Effect of adding soluble viscous fibers to diets containing coarse and finely ground insoluble fibers on digesta transit behavior and nutrient digestibility in broiler chickens

This paper aimed to study the interactive effects of the addition of soluble arabinoxylans (AX) and the particle size (PS) of soybean hulls (SBH) on digesta mean retention time (MRT) and nutrient digestibility in broiler chickens. A total of 288 one-day old Ross 308 female chicks were assigned to 32 pens (9 birds/pen) and fed a commercial starter diet for 10 d. At 10 d of age, pens were assigned to 1 of 4 dietary treatments (8 pens/diet) containing 120 g/Kg coarse or fine SBH, with or without addition of 50 g/Kg of soluble wheat AX, substituting maize starch. Titanium dioxide (4 g/Kg) and cobalt-EDTA (1 g/Kg) were added as inert markers. Excreta were quantitatively collected from d 22 to 25. Gastrointestinal tract and digesta were collected on d 28, 29, or 30. Arabinoxylans reduced the weight of the gizzard relative to body weight (RW) by 0.07% units (P = 0.005), and increased ceca RW (0.28 vs. 0.34%, P < 0.001) and length (10.45 vs. 11.21 cm/Kg BW, P < 0.001). Arabinoxylans increased digesta MRT in the crop (solids/liquids: +12 min, P < 0.05), small intestine (solids/liquids: +17 min, P < 0.01), and hindgut (liquids: +77.5 min, P < 0.05); and reduced apparent ileal digestibility (AID) and apparent total tract retention (ATTR) of DM (-5.4 and -3.9%, P < 0.001, respectively) and starch (-1.35 and -0.7%, P < 0.001, respectively). Particle size of SBH only affected the ATTR of non-starch polysaccharides, presenting higher retention values with fine SBH (-4.3%-units, P = 0.034). The addition of AX reduced AID of N by 4.3%-units, only in presence of fine SBH (interaction, P < 0.05). In conclusion, arabinoxylans greatly influenced digestion in the chicken GIT, while PS of SBH had marginal effects. Arabinoxylans reduced AID of N only with fine SBH, suggesting coarse SBH counteracted AX effects on N digestion, speculatively by modifying digesta viscosity.

Effect of whole foods on the microbial production of tryptophan-derived aryl hydrocarbon receptor agonists in growing pigs

Effects of whole foods on the microbial production of tryptophan-derived aryl hydrocarbon receptor (AhR) ligands in the intestine were investigated in a pig model. Ileal digesta and faeces of pigs after feeding of eighteen different foods were analyzed. Indole, indole-3-propionic acid, indole-3-acetic acid, indole-3-lactic acid, kynurenine, tryptamine, and indole-3-aldehyde were identified in ileal digesta, which were also identified in faeces but at higher concentrations except indole-3-lactic acid, together with skatole, oxindole, serotonin, and indoleacrylic acid. The panel of tryptophan catabolites in ileal digesta and faeces varied across different foods. Eggs induced the highest overall concentration of catabolites in ileal digesta dominated by indole. Amaranth induced the highest overall concentration of catabolites in faeces dominated by skatole. Using a reporter cell line, we observed many faecal samples but not ileal samples retained AhR activity. Collectively, these findings contribute to food selection targeting AhR ligands production from dietary tryptophan in the intestine.

Presence of Unabsorbed Free Amino Acids at the End of the Small Intestine Indicates the Potential for an Increase in Amino Acid Uptake in Humans and Pigs

BACKGROUND

Unabsorbed free amino acids (AAs) at the end of the small intestine result in a potential preventable nutritional loss.

OBJECTIVES

This study aimed to quantify free AAs in terminal ileal digesta of both humans and pigs to investigate its relevance for the nutritional value of food proteins.

