Cross‐Linked Resistant Starch: Preparation and Properties

Resistant starches (RS) were prepared by phosphorylation of wheat, waxy wheat, corn, waxy corn, high‐amylose corn, oat, rice, tapioca, mung bean, banana, and potato starches in aqueous slurry (≈33% starch solids, w/w) with 1–19% (starch basis) of a 99:1 (w/w) mixture of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) at pH 10.5–12.3 and 25–70°C for 0.5–24 hr with sodium sulfate or sodium chloride at 0–20% (starch basis). The RS₄ products contain ≤100% dietary fiber when assayed with the total dietary fiber method of the Association of Official Analytical Chemists (AOAC). In vitro digestion of four RS₄ wheat starches showed they contained 13–22% slowly digestible starch (SDS) and 36–66% RS. However after gelatinization, RS levels fell by 7–25% of ungelatinized levels, while SDS levels remained nearly the same. The cross‐linked RS₄ starches were distinguished from native starches by elevated phosphorus levels, low swelling powers (≈3g/g) at 95°C, insolubilities (<1%) in 1M potassium hydroxide or 95% dimethyl sulfoxide, and increased temperatures and decreased enthalpies of gelatinization measured by differential scanning calorimetry.     

Wet‐Milling Characteristics of 10 Lines from Germplasm Enhancement of Maize Project Compared with Five Corn Belt Lines

The use of corn (Zea mays L.) hybrids with high grain yield and starch extractability has steadily increased in the processing industry. In light of widespread corn seed industry participation in the Germplasm Enhancement of Maize Project (GEM), which seeks to enhance exotic germplasm, future hybrids may contain more exotic sources in genetic backgrounds. It is necessary to establish and monitor physical, compositional, and milling characteristics of the new exotic breeding materials to determine the processing value. The present study was conducted to determine the wet‐milling characteristics of a set of GEM lines compared with typical Corn Belt lines. Ten GEM lines introgressed with exotic materials from Argentina, Chile, Cuba, Florida, and Uruguay and previously identified as having different starch yields, three commercial inbred lines, and two public inbred lines (B73 and Mo17) were analyzed using both near‐infrared transmittance (NIT) and a 100‐g wet‐milling procedure. There were statistical differences (P < 0.05) in the yield of wet‐milled fractions (starch, fiber, gluten, and germ). The GEM lines AR16035:S19‐227‐1‐B and CUBA117:S1520‐562‐1‐B had similar or better starch yield and starch recovery than B73 and the other adapted inbred lines, indicating that they may be useful in improving the proportion of extractable starch present in kernels of hybrids. Residual protein levels in the starch and gluten fractions were 0.26–0.32% and 38–45%, respectively. The starch yield of GEM lines from wet milling correlated positively with starch content from NIT and was negatively correlated with protein content of the corn kernels. Oil content in the germ varied from 50 to 60%. Our results indicate that incorporating GEM lines in a breeding program can maintain or even improve wet‐milling characteristics of Corn Belt materials if lines with appropriate traits are used.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches I. Pasting Properties

A series of cross‐linked (0, 0.014, 0.018, 0.024, and 0.028% POCl₃, dry starch basis) hydroxypropylated (8%) corn starches were extruded using a Leistritz micro‐18 co‐rotating extruder. Process variables included moisture, barrel temperature, and screw design. Differential scanning calorimetry and X‐ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of the extruded starches were examined using a Rapid Visco Analyser. Pasting profiles of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content during extrusion and level of cross‐linking increased starch viscosity (P < 0.0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross‐linking and screw design and between extrusion temperature and starch moisture content (P < 0.0001).     

