Kit-Sum Wong

Effects of amylopectin branch chain length and amylose content on the gelatinization and pasting properties of starch

ABSTRACT Structures and properties of starches isolated from different botanical sources were investigated. Apparent and absolute amylose contents of starches were determined by measuring the iodine affinity of defatted whole starch and of fractionated and purified amylopectin. Branch chain-length distributions of amylopectins were analyzed quantitatively using a high-performance anion-exchange chromatography system equipped with a postcolumn enzyme reactor and a pulsed amperometric detector. Thermal and pasting properties were measured using differential scanning calorimetry and a rapid viscoanalyzer, respectively. Absolute amylose contents of most of the starches studied were lower than their apparent amylose contents. This difference correlated with the number of very long branch chains of amylopectin. Studies of amylopectin structures showed that each starch had a distinct branch chain-length distribution profile. Average degrees of polymerization (dp) of amylopectin branch chain length ranged from 18...

Branch-structure difference in starches of A- and B-type X-ray patterns revealed by their Naegeli dextrins☆

Abstract Naegeli dextrins and debranched Naegeli dextrins were prepared from native starches that display A- and B-type X-ray diffraction patterns. In comparison with their debranched counterparts, Naegeli dextrins prepared from the A-type starches consistently possessed substantially more singly branched molecules than those prepared from the B-type starches. The results indicated that the A-type starches had branch points scattered in both amorphous and crystalline regions. The branch linkages present in the crystalline region might be protected during the exhaustive acid hydrolysis. The B-type starch had most branch points clustered in the amorphous region, making them more susceptible to the acid hydrolysis. These models are consistent with the previously reported amylopectin structures that the A-type starch has more short A-chains (dp 6–12) than the B-type starch. The short A-chain is likely attached to a B-chain with the branch linkage located in the crystalline region. The branch linkages present in the crystalline region and the short double helices derived from the short A-chains provide the ‘weak points’, which are more susceptible to enzymatic hydrolysis and to generate pinholes and pits to the A-type starches. Banana starch, a C-type starch resistant to enzymatic hydrolysis, produced Naegeli dextrins with substantially less singly branched chains than the A-type starches. Naegeli dextrins prepared from starches that display A-, B-, and C-type X-ray patterns have different structures. The structures of the Naegeli dextrins indicate that the A-type starch amylopectin has a scattered branch structure and the B-type has a clustered branch structure.

Structural and functional characteristics of selected soft wheat starches

ABSTRACT Starches from eight soft wheat samples (two parent lines and six offspring) were isolated; relationships between their structures and properties were examined. Branch chain-length distributions of amylopectins were determined by using high-performance anion exchange chromatography equipped with an amyloglucosidase reactor and a pulsed amperometric detector (HPAEC-ENZ-PAD). Results showed that the average chain length of the eight samples varied at DP 25.6–26.9. Starch samples of lines 02, 60, 63, 95, and 114 consisted of amylopectins with more long chains (DP ≥ 37) and longer average chain length (DP 26.2–26.9) than that of other samples. These starch samples of longer branch chain length displayed higher gelatinization temperatures (55.3–56.5°C) than that of other samples (54.4–54.9°C) and higher peak viscosity (110–131 RVU) and lower pasting temperature (86.3–87.6°C) than others (83–100 RVU and 88.2–88.9°C, respectively). The Mw of amylopectins, determined by using high-performance size exclusi...

Structure and function of starch from advanced generations of new corn lines

Objectives of this research were to evaluate functions and structures of starches from exotic X adapted inbred lines and exotic lines, to confirm that the functional traits continue into the next generation of inbreeding, and to establish relationships between the fine structure and functional properties of the starches. Several lines were characterized from the successive generations of exotic crosses and exotic inbreds containing kernels with unusual, and potentially useful, thermal properties as measured by differential scanning calorimetry (DSC, gelatinization onset temperature 14 degreesC). The frequency of these traits increased with succeeding generations, when selection of the plants was based on the desired trait. Strong correlations were found between DSC and Rapid ViscoAnalyser properties and the granular structure (granular size distribution and branch-chain-length distribution of amylopectin)

Functional Interactions between Heterologously Expressed Starch-Branching Enzymes of Maize and the Glycogen Synthases of Brewer's Yeast