METHODS

Two studies with three diets were performed: a human study-ileal digesta from eight adult ileostomates were collected over 9 h after ingestion of a single meal unsupplemented or supplemented with 30 g zein or whey; pig study-12 cannulated pigs were fed for 7 d with a diet containing whey or zein or no-protein diet, and ileal digesta were collected on the last 2 d. Digesta were analyzed for total and 13 free AAs. True ileal digestibility (TID) of AAs was compared with and without free AAs.

RESULTS

All terminal ileal digesta samples contained free AAs. The TID of AAs in whey was 97% ± 2.4% (mean ± SD) in human ileostomates and 97% ± 1.9% in growing pigs. If the analyzed free AAs would have been absorbed, TID of whey would increase by 0.4%-units in humans and 0.1%-units in pigs. The TID of AAs in zein was 70% ± 16.4% in humans and 77% ± 20.6% in pigs and would increase by 2.3%-units and 3.5%-units, respectively, if the analyzed free AAs would have been fully absorbed. The largest difference was observed for threonine from zein: if free threonine was absorbed, the TID would increase by 6.6%-units in both species (P < 0.05).

CONCLUSIONS

Free AAs are present at the end of the small intestine and can potentially have a nutritionally relevant effect for poorly digestible protein sources, whereas the effect is negligible for highly digestible protein sources. This result provides insight into the room for improvement of a protein's nutritional value if all free AAs are to be absorbed. J Nutr 2023;xx:xx-xx. This trial was registered at clinicaltrials.gov as NCT04207372.

Insoluble fibers affect digesta transit behavior in the upper gastrointestinal tract of growing pigs, regardless of particle size

Physicochemical characteristics of dietary fibers may modulate digesta transit behavior. The present study was conducted to clarify the effect of level and particle size (PS) of insoluble fibers on digesta mean retention time (MRT) in the proximal gastrointestinal tract (mouth-ileocecal junction). Six ileal-cannulated pigs (26.8 ± 2.08 kg) were assigned to 3 dietary treatments in a 3 × 3 replicated Latin-square design. Finely ground (1 mm screen) or coarse (intact) oat husks (OH) and soybean hulls (SBH) were added (50:50, w/w) to a maize-whey protein-wheat-based diet at 50 (low) or 250 g/kg (high) inclusion levels to obtain a low-fine fiber (LF), high-fine fiber (HF), and high-coarse fiber (HC) diet. Markers to follow liquids (Co-EDTA), fine solids (Y3O2), or fibrous particles (Yb-mordanted OH and Cr-mordanted SBH) were given as a single pulse dose and marker concentrations were subsequently measured hourly in digesta for 13 h after administration. Mean retention time values were obtained from the concentration of markers in digesta observed over time by fitting a generalized Michaelis-Menten equation and calculating the time of peak. Fiber addition and fiber particle size neither affected the MRT of liquid nor solid digesta phases (P = 0.903). Segregation between solid and liquid digesta phases was observed for all diets (P < 0.0001), although the extent of segregation was greater for LF compared with HF and HC (P = 0.0220). The MRT of SBH particles, but not of OH-particles was longer for coarse vs fine PS (96 min, P < 0.05). In conclusion, digesta MRT was influenced by the dietary concentration but not by PS of insoluble fibers. The addition of insoluble fibers reduces digesta phase segregation from mouth to distal ileum in growing pigs.

Comparison of True Ileal Amino Acid Digestibility between Adult Humans and Growing Pigs

BACKGROUND

It is not feasible to determine the true ileal amino acid (AA) digestibility of protein sources in humans on a routine basis, and the growing pig has been recommended as an animal model for this purpose but requires further validation.

OBJECTIVES

To determine and compare true ileal AA digestibility between adult human ileostomates and growing cannulated pigs for a range of food proteins.

METHODS

Seven protein sources (black beans, bread, collagen, pigeon peas, wheat bran, whey protein isolate, and zein) that spanned the range of digestibilities typically seen in foods were evaluated. Six female growing pigs received each of the protein sources, as well as a protein-free diet, and digesta were collected via ileal T-cannula. Adult human ileostomates consumed the same protein sources (5-8 ileostomates, depending on the protein source), as well as a protein-free diet, and digesta were collected. Titanium dioxide and celite were included in the diets as indigestible markers. True ileal AA digestibility coefficients were determined.

