Study On The Degradation Of Intramuscular Connective Tissue In The Low Sodium Dry-Cured Loin During Processing

Special nutritional value and flavor are the keys to the traditional dry-cured meat,but high salt content(6%～12%)is the bottleneck,restricting its development.Thence,it is urgent to reduce the content of salt in the dried-cured meat.There are many researches on the low sodium of dried-cured meat,but the low sodium of dried-cured meat still has defects in the quality of food,such as texture and color.The intramuscular connective tissue(IMCT)is the residue in the mouth when the Jinhua ham or other dried-cured meat is chewed.However,the studies on IMCT are mainly concentrated in the correlation between collagen content,thermal solubility,covalent cross-linking and texture of different raw meat or cooked meat,but the study on the degradation of IMCT in the dried-cured meat and its processing has not been reported.Based on the above problems,this study was conducted to explore the degradation of IMCT in the dry-cured loin during processing.Therefore,the effect of low sodium salt on IMCT and its enzymes during the processing of dry-cured pork from M.longissimus dorsi was investigated.The aim of this study was to lay the foundation for the subsequent regulation of IMCT in the dry-cured loin.The specific research contents are as follows:1.Physicochemical properties in low sodium dry-cured loin during processingThe changes of physicochemical properties of low sodium group and salt group were similar in the processing of dry-cured loin.With the extension of processing time,the water content and the Aw decreased,the total nitrogen content increased slowly and the protein degradation index also increased.TBARs experienced the process of ascending and descending.The hardness,cohesiveness and chewiness of dry-cured loin increased,while the elasticity increased and then decreased.In the end of post-aging,the pH value,P.I and TBARs of low salt group were significantly higher than those of salt(P<0.05).The low sodium salt reduced the sodium content by 53.34%and the potassium content increased by 168.42%,which was in accordance with the idea of reducing sodium and adding potassium.2.The characteristics of IMCT in low sodium dry-cured loin during processingThe changes of IMCT of low sodium groups and salt groups were similar in the processing of dry-cured loin.With the extension of processing time,the total collagen,the thickness of the primary and secondary perimysium decreased,as well as the content of pyridinoline cross-linking,while the thermal solubility increased.Besides,the secondary structure of IMCT undid the helix,and the collagen fibers gradually dispersed from the tight sheet-like state to the scattered and regularly state of the final product.In the end of post-aging,the thermal solubility of collagen in the low-sodium group was 0.91%higher than that of salt(P<0.05),While total collagen,primary perimysium thickness and pyridinoline cross-linking were not found statistically significant(P>0.05).Compared with salt,the relative content of a-helix and β-turn were decreased by 8.86%and 12.87%(P<0.05)in the exist of low sodium salt,respectively.While aggreganted strands and random coil increased by 58.21%and 7.35%(P<0.05).In conclusion,low sodium salt is further promoting the degradation of IMCT than salt during the processing of dry-cured loin.3.Research of enzymes of IMCT in low sodium dry-cured loin during processingThe changes of enzymes of IMCT in low sodium groups and salt groups were similar in the processing of dry-cured loin.With the extension of processing time,the activities of MMPs,PRSS and Cath-L increased first and then decreased,while the activity of Cath-B decreased gradually,but they all remained activities at the end of processing.In the end of post-aging,the activities of MMPs and Cath-B in low salt group were significantly higher than those of salt(P<0.05).The results of regression analysis showed that the activity of MMPs was mainly related to the thermal solubility of collagen and the thickness of secondary perimysium,while PRSS and Cath-B were related to the changes of all the constitutive parameters of IMCT.But the role of Cath-L in the weakening of IMCT remains to be studied.4.Effects of different concentrations of low sodium salt and its components on enzymatic activities of collagenase and cathepsinIn the concentration range of 0-0.4 mol/L,the low sodium salt,NaCl,KC1 and His had a critical concentration on the relative enzyme activities of MMPs and PRSS.The critical concentrations of MMPs were 0.15 mol/L,0.20 mol/L,0.20 mo l/L,0.30 mol/L,and the critical concentrations of PRSS were 0.30 mol/L,0.30 mol/L,0.30 mol/L,and 0.10 mol/L,respectively.When the low sodium salt,NaCl and KCl were lower than their respective critical concentrations,the relative enzyme activities of MMPs and PRSS increased with the increase of concentration,but higher than the critical concentrations,MMPs and PRSS maintained the highest relative enzyme activity.When His below the critical concentration,His played a role in promoting MMPs and PRSS,but above the critical concentration,His inhibited these two enzymes.Lys significantly inhibited the activities of MMPs and PRSS.In the concentration range of 0-0.4 mol/L,Low sodium salt,NaCl and KCl had inhibitory effects on Cath-B and Cath-L.His inhibited the enzyme activity of Cath-B.Lys inhibited the enzyme activity of Cath-B when its concentration was lower than 0.20 mol/L.While Lys and His promoted the enzyme activity of Cath-L when their concentrations were lower than 0.20 mol/L.