Yong-Cheng Shi

The structure of four waxy starches related to gelatinization and retrogradation

Abstract Starches from two waxy rices, a waxy maize, a waxy barley showed onset temperatures ( T o ) of gelatinization in excess of water of 349.2, 340.5, 339.1, and 331.1 K, respectively, as determined by differential scanning calorimetry. The T o values, as well as peak ( T p ) and final ( T c ) transition temperatures, decreased in the same order as their X-ray crystallinity. Annealing the starches increased T o and T p , but the differences remained the same. After lintnerization in 2.2 m HCl at 30°, the acid-resistant fractions from the four starches gave the same d.s.c. thermograms and the same constitutive molecular dextrins before and after debranching, as determined by high-performance anion-exchange chromatography with pulsed amperometric detection. Gels (50% water) of the four starches all had the same, but reduced T o values after retrogradation. These results indicate that the molecular structure of the microcrystalline region is the same in the four granular starches, and that T o is controlled indirectly by the surrounding amorphous regions. The retrogradation of the four waxy starches appeared to be directly proportional to the mole fraction of unit chains with d.p. 14–24 and inversely proportional to the mole fraction of unit chains with d.p. 6–9.

Production of very-high-amylose potato starch by inhibition of SBE A and B

High-amylose starch is in great demand by the starch industry for its unique functional properties. However, very few high-amylose crop varieties are commercially available. In this paper we describe the generation of very-high-amylose potato starch by genetic modification. We achieved this by simultaneously inhibiting two isoforms of starch branching enzyme to below 1% of the wild-type activities. Starch granule morphology and composition were noticeably altered. Normal, high-molecular-weight amylopectin was absent, whereas the amylose content was increased to levels comparable to the highest commercially available maize starches. In addition, the phosphorus content of the starch was increased more than fivefold. This unique starch, with its high amylose, low amylopectin, and high phosphorus levels, offers novel properties for food and industrial applications.

Fine structure of maize starches from four wx-containing genotypes of the W64A inbred line in relation to gelatinization and retrogradation

Maize starches from four wx-containing genotypes (wx, du wx, ae wx, and ae du wx) of the W64A inbred line were examined to determine their gelatinization and retrogradation properties and the fine structure of their amylopectins (AP). Chain-length distribution profiles of the APs showed distinct patterns according to genotype. The wx and du wx starches had a large proportion of short chains and showed A-type X-ray patterns, whereas the ae wx and ae du wx starches had a large proportion of long chains and showed B-type X-ray patterns. The ae wx starch had the highest values of onset melting temperature (To) and heat uptake (ΔH), both for gelatinization and after retrogradation, which were attributed to a greater proportion of long chains (degree of polymerization > 16) in the AP. Debranching of β-limit dextrins also revealed that the interior chain-length distribution of AP from the ae wx genotype constituted a large proportion of long chains. The extent of retrogradation increased in the order wx, du wx, ae wx and ae du wx starches and appeared to be proportional to the level of unit chains with DP 16–30 and inversely proportional to the level of short chains with DP 6–11.

Structure and Functional Properties of Sorghum Starches Differing in Amylose Content

Starches were isolated from grains of waxy, heterowaxy, and normal sorghum. To study the relationship between starch structure and functionality and guide applications of these starches, amylose content, amylopectin chain-length distributions, gelatinization and retrogradation, pasting properties, dynamic rheological properties, and in vitro enzyme digestion of raw starches were analyzed. Heterowaxy sorghum starch had intermediate amylose content, pasting properties, and dynamic rheological properties. Stress relaxation was a useful indicator of cooked starch cohesiveness. Cooked heterowaxy sorghum starch (10% solids) had a viscoelastic-solid type of character, whereas cooked waxy sorghum starch behaved like a viscoelastic liquid. Amylopectin of normal sorghum starch had a slightly higher proportion of chains with degree of polymerization (DP) of 6-15 (45.5%) compared with amylopectin of heterowaxy starch (44.1%), which had a gelatinization peak temperature 2 degrees C higher than normal sorghum starch. Heterowaxy sorghum starch contained significantly lower rapidly digestible starch (RDS) and higher resistant starch (RS) than waxy sorghum starch.