RESULTS

There was a significant effect of protein source (P ≤ 0.001) for all AAs. The effect of species was not significant (P > 0.05) except for total lysine (but not for available lysine). When analyzed within diets, the statistically significant species effect for true lysine digestibility was found for black beans only. Pig and human digestibility values were generally highly and significantly (P ≤ 0.05) correlated. A linear regression equation derived for true ileal AA digestibility (given as coefficients) determined in the human and pig for the overall mean of all AAs was (y = human, x = pig) y = 1.00x - 0.010, with the slope not statistically significant (P > 0.05) from unity and the intercept not different (P > 0.05) from zero.

CONCLUSIONS

True ileal AA digestibility values determined in the growing pig can be directly used for predicting digestibility in adult humans.

Xylan alleviates dietary fiber deprivation-induced dysbiosis by selectively promoting Bifidobacterium pseudocatenulatum in pigs

BACKGROUND

Low dietary fiber intake has been shown to disturb the gut microbiome community, damage the mucus barrier, and promote pathogen susceptibility. However, little is known about the temporal response of the gut microbiome to dietary fiber deprivation and the recovery induced by dietary fiber inclusion in pigs.

OBJECTIVE

In the present study, temporal responses of ileal and fecal microbiota to dietary fiber deprivation were profiled using an ileum cannulated growing pig model. In addition, the potential of dietary-resistant starch, β-glucan, and xylan to alleviate gut dysbiosis throughout the gastrointestinal tract, as well as its possible mechanisms were investigated.

METHODS

Six cannulated growing pigs were fed a fiber deprivation diet for 35 days. Ileal digesta and feces were collected at days 0, 7, 21, and 35 for 16S rRNA sequencing and short-chain fatty acid (SCFA) determination. Another twenty-four healthy growing pigs were assigned to one of four dietary treatments including (1) fiber-free diet, (2) resistant starch diet, (3) β-glucan diet, and (4) xylan diet. These twenty-four pigs were fed a corresponding diet for 35 days and slaughtered. Gut microbiome and SCFA concentration were profiled along the gastrointestinal tract.

RESULTS

Dietary fiber deprivation-induced consistent microbiota extinction, mainly Bifidobacterium and Lactobacillus, and decreased SCFA concentrations in both ileum and feces. The community structure partially recovered at day 35 compared with baseline while SCFA concentrations remained low. Xylan supplementation alleviated gut dysbiosis by selectively promoting Bifidobacterium pseudocatenulatum within the large intestine. SCFA concentration increased significantly after xylan supplementation and exhibited a positive association with B. pseudocatenulatum abundance. An elevated abundance of xylan degradation-related enzyme genes was also observed in the gut microbiome after xylan supplementation. In vitro growth assay further verified the xylan utilization capacity of B. pseudocatenulatum.

CONCLUSIONS

Dietary fiber deprivation could induce probiotic extinction and loss of the SCFA production while potential pathogen was promoted. Xylan intervention could partially restore dietary fiber deprivation-induced gut dysbiosis through selectively promoting B. pseudocatenulatum and therefore normalizing the gut environment. These findings collectively provide evidence that dietary fiber-driven microbiota metabolism bridges the interplay between microbiome and gut health. Video abstract.

Presence of Unabsorbed Free Amino Acids at the End of the Small Intestine of Humans and Pigs: Potential Implications for Amino Acid Bioavailability

Objectives

The protein quality digestible indispensable amino acid scores (DIAAS) require determination of amino acid (AA) bioavailability, which is often quantified as the net disappearance of dietary AAs at the end of the small intestine, so-called true ileal digestibility. It is often assumed that bioavailability is mainly influenced by protein breakdown and that free AAs are completely absorbed by the small intestine. However, some studies report substantial amounts of free AAs in the unabsorbed protein fraction present in terminal ileal digesta. This study quantified free AAs in ileal digesta of humans and pigs and estimated their impact on AA bioavailability.

