Abstract
The effects of added oryzanol, BHT, sesamol and thiodipropionic acid on the decomposition of tocopherol (Toc), the coloring and oxidation of oils by heating, and their synergistic effects with ascorbyl stearate (As. S) were investigated. Vegetable oils (olive, soybean and hardened soybean oils) with or without additives were heated in glass tubes (2.7×20cm) at 180°C. The remaining amounts of Toc in the oils were determined by HPLC. Color, and the anisidine and carbonyl values of heated oils were determined by the JOCS official method 2. 3. 1. 1 b-7, 2. 4. 26-81, 2. 4. 22-73, respectively. Addition of oryzanol, BHT, sesamol and As. S had no, or only low preventive effects on the thermal decomposition of Toc in the oils. However, mixtures of oryzanol, BHT or sesamol and As. S showed high preventive effects (especially in olive oil). The synergistic effects of mixtures of oryzanol, BHT or sesamol and As. S on the thermal decomposition of Toc increased as the concentration of As. S became higher. A browning reaction of the oil due to heating was most pronunced in the oils containing sesamol than in oils containing oryzanol, BHT or As. S and mixtures of sesamol and As. S. On thermal decomposition of Toc, coloring or oxidation of oil mixtures with thiodipropionic acid and As. S showed greater preventive effects than mixtures of gallic acid, soya lecithin or catechin and As. S examined in the previous study.
