A dimeric oxidation product of γ-tocopherol in soybean oil

A dimeric oxidation product (5-γ-tocopheroxy-γ-tocopherol) has been isolated from soybean oil and identified. The dimer content in extracted oil was increased by elevating the moisture level in raw soybeans. With moisture increase, no change in the quantity of α-tocopherol was observed, but γ- and δ-tocopherol contents were greatly decreased and two kinds of dimer were formed from γ- and δ-tocopherols. When the moisture level in moistened beans was lowered, these dimers reverted to their corresponding original tocopherols. The same results were obtained by treating pulverized soybeans with various reducing agents. γ-Tocopherol added to autoxidizing soybean oil was oxidized more easily in the presence of oxidation products derived from tocopherols and turned into the dimeric product.