Martine Champ

Carbohydrate fractions of legumes: uses in human nutrition and potential for health

Starch and fibre can be extracted, using wet or dry processes, from a variety of grain legumes and used as ingredients for food. alpha-Galactosides can be isolated during wet processes from the soluble extract. Starch isolates or concentrates are mostly produced from peas, whereas dietary fibre fractions from peas and soyabean are commercially available. The physico-chemical characteristics of fibre fractions very much depend on their origin, outer fibres being very cellulosic whereas inner fibres contain a majority of pectic substances. Inner fibres are often used as texturing agents whereas outer fibres find their main uses in bakery and extruded products, where they can be introduced to increase the fibre content of the food. Most investigations on impacts on health have been performed on soyabean fibres. When positive observations were made on lipaemia, glucose tolerance or faecal excretion, they were unfortunately often obtained after non-realistic daily doses of fibres. Legume starches contain a higher amount of amylose than most cereal or tuber starches. This confers these starches a lower bioavailability than that of most starches, when raw or retrograded. Their low glycaemic index can be considered as beneficial for health and especially for the prevention of diseases related to insulin resistance. When partly retrograded, these starches can provide significant amount of butyrate to the colonic epithelium and may help in colon cancer prevention. alpha-Galactosides are usually considered as responsible for flatus but their apparent prebiotic effects may be an opportunity to valorize these oligosaccharides.

Non-nutrient bioactive substances of pulses.

Pulses supply many bioactive substances found in minor amounts in food, but which may have significant metabolic and/or physiological effects. These compounds have long been classified as antinutritional factors, but many studies have reconsidered their impact on health. Some could play a role in the prevention of the major diseases of affluent societies. As these compounds can be beneficial or adverse, depending on conditions, an assessment of their various physiological effects is necessary to determine whether they should be preserved or eliminated in each main nutritional situation.

Digestion of raw banana starch in the small intestine of healthy humans: structural features of resistant starch

The digestion of freeze-dried green banana flour in the upper gut was studied by an intubation technique in six healthy subjects over a 14 h period. Of alpha-glucans ingested, 83.7% reached the terminal ileum but were almost totally fermented in the colon. Structural study of the resistant fraction showed that a small part of the alpha-glucans which escaped digestion in the small intestine was composed of oligosaccharides from starch hydrolysis, whereas the rest was insoluble starch in granule form with physical characteristics similar to those of raw banana starch. Passage through the small intestine altered granule structure by increasing susceptibility to further alpha-amylase hydrolysis. Compared with resistant starch values in vivo, those obtained with the in vitro methods tested were inadequate to estimate the whole fraction of starch reaching the terminal ileum.

Restoration of the integrity of rat caeco-colonic mucosa by resistant starch, but not by fructo-oligosaccharides, in dextran sulfate sodium-induced experimental colitis.

Butyrate is recognised as efficient in healing colonic inflammation, but cannot be used as a long-term treatment. Dietary fibre that produces a high-butyrate level when fermented represents a promising alternative. We hypothesised that different types of dietary fibre do not have the same efficiency of healing and that this could be correlated to their fermentation characteristics. We compared short-chain fructo-oligosaccharides (FOS) and type 3 resistant starch (RS) in a previously described dextran sulfate sodium (DSS)-induced colitis model. Seventy-two Sprague-Dawley rats received water (control rats) or DSS (50 g DSS/l for 7 d then 30 g DSS/l for 7 (day 7) or 14 (day 14) d). The rats were fed a basal diet (BD), or a FOS or RS diet creating six groups: BD-control, BD-DSS, FOS-control, FOS-DSS, RS-control and RS-DSS. Caeco-colonic inflammatory injuries were assessed macroscopically and histologically. Short-chain fatty acids (SCFA) were quantified in caeco-colon, portal vein and abdominal aorta. At days 7 and 14, caecal and distal macroscopic and histological observations were improved in RS-DSS compared with BD-DSS and also with FOS-DSS rats. Caeco-colonic SCFA were reduced in FOS-DSS and RS-DSS groups compared with healthy controls. The amount of butyrate was higher in the caecum of the RS-DSS rats than in the BD-DSS and FOS-DSS rats, whereas distal butyrate was higher in FOS-DSS rats. Partially explained by higher luminal levels of SCFA, especially butyrate, the healing effect of RS confirms the involvement of some types of dietary fibre in inflammatory bowel disease. Moreover, the ineffectiveness of FOS underlines the importance of the type of dietary substrate.

