Formation of enzyme resistant starch during autoclaving of wheat starch: Studies in vitro and in vivo

New Techniques in Structural Tailoring of Starch Functionality

Inherent characteristics of native starches such as water insolubility, retrogradation and syneresis, and instability in harsh processing conditions (e.g., high temperature and shearing, low pH) limit their industrial applications. As starch properties mainly depend on starch composition and structure, structural tailoring of starch has been important for overcoming functional limitations and expanding starch applications in different fields. In this review, we first introduce the basics of starch structure, properties, and functionalities and then describe the interactions of starch with lipids, polysaccharides, and phenolics. After reviewing genetic, chemical, and enzymatic modifications of starch, we describe current progress in the areas of porous starch and starch-based nanoparticles. New techniques, such as using the CRISPR-Cas9 technique to tailor starch structures and using an emulsion-assisted approach in forming functional starch nanoparticles, are only feasible when they are established based on fundamental knowledge of starch. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Optimization of the autoclave preparation process for improving resistant starch content in rice grains

The autoclave preparation process to increase the content of resistant starch (RS) in rice grains was optimized, and the results showed that the optimal preparation process was obtained with a water content of 41.63%, a pH of 5.95, an autoclave time of 60.96 min, and a refrigeration time of 17.11 hr. Under these conditions, the theoretical value of RS content in rice grains reached 17.57%. After autoclaving, the estimated glycemic index (EGI) in rice grains was reduced from 78.35 to 66.08 measured after cooking, suggesting that autoclaving was capable of increasing the RS content in rice grains and reducing its EGI value. These results may help spark new concepts and methods for the development of specialized foods for specific populations, such as people with diabetes.

Tailoring Digestibility of Starches by Chain Elongation Using Amylosucrase from Neisseria polysaccharea via a Zipper Reaction Mode

Amylosucrase from Neisseria polysaccharea (NpAS) was applied to modify waxy corn starch (WCS) and irradiated WCS, whose attenuated digestibility was studied. Herein, the mobility of the reaction mixture did not affect the enzyme catalytic efficiency, and the reaction kinetics suggest that the enzyme elongated the starch chain via a zipper reaction mode. The A-type crystalline structure of native and irradiated WCS was changed to B type after NpAS treatment, and a longer chain length led to a further increase in the gelatinization temperature. Chain elongation increased the content of resistant starch (RS) from 22.3% (native WCS) to be as much as 64.4% for NpAS-modified WCS, accordingly decreasing the contents of both rapidly and slowly digestible starches. Pearson correlation analysis implies that the RS content of NpAS-modified starches was positively and negatively correlated to the proportion of intermediate chains [13 ≤ degree of polymerization (DP) ≤ 24] and short chains (DP ≤ 12), respectively.

Barley Products of Different Fiber Composition Selectively Change Microbiota Composition in Rats

Scope

Several dietary fiber properties are suggested to be important for the profiling of the microbiota composition, but those characteristics are rather unclear. Whether different physico‐chemical properties of barley dietary fiber influence the gut microbiota composition is investigated.

Methods and results

Seven diets containing equal amounts of dietary fiber from barley malts, brewer's spent grain (BSG), and barley extracts, resulting in varying amounts of β‐glucan, soluble arabinoxylan, and insoluble arabinoxylan in the diets were given to conventional rats. Malts increased microbiota alpha diversity more than BSG and the extracts. The intake of soluble arabinoxylan was related to Akkermansia and propionic acid formation in the cecum of rats, whereas β‐glucan and/or insoluble arabinoxylan were attributed to some potentially butyrate‐producing bacteria (e.g., Lactobacillus, Blautia, and Allobaculum).

Conclusion

This study demonstrates that there is a potential to stimulate butyrate‐ and propionate‐producing bacteria in the cecum of rats with malt products of specific fiber properties. Moreover, BSG, a by product from beer production, added to malt can possibly be used to further modulate the microbiota composition, toward a higher butyric acid formation. A complex mixture of fiber as in the malts is of greater importance for microbiota diversity than purer fiber extracts.

