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811.
Starches from normal, waxy, and sugary‐2 (su2) corn kernels were isolated, and their structures and properties determined. The total lipid contents of normal, waxy, and su2 corn starches were 0.84, 0.00, and 1.61%, respectively. Scanning electron micrographs showed that normal and waxy corn starch granules were spherical or angular in shape with smooth surfaces. The su2 starch granules consisted of lobes that resembled starch mutants deficient in soluble starch synthases. Normal and waxy corn starches displayed A‐type X‐ray patterns. The su2 starch showed a weak A‐type pattern. The chain‐length distributions of normal, waxy, and su2 debranched amylopectins showed the first peak chain length at DP (degree of polymerization) 13, 14, and 13, respectively; second peak chain length at DP 45, 49, and 49, respectively; and highest detectable DP of 80, 72, and 76, respectively. The su2 amylopectin showed a higher percentage of chains with DP 6–12 (22.2%) than normal (15.0%) and waxy (14.6%) amylopectins. The absolute amylose content of normal, waxy, and su2 starches was 18.8, 0.0, and 27.3%, respectively. Gel‐permeation profiles of su2 corn starch displayed a considerable amount of intermediate components. The su2 corn starch displayed lower gelatinization temperature, enthalpy change, and viscosity; a significantly higher enthalpy change for melting of amylose‐lipid complex; and lower melting temperature and enthalpy change for retrograded starch than did normal and waxy corn starches. The initial rate of hydrolysis (3 hr) of the corn starches followed the order su2 > waxy > normal corn. Waxy and su2 starches were hydrolyzed to the same extent, which was higher than normal starch after a 72‐hr hydrolysis period. 相似文献
812.
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). 相似文献
813.
Flours and starches from rough rice dried using different treatment combinations of air temperature (T) and relative humidity (RH) were studied to better understand the effect of drying regime on rice functionality. Rough rice from cultivars Bengal and Cypress were dried to a moisture content of ≈12% by three drying regimes: low temperature (T 20°C, RH 50%), medium temperature (T 40°C, RH 12%), and high temperature (T 60, RH 17%). Head rice grains were processed into flour and starch and evaluated for pasting characteristics with a Brabender Viscoamylograph, thermal properties with differential scanning calorimetry, starch molecular‐size distribution with high‐performance size‐exclusion chromatography (HPSEC), and amylopectin chain‐length distribution with high‐performance anion‐exchange chromatography with pulsed amperometric detection (HPAEC‐PAD). Lower head rice and starch yields were obtained from the batch dried at 60°C which were accompanied by an increase in total soluble solids and total carbohydrates in the pooled alkaline supernatant and wash water used in extracting the starch. Drying regime caused no apparent changes on starch molecular‐size distribution and amylopectin chain‐length distribution. Starch fine structure differences were due to cultivar. The pasting properties of flour were affected by the drying treatments while those of starch were not, suggesting that the grain components removed in the isolation of starch by alkaline‐steeping were important to the observed drying‐related changes in rice functionality. 相似文献
814.
James A. Patindol Terry J. Siebenmorgen Ya‐Jane Wang Sarah B. Lanning Paul A. Counce 《Cereal Chemistry》2014,91(4):350-357
The structural features of starch were examined to better understand the causes of variability in rice quality resulting from nighttime air temperature (NTAT) incidence during kernel development. Starch samples were isolated from head rice of four cultivars (Bengal, Cypress, LaGrue, and XL723) field‐grown in four Arkansas locations (Keiser, Pine Tree, Rohwer, and Stuttgart) in 2009 and 2010. Average NTATs recorded during the grain‐filling stages of rice reproductive growth in the four locations were 3.0–8.4°C greater in 2010 than 2009. Elevated NTATs altered the deposition of starch in the rice endosperm. Means pooled across cultivars and locations showed that amylose content was 3.1% (percentage points) less for the 2010 sample set. The elevated NTATs in 2010 resulted in a decrease in the percentage of amylopectin short chains (DP ≤ 18) and a corresponding increase in the percentage of long chains (DP ≥ 19) by an average of 1.3% (percentage points). The greater NTATs in 2010 also produced greater starch paste peak, final, and breakdown viscosities, whereas setback and total setback viscosities decreased. Changes in paste viscosity were highly correlated with the changes in the proportion of amylose and amylopectin. Onset gelatinization temperature was greater by 3.5°C, gelatinization enthalpy by 1.3 J/g, and relative crystallinity by 1.5% (percentage points) for the 2010 sample set. Changes in gelatinization parameters and granule relative crystallinity were highly correlated with the changes in amylopectin chain‐length distribution. Year × cultivar × location interaction effects were statistically insignificant, indicating that the four cultivars evaluated all showed some degree of susceptibility to the effects of temperature incidence during kernel development, regardless of the growing location. 相似文献