Effects of long-term low-glycaemic index starchy food on plasma glucose and lipid concentrations and adipose tissue cellularity in normal and diabetic rats

The present study aimed to assess the metabolic consequences of the chronic ingestion of two starches giving different postprandial glycaemic responses in normal and diabetic rats. The two starches chosen were mung-bean (Phaseolus aureus) starch (97% pure starch) and wheat starch presented as ground French toast. First, we studied the characteristics of these two starches. In vitro the alpha-amylase (EC 3.2.1.1) digestibilities of these starches were 40 (SE 3) and 62 (SE 4)% respectively at 30 min, whereas the contents of resistant starch were 77 (SE 4) and 22 (SE 4) g/kg respectively. In vivo the mung-bean starch produced lower postprandial glycaemic responses than the wheat starch (areas under the curve were: 91 (SE 28) and 208 (SE 33) mmol.min/l, P < 0.05) in normal rats (n 8). We then submitted twenty-eight normal and twenty-eight diabetic (neonatal streptozotocin on second day of birth) male Sprague-Dawley rats (6 weeks old) to a diet containing 570 g starch/kg as either mung-bean starch or wheat starch (n 14 rats/group). After 5 weeks on the diets food intakes and body weights were identical in each group. Liver and kidney weights were comparable when expressed as relative weight. The mung-bean-starch diet slightly decreased epididymal fat-pad weight (P < 0.14, ANOVA) and led to a marked decrease in adipocyte volume (P < 0.05). Plasma triacylglycerol and phospholipid concentrations were lower after the mung-bean-starch diet than after the wheat-starch diet in both normal and diabetic rats, whereas free fatty acid concentrations were lower only in normal rats. Similarly, non-fasting plasma glucose concentrations decreased (P < 0.05) in normal rats fed on mung-bean starch but not in diabetic ones (P < 0.14). Insulin levels tended to be lower, but not significantly, after mung-bean-starch feeding than after wheat starch. We conclude that the replacement of 570 g wheat starch/kg diet with mung-bean starch for 5 weeks resulted in (1) lowered non-fasting plasma glucose and free fatty acid levels in normal but not in diabetic rats, (2) a reduction in plasma triacylglycerol concentration and adipocyte volume in both normal and diabetic rats. Thus, the type of starch mixed into the diet may have important metabolic consequences in normal and diabetic rats.

Production of short-chain fatty acids from resistant starch in a pig model

This study was performed to estimate the pool of SCFA produced in the digestive tract of growing pigs after the consumption of diets containing dif-ferent sources of resistant starch (RS) (15 g per meal) (potato starch (PoS), high amylose maize starch (HS) and retrograded extruded HS (RHS)). SCFA production in vitro was respectively 19, 23 and 21 mmol g−1 of fermented PoS, HS and RHS. The highest butyric acid production was observed with PoS. Fifty six, 36 and 19% respectively of ingested PoS, HS and RHS escaped digestion in the small intestine, whereas residual starch was completely fermented in the large bowel. Luminal total SCFA in the caeco-colon 7 h after the experimental meal were respectively 33, 78 and 105 mmol for PoS, HS and RHS, with PoS providing the highest production of butyric acid. Theoretical in vivo SCFA production, calculated on the basis of results for in vitro fermentation and ileal digestibility, differed from in vivo results for PoS (+65%) and HS (-13%), but not for RHS. This study reveals different rates of disappearance of RS both in vitro and in vivo.

