Carlos A. Montoya

Susceptibility of phaseolin to in vitro proteolysis is highly variable across common bean varieties (Phaseolus vulgaris).

A study was conducted to investigate the amino acid (AA) composition and the susceptibility to in vitro proteolysis (pepsin, 120 min and pancreatin, 240 min) of a collection of purified phaseolins ( n = 43) in unheated or heat-treated form. The AA composition of phaseolin varied little across bean varieties. At 360 min of in vitro proteolysis, the degree of hydrolysis varied from 11 to 27% for unheated and from 57 to 96% for heated phaseolins ( P < 0.001). Heat treatment markedly increased the susceptibility of phaseolin to proteolysis ( P < 0.001). The AA scores (AAS) and the protein digestibility corrected for AAS indicated S-containing AA as the limiting AA (39 +/- 3 and 30 +/- 5%, respectively). In conclusion, susceptibility to proteolysis of heat-treated phaseolin rather than its AA composition affects the nutritional value of phaseolin estimated in vitro. Therefore, it should be the criterion of choice in breeding programs aimed at improving the nutritional value of common beans for humans.

Nonstarch polysaccharide-degrading enzymes alter the microbial community and the fermentation patterns of barley cultivars and wheat products in an in vitro model of the porcine gastrointestinal tract.

An in vitro experiment was carried out to assess how nonstarch polysaccharide (NSP)-degrading enzymes influence the fermentation of dietary fiber in the pig large intestine. Seven wheat and barley products and cultivars with differing carbohydrate fractions were hydrolyzed using pepsin and pancreatin in the presence or not of NSP-degrading enzymes (xylanase and β-glucanase) and the filter retentate was subsequently fermented with sow fecal bacteria. Dry matter, starch, crude protein and β-glucan digestibilities during hydrolysis were measured. Fermentation kinetics of the hydrolyzed ingredients were modelled. Short-chain fatty acids (SCFA) production and molar ratio were compared after 12, 24 and 72 h. Microbial communities were analyzed after 72 h of fermentation using terminal restriction fragment length polymorphism. The results showed an increase of nutrient digestibility (P<0.001), whereas fermentability and SCFA production decreased (P<0.001) with addition of the enzyme. SCFA and bacterial community profiles also indicated a shift from propionate to acetate and an increase in cellulolytic Ruminococcus- and xylanolytic Clostridium-like bacteria. This is explained by the increase in slowly fermentable insoluble carbohydrate and the lower proportion of rapidly fermentable β-glucan and starch in the retentate when grains were incubated with NSP-degrading enzymes. Shifts were also different for the four barley varieties investigated, showing that the efficiency of the enzymes depends on the structure of the carbohydrate fractions in cereal products and cultivars.

Determination of the digestible energy and prediction of the net energy content of toasted and non-toasted canola meals from Brassica junceae and Brassica napus in growing pigs by the total faecal collection and the indigestible marker method.

The study aimed to compare the digestible and net energy (DE and NE) contents of three canola meals (CM) toasted (95°C) or not after desolventization from yellow Brassica junceae (YBJ) and yellow and black Brassica napus (YBN and BBN) in growing pigs. A basal diet and six CM-based diets (2/3 basal diet and 1/3 CM) supplemented with acid-insoluble ash (indigestible marker) were prepared. The growing pigs (28 kg; six per treatment) were kept in metabolic cages for 18 d and their faeces were collected for the last 10 d. The digestibilities and DE content of the CM were determined based on the total faecal excretion and the indigestible marker method. NE was estimated with a prediction equation. The DE and NE contents of the YBN meal (3.98 and 2.73 Mcal kg-1 DM) were higher (P = 0.007) than that of the YBJ (3.76 and 2.59 Mcal kg-1 DM) and BBN (3.64 and 2.43 Mcal kg-1 DM) meals. Toasting had no effect (P > 0.05) on the DE and NE contents. Inconsistent values were obtained with the indigestible marker, as compa...

Gastrointestinal Endogenous Proteins as a Source of Bioactive Peptides - An In Silico Study