Effects of monobutyrin and tributyrin on liver lipid profile, caecal microbiota composition and SCFA in high-fat diet-fed rats

Butyric acid has been shown to have suppressive effects on inflammation and diseases related to the intestinal tract. The aim of the present study was to investigate whether supplementation of two glycerol esters, monobutyrin (MB) and tributyrin (TB), would reach the hindgut of rats, thus having an effect on the caecal profile of SCFA, microbiota composition and some risk markers associated with chronic inflammation. For this purpose, rats were fed high-fat diets after adding MB (1 and 5 g/kg) and TB (5 g/kg) to a diet without any supplementation (high-fat control; HFC). A low-fat (LF) diet was also included. In the liver, total cholesterol concentrations, LDL-cholesterol concentrations, LDL:HDL ratio, and succinic acid concentrations were reduced in rats given the MB and TB (5 g/kg) diets, compared with the group fed the HFC diet. These effects were more pronounced in MB than TB groups as also expressed by down-regulation of the gene Cyp8b1. The composition of the caecal microbiota in rats fed MB and TB was separated from the group fed the HFC diet, and also the LF diet, as evidenced by the absence of the phylum TM7 and reduced abundance of the genera Dorea (similar to LF-fed rats) and rc4-4. Notably, the caecal abundance of Mucispirillum was markedly increased in the MB group compared with the HFC group. The results suggest that dietary supplementation of MB and TB can be used to counteract disturbances associated with a HFC diet, by altering the gut microbiota, and decreasing liver lipids and succinic acid concentrations.

Tecnología del almidón resistente / Technology of resistant starch

In recent years the discovery of the starch fraction called resistant starch (RS) has lead to numerous investigations. The nature of this fraction is very heterogeneous, and it comprises different types of resistant starches. From a technological point of view, RS type III or retrograded starch is the most important fraction. This resistant starch is formed after heating and cooling processes which therefore may occur in numerous fresh foods and foodstuffs. This brief review describes the gela tinization and retrogradation, which occur during heating and cooling, involved in the formation of resistant starch. The influence on RS formation of technological processes used in the manu facture of cereals has been studied as well as the influence of certain treatments used in legumes. In addition, the interactions between starch and nutrients such as proteins, lipids and sugars have also been studied. Recently, a high pressure autoclave has been used in a gelatinization system, which allows a better technological control and an increase in RS yields in comparison to conven tional systems.

Effects of two whole-grain barley varieties on caecal SCFA, gut microbiota and plasma inflammatory markers in rats consuming low- and high-fat diets

Mixed-linkage β-glucans are fermented by the colon microbiota that give rise to SCFA. Propionic and butyric acids have been found to play an important role in colonic health, as well as they may have extraintestinal metabolic effects. The aim of the present study was to investigate how two whole-grain barley varieties differing in dietary fibre and β-glucan content affected caecal SCFA, gut microbiota and some plasma inflammatory markers in rats consuming low-fat (LF) or high-fat (HF) diets. Barley increased the caecal pool of SCFA in rats fed the LF and HF diets compared with those fed the control diet, and the effect was generally dependent on fibre content, an exception was butyric acid in the LF setting. Furthermore, whole-grain barley reduced plasma lipopolysaccharide-binding protein and monocyte chemoattractant protein-1, increased the caecal abundance of Lactobacillus and decreased the Bacteroides fragilis group, but increased the number of Bifidobacterium only when dietary fat was consumed at a low level. Fat content influenced the effects of barley: rats fed the HF diets had a higher caecal pool of acetic and propionic acids, higher concentrations of amino acids and higher amounts of lipids in the portal plasma and liver than rats fed the LF diets; however, less amounts of butyric acid were generally formed. Interestingly, there was an increase in the caecal abundance of Akkermansia and the caecal pool of succinic acid, and a decrease in the proportion of Bifidobacterium and the Clostridium leptum group. In summary, whole-grain barley decreased HF diet-induced inflammation, which was possibly related to the formation of SCFA and changes in microbiota composition. High β-glucan content in the diet was associated with reduced plasma cholesterol levels.

Barley malt increases hindgut and portal butyric acid, modulates gene expression of gut tight junction proteins and Toll-like receptors in rats fed high-fat diets, but high advanced glycation end-products partially attenuate the effects

Barley malt has been shown to give high levels of butyric acid in the cecum and serum of rats.

Prebiotic and synbiotic effects on rats fed malted barley with selected bacteria strains

BACKGROUND

Butyric acid, one of the key products formed when β-glucans are degraded by the microbiota in the colon, has been proposed to be important for colonic health. Glutamine bound to the fibre may have similar effects once it has been liberated from the fibre in the colon. Both β-glucans and glutamine are found in high amounts in malted barley. Lactobacillus rhamnosus together with malt has been shown to increase the formation of butyric acid further in rats.

