Plant Foods for Human Nutrition 47: 287-292, 1995. © 1995 Kluwer Academic Publishers. Printed in the Netherlands.

Effect of dietary fibre from cereal brans and legume seedcoats on serum lipids in rats

MONICA SHARMA & ASHA KAWATRA* Department of Foods & Nutrition, Haryana Agricultural University. Hisar 125004, India (* author for correspondence)

Received 29 October 1993; accepted in revised form 30 December 1994

Key words: Dietary fibre, Cerealbrans, Legume seedcoats, Serum lipids, Cholesterol, HDL- cholesterol, Phospholipids, Triglycerides, HemiceUulose, Plant foods, Cornbran, Blackgram seedcoat

Abstract. The present investigation was carried out to study the hypolipidemic effect of dietary fibre from cornbran and blackgram seedcoat in rats. Isoproteinous diet having one percent cholesterol and ten percent dietary fibre from cornbran and blackgram seedcoat was fed to four groups of albino rats for six weeks. With consumption of both the grain husks, total lipids, cholesterol and tryglycerides were lowered while HDL-cholesterol was found to be significantly increased. However, serum phospholipids were not affected significantly by grain husks. Cornbran was observed to be more hypolipidemic than blackgram seedcoat.

Introduction

Seedcoats and brans which are the by-products of shellers and dall millers are discarded as a waste but these can be effectively used as a potent source of dietary fibre. Dietary fibre has protective effect against a range of diseases, as constipation, diverficular disease, large bowel cancer, diabetes, coronary heart disease, obesity and gallstones. Hyper-cholesterolemia has moved to the forefront as a major risk factor for coronary heart disease which is emerging as the world's major health problem. Pectin, cellulose, some fruits and vegetables have been studied for their hypolipidemic properties but unconven- tional sources like grain husks still need exploitation. Hence, the present study was conducted to assess the hypolipidemic effect of dietary fibre from cereal brans and pulses seedcoats in rats.

Materials and methods

For the present study cornbran was obtained from a corn starch Mill, Yamunanagar and Blackgram were purchased from local market, Hisar soaked for 12 hours, dried and split to remove the seedcoat. Cornbran and blackgram

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seedcoat contained 78.06% and 71.95% total dietary fibre, respectively. Cor- nbran and blackgram seedcoat had hemicellulose, cellulose, lignin and pectin 57.93% and 23.76%; 16.63% and 39.23%; 3.26% and 7.00%; 0.02% and 1.95%, respectively.

Experimental design

Thirty-two disease free white albino rats were procured from the Disease Free Small Animal House of Haryana Agricultural University Hisar. These rats were divided into four groups (two experimental and two control groups) and fed isoproteinous (10%) diets containing one per cent cholesterol and ten percent dietary fibre from cornbran and blackgram seedcoat for six weeks. Both the control groups were fed with cellulose as the source of dietary fibre. One of the control groups was kept on cholesterol free diet (Table 1). In the last week of experimental period faecal matter was collected and analysed for faecal cholesterol (Ames blood analyser) and bile acids [11. On 42nd day, rats were anaesthetised and dissected. Serum samples were analysed for total lipids (gravimetrically), total cholesterol (Ames blood analyser based on Libermann- Burchard reaction) HDL-cholesterol (colorimetrically based on precipitating reagent method), triglyceride (Ames blood analyser based on enzymatic non colorimetric method) and phosphotipids [2].

Table I. Composition of experimental diets

Amount (g/kg diet)

Cellulose Cornbran Blackgram seedcoat

With Without With With cholesterol cholesterol cholesterol cholesterol

Albumen powder 111.1 111.1 99.6 95.9 (90% protein) Fat (hydrogenated 50 50 50 50

vegetable oil) Mineral mixture ~ 35 35 35 35 Vitamin mixture" 10 10 10 10 Sucrose 100 100 100 100 Choline chloride 3 3 3 3 DL-Methionine 3 3 3 3 Cholesterol 10 -- 10 10 Blackgram seedcoat . . . . . . . 139 C o r n b r a n . . . . . . I285 Cellulose 100 100 - - - - Starch 577.9 587.9 560.9 554.1

abased on the National Academy of Science recommended levels for rats (BARR Committee on Animal Nutrition, t972).

