Importance of Location of Digestion and Colonic Fermentation of Starch Related to Its Quality

For decades, quality of starch‐based foods has been associated with the in vivo measured glycemic index or the in vitro digestion rate‐based categories of rapidly digestible, slowly digestible, and resistant starch (RS). Glycemic index has been related to health‐based endpoints mostly through correlative or observational studies, with mechanisms proposed but not well established. Here, we bring forth the concept of locational delivery of glucose from dietary starches to the distal small intestine to elicit an ileal brake effect, as well as short‐chain fatty acid production from RS fermentation to cause a colonic brake. Both effects slow gastric emptying and, in turn, extend nutrient (i.e., energy) delivery to the body and may decrease appetite and promote weight management. Slowly digestible starches are currently a popular topic of research, although where they are digested and the released glucose is delivered in the small intestine is not known. A proposal is to further study and establish this mechanism of appetite and food intake regulation so that starch‐based ingredients and foods can be developed that promote both the ileal and colonic brake mechanisms.     

In Vitro Digestion of RS4‐Type Resistant Wheat and Potato Starches,and Fermentation of Indigestible Fractions

RS4‐type resistant wheat starch (RWS) and resistant potato starch (RPS) were subjected successively to in vitro digestion with pepsin and pancreatin‐bile, and the indigestible residues (82.1% db and 74.1% db, respectively) were recovered and subsequently fermented by in vitro techniques using fresh human fecal microbiota as inoculum. Scanning electron microscopy of the indigestible residues showed surface erosion on the residual granules. Total gas production during the in vitro fermentation increased almost linearly over time with the two resistant starches exhibiting similar gas production rates, as well as a similar rate of production of total short‐chain fatty acids (SCFA). The indigestible fractions from both starches produced acetate as the major SCFA and relatively higher levels of butyrate than propionate, but wheat starch tended to produce more butyrate over time than potato starch. Fractional molar ratios of acetate, propionate, and butyrate from the RWS and RPS were 0.586:0.186:0.228 and 0.577:0.200:0.223, respectively. The calculated caloric contributions of the RWS and RPS are ≈33% lower than for unmodified starch and are comparable to those reported in the literature for RS2 and RS3 high‐amylose maize starches.     

REVIEW: Cereal Carbohydrates and Colon Health

Providing balanced energy and nutrients for microbiota growth is essential for the maintenance of the colon ecosystem, and dietary fiber (DF) fermentation, particularly butyrogenic fermentation, augments colon health. Cereal DF, which are the complex carbohydrates of cereal grains that escape small intestine digestion and function either as substrate for colonic fermentation or as bulking material, are a dietary measure to mitigate the occurrence of certain colonic diseases, and perhaps to some degree act as therapeutic agents. In developed Western countries, as well as in many developing countries, colon cancer is one of the major causes for premature death and disability, and inflammatory bowel disease and other colonic disorders have become serious health issues. The function of DF in colon health is mediated through its physicochemical properties (e.g., water‐holding for laxative effect) or effect on colon microbiota (e.g., leading to immune regulation), as well as through colonic fermentation products, principally the short chain fatty acids (SCFA) of acetate, propionate, and butyrate. Due to the chemical diversity and complexity of DF and because not all DF materials function equally, new developments in DF fermentation behavior (pattern and end product profile) will be reviewed from a structure‐function viewpoint. The effect of cereal DF, mainly nonstarch cereal polysaccharides and resistant starch on colonic microbiota, fermentation products of SCFA, microbiota modulation, as well as on colon health will be summarized.     