Properties of Cross‐Linked Starch from Waxy Mutant Wheat Tanikei A6599‐4

Native starch from waxy mutant wheat Tanikei A6599‐4 is known to exhibit more stable hot paste viscosity than a typical waxy wheat (Tanikei H1881) and waxy corn. The objective of this study was to investigate the starch paste properties of Tanikei A6599‐4 after cross‐linking and compare with Tanikei H1881 and waxy corn. As an example of cross‐linking, the reaction (at 30, 60, 120, and 360 min) with sodium trimetaphosphate was used. In Rapid Visco Analyser (RVA) measurement, the unique characteristic was maintained in Tanikei A6599‐4 starch cross‐linked at low reaction time (<120 min) levels. Cross‐linking at a high reaction time (360 min) level suppressed the swelling of both Tanikei A6599‐4 and Tanikei H1881 starches but not waxy corn starch. Although unmodified Tanikei A6599‐4 starch showed the lowest paste clarity among unmodified waxy starches, this defect became unremarkable when starch was cross‐linked for ≥120 min. In gel‐dispersed dynamic viscoelasticity measurement, the order of G′ and G″ values was always Tanikei A6599‐4 > Tanikei H1881 > waxy corn. This indicates that cross‐linked Tanikei A6599‐4 and Tanikei H1881 starches have different starch properties and that swollen Tanikei A6599‐4 starch granules are more rigid than swollen Tanikei H1881 starch granules.     

Effect of Harvest Moisture Content on Selected Yellow Dent Corn: Dry‐Grind Fermentation Characteristics and DDGS Composition

Efficiently utilizing the nongrain portion of the corn plant as ruminant food and the grain for ethanol will allow the optimization of both food and fuel production. Corn and corn stover could be more effectively used if they were harvested earlier before dry down. Corn harvested at different moisture contents (MCs) may exhibit different processing characteristics for the ethanol industry, because of differences in physical and chemical properties. Therefore, the objective of this study was to investigate the effect of corn harvest MC on dry‐grind fermentation characteristics and dried distillers grains with solubles (DDGS) composition. Pioneer hybrid 32D78 was harvested at seven different dates from August 21 to November 23, 2009, with harvest MCs ranging from 73 to 21% (wb). The corn samples with different harvest MCs were evaluated by a conventional dry‐grind process. Final ethanol concentration from the corn with harvest MC of 54% (kernel dent stage) was 17.9% (v/v), which was significantly higher (0.5–1.2 percentage points) than the mature corn with lower harvest MCs (P < 0.05). Ethanol conversion efficiencies for the corn with harvest MCs of 73 and 54% (wb) were 98.5 and 93.2%, respectively, whereas ethanol conversion efficiencies for the corn with lower harvest MCs were significantly lower (P < 0.05), ranging between 83.2 and 88.3%. For DDGS composition, with corn harvest MC decreasing from 73 to 21% (wb), the residual starch concentration increased from 7.7 to 15.2%, the crude protein concentration decreased from 29.4 to 24.9%, and the neutral detergent fiber concentration decreased from 26.6 to 20.6%.     

Molecular Characterization of Corn Starch Using an Aqueous HPSEC‐MALLS‐RI System Under Various Dissolution and Analytical Conditions

Molecular characteristics based on absolute weight‐average molecular weight (M_w) and z‐average radius of gyration (R_g) of normal corn starch were analyzed by high‐performance size‐exclusion chromatography (HPSEC) attached to multiangle laser‐light scattering (MALLS) and refractive index (RI) detectors under different starch dissolution and analytical conditions. Autoclaving (121°C, 20 min) or microwave heating (35 sec) provided better HPSEC recovery and higher M_w for starch molecules than simple dissolution in hot water. The M_w for the autoclaved corn amylopectin and amylose fractions separated with a TSK G5,000 column at 60°C were 201 × 10⁶ and 3.3 × 10⁶, respectively. The specific volume for gyration (SV_g) calculated from M_w and R_g could be used for the comparison of molecular compactness which was inversely related to the degree of branching. The SV_g values of amylopectin and amylose fractions in the chromatogram (TSK G5,000, autoclaved for 20 min) were 0.092 and 0.529, respectively. But a portion (20–30%) of large amylopectin molecules did not pass the injection membrane filter (3.0 μm) and the SEC column, resulting in incomplete recovery. The unfiltered portion varied according to the dissolution treatment. Homogenization (7,000 rpm, 5 or 10 min) of the starch solution improved the recovery of the amylopectin fraction, but significantly increased the M_w of the amylose fraction (17 × 10⁶). Sonication for 5 min degraded starch molecules. For accurate analysis of a native starch using an aqueous SEC, the starch should be fully dissolved with proper treatment such as autoclaving or microwaving, and the column should be improved for full recovery of large amylopectin molecules.     

