Distillers grains (DG) contribute to cattle sarcoplasmic reticulum (SR) membrane instability by increasing poly-unsaturated fatty acid (PUFA) content in the SR membrane, possibly resulting in early postmortem calcium (Ca) leakage and improved tenderness. Mitochondria are relatively easy to isolate intact and provide the opportunity to study Ca in an SR model. The objective of this research was to determine the influence of diet and oxidation on Ca release from mitochondria. Cattle (n=48) were fed a corn-based finishing diet with or without deoiled, dried DG (50% DM basis). Steaks from each strip loin were aged for 2, 8, 14, and 21 days, powdered, and stored at -80oC for lab analysis. Samples (n=12) were randomly sub-sampled from each diet group for all aging periods. Mitochondria were isolated from day 2, 8, and 14 day-aged samples using high speed ultracentrifugation. The SR was isolated from each day 2 sample. Both mitochondria and SR samples were analyzed for PUFA content using gas chromatography, and phospholipid content using thin layer chromatography. Mitochondria from days 2 and 8 were artificially oxidized using an iron and ascorbic acid mixture. In both organelles, the DG diet samples had higher 18:2 and total PUFA content (P\u3c0.05) contents compared to day 2 and 8 mitochondria, as expected from aging of unsaturated fats. Phospholipid contents (phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol) of the mitochondria and SR were unaffected by diet. Oxidized mitochondria retained significantly less Ca than non-oxidized (P\u3c0.05) mitochondria. Day 2 mitochondria retained significantly less Ca than day 8 (P\u3c0.05) mitochondria. Overall, mitochondria from cattle finished on corn tended (P\u3c0.10) to retain more Ca than mitochondria from cattle finished on DG. Results indicate that greater PUFA content deposited in organelles by the DG diet may affect Ca flux by increased susceptibility to oxidation. A DG diet may influence Ca flux and ultimate tenderness by this mechanism.
Advisor: Chris R. Calkin