Dietary proteins are known to contain bioactive peptides that are released during digestion. Endogenous proteins secreted into the gastrointestinal tract represent a quantitatively greater supply of protein to the gut lumen than those of dietary origin. Many of these endogenous proteins are digested in the gastrointestinal tract but the possibility that these are also a source of bioactive peptides has not been considered. An in silico prediction method was used to test if bioactive peptides could be derived from the gastrointestinal digestion of gut endogenous proteins. Twenty six gut endogenous proteins and seven dietary proteins were evaluated. The peptides present after gastric and intestinal digestion were predicted based on the amino acid sequence of the proteins and the known specificities of the major gastrointestinal proteases. The predicted resultant peptides possessing amino acid sequences identical to those of known bioactive peptides were identified. After gastrointestinal digestion (based on the in silico simulation), the total number of bioactive peptides predicted to be released ranged from 1 (gliadin) to 55 (myosin) for the selected dietary proteins and from 1 (secretin) to 39 (mucin-5AC) for the selected gut endogenous proteins. Within the intact proteins and after simulated gastrointestinal digestion, angiotensin converting enzyme (ACE)-inhibitory peptide sequences were the most frequently observed in both the dietary and endogenous proteins. Among the dietary proteins, after in silico simulated gastrointestinal digestion, myosin was found to have the highest number of ACE-inhibitory peptide sequences (49 peptides), while for the gut endogenous proteins, mucin-5AC had the greatest number of ACE-inhibitory peptide sequences (38 peptides). Gut endogenous proteins may be an important source of bioactive peptides in the gut particularly since gut endogenous proteins represent a quantitatively large and consistent source of protein.

Human gut endogenous proteins as a potential source of angiotensin-I-converting enzyme (ACE-I)-, renin inhibitory and antioxidant peptides.

It is well known that endogenous bioactive proteins and peptides play a substantial role in the bodys first line of immunological defence, immune-regulation and normal body functioning. Further, the peptides derived from the luminal digestion of proteins are also important for body function. For example, within the peptide database BIOPEP (http://www.uwm.edu.pl/biochemia/index.php/en/biopep) 12 endogenous antimicrobial and 64 angiotensin-I-converting enzyme (ACE-I) inhibitory peptides derived from human milk and plasma proteins are listed. The antimicrobial peptide database (http://aps.unmc.edu/AP/main.php) lists over 111 human host-defence peptides. Several endogenous proteins are secreted in the gut and are subject to the same gastrointestinal digestion processes as food proteins derived from the diet. The human gut endogenous proteins (GEP) include mucins, serum albumin, digestive enzymes, hormones, and proteins from sloughed off epithelial cells and gut microbiota, and numerous other secreted proteins. To date, much work has been carried out regarding the health altering effects of food-derived bioactive peptides but little attention has been paid to the possibility that GEP may also be a source of bioactive peptides. In this review, we discuss the potential of GEP to constitute a gut cryptome from which bioactive peptides such as ACE-I inhibitory, renin inhibitory and antioxidant peptides may be derived.

Food-derived bioactive peptides – a new paradigm

Food-derived bioactive peptides are regarded as important modulators of several physiological processes occurring both systemically and locally within the gastrointestinal tract (GIT). However, the concentrations of food-derived bioactive peptides in the GIT, and therefore attendant physiological effects, are likely to be highly variable given the wide variation in the type and amount of dietary protein consumed either during the day or on a day-to-day basis. In contrast, gut endogenous proteins (e.g. cell proteins, mucin, serum albumin and digestive enzymes) are a consistent and significant potential source of peptides for the GIT. With up to 80% of gut endogenous proteins being digested in the GIT, it is possible that a wide range of peptides is generated, but until now the significance of the gut endogenous proteins as a source of bioactive peptides has not been considered. A hypothesis is promulgated that the gut endogenous proteins may have a hidden role as a consistent and quantitatively important source of bioactive peptides in the GIT.

Dietary Actinidin from Kiwifruit (Actinidia deliciosa cv. Hayward) Increases Gastric Digestion and the Gastric Emptying Rate of Several Dietary Proteins in Growing Rats

Dietary actinidin influences the extent to which some dietary proteins are digested in the stomach, and it is hypothesized that the latter modulation will in turn affect their gastric emptying rate (GE). In this study, the effect of dietary actinidin on GE and gastric digestion of 6 dietary protein sources was determined in growing rats. Each dietary protein source [beef muscle, gelatin, gluten, soy protein isolate (SPI), whey protein isolate, and zein] was included in 2 semisynthetic diets as the sole nitrogen source. For each protein source, 1 of the 2 diets contained actinidin [76.5 U/g dry matter (DM)] in the form of ground freeze-dried green kiwifruit (Actinidia deliciosa cv. Hayward), whereas the other diet contained freeze-dried gold kiwifruit (Actinidia chinensis cv. Hort16A), which is devoid of actinidin (3.4 U/g DM). For both diets, dietary kiwifruit represented 20% of the diet on a DM basis. The real-time GE was determined in rats gavaged with a single dose of the diets using magnetic resonance spectroscopy over 150 min (n = 8 per diet). Gastric protein digestion was determined based on the free amino groups in the stomach chyme collected from rats fed the diets (n = 8 per diet) that were later killed. GE differed across the protein sources [e.g., the half gastric emptying time (T(½)) ranged from 157 min for gluten to 266 min for zein] (P < 0.05). Dietary actinidin increased the gastric digestion of beef muscle (0.6-fold), gluten (3.2-fold), and SPI (0.6-fold) and increased the GE of the diets containing beef muscle (43% T(½)) and zein (23% T(½); P < 0.05). There was an inverse correlation between gastric protein digestion and DM retained in the stomach (r = -0.67; P < 0.05). In conclusion, dietary actinidin increased gastric protein digestion and accelerated the GE for several dietary protein sources. GE may be influenced by gastric protein digestion, and dietary actinidin can be used to modulate GE and protein digestion in the stomach of some dietary protein sources but not others.

