Knud Erik Bach Knudsen

Carbohydrate and lignin contents of plant materials used in animal feeding

A total of 115 samples representing 38 different feedstuffs was analysed for carbohydrates and lignin. The samples were analysed for low-molecular weight (LMW) sugars by high-performance liquid chromatography, starch, fructan and mixed linked β(1 → 3;1 → 4)-D-glucan by colorimetry, total, soluble and insoluble non-starch polysaccharides (NSP) by gas-liquid chromatography and lignin by gravimetry. For all but alfalfa meal, almost quantitative recovery of carbohydrates and lignin was obtained with a deviation between calculated and analysed values of less than 2 g kg−1 dry matter. The correlation between calculated and analysed values was 0.985 (P < 0.0001). The concentration (g kg−1 dry matter) of LMW-sugars varied from 5 g kg−1 and up to 137 g kg−1 with the lowest values found in cereal substitutes, whole grain cereals and by-products while the protein concentrates in general had the highest content of LMW-sugars (57–137 g kg−1). Starch was the main polysaccharide in whole grain cereals where it varied from 468 g kg−1 in oats to 690 g kg−1 in maize, in cereal by-products (93–902 g kg−1) and in tapioca (768 g kg−1). In contrast, the concentration of starch was low in all protein concentrates but peas and faba beans. The lowest levels of NSP and lignin were found in maize flour (NSP, 21 g kg−1; lignin, 4 g kg−1) and the highest levels in oat hull meal (NSP, 503 g kg−1; lignin, 148 g kg−1). There was also a significant variation in NSP and lignin in protein concentrates with the NSP value varying from 189 g kg−1 in faba beans to 451 g kg−1 in white lupins and with lignin varying from 12 g kg−1 in white lupins to 133 g kg−1 in sunflower cake. Grass meal, alfalfa meal and sugar beet fibre had in general high concentrations of NSP and lignin with values in grass and alfalfa meals of NSP: 329–426 g kg−1 and lignin: 128–169 g kg−1 and in sugar beet fibre 779 g kg−1 and 35 g kg−1, respectively.

Digestion of polysaccharides and other major components in the small and large intestine of pigs fed on diets consisting of oat fractions rich in β-D-glucan

The digestibility of polysaccharides and other major components and the metabolic response of the microflora in the small and large intestines to oat diets varying in mixed linked beta(1-->3; 1-->4)-D-glucan (beta-glucan) were studied in experiments with ileum-cannulated pigs. The oat fractions for diets were prepared in a dry milling process in which oat groats were milled into two endosperm fractions (oat flour 1 and oat flour 2) and oat bran. The digestibility of polysaccharides and the metabolic response of the microflora were followed for the two contrasting diets, oat flour 1 and oat bran, from ingestion to excretion while the digestibility of oat groats and oat flour 2 were estimated only at the ileum and in faeces. There was no degradation of beta-glucan from either oat flour 1 or bran in the stomach and the first, middle and distal thirds of the small intestine (average digestibility approximately 0), while in the terminal ileum digestibility increased to 0.30 to 0.17 respectively. The digestion of starch in the first third of the small intestine was lower for the high-beta-glucan oat-bran diet (0.49) than for the low-beta-glucan flour diet (0.64). However, digestibility differences between the two diets levelled out as the digesta moved aborally in the small intestine and the digestibility at the terminal ileum was almost complete (0.970-0.995) for all diets. Oat non-starch polysaccharides (NSP) were an easily digestible energy source for the microflora in the large intestine less than 13% of dietary NSP being recovered in faeces. The bulk of beta-glucan which survived the small intestine was degraded in the caecum and proximal colon while arabinoxylan was more slowly degraded. The amount of residues passing the ileo-caecal junction has little impact on the density of micro-organisms in the large intestine, which on the flour and bran diets were in the range of 10(10)-10(11) viable counts/g digesta, but a high impact on the activity of the flora in colon. Oat bran resulted in a higher proportion of butyric acid in large intestinal content compared with the flour diet. The faecal bulking effect of oat bran was mainly caused by an increased excretion of protein and fat, presumably of bacterial origin. Of all the diets tested the oat-bran diets had the lowest digestibilities of protein and fat at the terminal ileum and in the faeces.