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Results and discussion

Serum total Iipids. It was observed that rats in the cholesterol free cellulose fed group had significantly (p < 0.05) lower total lipids as compared to all the cholesterol supplemented groups (Table 2). The additional cholesterol fed might have been responsible for the higher value. Total serum lipids were significantly (p < 0.05) decreased when grain husks were supplemented as the source of dietary fibre in rats' diets, being lowest (503 mg/100 ml) in the group fed with cornbran. Similar reduction in total lipids was found in one of the earlier studies in which rats were fed with dietary fibre from peepaI banti, barbanti, 9ullar, teent, and khejri beans [3]. A 12 and 19 percent decrease in serum total lipids on feeding 10 g guar flour with each main meal for one and two weeks, respectively has also been reported [4]. Similar effect was observed when 25 g isabgol husk was added to the diet of 11 adolescent girls daily [5]. Hypolipidemic effect of cornbran and blackgram seedcoat may involve the ability of dietary fibre to sequester micellar components suggesting that the fibres may have direct interference with lipid absorption [6]. These fibres have been reported to reduce the rate of diffusion of products of digestion towards the absorptive mucosal surface of the gastrointestinal tract [7].

Serum total cholesterol. All the cholesterol supplemented groups had signifi- cantly (p < 0.05) higher serum cholesterol than the cholesterol free cellulose group. This may be attributed to the additional cholesterol fed. As compared to the rats in the cellulose fed group both cornbran and blackgram seedcoat groups had significantly (p < 0.05) lower serum total cholesterol which was 50.99% less in cornbran and 43.72% less in blackgram seedcoat groups (Table 2). The cholesterol lowering effect may be attributed to the high hemi-

Table 2. Effect of feeding different sources of dietary fibre on serum lipids of weanling rats fed with cholesterol (1%) supplemented diets (rag/100 ml)"

Dietary group Total Total HDL- Triglycerides Total lipids cholesterol cholesterol phospholipids

Cholesterol 503.4 _+ t0.63 87.0 __ 6.54 36.2 _+ 4.11 134.4 + 11.35 139.2 _+ 3.37 (without (41.60) cholesterol) Cellulose 717.8 _+ 7.85 231.0 _+ 10.37 62.0 +_ 3.40 254.4 __ 16.52 169.6 _ 6.18

(26.83) Cornbran 530.0 _+ 6.06 1132 _ 6.04 86.2 _+ 1.05 176.0 +_ 6.09 154.2 _+ 4.16

(76.14) Blackgram 560.8 _+ 7.85 130.0 + 6,57 74.8 _+ 3.54 197.8 _+ 7.08 152.4 _+ 8.93 seedcoat (57.53) SE(M) 4.1 3.8 2.4 5.5 3.0 CD ( p < 0.05) 12.4 11.4 7.2 16.6 9.1

aValues are means +SD of five independent determinations. Figures in parenthesis represent amount of high-density lipoprotein cholesterol expressed as percentage of total cholesterol.

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cellulose content present in both the fibre sources, which may be responsible for high cholesterol and bile acid excretion through faeces in case of cornbran and blackgram seedcoat observed in the present study. Blackgram seedcoat produced 0.26 g/t00 g increase in faecal cholesterol and 338.01 mg/100g bile acids excretion as compared to the cellulose group. Similar values for cornbran were 0.43 g/100 g and 382.11 mg/100 g. Increased excretion of faecal cholesterol and bile acid may be because of the cholesterol that might have been adsorbed on the dietary fibre components thereby making cholesterol unavailable for intestinal absorption. Similar results have been observed by earlier workers also [3, 8]. Among both the experimental fibre sources, cornbran was more hypocholesterolemic than blackgram seedcoat. Earlier workers have reported that with a supplementation of 4.2, 14.2 and 24.2 g hemicellulose to the daily diets of adult men, mean serum cholesterol levels decreased as dietary hemicel- lulose increased regardless of the fat source of the diet [9]. Neutral detergent fibre from blackgram when given as 30% of the diets to the rats fed on high fat and cholesterol or cellulose, produced significant reduction in serum cholesterol [10]. Similar effects have been observed in rats and men on feeding dietary fibre from various other sources also [3,11,123. In addition to increased faecal cholesterol and bile acids excretion hypocholesterolemic action of dietary fibre could be by reducing cholesterol and bile acids absorption as welt as by altering the metabolism and ratio of bile acids absorbed [13] which triggers denovo synthesis of bile acids and diverts cholesterol in serum to bile acid synthesis [14].