In vitro method for quantification of the fermentation of starch by human faecal bacteria

The major actions of undigested carbohydrates, such as non-starch polysaccharides and resistant starch, on the physiology of man are related to colonic fermentation. It is very difficult to study fermentation in vivo. In vitro models are often used but these models differ in almost every aspect even when only the simplest batch cultures of human faeces are considered. Factors such as composition of the medium, buffering capacity, inoculum concentration, and fermentation time vary considerably making direct comparison of the results from different studies impossible. The authors have devised a standard in vitro fermentation method for resistant starch and tested it in eight laboratories with a total of 40 individual faecal inocula. This simple method was well received and taking biological variation into account yielded comparable results for 24 h short chain fatty acid production and residual starch in all but one laboratory.

The definition of dietary fiber - discussions at the Ninth Vahouny Fiber Symposium: building scientific agreement

A definition for dietary fiber was adopted in June 2009 by the Codex Alimentarius Commission based on the recommendation for endorsement of the Codex Committee on Nutrition and Foods for Special Dietary Uses (CCNFSDU) in November 2008. The definition listed three categories of carbohydrate polymers that are not hydrolyzed by the endogenous enzymes in the small intestine of humans. However, the definition left the inclusion of carbohydrates with degrees of polymerization (DP) in the range of 3 and 9 to the discretion of national authorities and left the ‘physiological effect(s) of benefit to health’ as undefined. The ILSI Europe and ILSI North Americas committees on dietary carbohydrates organized a forum at the Ninth Vahouny Fiber Symposium in 2010 to discuss these implementation issues with the objective of building scientific consensus on how to resolve them. The results of this session are encouraging and indicated that the scientific community agrees on maintaining a worldwide consensus regarding the inclusion of non-digestible carbohydrates with ≥DP3 as dietary fiber and on a core, non-exhaustive list of beneficial physiological effects that dietary fibers have. These results are consistent with previous worldwide agreements.

Supplementation With Galactooligosaccharides and Inulin Increases Bacterial Translocation in Artificially Reared Newborn Rats

Supplementation of formulas with prebiotics enhances the growth of lactate producing bacteria, and fecal lactate, and acetate levels in infants. High concentrations of organic acids in intestinal lumen have, however, been shown to impair the intestinal barrier function. To determine whether stimulating the colonic microbiotal metabolism with prebiotics would impair the neonatal intestinal barrier function, artificially reared rats were fed milk formula with or without a mixture of galactooligosaccharides/inulin (GOS/Inulin, 88/12; 5.6 g/L) from the 7th d of life (d7) until weaning (d20). At d18, GOS/inulin supplementation had increased the concentrations of acetate and lactate in colonic lumen. Although neither ileum-associated microbiota nor colonic permeability (assessed in Ussing chambers), nor the expression of tight junction claudin-2 and claudin-3 mRNA were altered, GOS/inulin supplementation was associated with increased bacterial translocation (BT) toward spleen. None of these effects persisted at d40. We conclude that GOS/inulin supplementation may increase BT in an immature gut. The balance between the potential infectious risk of BT vs. its putative beneficial effect on the maturation of neonatal immune system clearly warrants further study.

Structural discrepancies in resistant starch obtained in vivo in humans and in vitro

Abstract In-vivo resistant starch (RS) was collected at the end of the human ileum by an intubation technique after ingestion of two partly resistant starches (retrograded (R) or complexed (C) high amylose maize starch). In-vitro RS fractions were prepared enzymatically from R and C according to three methods of RS determination in food. Physicochemical characteristics of these two different fractions were compared. The ileal RS appeared to consist of three fractions: a first population of high molecular weight α-glucans attributed to amorphous potentially digestible material, a second made of B-type retrograded amylose crystallites and a third containing oligosaccharides. The in-vitro RS fractions showed no high molecular weight molecules, due to more extensive hydrolysis in the in-vitro procedure. Therefore, none of the in-vitro RS determinations allowed the isolation of a fraction qualitatively similar to in-vivo RS.