Levels of fatty acids, tocopherols, and flavor volatiles in meat from lambs fed treated ground full-fat soybean supplements

Supplements containing ground full-fat soybeans mixed with casein and either untreated (control) or treated with acetaldehyde or diacetyl to form gels were prepared. Each of the three supplements (approximately 200 g dry matter or DM), 1 kg of a ground com basal diet and 0.3 3-kg hay were fed daily to each of six lambs from weaning to slaughter (90 days). Samples of the longissimus muscle (LD), intermuscular fat, back fat and kidney fat were obtained from each lamb carcass and analyzed for total lipid content. Fatty acid composition of LD nonpolar and polar lipids, intermuscular fat, back fat and kidney fat, and the α- and γ-tocopherol contents of the LD and back fat were determined. Flavor volatiles of a broiled LD from each lamb also were analyzed.

On a DM basis, the control (CO), acetaldehyde (AC), and diacetyl (DA) supplements contained, respectively, 49.7, 50.0 and 49.1% protein and 17.2, 15.5 and 17.4% fat. On a wet basis, the LD of lambs fed CO, AC and DA contained 3.7, 4.6, and 2.6% fat, respectively. Compared to lambs fed CO, lambs fed either AC or DA had (P < 0.05) a higher level of linoleic acid (C18:2) and linolenic acid (C18:3) in the LD nonpolar lipids, a higher level of C 18:2 but lower level of oleic (C18:1) acid in the LD polar lipids, and a higher level of C18:2 in the back fat and had higher levels of C18;2, C18;3 and stearic (C18:0) acid but a lower concentration of C18:1 in kidney fat. In the LD nonpolar lipids, lambs fed CO had 4.8% C18;2 while those fed AC and DA had 6.4 and 6.8%, respectively. In kidney fat, lambs fed CO, AC and DA had, respectively, 24.9, 27.2 and 26.9% CI8:0; 39.1, 35.4 and 36.3% C18;l; 4.5, 7.7 and 7.1% C18:2; and 0.5, 0.9 and 0.8% C1S:3. Lambs fed CO had lower levels of a-tocopherol in the LD (P < 0.10) and back fat (P < 0.05) than did lambs fed AC and DA. Compared with lambs fed AC, lambs fed DA had higher levels of y-tocopherol in the LD muscle (P < 0.05) and back fat (P < 0.10). In broiled LD muscle, twenty-one volatiles were identified and included seven alkanals, seven 2-alkenals, two 2,4-alkadienals, and five other compounds, but most differences existing in the volatile concentrations among lambs fed the different supplements did not correspond to like concentration differences in their precursor fatty acids. Results imply that compared with the CO supplement, the AC and DA supplements protected C18:2, C18:3 and vitamin E in the oil of the soybeans from degradation in the rumen of the lambs and increased their deposition in the lamb tissues.