Kinetics of tocopherol degradation during the storage of wheat germ oil

Abstract

Tocopherol degradation in wheat germ oil was studied during storage at different temperatures. Two types of wheat germ were used: heat-treated germ (HT) and raw germ (RG). The oil was extracted (Soxhlet, n-hexane) and stored at 25 and 47°C (82 days) and at -20 and 5 °C (600 days). Tocopherols were determined by HPLC. Total tocopherol, α-tocopherol, and β-tocopherol decreased following first-order kinetics. At 25 and 47 °C, the values of the degradation rate constants for total tocopherol were 5.00 × 10-3 days-1 (RG), 3.00 × 10-3 days-1 (HT), and 5.37 × 10-2 days-1 (RG), 2.57 × 10-2 days-1 (HT), respectively, indicating an increase in tocopherol degradation rate with increasing temperature. The reaction rates of total tocopherol were similarly affected at 5 and -20 °C, with lower rate constants (4 × 10-4 and 2 × 10-4 days-1, respectively). α-tocopherol degraded faster than β-tocopherol, presenting higher rate constants. Low temperatures favour the preservation of tocopherols.