High‐amylose rice improves indices of animal health in normal and diabetic rats

A high-amylose rice with 64.8% amylose content (AC) was developed by transgenic inhibition of two isoforms of starch branching enzyme (SBE), SBEI and SBEIIb, in an indica rice cultivar. The expression of SBEI and SBEIIb was completely inhibited in the transgenic line, whereas the expression of granule-bound starch synthase was normal. Compared with wild-type rice, drastic reductions in both SBEs in the transgenic rice increased apparent AC in flour from 27.2% to 64.8%, resistant starch (RS) content from 0% to 14.6% and total dietary fibre (TDF) from 6.8% to 15.2%. Elevated AC increased the proportion of long unit chains in amylopectin and increased onset gelatinization temperature and resistance to alkaline digestion; however, kernel weight was decreased. A rat feeding trial indicated that consumption of high-amylose rice decreased body weight gain significantly (P < 0.01); increased faecal mass, faecal moisture and short-chain fatty acids; and lowered the faecal pH. An acute oral rice tolerance test revealed that the high-amylose rice had a positive effect on lowering the blood glucose response in diabetic Zucker fatty rats. This novel rice with its high AC, RS and TDF offers potential benefits for its use in foods and in industrial applications.

X-ray scattering studies of lignocellulosic biomass: A review

The high processing cost of lignocellulosic ethanol is one of the most important barriers to its profitable commercialization. Pretreatments have been used to change the structure of biomass significantly and to improve sugar and ethanol yield. Great efforts have been made to understand the structural changes of biomass during these processes, including the molecular assembly of crystalline cellulose. Wide-angle and small-angle X-ray scattering are powerful techniques in studying the biomass structure at a molecular level. In this review, after we introduce the basic structure of lignocellulosic biomass, the effects of commonly used pretreatment methods on biomass structure, and the principle of X-ray scattering technique, the application of X-ray scattering, including studies of crystallinity, crystallite size, orientation distribution, and pore structure, and the related results in biomass conversion are summarized and discussed. Future study of biomass with X-ray scattering also is proposed.

Wheat bran particle size influence on phytochemical extractability and antioxidant properties

It is unknown if particle size plays a role in extracting health promoting compounds in wheat bran because the extraction of antioxidant and phenolic compounds with particle size reduction has not been well documented. In this study, unmilled whole bran (coarse treatment) was compared to whole bran milled to medium and fine treatments from the same wheat bran. Antioxidant properties (capacity, ability, power), carotenoids and phenolic compounds (phenolic acids, flavonoids, anthocyanins) were measured and compared. The ability of whole bran fractions of differing particle size distributions to inhibit free radicals was assessed using four in vitro models, namely, diphenylpicrylhydrazyl radical-scavenging activity, ferric reducing/antioxidant power (FRAP) assay, oxygen radical absorbance capacity (ORAC), and total antioxidant capacity. Significant differences in phytochemical concentrations and antioxidant properties were observed between whole bran fractions of reduced particle size distribution for some assays. The coarse treatment exhibited significantly higher antioxidant properties compared to the fine treatment; except for the ORAC value, in which coarse was significantly lower. For soluble and bound extractions, the coarse treatment was comparatively higher in total antioxidant capacity (426.72 mg ascorbic acid eq./g) and FRAP value (53.04 μmol FeSO4/g) than bran milled to the finer treatment (314.55 ascorbic acid eq./g and 40.84 μmol FeSO4/g, respectively). Likewise, the fine treatment was higher in phenolic acid (7.36 mg FAE/g), flavonoid (206.74 μg catechin/g), anthocyanin (63.0 μg/g), and carotenoid contents (beta carotene, 14.25 μg/100 g; zeaxanthin, 35.21 μg/100 g; lutein 174.59 μg/100 g) as compared to the coarse treatment. An increase of surface area to mass increased the ORAC value by over 80%. With reduction in particle size, there was a significant increase in extracted anthocyanins, carotenoids and ORAC value. Particle size does effect the extraction of phytochemicals.