Validation of the net energy content of canola meal and full-fat canola seeds in growing pigs

A study was conducted to estimate the net energy (NE) content of canola meal (CM) and full-fat canola seeds (FFCS) in growing pigs, and to validate the results through a growth trial. The digestible energy (DE) content of the canola products was measured in a digestibility study by the difference method, with diets containing two-thirds of a basal diet of known digestibility and one-third of the canola products. The NE content was estimated by means of a prediction equation based on the DE content and chemical composition of the canola products. The NE was 2.43 and 3.56 Mcal kg-1 DM for CM and FFCS, respectively. For the growth study, 31-kg pigs (18 per treatment) were fed for 35 d with wheat/barley-based diets containing either 0, 5, 10 or 15% FFCS or 0, 7.5, 15 or 22.5% CM. The gain-to-feed ratio was unchanged by the levels of CM or FFCS (P > 0.05), but the highest level of FFCS decreased feed intake (P < 0.001) and thus increased the gain-to-feed ratio (P < 0.05). In conclusion, the NE content was corr...

Nondietary Gut Materials Interfere with the Determination of Dietary Fiber Digestibility in Growing Pigs When Using the Prosky Method

BACKGROUND Reported negative ileal and total tract dietary fiber (DF) digestibility values are physiologically untenable and suggest the presence of nondietary material in the gut contents that interferes with the DF determination. OBJECTIVE The objective of this study was to demonstrate the importance of interfering material (IM) when the Prosky method was used to determine DF digestibility. METHODS Fourteen pigs (41.6 ± 3.0 kg) were surgically implanted with ileal T-cannulas. A semisynthetic fiber-free diet and 2 semisynthetic diets containing kiwifruit as the sole fiber source [25 or 50 g fiber/kg dry matter (DM)] were prepared. Titanium dioxide was used as an indigestible marker. Pigs were fed the kiwifruit-containing diets (n=7 per diet) for 44 d, followed by the fiber-free diet (n=14) for 7 d. Ileal digesta and feces were collected over 3 d, starting on days 42 and 49. The flow of IM and the soluble, insoluble, and total DF digestibility were determined. RESULTS Considerable amounts of IM were present when the Prosky method was applied to ileal digesta (12 g/kg DM intake) and feces (28 g/kg DM intake) collected from pigs fed the fiber-free diet after adaptation to the diet containing 50 g/kg DM of fiber. The pigs adapted to the highest fiber concentration had 0.9- and 0.7-fold greater ileal and fecal IM flows than their counterparts adapted to the lowest concentration. In the ileal digesta, crude mucin was the main IM source in the soluble DF fraction (66%). In the ileal digesta and feces, microbial cells were the main IM source in the insoluble DF fraction. The determined ileal soluble DF and total tract insoluble DF digestibilities increased by 44-54% and 78% respectively after correction for IM (P < 0.001). CONCLUSIONS Large amounts of IM are present in ileal digesta and feces of pigs when fiber is determined with the Prosky method, leading to a marked underestimation.

Potential misinterpretation of the nutritional value of dietary fiber: correcting fiber digestibility values for nondietary gut-interfering material

The aim of this review is to identify the origin and implications of a nondietary material present in digesta and feces that interferes with the determination of dietary fiber in gastrointestinal contents. Negative values for ileal and fecal digestibility of dietary fiber are commonly reported in the literature for monogastric animal species, including humans. As negative values are not possible physiologically, this suggests the existence of a nondietary material in the gastrointestinal contents and feces that interferes with the accurate determination of dietary fiber digestibility when conventional methods of fiber determination are applied. To date, little attention has been given to this nondietary interfering material, which appears to be influenced by the type and concentration of fiber in the diet. Interestingly, estimates of dietary fiber digestibility increase substantially when corrected for the nondietary interfering material, which suggests that currently reported values underestimate the digestibility of dietary fiber and may misrepresent where, in the digestive tract, fermentation of fiber occurs. A new perspective of dietary fiber digestion in the gastrointestinal tract is developing, leading to a better understanding of the contribution of dietary fiber to health.