| The changes in various physicochemical characteristics,shear force value and texture properties,and microstructure of Longissimus muscle with water content and NaCl content in pork dehydrated at different hot-air drying temperature(25??60?),and the change rule of hardness,chewiness,springiness,cohesiveness,shear force value as well as microstructure were also investigated.The details are listed as follows:1.The change rule of the dehydration rate and the physical characteristics of salted pork is as follows:(1)Under different temperatures,deceleration drying stage was the main stage of the drying process of pork: at 25?,for the same moisture content samples,when the dry basis moisture content between 130%~195%,except for 1% salted samples,drying rate of other salted samples was significantly higher than those of control group(p<0.05),and drying rate increased with the increase of NaCl content in the samples.At 60?,under the same water content,drying rate of 8%,12% and 16% salted samples increasesd with increase of NaCl content in the samples significantly(p<0.05).(2)Aw decreased with the decrease of moisture content gradually,when the concentration of NaCl was ? 8%,under the same water content,Aw decreased with the increase of NaCl concentration,when the concentration of NaCl was >8%,the difference between samples was not significant;(3)During the dehydration,the transverse shrinkage ratio,longitudinal shrinkage ratio,and volume change rate increases with the dehydration,and values of 60? were higher than that of 25?.Compared with the blank samples,the lower concentration salted sample changed little,volume change rate of 4% and 8% salted samples was less than that of blank samples,and 4% samples was less than 8%.The volume shrinkage was inhibited when the concentration of NaCl is higher than 4%,and the higher concentration,the more obvious inhibition;correlation analysis shows that the shear force,hardness,chewiness were negatively correlated with moisture content and Aw significantly(p<0.05),and the texture properties above were positively correlated with the transverse shrinkage ratio,longitudinalcontraction ratio and the volume change rate,the influence of water and volume change on shear force,hardness,chewiness was 8%>4%>1%.(4)Under the 60? dehydration,redness(a*)and lightness(L*)other than yellowness(b*)were mainly influenced by NaCl.When the water content was ? 36%,a* of 1% salted samples was higher than other samples,when water content was ?45%,L* of higher salt samples(12%,16%)was higher than other samples;(5)When the concentration of NaCl was ?8%,TBARS of samples was significantly higher than that of blank samples(p<0.05),and the difference between salted samples and blank ones decreased with the increase of NaCl concentration.When the water content was higher(48%~60%),the degree of lipid oxidation increased with the decrease of water content,and the TBARS of higher salted samples was constantly decreased with the reduction of water significantly(p<0.05).2.The change rule of the shear force and the texture properties of salted pork is as follows:(1)At both temperatures,shear force,hardness,chewiness(except for the samples dried at 25? with water content ?44%)of samples whose concentration was ?8% increased with the increase of NaCl concentration,for the samples of which NaCl concentration was >8%,the values above decreased with the increase of the NaCl concentration;at same water content,the springiness of 4%~16% salted samples decreased with the increase of NaCl content in samples significantly(p<0.05),while the cohesiveness was opposite.(2)In comparison,the extent of hardness increase with reduction of water for high salted samples dried at 60 ? was greater than that of 25?,indicating that high temperature had a good effect on the increase of hardness for high salted samples at lower water content,while the decrease extent of low salted samples(1% and 4%)was close at both temperatures.The chewiness of samples dried through 60? was higher than that of 25?,showing that high temperature can strengthen the chewiness of samples.the elasticity change of pork was inhabited by increasing the drying temperature from room temperature to 60?,this may be due to degeneration and shrinkage myofibrillar protein and collagen,and the presence of NaCl contributed to this change which leads to the springiness of salted samples wasgenerally lower than that of blank samples.(3)It can be concluded from the correlation analysis: at 25?,the shear force,hardness,chewiness were negatively correlated with Aw,water content significantly(p<0.01),and were positively correlated with volume change rate significantly(p<0.01);the springiness,cohesiveness were positively correlated with Aw,water content significantly(p<0.01),and were negatively correlated with volume change rate significantly(p<0.01).The effect index of water content on hardness,chewiness,shear force was: 1%<4%<8%,indicating that NaCl aggravated the hardening of samples with water reduction.At 60?,shear force,hardness,chewiness were positively correlated with volume change rate of samples significantly(p<0.01),but the correlation coefficent difference between blank samples and salted ones was not significant.3.It can be concluded from the SEM microstructure: at 25?,the effect of moisture reduction on the muscle fibers was obvious,for the samples salted by ? 8% NaCl,the reduction of muscle fiber diameters,endomysium,perimysium separation from muscle fibre and integrity failure,denaturation of sarcoplasmic protein occurred at relatively higher water content with the increasing of NaCl concentration,showed that NaCl exacerbated the destructive effects of water reduction on muscle fiber structure;at 60?,effect of heating on the muscle fiber and connective tissue is more intense,the change of blank samples presented when the moisture content was below 40%,while the change of muscle fiber structure had been clearly presented when the water content was just below 50%,especially for the 8%salted samples.The microstructure change of dried pork was related to its physicial properties(volume change rate,TSR,LSR),shear force,as well as texture properties(hardness,chewiness).4.At both temperatures,the salt soluble protein content of samples decreased during dehydration.For samples of which NaCl concentration was ?8%,their salt soluble protein content increased with NaCl concentration,and the salt soluble protein of high salted samples denatured obviously.5.At 25?,myofibrillar protein surface hydrophobicity of samples whose NaCl concentration was ? 8% increased during dehydration,at the same water content,thehydrophobicity of samples increased with the concentration of NaCl significantly(p<0.05),the high salted samples increased first and then decreased slightly,significantly less than the8% salted samples(p<0.05).At 60?,hydrophobicty was higher than that of 25?,especially for the 8% salted samples,the hydrophobicity of the samples increased until the moisture content was about 50%,and then the lower salt samples tended to be constant,higher salted(>8%)slightly reduced.6.At both temperatures,the sulfhydryl content of the samples decreased,the decreasing extent of 60? was greater.At 25?,the decreas extent of sulfhydryl content of the sample of which NaCl concentration was ?8% decreased with NaCl concentration increasing,until the concentration was >8%.At 60?,when the water content was 36%~52%,the sulfhydryl content of the samples whose NaCl content were >1% increased with the increasing of concentration significantly(p<0.05),the sulfhydryl content of high salted samples was less than 8% salted samples,and it decreased with the increasing of NaCl concentration(p<0.05).7.Correlation analysis of Physical indexs,chemical indexs,texture parameters,shear force shows: At 25 ?,the sarcoplasmic protein content and salt soluble protein of unsalted samples is not related,while it shows extremely significant negative correlation(p<0.01)for all salted samples(p<0.01).The surface hydrophobicity and sulfhydryl content were significantly related(p<0.01)for unsalted samples and salted samples whose concentration was <8%,and correlationship increased with the increase of NaCl concentration.Salt soluble protein content was significantly positive correlatied(p<0.01)with springiness,cohesiveness,while was significantly negative correlatied(p<0.01)with hardness,chewiness and shear force.It indicates that protein-protein form disulfide bond by cross-linking,combining to form larger molecules,which is great effect on the increase of shear force,chewiness and hardness at 25?.With the increase of salt concentration,the correlation coefficient increased,suggesting that NaCl promoted the formation of two disulfide bond between protein molecules.At 60?,negative correlation coefficients between hardness,chewiness,shear force and sulfhydryl content of the four group samples decreased,and the values of salted samples were less than that of blank samples,indicating that the denaturation and contraction of myofibrillar protein as well as collagen plays a decisive role on the formation of meat texture. |
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