Soft Wheat Starch Research Articles

Superheated steam treatment of soft wheat on the physicochemical properties and structure of wheat starch

AbstractSoft wheat grains were treated with superheated steam (SS) at 165 and 190°C, respectively for 1–5 min to understand the changes in the structures and properties of wheat starch following SS treatment. The damaged starch contents, amylose ratio, gelatinization properties, surface morphology, viscosity, and crystalline structure of the starch in wheat flour were determined. Damaged starch content, amylose ratio, and starch viscosity significantly increased after SS treatment. The onset temperature (To) and peak temperature (Tp) of wheat starch increased with the extending of treatment time, while an opposite variation trend was observed for (Tc − To). Additionally, the gelatinization enthalpy (ΔH) decreased after 3–5 min of SS treatment. Starch aggregation was observed in scanning electron microscopy (SEM) graphs. Compared to traditional heat treatment methods, SS treatment of wheat grains may be preferable for modifying the starch properties of soft wheat since much time and energy could be saved.Practical ApplicationThe physicochemical properties and structure of soft wheat starch significantly affect the quality of cakes made with soft wheat flour. After SS treatment of wheat kernels, the amylose ratio and damaged starch content in wheat starch significantly increased. Moreover, gelatinization properties and starch viscosity of wheat starch were also significantly affected. The changes in physicochemical properties were mainly due to the changes in the structure of starch granules and starch molecules. The above results in the physicochemical properties and structure of starch led to the increase in the viscosity and gas retention capacity of cake batter, which might be the reason why the specific volumes and texture of cakes could be improved after SS treatment of wheat. This research verified SS treatment may be preferable for improving cake quality compared to traditional heat treatment methods, which promotes the application of SS in wheat process engineering.

Effect of multiple freezing-thawing cycles on structural and functional properties of starch granules isolated from soft and hard wheat

Properties of starches isolated from soft and hard wheat dough after freezing/thawing (F/T) treatment were investigated. Significance of results was observed between isolated hard wheat starch (HWS) and soft wheat starch (SWS), but both cultivars showed an increase in the amounts of damaged starch and leaching proteins, lipids, and amylose with F/T cycles. The freezing-treated HWS exhibited a higher swelling power and peak, trough, breakdown and final viscosity than SWS after F/T treatment. The onset, peak and conclusion gelatinization temperatures and the enthalpy of the isolated HWS determined by differential scanning calorimetry, decreased throughout F/T cycles. Concomitantly, the bread containing freezing-treated HWS exhibited a lower bread specific volume and harder crumb firmness, which might be associated with its significant structural changes induced by F/T treatment.

Effects of high-pressure homogenization on thermal and electrical properties of wheat starch

To investigate the effects of high-pressure homogenization on wheat starch granules, soft wheat starch suspensions (5.0%) were homogenized at increasing pressures, ranging from 0 to 100MPa. The structural and thermal properties of the treated starches were determined by microscopy, particle size distribution, differential scanning calorimetry, and damaged starch measurements. A laboratory-scale ohmic heating setup was used to heat homogenized starch–KCl suspensions and measure the electrical characteristics. The wheat starch was partly gelatinized after high-pressure homogenization, and the degree of gelatinization increased to 25.96±1.0% when the homogenization pressure was 100MPa. The electrical conductivities of the treated starch–KCl suspensions increased linearly with increasing temperature during ohmic heating. The slopes of the electrical conductivity–temperature curves of the homogenized starch suspensions during ohmic heating correlated with the degree of starch gelatinization.

Physicochemical properties and amylopectin fine structures of A- and B-type granules of waxy and normal soft wheat starch

This work fractionated waxy and normal wheat starches into highly purified A- and B-type granule fractions, which were representative of native granule populations within parent native wheat starches, to accurately assess starch characteristics and properties of the two granule types. Wheat starch A- and B-type granules possessed different morphologies, granule specific surface area measurements, compositions, relative crystallinities, amylopectin branch chain distributions, and physical properties (swelling, gelatinization, and pasting behaviors). Within a genotype, total and apparent amylose contents were greater for A-type granules, while lipid-complexed amylose and phospholipid contents were greater for B-type granules. B-type (relative to A-type) granules within a given genotype possessed a greater abundance of short amylopectin branch chains (DP n < 13) and a lesser proportion of intermediate (DP n 13–33) and long (DP n > 33) branch chains, contributing to their lower relative crystallinities. Variation in amylose and phospholipid characteristics appeared to account for observed differences in swelling, gelatinization, and pasting properties between waxy and normal wheat starch fractions of a common granule type. However, starch granule swelling and gelatinization property differences between A- and B-type granules within a given genotype were most consistently explained by their differential amylopectin chain-length distributions.

