NATURAL ANTIOXIDANTS IN WINTER RAPE (BRAS SICA-NAPUS L) SEED

One of the most important factors, reducing the nourishing value of fa ts and oil, is their rancidity which is caused by chemical and enzymat ic factors. These are hydrolytic rancidity and oxidative rancidity. Hy drolytic rancidity is caused by lipases which are abundant in immature and budded seeds. In mature seeds their efficiency is small and there fore in the case of good storing of the first-quality rape seed has th ese factors of low significance. More significant is oxidative rancidi ty caused by lipoxygenases, their main substrate are free fatty acids. In the rape its linolic and linolenic acids are present. Lipoxygenase s cause enzymatic oxidation of essential fatty acid. Significant inhib itors of lipoxygenase activity in rape seed are the phenolic compounds . Rape seeds contain the natural antioxidants tocopherols and phenolic compounds. Tocopherols were determined by high pressure liquid chroma tography (HPLC). Their content for gamma-tocopherols ranged from 770 t o 450 ppm and for alpha-tocopherols from 200 to 400 ppm. One zero vari eties of rape seed had lowest content of gamma-and alpha-tocopherols c ompared with double zero varieties of rape seed (Tab. I). During stora ge of rape seed in silos, content of gamma-tocopherols decreased on av erage by 12.5% and alpha-tocopherols on average by 34%. This antioxida nt extracted with oil and during the technological process of producin g oil is distracted. Therefore the final product, considering their vi tamine value, must be fortificated. Phenolic compounds considering hig her content than other oilseeds are more significant antioxidants, whi ch inhibit activity lipoxygenase and can serve as a material for obtai ning antioxidants of natural origin, which carry out the requirements on hygienic, healthy harmless and economic modest accessibility, consi dering surplus of rapemeal. Free phenolic acid were determined by gas- solid chromatography on porous polymer Tenax (Tab. II). For determinat ion of sinapin spectrophotometric method in UV range at 334 nm and in visible range at 405 nm was used. Spectrophotometric methods have prio rity in easily practise without exacting purification technique. The r esults of spectrophotometric method in visible range are about 20% hig her than in UV range, considering interference of similar compounds (T ab. III). The main components of phenolic substances in rape seed are cholin ester of sinapic acid-sinapin and sinapic acid (Tab. II). The c ontent of free phenolic acid in the present varieties ranged from 0.56 to 0.92% where the main acid is sinapic acid with the highest antioxi dative effect (Tab. II). The content of sinapin ranged from 1.35 to 2. 27% (Tab. III). Phenolic compounds content was stable in the last phas e of maturing. Their decrease appeared in the samples which were desic cated with desiccant Reglone four days before the expected harvest (Ta b. IV) and it is similar to the content of phenolic compounds in immat ure seed 14 days before harvest (Tab. VI). The statistically significa nt are also differences among places, which are caused by agroecologic al influences (Tab. V). The content of phenolic compounds in rape seed is higher than that of other oilseeds and surplus rapemeal take their using into consideration as a good source of natural antioxidants. Th eir efficiency compared with synthetic antioxidants, which in some cas e are better, was examined. Provided that rape extract would not chang e the taste, colour and flavor of oil, it could be used for stabilizat ion of rape oil and other foodstuffs which contain lipids.