Physicochemical and Digestion Characteristics of Starch and Fiber‐Rich Subfractions from Four Pulse Bagasses

The aim of this study was to characterize the physicochemical, functional, and digestion properties of bagasses derived from broad beans, chickpeas, lentils, and white beans, and to isolate the starch and a fiber‐rich fraction that can be used as a food ingredient. The bagasses showed different chemical compositions that were related to their botanical origin. The further processing that involved mechanical separation of starch yielded up to 69.65% with ≥80.12% recovery and high purity (≥94.42%), and a fiber‐rich fraction (total dietary fiber content ≥72.75%) in which the majority was insoluble fiber. The starch digestion fractions of the isolated lentil starch showed the highest amount of slowly digestible starch (30.76%), whereas the white bean contained the highest resistant starch content (15.65%). All starches showed predicted glycemic indexes ≤ 66.90, which classify them as medium glycemic foods. In vitro protein digestion was higher for the bagasse fraction (up to 89.78%), followed by the fiber‐rich fraction (84.36%). This research demonstrates that it is possible to revalorize the use of pulses bagasse, which could contribute to enhance the technological and economic output of the protein isolation process, rendering two potentially functional fractions.     

In vitro starch digestibility and predicted glycemic index of corn tortilla, black beans, and tortilla-bean mixture: effect of cold storage

People in the rural areas of Mexico consume corn tortillas and beans as basic components of their diet. However, little is known about the nutritionally relevant features of starch present in such combined meals. The objective of the present study was to evaluate the in vitro bioavailability of starch in tortilla-bean mixtures stored at 4 degrees C for different times, as compared to that of corn tortilla and boiled black beans kept separately under the same conditions. Available starch (AS), resistant starch (RS), and retrograded resistant starch (RRS) contents were measured. The in vitro starch hydrolysis indices (HI) of freshly cooked and cold-stored samples were evaluated using a chewing/dialysis digestion protocol. HIs were used to predict glycemic indices (pGI) of the samples. AS in tortilla and beans decreased between 3 and 6% after 48-72 h, whereas values in the mixture fell by 3% after 48 h, with no further change by 72 h. Only minor rises in RS contents (1.5-1.6%) were recorded for tortilla and beans after 72 h of storage, and a lower increase (0.4%) was recorded in the mixture. Judging from RRS values, an important proportion of RS is due to starch retrogradation. The HI and pGI were higher in tortilla than in bean and the mixture. Hydrolysis rate values decreased in the stored samples, a pattern that corresponded with RS and RRS changes. The slow digestion features of common beans are largely retained by the legume-tortilla combination. Data support the perceived health beneficial properties of starch in this traditional cereal-legume food.     

Structural stability and prebiotic properties of resistant starch type 3 increase bile acid turnover and lower secondary bile acid formation

Microbial metabolism is essential in maintaining a healthy mucosa in the large bowel, preferentially through butyrate specific mechanisms. This system depends on starch supply. Two structurally different resistant starches type 3 (RS3) have been investigated with respect to their resistance to digestion, fermentability, and their effects on the composition and turnover of bile acids in rats. RSA (a mixture of retrograded maltodextrins and branched high molecular weight polymers), which is more resistant than RSB (a retrograded potato starch), increased the rate of fermentation accompanied by a decrease of pH in cecum, colon, and feces. Because they were bound to RS3, less bile acids were reabsorbed, resulting in a higher turnover through the large bowel. Because of the rise of volume, the bile acid level was unchanged and the formation of secondary bile acids was partly suppressed. The results proved a strong relation between RS3, short chain fatty acid production, and microflora. However, butyrate specific benefits are only achieved by an intake of RS3 that result in good fermentation properties, which depend on the kind of the resistant starch structures.     

Composite Durum Wheat Flour/Plantain Starch White Salted Noodles: Proximal Composition,Starch Digestibility,and Indigestible Fraction Content

In search of a way to improve the nutritional profile of noodles, we prepared them with various mixtures of durum wheat flour and isolated plantain starch, and tested their proximal composition. Cooked noodles were assessed for in vitro starch digestibility, indigestible fraction content, and predicted glycemic index. The protein content declined with the addition of plantain starch. Both total starch (TS) level and the content of starch available for digestible enzymes (AS) decreased as the plantain starch level increased, a pattern that may be related to increased starch lixiviation during cooking of noodles containing plantain starch. There was an inverse pattern for resistant starch (RS). RS content in control (durum wheat flour) noodles was ≈50% lower than in the samples containing plantain starch. The soluble indigestible fraction (SIF) content in all samples was higher than the insoluble counterpart (IIF). The total indigestible fraction varied according to the wheat substitution level. Although the hydrolysis index (HI) and predicted glycemic index (pGI) of plantain starch noodles were moderate and decreased as the plantain starch proportion rose. These composite noodles exhibited higher indices than the control sample, a phenomenon that may also be dependent on the product physical structure. Results indicate that in spite of the increased starch digestion rate, plantain starch noodles are a better source of indigestible carbohydrates than pure wheat starch pasta. This might have dietetic applications.     

