Lignin: a bile-salt sequestrating agent

Lignin - An underutilized, renewable and valuable material for food industry

Lignin is the second most abundant biorenewable polymers only next to cellulose and is ubiquitous in various plant foods. In food industry, lignin often presented as a major component of by-products from plant foods. In the last decade, the food and nutritional interests of lignin attracted more and more attentions and great progresses have been accomplished. In the present review, the structure, physicochemical properties, dietary occurrence and preparation methods of lignin from food resources were summarized. Then, the versatile activities of food lignin were introduced under the subtitles of antioxidant, antimicrobial, antiviral, antidiabetic and other activities. Finally, the potential applications of food lignin were proposed as a food bioactive ingredient, an improver of food package films and a novel material in fabricating drug delivery vehicles and contaminant passivators. Hopefully, this review could bring new insights in exploiting lignin from nutrition- and food-directed views.

New hypotheses for the health-protective mechanisms of whole-grain cereals: what is beyond fibre?

Epidemiological studies have clearly shown that whole-grain cereals can protect against obesity, diabetes, CVD and cancers. The specific effects of food structure (increased satiety, reduced transit time and glycaemic response), fibre (improved faecal bulking and satiety, viscosity and SCFA production, and/or reduced glycaemic response) and Mg (better glycaemic homeostasis through increased insulin secretion), together with the antioxidant and anti-carcinogenic properties of numerous bioactive compounds, especially those in the bran and germ (minerals, trace elements, vitamins, carotenoids, polyphenols and alkylresorcinols), are today well-recognised mechanisms in this protection. Recent findings, the exhaustive listing of bioactive compounds found in whole-grain wheat, their content in whole-grain, bran and germ fractions and their estimated bioavailability, have led to new hypotheses. The involvement of polyphenols in cell signalling and gene regulation, and of sulfur compounds, lignin and phytic acid should be considered in antioxidant protection. Whole-grain wheat is also a rich source of methyl donors and lipotropes (methionine, betaine, choline, inositol and folates) that may be involved in cardiovascular and/or hepatic protection, lipid metabolism and DNA methylation. Potential protective effects of bound phenolic acids within the colon, of the B-complex vitamins on the nervous system and mental health, of oligosaccharides as prebiotics, of compounds associated with skeleton health, and of other compounds such as alpha-linolenic acid, policosanol, melatonin, phytosterols and para-aminobenzoic acid also deserve to be studied in more depth. Finally, benefits of nutrigenomics to study complex physiological effects of the 'whole-grain package', and the most promising ways for improving the nutritional quality of cereal products are discussed.

Effects of bran on serum cholesterol, faecal mass, fat, bile acids and neutral sterols, and biliary lipids in patients with diverticular disease of the colon

Twenty-two patients with symptomatic diverticular disease of the colon were randomly allocated to control and high-fibre groups so that the long-term effect (up to 12 months) of bran on serum, faecal and biliary lipids could be studied. Even in cases of high initial values, faecal mass was increased by bran and the change was positively correlated with the change in dietary fibre. Faecal fat and dry weight were also increased. Faecal bile acids were initially slightly raised and were positively correlated with wet weight both off and on bran. The latter significantly decreased the excretion and concentration of bile acids, in particular the high initial values. The change in bile acids was not correlated with the change in dietary fibre or faecal wet weight. Sterol balance values indicated that the bran-induced decrease in faecal bile acids was associated with a lower cholesterol synthesis. Serum cholesterol decreased significantly in two hypercholesterolaemic individuals only. Correlations between different parameters revealed that the higher the initial level or the greater the drop in cholesterol synthesis, the greater the decrease in serum cholesterol. Bran had no effect on the biliary saturation of cholesterol. The percentage of biliary deoxycholate was negatively correlated with faecal mass (less so with faecal bile acid output) both before and during bran and was significantly decreased by bran. The percentage of cholic acid increased correspondingly and that of chenodeoxycholate remained unchanged. Faecal bile acids also indicated that the synthesis of the two primary bile acids was lowered by bran to the same degree.

Colonic response to dietary fibre from carrot, cabbage, apple, bran

Approximately 20 g/day of concentrated dietary fibre from carrot, cabbage, apple, bran, and guar gum was added to the controlled basal diet of nineteen healthy volunteers. Faecal weight increased by 12% on bran, 69% on cabbage, 59% on carrot, 40% on apple, and 20% on guar gum. These changes in faecal weight were correlated with an increased intake of pentose-containing polysaccharides from the fibre. On the basal diet there were pronounced individual differences in faecal weight, and from these the response of subjects to the fibre preparations could be predicted. Addition of fibre shortened mean transit-time through the gut and significantly diluted an inert marker in the faeces. Diet-induced changes in colonic function may explain international differences in the prevalence of colonic disease, whilst personal variation in the response to dietary fibre may determine individual susceptibility to large-bowel disease within a community.

Persistent post-enteritis diarrhoea

Clinical, biochemical, and gastroenterological data have been examined im 48 patients in two age groups, one under 12 months of age, the other between 12 and 30 months with persistent post-enteritis diarrhoea. In these patients, the illness consisted of chronic diarrhoea which followed acute enteritis. It brought about a mild malabsorption syndrome with impairment of growth, particularly in infants under one year of age. Chronic inflammation with mucosal damage due to alteration of the intestinal microflora by inappropriate diets and therapy seemed to be the cause of persistent diarrhoea in these patients.

