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Effects of antinutritional factors on protein digestibility and amino acid availability in foods.

Digestibility of protein in traditional diets from developing countries such as India, Guatemala, and Brazil is considerably lower compared to that of protein in typical North American diets (54-78 versus 88-94%). The presence of less digestible protein fractions, high levels of insoluble fiber, and high concentrations of antinutritional factors in the diets of developing countries, which are based on less refined cereals and grain legumes as major sources of protein, are responsible for poor digestibility of protein. The effects of the presence of some of the important antinutritional factors on protein and amino digestibilities of food and feed products are reviewed in this chapter. Food and feed products may contain a number of antinutritional factors that may adversely affect protein digestibility and amino acid availability. Antinutritional factors may occur naturally, such as glucosinolates in mustard and rapeseed protein products, trypsin inhibitors and hemagglutinins in legumes, tannins in legumes and cereals, phytates in cereals and oilseeds, and gossypol in cottonseed protein products. Antinutritional factors may also be formed during heat/alkaline processing of protein products, yielding Maillard compounds, oxidized forms of sulfur amino acids, D-amino acids, and lysinoalanine (LAL, an unnatural amino acid derivative). The presence of high levels of dietary trypsin inhibitors from soybeans, kidney beans, or other grain legumes can cause substantial reductions in protein and amino acid digestibilities (up to 50%) in rats and pigs. Similarly, the presence of high levels of tannins in cereals, such as sorghum, and grain legumes, such as fababean (Vicia faba L.), can result in significantly reduced protein and amino acid digestibilities (up to 23%) in rats, poultry, and pigs. Studies involving phytase supplementation of production rations for swine or poultry have provided indirect evidence that normally encountered levels of phytates in cereals and legumes can reduce protein and amino acid digestibilities by up to 10%. D-amino acids and LAL formed during alkaline/heat treatment of proteins such as casein, lactalbumin, soy protein isolate, or wheat proteins are poorly digestible (less than 40%), and their presence can reduce protein digestibility by up to 28% in rats and pigs. A comparison of the protein digestibility determination in young (5-week) versus old (20-month) rats suggests greater susceptibility to the adverse effects of antinutritional factors in old rats than in young rats. Therefore, the inclusion of protein digestibility data obtained with young rats, as the recommended animal model, in the calculation of PDCAAS (Protein Digestibility-Corrected Amino Acid Score) may overestimate protein digestibility and quality of products, especially those containing antinutritional factors, for the elderly. For products specifically intended for the elderly, protein digestibility should be determined using more mature rats.

Amino Acids↗

PubMed2005

Assessment of microwave-assisted enzymatic digestion by measuring glycated hemoglobin A1c by mass spectrometry.

Enzymatic digestion of proteins and analysis of the resulting peptides by mass spectrometry is an established approach in proteomics and in clinical and environmental chemistry. The long digestion times of several hours prevent the fast turnover of samples and results. Qualitative applications showed that microwave radiation profoundly shortens enzymatic digestion. However, its usefulness for quantitative applications had not been assessed. In this study, the microwave-assisted enzymatic digestion of hemoglobin at different temperatures, buffer concentrations, and digestion times was assessed and compared with conventional digestion for the proteolytic enzymes trypsin and Glu-C. A microwave-assisted enzymatic digestion method optimized for digestion time and temperature was applied for the analysis of glycated hemoglobin HbA1c and compared with a reference method. Using trypsin, complete digestion was obtained at 50 degrees C within 20 min. Under these conditions, the digestion efficiency was 20% higher than with conventional trypsin digestion. These effects were not observed with Glu-C as enzyme, probably because of the decreased stability of Glu-C at elevated temperatures in comparison with the trypsin used. The comparison of the optimized microwave-assisted digestion method using trypsin with the reference method for HbA1c using Glu-C gave a close correlation in the results (R2: 0.996). A significant bias of 0.33% HbA1c was observed, with higher values obtained with the microwave-assisted tryptic digest; this finding might have resulted from the use of a different enzyme. This study showed that microwave-assisted enzymatic digestion can substantially reduce digestion times to minutes and can be used in qualitative as well as quantitative applications.