Digestion residues of typical and high-beta-glucan oat flours provide substrates for in vitro fermentation

In vitro fermentabilities of the oat flour digestion residues (ODR) from two commercial oat lines with 4.7 and 5.3% beta-glucan and from two high-beta-glucan experimental lines with 7.6 and 8.1% beta-glucan were evaluated and compared with fermentations of lactulose, purified oat beta-glucan (POBG), and purified oat starch (POS). Substrates were fermented by using an in vitro batch fermentation system under anaerobic conditions for 24 h. The progress of the fermentation was studied by following the change in pH of the fermentation medium, production of short-chain fatty acids (SCFA) and gases, and consumption of carbohydrates. The substrate from the flour with the greatest amount of beta-glucan tended to have the greatest pH decline and the greatest total SCFA production. A significant correlation occurred between gas production and SCFA formation (R 2 = 0.89-0.99). Acetate was produced in the greatest amounts by all of the substrates except POBG, by which butyrate was produced in the greatest amount. More propionate and butyrate, but less acetate, were produced from high-beta-glucan ODR. With the given fermentation conditions, >80% of the total carbohydrate was depleted by the bacteria after 24 h. Glucose was the most rapidly consumed carbohydrate among other available monosaccharides in the fermentation medium. Overall, the high-beta-glucan experimental lines provided the best conditions for optimal in vitro gut fermentations.     

In Vitro Starch Digestibility of Tortillas Elaborated by Different Masa Preparation Procedures

Starch digestibility was evaluated in freshly prepared tortillas elaborated from masa obtained from different procedures (laboratory‐made masa, commercial masa, and nixtamalized corn flour) and from laboratory‐made masa with added commercial hydrocolloid, and stored for 24, 48, and 74 hr. Tortillas prepared with commercial masa had the highest available starch (AS) content and the commercial tortillas had the lowest, showing a decrease in AS content when storage time increased. Tortilla of commercial masa showed the lowest resistant starch (RS) content that agrees with the AS measured. However, tortilla of laboratory‐made masa presented the highest AS and RS contents. RS increased with storage time, a pattern that is related to the starch retrogradation phenomenon observed when retrograded resistant starch (RRS) was quantified. Commercial tortillas showed predicted glycemic index (pGI) values of 62–75% using a chewing/dialysis procedure (semi in vitro method). Index values were lower than those determined in vitro. The pGI of tortillas decreased, and the values were different depending on the method used to prepare the masa and tortilla. Commercial tortilla and tortilla of NCF had the lowest pGI. Therefore, the procedure to obtain masa and thereafter obtain tortillas influenced the starch digestibility of the product.     

Effect of green tea catechins on the postprandial glycemic response to starches differing in amylose content

The effect of tea polyphenols (TPLs), specifically tea catechins, on the postprandial glycemic response to cooked starches differing in amylose contents was investigated. The in vivo test using a mouse model showed a moderate reduction of the postprandial glycemic response to co-cooked normal (containing 27.8% amylose) or waxy corn starch with 10% TPLs (dry weight of starch), while an augmented glycemic response with a delayed blood glucose peak was observed when high amylose corn starch (HAC, containing 79.4% amylose) was used as the starch component. Enzyme kinetics results demonstrated that TPLs noncompetitively inhibit the digestion of waxy or normal corn starch, while the digestion rate of HAC starch was increased in the presence of TPLs, which supports the observed postprandial glycemic responses. Further studies using X-ray powder diffraction showed that the diffraction intensity (area under the diffraction curves) of normal and HAC starch was increased by 45% and 74%, respectively, whereas no change was observed for waxy corn starch. Consistently, dynamic laser light scattering studies using a solution of pure amylose showed an increased hydrodynamic radius of amylose molecules from ～54 nm to ～112 nm in the presence of TPLs. These experimental results indicate that there might exist an interaction between TPLs and amylose, which facilitates the association of amylose molecules to form a special nonordered structure that can produce a high and sustained postprandial glycemic response. Thus, a combination of tea polyphenols and specific starches could be used to manipulate postprandial glycemic response for glycemic control and optimal health.     

