Study On Flavor Formation And Lipid Metabolism During Processing And Storage Of Mutton Ham

Ham is a popular traditional cured meat product in China,but the quality of ham varies with different raw materials,processing techniques and storage methods.Xinjiang mutton ham has not yet realized the industrial production of products.It is of great theoretical significance to study the quality changes of mutton ham during processing and storage and the lipid changes that have an important impact on quality changes for the improvement of traditional mutton ham technology and the optimization of parameters.This study starts with the quality change of mutton ham during processing and storage,comprehensively analyzes the flavor components of mutton ham,determines the composition of the main flavor substances,and analyzes the oxidation changes of mutton ham itself.To find biologically meaningful differential lipids,exploring differential lipid metabolism pathways.The main contents are as follows:1.Take mutton ham physicochemical,texture,color,flavor and sensory as the inspection indicators to comprehensively monitor the quality changes of mutton ham during processing and storage.During the processing and storage of mutton ham,the moisture content and water activity decreased from 73.9% and0.97 in the raw material to 31.2% and 0.54 respectively(p<0.05).The p H value is in a slightly acidic environment and is maintained between 5.86 and 6.33.The Na Cl content was up to 10.83%,and finally maintained at 9.46% during storage.The nitrite content of ham products was 1.34 mg/kg,and the residual amount during storage was 1.69 mg/kg.During processing and storage of ham,the hardness,gumminess,and chewiness increased significantly,while adhesiveness and springiness decreased(p<0.05).The color of the ham gradually changes to rose red and pale yellow.The total response value of the electronic nose after processing and during storage was significantly higher than that of mutton ham in the raw period(p<0.05).The sensory evaluation results showed that the finished ham had the highest comprehensive score,followed by the 50-day storage sample.2.Comprehensive analysis and processing by gas chromatography-ion mobility spectrometry(GCIMS),headspace solid-phase microextraction combined with gas chromatography-mass spectrometry(SPME-GC/MS)and gas chromatography-olfactory(GC-O)techniques Changes in flavor substances of mutton ham during storage.The contents of 6 alcohols,5 ketones,3 aldehydes,3 esters and 2 other volatile compounds were found to increase with processing by GC-IMS;5 alcohols,3 ketones,5 aldehydes,1 The content of one ester and two other volatile compounds increased with storage;2-phenylethanol,n-hexanol,methanol,2-methyl-1-pentanol,3-heptanone,3-methyl-2-The content of crotonaldehyde,isopropyl acetate,dimethyldisulfide,benzene,ethylbenzene gradually decreases with the progress of storage.The VIP analysis results of GC-MS showed that 6-methylheptanol,2-heptanone,n-octanal,etc.were important volatile compounds during the processing of mutton ham;3-octanone,2-hexanone,2,3-octanedione,2-methylcinnamic acid,etc.are important volatile compounds during storage of mutton ham.The GC-O olfactory results showed that hexanal,nonanal,n-octanal,2-nonanone,2,6-dimethylpyrazine were the substances that most contributed to the flavor during the processing and storage of mutton ham,showing grass,Aromas of citrus,sweet orange,roasted and earthy.3.Monitor the degree of oxidation of mutton ham during processing and storage through the change of oxidation index,and determine the activity of endogenous enzymes induced by oxidation,the activity of endogenous antioxidant enzymes in mutton ham,and the changes in antioxidant capacity of mutton ham’s own antioxidant system to comprehensively evaluate Oxidative changes in mutton ham.During the processing and storage of mutton ham,the POV value kept increasing.It was 14.95 meq/kg in the finished product period and 31.11 meq/kg in the storage period of 300 d.The TBARS value reached a maximum of0.55 mg/kg after drying and remained at 0.13-0.29 mg/kg during storage.Diene value increased from 0.17 to 0.38;carbonyl value reached a maximum of 0.91 at the end of fermentation and remained at 0.65-0.67 during storage.The lipase activity of mutton ham showed a downward trend in general(p<0.05);LOX enzyme activity first increased and then decreased,and tended to be stable during storage;CAT enzyme activity increased first and then decreased,and continued to increase during storage;SOD and GSH-Px enzymes Vitality is on the decline.The polypeptide content in the crude peptide increased significantly,and its ability to inhibit lipid oxidation was gradually enhanced,with the strongest being 89.51% in the finished product stage;the metal ion reducing power reached the maximum value in the finished product stage;the chelating ferrous ion ability was the maximum in the finished product stage.66%;the scavenging capacity of ABTS and DPPH free radicals reached a maximum of 36.96 μg Trolox/m L and 36.96 μg Trolox/m L in the finished product stage,respectively;the superoxide anion scavenging rate reached a maximum of204.51 U/g protein at the end of fermentation;hydroxyl radical scavenging rate The rate reached a maximum of 76.82% at the end of fermentation.The PLSR results indicated that the antioxidant capacity of mutton ham had a certain regulatory effect on the flavor.4.Absolute quantification of various lipids by lipidomics technology and application of liquid phase secondary mass spectrometry(ESI-UPLC-MS/MS)to understand the changes in the content and structure of mutton ham lipids during processing and storage.A total of 581 lipid metabolites were identified in the processing stage of mutton ham and 579 lipid metabolites were identified in the storage stage.These lipid molecules were divided into 21 subclasses.GL was the most abundant lipid during processing and storage,and GP was the most abundant lipid subclass.Both processing and storage had significant effects on lipid types and lipid molecule content in dry-cured mutton ham,and had a greater impact on the content changes.The PCA results showed that the lipid molecules that contributed the most to grouping differences during the processing of mutton ham were glycerophospholipids,while those during storage were triglycerides and free fatty acids.According to the VIP score of lipids in the OPLS-DA model,it was found that mutton ham contained 512 differential lipids during processing and 367 differential lipids during storage.5.Combined with multivariate statistical analysis,according to the VIP variable weight value obtained by the OPLS-DA model to measure the impact strength and explanatory power of the expression pattern of each metabolite on the classification and discrimination of each group of samples,and combine the volcano plot to screen out the significantly different metabolites and find out important metabolic pathways through KEGG.The main change during processing is first degradation and then oxidation,and oxidation is the main process during storage.Glycerophospholipid metabolism and sphingolipid metabolism are the most important metabolic pathways during the processing and storage of mutton ham.LPC,LPE,PC,PE,DG and PS play important roles in the glycerophospholipid metabolic pathway during mutton ham processing.PI,LPE,PE,PC,PS,PG,DG,PA are important lipids involved in glycerophospholipid metabolism during the storage of mutton ham.SM(d18:1/26:1)was the most important lipid for sphingolipid metabolism during storage of mutton ham.The PLSR results showed that during the processing,the mutton ham was metabolized by glycerophospholipids to generate a large amount of PUFA,which participated in the formation of the characteristic flavor of the mutton ham.During the storage process,due to oxidation,the number of unsaturation of fat molecules decreased,and the important flavor substances related to differential lipid molecules were mainly aldehydes and ketones at 50 days and ketones at 300 days.To sum up,the quality of mutton ham has changed in all stages of processing and storage and is constantly oxidized,but the changes in the storage period are smaller than those in the processing period.In the proper oxidation process,mutton ham formed its unique flavor.Hexanal,nonanal,2,6-dimethylpyrazine,n-octanol and 2-nonanone were the main flavor substances in mutton ham.Both processing and storage had significant effects on lipid species and lipid molecule content in dry-cured mutton ham,and had a greater impact on content changes.Glycerophospholipid metabolism and sphingolipid metabolism are the most important metabolic pathways during the processing and storage of mutton ham,and the metabolized unsaturated free fatty acids affect the final ham flavor.