Catalysis↗

PubMed1997

Ruminal and total plant cell-wall digestibility estimated by a combined in situ method utilizing mathematical models.

Three ruminally and duodenally cannulated non-lactating Finnish Ayrshire cows were used to investigate ruminal and intestinal digestion of cell-wall carbohydrates by a combined in situ method. Five grasses cut at 10 d intervals were incubated in the rumen for 0, 6, 12, 24, 48, 72 and 96 h, and the undegraded residues were exposed to intestinal digestion. With advancing maturity of grass both the rate and extent of cell-wall digestion decreased. At early stages of growth the decreases were faster for the rate of digestion and at late stages of growth for the extent of digestion. Applying a passage rate of 0.02/h in one compartmental rumen model resulted in digestibility values markedly lower than typically observed in vivo. However, applying a rumen model incorporating a selective retention of particles and time-dependent release of particles from the non-escapable pool resulted in much higher digestibility values. Recovery of lignin after 96 h ruminal incubation with a subsequent mobile-bag incubation was very low (from 244 to 460 mg/g). Intestinal disappearance of neutral-detergent fibre (NDF) and hemicellulose decreased with advancing maturity of grass and with increasing length of preceding ruminal incubation period, i.e. with decreasing potential digestibility of the material. Disappearance of hemicellulose was much greater than that of cellulose for intact grasses but the difference diminished with increasing length of preceding rumen incubation period. On average, 195 mg/g of potentially digestible NDF disappeared from the mobile bags in the intestines. The post-ruminal digestion as a proportion of the total NDF digestibility varied between 0.034 and 0.058. Despite methodological problems both in ruminal in situ and intestinal mobile bag techniques, these methods can be used to investigate ruminal and intestinal cell-wall digestion and to partition cell-wall digestibility between ruminal and post-ruminal digestion providing that appropriate rumen models are used.

Animal Nutritional Physiological Phenomena↗

PubMed1995

Characteristics of plant cell walls affecting intake and digestibility of forages by ruminants.

Even under the intensive concentrate feeding systems of ruminant animal production in the United States, forages continue to represent the single most important feed resource. Cell-wall concentration and digestibility limit the intake potential and energy availability of forage crops in beef and dairy production. Identification of cell-wall characteristics that should be targets of genetic modification is required if plant breeders and molecular biologists are to successfully improve forages for livestock feeding. As the forage plant cell develops, phenolic acids and lignin are deposited in the maturing cell wall in specific structural conformations, and in a strict developmental sequence. Lignin is the key element that limits cell-wall digestibility, but cross-linkage of lignin and wall polysaccharides by ferulic acid bridges may be a prerequisite for lignin to exert its affect. Lignin composition and p-coumaric acid in the wall are less likely to affect digestibility. Voluntary intake of forages is a critical determinant of animal performance and cell-wall concentration is negatively related to intake of ruminants consuming high-forage diets. Cell walls affect intake by contributing to ruminal fill. A simple model of cell-wall digestion and passage in which ruminal fill is a function of rates of digestion and passage, as well as the indigestible fraction of the cell-wall indicates that cell-wall concentration and rate of passage are the most critical parameters determining ruminal fill. Plant factors that affect rate of passage include those that affect particle size reduction by chewing and those that affect particle buoyancy in the rumen. The latter is primarily affected by 1) the ability of the particulate matter to retain gases, which is probably related to plant anatomy and rate of digestion of the plant tissue, and 2) the rate at which the gas is produced, which is affected by the potentially digestible fraction of the particulate matter and the rate of digestion of this fraction. Increasing rate of digestion should increase rate of passage by diminishing the gas produced and increasing density over time. A reduction in the indigestible cell-wall fraction is beneficial because this will decrease fill and increase digestibility. Animal production and economic benefits from reduced cell-wall concentration and increased digestibility are significant. Because of the high cell-wall concentration and large digestible cell-wall fraction of grasses, reduction in cell-wall concentration would probably be of greater value than improving digestibility in these species. Legumes represent the opposite situation and may benefit more from improvements in the digestibility of their cell walls.