Channels within soft wheat starch A- and B-type granules

The nature of channels within wheat starch granules was investigated using scanning electron and confocal laser scanning microscopy. A-type granules stained with 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA, protein-specific probe) revealed a network of radially oriented, channel-like protein structures similar to those previously reported. However, treatment of the same starch granules with methanolic merbromin (fluorescent dye) solution, which is used to highlight external granule surfaces (including those of channels) under non-swelling conditions, revealed few, if any, channels extending into the granule interior. This discrepancy suggested that channels within wheat starch granules were filled at least in part with protein. Removal of protein with protease facilitated greater access of methanolic merbromin to channels and/or cavities for both granule types. For A-type starch granules, relatively large channels were observed in the equatorial groove region, while finer channels originated from other regions of the granule. This work reports the first visualization of B-type granule channels, which most frequently occurred as less-defined voids (as opposed to the fine, discrete channels of A-type granules) extending to granule surfaces. Channels of A- and B-type starch granules appeared to facilitate transfer of chemical reagent into the granule matrix, though this effect was aided by granule swelling (hydration) and/or removal of channel-associated protein.

Alkaline Dissolution of Starch Facilitated by Microwave Heating for Analysis by Size-Exclusion Chromatography

A rapid, straightforward starch dissolution method was developed to facilitate analysis of starch by size-exclusion chromatrography (SEC). Soft wheat starch was dispersed in 6 M urea and 1 M KOH and subjected to heating for 35, 45, or 60 s in a microwave oven as a potential means of starch dissolution. An increase in microwave heating time enhanced starch solubility but resulted in a steady decrease in amylopectin peak area and a consequent, artifactual increase in the amylose peak area due to molecular degradation. However, microwave heating for 35 s afforded a reasonable separation of starch fractions by SEC while minimizing molecular degradation of starch in comparison to a traditional starch dissolution procedure. This procedure provides a fast (<30 min), simple, and reproducible starch dissolution method for preparation of starches for SEC analysis and represents the first successful report of direct dissolution of granular starch via microwave heating.

PHYSICAL PROPERTIES OF SUGAR‐SNAP COOKIES USING GRANULE SURFACE DEPROTEINATED WHEAT STARCH

ABSTRACT The physical properties of soft wheat starch granule surface proteins and soy flours or isolates, which contribute to the texture of sugar‐snap cookies was studied. Soft wheat flour was deproteinated and cookies were produced containing 0, 10, 20 or 30% soy flour, or one of two types of ground, textured soy flour. Color, fracture force and spread ratio of cookies were determined. Cookies formulated with wheat starch stripped of the starch granule surface proteins exhibited significant alterations in diameter, fracture force, thickness and surface cracking. Cookies containing ground, textured soy flour and protein‐stripped starch granule wheat flour were larger, thinner and had more surface cracking than those produced with nontextured soy flour. Wheat starch granule surface proteins appear to partially mediate the interaction of proteins and starch in a sugar‐snap cookie system.

Soft Wheat Starch Pasting Behavior in Relation to A‐ and B‐type Granule Content and Composition

ABSTRACTFlours of two soft wheat cultivars were fractionated into native, prime, tailing, A‐, and B‐type starch fractions. Starch fractions of each cultivar were characterized with respect to A/B‐type granule ratio, amylose content, phosphorus level (lysophospholipid), and pasting properties to investigate factors related to wheat starch pasting behavior. While both cultivars exhibited similar starch characteristics, a range of A‐type (5.7– 97.9%, db) and B‐type granule (2.1–94.3%, db) contents were observed across the five starch fractions. Though starch fractions displayed only subtle mean differences (&lt;1%) in total amylose, they exhibited a range of mean phosphorus (446–540 μg/g), apparent amylose (18.7–23%), and lipid‐complexed amylose (2.8–7.5%) values, which were significantly correlated with their respective A‐ and B‐type granule contents. A‐type (compared with B‐type) granules exhibited lower levels of phosphorus, lipid‐complexed amylose, and apparent amylose, though variability for the latter was primarily attributed to starch lipid content. While starch phosphorus and lipid‐complexed amylose contents exhibited negative correlation with fraction pasting attributes, they did not adequately account for starch fraction pasting behavior, which was best explained by the A/B‐type granule ratio. Fraction A‐type granule content was positively correlated with starch pasting attributes, which might suggest that granule size itself could contribute to wheat starch pasting behavior.

