Improvement of the nutritive value of rapeseed by selecting varieties with very low glucosinolate content

S.K. Jensen

Danish Institute of Agricultural Science, Department of Animal Nutrition and Physiology

Research Centre Foulum, DK-8830 Tjele, Denmark

E-mail: Sorenkrogh.Jensen@agrsci.dk

ABSTRACT

Double low rapeseed meal with a glucosinolate content <10 µmol/g seed has in feeding experiments with broilers and piglets shown to be of higher nutritional value, than rapeseed varieties with around 20 µmol/g seed. The measured parameters included feed intake, feed utilization, liver and thyroid enlargement, as well as production of the hormone T3. Heating the rapeseed at 107 °C for 25 min reduced the level of intact glucosinolates with one third and did also reduce the negative effect of glucosinolates on animal performance.

KEYWORDS: Heat treatment, broiler, pigs, animal performance, liver and thyroid enlargement.

INTRODUCTION

Double low rapeseed is the most important oil and protein crop in Denmark, due to its high yield and high nutritive quality of both oil and protein. However, the content of anti-nutrients, as glucosinolates, aromatic choline esters, phytate and dietary fibres, restricts the use of rapeseed meal to sensitive animals (Bjergegaard et al., 1998).

The negative effects of the antinutrients can be reduced or eliminated by plant breeding, proper processing or a combination of breeding and processing (Jensen, et al., 1995 a,b; Liu et al., 1995). With respect to glucosinolates the wide spread growing of double low rapeseed (<20 mmol glucosinolates/g seed) has greatly reduced the negative effect of glucosinolates on animal performance and health. However, even the double low rapeseed varieties are only used in restricted amounts to monogastric animals (Sørensen, 1988). Therefore, it is still relevant to breed for lower glucosinolate content and look at the effect of processing on the nutritional value of rapeseed meal. The present paper comprises results from studies of the effect of heat treatment on rapeseed meal with different glucosinolate concentrations.

EXPERIMENTAL

The rapeseed investigated in this experiment was obtained from a Danish rapeseed breeding Company, DLF-Trifolium, DK-4660 St. Heddinge. Prior to the feeding experiments the seeds were defatted by screw pressing by a pilot plant scale Reinartz oil press at Biotechnologic Institute, DK-6000 Kolding. Prior to pressing all seeds were autoclaved for 25 min at 95^o C in order to inactivate myrosinase and lipoxygenase. After pressing half of the meal from the four varieties with different glucosinolate content were autoclaved at 107^o C for 25 min in order to degrade roughly one third of the glucosinolates.

Rapeseed meal constituted 25% of the diets and the feed was formulated according to common practice with respect to nutrients, energy content and amino acids. Details regarding the feeding experiments has previous been described (Danielsen et al., 1994), Jensen et al., 1995 a,b; Liu et al., 1995). Analyses of glucosinolates were performed by HPLC of desulfoglucosinolates as described by Sørensen (1990).

RESULTS AND DISCUSSION

Glucosinolates

The glucosinolate content in the pressed rapeseed meal of the four different varieties and in their respective autoclaved meal samples is presented in table 1.

Table 1. Glucosinolate content in four rapeseed meal samples before (1-4) and after heat treatment (1h-4h)

	mmol/g meal
Sample	PRO^(1	GNP^(2	GBC^(3	4-HG^(4	GLB^(5	Total
1	1.49	0.55	0	1.26	0.10	3.39
2	8.31	1.74	0.25	1.74	0.13	12.16
3	11.09	2.62	0.91	2.89	0.67	17.86
4	21.59	8.47	2.90	2.71	0.29	35.95
1h	1.28	0.38	0	0.28	0.06	1.99
2h	6.79	1.37	0.29	0.62	0.09	9.16
3h	8.40	2.11	0.79	0.94	0.25	12.49
4h	14.36	5.74	2.03	0.70	0.15	22.97

¹⁾Progoitrin, ²⁾Gluconapin,  ³⁾Glucobrassicanapin, ⁴⁾4-Hydroxyglucobrassicin, ⁵⁾Glucobrassicin

On average one third of the glucosinolates were degraded by autoclaving. 4-Hydroxyglucobrassicin was the most sensitive glucosinolate to auto claving with an average degradation of 71%, while the aliphatic glucosinolates on average only were degraded 20-25%.

Animal performance and health

In table 2 feed consumption, weight gain/week and feed utilization for the broilers and piglets fed the eight experimental diets is shown.

