Influence of drying and storage on the lipophilic antioxidants content in rapeseed

During storage, lipids contained in seeds undergo adverse chemical and biochemical processes. The range of these transformations is conditioned mainly by the presence of water and also by the content of natural antioxidants. Among the lipophilic antioxidants occurring in the seeds of oil plants — also rape — are: tocochromanols (-T), plastochromanol-8 (PC-8) and β -carotene. In our climatic zone, the harvested rape seeds require additional drying until their moisture content drops to below 7%. The moisture content of 5–6% is considered the optimum due to high mechanical resistance of the stored seeds, resistance to microorganisms etc. Also the influence of these processes upon the native lipohilic antioxidants significantly determining the stability of lipids in the stored seeds, is of importance. The aim of this study was to investigate the influence of preliminary seed drying — in high as well as in low air temperatures — on the content of natural lipophilic antioxidants immediately after the harvest and after one-year storage. Two rape varieties were considered — Lisek and Kronos (00). Drying temperatures ranged from 60 up to 120°C and also some low air temperatures were applied. After reaching ca 6% moisture content, the seed samples were stored for a year at 18±1°C in darkness. After 12 months, tocopherols, PC-8 and β -carotene were determined again. Qualitative separation and quantitative determination of antioxidants in seeds were carried out by HPLC. It was noted that drying after the harvest resulted in ca 10% total tocopherol loss, and a year storage caused further loss of 50% of these compounds. Similar values were determined for PC-8 (ca 55% in relation to the original content). The smallest loss was determined for β -carotene, and its content in both varieties, Lisek and Kronos, did not exceed 35% and was the lowest in seeds dried at 60°C.