OBJECTIVE

To investigate whether Lactobacillus rhamnosus 271, Lactobacillus paracasei 87002, Lactobacillus plantarum HEAL 9 and 19, and Bifidobacterium infantis CURE 21 affect the levels of short-chain fatty acids and glutamine in caecum and portal blood of rats fed barley malt.

DESIGN

The experimental diets were fed for 12 days. The daily dose of the probiotic strain was 1×10(9) colony forming units and the intake of fibre 0.82 g/day.

RESULTS

The malt mostly contained insoluble fibre polymers (93%), consisting of glucose and xylose (38-41 g/kg) and some arabinose (21 g/kg). The fibre polysaccharides were quite resistant to fermentation in the rats, regardless of whether or not probiotics were added (25-30% were fermented). Caecal and portal levels of acetic acid decreased in the rats after the addition of L. plantarum HEAL 9 and L. rhamnosus 271, and also the levels of butyric acid. Viable counts of Lactobacillus, Bifidobacterium and Enterobacteriaceae were unaffected, while the caecal composition of Lactobacilli was influenced by the type of strain administrated. Portal levels of glutamine were unchanged, but glycine levels increased with L. plantarum HEAL 9 and 19 and phenylalanine with L. rhamnosus 271.

CONCLUSIONS

Although the probiotic strains survived and reached the caecum, except B. infantis CURE 21, there were no effects on viable counts or in the fermentation of different fibre components, but the formation of some bacterial metabolites decreased. This may be due to the high proportion of insoluble fibres in the malt.

Effects of soluble and insoluble fractions from bilberries, black currants, and raspberries on short-chain fatty acid formation, anthocyanin excretion, and cholesterol in rats

Dietary fiber and flavonoids, important components in berries, are suggested to improve metabolic health. This study investigates whether soluble and insoluble fractions isolated from bilberry, black currant, and raspberry affect the formation of short-chain fatty acids (SCFAs), uptake and excretion of flavonoids, and levels of cholesterol differently. Cecal SCFA pools were higher in rats fed the soluble than the insoluble fractions (525 vs 166 μmol, P < 0.001), whereas higher concentrations of butyric acid were found in the distal colon and serum of rats fed the insoluble fractions (5 vs 3 μmol/g and 58 vs 29 μmol/L, respectively, P < 0.001). The soluble bilberry fraction gave lower amounts of liver cholesterol (56 mg) than the other berry fractions (87 ± 5 mg), formed the highest amount of SCFAs (746 vs 266 ± 21 μmol), and contributed the highest intake of anthocyanins. Cyanidin-3-glucoside monoglucuronide was detected in the urine of all groups, whereas anthocyanins were found only in groups fed soluble black currant and raspberry.

High-fat diet reduces the formation of butyrate, but increases succinate, inflammation, liver fat and cholesterol in rats, while dietary fibre counteracts these effects

INTRODUCTION

Obesity is linked to type 2 diabetes and risk factors associated to the metabolic syndrome. Consumption of dietary fibres has been shown to have positive metabolic health effects, such as by increasing satiety, lowering blood glucose and cholesterol levels. These effects may be associated with short-chain fatty acids (SCFAs), particularly propionic and butyric acids, formed by microbial degradation of dietary fibres in colon, and by their capacity to reduce low-grade inflammation.

OBJECTIVE

To investigate whether dietary fibres, giving rise to different SCFAs, would affect metabolic risk markers in low-fat and high-fat diets using a model with conventional rats for 2, 4 and 6 weeks.

MATERIAL AND METHODS

Conventional rats were administered low-fat or high-fat diets, for 2, 4 or 6 weeks, supplemented with fermentable dietary fibres, giving rise to different SCFA patterns (pectin - acetic acid; guar gum - propionic acid; or a mixture - butyric acid). At the end of each experimental period, liver fat, cholesterol and triglycerides, serum and caecal SCFAs, plasma cholesterol, and inflammatory cytokines were analysed. The caecal microbiota was analysed after 6 weeks.

