Chemical composition of rape seed from low glucosinolate varieties grown in Poland

Basal nutrients, fatty acids, macro-and microelements, and antinutrients: glucosinolates, tannins and phytates, were determined in 26 samples of sowing seed of 5 varieties of low glucosinolate rape obtained from local branches of Seed Company covering an area of Poland. Amino acids, carotene, and xanthophyll were assayed in pooled samples of each variety. The differences among the samples representing each variety were rather small. Crude protein content was from 19.1 to 22.7% D M , in Libravo and Bolko varieties, respectively, lysine from 6.48 to 7.30 g/16 g N , substantial intervarietal differences in erucic acid content were found; mean value was 0.99%. Aliphatic glucosinolate content ranged from 8.1 in Bolko to 15.7 /miol/g defatted matter in Ceres and was closely correlated with sulphur content. Phytic phosphorus comprised 74.8% of total P content.


INTRODUCTION
Rape seed production in Poland amounted to 1.043 million tons in 1991, and dropped by about 27% in 1992 because of unfavourable climatic and economical conditions.Low glucosinolate (LG) rape accounts for about 98% of total rape production in Poland (Krzymariski, 1993).The main varieties grown are: Bolko, Ceres, Liporta, Libravo and Mar.According to Polish Standard (1990) glucosinolate content in LG rape seeds should not exceed 25 micromoles per gram of defatted seed.
Due to an almost total elimination of glucosinolates and erucic acid, the full fat rape seed may be considered as a dietary component for poultry and pigs.However, the level of inclusion of seeds is limited by the residual glucosinolates, tannins, phytate and fibre which decrease its nutritive value.
An assay of chemical composition of LG rape seed grown in North-Eastern Poland by Matyka et al. (1992) did not include the intervarietal comparison.It seemed therefore important to take into account possible changes in seed composition associated with development of new varieties of LG rape seed and to repeat the study on the chemical composition of LG rape seed grown in Poland.

MATERIAL AND METHODS
Twenty-six samples of sowing seed of LG rape obtained from regional stores of Seed Company from all of Poland, were represented 5 varieties: Bolko (9 samples), Ceres (7), Liporta (4), Libravo (3), Mar (3).The number of samples per variety was related to the proportion of the variety in total crop of rape seed.Bolko, Ceres, Liporta and Libravo were obtained from 1991 harvest, Mar from 1992.
The seeds were finely ground for analysis, the fat-free samples were prepared for glucosinolate, phytate and tannin determinations.
Basal nutrients were assayed using Weende methods with modifications presented in Poland Standards.
For amino acid (AA) analyses, composite samples were prepared by pooling 5 g of each sample within the variety.AA concentration was measured using a Beckmann Model 119 CL Liquid Chromatograph with an ion-exchange system after 20 h hydrolysis in 6 N HC1 at 110°C.Methionine and cystine were defermined after oxidation according to Moore et al. (1958) and tryptophan after alkaline hydrolysis according to Miller (1967).
After estrification of FA with a boron trifluoride catalyst in methanol (Matyka, 1976), the fatty acid (FA) composition of lipid fraction was determined by gas chromatography using Hewlett-Packard 8750 Serie II chromatograph.
Carotene and xanthophyll were estimated according to La Roche method (Keller, 1988) in composite samples prepared as for AA analysis.
The isothiocyanate level was estimated by gas chromatography (Polish Standard, 1986) and recalculated as glucosinolates.Tannin content in defatted samples was estimated by a spectrophotometric method (Tyczkowska, 1977).
Phytates were extracted and phytic acid was precipitated with ferric chloride and analysed for P after digestion (Oberleas, 1971).
The data was subjested to analysis of variance.

RESULTS AND DISCUSSION
With the exception of crude protein and nitrogen-free extractives, the basal nutrient contents did not differ among five varieties of LG rape (Table 1).The CP means ranged from 19.1 to 22.7% DM for Libravo and Bolko varieties,  Matyka et al. (1992).
The Polish LG rape seed, except var.Bolko, had slightly lower CP than the Canadian rape of Canola type (Nwokolo and Sim, 1989;Sibbald, 1986).The contents of ether extract, crude fibre and ash in Polish rape seed were in agreement with Canadian data, except for lower fibre content than 13.5% in Canola seed found by Nwokolo and Sim (1989) but this result probably refers to defatted sample.
Differences in AA concentration in seeds (% DM) were associated with variation in crude protein values (Table 1).The highest levels of AA were found in Bolko and the lowest in Libravo but when expressed as g/16 g N the levels of most essential amino acids were the highest in Libravo.The lysine content was in the range from 1.39 to 1.57% DM and from 6.48 to 7.30 g/16 g N (Table 2).Lower values for lysine are given in INRA Tables (1.21% and 5.59%; Raw Material Compendium, 1992).Bell and Keith (1991) noted 5.96% of lysine in rape seed protein.
The fatty acid composition of seeds (Table 3) was rather uniform, but some differences, especially in palmitic, oleic, eicosenoic and erucic acid content were  The aliphatic glucosinolate content was low and did not exceed 25 /rniol/g of defatted matter in all samples (Table 6).The values ranged from 8.1 jumol/g (Bolko) to 15.7 /miol/g (Ceres), (P ^ 0.05).Glucosinolate content Y (/miol/g) was correlated with sulphur content X (g/kg) with the respective regression equation: Y-8.25X -27.7 ±0.76, r = 0.955 Mean tannin content was 10.8 ± 1.2 g/kg DM.Phytate level amounted to 19.5 g/kg DM.Phytic phosphorus, poorly utilized by monogastric animals, comprised 74.8% of total phosphorus content.A ratio of molar content of phytate, expressed as phytic acid, to zinc amounted to 39.6 and was not favourable.At the high inclusion of rape seed in diet, attention should be paid to meeting requirement of animals for zinc.Similar values were obtained in ealier studies (Matyka et al., 1993).
Differences in chemical composition of samples representing each rape variety were rather small, irrespectively of the origin of sample.This indicates the uniformity of the analysed material and shows that the growing conditions in Poland do not affect to a great extent the levels of major nutrients, minerals, and amino acids.
(P ^ 0.05).Similar high protein content (23.3% DM) in LG rape seed produced in North-Eastern Poland (mainly var.Bolko) was found by values in the same line followed by different letters are significantly different (P<0.05)respectively

TABLE 5
values in the same line followed by different letters are significantly different (P<0.05)