Effect of Roasting on Moisture Migration and Key Aroma Compounds of Mutton Tallow

Moisture distribution and migration in the tallow of Tan sheep from Yanchi, Ningxia roasted for different periods were analyzed by low field-nuclear magnetic resonance (LF-NMR). Head space solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and an electronic nose (E-Nose) were used to analyze the volatile components of mutton tallow. The results showed that the L^* value of mutton tallow decreased, and the a^* and b^* values increased with roasting time. The percentage of weakly bound water showed an increasing trend, and the percentage of immobile water showed a decreasing trend. The relaxation time T₂₃ showed a significantly decreasing trend with roasting time, indicating tighter binding of water molecules to macromolecular substances. A total of 78 volatile compounds were detected in 10 samples, including 12 aldehydes, 11 alcohols, 9 ketones, 4 alkanes, 10 acids, 12 esters, 12 heterocyclic compounds and 8 other compounds, with hexanal, nonanal, 1-octene-3-ol, 3-hydroxy-2-butanone, 7-methyl-3-methylene-1,6-octadiene and toluene being the major ones. Esters were found mainly in the early stage of roasting, while heterocyclic compounds, especially pyrazine compounds, mainly in the late stage. Principal component analysis performed on E-nose data showed that different roasting periods had significant effects on the contents of nitrogen oxides, benzenes, organic sulfur compounds and alcohols in mutton tallow, but little effect on alkanes, hydrides and ammonia compounds.