Study On The Quality Change Of Mutton During Roasting Process

Roasted mutton is a common mutton delicacy in the diet of the northwest region.The unique processing method endows mutton with unique flavor,color and texture.Tan sheep is a dominant characteristic livestock breed in the Ningxia region,with characteristics such as tender meat,pleasant flavor,and rich nutrition.Taking Ningxia Tan mutton as the material,the variation law of quality of Tan mutton during the roasting process was studied.The research results were as follows:The response of heat and mass transfer of mutton to the brightness value(L*value)was studied at three roasting temperatures(250 ℃,220 ℃,and 190℃).The water content of mutton has decreased from 73%to 50%.When roasting for 20 min,the external temperature of the mutton was above 140℃,and the internal temperature of the mutton was close to 95℃.The L*e value on the surface of mutton generally showed an increasing trend first and then decreased,and reached the maximum value during 6～8 min of roasting.The surface a*value showed a significant downward trend after 0～6 min,but tended to balance after 6 min of roasting.The surface b*value showed an upward trend during 0 to 4 minutes of roasting,and tended to balance after 4 min of roasting.The ΔE value significantly increased within 0～6 min of roasting and decreased during 8-20 min of roasting,with an overall trend consistent with the change in L*value.The BI value on the surface of the mutton slightly decreased at first and then increased.The internal L*value of mutton generally increased first and then stabilized.The internal a*value showed a significant increasing trend first and then decreased,and finally tended to balance.The internal b*value showed an upward trend first,and then tended to balance after 8 min of roasting.The internal ΔE value significantly increased and remained constant after 8 min of roasting.The internal BI value showed a downward trend first and then increased,and finally tended to balance.Based on the dynamics of mutton color changes induced by heat,mass,and temperature,a three-dimensional numerical model was established to simulate the coupled transport phenomena and color changes during mutton roasting.Utilizing COMSOL Multiphysics 5.3a solved partial differential equations describing the dynamics of color change and ordinary differential equations for mass transfer.The predicted color(L*value)development was validated by experimental values.The distribution and migration of water during the roasting process of mutton at three different roasting temperatures were studied.The combined water content of the three roasting temperatures showed a gradual upward trend,and the non-flowing water content all showed a downward trend.The free water content did not significantly differ during the roasting process(P<0.05).The non-flowing water and free water migration corresponding to the relaxation time of mutton under different roasting times were obvious,indicating that the fluidity of water becomes smaller,and the water with a high degree of freedom gradually transfers to the water with a low degree of freedom.The brightness of the hydrogen proton density image of mutton at the three roasting temperatures showed a decreasing trend with the increase of roasting time,and the roasting temperature of 250℃ was the most obvious,indicating that its internal water content rapidly decreased The total area of low-field nuclear magnetic resonance peaks and the water content of mutton in the roasting process showed a significant linear relationship(P<0.05).The sensory evaluation found that roasting for 12,14 and 18 minutes can be used as the best flavor time and color time for mutton roasting at 250℃,220℃ and 190℃,respectively.The changes in key aroma compounds of mutton were studied at 250℃ roasting temperature.The results indicated that the mutton roasted for 0-20 min could be discriminated by E-nose.A total of 47 volatile compounds were identified by GC-MS,including 10 alcohols,14 aldehydes,6 ketones,3 esters,6 acids,1 furan,and 7 other substances.13 compounds were identified as the key aroma compounds by the odor activity values(OAVs),including 1-octen-3-ol,1-heptanol,hexanal,heptanal,octanal,nonanal,(E)-2-octenal,decanal,(E)-2-nonenal,(E,E)-2,4-decadienal,1-octen-3-one,2-pentylfuran and toluene.Significant increases in concentrations and OAV value of key aroma compounds in samples roasted for 0～8 min were observed during the roasting process,in which hexanal and 1-octen-3-ol had the highest concentration.In comparison with raw meat,the OAVs of 8 key aroma compounds were maintained at high levels in mutton roasted for 12 min.Samples with different roasting times could not be discriminated by the concentration of the volatile compound except for roasting for 20 min.The changes in fatty acids,amino acids,and nucleotides of mutton were analyzed under 250℃ roasting temperature.The results showed that the content of total protein and total fat in Tan mutton increased with roasting time.The total fatty acid content increased first and then decreased and increased finally with no significant difference(P>0.05),and the content of oleic acid,stearic acid and palmitic acid were the highest.The content of total hydrolyzed amino acids increased significantly(P<0.05),especially lysine,leucine and cysteine.Among the free amino acids,the contents of arginine and alanine showed an increasing trend,and the changes of other free amino acids were not significant(P>0.05).The TAV(taste activity value,TAV)method identified that the key umami amino acids in roasted Tan mutton was glutamic acid,the key sweet amino acid was alanine,and the key bitter amino acids were methionine,phenylalanine,valine,and arginine.The main taste substances 5’-inosinic acid and 5’-guanylic acid in roasted Tan mutton increased significantly with the increase of time.The effects of different roasting times on the changes of mutton pH,texture,microstructure,protein degradation and protein secondary structure were investigated under 250℃ roasting temperature.The results showed that the pH value of mutton showed a gradual increase with the increase of roasting time.The shear force,hardness,gumminess and chewiness of mutton samples showed an increasing trend.Electron microscopy results showed that the histological structure of mutton changed significantly with the prolongation of roasting time,both on the surface and inside.The roasted mutton samples showed more structural changes,including the division along muscle fibres,the increase of the space between muscle fibres and the coagulation of connective tissue.Protein secondary structure analysis showed that α-helix(%)decreased and β-sheet(%)increased,the changes of β-turn and random coil were not significant.The bands of myosin heavy chains in the mutton samples gradually became thinner,and the actin bands became blurred.The main peak at 22～24 ? X-ray diffraction indicated the presence of cellulose crystals in the roasted mutton,but this peak gradually disappeared.During the roasting process of mutton,there was a strong positive or negative correlation between the key volatile flavor compounds of mutton and the surface and internal color and temperature of mutton,water content,proteins,fatty acids,amino acids(bonded and free amino acids),nucleotides,pH,texture and secondary structure of the protein.In summary,the response of heat and mass transfer to color(L*value)during the mutton roasting process and the correlation analysis of key volatile flavor substances on meat quality have been established,in order to provide theoretical reference for the research and development of high-quality mutton roasting products.