Hongxin Jiang

Variations in starch physicochemical properties from a generation-means analysis study using amylomaize V and VII parents.

GEMS-0067 (PI 643420) maize line is a homozygous mutant of the recessive amylose-extender (ae) allele and an unknown number of high-amylose modifier (HAM) gene(s). GEMS-0067 produces starch with a approximately 25% higher resistant-starch (RS) content than maize ae single-mutant starches. The objective of this study was to understand how the HAM gene(s) affected the RS content and other properties of ae-background starches. Nine maize samples, including G/G, G/F1, G/H, F1/G, F1/F1, F1/H, H/G, H/F1, and H/H with HAM gene-dosages of 100, 83.3, 66.7, 66.7, 50, 33.3, 33.3, 16.7, and 0%, respectively, were produced from self- and intercrosses of GEMS-0067 (G), H99ae (H), and GEMS-0067xH99ae (F1) in a generation-means analysis (GMA) study. RS contents of examined starches were 35.0, 29.5, 28.1, 32.0, 28.2, 29.4, 12.9, 18.4, and 15.7%, respectively, which were significantly correlated with HAM gene-dosage (r = 0.81, p < 0.01). Amylose content, number of elongated starch granules, and conclusion gelatinization temperature increased with the increase in HAM gene-dosage. X-ray diffraction study showed that the relative crystallinity (%) of starch granules decreased with the increase in HAM gene-dosage. The results suggested that the HAM gene-dosage was responsible for changes in starch molecular structure and organization of starch granules and, in turn, the RS formation in the maize ae mutant starch.

Starch characterization and ethanol production of sorghum.

This study aimed to characterize and compare the chemical structures, physical properties, and enzymatic hydrolysis rates of five sorghum starches (6B73, 6C21, 6C69, 7R34, and X789) with that of corn starch (B73). Sorghum kernels consisted of 68.7-70.6% starch, more than the B73 corn (67.4%). Sorghum starches displayed higher gelatinization temperatures (66.6-67.4 °C), greater gelatinization enthalpy changes (13.0-14.0 J/g), and greater percentages of retrogradation (60.7-69.1%), but slower enzymatic hydrolysis rates (83.8-87.8% at 48 h) than the B73 corn starch (61.7 °C, 10.1 J/g, 51.5%, and 88.5%, respectively). These differences could result from the sorghum amylopectins consisting of fewer short branch chains (DP 6-12) (12.8-14.0%) than the corn amylopectin (15.0%). The sorghum starches showed greater peak and breakdown viscosities but lower setback viscosities than the B73 corn starch, resulting from the lower amylose content of the sorghum starches. After 96 h of fermentation, most ground sorghums exhibited lower ethanol yields (30.5-31.8%) than the ground B73 corn (31.8%).

Resistant-Starch Formation in High-Amylose Maize Starch during Kernel Development

The objective of this study was to understand the resistant-starch (RS) formation during kernel development of a high-amylose maize, GEMS-0067 line. The RS content of the starch, determined using AOAC method 991.43 for total dietary fiber, increased with kernel maturation and increase in the amylose/intermediate component (IC) content of the starch. Gelatinization of the native starches showed a major thermal transition with peak temperature at 76.6-81.0 degrees C. An additional peak ( approximately 97.1 degrees C) first appeared 20 days after pollination and then developed into a significant peak on later dates. After removal of lipids from the starch, this peak disappeared, but the conclusion gelatinization temperature remained the same. The proportion of the enthalpy change of the thermal transition above 95 degrees C, calculated from the thermogram of the defatted starch, increased with kernel maturation and was significantly correlated with the RS content of the starch (r = 0.98). These results showed that the increase in crystallites of amylose/IC long-chain double helices in the starch resulted in the increase in the RS content of the starch during kernel development.

