Changes in the structure and enzyme binding of starches during in vitro enzymatic hydrolysis using mammalian mucosal enzyme mixtures.

Starches are hydrolyzed into monosaccharides by mucosal α-glucosidases in the human small intestine. However, there are few studies assessing the direct digestion of starch by these enzymes. The objective of this study was to investigate the changes in the structure and enzyme binding of starches during in vitro hydrolysis by mammalian mucosal enzymes. Waxy maize (WMS), normal maize (NMS), high-amylose maize (HAMS), waxy potato (WPS), and normal potato (NPS) starches were examined. The order of the digestion rate was different compared with other studies using a mixture of pancreatic α-amylase and amyloglucosidase. NPS was digested more than other starches. WPS was more digestible than WMS. Hydrolyzed starch from NPS, NMS, WPS, WMS, and HAMS after 24 h was 66.4, 64.2, 61.7, 58.7, and 46.2 %, respectively. Notably, a significant change in the morphology, reduced crystallinity, and a decrease in the melting enthalpy of the three starches (NPS, NMS, and WPS) after 24 h of hydrolysis were confirmed by microscopy, X-ray diffraction, and differential scanning calorimetry, respectively. The bound enzyme fraction of NPS, NMS, and WPS increased as hydrolysis progressed. In contrast, HAMS was most resistant to hydrolysis by mucosal α-glucosidases in terms of digestibility, changes in morphology, crystallinity, and thermal properties.

Unveiling the significance of gastric digestion in gastrointestinal fate of octenylsuccinylated starch-stabilized emulsions.

The importance of gastric digestion in starch-based emulsion is often overshadowed compared to intestinal digestion, despite acknowledging the activity of salivary α-amylase in the stomach. This study aimed to address this gap by investigating the digestion of starch-based emulsions through orogastrointestinal digestion experiments. Our observations revealed the crucial role of salivary α-amylase, which hydrolyzed ∼8 %, ∼56 %, and âˆ¼ 28 % of starch in emulsions stabilized by octenylsuccinylated maize starch (OMS-E), gelatinized OMS (GOMS-E), and retrograded OMS (ROMS-E), respectively, during the gastric phase. Consequently, ∼23 % of the oil in GOMS-E underwent lipolysis during this phase, whereas ∼13 and âˆ¼ 6 % of the oil was lipolyzed in OMS-E and ROMS-E, respectively. These phenomena significantly influenced their small intestinal digestion and the bioaccessibility of encapsulated curcumin. Notably, GOMS-E exhibited ∼28 % lower curcumin bioaccessibility than that of curcumin encapsulated in OMS-E or ROMS-E. This difference was attributed to premature gastric digestion and subsequent encapsulant release in the case of GOMS-E. This understanding can be utilized to manipulate the delivery and digestion of starch-based emulsions. Importantly, our findings highlight the necessity of considering gastric amylolysis and lipolysis when investigating the gastrointestinal fate of starch-based emulsions.

Pasting properties of A- and B-type wheat starch granules and annealed starches in relation to swelling and solubility.

Wheat starch contains two distinct groups of granules, A-type and B-type, which have different compositions and properties. The aim of this study was to investigate the differences in pasting properties of A- and B-type wheat starch granules and their annealed starches, and to relate them to swelling properties and solubility. A- and B-type wheat starch granules were fractionated. The differences in pasting properties between A- and B-type wheat starch granules depended on starch solids content. The A-type starch had a higher pasting viscosity at ≥8 % solids content, but the trend was reversed at a lower solids content (5 %). This cross-over phenomenon in the pasting viscosity can be explained because A-type wheat starch granules have more starch molecules leached out, while swelled less at high temperatures and are probably more rigid than B-type wheat starch granules. This is the first study to show the cross-over in the pasting viscosity-starch concentration between A-type and B-type wheat starches and that B-type wheat starch has higher pasting viscosity than A-type at a low solids content. When annealed in warm water, both annealed A- and B-type wheat starch granules had higher pasting viscosities than untreated counterparts by altering the swelling of starch.

Conformational properties of heterogeneous arabinoxylan protein gums from corn bran and distillers grains in comparison with gum arabic.