New insight into butyrate metabolism.

Butyrate is a C4 acid produced by microbial fermentation of carbohydrates and protein in the large intestine of all animal species. The factor of prime importance for the production rate of butyrate in the lower gut is type and levels of non-digestible carbohydrates entering the large intestine. It was previously believed that 85-90 % of the butyrate produced in the gut was cleared when passing the gut epithelium, but recent studies with catheterised pigs have shown that the concentration of butyrate in the portal vein is strongly influenced by the production rate in the large intestine. Increased gut production of butyrate further raises the circulating level of butyrate. For good reason it is not possible with current technologies to perform direct measurements of the variation in the butyrate concentration in the portal vein of human subjects, but short-chain fatty acid levels in portal blood from sudden-death victims, subjects undergoing emergency surgery or planned surgery have indicated a higher gut production and absolute and relative concentration of butyrate in non-fasted as compared with fasted human subjects. However, despite an expected higher gut production of butyrate when feeding a high-fibre rye-bread-based diet as compared with a low-fibre wheat-bread-based diet, there was no difference in absolute or relative levels of butyrate in the peripheral blood of human subjects.

Content of nutrients and lignans in roller milled fractions of rye

Rye grain was roller milled into six flour fractions (607 g kg-1), a short (341 g kg-1) and a bran (52 g kg-1) in a B???hler laboratory mill. In the different flours (F1-F6) a progressive increase in ash (4-13 g kg-1), crude protein (39-87 g kg-1) and crude fat (5-17 g kg-1) concentration was found and a corresponding decrease in starch (853-699 g kg-1) concentration. Total dietary fibre (55-109 g kg-1) constituents and the lignans, matairesinol (0???05-0???22 mg kg-1) and secoisolariciresinol (0???21-0???38 mg kg-1), showed a different distribution with a maximal concentration in F5. The short and bran had higher concentrations of ash, crude protein, crude fat, dietary fibre components and lignans but a lower concentration of starch than the flours. Compared to the short, the bran contained more of all constituents analysed except mixed-linked beta-glucan and starch. A very high proportion of total dietary fibre components of the rye, such as arabinoxylan (72%), cellulose (76%) and Klason lignin (79%) as well as of matairesinol (87%) and secoisolariciresinol (73%), was found in the short and bran together. ??? 1997 SCI.

A Cereal-Based Evening Meal Rich in Indigestible Carbohydrates Increases Plasma Butyrate the Next Morning

Epidemiological studies have shown an inverse relation between a whole grain consumption and risk of type-2 diabetes and cardiovascular disease. One tentative mechanism relates to colonic metabolism of indigestible carbohydrates. In a previous study, we reported a positive relation between colonic fermentation and improved glucose tolerance. This work can be seen as an extension of that study, focusing on the tentative role of specific colonic metabolites, i.e. SCFA. Plasma concentrations of acetate, propionate, and butyrate were determined in the morning in healthy participants (5 women and 10 men, mean ± SD: 25.9 ± 3.2 y, BMI < 25) following 8 different cereal-based evening meals (50 g available starch) varying in content of indigestible carbohydrates. Each participant consumed all test meals in a random order on separate evenings. At a standardized breakfast following evening test meals, the postprandial glucose response (incremental area under the curve, 0-120 min) was inversely related to plasma butyrate (r = -0.26; P < 0.01) and acetate (r = -0.20; P < 0.05) concentrations. Evening meals composed of high-amylose barley kernels or high-β-glucan barley kernels resulted in higher plasma butyrate concentrations the following morning compared with an evening meal with white wheat bread (P < 0.05). The results support the view that cereal products rich in indigestible carbohydrates may improve glucose tolerance through a mechanism involving colonic fermentation and generation of SCFA, where in particular butyric acid may be involved. This mechanism may be one explanation by which whole grain is protective against type 2 diabetes and cardiovascular disease.

