ABSTRACT

From natural antioxidants rapeseed contents tocopherols , phenolic compounds and tannins Content phenolic compounds in rapeseed is higher than in other oilseeds.

Tocoferols are represented in rapeseed as:

alpha tocopherol in content 200 - 400 ppm

gamma tocopherol in content 450 - 700 ppm

One of the zero varieties of rape seed had the lowest content of gamma and alpha - tocopherols compared with double zero varieties of rapeseed.

During rapeseed the storage in silos, content of gamma- tocopherols decreased on average by 12,5% and alpha -tocopherols on average by 34%.

This antioxidant extracted with oil and during the technological process of producing oil is distracted. Therefore the final product , considering their vitamine value , must be fortificated.

Phenolic compounds considering higher content than other oilseeds are more significant antioxidants, which inhibit activity of lipoxygenase and can serve as material for obtaining antioxidants of natural origin, which carry out the requirements on hygienic, healthy harmless and economic modest accessibility, considering surplus of rapeseed meal.

The main components of phenolic substances in rapeseed are cholin ester of sinapic acid - sinapin and sinapic acid.

The content of free phenolic acid in the present varieties ranged from 0,56 - 0,92%.

The content of sinapin ranged from 1,35 - 2,27 %.

Phenolic compound content was stable in the last phase of maturing. Their decrease appeared in the samples which were desiccated with Reglone the desiccant four days before the expected harvest. Oxidative test showed, that the addition of ethanolic extract of rapeseed is more efficiency than synthetic antioxidants.

Tannins ranges at present varieties from 1,50% to 1,96 . During the ripening the content of tannins increases and its maximum is between the harvest time and 7 days after.

Introduction.

Antioxidants are major ingredients that protect food guality by retarding oxidation. Although the use of synthetic antioxidants is common, there is general desire to replace synthetic food additives with natural alternatives (HOWELL,1986).

Sources of natural antioxidants include :

• phenolic coumpounds

• flavonoids.

These substances are in different parts of plants (PRATT and HUDSON, 1990). One of these good sourses is rapeseed

The aim of this work is to determine the composition and content of natural antioxidants in rapeseed and their changes during maturation and storage.

MATERIAL and METHODS

The content of tocopherols and their change in during storage was observed at double zero rapeseed varieties in 12 silos in Czech republic.

Phenolic compounds and tannins were determined at the present varieties together with their changes during maturation at Lirajet on 6. localities.

Determination of tocopherols.

Tocopherols was extracted by petrolether without the presence of light.Surplus of petrolether was evaporated and 1g oil was dissolved in 10ml hexane . This sample was analyzed on HPLC

Determination of phenolic compounds.

Determinarion of sinapine

. Sinapine was determined by the spectrophotometric procedure which was based on the absorption of phenolic compounds in UV range (EVRARD,1985) at 334nm .Aliquots of methanolic extracts of rapeseed meal was measured directly at 334nm

The quantity was determined according to the calibration curve.

Determination of free phenolic acids .

Free phenolic acids are measured by the method of gas - solid chromatography on porous polymer Tenax .Methanolic extract was purified on Presep -C₁₈ and the cleaned extract was chromatographed by HP 5890A in these condition:

Column: 2,5m packed column

Adsorbent : Tenax - GC ( poly ( 2,6 - diphenyl- p- phenylen oxid))

Injector and FID detector - 300^oC

Carrier gas : N₂ - flow rate 30 ml/min

Temperature programm: 10 min 160⁰ C and than 2⁰ C /min up to 250⁰ C.

Free phenolic acids were identified by the comparison of the retention times with standard phenolic acids and their content was determined by external standardization technique.

Determination of condensed tannins.

Condensed tannins were assayed colourimetrically by the method of PRICE et al. (1978)

RESULTS AND DISCUSSION

The winter rapeseed contained from natural antioxidants:

1.Tocopherols

2. Phenolic compounds

1. Condensed tannins

1. Tocopherols are heterocyclic compounds, be called vitamin E.

The seed of harvested rapeseed (WHITTLE 1967) had 770-450 ppm gama tocopherol and 400-200 ppm alfa tocopherol. These contents of gama and alfa tocopherol are in accordance with literature data, when „O“varieties rapeseed had the lowest content of gamma - and alpha -tocopherols compared with double zero varieties of rape seed (Tab.1)

Tab. 1 : Gamma- and alpha -tocopherol content in winter rape (ppm)

variety	GLS(μmol/g semene)1	γ (ppm)2	s(ppm)	v	α(ppm)2	s(ppm)	v
„00“	18,30	741,03	23,19	0,031	384,60	9,10	0,024
„0“	62,50	628,73	19,82	0,031	328,68	15,79	0,048

1 - content of glucosinolates

2 - arithmetic mean of 10 determined data

s - standard deviation

v - variation coefficient

During the storage of rapeseed in silos, the content of gamma- tocopherols decreased on average by 12,5% and alpha - tocopherols on average by 34% ( Fig.1).

Alpha tocopherol is the most weaker antioxidant with the most highest biological activity. This antioxidant extracted with oil and during the technological process of producing oil was distracted. Therefore the final product, considering their vitamine value , must be fortificated.