Methods

Two studies were performed with 3 diets, i.e., zein, whey or protein-free. In study 1, ileal digesta of 8 human ileostomates was collected over 9 hours after ingestion of a single meal. In study 2, 12 pigs

were fed 7 days with one of the 3 diets and ileal digesta was collected over 9 h on the last 2 days according to a standardized digestibility protocol. Total and free AA content were analyzed in ileal digesta.

Results

All ileal digesta contained free AAs. If the analyzed free AAs would have been absorbed in the small intestine the bioavailability for whey, which was &gt; 95%,  would only increase 0.4%-unit on average for the different AAs in humans and 0.1%-unit in pigs. For zein protein, which is ∼70% bioavailable, the impact of unabsorbed free AAs on bioavailability was on average 2.3 ± 1.2%-unit in humans and 3.5 ± 5.1%-unit in pigs. In both species, the biggest impact was seen for the free essential AA threonine; its potential absorption could increase threonine bioavailability of zein by 6.6 ± 4.0%-units for humans and  6.6 ± 8.6%-units for pigs. Moreover, for both species the proportion of threonine in free form, relative to total threonine, was significantly higher in ileal digesta after ingestion of zein compared to whey or the protein-free condition (p &lt; 0.05).

Conclusions

Our results show that not all free AAs are fully absorbed by the end of the small intestine. When the AA bioavailability of a protein is low, these unabsorbed AAs can be a quantitatively sizable fraction of ingested AAs.

Funding Sources

Proteos project, funded by a consortium of food companies and food sectors, coordinated by Global Dairy Platform, USA.

ASAS-NANP symposium: digestion kinetics in pigs: the next step in feed evaluation and a ready-to-use modeling exercise

Growing importance of upcycling agricultural by-products, food waste, and food processing by-products through livestock production strongly increased the variation in the nutritional quality of feed ingredients. Traditionally, feed ingredients are evaluated based on their measured extent of digestion. Awareness increases that in addition to the extent, the kinetics of digestion affects the metabolic fate of nutrients after absorption. Together with a growing body of evidence of complex interactions occurring within the lumen of the digestive tract, this urges the need of developing new approaches for feed evaluation. In a recently developed approach, we propose combining in vitro and in silico methods for feed ingredient evaluation. First steps in the development of such a systems were made by (1) evaluating in vitro the digestion potential of feed ingredients, regarding this as true ingredient properties and (2) predicting in silico the digestive processes like digesta transit, nutrient hydrolysis and absorption using dynamic, mechanistic modeling. This approach allows to evaluate to what extent the digestion potential of each ingredient is exploited in the digestive tract. Future efforts should focus on modeling digesta physicochemical properties and transit, applying in vitro digestion kinetic data of feed ingredients in mechanistic models, and generating reliable in vivo data on nutrient absorption kinetics across feed ingredients. The dynamic modeling approach is illustrated by a description of a modeling exercise that can be used for teaching purposes in digestive physiology or animal nutrition courses. A complete set of equations is provided as an on-line supplement, and can be built in modeling software that is freely available. Alternatively, the model can be constructed using any modeling software that enables the use of numerical integration methods.

