Kerry C. Huber

Channels of maize and sorghum starch granules

The radial, tube-like channels of corn/maize and sorghum starch granules, which penetrate from the external surface inward toward a cavity at the hilum, were found to vary in depth of penetration from granule to granule. Most, but not all, channels spanned the entire granule matrix, from the outer surface to the central cavity. Under slight swelling conditions (water), cavities swelled somewhat closed, while channels appeared to remain open. Swelling also affected the permeability of the granule matrix to dye molecules. Penetration of an aqueous dye solution occurred primarily from the central cavity outward and laterally from channels. Even under the slight swelling conditions, colloidal gold particles filled channels and cavities, showing that they are voids.

Visualization of channels and cavities of corn and sorghum starch granules

ABSTRACT Evidence is presented that corn (maize) and sorghum starch granules have channels that connect a central cavity to the external environment. A mutant sorghum starch with numerous, large surface pores was treated with a methanolic solution of merbromin and sectioned. Light, fluorescence, and compositional backscattering electron microscopy revealed channels connecting an internal cavity to the external surface in most granules. Cavities and channels could also be seen in whole corn and sorghum starch granules treated with merbromin in methanol and viewed by fluorescence microscopy. Treatment of sorghum starch granules with an aqueous solution of merbromin revealed that the molecule penetrated the granule matrix under even slightly swelling conditions. Light microscopy showed cavities in unstained, whole, dry corn and sorghum starch granules mounted in immersion oil.

Location of sites of reaction within starch granules

ABSTRACT To observe granular reaction patterns within modified starch granules, starch derivatives were converted to thallium(I) salts and viewed by scanning electron microscopy compositional backscattered electron imaging. Observation of phosphorylated potato and sorghum starches and a hydroxypropyl analog of waxy maize starch revealed that granular patterns of reaction were influenced by both starch and reagent types. In waxy maize and sorghum starches, flow of reagent into the granule matrix occurred from channels (laterally) and cavities (from the inside outward). In potato starch granules, which do not possess channels, reagent diffused inward through exterior granule surfaces. Phosphoryl chloride (highly reactive) reacted to a large extent at granule surfaces, while the propylene oxide analog (less reactive) appeared to diffuse into the granule matrix prior to reacting.

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

ABSTRACT Flours 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 (<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 wa...

Composition and reactivity of A- and B-type starch granules of normal, partial waxy, and waxy wheat

ABSTRACT Wheat has great potential to make inroads into starch markets with the advent of partial waxy and waxy starches of diverse composition and properties. The majority of isolated starch utilized in food applications is chemically modified to improve starch properties according to the intended use. Therefore, it is critical to understand factors that affect wheat starch reactivity. This work investigated the relative reactivities of normal, partial waxy, and waxy wheat starches and their respective A- and B-type starch granule fractions. Native starch isolated from four closely related soft wheat lines (normal, partial waxy, and full waxy) was modified through 1) substitution (propylene oxide analog) and 2) cross-linking (phosphorus oxychloride) reactions to generate both types of modified starch products for each wheat line. Characterization of the unmodified starch fractions confirmed compositional differences among the cultivars and their respective granule types. In cross-linking reactions, B-typ...

Composition and Properties of A- and B-type Starch Granules of Wild-Type, Partial Waxy, and Waxy Soft Wheat

ABSTRACT Starch A- and B-type granules were isolated from soft wheat (Triticum aestivum L.) genotypes representing the four granule bound starch synthase I (GBSSI) classes, and characterized according to composition and properties. While total (TAM) and apparent (AAM) amylose contents of both granule fractions decreased as starch waxy character increased, the A-type granules possessed higher TAM and AAM contents than B-type granules for a given genotype. From wild-type to waxy, a general transition was observed from B- to A-type starch granule fractions with higher levels of lipid-complexed amylose (LAM) and phospholipid. Within a genotype, A-type (relative to B-type) granules possessed higher gelatinization enthalpies, while B-type granules exhibited higher gelatinization peak and completion temperatures (broader gelatinization ranges) than A-type granules. Normal (wild-type) and waxy A- and B-type starch granule pasting rates were affected by starch granule lipids; the granule type within a genotype wit...