Animal Feed↗

PubMed1999

Steam-processed corn and sorghum grain flaked at different densities alter ruminal, small intestinal, and total tract digestibility of starch by steers.

Crossbred steers (n = 7; 400 kg BW), fitted with T-type cannulas in the duodenum and ileum, were used to examine the effects of processing method, dry-rolled (DR) vs. steam-flaked (SF) sorghum grain, and degree of processing (flake density; FD) of SF corn (SFC) and SF sorghum (SFS) grain on site and extent of DM, starch, and N digestibilities and to measure extent of microbial N flow to the duodenum. In Exp. 1, diets contained 77% DRS or 77% SFS with FD of 437, 360, and 283 g/L (SF34, SF28, and SF22). In Exp. 2, diets contained 77% SFC with FD of SF34 or SF22. For sorghum and corn diets, respective average daily intakes were as follows: DM, 6.7 and 8.1 kg; starch, 3.8 and 4.7 kg; N, 136 and 149 g. Steers fed SFS vs. DRS increased (P = .01) starch digestibilities (percentage of intake) in the rumen (82 vs. 67%) and total tract (98.9 vs. 96.5%) and decreased digestibilities in the small intestine (16 vs. 28%; P = .01) and large intestine (.5 vs 1.2%; P = .05). As a percentage of starch entering the segment, digestibility was increased (P = .01) within the small intestine (91 vs. 85%) but was not altered within the large intestine by steers fed SFS vs. DRS. Decreasing FD of SFS and of SFC, respectively, linearly increased starch digestibilities (percentage of intake) in the rumen (P = .03, .02) and total tract (P = .03, .09) and linearly diminished starch digestibilities in the small intestine (P = .04, .09). Starch digestibilities (percentage of entry) within the small or large intestine were not changed by FD. The percentage of dietary corn or sorghum starch digested in the large intestine was very small, less than 2% of intake. Microbial N flow to the duodenum was not altered by SFS compared to DRS, or by decreasing FD of SFS and SFC. Reducing FD of SFS, but not of SFC, tended to decrease (P = .07) microbial efficiency linearly and tended to increase (P = .06) total tract N digestibilities linearly. Steam flaking compared to dry rolling of sorghum grain and decreasing FD of SFC and SFS grain consistently increased starch digestibility in the rumen and total tract of growing steers. The greatest total digestibility of dietary starch occurred when the proportion digested in the rumen was maximized and the fraction digested in the small intestine was minimized. These changes in sites of digestion account, in part, for the improved N conservation and greater hepatic output of glucose by steers fed lower FD of SFS reported in our companion papers.

Animals↗

PubMed2003

Relationship between body weight and level of fat supplementation on fatty acid digestion in feedlot cattle.

Eight Holstein steers with cannulas in the rumen and proximal duodenum were used in a split-plot design experiment to evaluate the interaction of body weight (175 vs. 370 kg) and level of fat supplementation (0, 3, 6, and 9% yellow grease) on characteristics of digestion and feeding value of fat in finishing diets. Dry matter intake was restricted to 2% of BW. There were no interactions between BW and level of fat supplementation (P > 0.10) on ruminal or total-tract digestion. Level of supplemental fat decreased (linear, P < 0.01) ruminal digestion of OM and NDF, and increased (linear, P < 0.05) ruminal N efficiency. There were no treatment effects (P > 0.10) on postruminal digestion of OM, NDF, and N. There tended to be an interaction (P < 0.10) between BW and level of fat supplementation on postruminal starch digestion. Increasing level of fat supplementation increased postruminal digestion of starch in heavier steers but did not affect starch digestion in lighter steers. There were no interactions (P > 0.10) between BW and level of fat supplementation on postruminal fatty acid digestion. Increasing level of fat supplementation decreased (linear, P < 0.01) postruminal fatty acid digestion, which was due to a decreased (linear, P < 0.01) postruminal digestion of C16:0 and C18:0. Supplemental fat decreased (linear, P < 0.01) total-tract digestion of OM and NDF. The estimated NEm (Mcal/kg) of yellow grease averaged (linear, P < 0.01) 6.02, 5.70, and 5.06 for the 3, 6, and 9% of level supplementation, respectively. We conclude that intestinal fatty acid digestion (FAD, %) is a predictable function (r2 = 0.89; P < 0.01) of total fatty acid intake per unit body weight (FAI, g/kg BW): FAD = 87.560 - 8.591FAI. Depressions in fatty acid digestion with increasing level of intake were due primarily to decreased intestinal absorption of palmitic and stearic acid. Level of fatty acids intake did not appreciably affect intestinal absorption of unsaturated fatty acid. Changes in intestinal fatty acid digestion accounted for most of the variation in the NE value of supplemental fat.

