Chemical Composition and Structure of Granule Periphery and Envelope Remnant of Rice Starches as Revealed by Chemical Surface Gelatinization

The evolution of granular surface structure and functional properties in rice starch during grain filling

The developmental changes in the granular surface structure and functional properties of starch during the entire grain filling period of rice (around 40 days) were investigated. The specific surface area of rice starch significantly decreased firstly then stabilized during growth due to increasing granular size. The pore volume decreased from 5.40 cm3/g at 6th day after anthesis (DAA-6) to 3.02 cm3/g (DAA-46). More starch granule-associated proteins (SGAPs) accumulated on the surface and in channels. Swelling power decreased by 46 %, whereas the flow behavior index (n) decreased by 32 % in upward curve during starch development from DAA-6 to DAA-30. Tan δ first dropped then remained steady at DAA 22-34 and lightly rebounded at the final stage, indicating that starch in the middle stage tended to have greater viscoelastic gel behavior at all sweeps. Mature starch showed lower in vitro hydrolysis rate and exhibited stronger enzymatic resistance. The results showed that granular surface features of rice starch may be an essential factor in determining rheological behavior and resistance to hydrolysis.

Physicochemical properties of starch in sodium chloride solutions and sucrose solutions: Importance of starch structure

The influences of sodium chloride (NaCl)/sucrose on starch properties as affected by starch structural characteristics are little understood. In this study, the effects were observed in relation to the chain length distribution (from size exclusion chromatography) and granular packing (inferred through morphological observation and determination of swelling factor and paste transmittance) of starches. Adding NaCl/sucrose dramatically delayed the gelatinization of starch that had a high ratio of short-to-long amylopectin chains and had loose granular packing. The effects of NaCl on the viscoelasticity of gelatinizing starch were related to the flexibility of amylopectin internal structure. Effects of NaCl/sucrose on starch retrogradation varied with starch structure, co-solute concentration, and analytical method. The co-solute-induced changes in retrogradation were highly associated with amylose chain length distribution. Sucrose strengthened the weak network formed by short amylose chains, while the effect was not significant on amylose chains that were capable of forming strong networks.

Study of heat-moisture treatment of potato starch granules by chemical surface gelatinization

BACKGROUND

Native potato starch was subjected to heat-moisture treatment (HMT) at 12%, 15%, 18%, 21%, and 24% of moisture content at 110 °C for 1 h, and the effects on morphology, structure, and thermal and physicochemical properties were investigated. To reveal the internal structure, 30% and 50% of the granular surface were removed by chemical surface gelatinization in concentrated LiCl solution.

RESULTS

At moisture contents of 12% and 15%, HTM reduced the gelatinization temperatures and relative crystallinity of the starches, while at moisture contents of 21% and 24 % both increased. The alterations on morphology, X-ray pattern, physicochemical properties, and increase of amylose content were more intense with the increase of moisture content of HMT.

CONCLUSION

The removal of granular layers showed that the changes promoted by HMT occur throughout the whole granule and were pronounced at the core or peripheral region, depending of the moisture content applied during HMT. © 2016 Society of Chemical Industry.

Physicochemical, digestibility and structural characteristics of starch isolated from banana cultivars

Banana starches from diverse varieties (Macho, Morado, Valery and Enano Gigante) were studied in their physicochemical, structural and digestibility features. X-ray diffraction indicated that the banana starches present a B-type crystallinity pattern, with slight difference in the crystallinity level. Macho and Enano Gigante starches showed the highest pasting temperatures (79 and 78°C, respectively), whilst Valery and Morado varieties presented a slight breakdown and higher setback than the formers. Morado starch presented the highest solubility value and Valery starch the lowest one. The swelling pattern of the banana starches was in agreement with their pasting profile. All banana starches showed a shear-thinning profile. The resistant starch (RS) fraction was the main fraction in the uncooked banana starches. Morado variety showed the highest amount of slowly digestible starch (SDS) and the lowest RS content reported until now in banana starches. Banana starch cooked samples presented an important amount of SDS and RS. Molecular weight and gyration radius of the four banana starches ranged between 2.88-3.14×10(8)g/mol and 286-302nm, respectively. The chain-length distributions of banana amylopectin showed that B1 chains (DP 13-24) is the main fraction, and an important amount of long chains (DP≥37) are present. The information generated from this study can be useful to determine banana varieties for starch isolation with specific functionality.