Study On Fungal Group And Control Of Lump Beef Jerky

Beef jerky is one of the most popular meat products.Beef is a kind of healthy snack food with good flavor,high nutritional value and easy to carry.Although the water content and water activity of dried beef are usually low,the phenomenon of resource waste,factory loss and poisoning caused by mildew of dried beef never disappeared.Therefore,it is necessary to systematically study mildew induced by beef jerky and mildew prevention and control technology.In this paper,normal and moldy beef jerky samples from different areas of Guizhou(Anshun,Tongren,Guiyang)were used as experimental materials.The differences of flavor compounds and microbial diversity between normal and moldy beef jerky were studied to reveal the effects of core microorganisms on volatile compounds of normal and moldy beef jerky and the microorganisms causing moldy.In order to develop a reasonable and efficient composite preservative,the traditional culture method was used to isolate,purify and identify the moldy fungi in the moldy beef jerky,and the antibacterial experiment was carried out,which provided a certain guiding significance for the quality stability of beef jerky and laid a foundation for the follow-up research of beef jerky.The main results are as follows:(1)Based on the annotation results of high-throughput sequencing(HTS),2,798,226 effective sequences were obtained from 18 samples,respectively 1,429,384 for fungi and 1,368,842 for bacteria.The Ace,Chao1 and Shannon indexs of fungi in normal beef jerky were significantly higher than those in moldy beef jerky.At the same time,the rarefaction and Shannon curve of fungi and bacteria were tended to be flat,indicated that the amount and depth of sequencing were reasonable.The community composition of normal and moldy samples was significantly different at the phylum level,10 phylum of bacteria and 3 phylum of fungi were observed,respectively.Ascomycota and Unclassified dominated in normal beef jerky,while in moldy beef jerky Ascomycota was the most abundant,followed by Basidiomycota.The main fungi causing mildew in beef jerky were Aspergillus,Xeromyces and Wallemia.It was proved that the mildew was caused by the sharp increase of fungi.(2)The characteristics of environmental factors showed that due to the growth of mold,the p H of normal beef jerky in three areas were significantly higher than that of moldy beef jerky(P<0.05);in addition,there was no significant difference in color difference and Na Cl content between moldy and normal beef jerky(P>0.05).The a_w of normal beef jerky was 0.51-0.68,while that of moldy beef jerky was 0.80-0.83.When a_w<0.68,it is beneficial to control the spoilage caused by fungi and the production of aflatoxin.Moisture content and aw in the moldy beef jerky were significantly higher than that in the normal beef jerky,so moisture content may be the key factor leading to the moldy beef jerky.Nutrient components such as carbohydrate,fat and protein were consumed after beef jerky was polluted by mold,which made the calories of beef jerky after mold decreased significantly(P<0.05).The normal and moldy beef jerky from 3regions were detected by HS-SPME-GC-MS technology,The results showed that 82 volatile compounds were detected in all dried beef samples,including hydrocarbons(4),aldehydes(8),ketones(2),alcohols(23),acids(12),esters(10),terpenes(4)and other compounds(5).Among them,22 are unique to normal beef jerky and 17 are unique to moldy beef jerky.The contents of49 volatile compounds in normal and moldy beef jerky were significantly different(P<0.05),accounting for 59.76%of all volatile compounds.(3)The pathogenic fungi were isolated and purified from moldy beef jerky by traditional culture method,and identified by morphological observation and pyrosequencing(R DNA-ITS sequence anal ysis).The results showed that 29 strains of fungi were isolated from the three areas of Guizhou Province,and there were 18 genera of fungi,including Aspergillus(No.1 and 71),Cercospora(No.14 and 90),Cladospora(No.10,33,36 and 37),Colletotrichum(No.49,59 and78),Penicillium(No.44,32,77 and 24),and Cladospora(No.81 and 20).Combined with high-throughput sequencing,strains 1,10,27,33,59 and 71 were selected as the antibacterial targets of preservatives,namely Aspergillus niger,Cladosporium extremely,Alternaria,Cladosporium and Colletotrichum?SP,Aspergillus?jensenii?A kind of high effective compound preservative was studied by bacteriostatic experiment,that is,the best bacteriostatic effect was obtained when the addition amount of?-polylysine was 0.1 g/kg,natamycin was 0.12 g/kg,sodium diacetate was 0.3 g/kg and sodium dehydroacetate was 0.05 g/kg,and the inhibition rate of the compound preservative to strain No.1 could reach 75.94%.(4)Through the correlation analysis of microbe and environmental factors,microbe and volatile compounds,and microbe and microbe,the results showed that:Wallemia was antagonistic to Xeromyces and Hyphopichia.Aspergillus was only antagonistic to Genolevuria,and Cladosporium was only positively correlated with Penicillium.The RDA was used to reveal the correlation among physical and chemical factors and core microbial community.Low a_w can inhibit the growth of Aspergillus,so as to achieve a certain mold control effect.Aspergillus has a weak positive correlation with p H.In the range of 3.07%-4.82%Na Cl content and p H 5.29-5.76,Wallemia increased with the decrease of Na Cl content,and the living environment tended to the p H value of 5.29.The heatmap of correlation between microorganisms and volatile compounds in normal and moldy beef jerky showed that there were 8 core microbial genera and 25 volatile compounds,among which 5 were fungi,namely Wallemia,Xerochrysium,Aspergillus,Colletotrichum,and 3 were bacteria,namely Bacillus,Staphylococcus,and Salvia?pomifera The content of phenylethanol increased after the beef jerky became moldy.After mildewy beef jerky,the content of phenylethanol increases.At low concentration,phenylethanol will produce fruit aroma,but at high concentration,it will produce strong pungent smell and taste,which leads to the change of quality of beef jerky.Bacillus,Staphylococcus,Anthrax,Xerochrysium and Salvia?Pomifera and other microorganisms had significant effects on 18 compounds(P<0.05),such as p-dimethyl ether,n-17-alkane,thymol and so on.