Unexpected High Digestion Rate of Cooked Starch by the Ct-Maltase-Glucoamylase Small Intestine Mucosal α-Glucosidase Subunit

For starch digestion to glucose, two luminal α-amylases and four gut mucosal α-glucosidase subunits are employed. The aim of this research was to investigate, for the first time, direct digestion capability of individual mucosal α-glucosidases on cooked (gelatinized) starch. Gelatinized normal maize starch was digested with N- and C-terminal subunits of recombinant mammalian maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) of varying amounts and digestion periods. Without the aid of α-amylase, Ct-MGAM demonstrated an unexpected rapid and high digestion degree near 80%, while other subunits showed 20 to 30% digestion. These findings suggest that Ct-MGAM assists α-amylase in digesting starch molecules and potentially may compensate for developmental or pathological amylase deficiencies

Formation, Analysis, Structure and Properties of Type-III Enzyme Resistant Starch

During the retrogradation of starch a fraction becomes resistant to amylolytic enzymes. This undigestible fraction is described as enzyme resistant starch (RS) type III. RS type III is composed of short linear segments of alpha-(1-4)-glucans arranged in an A or B-type crystalline structure and is thermally very stable. Different factors have an impact on the formation (crystallisation) of these structures. Apart from the starch type, which defines the amylose/amylopectin ratio, polymer chain length and lipid content, process conditions following starch gelatinisation and the presence of other components, have an influence on the amount and on the quality of RS formed. Several in vitro and in vivo procedures to quantify RS have been used. However, RS levels may be affected by the analytical procedure. (C) 1995 Academic Press Limitedstatus: publishe

Enzyme-Resistant Starch .2. Influence of Amylose Chain-Length on Resistant Starch Formation

Potato starch amylose was hydrolyzed to varying degrees by incubation with barley beta-amylase for different periods. Determination of reducing sugars and gel-permeation chromatography showed that amylose fractions with different number average chain lengths (DP(n)BAR 40-610) were obtained. Enzyme-resistant starch (RS) was formed from the fractions in aqueous solutions (0.83%, w/v) at 4-degrees-C. Under the experimental conditions, the yield of RS increased with DP(n)BAR to plateau values of 23-28% within a region of DP(n)BAR of 100-610. X-ray diffraction showed a B-pattern for all RS samples obtained. The DP(n)BAR of the RS varied only between 19 and 26 and, thus, it is independent of the chain length of the amylose from which it was formed (DP(n)BAR 40-610). The results suggest that RS may be formed by aggregation of amylose helices in a crystalline B-type structure over a particular region of the chain (about 24 glucose units).status: publishe

Enzyme-Resistant Starch .1. Quantitative and Qualitative Influence of Incubation-Time and Temperature of Autoclaved Starch on Resistant Starch Formation

Wheat starch was autoclaved (121-degrees-C) for 1 hr in excess water. The subsequent formation of enzyme-resistant starch (RS) was studied as a function of time (at different incubation temperatures, i.e., 0, 68, and 100-degrees-C). The rate of formation and the maximum yields of RS (4, 6, and 10%, respectively) varied to a great extent. The relationship between incubation time, temperature, and the yields of RS was interpreted in terms of crystallization in an amorphous matrix, the starch gel being a partially crystalline polymer system. Upon incubation at 0-degrees-C, the nucleation rate was high and the propagation rate was low; the opposite was the case upon incubation at 100-degrees-C. At 68-degrees-C, an intermediate pattern was observed. Incubation of the autoclaved starch samples at two subsequent temperatures (0 and 68-degrees-C or 0 and 100-degrees-C)(two-step procedure) did not increase the RS yield significantly. X-ray diffraction showed qualitative differences among the crystallites formed at different temperatures. RS formed at 100-degrees-C (A pattern) was different from that formed by incubation at 0 or 68-degrees-C (B pattern). X-ray diffraction of RS formed in a process with two storage steps at different temperatures (0 and 68-degrees-C or 0 and 100-degrees-C), aiming at increasing yields by first favoring nucleation and then propagation, yielded B-type diffractograms.status: publishe

Effects of hydrothermal treatments on the rheological properties of potato starch

Potato starch was hydrothermally treated at moisture levels ranging from 20 to 40% and at temperatures 3% below the gelatinization peak temperatures (in K). The treatments had a great impact on the rheological behavior as studied with a rapid visco analyzer (RVA) and dynamic viscoelastic measurements. The extent of the observed effects did not only depend on the specific treatment but also on the starch concentrations investigated (3.0, 6.6, and 20.0%). For the dynamic measurements, the gel storage moduli were related td swelling power and close packing concentration. The increase in onset temperature of viscosity development and the decrease in peak viscosity observed with RVA as a consequence of hydrothermal treatments, were also attributed to the decreases in swelling power and solubility. (C) 1997 Elsevier Science Ltd.status: publishe

Influence of Annealing on the Pasting Properties of Starches from Varying Botanical Sources