Animal Feed↗

PubMed2006

Sites of nutrient digestion in growing pigs: effect of dietary fiber.

The impact of dietary fiber on fecal digestion is well-known and provides a comprehensive approach toward nutrient digestibility and availability. Little quantitative information is available on digestion of fiber in the different segments of the gastrointestinal tract (GIT). The objectives of this study were to obtain a method allowing the quantification of the digestive process in different segments of the GIT and to study the impact of dietary fiber on nutrient digestibility. Six barrows (average initial BW of 30 kg and fitted with a simple T-cannula at the proximal duodenum and caudal ileum) were used in a replicated 3 x 3 Latin square design. In each period, pigs were offered 1 of 3 diets differing in fiber content (low, medium, and high). Differences in fiber content were created by replacing wheat and barley with wheat bran. Titanium dioxide was included in the diet as an indigestible marker to determine the apparent digestibility coefficients in different segments of the GIT. The apparent digestibility of ash, CP, DM, and OM increased in the different segments of the GIT. Duodenal digestibility coefficients were negative for ash (e.g., -39.9% for the medium- and high-fiber diets), indicating important endogenous mineral secretions by the stomach and digestive glands. The duodenal digestibility of other nutrients and OM were positive but close to zero and numerically lower in the diets with the greater fiber contents. The fiber content in the diet did not affect the apparent ileal digestibility of nutrients. Increasing the fiber content in the diet affected the fecal digestibility of CP, ether extract, and energy (P < 0.01). The method used for studying sites of digestion in the digestive tract provides promising results, but it is limited due to the high variability that is likely caused by sampling limitations and variation between animals.

Animal Feed↗

PubMed2006

Effects of fatty acid supplements on ruminal and total tract nutrient digestion in lactating dairy cows.

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on ruminal digestion kinetics, and ruminal and postruminal nutrient digestion. Eight early lactation ruminally and duodenally cannulated cows (77 +/- 12 days in milk, mean +/- SD) were used in a replicated 4 x 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Saturated FS linearly decreased ruminal digestibility of dry matter and organic matter and linearly decreased ruminal neutral detergent fiber (NDF) digestibility. The reduction in ruminal NDF digestibility was because of a linear decrease in digestion rate and a linear increase in passage rate of potentially digestible NDF with increasing saturated FS. Total tract digestibility of NDF was not different between treatments because of compensatory postruminal digestion. Ruminal fatty acid and C18 fatty acid digestibility tended to increase linearly with increasing unsaturated FS, and postruminal C18 fatty acid digestibility decreased with increasing saturated FS. Saturated FS linearly decreased ruminal organic matter digestibility and decreased intestinal long-chain fatty acid digestibility, although differences in fatty acid digestibility may be partially explained by fatty acid intake.

Animals↗

PubMed2002

Increased digestibility of two products in genetically modified food (CP4-EPSPS and Cry1Ab) after preheating.