Differences in Carbohydrate Composition and Digestion In Vitro of Selected Barley Cultivars as Influenced by Pearling and Cooking

Among common cereals, barley is a low glycemic index food. In an attempt to better understand this character, the nutritional properties of glycemic carbohydrates and dietary fiber concentrations of nine cultivars were evaluated. The cultivars were selected based on botanical variations and commercial value to investigate the impact of pearling and cooking on nutritional properties. Each cultivar was pearled into four fractions ranging from hull removal only to hull, bran, germ, and crease removal. The study showed that botanical class and degree of pearling significantly affect the carbohydrate composition and digestion indices of barley. Waxy starch cultivars had less total starch and more rapidly digestible starch (RDS), rapidly available glucose (RAG), and β‐glucan than the other nonwaxy cultivars. Regardless of the barley type, the less pearled kernels had significantly lower total starch and higher total low molecular weight sugars, insoluble, and total fiber. However, β‐glucan content was fairly comparable in the whole grain and pearled fractions. Cooking had a significant effect on nutritional properties of Celebrity and AC Klinck cultivars. The only consistent significant difference between raw and cooked barley was resistant starch (RS), which increased after cooking regardless of cultivar or fraction. The study showed that barley cultivar and carbohydrate composition significantly affected starch digestion with some cultivar fractions holding a promise for the development of low glycemic index foods.     

Effects of chemical modification on in vitro rate and extent of food starch digestion: an attempt to discover a slowly digested starch.

Differences in glycemic and insulinemic responses to dietary starch are directly related to the rate of starch digestion. Chemical modification of starch may allow for the production of a slowly digested starch that could be used for the treatment of certain medical modalities. An in vitro method was utilized to evaluate the effects of chemical modification on the rate and extent of raw and cooked starch digestion. The extent of starch digestion was significantly reduced by dextrinization, etherification, and oxidation. However, the rate of starch digestion was not significantly affected by chemical modification. For most modified starches, as the degree of modification increased, the extent of digestion decreased, suggesting an increase in the amount of resistant starch. The results of this study suggest that chemically modified starch has a metabolizable energy value of <16.7 kJ/g. Chemically modified starch ingredients may serve as a good source of resistant starch in human and animal diets.     

Physiological responses to novel carbohydrates as assessed using canine and avian models

The objective was to quantify in vitro digestion, true metabolizable energy (TME(n)) content, glycemic and insulinemic responses, and gastrointestinal tolerance to fructose (Fruc), maltodextrin (Malt), polydextrose (Poly), pullulan (Pull), resistant starch (RS), sorbitol (Sorb), and xanthan gum (Xan). Limited digestion of RS, Poly, and Xan occurred. Fruc, Malt, and Sorb resulted in the highest (P < 0.05) TME(n) values, Pull was intermediate, and RS and Poly were lowest. Malt had the highest (P < 0.05) area under the curve for glucose and insulin in the glycemic tests. Gastrointestinal tolerance was examined for diets containing carbohydrates at either 100 or 200% of the adequate intake (AI) value for dietary fiber. At 100% and 200% AI, Malt, RS, and Sorb resulted in ideal fecal scores, while Pull and Xan resulted in looser stools and Poly resulted in diarrhea. The carbohydrates studied varied widely in physiological outcomes. Certain carbohydrates could potentially benefit large bowel health.     