Pea, potato, wheat, and rice starches were annealed for 24 hr. Differential scanning calorimetry data were collected; pasting characteristics were determined using the Brabender Viscoamylograph and the Newport Scientific Rapid Visco-Analyser (RVA); and amylose leaching during heating in the viscoamylograph was examined. Differential scanning calorimetry data showed an increased gelatinization temperature and enthalpy, and a narrower gelatinization temperature range for all starches. Viscoamylograph viscosity curves showed that annealing resulted in an increased peak viscosity (except for potato starch), and an increased viscosity upon cooling. The amount of amylose leached from the granules was not linked to viscosity changes. Less amylose was leached from the granules of annealed pea and potato starches. The amount of solubilized amylose was practically unchanged (slightly decreased) after the annealing treatment for rice starch, whereas annealed wheat starch showed a slightly increased leaching of amylose. Except for pea starch, RVA results were comparable to the results from the viscoamylograph. In a dimethyl sulfoxide (DMSO) and water mixture (92.5:7.5, w/w), viscosity changes were not consistent for all annealed starches. For annealed pea, wheat, and rice starches, the onset of solubilization occurred at lower temperatures. The increased peak viscosity was attributed to a higher rigidity and resistance to shear of the starch granules. For annealed potato starch, the viscosity was decreased. A higher rigidity and increased resistance to heat and shear of the starch granules are probably the main causes of the viscosity changes due to annealing, both in water and in a DMSO-water mixture.status: publishe

Enzyme-Resistant Starch .6. Influence of Sugars on Resistant Starch Formation

Solutions of glucose, ribose, maltose, and sucrose were added to autoclaved (1 hr at 121-degrees-C in excess water) wheat starch and high-amylose corn starch. After storage of the starch gels for 20- to 350-min intervals, enzyme-resistant starch (RS) yields were determined. Sugars had an influence on RS levels in starch gels only when added in high concentrations (final starch-water-sugar ratio of 1:10:5, w/w). In wheat starch gels, the RS yields decreased from approximately 3.4% to approximately 2.8% when sucrose or glucose was present; they decreased to approximately 2.5% in the presence of ribose or maltose. An increase in RS yield was observed with high-amylose corn starch. The experiments showed that the differences in gelatinization temperature, lipid content, and apparent amylose content of the two starches were not the main causes of the different impact of sugars on the RS yields. RS quality of the isolated RS fractions, determined by X-ray diffraction and differential scanning calorimetry, was not affected by the sugars studied (except for a higher melting enthalpy of isolated RS when it was formed in the presence of ribose).status: publishe

Evaluation of the impact of annealing on gelatinisation at intermediate water content of wheat and potato starches: A differential scanning calorimetry and small angle X-ray scattering study

The DSC (differential scanning calorimetry) thermograms of wheat and potato starches at 50% (w/w) wa.ter content are characterised by two gelatinisation endotherms, Two separate phenomena coinciding with the two DSC endotherms can be distinguished in the SAXS patterns of 50% (w/w) suspensions of wheat and potato starches during heating from 25 to 95 degrees C at 2 degrees C/min: an increase in peak integral in the temperature domain of the first (G) endotherm and a marked decrease in peak integral in the temperature domain of the second (M1) endotherm, One- and two-step annealing affect only the G endotherm, leading to a shift to a higher temperature of up to 8 degrees C, sharpening of the peak and an increase in enthalpy, while the completion temperature of the M1 endotherm remains unchanged, Static SAXS measurements indicate that the repeat distances of crystalline and amorphous lamellae in wheat (105 Angstrom) and potato (99 Angstrom) starch granules are unaffected by annealing, One- and two-step annealing intensify the SAXS peaks, The most striking difference between the SAXS gelatinisation profiles of native and annealed starches is that there is no increase in peak integral at the onset of gelatinisation of annealed starches, The effects following annealing are interpreted as a decreased water absorption during gelatinisation. Annealing leads to a retardation of the initial swelling and cooperative melting of the granules, without altering the stability of the most perfect crystallites. (C) 1998 Elsevier Science Ltd. All rights reserved.status: publishe

Amido resistente e suas propriedades físico-químicas Resistant starch and its physicochemical properties

A partir da década de 80, começou a ser observado que uma fração do amido escapava da digestão no intestino delgado e chegava ao cólon, onde servia de substrato para a flora bacteriana. Essa fração foi denominada amido resistente e, a partir de então, constatou-se que determinados efeitos fisiológicos, inicialmente atribuídos às fibras alimentares, poderiam também ser atribuídos ao amido resistente. Vários fatores podem estar envolvidos na sua formação e eles, por sua vez, afetam a sua resposta fisiológica. Deste modo, torna-se importante o conhecimento dos aspectos físico-químicos envolvidos na formação do amido resistente.<br>Since the 1980s, it has been observed that a starch fraction was not digested in the small intestine, reaching the colon as a substrate for the bacterial flora. This fraction was called resistant starch and, from this time on, it was noticed that certain physiological effects, initially attributed to the dietary fiber, could also be attributed to the resistant starch. Several factors can be involved in its formation, and they, in turn, affect its physiological response. Therefore, the knowledge on the physicochemical aspects involved in the formation of the resistant starch becomes important