The molecular structure and conformation of arabinoxylan-protein gum, commonly referred as corn fiber gum (CFG) were analyzed by high-performance size-exclusion chromatography (HPSEC) coupled with RI, UV, light scattering and viscometer detectors. CFG had a heterogeneous structure. The detailed conformation of CFG at different molecular weights was compared with that of hemicellulose fiber gum (HFG) from dried distiller's grains with solubles and gum arabic. The CFG molecules mainly had random coil conformation; only 10 % of them exhibited rigid rod conformation. Approximately 80 % of the CFG had a molecular weight between 105 and 105.4 Da, while the other 20 % of molecules were between 105.4 and 1.5 × 107.7 Da. The overall conformational properties of CFG and HFG were closer but differed from that of gum arabic. The intrinsic viscosity and radius of gyration of both CFG and HFG were greater than those of gum arabic although the average molecular weight of CFG and HFG was lower. The protein and carbohydrate were covalently linked in CFG molecules as shown by the HPSEC-multiple detectors combined with partial acid hydrolysis. Based on the detailed conformation of CFG and the methylation analysis, 1D and 2D NMR spectroscopy results, the molecular structure of CFG was proposed.

Facile synthesis of lipase-loaded starch nanoparticles as recyclable biocatalyst in Pickering interfacial systems.

To develop recyclable biocatalyst used in Pickering interfacial systems, the pH-responsive monomer [2-(dimethylamine)ethyl methacrylate] (DMAEMA) was grafted onto the maize starch molecule via free radical polymerization. Subsequently, combined with the gelatinization-ethanol precipitation and lipase (Candida rugosa) absorption process, an enzyme-loaded starch nanoparticle with DMAEMA grafting (D-SNP@CRL) was tailor-made, showing a nanometer size and regular sphere. X-ray photoelectron spectroscopy and confocal laser scanning microscopy confirmed a concentration-induced enzyme distribution within D-SNP@CRL, thereof the outside-to-inside enzyme distribution was proved to be optimum in achieving the highest catalytic efficiency. Benefited from the tunable wettability and size of D-SNP@CRL under pH variation, the generated Pickering emulsion could be readily applied as the recyclable microreactors for the n-butanol/vinyl acetate transesterification. This catalysis exhibited both highly catalytic activity and good recyclability, making the enzyme-loaded starch particle a promising green and sustainable biocatalyst in the Pickering interfacial system.

Wheat bran layers: composition, structure, fractionation, and potential uses in foods.

Wheat bran, the main by-product of dry milling of wheat, is currently mainly used in the animal feed industry, but has attracted attention as a food ingredient owing to its high dietary fiber and phytochemical contents, providing excellent physiological effects. The bran layers (aleurone layer, outer pericarp and intermediate layer) contain different compositions, structures, and nutrients, and have different properties. Each layer, when separated and isolated, potentially could find more extensive applications in foods. This triggered interest in isolating the bran layers using milling and wet- or dry-fractionation techniques based on their chemical or physical properties. The recent progress has allowed the production of commercial products from wheat bran layers, particularly aleurone-rich products, enhancing the value of wheat bran layers and their applications in food. The present review highlights the recent advances in studying the chemical composition including distribution of chemical components, physical structure, biopolymer matrix, and physicochemical properties of each wheat bran layer. Technologies to fractionate wheat bran layers and utilization of different bran layers in foods are discussed and reviewed, providing new strategies for improving the value of wheat bran and utilization of wheat bran in foods.

Microstructures of Starch Granules with Different Amylose Contents and Allomorphs as Revealed by Scattering Techniques.

In this study, as-is (ca. 12% moisture by mass) and hydrated (50% water by mass) granules of waxy potato (WP), waxy wheat (WW), waxy maize, normal maize, and high-amylose maize (HAM) starches were investigated by using small-angle neutron and X-ray scattering (SANS and SAXS), wide-angle X-ray scattering, and ultra-small-angle neutron scattering. The SANS and SAXS data were fitted using the two-phase stacking model of alternating crystalline and amorphous layers. The partial crystalline lamellar structures inside the growth rings of granules were analyzed based on the inter-lamellar distances, thicknesses of the crystalline lamellae and amorphous layers, thickness polydispersities, and water content in each type of layer. Despite having a longer average chain length of amylopectin, the WP and HAM starches, which had B-type allomorph, had a shorter inter-lamellar distance than the other three starches with A-type allomorph. The WP starch had the most uniform crystalline lamellar thickness. After hydration, the amorphous layers were expanded, resulting in an increase of inter-layer distance. The low-angle intensity upturn in SANS and SAXS was attributed to scattering from interfaces/surfaces of larger structures, such as growth rings and macroscopic granule surfaces. Data analysis methods based on model fitting and 1D correlation function were compared. The study emphasized─owing to inherent packing disorder inside granules─that a comprehensive analysis of different parameters was essential in correlating the microstructures with starch properties.