RESULTS AND DISCUSSION

Fermentable dietary fibre decreased weight gain, liver fat, cholesterol and triglyceride content, and changed the formation of SCFAs. The high-fat diet primarily reduced formation of SCFAs but, after a longer experimental period, the formation of propionic and acetic acids recovered. The concentration of succinic acid in the rats increased in high-fat diets with time, indicating harmful effect of high-fat consumption. The dietary fibre partly counteracted these harmful effects and reduced inflammation. Furthermore, the number of Bacteroides was higher with guar gum, while noticeably that of Akkermansia was highest with the fibre-free diet.

Formation of short-chain Fatty acids, excretion of anthocyanins, and microbial diversity in rats fed blackcurrants, blackberries, and raspberries

Introduction. Berries contain high amounts of dietary fibre and flavonoids and have been associated with improved metabolic health. The mechanisms are not clear but the formation of SCFAs, especially propionic and butyric acids, could be important. The potent antioxidant and antimicrobial properties of flavonoids could also be a factor, but little is known about their fate in the gastrointestinal tract. Aim. To compare how blackcurrants, blackberries, raspberries, and Lactobacillus plantarum HEAL19 affect formation of SCFAs, inflammatory status, caecal microbial diversity, and flavonoids. Results and Conclusions. Degradation of the dietary fibre, formation of SCFAs including propionic and butyric acids, the weight of the caecal content and tissue, and the faecal wet and dry weight were all higher in rats fed blackcurrants rather than blackberries or raspberries. However, the microbial diversity of the gut microbiota was higher in rats fed raspberries. The high content of soluble fibre in blackcurrants and the high proportion of mannose-containing polymers might explain these effects. Anthocyanins could only be detected in urine of rats fed blackcurrants, and the excretion was lower with HEAL19. No anthocyanins or anthocyanidins were detected in caecal content or blood. This may indicate uptake in the stomach or small intestine.

Propionic and butyric acids, formed in the caecum of rats fed highly fermentable dietary fibre, are reflected in portal and aortic serum

SCFA are important end products formed during colonic fermentation of dietary fibre (DF). It has been suggested that propionic and butyric acids affect metabolic parameters, low-grade systemic inflammation, insulin resistance and obesity. The aim of the present study was to investigate whether the various SCFA profiles observed after fermentation in the caecum of rats fed pectin, guar gum and fructo-oligosaccharides (FOS) were also represented in hepatic portal and aortic serum. The SCFA in serum were extracted using hollow fibre-supported liquid membrane extraction before GLC analysis. The concentrations of acetic, propionic and butyric acids in caecal content correlated well with those in portal serum (P< 0·001) for all the three diets. A weaker correlation was found for propionic and butyric acids between the caecal content and aortic serum (P< 0·05). Butyric acid concentration in caecal content was also reflected in the aortic serum (P= 0·019) of rats fed FOS. FOS gave rather low amounts of the SCFA, especially butyric acid, but caecal tissue weight was higher with FOS than with the other two diets. This may be explained by rapid fermentation and quick utilisation/absorption of the SCFA. The present study also showed that propionic acid was metabolised/utilised to a higher extent than butyric acid by colonocytes before reaching the liver. We conclude that the formation of propionic and butyric acids in the caecum is reflected by increased concentrations in the aortic blood. This approach may therefore simplify the evaluation and study of SCFA from DF in human subjects.

Malt in combination with Lactobacillus rhamnosus increases concentrations of butyric acid in the distal colon and serum in rats compared with other barley products but decreases viable counts of cecal bifidobacteria

Several substances, including glutamine and propionic acid but in particular butyric acid, have been proposed to be important for colonic health. β-Glucans lead to the formation of comparatively high amounts of butyric acid, and germinated barley foodstuff obtained from brewer's spent grain (BSG), containing high amounts of β-glucans and glutamine, has been reported to reduce the inflammatory response in the colon of patients with ulcerative colitis. The present study examines how 3 barley products, whole grain barley, malt, and BSG, affect SCFA in the hindgut and serum of rats and whether the addition of Lactobacillus rhamnosus 271 to each of these diets would have further effects. Amino acids in plasma and the cecal composition of the microbiota were also analyzed. The butyric acid concentration in the distal colon and serum was higher in the malt groups than in the other groups as was the serum concentration of propionic acid. The concentrations of propionic and butyric acids were higher in the cecum and serum of rats given L. rhamnosus than in those not given this strain. The proportion of plasma glutamine and the cecal number of bifidobacteria were lower in the malt groups than in the other groups. L. rhamnosus decreased the number of cecal bifidobacteria, whereas plasma glutamine was unaffected. We conclude that malt together with L. rhamnosus 271 had greater effects on propionic and butyric acid concentrations in rats than the other barley products. This is interesting when developing food with effects on colonic health.

