Protein Degradation And Its Effect On Ham Flavor During The Processing Of Xuan'en Ham

Dry-cured ham is a kind of traditional meat product,which has a long history and is famous at home and abroad for its "delicious taste,richness taste,nutrient-rich,but not greasy" characters,protein degradation would occur during the processing of dry-cured ham,which has a significant impact on the flavor and quality of ham.Foreign scholars have done a lot of systems and in-depth studies on the protein degradation and the relationship between protein degradation and flavor formation on dry-cured ham,domestic researches on the protein degradation of Jinhua ham,Xuanwei ham and Rugao ham were relative more,but Xuan'en ham was rarely reported.The aim of this study was to analysis the protein degradation,to discuss the impact of protein degradation on the flavor of Xuan'en hams at different times during the processing,to have a scientific understanding of the mechanism of flavor formation in Xuan'en ham,and then to provide a theoretical basis of traditional techniques and perematers.The experiment materials were Xuan'en hams obtained from Enshi of the Hubei Province in China.The ham samples were collected from the first sign,second sign and third sign of Xuan'en hams at different times during the processing(remove bones,epidermis,fat,tendons,membranes,etc).The main conclusions are as follows:(1)During the processing of Xuan'en ham,the water content decreased from 75.68% to 41.68%,and the salt content increased from 0 to 24.23%.The pH was relatively stable,which maintained between 5.99-6.22.(2)During the processing of Xuan'en ham,the total nitrogen content decreased at first and then increased,the water-soluble nitrogen content increased at first,finished down slightly from the end of fermentation,at the first the non-protein nitrogen content continues to rise,and then began to decline from the mid-fermentation.The results showed that the muscle protein was significantly degraded from the raw material stage to the mid-fermentation,and the formation of the flavor substance was significant began from the mid-fermentation.(3)SDS-PAGE gel electrophoresis results showed that:during the processing of Xuan'en ham,the sarcoplasmic and myofibrillar protein in biceps femoris were degraded to different degrees,and they were mainly degraded during the salting and initial fermentation period.(4)The study on the interaction and structural changes of muscle protein in the biceps muscle during the processing of Xuan'en ham showed that,hydrogen bonds,hydrophobic interactions and disulfide bond played an important role in stabilizing protein structure,while the contribution of electrostatic interaction force is small.During the processing of Xuan'en ham,the carbonyl content in sarcoplasmic protein increased slowly,while it in myofibrillar protein increased sharply at first and then decreased rapidly,its highest value was at the mid-fermentation state,which indicated that the muscle protein in Xuan'en ham was continuous oxidated from the raw material stage to the mid-fermentation.And the transformation between sulfhydryl and disulfide bonds was occurred during the processing of Xuan'en ham.Protein degradation and thermal effects were significantly affected the surface hydrophobicity of sarcoplasmic and myofibrillar protein during the processing of Xuan'en ham.(5)The activities of cathepsin B and L were decreased during the processing of Xuan'an ham.The activities of both cathepsin were significantly decreased from raw ham to salting ham.In the initial fermentation,the processing temperature increased gradually,and the promoting effect of high temperature was greater than that of salt,so the activity of both cathepsin increased slightly.However,with the fermentation process,the water evaporation and salinity increased,the activity of both cathepsin has a different degree of decline.(6)The results of electronic tongue analysis showed that,the degradation of protein during processing can result in a good taste in Xuan'en ham,while it can inhibited the bad taste to a certain extent,which has a very important effect on the flavor substances formation in Xuan'en ham.(7)The change of free amino acid content during the processing of Xuan'en ham was analyzed by high performance liquid chromatography.The results showed that: sixteen free amino acids(glycine,leucine,valine,etc.)were detected in Xuan'en ham,flavor amino acids are produced in large amount during the salting stage,there was no significant change in the content of amino acids at the initial fermentation,while it was significantly increased in the middle and the end of fermentation.It was also found that all of these free amino acids were predominantly non-polar amino acids(hydrophobic amino acids),and that the increase in non-polar amino acids was also most pronounced during the processing of Xuan'en ham.(8)The changes of the volatile flavor content of the biceps femoris(lean meat)during the processing of the ham was analyzed by the GC-MS.The results showed that:The product derived from the protein and the amino acid degradation is generally carboxylic acid moiety in a branched alcohol,aldehyde,ketone,aromatic,ester,and the like,and the proportion of these substances in the detected flavor is also large.The change of these substances is significant in the mid-fermentation and the end of fermentation,during the mid-fermentation,the temperature is high,this has a promote effect on the protein degradation.The results of the above analysis showed that:The biceps femoris muscle protein was significantly degraded during the processing of Xuan'en ham,and the degradation of protein was one of the main sources of the unique flavor in Xuan'en ham.