Effects of protein digestion on in vitro digestibility of starch in sorghum differing in endosperm hardness and flour particle size.

In vitro digestibility of starch in sorghum grains differing in endosperm hardness and flour particle size was investigated. The starch digestibility increased as the particle size of flour decreased, but no clear trend was observed in digestibility of starch in sorghum flours milled from grains with different hardness. The protein matrix affected the digestion of starch. The pH value (2.0 vs. 1.3) was a critical factor affecting protein digestion. Optimum pH (pH 2.0 for pepsin) digested more protein, resulting in a greater digestion of starch. Resistant starch (RS) content was 8.5-26.3% in isolated sorghum starch but higher (10.6-29.5%) in sorghum flours. Protein digestibility decreased after cooking while starch digestibility increased compared to native sorghum flours; disulfide bonds formed between protein molecules. RS content of cooked sorghum flour was much higher without pepsin treatment (16.93-23.99%) than that of cooked sorghum flour with pepsin treatment (4.86-12.53%).

Dissolution of waxy maize pyrodextrin granules in mixtures of glycerol and water, separating loss of crystallinity from loss of birefringence.

Pyrodextrins were prepared by heating waxy maize starch for 4 h at pH 3 & 150 °C, pH 3 & 170 °C, and pH 2 & 150 °C. Those pyrodextrins were soluble in water at 25 °C, but insoluble in glycerol. The objectives of this study were to investigate dissolution of the pyrodextrins in glycerol/water mixtures, and to determine how crystallinity and birefringence of the pyrodextrins were affected by swelling. Pyrodextrins prepared at pH 3 & 170 °C and pH 2 & 150 °C either dissolved or swelled little in glycerol/water mixtures at 25 °C. In contrast, the pyrodextrin prepared at pH 3 & 150 °C, which showed the least depolymerization, swelled in 40% glycerol to increase granule diameter ~80%. Despite that significant swelling, those swollen granules still displayed a Maltese cross pattern but were amorphous, demonstrating the separation of loss of crystallinity from loss of birefringence.

Extraction of non-starch lipid from protease-treated wheat flour.

BACKGROUND: Lipids account for 2.0-2.5% of wheat flour by dry weight and affect properties and quality of cereal foods. A new method was developed to extract non-starch lipids from wheat flour. Wheat flour was first hydrolyzed with a protease and followed by extraction of non-starch lipids by water-saturated butanol (WSB). RESULT: Protein hydrolysis by protease followed by extraction of non-starch lipids with WSB increased yield to 1.9 ± 0.3% from 1.0 ± 0.1% with no protease treatment. The lipid profile showed a significant increase in phospholipid compounds extracted with protease hydrolysis (5.9 ± 0.8 nmol·g-1 ) versus without enzymatic treatment (2.4 ± 1.3 nmol g-1 ). CONCLUSION: Improved lipid extraction yield and phospholipid compounds following protease-assisted extraction method provided additional insight towards the understanding of protein-lipid interaction in wheat flour. The new protease-assisted extraction method may be applied to analyzing non-starch lipids in other types of wheat flours and other cereal flours. © 2021 Society of Chemical Industry.

Molecular structure and properties of cassava-based resistant maltodextrins.

In-depth molecular structure and properties of cassava-derived resistant maltodextrins (RMDs) were determined. Cassava starch was dextrinized with 0.04% or 0.06% HCl at 120 °C for 60-180 min to obtain resistant dextrins (RDs), which were further hydrolyzed by α-amylase to produce RMDs. Prolonging dextrinization duration decreased proportion of α-1,4 linkages and α-/ß-reducing ends but increased fraction of indigestible α-/ß-1,6, ß-1,4, ß-1,2 linkages, degree of branching (DB), degree of polymerization, relative molecular weight, and total dietary fiber (TDF) content of the RMDs. Moreover, RMDs had greater proportion of ß-glycosidic linkages, α-/ß-reducing end, DB, TDF, and low molecular weight dietary fiber (LMWDF) content than their RD counterparts. Potential prebiotic activity score was higher in RMDs with abundant LMWDF fraction but low DB. Slight difference in the glass transition temperature of maximally freeze-concentrated unfrozen phase (Tg') and unfrozen water content was found among RMDs. However, RMDs had lower Tg' than their RD counterparts.

Structure, birefringence and digestibility of spherulites produced from debranched waxy maize starch.