Structure and in vitro digestibility of normal corn starch: effect of acid treatment, autoclaving, and beta-amylolysis

The goal of this study was to explore a new strategy to reduce the digestibility of normal corn starch (NCS). NCS was treated using 1.0% hydrogen chloride at 55 degrees C. After neutralization and desalting, starches were adjusted to 35% moisture content and subjected to autoclaving. Thereafter, starches were subjected to beta-amylolysis. At different stages, starches were characterized for chain length distribution, ordered structure including the crystalline pattern, and in vitro digestibility. The results showed that acid treatment reduced amylose molecular weight and increased the thermal resistance of A-type crystallites. V-type crystallites promoted by autoclaving were increased by acid treatment, suggesting the beneficial effect of reduced amylose molecular weight on crystallization. beta-Amylolysis had minor impact on the crystalline pattern; however, it significantly reduced the in vitro digestibility of starch by enriching linear chains. At higher levels of acid treatment, the effect of beta-amylolysis was more pronounced.

Blueberry husks, rye bran and multi-strain probiotics affect the severity of colitis induced by dextran sulphate sodium

OBJECTIVE

The enteric microbiota is a pivotal factor in the development of intestinal inflammation in humans but probiotics, dietary fibres and phytochemicals can have anti-inflammatory effects. The aim of this study was to evaluate the therapeutic effect of multi-strain probiotics and two conceivable prebiotics in an experimental colitis model.

MATERIAL AND METHODS

Sprague-Dawley rats were fed a fibre-free diet alone or in combination with Lactobacillus crispatus DSM 16743, L. gasseri DSM 16737 and Bifidobacterium infantis DSM 15158 and/or rye bran and blueberry husks. Colitis was induced by 5% dextran sulphate sodium (DSS) given by oro-gastric tube. Colitis severity, inflammatory markers, gut-load of lactobacilli and Enterobacteriaceae, bacterial translocation and formation of carboxylic acids (CAs) were analysed.

RESULTS

The disease activity index (DAI) was lower in all treatment groups. Viable counts of Enterobacteriaceae were reduced and correlated positively with colitis severity, while DAI was negatively correlated with several CAs, e.g. butyric acid. The addition of probiotics to blueberry husks lowered the level of caecal acetic acid and increased that of propionic acid, while rye bran in combination with probiotics increased caecal CA levels and decreased distal colonic levels. Blueberry husks with probiotics reduced the incidence of bacterial translocation to the liver, colonic levels of myeloperoxidase, malondialdehyde and serum interleukin-12. Acetic and butyric acids in colonic content correlated negatively to malondialdehyde.

CONCLUSIONS

A combination of probiotics and blueberry husks or rye bran enhanced the anti-inflammatory effects compared with probiotics or dietary fibres alone. These combinations can be used as a preventive or therapeutic approach to dietary amelioration of intestinal inflammation.

Effects of autoclaving and pullulanase debranching on the resistant starch yield of normal maize starch

In this study, resistant starch (RS), type 3, was prepared by the autoclaving and debranching of normal maize starch isolated from a selected ZP genotype. The objectives of this study were to optimize both starch autoclaving and debranching with pullulanase (PromozymeBrewQ) for the production of RS. Autoclaving at 120?C (30 min) increased the RS content of all samples, whereas freezing at -20?C did not have an obvious effect on the RS contents. The highest RS yield in the autoclaved starch samples was 7.0 % after three autoclaving-cooling cycles. After pullulanase debranching at 50?C and retrogradation at 4?C, the RS yields ranged from 10.2% to 25.5 % in all samples (depending on the hydrolysis time). Debranched starch samples with a maximum RS yield of 25.5 % were obtained after a debranching time of 24 h. This study showed that starch from the selected ZP maize genotype is suitable for pullulanase treatment and RS preparation but that additional studies with a greater number of different treatments (incubation time/temperature) are necessary to manipulate and promote crystallization and enhance RS formation.