Kinetics of in situ and in vitro gelatinization of hard and soft wheat starches during cooking in water

Kinetics of in situ and in vitro gelatinization of hard ( T. durum) and soft T. aestivum wheat starches were investigated during cooking in water at 60°C, 70°C, 80°C, 90°C, and 100°C. At the given temperatures, the gelatinization process ceased before 100% completion at a final degree of gelatinization (FDG) for all starches. At the same temperature, the FDG was higher for the in vitro gelatinization than the in situ gelatinization for both hard and soft wheat starches. It was higher for the soft wheat starch than the hard wheat starch for both in situ and in vitro processes. Effect of temperature on the FDG was assessed through a Clausius–Clapeyron type equation. Starch gelatinization followed first-order reaction kinetics for both in situ and in vitro processes. The reaction rate constant ( k r) was higher for the in vitro gelatinization than the in situ gelatinization for both starches. It was higher for the soft wheat starch than the hard wheat starch for both processes. The k r values were in the order of 10 −5 to 10 −4 s −1 for the in situ gelatinizations and 10 −4 to 10 −3 s −1 for the in vitro gelatinizations. The rate of the gelatinization reaction increased with increasing temperature and the effect of temperature on k r was evaluated using an Arrhenius type equation. In vitro gelatinizations had an average activation energy ( E a) of 76 kJ/mol between 60°C and 100°C. In situ gelatinizations had an average E a of 137 below 75°C, and 79 kJ/mol above 75°C. Assuming the in vitro gelatinizations were effectively controlled by the reaction of starch with water between 60°C and 100°C, the in situ gelatinizations were effectively controlled by water transfer below 75°C and reaction of starch with water above 75°C.

Characterisation of Friabilin Polypeptides

Analysis by two dimensional electrophoresis (NEPHGE × SDS-PAGE) of proteins extracted with cold SDS solution from starch granules isolated from flour of the soft wheat cv. Galahad showed the presence of two very basic, approx. M r 15 k polypeptides with mobilities very similar to those of the surface-active, lipid-binding proteins, puroindoline-a and puroindoline-b. Whereas the puroindoline-a component predominated in the flour extract, the two analogous polypeptides extracted from isolated starch granules appeared to be present in similar amounts. When the starch proteins were fractionated by Triton X-114 extraction and phase partioning, the puroindoline-like polypeptides were found in the detergent-rich phase, as would be expected for puroindoline proteins. Purification of the Triton X-114-fractionated proteins from cvs. Galahad and Norin 61 by gel filtration and cation exchange chromatography allowed the separation of three polypeptides, the first having a slightly lower mobility on SDS-PAGE than the other two. The N-terminal sequence of the first 15 amino acids of the first of those proteins isolated form cv. Norin 61 was identical to those of 0·19 and 0·53 alpha -amylase inhibitors, whereas the N-terminal sequences of the second and third were identical to those of puroindolines-a and -b, respectively, apart from the eighth amino acid of the puroindoline-b homologue, which was glycine in the starch protein, whereas it is reported to be serine in puroindoline-b. The similarities between the electrophoretic, detergent fractionation and N-terminal sequence properties of two of the cold SDS-extractable starch friabilin polypeptides and those of puroindolines-a and -b strongly suggest that friabilin comprises a mixture of proteins in which the puroindoline polypeptides are important components. The amino acid sequence data indicate that some alpha -amylase inhibitor proteins are also significant components of friabilin. The reason for the differential binding of these proteins to the surfaces of hard and soft wheat starch granules remains to be found, but elucidation of that reason may be important in defining the molecular mechanisms by which endosperm texture variation is controlled.

Review on the significance of starch and protein to wheat kernel hardness

AbstractWheat starch contains large lenticular (A‐type) and small spherical (B‐type) granules, with some intermediate (underdeveloped A‐type), composed of two structurally different polysaccharides, amylose (20–30%) and amylopectin (70–80%), plus small amounts of lipids, nitrogen and phosphorus. Vitreous character is related to air spaces between granules, whereas hardness relates to protein‐starch bond strength and protein matrix continuity between granules. Grain hardness is controlled genetically by one or more major genes, modified by one or more minor genes. Environmental factors also exert effects. Most hardness measurements are grouped into categories based on grinding, crushing, abrasion or indentation. Recent methods, viz microscopy, NIR, single kernel cutting, tensile strength and an acoustical technique, seem to have promise.Three basic mechanisms of grain hardness have been postulated: (a) chemically induced adhesion between the protein matrix and starch granule, (b) continuity of the protein matrix, and (c) net charge on the protein. Some recent studies have revealed small amounts of protein as an integral component of the starch granule. The surface granule proteins showed relatively low molecular weight polypeptide bands (5–30 kDa), whereas the integral starch granule proteins had higher molecular weights (59–149 k Da). The 59 kDa protein is postulated to be the enzyme that synthesises amylose. The 15 kDa polypeptide is related to kernel softness, because it is strong in soft wheats, weak or faint in hard wheats, and absent in durum wheats. Reconstituted tablets made from hard wheat starch showed higher tensile strength than those made from soft wheat. Tablets reconstituted from soft wheat starch free from 15 kDa protein exhibited increased tensile strength, suggesting that the 15 kDa protein acts as a ‘non‐sticking’ agent between the starch granules and the protein matrix. Some lipids are associated with arnylose and the starch granule surface but their significance is not clear. Key words. Starch, kernel hardness measurement, hardness mechanism, starch granule proteins.