Starch-branching enzymes (SBEs) catalyze the formation of α(1→6) glycoside bonds in glucan polymers, thus, affecting the structure of amylopectin and starch granules. Two distinct classes of SBE are generally conserved in higher plants, although the specific role(s) of each isoform in determination of starch structure is not clearly understood. This study used a heterologous in vivo system to isolate the function of each of the three known SBE isoforms of maize (Zea mays) away from the other plant enzymes involved in starch biosynthesis. The ascomycete Brewers yeast (Saccharomyces cerevisiae) was employed as the host species. All possible combinations of maize SBEs were expressed in the absence of the endogenous glucan-branching enzyme. Each maize SBE was functional in yeast cells, although SBEI had a significant effect only if SBEIIa and SBEIIb also were present. SBEI by itself did not support glucan accumulation, whereas SBEIIa and SBEIIb both functioned along with the native glycogen synthases (GSs) to produce significant quantities of α-glucan polymers. SBEIIa was phenotypically dominant to SBEIIb in terms of glucan structure. The specific branching enzyme present had a significant effect on the molecular weight of the product. From these data we suggest that SBEs and GSs work in a cyclically interdependent fashion, such that SBE action is needed for optimal GS activity; and GS, in turn, influences the further effects of SBE. Also, SBEIIa and SBEIIb appear to act before SBEI during polymer assembly in this heterologous system.

Simultaneous monitoring of glutathione and major proteins in single erythrocytes

To gain more information from single-cell analysis, multiple detection schemes can be implemented in capillary electrophoresis. Red blood cells pre-treated with monobromobimane allow fluorescent tags to be attached to various thiol-containing compounds. Both derivatized glutathione and derivatized hemoglobin-A0 can be detected by observing emission at 495 nm when 275 nm excitation is used. At the same time, a second emission channel at 350 nm can be used to monitor the native fluorescence from carbonic anhydrase and from hemoglobin. Cross-correlation of the intracellular amounts of these provides additional insight into the cell-aging process.

Structural Properties of Starch Fractions Isolated from Normal and Mutant Corn Genotypes Using Different Methods

ABSTRACT The objectives of this research study were to isolate, evaluate, and compare the fine structures of starch fractions obtained from a wild-type (normal) corn starch and amylose-extender25, dull39, sugary2, and sugary1 corn mutants in the same genetic background using three different fractionation procedures based on gel-permeation chromatography or alcohol-precipitation methods. Starch fractions obtained from each of the three methods were enzymatically debranched and analyzed using high-performance anion-exchange chromatography with a postcolumn amyloglucosidase reactor and a pulsed amperometric detector. The separations were performed by fractionation on a GPC column, by precipitation with 1-butanol, and by preferential precipitation with 1-butanol and isoamyl alcohol. Using any of these methods, no apparent differences in the molecular weight distributions of amylopectin or of amylose among the different starches were observed. The proportions of branch chain lengths of the starch components ob...

Chapter 12 Starch chain length analysis by using an anion-exchange chromatography system equipped with an enzyme reactor and a PAD detector

Publisher Summary This chapter describes starch chain-length analysis using an anion-exchange chromatography system equipped with an enzyme reactor and a pulsed amperometric detector (PAD). Starch is the major source of energy in the diet of humans and animals. A starch granule is made up of amylose and amylopectin with trace amounts of other ingredients such as lipids and phosphate derivatives. With the knowledge of starch chemical structures and the effects of chemical structures on its functional properties and biosynthesis, starch can be genetically modified to induce a specific structure and achieve desired functional properties. The study of starch chain length is essential for understanding the chemical structure and biosynthesis of starch. Various techniques are adapted for starch chain-length analysis including high-performance anion exchange chromatography with pulsed amperometric detector (HPAEC–PAD), gel permeation chromatography (GPC) with total carbohydrates and reducing end analyses, high-performance size-exclusion chromatography (HPSEC) with a refractive index (RI) detector , and HPSEC with an on-line laser light-scattering detector (LLS) and an RI (HPSEC–LLS–RI). All of these methods are widely used in the field and have their advantages and disadvantages in starch chain-length analysis.