Structural Changes of High-Amylose Rice Starch Residues following in Vitro and in Vivo Digestion

High-amylose cereal starch has a great benefit on human health through its resistant starch content. In this paper, starches were isolated from mature grains of high-amylose transgenic rice line (TRS) and its wild-type rice cultivar Te-qing (TQ) and digested in vitro and in vivo. The structural changes of digestive starch residues were characterized using DSC, XRD, (13)C CP/MAS NMR, and ATR-FTIR. TQ starch was very susceptible to digestion; its residues following in vitro and in vivo digestion showed similar structural characteristics with TQ control starch, which suggested that both amorphous and crystalline structures were simultaneously digested. Both amorphous and the long-range order structures were also simultaneously hydrolyzed in TRS starch, but the short-range order (double helix) structure in the external region of TRS starch granule increased with increasing digestion time. The A-type polymorph of TRS C-type starch was hydrolyzed more rapidly than the B-type polymorph. These results suggested that B-type crystallinity and short-range order structure in the external region of starch granule made TRS starch resistant to digestion.     

Influence of genotype and processing on the in vitro rate of starch hydrolysis and resistant starch formation in peas (Pisum sativum L.).

The formation of resistant starch (RS) and the rate of starch hydrolysis were evaluated in vitro in a wild type of green-seeded pea genotype RRRbRb BC3 (33-Am) with 32.7% amylose content and in two mutants RRrbrb BC3 (23-Am) and rrRbRb BC3 (65-Am) with amylose contents of 23.3 and 65.1%, respectively. Pea samples were intact or homogenized and subjected either to autoclaving or to boiling at atmospheric pressure. The amount of RS (total starch basis) varied from 6.2 to 12.9% in the 23-Am products and from 31.2 to 33.4% in the 65-Am products. The RS level of the 33-Am product with a regular amylose content was 11.0%. Both the 23-Am and the 65-Am products were abundant sources of dietary fiber (39 and 34%, dry matter basis, respectively) versus 23% in the regular pea product. The amylose/amylopectin ratio was an important determinant of the rate of starch hydrolysis. The hydrolysis indices (HI) and predicted glycemic indices were lowest in the 65-Am peas (HI range = 42-59) as compared to the 23-Am peas (HI range = 53-84). It is concluded that the pea genotypes covered a wide range in starch availability, which is likely to affect nutritional parameters such as glycemic responses and colonic delivery of starch.     

Influence of storage conditions on the structure, thermal behavior, and formation of enzyme-resistant starch in extruded starches

Starch structures from an extrusion process were stored at different temperatures to allow for molecular rearrangement (retrogradation); their thermal characteristics (DSC) and resistance to amylase digestion were measured and compared. The structure of four native and processed starches containing different amylose/amylopectin compositions (3.5, 30.8, 32, and 80% amylose content, respectively) before and after digestion was studied with small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). Rearrangement of the amylose molecules was observed for each storage condition as measured by the DSC endotherm at around 145 degrees C. The crystalline organization of the starches after processing and storage was qualitatively different to that of the native starches. However, there was no direct correlation between the initial crystallinity and the amount of enzyme-resistant starch (ERS) measured after in vitro digestion, and only in the case of high-amylose starch did the postprocess conditioning used lead to a small increase in the amount of starch remaining after the enzymatic treatment. From the results obtained, it can be concluded that retrograded amylose is not directly correlated with ERS and alternative mechanisms must be responsible for ERS formation.     

Effects of β-amylolysis on the resistant starch formation of debranched corn starches

Retrograded amylose is resistant to digestion by amylolytic enzymes, which is known as resistant starch type III (RS3). In this study we investigated the effect of β-amylase hydrolysis on the formation and physicochemical properties of RS3 from debranched corn starches. Three types of corn starch (Hylon VII, Hylon V, and common corn) were first gelatinized and then hydrolyzed using β-amylase to varying degrees. The resultant hydrolyzed starch was debranched with isoamylase and then exposed to temperature cycling to promote RS formation. A broad endotherm from approximately 45 to 120 °C and a small endotherm above 150 °C were noted for all retrograded starches. All three corn starches had increased RS contents after moderate β-amylolysis, with Hylon V having the highest RS content at 70.7% after 4 h of β-amylolysis. The results suggest that RS3 formation is affected by the starch composition as well as the starch structure and can be increased by moderate β-amylolysis.     