Autoclave and beta-amylolysis lead to reduced in vitro digestibility of starch

In this study, a combination of autoclave and beta-amylolysis was used to modulate the digestibility of normal corn starch (NCS) and wheat starch (WS). The modification procedure comprised three cycles of autoclave at 35% moisture content and 121 degrees C, beta-amylolysis, and one additional cycle of autoclave. Starch materials were sampled at each stage and characterized. The fine structure of starch was determined using high-performance size-exclusion chromatography, the micromorphology of starch dispersion was imaged using cryo-SEM, the crystalline pattern was evaluated using wide-angle X-ray powder diffraction, and the digestibility was measured using Englyst assay. After beta-amylolysis, amylose was enriched (from 25.4 to 33.2% for NCS and from 27.5 to 32.8% for WS) and the branch density was increased (from 5.2 to 7.7% for NCS and from 5.3 to 7.9% for WS). Cryo-SEM images showed that the autoclave treatment led to the formation of a low-swelling, high-density gel network, whereas beta-amylolysis nearly demolished the network structure. The loss of A-type crystalline structure and the formation of B- and V-type structures resulted from autoclave, which suggests the formation of amylose-based ordered structure. Englyst assay indicated that, due to beta-amylolysis, the resistant starch (RS) content was increased to 30 from 11% of native NCS and to 23 from 9% of native WS. In contrast, autoclave showed only minor impact on RS levels. The increase of RS observed in this study is associated with enhanced branch density, which is different from the four types of RS commonly defined.

Blueberry husks and multi-strain probiotics affect colonic fermentation in rats

The aim was to investigate how blueberry husks and/or mixtures of probiotic strains (Lactobacillus crispatus DSM16743, L. gasseri DSM16737 and L. plantarum DSM15313 (LABmix), or Bifidobacterium infantis DSM15159 and DSM15161 (BIFmix)) affect colonic fermentation, caecal counts of lactobacilli, bifidobacteria and Enterobacteriaceae, body weight gain, and blood concentrations of carboxylic acids (CA) and ammonia in rats. Dietary fibres in blueberry husks were fermented to 61 % in colon, and the elevated faecal excretion of fibre and protein contributed to the high faecal bulking capacity (1.3). The caecal pool of CA was higher in rats fed blueberry husks than the fibre-free control (P < 0.05), and the propionic acid proportion was higher in the distal colon than in the control group (P < 0.05). Probiotics lowered the caecal amount of CA when added to blueberry husks (P < 0.001), while the propionic acid proportion was higher with LABmix (P < 0.01) than blueberry husks only. The propionic acid and butyric acid concentrations in blood were higher in rats fed blueberry husks and probiotics than those fed blueberry husks only (P < 0.01), implying that the absorption of these acids was facilitated by the bacteria. The caecal counts of lactobacilli, bifidobacteria and Enterobacteriaceae were lower in rats fed blueberry husks than the control diet (P < 0.05). The body weight gain was partly influenced by the caecal tissue and contents weights, and BIFmix decreased the ammonia concentration in blood (P < 0.05). We conclude that colonic fermentation is differentially affected by dietary fibre and probiotics, which may be of importance when developing foods with certain health effects.

Short-chain fatty acid formation in the hindgut of rats fed oligosaccharides varying in monomeric composition, degree of polymerisation and solubility

The contents of short-chain fatty acids were investigated in rats fed lactitol, lactulose and four fructo-oligosaccharides of different degree of polymerisation and solubility. Fructo-oligosaccharides with a low degree of polymerisation (2–8) generated the highest levels of butyric acid all along the hindgut, whereas fructo-oligosaccharides with a high degree of polymerisation (10–60) generated the highest levels of propionic acid. These specific differences were also generally reflected in the caecal pools and molar proportions of short-chain fatty acids. The lower solubility of the fructo-oligosaccharides was related to a lower degree of caecal fermentation. Lactulose and lactitol yielded high proportions of acetic acid and low proportions of butyric acid. It is concluded that both the degree of polymerisation and the solubility may affect short-chain fatty acid formation, whereas the fructose contentper seseem to be of less importance. This may be of interest when designing foods with specific health effects.