Serum HDL-cholesterol. HDL-cholesterol in serum was highest in the cornbran group (86.2mg/100ml) and lowest in the cholesterol free cellulose group (36.2 mg/100 mt) (Table 2). Among cholesterol supplemented groups, corn bran had 39.03% and blackgram seedcoat had 20.64% higher HDL-cholesterol than the cellulose group. Similar results were obtained in serum of healthy volun- teers for mineralized multi fibre powder or maize fibre tablets [11]. Mechanism involved in observed changes may be due to the reason that dietary fibre alters the site of lipid absorption along the intestine. Composition of tipoproteins synthesized by the intestine changes as the site of absorption is moved more distal in the small intestine [15]. Affinity of these fibres for micellar phos- pholipids may also contribute to alteration in composition of chylomicrons synthesis by limiting phospholipid availability all along the intestine [16]. Since the HDL-cholesterol is negatively correlated to coronary heart disease, the higher serum HDL-cholesterot obtained with consumption of both the fibres will be beneficial for heart patients.

Serum triglycerides. Serum triglyceride level was highest in the cholesterol supplemented cellulose group (254.4 rag/100 ml), followed by blackgram seed- coat (197.8), cornbran (176.0) and the cholesterol free cellulose group (134.4 rag/100 ml) (Table 2). When compared with the cellulose group cornbran had 30.81% and blackgram seedcoat had 22.24% lower serum triglycerides.

Table 3. Effect of feeding different sources of dietary fibre on faecal excretion of cholesterol and bile acids of weanling rats with cholesterol (1%) supplemented diets a

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Dietary group Cholesterol Bile acids (g/100 g) (mg/100 g)

Cellulose (without cholesterol) 0.17 + 0.01 t90.00 _+ 6.42 Cellulose 1.44 ± 0.06 547.32 ± t6.24 Cornbran 1.87 + 0.05 929.43 ± 6.20 Blackgram seedcoat 1.70 ± 0.05 885.33 ± 12.51 SE(m) 0.07 5.59 CD (p < 0.05) 0.20 16.76

~Vatues are means _+SD of Five independent determinations.

Out of both the dietary fibre sources used cornbran was more effective in lowering serum triglycerides as compared to blackgram seedcoat. The hypot- riglyceridemic effect may also be attributed to higher amounts of hem±cellulose present in both the fibres. Triglycerides in serum were reported to the lowest when teent provided dietary fibre which contained hem±cellulose as the major fibre constituent [3]. Wheatbran and mineralised multi-fibre powder or maize fibre tablet have been reported to produce triglyceride lowering effect in rats and humans [15, 17, 18]. Alteration in intestinal binding of triglycerides may be responsible for the reduced triglyceride level. With consumption of dietary fibre, faecal excretion is often increased [7]. Absorption of fat is slower and may occur in intestinal tract when these fibres are present [19]. This demon- strates lower post-prandial peak values for serumtriglycerides and suggest that these dietary fibres may alter the post prandial rise in chylomicrons.

Serum phospholipids. Serum phospholipids were found to be maximum in the cholesterol supplemented cellulose group followed by cellulose without choles- terol, cornbran and blackgram seedcoat. Among cholesterol supplemented groups cornbran had 9.08% and blackgram seedcoat had 10.14% total phospholipids lower than the cellulose group (Table 2). Non significant differences were observed in serum total phospholipids among experimental groups. Similarly, no significant differences were found in serum phospholipids in rats on feeding dietary fibre from various plant foods, viz. peepal banti, barbanti, qullar, teent and khejri beans [3].

Conclusion

It may be inferred from the findings of the present investigation that both the cornbran and blackgram seedcoats when given at 10% level resulted in the lowering of serum total lipids, total cholesterol, phospholipids and triglycer- ides. Rats fed with grain husks also had higher HDL-cholesterol in rats. Therefore, the inclusion of grain husks in the diet can be beneficial for individuals having the risk of atheroscterosis and coronary heart disease as

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they generally have higher levels of cholesterol and other blood lipids. However, further researches are required to be conducted for transferring the results of the animal experiments for humans and to further standardise the dose and duration of fibre intake for beneficial effects. Efforts are also needed to standardise various recipes for the incorporation of these grain husks in our daily diets, which have both economical as well as health benefits.

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