Physico‐Chemical Properties and the Degradation of Oat Bran Polysaccharides in the Gut of Pigs

Physico-chemical properties and the digestibility of carbohydrates (starch, β-glucan and arabinoxylan (AX)) were studied in the gastrointestinal contents of pigs fed diets based on oat bran. One diet was made of commercially prepared oat bran and another of oat bran milled to pass a 1 mm screen. The pigs were slaughtered and samples were collected quantitatively from 10 sites of the gastrointestinal tract either 1 or 3 h after the morning feeding. The viscosity of the liquid phase (obtained by centrifugation) of the stomach and small intestinal contents varied greatly between animals, and was not significantly different between segments of the upper gastrointestinal tract. The molecular weight of β-glucan was reduced up to 20-fold in the upper gastrointestinal tract but was of a relatively low digestibility until the terminal ileum. The solubility (the fraction of the total content in the liquid phase of digesta after centrifugation) of β-glucan varied from 0·25 to 0·58 in the stomach and small intestine, whereas the solubility of AX was in the range of 0·04–0·16. Microscopic examination of digesta showed that β-glucan was retained in intact endospermic cell wall structures, which remained evident until the distal small intestine but was completely disrupted in the caecum. In spite of a cumulative digestibility of non-starch polysaccharides and AX of ∽0·90 in the large intestine, identifiable fragments of aleurone cell walls resistant to complete microbial degradation remained.

The role of whole-wheat grain and wheat and rye ingredients on the digestion and fermentation processes in the gut--a model experiment with pigs.

The effect of wheat and rye breads made from white wheat flour with added refined fibre (WFL), whole-wheat grain, wheat aleurone flour (WAF) or rye aleurone flour (RAF) on digestion and fermentation processes in the gut was studied in a model experiment with pigs. The diets were similar in dietary fibre (DF) but differed in arabinoxylan (AX) content and composition. Twenty pigs were fed the breads three times daily (08.00, 13.00 and 18.00 hours) and the digesta collected through a T-cannula for two successive periods (breakfast: 8.00-13.00; lunch: 13.00-18.00 hours). Faeces were collected for 24 h and caecal and colonic contents at slaughter. The rigid nature of the aleurone cell walls encapsulated nutrients, which resulted in reduced (P < 0.01) digestibility of protein (WAF and RAF breads) and fat (RAF bread). For the RAF bread, the digestibility of starch was also lower (P < 0.001) than of the wheat-based diets primarily due to the higher intestinal viscosity. The DF composition had an impact on (P < 0.001) the site for fibre degradation in the large intestine. Thus, AX of the WAF bread, with the lowest degree of substitution, were fermented as much in the caecum as in the colon, whereas AX of the RAF bread, with an intermediary degree of substitution, were mainly fermented in the caecum. The WFL bread, rich in cellulose, was fermented more distally. Fermentation of experimental breads in the large intestine had no effect (P>0.05) on the production of metabolites, except for butyrate which was higher (P < 0.01) after the WAF bread consumption.

