Gelatinization of Starch in Excess Water:  Beyond the Melting of Lamellar Crystallites. A Combined Wide- and Small-Angle X-ray Scattering Study

Abstract

The gelatinization of waxy rice, regular rice, and potato starch suspensions (66% w/w moisture) was investigated by real-time small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) during heating and by fast ramp differential scanning calorimetry (DSC). The high-angle tail of the SAXS patterns suggested the transition from surface to mass fractal structures in the DSC gelatinization range. Amylose plays a major role in determining the dimensions of the self-similar structures that develop during this process as the characteristic power-law scattering behavior extends to lower scattering angles for regular than for waxy starches. Crystallinity of A-type starches is lost in the temperature region roughly corresponding to the DSC gelatinization range. At the end of the gelatinization endotherm, the B-type potato starch showed residual crystallinity (WAXD), while SAXS-patterns exhibited features of remaining lamellar stacks. Results indicate that the melting of amylopectin crystallites during gelatinization is accompanied by the (exothermic) formation of amorphous networks.

On the lamellar width distributions of starch

“…The results obtained (Table 1) are smaller than those previously determined for rice and potato starches (Vermeylen et al, 2006) and may be an artefact of the extrapolation procedure adopted here. Nevertheless, we interpret these results as a consequence of enzymatic trimming (Ball et al, 1996;Mouille et al, 1996) required to generate order in the amorphous lamella for subsequent synthesis of the crystalline lattice, as illustrated in Fig.…”

Effect of alkali treatment on structure and function of pea starch granules

“…The endothermic transition of native starch in the DSC profile represents the incomplete gelatinization of starch granules under low water conditions (starch:water ratio 1:2) . Substantial residual crystallinity and lamellar organisation remain after native starch granules are allowed to swell in limited water (Jenkins & Donald, 1998;Vermeylen et al, 2006). In a separate experiment, the swelling of alkali-treated starch granules was also shown to be incomplete at a starch:water ratio of 1:2 (data not shown).…”

Shear degradation of corn starches with different amylose contents

“…4 that the lamellar peak disappeared rapidly (as early as 2 min), which meant that the crystalline lamellar structure was damaged by shear. The kneading process is different from a general gelatinization process where heating (Vermeylen et al, 2006;Zhang et al, 2015), microwave heating (Fan et al, 2013(Fan et al, , 2014, or ultra-high hydrostatic pressure (Yang et al, 2016a) was applied. The in-situ SAXS data showed that the change under mechanical kneading was a more gradual process.…”