2. Phenolic compounds.

Phenolic acid and their derivatives are commonly occuring compounds in the plant world. Their presence in seed causes a deterioration in the taste, odor and color of protein concentrates. Besides this fact unfavourable organoleptic changes can oxidize phenolic compounds which are bound with essential amino acid such as lysine or methionine forming complexes which are unassimilable in the digestive tract of animals and man. (Van SUMMERE et al. 1975). In the same way phenolic compounds bind heavy metals into complexes and thus decrease their usability..Besides the mentioned taste effects also they have negative physiological effects on the production of off-flavour or „fishy eggs“ laid by susceptible hens having insufficient trimethylamine oxidase.

Besides these negative characters, on the other side, there are their positive antioxidative characteristics, which inhibit odd activity lipoxygenase in rapeseed and restrict oxidative rancidity and increase the oil stability towards autooxidation..

The seed of rape contains a wide range of different phenolic compounds (KOZLOWSKA et al.1983), which are deriving from benzoic and cinnamic acid in the form free phenolic acids , esterified phenolic acid and insoluble bound phenolic acids.

From free phenolic acid salicylic, o - coumaric, protocatechuic, ferulic, syringic, cinnamic, and sinapic were observed

The main components of phenolic substances in rapeseed are sinapic acid and sinapin ( cholin ester of 3,5- dimethoxy-4-hydroxycinnamic acid). The other phenolic acid and their esters are the minor substitutes in rapeseed. The content of free phenolic acid in the present varieties ranged from 0,56 - 0,92 % where the main acid is sinapic acid with the highest antioxidative effect (Tab.2.) . The content of sinapin ranged from 1,35 - 2,27% , while the lowest content had the variety Stela, of czech origin (Tab.3.).

Tab.2: Composition and content of free phenolic acids in winter rape. (mg/100g)

Variety	free phenolic acid
	salicylic	o-coumaric	protocatechuic	ferrulic1	syringic	cinnamic	sinapic
Lirajet	15,65	0,97	16,99	3,98	52,97	1,22	540,94
Falcon	24,67	0,21	15,96	8,45	32,35	0,55	707,56
Olymp	18,94	0,38	21,71	13,67	67,43	0,47	798,77
Idol	22,46	0,29	14,99	15,02	25,57	1,19	703,94
Stela	9,17	-	3,30	4,58	30,79	1,09	513,77

1.Ferrulic acid has the same retention time as gentisic acid

Tab. 3:The content of total and free(GSC) phenolic compounds in rape meal (%).

Variety	Analytical method used
	GSC	SPECTROPHOTOMETRY
		334 nm
Lirajet	0,64	1,96
Falcon	O,79	1,96
Olymp	0,92	2,27
Idol	0,78	1,47
Stela	0,56	1,35

The spectrophotometric method determines sinapine as the main phenolic compounds rapeseed and their rapemeal.

Phenolic compounds content was stable in the last phase of maturing. Their decrease appeared in the samples which were desiccated with the desiccant Reglone four days before the expected harvest(Tab.4.).

Statistically significant are also the differences among places, caused by agroecological influences(Tab.4)

Tab.4: Dynamics of phenolic compounds production during winter rape seed ripening (the Lirajet variety) on six sites (%)

Site	14 day before harvest	7 day before harvest	harvest	7 day after harvest	desiccated 1
Jaromìøice	1,54	1,48	1,56	1,68	1,29
Kujavy	1,08	1,15	1,18	1,12	0,98
Hradec n. Svit.	1,62	1,59	1,65	1,65	1,35
Vysoká	1,40	1,50	1,55	1,59	1,42
Staòkov	1,15	1,37	1,45	1,19	1,06
Èerv.Újezd	1,35	1,40	1,48	1,45	1,36

1 - stand desiccated 4 days before the predicted harvest

3. Tannins

Content of condensed tannins at present varieties is from 1,50% at variety Lirajet to 1,96% at Falcon. Our dominate variety - Lirajet has the lowest content of tannins (Tab.5). During the winter rape seed ripening the content of tannins increases and his maximum is between the harvest and 7 day after the harvest time.(Tab. 6)

Tab.5: Content of tannins at present varieties.

Variety	Tannin ( % )
Lirajet	1,50
Falcon	1,96
Zeus	1,83
Idol	1,71
Ceres	1,90

Tab.6: Dynamics of condensed tannins during the winter rape seed ripening (the Lirajet variety) in six sites (%)

Site	14 day before harvest	7 day before harvest	harvest	7 day after harvest	desiccated 1
Jaromìøice	1,60	1,60	1,81	1,90	1,55
Kujavy	0,80	0,80	1,10	1,30	1,15
Hradec n. Svit.	1,70	1,82	1,82	1,57	1,20
Vysoká	1,46	0,99	1,38	1,50	1,17
Staòkov	1,38	1,43	1,28	1,60	1,13
Èerv.Újezd	0,95	0,95	1,80	1,80	1,50

stand desiccated 4 days before the predicted harvest

Acknowledgements

The authors gratefully acknowledge support from the Grant Agency of Czech Republic.

This work was supported in part from research grant N o.521/99/047

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