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ABSTRACT: Starch gelatinization and flour pasting properties were determined and correlated with four different levels of starch structures in rice flour, i.e. flour particle size, degree of damaged starch granules, whole molecular size, and molecular branching structure. Onset starch-gelatinization temperatures were not significantly different among all flour samples, but peak and conclusion starch-gelatinization temperatures were significantly different and were strongly correlated with the flour particle size, indicating that rice flour with larger particle size has a greater barrier for heat transfer. There were slight differences in the enthalpy of starch gelatinization, which are likely associated with the disruption of crystalline structure in starch granules by the milling processes. Flours with volume-median diameter ≥56μm did not show a defined peak viscosity in the RVA viscogram, possibly due to the presence of native protein and/or cell-wall structure stabilizing the swollen starch granules against the rupture caused by shear during heating. Furthermore, RVA final viscosity of flour was strongly correlated with the degree of damage to starch granules, suggesting the contribution of granular structure, possibly in swollen form. The results from this study allow the improvement in the manufacture and the selection criteria of rice flour with desirable gelatinization and pasting properties.
Carbohydrate polymers. 01/2013; 92(1):682-90.
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ABSTRACT: Statistically and causally meaningful relationships are established between starch molecular structures (obtained by size-exclusion chromatography, proton NMR and multiple-angle laser light scattering) and digestibility of cooked rice grains (measured by in vitro digestion). Significant correlations are observed between starch digestion rate and molecular structural characteristics, including fine structures of the distributions of branch (chain) lengths in both amylose and amylopectin. The in vitro digestion rate tends to increase with longer amylose branches and smaller ratios of long amylopectin and long amylose branches to short amylopectin branches, although the statistical analyses show that further data are needed to establish this unambiguously. These new relationships between fine starch structural features and digestibility of cooked rice grains are mechanistically reasonable, but suggestive rather than statistically definitive.
Food Chemistry 01/2013; 136(2):742-9. · 3.65 Impact Factor
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ABSTRACT: Chemical composition, molecular structure and organization, and thermal and pasting properties of maize and potato starches fractionated on the basis of granule size were investigated to understand heterogeneity within granule populations. For both starches, lipid, protein, and mineral contents decreased and apparent amylose contents increased with granule size. Fully branched (whole) and debranched molecular size distributions in maize starch fractions were invariant with granule size. Higher amylose contents and amylopectin hydrodynamic sizes were found for larger potato starch granules, although debranched molecular size distributions did not vary. Larger granules had higher degrees of crystallinity and greater amounts of double and single helical structures. Systematic differences in pasting and thermal properties were observed with granule size. Results suggest that branch length distributions in both amylose and amylopectin fractions are under tighter biosynthetic control in potato starch than either molecular size or amylose/amylopectin ratio, whereas all three parameters are controlled during the biosynthesis of maize starch.
Journal of Agricultural and Food Chemistry 08/2011; 59(18):10151-61. · 2.82 Impact Factor
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ABSTRACT: Whole polished rice grains were ground using cryogenic and hammer milling to understand the mechanisms of degradation of starch granule structure, whole (branched) molecular structure, and individual branches of the molecules during particle size reduction (grinding). Hammer milling caused greater degradation to starch granules than cryogenic milling when the grains were ground to a similar volume-median diameter. Molecular degradation of starch was not evident in the cryogenically milled flours, but it was observed in the hammer-milled flours with preferential cleavage of longer (amylose) branches. This can be attributed to the increased grain brittleness and fracturability at cryogenic temperatures, reducing the mechanical energy required to diminish the grain size and thus reducing the probability of chain scission. The results indicate, for the first time, that branching, whole molecule, and granule structures of starch can be independently altered by varying grinding conditions, such as grinding force and temperature.
Journal of Agricultural and Food Chemistry 03/2011; 59(8):3964-73. · 2.82 Impact Factor
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ABSTRACT: The time evolution of the size distributions of (fully branched and debranched) starch molecules during in vivo and in vitro digestion was analyzed using size exclusion chromatography (SEC) and compared. In vivo digesta were collected from the small intestine of pigs fed with raw normal maize starch; in vitro digestion was carried out on the same diet fed to the pigs using a method simulating digestion in the mouth, stomach, and small intestine. A qualitative difference was observed between the in vitro and the in vivo digestion. The former showed a degradation of starch molecules to a more uniform size, whereas the in vivo digestion preserved the size distribution of native starch before producing a multimodal distribution, the heterogeneous nature of which current in vitro methods do not reproduce. The use of in vitro digestion to infer in vivo digestion patterns and, hence, potential nutrition benefits need to take account of this phenomenon.
Biomacromolecules 10/2010; 11(12):3600-8. · 5.48 Impact Factor
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ABSTRACT: Inhibition of plant growth by Trinexapac-ethyl, TE, a gibberellin-biosynthesis inhibitor, can produce a shorter stemmed plant, requiring less nutrients and water to grow, while maintaining grain yield. Although TE and other plant growth regulators are commonly used in grain crops, their effects on starch biosynthesis in the grains have not been systematically examined. The changes in the structural and functional properties of starch in grains harvested from TE-treated sorghum (Sorghum bicolor (L.) Moench) were examined, and the results compared with those from the untreated controls. TE treatment had little or no effects on the molecular structures of starch, starch granule morphology, and starch and amylose contents, but increased the protein content of the grains significantly. Consistent with the lack of change in the molecular structure, there were no significant effects on the thermal properties of the starch. The pasting properties of TE-treated sorghum flours, however, showed lower peak viscosity, trough, and final viscosity, which were attributed to their higher protein contents. The TE treatment thus does not have an appreciable effect on the biosynthesis of starch during grain development in sorghum.
Journal of Cereal Science 53(3):328-334. · 2.07 Impact Factor
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ABSTRACT: Milling of starch granules is important for many food applications and involves a combination of mechanical and thermal energy. In order to understand the effects of mechanical force alone, four commercial starches including maize starch (MS), potato starch (PS), and two high amylose maize starches (HAMS) (Gelose 50 and Gelose 80) were cryo-milled for 20 min under the same conditions. The structural and conformational changes of the starches after cryo-milling were evaluated using X-ray diffraction, NMR spectroscopy, IR and Raman spectroscopy, and size exclusion chromatography (SEC). The cryo-milled starches had less crystallinity (15–35%) and 35–50% less ordered structure (double and single helices) than the native starch counterparts. The gelatinisation temperatures of the starches were not significantly altered by cryo-milling, but the gelatinisation enthalpies were significantly reduced in line with the reductions in the amount of double helices. Although, all four starches showed similar extent of degradation of crystalline/ordered structure, SEC results showed a greater degradation of amylopectin molecule in MS and PS than in HAMS. Increased amylose content in starch seemed to reduce the molecular degradation during milling, which is consistent with a role for amylose as a mechanical plasticiser in starch granules. It is concluded that (i) cryo-milling has differential effects on molecular size and conformation depending on starch granule type, and (ii) deterioration of starch crystalline and molecular order by mechanical treatment is not necessarily linked with the reduction in molecular size. The implication from the results is that the mechanical forces acting during cryo-milling are capable of disrupting helical and crystalline structures without breaking covalent bonds of starch molecules.
Carbohydrate Polymers.
