Antioxidant Distribution and Effectiveness in a Model Muscle System
This dissertation has been moved to the following series:
Gallic acid esters (GAE) of varying alkyl chain length were used to determine how antioxidant physical location and partitioning influence hemoglobin-catalyzed lipid oxidation. Specific GAE used were propyl gallate (PG), octyl gallate (OG), and lauryl gallate (LG). GAE partitioning experiments were performed with either isolated cod muscle membranes or washed cod muscle, which primarily contain polar membrane lipids and myofibrillar proteins. Canola oil was used in some experiments to determine how neutral lipids impact partitioning behavior. GAE distribution was determined spectrophotometrically in the recovered membranes, aqueous phase, and oil layer after employing differential centrifugation. Oxidation was monitored by measuring thiobarbituric acid reactive substances (TBARS) and lipid hydroperoxides development. When GAE were added to the membrane suspensions, significant differences (p < 0.05) in GAE partitioning were observed in the aqueous phase and membrane sediment, where increases in GAE alkyl chain length corresponded with a decrease in aqueous phase concentrations and increases in the membranes. GAE partitioning in the oil fraction did not show significant differences. Also, increases in GAE alkyl chain correlated with increases in GAE membrane detection when GAE were added to the washed fish muscle (p < 0.05). Adding GAE to the washed cod muscle before the canola oil was the most effective sequence of addition for extending the storage time before lipid oxidation was detected. Among the three GAE tested, PG showed the greatest inhibition against lipid oxidation. The effectiveness of the GAE in the washed cod-canola oil system follows the order, PG > OG > LG, which corresponds with decreasing hydrophobicity. The conclusions of this study are twofold. First, GAE partitioning into the muscle membranes was not the primary factor for delaying the onset of lipid oxidation. Rather, solubility in the aqueous phase showed the greatest impact on extending storage time. Secondly, the order in which GAE and canola oil were added to the washed cod (WC) muscle system influenced hemoglobin-catalyzed lipid oxidation behavior. Adding GAE before the neutral oil may have allowed the GAE to partition more easily into the polar regions of the washed muscle, which in turn provided the most effective protection against oxidation.