Mechanism and Enzymatic Contribution to In Vitro Test Method of Digestion for Maize Starches Differing in Amylose Content

To determine the rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) contents in a starch sample, the addition of amyloglucosidase is often used to convert hydrolyzates from α-amylase digestion to glucose. The objectives of this study were to investigate the exact role of amyloglucosidase in determining the digestibility of starch and to understand the mechanism of enzymatic actions on starch granules. Four maize starches differing in amylose content were examined: waxy maize (0.5% amylose), normal maize (≈27% amylose), and two high-amylose starches (≈57 and ≈71% amylose). Notably, without amyloglucosidase addition, the RS content increased from 4.3 to 74.3% for waxy maize starch, 29.7 to 76.5% for normal maize starch, 65.8 to 88.0% for starch with 57% amylose, and 68.2 to 90.4% for the starch with 71% amylose. In the method without α-amylase addition, less RS was produced than without added amyloglucosidase, except in maize at 71% amylose content. Scanning electron microscopy (SEM) revealed the digestive patterns of pinholes with α-amylase and burrowing with amyloglucosidase as well as the degree of digestion between samples. To understand the roles of amyloglucosidase and α-amylase in the in vitro test, multiple analytical techniques including gel permeation chromatography, SEM, synchrotron wide-angle X-ray diffraction, and small-angle X-ray scattering were used to determine the molecular and crystalline structure before and after digestion. Amyloglucosidase has a significant impact on the SDS and RS contents of granular maize starches.

Ethanol Fermentation Performance of Grain Sorghums (Sorghum bicolor) with Modified Endosperm Matrices

We tested 13 sorghum entries (lines and hybrids) with different endosperm matrices for ethanol production using a laboratory dry grind process. Waxy and heterowaxy samples had the highest efficiencies. Free amino nitrogen (FAN) contents in sorghum samples were positively related to the fermentation rate during fermentation (R2=0.8618). Dried distillers grain with solubles (DDGS) from different sorghums had significantly different crude protein and crude fat contents. Residual starch content in DDGS ranged from 0.60% for the most efficient sample to 2.66% for the least efficient sample. This study showed that the HD lines (TX1, TX3, TX5, TX7, and TX9) with modified endosperm protein matrix have several attributes desirable for ethanol production: easily pasted starch granules, significantly higher FAN content in finished mashes, 30-45% faster ethanol fermentation rate during early stages, and 50-60% higher lysine content in DDGS.

Fourier transform infrared (FT-IR) microspectroscopic census of single starch granules for octenyl succinate ester modification.

Fourier transform infrared (FT-IR) microspectroscopy was used to investigate reaction homogeneity of octenyl succinic anhydride modification on waxy maize starch and detect uniformity of blends of modified and native starches. For the first time, the level and uniformity of chemical substitution on individual starch granules were analyzed by FT-IR microspectroscopy. More than 100 starch granules of each sample were analyzed one by one by FT-IR microspectroscopy. In comparison to the native starch, modified starch had two additional bands at 1723 and 1563 cm(-1), indicative of ester formation in the modified starch. For the 3% modification level, the degree of substitution (DS) was low (0.019) and the distribution of the ester group was not uniform among starch granules. For the modified starch with DS of 0.073, 99% of individual starch granules had a large carbonyl band area, indicating that most granules were modified to a sufficient extent that the presence of their carbonyl ester classified them individually as being modified. However, the octenyl succinate concentration varied between granules, suggesting that the reaction was not uniform. When modified starch (DS = 0.073) was blended with native starch (3:7, w/w) to achieve a mixture with an average DS of 0.019, FT-IR microspectroscopy was able to detect heterogeneity of octenyl succinate in the blend and determine the ratio of the modified starch to the native starch granules.