309 ASAS-EAAP Talk: Modelling digestion kinetics: the next step in the evaluation of feed ingredients

There is increasing importance of upcycling of low-opportunity-cost feed, food waste, and food processing byproducts into animal products, strongly increasing the variation in the nutritional quality of feed ingredients. Traditionally, feed ingredients are evaluated based on their measured extent of digestion. Increasing awareness that not only the total yield of nutrients, but also their absorption kinetics, affect their metabolic fate after absorption, and a growing body of evidence of complex interactions taking place inside the gastro-intestinal tract urges development of new approaches. In a recently developed approach (Schop, 2020), we propose a combination of in vitro methodology and dynamic modelling of the digestion process as an alternative to conventional feed ingredient evaluation, and made the first steps in the development of such a system. The digestion potential, evaluated in vitro, is considered as the true property of feed ingredients. Then, prediction of digesta transit, nutrient hydrolysis and absorption, following the intake of a complete feed, determines the extent to which the digestion potential of each ingredient is exploited. The dynamic, mechanistic model developed by Schop for growing pigs comprises 48 state variables representing dietary nutrients, hydrolysis products, endogenous components, and microbial biomass. Driving variables are ingested nutrients from feed ingredients, characterized in vitro (solubility, undegradable fraction, maximum rate of digestion). Passage of digesta is modelled as a function of nutrient solubility, diet viscosity and feed intake. The extent of protein digestion and extent and rate of starch digestion, but not absorption of amino acids, were adequately predicted by the model. Future efforts should focus on modelling digesta properties and transit, translation of in vitro digestion kinetic data and generating reliable in vivo data on nutrient absorption kinetics across feed ingredients. Schop, T.A. 2020 Modelling digestion kinetics in pigs. Predicting nutrient absorption based on diet and ingredient properties. PhD thesis, Wageningen University, Wageningen, NL.

Determination of True Ileal Amino Acid Digestibility in the Growing Pig for Calculation of Digestible Indispensable Amino Acid Score (DIAAS)

Digestible indispensable amino acid score (DIAAS) has been recommended by the FAO for the evaluation of protein quality in human foods, but the application of DIAAS is currently limited because of a lack of published data on the true ileal amino acid (AA) digestibility of AAs in foods. The importance of DIAAS is highlighted. To calculate DIAAS, it is necessary to determine the true ileal AA digestibility of human foods using the growing pig as an animal model for the human based on previous FAO recommendations. A method is described in detail in Supplemental Methods to determine the true ileal AA digestibility of foods for humans using the pig as a model for the adult human. Adoption of the method will enable consistency in the development of databases on predicted true ileal AA digestibility in human foods for the calculation of DIAAS.

Effects of Early Nutrition and Sanitary Conditions on Oral Tolerance and Antibody Responses in Broiler Chickens

Greater antigenic exposure might accelerate activation and maturation of the humoral immune system. After hatch, commercial broiler chickens can have early (EN) or delayed (DN) access to nutrition, up to 72 h after hatch. The immune system of EN versus DN broilers is likely more exposed to antigens after hatch. This might contribute to activation and maturation of the immune system, but might also influence the development of oral tolerance, thereby altering later life antibody responses. We studied antibody (IgM, IgY, IgA) responses between 21 and 42 d of age in fast-growing EN and DN broilers, kept under low (LSC) or high sanitary conditions (HSC). In a first experiment (n = 51 broilers), we tested whether early oral exposure to bovine serum albumin (BSA) affected later life antibody responses towards BSA and a novel antigen-rabbit γ-globulin (RGG), under HSC. In a second experiment, a total of 480 EN and DN broilers were housed under either LSC or HSC, and we studied antibody responses against both BSA and RGG (n = 48 broilers per treatment) and growth performance. Broilers kept under LSC versus HSC, had higher antibody levels and their growth performance was severely depressed. Interactions between feeding strategy (EN versus DN) and sanitary conditions, or main effects of feeding strategy, on natural and specific antibody levels, and growth performance were not observed. Levels of IgA were elevated in EN versus DN broilers, in experiment I and in batch 2 of experiment II, but not in the other batches of experiment II. We concluded that EN versus DN contributes minimally to the regulation of antibody responses, irrespective of antigenic pressure in the rearing environment.

