Palatability control points for grass-fed beef: Revealing the key compounds contributing to beef flavor or off-flavor

Due to the variety of cattle breeds, finishing end point, grass quality, and postmortem management, the quality of grass-fed beef is criticized as inconsistent. To improve the eating quality of grass-fed beef, this dissertation focused on investigating (i) the impact of long chain ω-3 fatty acids on beef palatability; (ii) fatty acid composition of different fat depots; and (iii) the impact of diet and aging on beef palatability, fatty acid composition, and aroma-active compounds contributing to beef flavor and off-flavor associated with grass-feeding systems. The results indicated that ground beef flavor decreased linearly (P < 0.001) with increasing levels of eicosapentaenoic acid (EPA; C20:5n3) and docosahexaenoic acid (DHA; C22:6n3) and that offaroma and off-flavor increased linearly and then plateaued ( P < 0.0001) with increasing levels of EPA. Finishing diet (70 vs. 85 % concentrate) had little impact on Jersey beef palatability. However, increased concentrate level decreased polyunsaturated fatty acids (PUFA) in muscle and increased trans fatty acids in all fat depots (P < 0.05). In addition, monounsaturated fatty acid: saturated fatty acid (MUFA: SFA) ratio was the highest in subcutaneous fat, moderate in muscle and seam fat, and the lowest in kidney, pelvic and heart fat (KPH) and visceral fat (VIS). The PUFA: SFA ratio was the highest in muscle, moderate in subcutaneous and seam fat, and the lowest in KPH and VIS. When comparing Feedlot, TR (triticale and annual ryegrass) and Pasture (fescue, brome, clover and orchard grass) dietary treatments, pasture-feeding had negative impacts on beef palatability. Cooked Feedlot beef steaks had higher percentages of C14:0 and C16:0 and lower percentages of c-9, t-11 CLA and trans fatty acids than pasture-raised steaks. Pentanal was higher in pasture-raised ground beef and nonanal was higher in TR beef compared to Feedlot beef. In addition, wet aging decreased ground beef intensity and increased off-flavor of ground beef. Aging improved the tenderness of beef steaks and increased the concentrations of 1-pentanol, 1-hexanol, and 1-octen-3-ol in ground beef. The results of this dissertation will provide valuable information to grass-fed beef producers to improve their management and eventually product quality.;Keywords: Grass-fed beef; Aging; Palatability; Fatty acids; Aroma-active compounds.