The objectives of this study were to debranch waxy maize starch by pullulanase, produce spherulites with different crystalline structures and birefringent properties by controlling crystallization conditions and determine how their structures were correlated with their digestibilities. The spherulites formed in water or 50% ethanol at 4 °C without mixing had a B-type crystalline structure. The birefringence sign was not uniform for the spherulites formed in water at 4 °C; some spherulites displayed negative birefringence. However, positive birefringence was observed for the spherulites formed in 50% ethanol at 4 °C, indicating starch chains were radially arranged. The spherulites crystallized in water at 50 °C followed by further crystallization at 4 °C had a predominate A-type crystalline pattern with positive birefringence in some particles, the highest resistant starch content (73.0%) and the highest degree of crystallinity (76%).

Changes in molecular size and shape of waxy maize starch during dextrinization.

The conformational properties of pyrodextrins from waxy maize starch were investigated by high performance size exclusion chromatography with multiple detectors, and the relationships (Mark-Houwink equations) between molecular weights and intrinsic viscosities of pyrodextrins in water were established. Pyrodextrin was prepared by adjusting waxy maize starch to pH 3 or 2, heating at 170 °C or 150 °C. As heating time increased from 0.5 to 4 h, the molecular size was decreased in the order of pH 2 and 150 °C > pH 3 and 170 °C > pH 3 and 150 °C. The measured exponent α values in Mark-Houwink equation indicated that the pyrodextrins prepared at pH 3, 170 °C and 150 °C only had one compact spherical conformation (α 0.27-0.31) during dextrinization, whereas the pyrodextrins prepared at pH 2 and 150 °C had a mixture of two shapes of molecules: compact sphere (α 0.26) and rigid coil (α 0.89) conformation.

Properties of flour from pearled wheat kernels as affected by ozone treatment.

Two different pearling degrees of wheat kernels (lightly-pearled: 14.4% and heavily-pearled: 38.9%) and un-pearled kernels were treated with ozone and evaluated for flour compositions and properties. Ozonation did not change main compositions and damaged starch content of three kernels' flours. Flour brightness of all three kernels was improved after ozone treatment. Ozonation enhanced the dough strength of the flours from un-pearled and pearled kernels and the effect elevated with increasing pearling degree. Ozone treatment increased the peak viscosity of flour and the level of increase in heavily-pearled kernels was greater than un-pearled and lightly-pearled. Ozonation resulted in an increase in the insoluble protein polymer content of heavily-pearled kernels' flour, but only had a slight effect on un-pearled lightly-pearled kernels. After ozone treatment, un-pearled and lightly-pearled kernels exhibited increases in molecular weight of starch, but heavily-pearled resulted in the opposite trend.

Properties of extruded cross-linked waxy maize starches and their effects on extruded oat flour.

The objectives of this study were to study the extrusion of cross-linked waxy maize starches (CLWMS) with different cross-linking levels and their function as a secondary ingredient in extruded oat flour (OF) formulations. CLWMS (18 %) and OF (82 %) were hydrated to 20 % moisture content and subjected to twin-screw extrusion at the screw speed of 350 rpm. Low cross-linking level of CLWMS (0.05 % sodium trimetaphosphate/sodium tripolyphosphate) in OF formulation increased the void fraction and reduced the breaking strength of extrudates. The low cross-linked starch was more resistant to breakdown and had a higher pasting viscosity than the unmodified starch. Higher cross-linking levels of CLWMS restricted swelling of starch granule and increased the resistant starch level of OF formulation but had very poor structural and textural properties. Varying the level of cross-linking offers an alternative way to manipulate the structural, textural and nutritional properties of extrudates in snack and cereal applications.

Pyrodextrins from waxy and normal tapioca starches: Molecular structure and in vitro digestibility.

Pyrodextrins were prepared from acidified waxy and normal tapioca starches (pH∼3) at 3 temperatures (130, 150 and 170 °C) and 3 times (1, 2 and 4 h) to determine their in vitro digestibility and molecular structure. Pyrodextrin from waxy tapioca starch produced at 170 °C/4 h had 5% higher total indigestible carbohydrate than pyrodextrin from normal tapioca starch (45.2 % and 40.4 %, respectively) as determined by a modified AOAC Method 2011.25. The low-molecular weight indigestible carbohydrate content at this condition was also higher for waxy tapioca starch than normal tapioca starch (40.6 % and 34.9 %, respectively). Gel permeation chromatography and nuclear magnetic resonance spectroscopy were used to study changes in molecular structure and correlate with digestibility of the pyrodextrins. Molecular size distribution indicated that waxy tapioca starch underwent thermal modification more readily than normal tapioca starch. Non α-1,4/α-1,6 glucosidic linkages were increased in the pyrodextrins with increasing in indigestible carbohydrate content.

