Distribution and effectiveness of exogenous antioxidants in a mixture of minced cod muscle and canola oil
The membrane lipids of muscle foods are reported to be more susceptible to oxidation than triacylglycerols. The objective of this research was to determine the factors influencing the distribution of a lipid-soluble antioxidant, δ-tocopherol, between the membranes and triacylglycerol fractions of a cod muscle-canola oil system. The membrane and triacylglycerol fractions were separated physically by centrifugation and analyzed for their δ-tocopherol content using HPLC. Chemical and sensory studies were used to follow oxidative stability.
Addition of ethanolic-δ-tocopherol to the muscle before the triacylglycerol incorporated more tocopherol into the membranes and increased the oxidative stability than the reverse order of addition. When triacylglycerol was solid, the amount of tocopherol incorporated into the membranes was higher than if the triacylglycerol was liquid, and the amount of tocopherol incorporated into the membranes was less dependent on the order of tocopherol and triacylglycerol addition. Some of the tocopherol did not enter either the membrane lipid or triacylglycerol phases.
The dielectric constant of the antioxidant carrier solvent for the optimum incorporation of δ-tocopherol into muscle membranes when the tocopherol was added before the oil was approximately 21–24. This value shifted to 27 when oil was present in the system before antioxidant addition. Tocopherol concentration in the oil fraction decreased continuously with an increase of dielectric constant of the carrier solvent from 17 to 32 when the antioxidant was added before the oil. When oil was added first, no change in tocopherol concentration of the oil fraction was observed except at a dielectric constant of 32 (propylene glycol). The uptake of tocopherol was low in both the oil and membrane fractions when the carrier was propylene glycol.
In herring muscle and a lean muscle-canola oil model system, hydrophilic antioxidants such as propyl gallate and TBHQ were more effective than lipophilic antioxidants such as δ-tocopherol and BHT, in increasing the oxidative stability. The oxidative stability of a lean muscle-canola oil system in the presence of propyl gallate and δ-tocopherol was not affected by the dielectric constant of carrier while that of BHA was.