Enrichment of Tocopherols and Phytosterols in Canola Oil during Seed Germination

Abstract

The effect of canola (Brassica napus L.) seed germination under illuminated and dark environments on the total concentration and the composition of tocopherols and phytosterols in seedlings and extracted oil were investigated. During the first 10 days of germination, a decrease in gamma-tocopherol was offset by an increase in alpha-tocopherol, indicating the interconversion of these isomers. From day 10 to day 20 under illumination, there was a net increase in alpha-tocopherol and total tocopherols suggesting the synthesis of new tocopherols, whereas there was no net increase in tocopherols in dark. Tocopherols were mainly concentrated in the leafy seedling tops rather than in the non-photosynthesizing bottoms, whereas phytosterols were equally distributed across both sections. The total tocopherol content of oil extracted from 20-day-old seedlings was 4.3- to 6.5-fold higher than that of intact seeds. On a dry seedling basis, the content and composition of phytosterols did not change significantly (p > 0.05) over the sprouting period, but the concentration of total phytosterols in the oil fraction increased 4.2- to 5.2-fold. The concentration of these valuable phytochemicals in the oil fraction is largely due to the depletion of oil reserves during germination, as well as the de novo synthesis of new alpha-tocopherol stimulated by the presence of light. Germination may represent a viable means to naturally concentrate these high-value constituents in canola oil, offering improvements in oil quality based on the nutritional value and oxidative protection offered by tocopherols and the health benefits provided by both tocopherols and phytosterols.