Cellulase and Alkaline Treatment Improve Intestinal Microbial Degradation of Recalcitrant Fibers of Rapeseed Meal in Pigs

The aim of the current study was to investigate whether degradation of rapeseed meal (RSM) by a swine gut microbiota consortium was improved by modifying RSM by treatment with cellulase (CELL), two pectinases (PECT), or alkaline (ALK) compared to untreated RSM and to assess whether microbiota composition and activity changed. The predicted relative abundances of carbohydrate digestion and absorption, glycolysis, pentose phosphate pathway, and pyruvate metabolism were significantly increased upon CELL and ALK feeding, and CELL and ALK also exhibited increased total short-chain fatty acid (SCFA) production compared to CON. Megasphaera, Prevotella, and Desulfovibrio were significantly positively correlated with SCFA production. Findings were validated in ileal cannulated pigs, which showed that CELL and ALK increased fiber degradation of RSM. In conclusion, CELL and ALK rather than PECT1 or PECT2 increased fiber degradation in RSM, and this information could guide feed additive strategies to improve efficiency and productivity in the swine industry.

Differently Pre-treated Rapeseed Meals Affect in vitro Swine Gut Microbiota Composition

The aim of the study was to investigate the effect of untreated and processed rapeseed meal (RSM) on fiber degradability by pig gut microbiota and the adaptation of the microbiota to the substrate, by using the Swine Large Intestine in vitro Model (SLIM). A standardized swine gut microbiota was fed for 48 h with pre-digested RSM which was processed enzymatically by a cellulase (CELL), two pectinases (PECT), or chemically by an alkaline (ALK) treatment. Amplicons of the V3-V4 region of the 16S rRNA gene were sequenced to evaluate the gut microbiota composition, whereas short chain fatty acids (SCFA) were measured to assess fiber degradation. Adaptive gPCA showed that CELL and ALK had larger effects on the microbiota composition than PECT1 and PECT2, and all substrates had larger effects than CON. The relative abundance of family Prevotellaceae was significantly higher in CELL treatment compared to other treatments. Regardless of the treatments (including CON), the relative abundance of Dorea, Allisonella, and FamilyXIIIUCG_001 (in the order of Clostridiales) were significantly increased after 24 h, and Parabacteroides, Mogibacterium, Intestinimonas, Oscillibacter, RuminococcaceaeUCG_009, Acidaminococcus, Sutterella, and Citrobacter were significantly higher in abundance at time point 48 compared to the earlier time points. Prevotella 9 had significant positive correlations with propionic and valeric acid, and Mogibacterium positively correlated with acetic and caproic acid. There was no significant difference in SCFA production between untreated and processed RSM. Overall, degradability in the processed RSM was not improved compared to CON. However, the significantly different microbes detected among treatments, and the bacteria considerably correlating with SCFA production might be important findings to determine strategies to shorten the fiber adaptation period of the microbiota, in order to increase feed efficiency in the animal, and particularly in pig production.

β-Glucans and Resistant Starch Alter the Fermentation of Recalcitrant Fibers in Growing Pigs

Interactions among dietary ingredients are often assumed non-existent when evaluating the nutritive value and health effects of dietary fiber. Specific fibers can distinctly affect digestive processes; therefore, digestibility and fermentability of the complete diet may depend on fiber types present. This study aimed to evaluate the effects of readily fermentable fibers (β-glucans and resistant starch) on the degradation of feed ingredients containing more persistent, recalcitrant, fibers. Six semi-synthetic diets with recalcitrant fibers from rapeseed meal (pectic polysaccharides, xyloglucans, and cellulose) or corn distillers dried grain with solubles (DDGS; (glucurono)arabinoxylans and cellulose) with or without inclusion of β-glucans (6%) or retrograded tapioca (40%) substituted for corn starch were formulated. Six ileal-cannulated pigs (BW 28±1.4 kg) were assigned to the diets according to a 6×6 Latin square. β-glucan-extract increased apparent total tract digestibility (ATTD) of non-glucosyl polysaccharides (accounting for ~40% of the fiber-fraction) from rapeseed meal (6%-units, P<0.001), but did not affect non-glucosyl polysaccharides from DDGS. Retrograded tapioca reduced ATTD of non-glucosyl polysaccharides from rapeseed meal and DDGS (>10%-units, P<0.001), indicating that the large amount of resistant starch entering the hindgut was preferentially degraded over recalcitrant fibers from rapeseed meal and DDGS, possibly related to reduced hindgut-retention time following the increased intestinal bulk. Fermentation of fiber sources was not only dependent on fiber characteristics, but also on the presence of other fibers in the diet. Hence, interactions in the gastrointestinal tract among fibrous feed ingredients should be considered when evaluating their nutritive value.

