Effect of lignin linkages with other plant cell wall components on in vitro and in vivo neutral detergent fiber digestibility and rate of digestion of grass forages

The objective of this study was to correlate in vitro and in vivo neutral detergent fiber (NDF) digestibility (NDFD) with the chemical composition of forages and specific chemical linkages, primarily ester- and ether-linked para-coumaric (pCA) and ferulic acids (FA) in forages fed to dairy cattle. The content of acid detergent lignin (ADL) and its relationship with NDF does not fully explain the observed variability in NDFD. The ferulic and p-coumaric acid linkages between ADL and cell wall polysaccharides, rather than the amount of ADL, might be a better predictor of NDFD. Twenty-three forages, including conventional and brown midrib corn silages and grasses at various stages of maturity were incubated in vitro for measurement of 24-h and 96-h NDFD. Undigested and digested residues were analyzed for NDF, acid detergent fiber (ADF), ADL, and Klason lignin (KL); ester- and ether-linked pCA and FA were determined in these fractions. To determine whether in vitro observations of ester- and ether-linked pCA and FA and digestibility were similar to in vivo observations, 3 corn silages selected for digestibility were fed to 6 ruminally fistulated cows for 3 wk in 3 iso-NDF diets. Intact samples and NDF and ADF residues of diet, rumen, and feces were analyzed for ester- and ether-linked pCA and FA. From the in vitro study, the phenolic acid content (total pCA and FA) was highest for corn silages, and overall the content of ester- and ether-linked pCA and FA in both NDF and ADF residues were correlated with NDF digestibility parameters, reflecting the competitive effect of these linkages on digestibility. Also, Klason lignin and ADL were negatively correlated with ether-linked ferulic acid on an NDF basis. Overall, esterified FA and esterified pCA were negatively correlated with all of the measured fiber fractions on both a dry matter and an NDF basis. The lignin content of the plant residues and chemical linkages explained most of the variation in both rate and extent of NDF digestion but not uniformly among forages, ranging from 56 to 99%. The results from the in vivo study were similar to the in vitro data, demonstrating the highest total-tract aNDF digestibility (70%; NDF analysis conducted with α-amylase and sodium sulfite) for cows fed the corn silage with the lowest ester- and ether-linked pCA content in the NDF fraction. In this study, digestibility of forage fiber was influenced by the linkages among lignin and the carbohydrate moieties, which vary by hybrid and species and most likely vary by the agronomic conditions under which the plant was grown.     

Lignin in the ‘cell contents’ fraction of tropical forages

In several tropical forage species the neutral detergent extraction used to determine cell wall and cell contents fractions solubilised a substantial UV‐absorbing polymeric fraction which appeared to be a soluble lignin–carbohydrate complex. A crude product was isolated from spear grass (Heteropogon contortus) with a yield of 30 g kg^?1. In other forages an acetyl bromide method was used to estimate lignin extractable by neutral detergent. For eight species of tropical grasses this gave the following values: Aristida calcyna, 38; Mitchell grass (Astrebla squarrosa), 37; Chloris gayana, 31; Eragrostis sp, 37; spear grass, 49; Iseilema membranaceum, 35; Panicum maximum, 36; Sorghum sp, 42; Themeda triandra, 79 g kg^?1. The levels in two legumes were: Alysicarpus bupleurifolius, 29; Macroptilium atropurpureum, 27 g kg^?1 dry matter. Sequential extractions on spear grass and Mitchell grass showed that most of the 50% dioxan‐soluble fraction was also soluble in neutral detergent, raising the possibility that ‘dioxan lignin’, on which studies of forage lignin structure in other species have been conducted, would be found in the cell contents fraction rather than in the fibre fractions on which lignin analyses have been performed. Addition of dioxan extractives reduced the in vitro neutral detergent fibre (NDF) digestibility of spear grass and Mitchell grass. © 2002 Society of Chemical Industry     

