| Hui-style bacon is a special cured meat product in Huizhou,Anhui Province.Using excellent raw materials,the production process is complicated,and it is fatty but not greasy.Hui-style bacon is deeply loved by consumers.However,Hui-style cured meat is currently produced in summer and winter by traditional technology.The product quality is unstable and the flavor formation mechanism is unknown,which limits the commercial development of Hui Style cured meat.In this study,Hui-style bacon in summer and winter was divided into fat portion and muscle as the research object.The changes of volatile flavor components,metabolic characteristics,microbial community succession,lipid hydrolysis and oxidation and protein degradation were studied.The formation mechanism of Hui-style bacon flavor was analyzed.The results show that:(1)The main volatile flavor compounds of Huizhou bacon are aldehydes,alcohols,ketones or acids.The key volatile flavor compounds of fat portion in summer are 1-octene-3-alcohol,hexanal,nonanal,heptanaldehyde,(E)-2-octenal,ethyl hexanoate,pentanal,2,4-nonadienal and 2-pentylfuran.The key volatile flavor compounds of fat portion in winter are 1-octene-3-alcohol,hexanal,nonanal,heptanaldehyde,(E)-2-octenal,ethyl hexanoate,(E,E)-2,4-nonadienal,3-Methylbutyraldehyde,p-cresol and 3-octene-2-one.The types and contents of key volatile flavor compounds in winter fat portion were higher than those in summer,so the flavor characteristics of winter fat portion were richer.The flavor differences between the two seasons fat portion mainly came from 1-octene-3-alcohol,hexanal,heptanaldehyde and nonanal.The key volatile flavor compounds of muscle in summer are hexanal and glutaraldehyde,and the key volatile flavor compounds of muscle in winter are hexanal and nonanal.The difference of flavor quality between muscle in two seasons mainly comes from nonanal.(2)Under the LC-MS/MS positive and negative ion mode,the metabolome of summer fat meat,winter fat meat,summer lean meat and winter lean meat is mainly composed of lipids and lipid-like molecules,organic acids and their derivatives,organic heterocyclic compounds and oxygenated organic compounds.Based on the principle of P < 0.05 and VIP > 1.5,19,31,23 and 30 differential metabolites were screened out in the processing of fat portion in summer and winter,muscle in summer and winter.The different metabolites identified in Hui-style bacon in winter were more abundant.The contents of lipids and lipid-like molecules and alcohols in winter fat portion were higher than those in summer,the contents of amino acids,peptides and analogues were lower than those in summer,and the total content of differential metabolites was higher summer;The contents of lipids and lipid-like molecules in winter muscle were higher than summer muscle,the contents of amino acids,peptides and analogues were similar,and the contents of carbohydrates and nucleotides were lower than those in summer muscle.There was no significant difference in the total content of differential metabolites between muscle in summer and winter.Through the enrichment analysis of KEGG metabolic pathway,4,13,17 and 10 significant enrichment metabolic pathways that may play a major role in the formation of Hui-style bacon quality were selected for summer fat portion,winter fat portion,summer muscle and winter muscle respectively.(3)During the processing of Hui-style bacon,lipids are gradually hydrolyzed to form FFA,and phospholipids are the main degraded lipids.The lipase and phospholipase activities of fat portion increased firstly and then decreased in summer and winter,while the lipase and phospholipase activities of muscle gradually decreased.Lipid oxidation increased gradually during the processing,and the oxidation rate in the later stage of processing was lower than that in the early stage.LOX activity increased firstly and then decreased in the processing.Protein degradation and FAA were generated in the processing of muscle in summer and winter.The degree and rate of protein degradation of muscle in winter were higher than that in summer.(4)During the processing of Hui-style bacon,the overall bacterial alpha-diversity showed a downward trend.The results of beta-diversity showed that the succession direction of bacterial community of fat portion and muscle in summer and winter was the same,and the composition of bacterial community in drying period was similar to that of final products.At the phylum level,Firmicutes and Proteobacteria are the dominant phyla of Huizhou bacon in summer and winter.At the genus level,15 and 16 core bacterial genera(relative abundance greater than 1%)were detected in fat and muscle in summer,and Salinivibrio was the most dominant bacteria;In winter,8 and 10 core bacterial genera were detected in fat and muscle respectively,and Vibrio was the most dominant genus.Canonical correlation analysis showed that the main environmental factors affecting the microbial composition of Huizhou bacon in the early stage of processing were p H,moisture content and Aw,and the salt content is the main environmental factors in the later stage of processing.The results of correlation analysis showed that microorganisms had an important contribution to the metabolic characteristics of Hui-style bacon.(5)The flavor quality of Hui-style bacon in summer and winter mainly comes from the promotion on lipid hydrolysis,oxidation and protein degradation by the endogenous enzymes in meat and extracellular enzymes secreted by microorganisms such as Brochothrix,Acinetobacter and Psychrobacter in the curing period,as well as the promoting effect of extracellular enzymes secreted by Salinivibrio,Vibrio,Cobetia and Staphylococcus in the drying period.The difference of flavor quality of Hui-style bacon between summer and winter may be related to different temperature and salt amount. |
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