We performed experiments on in vitro digestion of newly expressed proteins by SGF (simulated gastric fluid) and SIF (simulated intestinal fluid) to assess the allergenicity of food components derived from biotechnological modification. For newly expressed proteins, we chose CP4-EPSPS (5-enolpyruvylshikimate-3-phosphate synthase from Agrobacterium sp. strain CP4) and Cry1Ab derived from Bacillus thuringiensis subsp. kurstaki strain HD-1. The former is expressed in GM-soybeans and the latter is expressed in GM-corns. Firstly, we examined the digestibility of purified CP4-EPSPS and Cry1Ab by SGF. Both proteins were rapidly digested within 60 sec. After preheating, the digestibility by SGF was slightly increased. Secondly, CP4-EPSPS in GM-soybean extracts and Cry1Ab in GM-corn extracts were digested by SGF. The digestion time of both proteins by SGF was almost the same as that of the purified proteins. Thirdly, the digestibility of CP4-EPSPS and Cry1Ab by SIF was examined. The digestion time of these proteins was 240 min or more. However, digestibility of these proteins by SIF was dramatically increased by preheating, and the digestion time was less than 5 sec. Fourthly, CP4-EPSPS in GM-soybean extracts and Cry1Ab in GM-corn extracts were digested by SIF. Digestion time of both proteins by SIF was almost the same as that of the purified proteins. From these results, we concluded that the digestibility of both CP4-EPSPS and Cry1Ab by SGF and SIF was increased by preheating. Therefore, we suggest that the allergenicity of both proteins should be extremely low because of the easy digestibility of these proteins by SGF and also by SIF with preheating.

Allergens↗

PubMed1996

Evaluation of the digestibility of nutrients in pigs by ileal cannulation technique.

A simple T-cannula was surgically inserted into the ileum of growing female Large White x Dutch Landrace swine. Chymus samples collected with the help of the cannula were analysed to determine the apparent digestibility of different dietary nutrients such as dry matter, crude protein and starch, as well as of some essential amino acids. The following three experiments were conducted: (I) of the cereals, the "Tewo" triticale variety fed alone and in 1:1 concentrate mixtures with wheat or maize was studied; (II) waxy maize hybrids and maize hybrids of normal endosperm were compared without treatment and after treatment by the Bocchi technology; (III) untreated and extruded maize supplemented either with extracted soybean or with extracted sunflower was also tested. The ileal digestibility of protein, amino acids and starch was determined and compared with values obtained by conventional (faecal) analysis. When feeding triticale alone or in combination with wheat or maize, the ileal digestibility of crude protein and amino acids increased as a result of feeding the cereal combinations (e.g. crude protein 72-79%, lysine 75-79%, threonine 63-78%, methionine 74-86%). Comparison of the two maize hybrids revealed that, with the exception of methionine, lysine and tyrosine, the amino acids of the waxy hybrid had higher ileal digestibility. Treatment of the normal hybrid by the Bocchi technology caused a significant improvement in the ileal digestibility of cystine, isoleucine, lysine, valine, and dry matter. This treatment also improved the faecal digestibility of all test nutrients but methionine. Bocchi treatment of the waxy hybrid significantly improved the ileal digestibility of isoleucine, leucine, methionine, tyrosine and valine, and the faecal digestibility of cystine, dry matter, and crude protein. No major variety- or treatment-related differences were found in the digestibility of starch. As a result of extrusion, the digestibility of nutrients of the soybean + maize mixture increased from 61.6% to 70.3% (crude protein), from 41.1% to 59.4% (threonine), from 60.1 to 72.0% (methionine), and from 70.7% to 82.7% (lysine). The same treatment of the sunflower + maize mixture increased the digestibility of crude protein from 80.6% to 84.5%, that of threonine from 78.1% to 80.6%, that of methionine from 79.7% to 84.3%, while that of lysine from 61.4% to 72.3%. The ileal digestibility of starch was 97-98% for both mixtures. As a result of extrusion, most of the faecal digestibility values showed a significant improvement for both the soybean- and the sunflower-containing mixtures. The favourable effect exerted by extrusion on the digestibility of nutrients is markedly influenced by the feed components.

Amino Acids↗

PubMed2000

Estimating digestion rate and the problem of individual variability, exemplified by a scyphozoan jellyfish.