Apparent inhibition to digestion by lignin in normal and brown midrib stems

Lignin, a cell wall component, limits digestibility of plant cell walls. Brown midrib (bmr) mutants of forages have lignin with altered chemical composition compared with their normal counterparts. The objectives of this study were to determine if bmr lignin is more inhibitory to digestion than is normal lignin and if bmr has a consistent effect on rate of digestion across species and environments. Extent and rate of in-vitro cell wall digestion of normal and bmr stems of sorghum (Sorghum bicolor (L) Moench, two comparisons), millet (Pennisetum americanum (L) Leeke) and maize (Zea mays L, two comparisons) were determined. Samples were incubated in rumen fluid, and data were fitted with a first-order, nonlinear model to estimate concentrations of potentially digestible neutral detergent fibre (PDNDF), digestion rate of PDNDF, concentration of indigestible residue (IR), and lag time before digestion. The NDF, acid-detergent fibre (ADF), and acid-detergent lignin (ADL) analyses were conducted sequentially on undigested samples. The IR: ADL ratio was 37% greater for bmr than for normal plants, which indicates that bmr lignin inhibits digestion more than normal lignin per unit of lignin. Digestion rate of PDNDF was faster in bmr than in normal counterparts in one of the two sorghum comparisons (difference of 59%) and in the millet comparison (difference of 27%), but in neither maize comparison. The bmr mutants were lower than normal genotypes in NDF (9%) and ADL (47%) concentrations. The PDNDF concentration was 19% greater for bmr than for normal lines. Thus, decreased lignin concentration in bmr mutants increased the extent of NDF digestion but did not consistently increase the rate of digestion.     

Dietary fibre and components of the nitrogen-free extract of almond kernels

Determinations of neutral and acid detergent fibre residues (NDF and ADF), hemicellulose, cellulose and lignin in almond nuts (Prunus amygdalus) were carried out. The NDF content was about 5% while the crude fibre content was only approximately 2%. The composition of several components of nitrogen-free extract (NFE) such as soluble sugars, starch, gums and mucilages and pectins were also determined, and the results are discussed.     

Lax leaf maize: cell wall composition and nutritional value

Forage nutritive value, which comprises traits such as digestibility, fibre, lignin and protein content, is an important criterion for maize (Zea mays L) harvested as silage. Lines with a characteristic phenotype (‘lax leaf’) could be useful sources of genes for improved nutritive value in maize. A study was conducted to characterise the cell wall composition of the lax leaf line. Lax leaf inbreds and inbreds representing ‘normal’ maize were evaluated for cell wall neutral sugars, uronic acids, Klason lignin and phenolic acids in five tissues from the ear node and the internode above it. Acid detergent fibre (ADF) and neutral detergent fibre (NDF) and 48 h in vitro true digestibility (IVTD) were predicted using near‐infrared reflectance spectrophotometry (NIRS) calibrated with a subset of the scanned samples. Lax leaf inbred tissues had lower levels of ADF, NDF, lignin and xylose and were more digestible than tissues from the inbreds representing ‘normal’ maize. It was not known whether the lax leaf phenotype resulted from alterations in nutritive value traits or whether laxness and nutritive value traits are independent from one another. A second study was conducted to determine the nature of genetic control of the lax leaf character and to determine the genotypic relation between the lax leaf character and nutritive value. A recombinant inbred mapping population was developed from a cross between the lax leaf line and an inbred line with stiff upright leaves. Whole‐plant samples from each recombinant inbred line were evaluated for ADF, NDF, acid detergent lignin (ADL) and IVTD of dry matter using NIRS. Laxness, measured by number of broken leaves, was associated with lower nutritive value in this population (genetic correlations 0.16–0.34), which was contrary to expectation. Amplified restriction fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers were used to identify linkage groups associated with the lax leaf character, digestibility and fibre content. Several linkage groups were associated with both the lax leaf character and nutritive value. Where these characters were associated with the same linkage group, the lax leaf parent allele was associated with greater laxness but reduced nutritive value. The lax leaf parent allele was associated with increased nutritive value in linkage groups unassociated with the lax leaf character. While the lax leaf line may be a good source for alleles for improved nutritive value, selection for laxness will not likely be accompanied by improvement in forage quality. © 2000 Society of Chemical Industry     