Nutritive value of cereal products with emphasis on the effect of milling

Article de synthese sur 5 cereales: ble, mais, riz, orge, seigle. Pour chacune, rappels de la structure et de la composition chimique, effet de la mouture: aspects nutritionnels, energie, composition (aminoacides, vitamines, mineraux entre autres)

Fiber and nonstarch polysaccharide content and variation in common crops used in broiler diets

The current paper reviews content and variation in fiber and nonstarch polysaccharides (NSP) of common crops used in broiler diets. The cereal grain is a complex structure, and its cell walls (CW) differ in their composition and hence properties. Arabinoxylan (AX), mixed linkage (1→3; 1→4)-β-glucan (β-glucan), cellulose, and the noncarbohydrate component lignin are the predominant polymers in cereals. They occur in different proportions depending on the species and tissue type. Rye, triticale, wheat, corn, and sorghum are all rich in AX, whereas barley and oats contain a high level of β-glucan. The AX from rye, wheat, and triticale and β-glucan from barley and oats are to a large extent soluble, whereas the solubility of AX found in corn and sorghum is lower than the other cereals. The ratio of arabinose to xylose gives a crude indication of the AX structure, which varies between the endosperm, the aleurone and the outer grain layers as well as between the same tissues from different grains. Varietal differences in AX structure of the endosperm are also identified. From the analysis of the released oligomers after hydrolysis with a specific (1→3,1→4)-β-d-glucan hydrolase, it is found that the ratio of trisaccharides (degree of polymerization 3) and tetrasaccharides (degree of polymerization 4) varies depending on the source, being higher in barley than in oats but lower than in wheat. The molecular weight of β-glucan is higher than that of AX, and both polymers contribute to the viscosity of the extract. However, because AX molecules are more resistant to degradation than β-glucan, the use of AX rich grains in broiler diets is usually more problematic than those containing high concentrations of β-glucan. The cereal coproducts (brans and hulls) are concentrated sources of cellulose, lignin, and insoluble AX, but β-glucan can also be present mainly in rye and wheat brans. The CW composition of seeds and grains of protein crops and feedstuffs are different from that of cereals. The main CW polymers are pectic substances (homogalacturonan, rhamnogalacturonan type I and II, xylogalacturonan, and arabinogalactans type I and II), xyloglucans, and cellulose, but there are significant differences in the composition of the parenchymatous (cotyledon) tissues and that of the hulls. In the hulls, cellulose is the predominant polysaccharide, followed by acidic xylans and pectic substances. The implications of the heterogeneous CW for the action of exogenous enzymes are discussed.

Breakdown of plant carbohydrates in the digestive tract of pigs fed on wheat- or oat-based rolls

Cell wall materials from various cellular tissues of cereals may potentially influence the digestion and absorption processes in different ways. The objective of the present investigation was to study the breakdown of plant carbohydrates in the gastrointestinal tract of pigs fed a low-fibre (LF; 65 g kg−1 dry matter) wheat flour-based diet and two high-fibre diets with added insoluble fibre from wheat bran (HFWB; 112 g kg−1 dry matter) or soluble fibre from oat bran (HFOB; 108 g kg−1 dry matter). The diets were formulated to provide ∼0.31 energy from fat, ∼0.18 energy from protein and ∼0.51 energy from carbohydrates and were offered as baked rolls to eight ileum-cannulated hypercholesterolemic pigs in a crossover design. Carbohydrates were the predominant ileal constituent, with most of the carbohydrates present as non-starch polysaccharides (NSP). Starch in all diets was almost completely digested at this site of the gastrointestinal tract, with digestibility values above 0.99. The ingested amount of NSP was quantitatively recovered in ileal materials with the wheat-based diets, while there was a significant loss of 0.27 of NSP primarily as mixed linked (13)(14)--D-glucan with diet HFOB. The concentration and flow of lactic acid were also highest in the ileum after feeding diet HFOB, indicating that -glucan stimulated lactic acid formation. Any soluble components that reached the large intestine were almost completely broken down, while the digestibility of insoluble NSP constituents was significantly lower for diets LF and HFWB than for diet HFOB. The high degradation of oat bran resulted in a lower effect on faecal dry and wet bulking than was found with wheat bran. In conclusion, cereal starch was practically completely degraded in the small intestine, while the site and extent of NSP degradation, lactic acid formation and bulking properties were influenced by the fibre source. © 2000 Society of Chemical Industry