Cover‐crop seeding‐date influence on fall nitrogen recovery

Planting cover crops after corn‐silage harvest could have a critical role in the recovery of residual N and N from fall‐applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004–2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover‐crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover‐crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha^–1, respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha^–1. While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover‐crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no–cover crop treatment. Corn‐silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid‐October. Corn‐ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter‐kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn‐ear yield up to 59% compared with corn‐ear yield planted after no cover crop.     

Extraction of β‐Glucan from Oats for Soluble Dietary Fiber Quality Analysis

Extraction protocols for β‐glucan from oat flour were tested to determine optimal conditions for β‐glucan quality testing, which included extractability and molecular weight. We found mass yields of β‐glucan were constant at all temperatures, pH values, and flour‐to‐water ratios, as long as sufficient time and enough repeat extractions were performed and no hydrolytic enzymes were present. Extracts contained about 30–60% β‐glucan, with lower proportions associated with higher extraction temperatures in which more starch and protein were extracted. All commercial starch hydrolytic enzymes tested, even those that are considered homogenous, degraded β‐glucan apparent molecular weight as evaluated by size‐exclusion chromatography. Higher concentration β‐glucan solutions could be prepared by controlling the flour‐to‐water ratio in extractions. Eight grams of flour per 50 mL of water generated the highest native β‐glucan concentrations. Routine extractions contained 2 g of enzyme‐inactivated flour in 50 mL of water with 5mM sodium azide (as an antimicrobial), which were stirred overnight, centrifuged, and the supernatant boiled for 10 min. The polymer extracted had a molecular weight of about 2 million and was stable at room temperature for at least a month.     

Influence of Yellow Foxtail on Corn Growth and Yield

Abstract

Yellow foxtail [Setaria pumila syn. Setaria glauca (L.) Beauv.] competitive influence on corn (Zea mays L.) growth and yield was investigated at Brookings, South Dakota, and Morris, Minnesota, in 1995 and 1996. Yellow foxtail was seeded at different densities, and at Morris, two levels of nitrogen (N) were applied. Corn biomass measured at V‐6 or V‐8, silking, and harvest and grain yield were correlated negatively to foxtail biomass and density, but the loss differed between years and sites. Nitrogen increased corn growth and decreased yield loss. Defining a single foxtail density or biomass that resulted in a maximum yield loss of 10% was not possible. The most conservative estimate was 3 yellow foxtail plants m^?2 or 24 g m^?2 of yellow foxtail biomass, but ranged up to 55 plants m^?2 and 256 g m^?2 when weather conditions and N were optimal.     

Synergistic Hydrolysis of Crude Corn Starch by α‐Amylases and Glucoamylases of Various Origins

Four α‐amylases and two glucoamylases from various sources, in eight combinations, were used to study the synergistic hydrolysis of crude corn starch at various temperatures. At 40 and 50°C, the combinations containing Rhizopus mold glucoamylase enhanced hydrolysis of corn starch compared wth that obtained with the combinations from Aspergillus niger. At 60°C, Rhizopus mold combinations gave low reaction yields as the enzyme was inactivated. The differences observed between α‐amylases are smaller, with the exception of Bacillus licheniformis α‐amylase, which presented more than twice the productivity of the other α‐amylases, at all temperatures. In terms of substrate conversion at 5 hr of hydrolysis, the combination of B. licheniformis α‐amylase with Rhizopus mold glucoamylase at 50°C presents 76% substrate conversion, whereas, with all the other combinations, starch conversion was 13–73%. HPLC analysis of the reaction products obtained at 50°C showed that the main product of corn starch hydrolysis was glucose at 85–100%. Further experiments showed that A. niger glucoamylase and B. licheniformis α‐amylase were the only enzymes that retained their initial activity after incubation at the temperatures studied.     

Gelatinization Properties of Starches from Three Successive Generations of Six Exotic Corn Lines Grown in Two Locations