Storage of fresh and ensiled forages by freezing affects fibre and crude protein fractions

The effect of freezing on fibre and crude protein fractions of forages was determined. Fresh and ensiled lucerne and fresh bromegrass were processed immediately after collection or stored at ?25°C for 1 day or 1, 6 or 12 months before drying at 55°C. Samples were frozen quickly by submersion in liquid nitrogen or slowly at ?25°C. Samples which were not frozen were processed immediately or after 1 h delay at room temperature. All treatments were replicated (n = 3). Samples were analysed for crude protein (CP), trichloroacetic acid soluble CP (TSCP), phosphate buffer soluble CP (BSCP), neutral detergent insoluble CP (NDCP), acid detergent insoluble CP (ADCP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent sulphuric acid lignin (lignin) and ash. Freezing decreased BSCP and increased NDCP by more than 40% for bromegrass. Freezing also changed NDF, ADF, lignin, ash, CP and ADCP in different ways depending on forage type and length of time frozen. No significant effects were observed for method of freezing or a 1-h delay in processing. An additional experiment showed that freeze-drying resulted in less insoluble protein than ovendrying. Prior freezing of forages appeared inconsistently to change the extent of gaseous loss during drying, and resulted in precipitation of protein. These changes also affected fibre estimates. Fresh forages should not be frozen and thawed before analysis of protein or fibre fractions.     

The analysis of dietary fibre—the choices for the analyst

The analysis of dietary fibre (which is defined as the sum of lignin and the polysaccharides not digested by the endogenous secretions of the human digestive tract) presents several problems to the analyst. Dietary fibre is a mixture of substances derived from the structural materials of the plant cell wall and a range of polysaccharides of a non-structural nature either present naturally in foods or derived from food additives. The complete analysis of such a complex mixture would be difficult and time consuming and a number of practical alternatives have been used. These include methods based on the enzymatic removal of protein and starch to give an ?indigestible residue’? and procedures based on extraction with neutral detergent solutions. These procedures in their present form do not measure water-soluble components and therefore underestimate dietary fibre. More detailed methods in which the water-soluble and water-insoluble non-cellulosic polysaccharides, cellulose and lignin were measured separately are described. In these the non-cellulosic fraction was characterised in terms of its component sugars. It is suggested that methods of this type are necessary to characterise dietary fibre analytically in order to account for the properties of dietary fibre.     

Composition and in-vitro digestibility of carbohydrates of wheat plants harvested at bloom and soft-dough stages

Wheat plants (Triticum aestivum) were harvested at the bloom and soft-dough stages, separated into leaves + sheaths, stems and spikes, and the effect of stage of maturity on neutral detergent fibre (NDF) composition and degradability was studied, the accumulation of starch in the spikes compensated for the decrease in the degradability of NDF polysaccharides so that the in-vitro digestibility of the organic matter (OM) was not changed between the bloom and soft-dough stages. Minor compositional changes occurred in the NDF of the various botanical fractions which can hardly explain the drop in NDF degradability with maturity. There was a decline in the ratio of hemicellulose to lignin, and the changes in NDF-monosaccharide degradability were probably related to the extension of covalent bonding between those matrix components during maturation. Irrespective of botanical fraction and maturity stage, NDF xylose was less digestible than NDF glucose. Between bloom and soft-dough stages there was an increase of 36% in the yield of digestible OM.     

