Partitioning of an exogenous lipid -soluble antioxidant between the neutral- and polar lipids of minced muscle
Lipids of minced or comminuted muscle foods are particularly susceptible to oxidative deterioration. As a result, antioxidants are added to these products to retard the undesirable changes accompanying oxidation. The efficiency of an added antioxidant is related to its particular location within the product. Thus, directing the added antioxidant to the site where oxidation is initiated and/or propagated is of significant importance. The partitioning of δ-tocopherol between the neutraland the polar lipids of chicken leg muscles was investigated. The two lipid fractions were separated using differential ultracentrifugation techniques. Neutral lipids were obtained after high speed centrifugation of the minced muscle at 130,000 g for 30 min. The polar membrane lipids were collected from a muscle-buffer homogenate (pH 7.5) between 10,000 g for 20 min and 130,000 g for 30 min.
The neutral oil collected represented from 11 to 90% of the to triacylglycerols of the minced muscle. The polar membrane lipids represented from 25 to 35% of the total membrane lipids of the muscle. The partitioning of δ-tocopherol between the two lipid fractions depended on the amount of tocopherol added. At low total lipid contents the added δ-tocopherol was present in approximately the same concentration in both muscle lipid fractions. At higher total lipid contents the δ-tocopherol concentration in the membrane lipids increased relative to the neutral lipids.
The δ-tocopherol uptake by the lipids of the membranes suspended in buffer increased linearly with tocopherol concentration added in the range of 4 to 4,000 ppm δ-tocopherol on a lipid basis. The membrane lipids contained up to 50% of the added tocopherol. This indicates a high capacity of the membranes for tocopherol incorporation or binding. Studies with model systems consisting of suspended membrane lipids and chicken oil suggested an insignificant exchange of δ-tocopherol between the two lipid fractions when the tocopherol was initially residing in either fraction. This may be due to strong hydrophobic interactions between the antioxidant and the lipids in which it resides. An insignificant uptake of δ-tocopherol by the membrane lipids was also observed when the tocopherol was added in corn oil to a model membrane lipid-chicken oil system. In contrast, when δ-tocopherol was added to the model system dissolved in ethanol the uptake of the membrane lipids increased dramatically.
It is proposed that the partitioning of tocopherol between the different lipids of a minced muscle is governed mainly by the relative surface areas of the lipids and the tocopherol concentration in the aqueous phase immediately after its addition. For this purpose the polarity of the tocopherol carrier (solvent) is of particular importance.
Anatomy & physiology;
0433: Anatomy & physiology