Short-term (h) and long-term (days) individual variability and the effects of momentary change in feeding intensity on digestion time were studied in the scyphomedusa Aurelia aurita as a basis for developing a method to experimentally measure the digestion rate with a high precision. Ten individual medusae showed only small, non-significant differences in average digestion time (range, 2.1-2.5 h at 10 degrees C) over a 9-day experiment, whereas variability within and between days and between individuals at a given occasion was high. When medusae were manually kept at a constant feeding intensity, stomach fullness showed high variability both between individuals and within an individual over time. With a feeding intensity of, respectively, 1, 2, 4 and 8 prey h(-1) over a 5-h experimental period, stomach fullness of most individuals corresponded to a theoretical digestion time of 1-3 h, whereas single meals of the same size usually gave somewhat higher digestion time. Medusae subject to a switching from a low to a high feeding intensity tended to increase the variability, but most individuals showed a digestion time of 1-3 h. An opposite switching tended to increase the digestion time and its variability. It is concluded that the digestion time of A. aurita is randomly variable over time within given limits for a given food and environmental condition. This variability is non-synchronised in the population, causing high variability between individuals, and changes in the feeding intensity cause additional variability. However, the average digestion time of A. aurita in a physically and nutritionally stable environment is robust, and changes in the feeding intensity give predictable effects. The use of field collected data on stomach contents and laboratory determined digestion times is therefore an attractive method to calculate predation rate, but the inherent high variability in digestion time must be taken into consideration when designing the digestion experiments. Based on these findings a simple experimental method to determine the digestion time of aquatic animals is outlined and evaluated. The digestion time is simply given as the ratio between number of prey in stomach and total number of prey eaten, times the incubation time, assuming that the feeding intensity is constant.

Journal Article↗

PubMed2005

Effect of hydraulic retention time on the efficiency of vertical tubular anaerobic sludge digester treating waste activated sludge.

Treating waste activated sludge at a temperature of 35 degrees C was investigated in vertical tubular anaerobic sludge digester and common anaerobic sludge digester, with the working volume of 2.5 m3 each. Compared with common anaerobic sludge digester, the vertical tubular anaerobic sludge digester greatly improved volatile solids and COD removal efficiencies, the methane production and the stability of the anaerobic digestion system under the same condition of hydraulic retention time. The minimum hydraulic retention time of the vertical tubular anaerobic sludge digester was 5 days, when the organic loading remained at 5.28 kg m(-3) d(-1) (as volatile solids) and the volatile solids removal rate was 41.7%. The suitable hydraulic retention time for vertical tubular anaerobic sludge digester was 5 days, while to get the same COD removal rate it was 10 days for common anaerobic sludge digester. At optimum hydraulic retention time of 5 days, the methane production of the two digesters achieved the maximum difference of 0.06 l g(-1) volatile solids (0.26, 0.20 l g(-1) volatile solids for vertical tubular anaerobic sludge digester and common anaerobic sludge digester, respectively). The advantage of vertical tubular anaerobic sludge digester was especially obvious when the hydraulic retention time was relatively short. Furthermore, it was found that the vertical tubular anaerobic sludge digester in which more anaerobic bacteria lived has significantly intensified the sub-micro mass transfer between the substrate and the microorganisms, which resulted in a remarkable effect on shortening the hydraulic retention time of anaerobic sludge digestion.

Bacteria, Anaerobic↗

PubMed1985

Examination of thermophilic methane-producing digesters by analysis of bacterial lipids.

Thermophilic methane-producing digesters were examined by the analysis of lipids to determine the microbial biomass, community structure, and nutritional status of the microbes within the digesters. The digesters received a daily feedstock of cattle feed and Bermuda grass, with some digesters receiving additional supplements of propionate, butyrate, or nitrate. Microbial biomass, measured as total extractable lipid phosphate, was decreased in slurries from digesters receiving continuous addition of the fermentation intermediates propionate or butyrate as compared with slurries from control digesters receiving the feedstock alone. In slurries from digesters that received continuous addition of nitrate, the microbial biomass was higher than in the slurries from control digesters. The control digesters had ca. 2.5 x 10 bacteria per g (dry weight) as determined from total extractable lipid phosphate. Shifts in microbial community structure were observed by analysis of ester-linked phospholipid fatty acids. Statistical analysis of the patterns of phospholipid fatty acids indicated that the digesters receiving different supplements could be distinguished from the control digester and from each other. Poly-beta-hydroxybutyric acid, an indicator of metabolic stress, was detected in slurries from all the digesters. Slurries from the nitrate-amended digester had the highest concentration of poly-beta-hydroxybutyric acid, whereas slurries from the propionate-amended digester had the lowest concentration. These chemical analyses offer a quantitative means to correlate shifts in microbial biomass, community structure, and nutritional status in complex fermentation systems to the production of a specific end product.