Effects of Milling and Cooking Conditions of Rice on In Vitro Starch Digestibility and Blood Glucose Response

The objective of this study was to investigate the effects of milling and cooking conditions of cooked rice prepared from cultivar Koshihikari on in vitro starch digestibility and in vivo glucose response in humans. In addition, compression and adhesiveness tests were conducted for texture analysis of the cooked rice. Brown rice (BR) and surface‐abraded BR (SABR, ≥99.5% of the original weight) were digested more slowly than white rice (91% of the original weight) when cooked rice grain was used for the in vitro test, but they were digested more rapidly in the initial stage of the reaction when cooked rice ground by a meat grinder was used. The increase in water added for cooking significantly increased the extent of starch digestion with BR and SABR. The changes in blood glucose levels after the ingestion of cooked rice were dependent on the sample type. The cooking conditions dramatically influenced the glucose response after the ingestion of BR. A significant correlation was found between blood glucose levels at 45 min and the extent of starch digestion with ground samples, whereas no relationship was found with cooked rice grain samples for in vitro digestibility.     

Effect of Storage Time on In Vitro Digestibility and Resistant Starch Content of Nixtamal,Masa, and Tortilla

Nixtamal, masa, and tortilla samples were stored for 24–96 hr and their chemical composition, retrogradation, and in vitro starch digestibility features were evaluated. Ash and fat contents in the three products were smaller than in the original corn sample, but protein levels were higher, all in accordance with previous studies. In general, a minor decrease in available starch (AS) content was observed with storage time. Masa showed the greatest AS values, followed by tortilla and nixtamal. Tortilla presented slightly higher retrograded resistant starch (RS3) values (1.1–1.8%, dmb) than masa (0.7–0.9%) and nixtamal (0.7–0.8%) and only minor increases were observed after 24 hr of storage, suggesting that retrogradation phenomenon in these samples takes place very rapidly and is more pronounced in the final product (tortilla). The development of RS3 explains the observed decrease in AS. Higher total resistant starch values were found in all samples at a range of 2.1–2.6% for nixtamal and masa, and a range of 3.1–3.9% in tortilla. This indicates that, apart from retrograded resistant starch, some ungelatinized fractions appear to contibute to the indigestible content of these products. The α‐amylolysis rate of the three materials decreased with storage. Tortilla showed the greatest hydrolysis indices. Differential scanning calorimetry (DSC) analysis showed that the nixtamal, masa, and tortilla did not show differences in amylopectin crystal melting temperature with storage time, but tortilla exhibited higher enthalpy values after 72 hr of storage, in accordance with the greater total RS contents recorded after prolonged storage.     

Starch characteristics and their influences on in vitro and pig prececal starch digestion

The main objective of this research was to study the characteristics of starch granules and their influences on in vitro and pig prececal starch digestion of corn, dehulled barley, wheat, and potato. Scanning electron microscopy was used to study the starch endosperm structure in the parent material as well as in vitro starch digestion. The results showed that corn starch granules were polyhedral, with a diameter ranging from 2 to 10 μm, whereas those of dehulled barley and wheat were spherical, with a diameter ranging from 5 to 20 μm. Potato had the largest starch granules among starch sources reported herein, with oval spheres of 10-50 μm in diameter. In vitro starch hydrolysis showed that starch granules of corn degraded faster than the starch of dehulled barley and wheat, with the potato starch being degraded the slowest. The in vivo digestibility trial using ileal-cannulated pigs confirmed the starch degradation of grains. The in vitro (x, %) and in vivo (y, %) digestibility were highly correlated [y = 6.5304x - 538.48 (R(2) = 0.9924)]. On the basis of the results, in vitro starch hydrolysis might be useful in predicting in vivo prececal starch digestibility. The digestion kinetic characteristics of different starch sources might be employed to evaluate the starch digestive rate at the pig ileum.