Effect Of Intramuscular Fat On The Formation Of Volatile Compounds In Lamb

Intramuscular fat(IMF)plays a key role in lamb grading,and is a strong driver of lamb flavor formation.IMF in lamb is affected by many factors such as breed and feeding system.Here,lamb within and between breeds,and under castration were established to investigate the effect of intramuscular fat on volatile compounds,which may provide a basis for meat quality improvement.The results are as follows:(1)Effect of IMF variation within Hu sheep on volatile compoundsA flock of 195 male new-born Hu sheep with similar weights were housed in individual units,and fed the same experiment diets ad libitum to 180 days of age until slaughtering.The IMF characteristics of Hu sheep varied between individuals(ranging from 1.91% to 7.93%).According to IMF content,24 samples were selected and allocated to two groups,including the low-IMF(LIMF,2.24% ± 0.25%)and high-IMF groups(HIMF,5.17% ± 0.53%,P < 0.01).Then we investigated the influence of IMF variation within breeds on lipid and volatile compound profiles using lipidomics and volatilomics.Lipidomic analyses indicated that triglyceride,diglyceride,and 69 lipid molecules in the HIMF group were significantly higher than those in the LIMF group(P < 0.05).Volatilomic analyses revealed that concentrations of lipidderived compounds,including nonanal,octantal,(E,E)-2,4-decadienal,and(E)-2-nonenal significantly decreased in the HIMF group relative to the LIMF group while dimethyl trisulfide significantly increased(P < 0.05).By performing partial least squares regression,differences of odorants between the LIMF and HIMF groups might be related to oleic acid,linoleic acid,and linolenic acid profiles in triglycerides and diglycerides.Therefore,IMF variations within Hu sheep altered fatty acid profiles in glycerides,and played a critical role in the formation and release of lipid-derived compounds through oxidation degradation or molecular binding.(2)Effect of castration on IMF and volatile compounds in psoas major muscle of Hu sheepIn this study,twenty-four male new-born Hu sheep with similar weights were randomly assigned to a castration group or a control group.Animals in the castration group were sterilized with veterinary external disinfectant and castrated at 3 d of age using a rubber ring with a Burdizzo clamp.All sheep were housed in individual units and fed the same experiment diets ad libitum to 27 weeks of age until slaughtering.Here,we investigated the effect of castration on IMF and volatile compound profiles using lipidomics and volatilomics.Castration increased intramuscular fat content(3.75% ± 0.16%,P < 0.05).Lipidomic analyses suggested that levels of phosphatidylcholine,phosphatidylethanolamine,diglyceride,and 224 lipid molecules significantly increased in castration group against the control group(P < 0.05).Volatilomic analyses indicated that concentrations of 1-octen-3-ol and hexanal were significantly higher in castrated sheep relative to the intact sheep(P < 0.05).By performing partial least squares regression,differences of odorants between the intact and castrated sheep might be related to oleic acid,linoleic acid,and palmitoleic acid profiles in triglycerides,diglycerides,phosphatidylcholines,phosphatidylethanolamines,and free fatty acids.Therefore,castratsion increased IMF content,altered fatty acid profiles in glyderides and phospholipids,and influenced the formation of aroma compounds through altering oxidation degradation.(3)Comparison of volatile compounds in psoas major muscle from Hu sheep and Tan sheep with similar IMFA flock of 176 male new-born Hu sheep and 76 male new-born Tan sheep with similar weights were housed in individual units,and fed the same experiment diets ad libitum to 180 days of age until slaughtering.We investigated differences in IMF and volatile compounds between Hu sheep and Tan sheep.No difference was observed in IMF between breeds(P > 0.05).Representative samples of each population were selected.Concentrations of oleic acid,linoleic acid,mono-and ploy-unsaturated fatty acids were similar between Hu sheep and Tan sheep(P > 0.05).Concentrations of(E)-2-octenal and 2-acetyl-2-thiazline significantly increased in Hu sheep against Tan sheep(P < 0.05).These results indicated that IMF and unsaturated fatty acid composition were similar between Hu sheep and Tan sheep,and(E)-2-octenal and 2-acetyl-2-thiazline were significantly different.In conclusion,(i)IMF variations within Hu sheep existed,could be mainly ascribed to changes in glycerides,and contributed to the formation and release of lipid-derived compounds through altering oxidation degradation and molecular binding.(ii)Castration increased IMF,altered fatty acid profiles in glycerides and phospholipids,and led to changes in aroma compounds through oxidation degradation.(iii)The profiles of IMF were similar between Hu sheep and Tan sheep,and(E)-2-octenal and 2-acetyl-2-thiazline were significantly different.These results may provide a basis for a deeper understanding of the relationship between intramuscular fat and flavor quality.