Relationship of cell wall composition to in vitro cell wall digestibility of maize inbred line stems

The phenolic equipment of maize stem tissues was investigated in relation to the feeding value of the detergent fibre components. Sixteen maize inbred lines, including three brown‐midrib 3 mutants and their normal counterparts, were selected for highly divergent in vitro cell wall digestibility. These lines were grown during two years. Maize stems were analysed for detergent fibre concentration, esterified and etherified p‐hydroxycinnamic acids, lignin content and structure and in vitro digestibility. A large genotypic variation was found for neutral detergent fibre, cell wall phenolic composition and cell wall digestibility. Within the normal maize lines the in vitro neutral detergent fibre digestibility (IVNDFD) of stem fractions was negatively correlated with their Klason lignin content. A multiple regression model based on esterified p‐coumaric acid and lignin composition as two explanatory variates accounted for 58% of the IVNDFD variation. In this study, three normal maize inbred lines displaying a lignin content and a cell wall digestibility level close to those observed in the three bm3 lines could be detected, which opens up new breeding avenues. © 2000 Society of Chemical Industry     

Effect of drying conditions on tannin,fibre and lignin levels in mature oak (Quercus incana) leaves

Oak (Quercus incana Roxb) leaves are rich in tannins and produce adverse effects when fed to livestock. The effects of shade and sun drying and oven drying at 60°C and 90°C for different lengths of time (24 to 72 h) on total phenolics, condensed tannins, protein precipitation capacity, degree of polymerisation, specific activity (protein bound per unit tannins), fibre-linked proanthocyanidins, acid and neutral detergent fibres and lignin levels in mature oak leaves were studied. Removal/inactivation of tannins was not observed on wilting or drying under several conditions. Similarly the drying conditions had no effect on fibre composition. The adverse effects on feeding fresh or dried oak leaves are expected to be of similar magnitude.     

Chemical composition of some forages and various residues from feeding value determinations

NDF, ADF, ‘cellulose’ and IVOMD residues, from feeding value determinations, were prepared from some forages, including straw, alkali-treated straw, grass and lucerne samples. The crude protein, cellulose, hemicellulose, uronic acid, Klason lignin, lignin and ash contents of these residues and the corresponding original forage samples were determined together with the relative composition of the neutral sugar constituents after acid hydrolysis. Cellulose, hemicellulose and Klason lignin were the main components in the NDF fractions but substantial amounts of crude protein (1–6%) also remained. Cellulose and Klason lignin were the main components in the ADF fractions, but 7–14% of the fractions was hemicellulose and 1–4% crude protein. Cellulose was the main component in the ‘cellulose’ fractions, but they also contained 8–13% hemicellulose, 2–7% Klason lignin and 2–11% ash. The composition of the IVOMD residues showed that cellulose and hemicellulose had been dissolved to about the same amounts (70–80%) and that most of the Klason lignin remained.     

Effect of reduced ferulate-mediated lignin/arabinoxylan cross-linking in corn silage on feed intake, digestibility, and milk production