Journal Article↗

PubMed2003

Novel trends in anaerobic digestion of municipal solid waste.

Anaerobic digestion capacity has been installed on a large scale for the treatment of biowaste coming from municipal solid waste in the 90's. However, in recent years, a new trend has developed in which anaerobic digestion is applied more and more for the treatment of mixed or grey waste. It is expected that the installed capacity for grey/mixed waste will surpass the capacity installed for biowaste digestion. Five years ago, more than 85% of the treatment capacity was for biowaste digestion and only 15% for grey/mired waste digestion, derived from two old plants that were constructed prior to 1990. By the end of 2004, a digestion capacity of 1,285,000 ton per year will be available in Europe for the treatment of grey or mixed MSW, while digestion capacity for biowaste will only amount to 1,270,000 ton per year. Especially dry digestion offers new perspectives. Dry digestion is particularly suited for the treatment of grey/mixed waste due to its insensitivity to the presence of heavy inerts and light materials. Heavy inerts such as sand, glass and stones cause sedimentation and the light materials cause floatation and scum formation in the more conventional wet and semi-dry systems. Due to the high initial dry solids content, the digestate coming from dry digestion can be treated in a variety of ways. Besides the conventional mechanical dewatering, drying with waste heat or aerobic drying by addition of a fresh waste can be utilized for the production of a high-quality compost in case of the treatment of biowaste. Digestate from mixed or grey waste is not immediately suitable for the production of a high-quality compost. However, integration with incineration plants and landfills can be optimized easily with such a dry digestate and offers various interesting alternatives. In case a maximum of recyclables is pursued, the dry digestion can be followed by a wet separation in order to produce marketable endproducts such as sand and fibers.

Anaerobiosis↗

PubMed1993

Adaptation to the digestion of non-starch polysaccharide in growing pigs fed on cereal or semi-purified basal diets.

Pigs (25-45 kg) were fed on either cereal or semi-purified basal diets supplemented with either high or low levels of sugar-beet pulp or wood cellulose (Solka-floc). The apparent digestibility and retention of N and apparent digestibility and metabolizability of energy (GE) and the apparent digestibility of non-starch polysaccharides (NSP) and their constituent monomers were measured during weeks 2, 4 and 6 of the trial. N and GE were less well-digested, retained or metabolized from cereal basal diets than from the corresponding semi-purified diets during all three periods. NSP from sugar-beet pulp was highly digestible, unlike that from Solka-floc which was relatively poorly digested. These differences of NSP digestibility were seen more clearly when incorporated in semi-purified diets. There was no significant increase in the digestibility or retention of N, or digestibility or metabolizability of GE, or in the digestibility of sugar-beet pulp NSP with increasing time-period on the diets. In contrast, the digestibility of Solka-floc NSP tended to increase with the time-period. The digestibility of NSP from the semi-purified diet with the high level of Solka-floc inclusion was much lower than that for the low level of inclusion, indicating that microbial activity had been reduced. In conclusion, adaptation to the diets in terms of N and GE balance may be complete after 1 week, but 3-5 weeks may be necessary before stability of measurements of the digestibility of resistant NSP monomers can be obtained.

Adaptation, Physiological↗

PubMed1994

Digestibility of energy, protein, fat and non-starch polysaccharides in mixed diets: comparative studies between man and the rat.