Short-chain fatty acid formation in the hindgut of rats fed native and fermented oat fibre concentrates

The formation of SCFA in rats fed fermented oat fibre concentrates was compared with that of rats fed native oat fibre concentrate. The cultures used were lactic acid bacteria consisting of Lactobacillus bulgaricus and Streptococcus thermophilus (V2), the exopolysaccharide-producing strain Pediococcus damnosus 2.6 (Pd) and L. reuteri (Lr). The materials were incorporated into test diets yielding a concentration of indigestible carbohydrates of 80 g/kg (dry weight). Rats fed the V2-fermented fibre-concentrate diet yielded higher caecal and distal concentrations of acetic acid (P < 0.01) than rats fed the native fibre concentrate. All the fermented fibre concentrates resulted in a higher propionic acid concentration in the distal colon (P < 0.05), while rats fed Pd-fermented fibre concentrate resulted in lower concentration of butyric acid (P < 0.05, P < 0.01) in all parts of the hindgut as compared with rats fed the native fibre concentrates. Butyrate concentrations ranged between 5-11 micromol/g (distal colon) and 6-8 micromol/g (13 d faeces). Higher proportions of acetic acid (P < 0.05; P < 0.01) were observed in the caecum of rats fed the fermented fibre concentrates. Rats fed Pd- and Lr-fermented fibre concentrates produced higher proportions of propionic acid (P < 0.05; P < 0.01) in the caecum. Changes in SCFA formation in the caecum, distal colon and faeces of rats fed the fermented samples compared with the native sample indicate that these microbes probably survive in the hindgut and that modification of the microflora composition with fermented foods is possible. This may be important for the gastrointestinal flora balance in relation to colonic diseases.

Bifidobacterium lactis Bb-12 and Lactobacillus salivarius UCC500 modify carboxylic acid formation in the hindgut of rats given pectin, inulin, and lactitol

The effect of Bifidobacterium lactis (Bb-12) and Lactobacillus salivarius (UCC500) on the formation of carboxylic acids (CAs) was studied in the hindgut of rats fed pectin, inulin of low solubility, and lactitol. When the pectin diet was supplemented with Bb-12, the formation of CAs was larger throughout the colon of rats, due to increased formation of acetic acid (P < 0.01) and, in the distal part of the colon, also because of propionic and butyric acids (P < 0.01). In rats fed pectin and UCC500, there was a shift in the formation of CAs from the cecum to the distal colon. Thus, the cecal pool of CAs in the rats was lower (P < 0.05), whereas the concentration of CAs in the distal part of colon was larger (P < 0.01) than without this strain. Concerning the slowly fermentable inulin, there was a greater formation of CAs in the cecum (P < 0.05) of rats, especially propionic acid, and a lower formation in the distal part of the colon (P < 0.01) when the diets were supplemented with Bb-12, whereas UCC500 had no effect except for a lower proportion of acetic acid in the distal part of the colon (P < 0.001). In rats fed lactitol and Bb-12, the concentration of CAs was lower in the distal part of colon (P < 0.001) than without this strain, whereas the cecal pool of CAs was greater in rats supplemented with UCC500 (P < 0.001). We conclude that the probiotic bacteria affect the amount, the pattern, and the site of release of CAs in the hindgut of rats, but the combination of pre- and probiotics is of great importance for the outcome.

Response of turkey poults to soybean lectin levels typically encountered in commercial diets. 1. Effect on growth and nutrient digestibility

Lectins are known to bind to the intestinal brush border membrane and induce antinutritional effects such as disruption of the brush border membrane (BBM) and reduced nutrient digestibility in laboratory rodents. Because soybean lectin (SBL) is usually present in poult starter diets, 2 similar experiments with starting turkey poults were conducted to investigate the effects of purified SBL on growth performance and nutrient digestibility. Experimental diets were a corn starch-casein based control (lectin-free) semipurified diet (PD), semipurified diets containing 0.024 or 0.048% soybean lectin (PDL, PDH), and a corn-soybean meal diet (SBD). Experimental diets were fed from hatch to 14 d. Antibodies specific for soybean lectin were detected in the serum of poults fed the PDL and PDH diets, implying that the SBL in these diets remained active in the digestive tract. Poults fed the control PD or SBD grew equally well. The 0.024% SBL level in PDL had no significant detrimental effect on any parameters assessed in the 2 experiments. In contrast, the 0.048% SBL level in the PDH gave inconsistent results for feed efficiency (FE) and brush border enzyme levels. For instance, on d 6 in experiment 2, poults fed the PDH had poorer FE (P < 0.05) compared with the control PD treatment, but had similar FE to poults fed the PD in experiment 1. In conclusion, SBL present at levels up to 0.024% of the diet would not cause antinutritional effect in turkey poults up to 2 wk of age.