Cross-linking of lignin to arabinoxylan by ferulates limits in vitro rumen digestibility of grass cell walls. The effect of ferulate cross-linking on dry matter intake (DMI), milk production, and in vivo digestibility was investigated in ad libitum and restricted-intake digestion trials with lambs, and in a dairy cow performance trial using the low-ferulate sfe corn mutant. Silages of 5 inbred corn lines were fed: W23, 2 W23sfe lines (M04-4 and M04-21), B73, and B73bm3. As expected, the W23sfe silages contained fewer ferulate ether cross-links and B73bm3 silage had a lower lignin concentration than the respective genetic controls. Silages were fed as the sole ingredient to 4 lambs per silage treatment. Lambs were confined to metabolism crates and fed ad libitum for a 12-d adaptation period followed by a 5-d collection period of feed refusals and feces. Immediately following the ad libitum feeding trial, silage offered was limited to 2% of body weight. After a 2-d adaptation to restricted feeding, feed refusals and feces were collected for 5 d. Seventy Holstein cows were blocked by lactation, days in milk, body weight, and milk production and assigned to total mixed ration diets based on the 5 corn silages. Diets were fed for 28 d and data were collected on weekly DMI and milk production and composition. Fecal grab samples were collected during the last week of the lactation trial for estimation of feed digestibility using acid-insoluble ash as a marker. Silage, total mixed ration, feed refusals, and fecal samples were analyzed for crude protein, starch, neutral detergent fiber (NDF), cell wall polysaccharides, and lignin. The W23sfe silages resulted in lower DMI in the ad libitum trial than the W23 silage, but DMI did not differ in the restricted trial. No differences were observed for NDF or cell wall polysaccharide digestibility by lambs with restricted feeding, but the amount of NDF digested daily increased for lambs fed the M04-21 W23sfe silage ad libitum. Lambs were less selective against NDF and lignin when offered W23sfe silages. The B73bm3 silage did not affect DMI or digestibility of cell walls at the restricted feeding level, but total daily NDF digested was greater at ad libitum intake. Intake, milk production, and cell wall digestibility were greater for cows fed diets containing W23sfe silages than for those fed W23 silage. Although milk production was greater for the B73bm3 diet, DMI and cell wall digestibility were not altered. Cows were less selective against cell wall material when fed both W23sfe and B73bm3 silages. Reduced ferulate cross-linking in sfe corn silage is a new genetic mechanism for improving milk production.     

Digestion of cell wall components by dairy heifers fed diets based on alfalfa and chemically treated oat hulls.

Four Holstein heifers were used in a 4 X 4 Latin square design to measure total tract digestion of cell wall components from diets based on alfalfa haylage and alkaline hydrogen peroxide-treated oat hulls. Diets contained 90% forage and 10% concentrate. Treatments were diets containing 90, 70, 50, or 30% alfalfa haylage with treated oat hulls supplying the remainder of the forage portion. Total tract digestion of cell wall-associated uronic acids, arabinose, galactose, mannose, rhamnose, and lignin were not affected by forage source. Digestibilities of cell wall glucose and xylose increased with increasing level of dietary treated oat hulls, reflecting the positive effect of alkaline hydrogen peroxide treatment on cell wall digestion. Cellulose (ADF minus acid detergent lignin) digestibilities were similar to those for cell wall glucose, whereas hemicellulose (NDF minus ADF) digestibilities were similar to those for cell wall arabinose plus xylose. Low digestibilities of alfalfa cell wall xylose indicate that some cell wall structure inhibits the degradation of alfalfa xylans. Low degradabilities of core lignin, esterified p-coumaric acid, and esterified acetyl groups suggest that these components may be involved primarily in depressing fermentation of cell wall polysaccharides.     

Factors affecting ANKOM™ fiber analysis of forage and browse varying in condensed tannin concentration

BACKGROUND: Browse species containing condensed tannins (CTs) are an important source of nutrition for grazing/browsing livestock and wildlife in many parts of the world, but information on fiber concentration and CT–fiber interactions for these plants is lacking. RESULTS: Ten forage or browse species with a range of CT concentrations were oven dried and freeze dried and then analyzed for ash‐corrected neutral detergent fiber (NDFom) and corrected acid detergent fiber (ADFom) using separate samples (ADFSEP) and sequential NDF‐ADF analysis (ADFSEQ) with the ANKOM^? fiber analysis system. The ADFSEP and ADFSEQ residues were then analyzed for nitrogen (N) concentration. Oven drying increased (P < 0.05) fiber concentrations with some species, but not with others. For high‐CT forage and browse species, ADFSEP concentrations were greater (P < 0.05) than NDFom values and approximately double the ADFSEQ values. Nitrogen concentration was greater (P < 0.05) in ADFSEP than ADFSEQ residues, likely due to precipitation with CTs. CONCLUSION: Sequential NDF‐ADF analysis gave more realistic values and appeared to remove most of the fiber residue contaminants in CT forage samples. Freeze drying samples with sequential NDF‐ADF analysis is recommended in the ANKOM^? fiber analysis system with CT‐containing forage and browse species. Copyright © 2010 Society of Chemical Industry     