The objectives of this research were to evaluate the intra‐ and interpopulation variability in gelatinization properties of starches from exotic corn lines and their derivatives when grown 1) during two successive years in the same location; and 2) in both temperate and tropical environments. Six novel exotic corn lines (two 100% exotic and four 25% exotic derived from a breeding cross developed by crossing an exotic hybrid with Corn Belt lines) were selected for this research because their starches have significantly different (and potentially useful) thermal properties from those found in starch from normal Corn Belt corn. The S_n (n = 3 for 25% exotic lines and n = 1 for 100% exotic lines) generations of the six exotic lines were self‐pollinated and grown in the winter nursery in Puerto Rico. Two successive generations (S_n+1 and S_n+2) of lines selected for low onset of gelatinization temperature were self‐pollinated and grown in the same environment near Ames, IA. To evaluate the effect of environment, the S_n+2 generation also was self‐pollinated and grown in the winter nursery in Puerto Rico. Thermal properties of starches from 10 single kernels from each line were analyzed by using differential scanning calorimetry (DSC) at a ratio of 4 mg of dry starch to 8 mg of distilled water. After subsequent generations, the differences in DSC gelatinization properties between selected kernels within each progeny line narrowed, suggesting increased homogeneity of starch structural properties within each line. Unusual thermal properties were fixed in some progeny lines. Environmental factors also affected the thermal properties of starch and a significant interaction between environment and genotype was observed. These results suggest that introgression of adapted germplasm with useful genes from exotic corn would increase the available genetic variability for starch functionality and allow the development of hybrids with important value‐added traits.     

Chemical and Physical Characteristics of Proso Millet (Panicum miliaceum)‐Based Products

Celiac disease and gluten sensitivities, as well as obesity and overweight‐related disorders, have led to the investigation of gluten‐free grains and development of new food products. To address this, refined proso millet and refined corn (control), both gluten‐free grains, were used to produce four different product types (muffin, couscous, extruded snack, and porridge). The products contained four different grain combinations (100% proso millet, 75% proso millet/25% corn, 25% proso millet/75% corn, and 100% corn). All products were evaluated for their nutritional composition, in vitro starch digestibility, and expected glycemic index (eGI). Products made with refined proso millet had increased protein (7.6–11.3%), lipid (1.2–6.1%), fiber (7.0–8.8%), and phenolic content (323.5–425 μg/g) compared with those incorporating corn flour (2.5–9.0%, 0.8–4.0%, 2.1–4.1%, and 213–315 μg/g, respectively). As the proso millet content increased, the eGI decreased significantly (P < 0.05). Products made from refined proso millet appear to be good candidates for producing low‐GI, gluten‐free foods.     

Maize Proximate Composition and Physical Properties Correlations to Dry‐Grind Ethanol Concentrations

Dry‐grind ethanol plants incur economic losses because of seasonal variations in ethanol yields. One possible cause associated with ethanol yield variability is incoming grain quality. There is little published information on factors causing variation in dry‐grind ethanol concentrations. The objective of this study was to determine relationships between rapidly measurable corn quality attributes (physical parameters and chemical composition) and dry‐grind ethanol concentrations. Corn samples obtained from a Midwestern ethanol plant were analyzed for physical quality parameters (test weight, kernel weight, true density, percent stress cracks, and moisture content) and composition (starch, protein, oil, and soluble sugars contents) and then processed with a laboratory‐scale dry‐grind procedure. There were significant (P < 0.05) variations in corn quality parameters and ethanol concentrations. Correlation coefficients were significant (P < 0.05) but low (–0.50 < r < 0.50) between starch content and final ethanol concentrations (72 h) and total soluble sugar content and ethanol concentrations at 72 and 48 h. Ethanol concentrations (at 24, 48, and 72 h) were predicted as a function of a combination of grain quality factors using multiple regression methods; however, the R² values obtained were low. Variations in ethanol concentrations were not related to physical and chemical composition quality factors. Other factors, such as structural and physiologic attributes of corn grain, need to be evaluated.     

Effect of Stress Cracks on Corn Wet‐Milling Yields

U.S. No. 2 yellow dent corn was randomly probe‐sampled from rail cars being shipped to a wet‐milling plant from a Corn Belt local elevator. The probe samples were blended together and kernels were sorted into four levels of stress cracks (0, 1, 2, or multiple). Each level of stress cracking was then laboratory wet‐milled in triplicate. The only statistically observed differences were in total fiber and in protein content of the gluten meal fraction. The starch yield difference between zero stress cracked corn and multiple stress cracked corn was smaller (0.8%) than would be expected if stress cracking were an indicator of damage to the wet‐milling characteristics of the corn.     