Physical Modification of Food Starch Functionalities

Because, in general, native starches do not have properties that make them ideally suited for applications in food products, most starch is modified by dervatization to improve its functionality before use in processed food formulations, and because food processors would prefer not to have to use the modified food starch label designation required when chemically modified starches are used, there is considerable interest in providing starches with desired functionalities that have not been chemically modified. One investigated approach is property modification via physical treatments, that is, modifications of starches imparted by physical treatments that do not result in any chemical modification of the starch. Physical treatments are divided into thermal and nonthermal treatments. Thermal treatments include those that produce pregelatinized and granular cold-water-swelling starches, heat-moisture treatments, annealing, microwave heating, so-called osmotic pressure treatment, and heating of dry starch. Nonthermal treatments include ultrahigh-pressure treatments, instantaneous controlled pressure drop, use of high-pressure homogenizers, dynamic pulsed pressure, pulsed electric field, and freezing and thawing.

Effects of amylosucrase treatment on molecular structure and digestion resistance of pre-gelatinised rice and barley starches

Structural modification of rice and barley starches with Neisseria polysaccharea amylosucrase (NpAS) was conducted, and relationship between structural characteristics and resistant starch (RS) contents of NpAS-treated starches was investigated. Pre-gelatinised rice and barley starches were treated with NpAS. NpAS-treated starches were characterised with respect to morphology, X-ray diffraction pattern, amylopectin branch-chain distribution, and RS content, and their structural characteristics were correlated to RS contents. Regardless of amylose contents of native starches, NpAS-treated (relative to native) starches possessed lower and higher proportions of shorter (DP 6-12) and intermediate (DP 13-36) amylopectin (AP) branch-chains, respectively. RS contents were higher for NpAS-treated starches relative to native starches, and maximum RS contents were obtained for NpAS-treated starches of waxy rice and barley genotypes. Amylose contents were not associated with RS contents of NpAS-treated starches. However, shorter and intermediate AP branch-chain portions were negatively and positively correlated to RS contents of NpAS-treated starches, respectively.

Heat-moisture treatment under mildly acidic conditions alters potato starch physicochemical properties and digestibility.

Potato starch was subjected to heat-moisture treatment (HMT; 120 °C, 3 h) under mildly acidic conditions (pH 5, 6, or 6.5 [control]) at moisture levels of 15, 20 or 25%. HMT starches exhibited significantly delayed pasting times and reduced overall paste viscosities, amylose leaching, and granular swelling characteristics relative to native starch, as well as enhanced levels of thermo-stable resistant starch (≈24%). HMT appeared to alter/enhance short-range chain associations (FT-IR) within amorphous and/or crystalline regions of starch granules. However, the extent of physicochemical change and RS enhancement during HMT was most facilitated by a mildly acidic condition (pH 6) at higher treatment moisture levels (20 or 25%). These conditions promoted limited hydrolysis of amylopectin molecules, primarily at α-(1→6) branch points, likely enhancing mobility and interaction of starch chains during HMT. Thus, a slightly acidic pH might reduce conditions and/or timeframe needed to impart physicochemical changes and reduced digestibility to potato starch.

Isolation and characterization of atriplex hortensis and sweet chenopodium quinoa starches

ABSTRACT Starches from garden orach (Atriplex hortensis) and sweet quinoa (Chenopodium quinoa Willd. ‘Surumi’) seeds were isolated, examined for compositional characteristics, and compared with bitter quinoa (Cheno-podium quinoa Willd.) starch. Garden orach and sweet quinoa seeds were similar in fat and ash contents, while garden orach seeds contained ≈10% more protein. Starches were isolated from seeds following a 12-hr soak in dilute alkaline solution using a series of grinding, screening, centrifugation, and washing steps. Isolated starches viewed by scanning electron microscopy yielded angular, polygonal granules ≈1–2 μm in diameter. Starches displayed typical A-type crystalline packing arrangements as determined by X-ray powder diffractometry. Apparent amylose contents for garden orach (21.2%), sweet quinoa (20.6%), and bitter quinoa (19.8%) were determined according to colorimetric procedure. Differential scanning calorimetry data indicated a higher and wider gelatinization temperature range for gar...