Development of an in vitro method to determine rumen undigested aNDFom for use in feed evaluation

A portion of the forage cell wall, defined as neutral detergent fiber (NDF), is indigestible to anaerobic microbial digestion in ruminants. This fraction has been characterized by surface area relationships between acid detergent lignin, but recently, data have been published describing the dynamic nature of this relationship. In situ approaches have been described to estimate indigestible NDF, recovering the undigested NDF after long-term fermentations (uNDF). To be applicable to nutritionists and diet formulation, determining uNDF needs to be conducted in a commercial laboratory similar to other routine analyses of forage chemistry. A series of studies were conducted to evaluate an in vitro approach, to describe uNDF, which is repeatable and adaptable for routine feed evaluation. One hundred and two forages of several species were analyzed for NDF, acid detergent lignin, and uNDF. The uNDF was estimated by several approaches involving long-term fermentations and filtration steps to evaluate the length of time necessary to exhaust the digestible NDF and a filtration method necessary to maintain sample integrity by ensuring low sample loss and uniform recovery with residues from long-term in vitro fermentation. To determine uNDF, in vitro fermentations were conducted on 0.50 or 0.75 g of dry matter samples, in triplicate, at multiple time points up to 504 h and initially used Gooch crucibles with Celite (Thermo Fisher Scientific, Waltham, MA) as a filtering aid. The final method utilized a 1.5-µm pore size glass microfiber filter, which allowed for increased repeatability and improved sample recovery (lowest standard deviation). In this study, in vitro fermentations of 240 h were adequate to characterize and identify uNDF, which was repeatable among conventional forages provided the samples, after NDF analyses, were filtered through the same glass fiber filter. This approach could be adapted by commercial laboratories and would provide opportunities to develop near-infrared reflectance spectroscopy equations and calibrations.     

Effects of sodium hydroxide on cereal straws in relation to the enhanced degradation of structural polysaccharides by rumen microorganisms

The action of sodium hydroxide on the rate and extent of loss of wall polysaccharides from wheat and barley straws incubated in the rumen of the sheep was studied using a nylon bag technique. Cellulose loss reached a maximum in straws treated with 10 g NaOH 100 g^?1 straw. Further increase in amounts of alkali applied resulted in additional solubilisation of straw constituents, particularly xylan, but did not further enhance cellulose degradation. Rates of degradation of isolated straw, cotton and wood celluloses correlated with three of four measures of cellulose crystallinity obtained by X-ray diffraction and infrared analysis. Treatment of cellulose samples with 20 g NaOH 100 g^?1 cellulose did not affect rates of loss or produce detectable changes to cellulose morphology. Loss of acetic acid esters, which accompanied alkali treatment, did not relate to improvements to digestibility. The rate of loss of cellulose from delignified neutral detergent fibre (NDF) was that shown by the isolated straw cellulose, despite the presence of acetylated hemicellulose. Deacetylation of delignified NDF with NaOH or sodium methoxide did not enhance rates of xylose or cellulose loss. In lignified wall material (NDF) the molar ratio acetyl:xylose (approximately 1:3.5) and proportion of the major phenolic acids (p-coumaric and ferulic acids) remained essentially constant throughout the course of degradation in the rumen. It is suggested that loss of phenolic acids, while not directly contributing to digestibility enhancement, may model the susceptibility of ester linkages formed between polysaccharide and polyphenolic material to alkali. The extent of solubilisation of p-coumaric acid produced by NaOH showed a linear relationship with cellulose digestibility. An upper limit of 40% acid detergent lignin and 55% of total phenolics were released by NaOH, the extent of release closely paralleling cellulose digestibility. Phenolic material resistant to alkali remained associated with wall polysaccharides and was not released from nylon bags until over 50% of cellulose (and hemicellulose) had been degraded.     