Influence of Stenocarpella maydis Infected Corn on the Composition of Corn Kernel and Its Conversion into Ethanol

Widespread epidemics of Stenocarpella ear rot (formerly Diplodia ear rot) have occurred throughout the central U.S. Corn Belt in recent years, but the influence of S. maydis infected grain on corn ethanol production is unknown. In this study, S. maydis infected ears of variety Heritage 4646 were hand‐harvested in 2010 from a production field in central Illinois and segregated into one of five levels of ear rot severity based upon visual symptoms. The concentration of ergosterol, a sterol produced by fungi but not plants, was observed to increase with the severity of ear rot (127–306.5 μg/g), and none was detected in the control corn. Corn test weight declined with progression of the disease and was 42.6% lower for the most severely rotted grain from ears infected early in their development. Accompanying changes in composition were also apparent. Crude fat and oil contents decreased (from 4.7 to 1.5%) and fiber increased (from 6.6 to 9.6%), but starch content remained largely invariant. Oil composition also varied among the infected samples. Control and infected corn samples were subjected to ethanol fermentation with a laboratory‐scale corn dry‐grind ethanol process. Ethanol yields for control and infected samples were similar on an equivalent weight basis (2.77–2.85 gal/bu). In comparison with the control, S. maydis infection altered the distillers dried grains with solubles (DDGS) properties, wherein the crude protein was significantly higher and oil significantly reduced, and ash, fiber, and yield per ton were not significantly different. Based upon these results, we conclude that Stenocarpella ear rot has the potential to affect DDGS composition but not ethanol yield on an equivalent weight basis.     

Effects of Amylose,Corn Protein,and Corn Fiber Contents on Production of Ethanol from Starch‐Rich Media

The effects of amylose, protein, and fiber contents on ethanol yields were evaluated using artificially formulated media made from commercial corn starches with different contents of amylose, corn protein, and corn fiber, as well as media made from different cereal sources including corn, sorghum, and wheat with different amylose contents. Second‐order response‐surface regression models were used to study the effects and interactions of amylose, protein, and fiber contents on ethanol yield and conversion efficiency. The results showed that the amylose content of starches had a significant (P < 0.001) effect on ethanol conversion efficiency. No significant effect of protein content on ethanol production was observed. Fiber did not show a significant effect on ethanol fermentation either. Conversion efficiencies increased as the amylose content decreased, especially when the amylose content was >35%. The reduced quadratic model fits the conversion efficiency data better than the full quadratic model does. Fermentation tests on mashes made from corn, sorghum, and wheat samples with different amylose contents confirmed the adverse effect of amylose content on fermentation efficiency. High‐temperature cooking with agitation significantly increased the conversion efficiencies on mashes made from high‐amylose (35–70%) ground corn and starches. A cooking temperature of ≥160°C was needed on high‐amylose corn and starches to obtain a conversion efficiency equal to that of normal corn and starch.     

Comparison of Methods for Amylose Screening Among Amylose‐Extender (ae) Maize Starches from Exotic Backgrounds

Breeding for high‐amylose corn requires a rapid analytical method for determining starch amylose so that generating wet chemistry values does not pose a major limitation in the volume of materials that can be screened. Two methods for determining apparent amylose content (AAC) were examined and compared with an iodine‐binding method involving the solubilization of isolated starch in a sodium hydroxide solution (method 1). These methods included one based on near‐infrared transmittance spectroscopy (NIRT) (method 2) and another iodine‐binding method involving the solubilizing of starch from ground whole corn with a DMSO‐iodine solution (method 3). These methods were chosen because, aside from initial set up costs, they are relatively rapid and inexpensive to perform. The materials evaluated consisted of various exotic corn populations including plant introductions and experimental materials generated from the Germplasm Enhancement of Maize (GEM) project. Crosses were made between these materials and a Corn Belt dent hybrid (OH43 × H99) converted with the amylose‐extender (ae) allele. Grain from F2 ears, presumed to be homozygous for the ae allele based on visual selection of mutant kernels on F1 ears from which they were planted, were then evaluated to identify possible modifiers of ae conditioning high starch AAC. From a total of 1,006 F2 ears, a core set consisting of 155 samples was established and only these were subjected to starch AAC analysis, using all three methods to compare the methods. Method 2 showed poor correlation to method 1 (r = 0.88), however, NIRT did appear to discriminate between samples converted to ae vs. those with a normal or possibly segregating endosperm type. Method 3 showed a slightly better correlation with method 1 (r = 0.92) and appeared to more fully discriminate among samples with AAC values >65% from those at ≈55%. Results from this study suggest that NIRT may be useful when a quick screening method is needed to discriminate mutant from nonmutant genotypes within grain samples of exotic germplasm especially when visual identification is difficult. In addition, method 3 could be used to replace the more time‐consuming method 1 when trying to identify high AAC levels among ae genotypes, even though some inconsistency was observed between the two methods. Finally, this study revealed that exotic germplasm may be an important source of new modifiers to the ae allele because values as high as 70% AAC were identified.     