Physicochemical properties and digestibility of common bean (Phaseolus vulgaris L.) starches

Physicochemical properties and digestibility of pinto bean, red kidney bean, black bean and navy bean starches were analyzed. All the common bean starches had oval and spherical granules with average diameter of 25.3-27.4 μm. Amylose contents were 32.0-45.4%. Black bean starch showed the highest peak viscosity, breakdown, final viscosity and setback, whereas red kidney bean starch showed the lowest pasting temperature, peak viscosity, breakdown, and setback. Pinto bean starch showed the highest onset and peak gelatinization temperatures, and the lowest gelatinization temperature range; whereas navy bean starch exhibited the lowest values. Amylopectin of red kidney bean had the highest molecular weight (Mw) and z-average gyration radius (Rz), whereas black bean amylopectin had the lowest values of Mw and Rz. The proportions of DP 6-12, DP 13-24, DP 25-36, and DP ≥ 37 and average branch-chain lengths were 23.30-35.21%, 47.79-53.53%, 8.99-12.65%, 6.39-13.49%, and 17.91-21.56, respectively. All the native bean starches were highly resistant to enzyme digestion.

Characterization of normal and waxy corn starch for bioethanol production.

Objectives of this study were to compare ethanol production between normal and waxy corn using a cold fermentation process and to understand effects of starch structures and properties on ethanol production. Ethanol yields positively correlated (p < 0.01) with starch contents of kernels of the normal and waxy corn. The average starch-ethanol conversion efficiency of waxy corn (93.0%) was substantially greater than that of normal corn (88.2%). Waxy corn starch consisted of very little amylose and mostly amylopectin that had a shorter average branch chain length than normal corn amylopectin. Regression analyses showed that average amylopectin branch chain lengths and percentage of long branch chains (DP > 37) of waxy corn starch negatively correlated with the starch hydrolysis rate and the ethanol yield. These results indicated that starch structures and properties of the normal and waxy corn had significant effects on the ethanol yield using a cold fermentation process.

Increased Butyrate Production During Long-Term Fermentation of In Vitro-Digested High Amylose Cornstarch Residues with Human Feces

An in vitro semi-continuous long-term (3 wk) anaerobic incubation system simulating lower gut fermentation was used to determine variability in gut microbial metabolism between 4 predigested high amylose-resistant starch residues (SR): SRV, SRVI, SRVII, and SRGEMS in human fecal samples. Subjects participated twice, 5 mo apart: 30 in Phase I (15 lean, 9 overweight and 6 obese), 29 in Phase II (15 lean, 9 overweight, 5 obese); 13 of 15 lean subjects participated in both phases. Of the 4 SRs, SRV displayed the highest gelatinization temperature, peak temperature, enthalpy changes, and the least digestibility compared with the other SRs. In both phases, compared with blank controls, all SRs increased butyrate ∼2-fold which stabilized at week 2 and only SRV caused greater propionate concentration (∼30%) after 3 wk which might have been partly mediated by its lesser digestibility. Fecal samples from lean and overweight/obese subjects incubated with SRs showed similar short-chain fatty acid production across both time points, which suggests that resistant starch may benefit individuals across BMIs.

Dosage Effect of High-Amylose Modifier Gene(s) on the Starch Structure of Maize amylose-extender Mutant

The objective of this study was to investigate how dosages of high-amylose modifier (HAM) gene(s) affected the structure of maize amylose extender (ae) mutant starch. GEMS-0067 (G), a homozygous mutant of ae and the HAM gene(s), and H99ae (H), an ae single mutant, were self-pollinated or inter-crossed to produce maize endosperms of G/G, G/H, H/G, and H/H with 3, 2, 1, and 0 doses of HAM gene(s), respectively. Endosperm starch was fractionated into amylopectin, amylose, and intermediate component (IC) of large and small molecular weights using 1-butanol precipitation of amylose followed by gel-permeation chromatography. Increases in the dosage of HAM gene(s) from 0 to 3 decreased the amylopectin content. The HAM-gene dosage significantly changed the branch chain-length of small-molecular-weight IC, but had little effect on the branch chain-length distributions of amylopectin and large-molecular-weight IC and the molecular structure of amylose.