Evaluation of tropical grasses for milk production by dual-purpose cows in tropical Mexico.

Two experiments using the Cornell Net Carbohydrate and Protein System were conducted to characterize the carbohydrate and protein fractions and corresponding rates of digestion of 15 tropical pasture grasses and to evaluate their ability to support milk production by dual-purpose cows. In the first experiment, ranges in carbohydrate and protein fractions of 15 grasses at 35 to 42 d of regrowth were: neutral detergent fiber (NDF) 63.5 to 74.9% of DM; permanganate lignin 4.7 to 7.8% of NDF; CP 5.5 to 11.9% of DM; and soluble protein 15.1 to 44.1% of crude protein (CP). The ranges of rates of digestion expressed as percent per hour were neutral detergent solubles (7.5 to 27.4); NDF (3.8 to 8.4); and neutral detergent insoluble protein (2.9 to 9.5). Predictions of the amount of milk that could be produced based on the amount of metabolizable energy supplied by the diet decreased 35% when NDF increased from 60 to 80%, and increased 88% when the rate of digestion of NDF increased from 3 to 6%/h. The milk production that could be sustained based on metabolizable protein in the diet doubled as CP increased from 4 to 12%. In the second experiment, nitrogen fertilization reduced NDF 7.3% and increased CP 84% without changing protein solubility, resulting in increased rumen nitrogen and metabolizable protein balances. With all forages, the Cornell Net Carbohydrate and Protein System predicted that availability of metabolizable protein would limit milk production. Predicted microbial growth was limited by ruminally available protein rather than by available carbohydrate.     

Fiber and lignin analysis in concentrate, forage, and feces: detergent versus enzymatic-chemical method

Hemicelluloses, cellulose, and lignin contents of contrasting feeds, with emphasis on concentrate ingredients and complete concentrates, were analyzed using the Van Soest detergent procedure (analyzing neutral detergent fiber, acid detergent fiber, and acid detergent lignin) and the enzymatic-chemical procedure (analyzing cellulose, soluble and insoluble noncellulosic polysaccharides, and Klason lignin). Also, feces from cows fed concentrates differing in carbohydrate composition were analyzed by the 2 procedures. The correlation between acid detergent lignin and Klason lignin was significant, but not as close as the one between individual structural polysaccharides measured with the 2 procedures. The correlation between the results of the 2 procedures was highly significant for apparent cellulose digestibility, as were the correlations between digestibilities of hemicelluloses with total as well as with insoluble noncellulosic polysaccharides. The relationship between dietary lignin content and fiber digestibility was weak. The exclusion of a group of cows fed a concentrate with apple pulp, however, improved the respective correlations. Klason lignin correlated more closely with the measured fiber digestibility than acid detergent lignin. The study showed that results of the detergent method were comparable to those of the enzymatic-chemical method with cellulose, hemicelluloses, and their digestibilities. However, acid detergent lignin was much lower than Klason lignin. When the carbohydrate composition of concentrate varied widely, lignin was not suitable for the prediction of fiber digestibility.     

Measuring Dietary Fiber in Human Foods

Compositions of neutral detergent fiber (NDF) residues and water insoluble fiber fractions extracted by the Southgate method from five foods were determined quantitatively and compared. Neutral saccharide compositions of the two fiber residues, measured by HPLC, were similar for four of the five foods. Uranic acids constituted 4 - 8% of fiber in all foods. When adjustments were made for protein, starch and moisture contents, mean recovery of the two fibers was 97.9 f 3.9%. Gravimetric quantitation of NDF or of a Southgate-derived insoluble fiber usually yielded a fiber content similar to the chemically determined value, although each of the Southgate residues had to be corrected for starch and/or crude protein content.