The apparent digestibility of energy, protein, fat and non-starch polysaccharides (NSP) of low and high dietary fibre (DF) mixed diets were studied in three series of experiments with man and the rat. Low DF diets were used as control diets in each experimental series and the DF level was increased by adding fruits and vegetables (Study 1), citrus fibre concentrate (Study 2) and insoluble barley fibre (Study 3). In Study 3 the high DF diet was fed at two protein levels. There was in most cases good agreement between the digestibility of energy between man and the rat, with the digestibility of energy of the low DF control diets of 0.941-0.950 in man compared with 0.933-0.952 in the rat and of the high DF diets of 0.897-0.931 in man and 0.865-0.920 in the rat. The biggest difference in digestible energy between the two species was found for the diet enriched with fruits and vegetables (0.032 absolute units) and citrus fibre concentrate (0.025 absolute units). Apparent digestibility of protein was slightly lower in man than in the rat for all diets in Studies 1 and 2. In Study 3, however, apparent digestibility of protein was consistently lower in man than in the rat with differences in absolute digestibilities between the two species varying from 0.023 (high DF/high protein) to 0.071 (high DF/low protein). The digestibility of fat was the same in man and in the rat in all but the high DF diet of Study 2. The rat appears to have a lower capacity to digest fibre polysaccharides than man and the digestibility of NSP was consistently lower in the rat than in man. The biggest difference between the two species was found for the diets in Study 2 where the digestibility of NSP in man was measured to be 0.774-0.885 compared with only 0.501-0.517 in the rat. For the other diets the differences in NSP digestibility were 0.077-0.137 absolute units. In spite of some differences between man and the rat in their ability to digest nutrients the various diets are ranked in the same order by the two species.

Adult↗

PubMed1987

Digestion of starch and fibre carbohydrates in peas by adult cockerels.

The digestion of starch and fibre by adult cockerels fed peas which were whole, ground, autoclaved, heated, dehulled, cooked or supplemented with a cellulose degrading enzyme was studied. The starch in ground peas that had been autoclaved, heated or dehulled was slightly, though not significantly, better digested than the starch in peas that had been ground only. Feeding peas whole greatly reduced starch digestibility. Cooking failed to improve starch digestibility as retrograded starch produced in the cooking process was not digested. The more finely ground the foodstuff, the better the in vitro enzymatic hydrolysis of starch. Starch digestibility correlated well (r2 = 0.80) with the true metabolisable energy values obtained for the different pea treatments. In experiment 1 cockerels digested on average 0.22 of the pea fibre from the different forms of peas. A significant decrease in xylose digestion was observed when birds were fed dehulled peas, birds excreting more xylose than they ingested. In experiment 2, cockerels digested on average 0.38 of the pea fibre from different forms of peas. A reduction in fibre digestion was observed when birds were fed cooked peas as a consequence of a decreased digestibility of all monosaccharide residues. A slight increase in fibre digestion was observed when peas were augmented with 'cellulase', entirely because of an increase in xylose digestion.

Animals↗

PubMed1993

Use of a combined synthetic fibre bag method to estimate the true total tract digestion of organic matter and nitrogen of hay and grass silage in cows.

A 4 x 4 Latin square experiment was designed to determine and compare the total tract digestion of organic matter (OM) and nitrogen of hay and grass silage by combining the ruminal and intestinal digestion estimates obtained by the rumen bag and mobile bag methods. The diets were composed of forage alone or 30% forage and 70% barley. The rumen degradation (RD) was calculated using the degradation constants a, b, and c obtained to the forages, according to the equation RD = a+bc/(c+k). Intestinal digestion of escape feeds was estimated using the feed residues that resisted rumen degradation during 16 hours. For comparative purposes, the total tract digestion was also calculated based on the actual rumen degradation of forages during 16 hours rumen incubation. The effect of dietary interaction on the digestion of forages was assessed. Rumen degradation values obtained by 16 hours incubation did not provide sufficient basis to estimate reliably the total tract digestion by the combined bag method. Using calculated RD total tract digestion of OM of hay and grass silage were rather close to conventional in vivo digestion coefficient of respective feeds similar in chemical composition, when barley was not included in the diet. With hay, but not with grass silage, barley always markedly reduced the rumen degradation and total digestion of OM. Barley supplementation always increased the proportion of feed digested in the intestine. Nitrogen digestion was always higher with grass silage than with hay, and the combined bag method produced N digestion values 17.6-22.0%-units higher than those in the feed table. Barley supplementation did not affect the N digestion of the forages.(ABSTRACT TRUNCATED AT 250 WORDS)

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