Intact endosperm cells in buckwheat flour limit starch gelatinization and digestibility in vitro.

The objective of this study was to determine the biophysical properties of buckwheat (BW) endosperm and their influences on detachment of intact cells, starch gelatinization and digestibility. The intact cells were isolated from BW kernels by dry milling and sieving. The microscopy and texture analysis showed intact endosperm cells could be detached easily due to the fragile structure and low hardness of BW endosperm. More than 70% intact cells were found in commercial light flour. The starch granules entrapped in intact cells exhibited a delay gelatinization and restricted swelling behavior (2-3 â„ƒ higher onset gelatinization temperature than isolated starch). Starch in BW flour had a markedly lower extent of digestion compared to the broken cells and isolated starch. This study provided a new mechanistic understanding of low glycemic index of BW food, and could guide the processing of BW flour to retain slow digestion properties.

Preparation and textural properties of white salted noodles made with hard red winter wheat flour partially replaced by different levels of cross-linked phosphorylated RS4 wheat starch.

BACKGROUND: Resistant starch (RS) has health benefits and can be used as a functional ingredient in various food products. Kansas hard red winter (HRW) wheat is conventionally used for bread making and this is attributed to its strong gluten network. To develop Asian white salted noodles with a high RS content, HRW wheat flour was partially replaced with cross-linked phosphorylated RS4 wheat starch. Vital wheat gluten or wheat protein isolate was added to compensate for textural changes due to the addition of RS. RESULTS: The maximum recommended level of RS4 starch to replace HRW wheat flour was 40%. The substitution of 10-40 parts of RS4 for flour did not change hardness in cooked noodles but it did reduce their extensibility, cohesiveness, and springiness, which was probably due to the non-swelling properties of RS4. At 40 parts of RS4 replacement, supplementation of 2-8 parts of vital wheat gluten or wheat protein isolate in the composite flour notably enhanced the hardness and extensibility of cooked noodles, whereas cohesiveness and springiness were minimally affected. Supplemental vital wheat gluten produced a thicker protein network than endogenous protein or added wheat protein isolate, giving cooked noodles greater breaking force and distance. CONCLUSION: RS4 could be used as a functional ingredient to replace up to 40% of hard wheat flour for making Asian noodles while maintaining their hardness after cooking. The extensibility of cooked noodles with high RS4 could be noticeably enhanced by supplementation with vital wheat gluten in the composite flour (RS/flour = 40/60). © 2020 Society of Chemical Industry.

Structure and physicochemical properties of two waxy wheat starches.

The objective of this study was to determine the primary influences of amylopectin (AP) on starch properties using two waxy wheat starches with different pasting properties. Compared with Yang Nuo Mai 1 (YNM1) starch, Ning Nuo Mai 1 (NNM1) starch had a greater average granule diameter, hot water solubility, gelatinization enthalpy, higher pasting viscosity, but lower retrogradation enthalpy. NNM1 starch had a greater proportion of AP long chains, and lower proportion of AP short chains. Therefore, NNM1 starch had a greater degree of crystallinity as well as stronger resonance intensities at the C1, C2, C3, C5, and C6 by solid-state 13C CP/MAS NMR. These results suggested that the proportion of long AP chains (DP ≥ 37) is the main influencing factor in determining waxy starch physicochemical properties. In addition, the proportion of short AP chains (DP 13-24) plays a role in promoting retrogradation of waxy wheat starch.

An improved method to determine the hydroxypropyl content in modified starches by 1H NMR.

Hydroxypropyl (HP) starches are used as thickeners and stabilizers in foods. The properties of the etherified starches are dependent on the degree of hydroxypropylation. The objective of this study was to develop an improved acid hydrolysis method to degrade and solubilize HP starches for determining HP content in modified starches by 1H NMR. The effects of acid (DCl) concentration and temperature on hydrolysis and solubilization of hydroxypropylated starches were examined. The optimal conditions proposed to hydrolyze HP starches were 10% starch solid content, 3.5% (wt%) DCl in D2O as the solvent, sodium acetate as an internal standard, and heating at 90 °C for 1 h. Optionally, 6% (v/v) TFA-d may be added as the water-peak shifting reagent. Six hydroxypropylated starches and two cross-linked and hydroxypropylated starches were hydrolyzed with this improved acid method, and the results of the HP content were in agreement with those from an enzyme-catalyzed method.