Table 2. Effect of glucosinolate content and heat treatment on feed consumption, weight gain and feed utilization by broilers (10-38 days) and piglets (4-8 weeks) fed diets containing 25 % rapeseed meal.

Sample	Feed consumption kg/week		Weight gain kg/week		Feed utilization kg feed/kg gain
	Broilers	Piglets	Broilers	Piglets	Broilers	Piglets
1	0.950^a	4.03	0.401^a	3.04	2.41	1.33^b
2	1.036^a	4.00	0.401^a	2.60	2.46	1.68^a
3	0.971^a	4.02	0.375^a	2.80	2.62	1.50^ab
4	0.775^b	4.01	0.340^b	2.58	2.29	1.69^a
P-value	0.001	0.18	0.004	0.091	0.16	0.006
1h	1.086^b	4.04	0.422^b	3.03	2.57	1.28
2h	1.237^a	4.03	0.453^a	3.02	2.74	1.47
3h	1.115^ab	4.02	0.417^b	2.91	2.68	1.45
4h	0.920^c	4.04	0.383^c	3.03	2.46	1.30
P-value	0.001	0.61	0.0001	0.91	0.11	0.19

The broilers were fed ad libitum and the feed consumption decreased with the highest glucosinolate concentration in the diet (table 2). Furthermore, autoclaving had a positive effect on feed consumption for all four varieties. The piglets were only fed semi ad libitum and were, therefore, not expected to show any differences in feed consumption. The weight gain of the broilers decreased with the highest glucosinolate content in the feed and the feed utilization decreased for the piglets with increasing glucosinolate content in the feed.

The negative effects of the glucosinolates on production parameters were accompanied by an enlargement of liver and thyroid as well as production of the hormone T3 by the thyroid (Table 3).

Table 3. Effect of glucosinolate content and heat treatment on size of liver and thyroid, and production of the hormone T3 in broilers and piglets

Sample	Liver g/kg		Thyroid mg/kg		T3 nmol/l
	Broilers	Piglets	Broilers	Piglets	Broilers	Piglets
1	19	30^b	83^b	119^b	2,17	2,16
2	22	32^b	124^ab	137^b	2,30	2,90
3	21	31^b	169^a	167^ab	2,27	3,01
4	21	37^a	177^a	192^a	1,68	2,59
P-value	0.08	0.006	0.001	0,01	0,3	0,2
1h	19^b	27	85	100	1,73^b	2,95
2h	21^ab	27	107	105	2,61^a	2,58
3h	24^a	28	125	105	2,53^a	3,01
4h	24^a	30	128	117	2,77^a	3,02
P-value	0.001	0.2	0.06	0,4	0,001	0,8

The present study shows that meal from rapeseed varieties with a glucosinolate content less than 10 mmol glucosinolate/g seed is of a higher nutritive value for broilers and pigs than meal from rapeseed varieties with 15-20 mmol glucosinolate/seed.

REFERENCES

Bjergegaard, C., Jensen, S.K., Quinsac, A. and Sørensen, H. 1998. Analyses of antinutritional compounds in rapeseed. In.: Recent advances of research in antinutritional factors in legume seeds and rapeseed. Wageningen, The Netherlands 8-10 July. EAAP publication 93: 67-90.

Danielsen, V., Eggum, B.O., Jensen, S.K. and Sørensen, H. 1994. Dehulled protein-rich rapseed meal as a protein source for early weaned piglets. Animal Feed Science and Technology 46: 239-250.

Jensen, S.K., Liu, Y.-G. and Eggum, B.O. 1995a. The effect of heat treatment on glucosinolates and nutritional value of rapeseed meal in rats. Animal Feed Science and Technology 53: 17-28.

Jensen, S.K. Liu, Y.-G. and Eggum, B.O. 1995b. The influence of feed size and hull content on the composition and digestibility of rapeseed in rats. Animal Feed Science and Technology 54: 9-19.

Liu, Y.-G., Jensen, S.K. and Eggum, B.O. 1995. The influence of seed size on digestibility and growth performance of broiler chickens fed full-fat rapeseed. Jounal of Science Food and Agriculture 67: 135-140.

Sørensen, H. 1988. Analysis of glucosinolates and acceptable concentrations of glucosinolates in oilseed rape and products thereof used as feed to different animals. GCIRC Bulletin 4: 17-19.

Sørensen, H. 1990. Glucosinolates: Structure-Properties-Function. Ch. 9, pages 149-172, in F. Shahidi (ed.), Canola and rapeseed. Production, chemistry, nutrition and processing technology. Van Nostrand Reinhold New York, NY. 355 pp.