Effects of two types of dietary fibre on faecal steroid and lipid excretion

Fibre supplements from wheat bran and sugar cane residue (bagasse) were added to the normal diet of volunteers for 12-week periods in a controlled metabolic study. Stool weights and stool fat excretion increased on both dietary fibres. Bagasse increased the daily loss of acid steroids, but bran failed to affect bile acid excretion. Decreased transit time without alteration in faecal flora occurred with bagasse. The raised excretion of bile acids and fatty acids failed to lower the plasma cholesterol and triglycerides after 12 weeks. Thus different fibre sources with variable components have dissimilar metabolic effects.

Effects of two types of dietary fibre on faecal steroid and lipid excretion

Fibre supplements from wheat bran and sugar cane residue (bagasse) were added to the normal diet of volunteers for 12-week periods in a controlled metabolic study. Stool weights and stool fat excretion increased on both dietary fibres. Bagasse increased the daily loss of acid steroids, but bran failed to affect bile acid excretion. Decreased transit time without alteration in faecal flora occurred with bagasse. The raised excretion of bile acids and fatty acids failed to lower the plasma cholesterol and triglycerides after 12 weeks. Thus different fibre sources with variable components have dissimilar metabolic effects.

Dietary fibre and sterol metabolism in the rat

1. Sterol metabolism was studied in rats fed on a semi-synthetic fibre-free diet and in rats fed on diets containing cellulose (200 or 100 g/kg) or sugar-cane fibre (bagasse) at the same levels.

2. Rats fed on the diets containing cellulose or bagasse produced significantly greater quantities of faeces than did rats fed on the fibre-free diet.

3. Rats given bagasse excreted more bile acid and more neutral sterol in their faeces than did rats fed on cellulose or on the fibre-free diet.

4. After 28 d, hepatic synthesis of cholesterol (from acetate) and cholesterol 7α-hydroxylase activity were significantly higher in animals fed on bagasse than in animals fed on the other two diets.

5. No significant differences in serum cholesterol levels were seen in rats fed on any of the three diets.

6. Food consumption was not substantially altered by the inclusion of bagasse or cellulose in the diets, although the efficiency of foodstuff utilization was generally lower.

7. Bagasse adsorbed substantial quantities of cholic acid in vitro, whereas cellulose did not. The lignin fraction prepared from bagasse contributed only slightly to the total bile acid-binding capacity of bagasse.

8. The results are discussed in the light of possible effects of dietary fibre on sterol metabolism in man.

Bile acids in the diarrhoea of ileal resection

Twenty individual diarrhoeal stools from three patients with ileal resection were centrifuged at 14 000 g for one hour at 10 degrees C to separate the stool into pellet and supernatant. Bile acids and electrolytes were measured in each phase. Relationships were examined between chenodeoxycholic acid and cholic acid in each phase and in toto to electrolyte and water loss. Chenodeoxycholic acid was associated with electrolyte and water loss whether present in solid or liquid phase. The association varied between individuals. The cholic acid content of the stool showed no association with electrolyte and water loss. It would appear that it is the total amount of chenodeoxycholic acid entering the colon, irrespective of its physical state, that is important in the diarrhoea of ileal dysfunction.

Bile acids and vitamin A absorption in man: the effects of two bile acid-binding agents, cholestyramine and lignin

In 14 healthy volunteers, the addition of 12 g cholestyramine to a vitamin A-containing test meal reduced the expected rise in serum vitamin A by 59.5% (p<0.001). By contrast, lignin had no significant effect in 12 subjects. This study confirms the importance of bile acids in vitamin A absorption and the ineffectiveness of lignin as a sequestrator of conjugated bile acids.

Colonic secretion of water and electrolytes induced by bile acids: perfusion studies in man

Each of the three major bile acids of man was tested for its influence on electrolyte and water absorption in the human colon. Transport from isotonic solutions, with or without added bile acids, was compared in 35 studies on 20 healthy volunteers by colonic perfusions under steady-state conditions. Electrolytes and water were always absorbed from control solutions, but dihydroxy bile acid solutions induced continuous secretion or inhibition of sodium, potassium, and water absorption, which was reversible. Deoxycholic acid caused consistent secretion at 3 mm concentrations, whereas chenodeoxycholic acid did not induce secretion until the concentration was 5 mm. The trihydroxy bile acid (cholic acid) produced no significant change in absorption at 10 mm. Inhibition of absorption was also induced by mixtures of the glycine or taurine conjugated bile acids. Secretion of sodium and chloride, induced by bile acid perfusion, was linearly correlated with secretion of water; potassium secretion was relatively constant regardless of the volume of secretion. These results establish a striking influence of bile acids on colonic absorptive activity, provide an explanation in part for the diarrhea that frequently accompanies ileal disease or resection, and imply that diarrhea should occur in other disease states that produce elevated concentrations of dihydroxy bile acids in the colonic lumen.

The role of bile salts in diarrhoea of patients with ulcerative colitis

Faecal bile salt elimination, which was determined in patients with ulcerative colitis, was mostly within normal limits, suggesting that in this disease water and electrolyte diarrhoea was hardly contributed to by excessive amounts of bile salts in the large bowel. In a therapeutic trial cholestyramine had no beneficial effect on the general condition, diarrhoea, or faecal composition, findings which further strengthen the view that bile salts play no role in the diarrhoea of ulcerative colitis, provided that the disease is limited to the large bowel. Faecal elimination of cholesterol as bile salts and neutral steroids tended initially to be higher than normal, but increased less than in controls during treatment with cholestyramine, particularly in the heavier patients. Serum cholesterol was low in the patients with ulcerative colitis and decreased by cholestyramine less (27%) than in controls (39%).