Understanding carbohydrate structures fermented or resistant to fermentation in broilers fed rapeseed (Brassica napus) meal to evaluate the effect of acid treatment and enzyme addition

Unprocessed and acid-extruded rapeseed meal (RSM) was fed to broiler chickens, with and without addition of commercial pectolytic enzymes. Nonstarch polysaccharide (NSP) fermentability and unfermented NSP structures from RSM were studied in the excreta in detail. From unprocessed RSM, 24% of the nonglucose polysaccharides could be fermented. Acid treatment did not have a significant effect, but enzyme addition did improve fermentability to 38%. Most likely, the significant increase in NSP fermentability can be ascribed to the addition of pectolytic enzymes, which decreased branchiness of the water-soluble arabinan. Mainly xyloglucan, (glucurono-)xylan, (branched) arabinan, and cellulose remained in the excreta. The proportion of unextractable carbohydrates increased in excreta from broilers fed acid-extruded RSM. Probably, acid extrusion resulted in a less accessible NSP matrix, also decreasing the accessibility for pectolytic enzymes added in the diet. During alkaline extraction of the excreta, 39 to 52% (wt/wt) of the insoluble carbohydrates was released as glucosyl- and uronyl-rich carbohydrates, probably originally present via ester linkages or hydrogen bonding within the cellulose-lignin network. These linkages are expected to hinder complete NSP fermentation and indicate that digestibility of RSM may benefit substantially from an alkaline treatment or addition of esterases.

Processing technologies and cell wall degrading enzymes to improve nutritional value of dried distillers grain with solubles for animal feed: an in vitro digestion study

Currently, the use of maize dried distillers grain with solubles (DDGS) as protein source in animal feed is limited by the inferior protein quality and high levels of non-starch polysaccharides (NSP). Processing technologies and enzymes that increase NSP degradability might improve digestive utilization of DDGS, enhancing its potential as a source of nutrients for animals. The effects of various combinations of processing technologies and commercial enzyme mixtures on in vitro digestion and subsequent fermentation of DDGS were tested. Wet-milling, extrusion, and mild hydrothermal acid treatment increased in vitro protein digestion but had no effect on NSP. Severe hydrothermal acid treatments, however, effectively solubilized NSP (48-78%). Addition of enzymes did not affect NSP solubilization in unprocessed or processed DDGS. Although the cell wall structure of DDGS seems to be resistant to most milder processing technologies, in vitro digestion of DDGS can be effectively increased by severe hydrothermal acid treatments.

Residual carbohydrates from in vitro digested processed rapeseed ( Brassica napus ) meal

Rapeseed meal (RSM) was subjected to different physical or chemical pretreatments to decrease residual, hard to degrade carbohydrates and to improve fermentability of RSM polysaccharides. Next, these pretreated samples were in vitro digested and fermented, with or without the addition of commercial pectinolytic enzymes. Remaining carbohydrates were quantified, and two physical characteristics were analyzed: (1) water-binding capacity (WBC) of the insoluble residue and (2) viscosity of the soluble fraction. Mild acid pretreatment in combination with commercial pectinolytic enzyme mixtures showed best digestion of RSM carbohydrates; only 32% of the total carbohydrate content remained. For most pretreatments, addition of commercial pectinolytic enzymes had the strongest effect on lowering the WBC of the in vitro incubated RSM. In the cases that less carbohydrate remained after in vitro digestion, the WBC of the residue decreased, and less gas seems to be produced during fermentation.