Influences of dietary adaptation and source of resistant starch on short-chain fatty acids in the hindgut of rats

The effect of adaptation time on the concentration and pattern of short-chain fatty acids (SCFA) formed in the hindgut of rats given resistant starch (RS) in the form of raw potato starch (RPS) or high-amylose maize starch (HAS) was evaluated. Each starchy material was tested in diets containing 100 g indigestible carbohydrates/kg DM, and fed for 13, 28 and 42 d. At the end of each period, the content of SCFA was determined in caecum, distal colon and faeces. The caecal concentration of total and individual SCFA increased for both diets with increasing adaptation time. The concentration of butyric acid was higher in the group fed RPS than in that fed HAS at all adaptation times. The caecal proportion of butyric acid was low both in rats fed RPS and HAS (6 and 4 %, respectively) following 13 d of adaptation. However, after 28 d of adaptation, the proportion of butyric acid had increased to 19 % in rats given RPS. A longer adaptation period (42 d) did not increase the proportion of butyric acid further. With HAS, there was also a significant (P<0.01) increase in the proportion of butyric acid with longer adaptation time. However, the increase was much slower and the proportion of butyric acid reached 6 and 8 % after 28 and 42 d respectively. It is concluded that the pattern of SCFA formed from RS in rats is dependent on adaptation time. It cannot be excluded that the different patterns of SCFA reported in the literature for RS may be due to the time of adaptation.

Heat moisture treatment of high amylose cornstarch increases its resistant starch content but not its physiologic effects in rats

To examine whether the physiologic effects of high amylose cornstarch (HACS) are affected by gelatinization or heat moisture treatment, male rats were fed for 21 d a fiber-free purified diet containing 40 g/100 g gelatinized normal cornstarch (G-CS), HACS, gelatinized high amylose cornstarch (G-HACS) or heat moisture-treated HACS (HMCS). Dietary fiber (DF) content in G-HACS was 87% lower than that in HACS. The apparent starch and protein digestibilities were higher in the G-HACS group than in the HACS group. Fecal wet weight and fecal bile acid excretion were lower in the G-HACS group than in the HACS group. The cecal tissue weight, cecal surface area, cecal content weight and cecal pH were lower in the G-HACS group than in the HACS group. The cecal n-butyric acid and succinic acid concentrations were higher and lower, respectively, in the G-HACS group than in the HACS group. The plasma cholesterol and triacylglycerol concentrations did not differ between the G-HACS group and the HACS group. On the other hand, the DF content in HMCS was 330% higher than that in HACS, but the HMCS and HACS groups generally did not differ except in cecal surface area. Dietary starch did not affect fecal moisture, fecal neutral sterol (cholesterol + coprostanol) excretion, liver cholesterol level, total short-chain fatty acid (SCFA) concentration or apparent Ca, Fe, Mg and Zn absorptions. These results show that the heat moisture treatment of HACS for the most part does not alter its physiologic effects despite the greater DF content.

Content of short-chain fatty acids in the hindgut of rats fed processed bean (Phaseolus vulgaris) flours varying in distribution and content of indigestible carbohydrates

Red kidney beans (Phaseolus vulgaris) processed to differ in distribution and content of indigestible carbohydrates were used to study hindgut fermentability and production of short-chain fatty acids (SCFA). Bean flours with low or high content of resistant starch (RS), mainly raw and physically-inaccessible starch, were obtained by milling the beans before or after boiling. Flours containing retrograded starch and with a high or low content of oligosaccharides were prepared by autoclaving followed by freeze-drying with or without the boiling water. Six diets were prepared from these flours yielding a total concentration of indigestible carbohydrates of 90 or 120 g/kg (dry weight basis). The total fermentability of the indigestible carbohydrates was high with all diets (80-87 %). Raw and physically-inaccessible starch was more readily fermented than retrograded starch (97-99 % v. 86-95 %; ). Non-starch glucans were fermented to a lesser extent than RS, but the fermentability was higher in the case of autoclaved (50-54 %) than boiled beans (37-41 %). The distribution between acetic, propionic and butyric acid in the caecum was similar for all diets, with a comparatively high percentage of butyric acid (approximately 18). However, with diets containing the high amounts of RS, the butyric acid concentration was significantly higher in the distal colon than in the proximal colon ( and for the high- and low-level diets respectively), whereas it remained constant, or decreased along the colon in the case of the other diets. Furthermore, the two diets richest in RS also promoted the highest percentages of butyric acid in the distal colon (24 and 17 v. 12 and 12-16 for the high- and low-level diets respectively).