05%?-polylysine+0.005%lysozyme).(3)The samples treated with UHP and A1B1C1D1 were refrigerated in(4 ± 1)? for 30 d.The TVC,pH,TVB-N content,TBARs value and sensory of those samples were 3.83 log10(cfu g-1),7.34,12.88 mg.100g-1,2.26 mg.kg-1 and 8.01 points,respectively,which were significantly(P<0.05)lower than those in control.Since the combination of natural chemicals(A1B1C1D1)and 300 MPa UHP gives even better effect than either treatment alone,it is suggested that the combination treatment could be commercially used to maintain the quality and safety of pickled raw B.exarata.4.With UHP combining with natural chemicals processing pickled raw B.exarata.as the research object,in 1 year-20? storage,using Illumina HiSeq high-throughput sequencing technologies of 16s rDNA,sequencing,V3-V4 area and OTU clustering analysis,Alpha diversity analysis,determination of species classification analysis of three aspects.The results showed that:(1)There was diversity in the microflora of the samples with different treatments,and the microflora diversity was the most abundant in the control group at 0 days,and the microflora diversity of the samples with 300MPa+natural chemicals was the lowest.(2)The microflora abundance was the highest in the control group of one-year pickled raw B.exarata.,followed by the microflora abundance of 300 MPa+natural chemicals samples,and the microflora abundance was the lowest in the control group of 0-day samples.(3)The dominant microflora in the control group at 0 days were Legionella,Mycoplasma,Marinifilum,Aestuariispira,Methylophaga and Burkholderia.-20? storage 1 year all the advantage bacterium group in the samples are:Pseudomonas,Psychrobacter and Mycoplasma.In addition,the dominant microflora of the pickled raw B.exarata.,with UHP combining with natural chemicals,include Sphingomonas;The Legionella was the dominant bacteria in the naturals pickled raw B.exarata treated with 300 MPa+natural chemicals.