Plant‐available nitrogen in the soil: Relationships between pre‐plant and pre‐sidedress nitrate tests for corn production

Corn (Zea mays L.) producers in the rainfed regions sometimes sidedress fertilizer N according to pre‐plant–nitrate test (PPNT) results based on the assumption that there is a linear relationship between pre‐sidedress nitrate test (PSNT) and the PPNT. There has been no report on such relationship in Ontario (Canada) and elsewhere in the nonirrigated corn‐growing regions. A field study was conducted near Ottawa, Canada for 7 y to (1) determine changes in soil available N from pre‐planting to shortly after the sidedress stage (late June) for corn and (2) establish a quantitative relationship between PPNT and PSNT. In each year, soil samples from fields of three to four plot experiments with different cropping histories, soil textures, and management levels, taken at 7 to 10 d intervals, and from on‐farm trials taken at pre‐planting and pre‐sidedress, were extracted with 2 M KCl. The concentrations of NO ‐N were determined colorimetrically. It was found that soil NO ‐N concentration of PSNT was a linear function of PPNT with an average slope of 1.7. However, the slope of the regression equations differed dramatically among cropping sequences, and to a lesser extent, soil textures. The NO ‐N concentration after planting to pre‐sidedress was influenced by air temperature and precipitation during this period of time. Both PPNT and PSNT positively correlated with corn‐grain yield. Our data suggest that cautions must be taken when deciding the rate of fertilizer N for sidedress application to corn based on PPNT test, especially under more humid northern climate conditions.     

Starch Characteristics of the Rice Mutant du2‐2 Taichung 65 Highly Affected by Environmental Temperatures During Seed Development

The effects of environmental temperature (21 vs. 28°C) during rice seed development on the starch characteristics (apparent amylose content, amylopectin chain length distribution, and gelatinization properties) of nonwaxy Taichung 65 (T65), waxy Taichung (T65wx), du2‐2 mutated low‐amylose strain Taichung (76‐3/T65), and Koshihikari were studied. Amylose contents increased with decreasing environmental temperatures. Analysis of the amylopectin chain length distribution showed that the relative amounts of long chains with degree of polymerization (DP) > 25 in all starches decreased if maturation occurred at 21°C. Gelatinization onset, peak, and conclusion temperatures and enthalpies decreased with decreasing environmental temperatures. Of all starches studied, the du2‐2 mutated low‐amylose Taichung (76‐3/T65) was most affected by maturation temperatures. These results indicate that the du2‐2 mutated low‐amylose Taichung (76‐3/T65) may be a useful strain in understanding biochemical and genetic starch biosynthesis response to slight changes in temperature.     

Preparation and Properties of Oxidized Corn Starches by Semi-Dry Process

Oxidized corn starch prepared by a semi-dry process using hydrogen peroxide as an oxidant was studied. The optimum oxidation conditions of corn starch were mole ratio of H₂O₂ and anhydroglucose unit (0.219); mole ratio of NaOH and anhydroglucose unit (0.144); moisture content of the reaction mixture (27.2%); and reaction temperature (65°C). Compared with oxidized corn starch produced by reacting starch with sodium hypochlorite in alkaline slurry, oxidized corn starches produced by a semi-dry process apparently had different properties. Oxidation by a semi-dry process for corn starch resulted in significant changes in the degree of crystallinity of starch and the changes increased with the increase of carboxyl content of starch. Peak viscosities of oxidized starches produced by a semi-dry process were lower than those of commercial corn starch at similar carboxyl contents, while the final viscosities and setbacks of the former were much higher than the latter. There were apparent differences for texture properties among oxidized starches prepared by different processes. Onset temperature, peak temperature, and conclusion temperature of semi-dry oxidation starches were higher than those of commercial oxidized starch, while the enthalpy of gelatinization of the former were lower than the latter.