Structural Transformations during Gelatinization of Starches in Limited Water:  Combined Wide- and Small-Angle X-ray Scattering Study

Abstract

Rice flour (18-25% moisture) and potato starch (20% moisture) were heated with continuous recording of the X-ray scattering during gelatinization. Rice flours displayed A-type crystallinity, which gradually decreased during gelatinization. The development of the characteristic 9 nm small-angle X-ray scattering (SAXS) peak during heating at sub-gelatinization temperatures indicated the gradual evolution into a stacked lamellar system. At higher temperatures, the crystalline and lamellar order was progressively lost. For potato starch (B-type crystallinity), no 9 nm SAXS peak was observed at ambient temperatures. Following the development of lamellar structures at sub-gelatinization temperatures, B-type crystallinity and lamellar order was lost during gelatinization. On cooling of partially gelatinized potato starch, A-type crystallinity steadily increased, but no formation of stacked lamellar structures was observed. Results were interpreted in terms of a high-temperature B- to A-type recrystallization, in which the lateral movement of double helices was accompanied by a shift along their helical axis. The latter is responsible for the inherent frustration of the lamellar stacks.

Understanding starch gelatinization: The phase diagram approach

“…In the studied temperature range we did not observe any B to A type transition with increasing temperature that was previously observed for potato starch with limited hydration (Vermeylen et al, 2006b). Interestingly, heat-induced lamellar ordering in a sample containing 80.1 wt% of starch was observed ( Figure S7, Supplementary data).…”

“…The location of Peak 1, often referred to as the 9 nm peak, was found to vary with starch concentration only in a narrow range of composition. Indeed, it has previously been reported that slightly higher repeat distances are obtained with increased water content (Vermeylen et al, 2006b). However, up till now there was a lack of a systematic study that reveals the swelling behavior of the lamellar spacing of starch.…”

Crystal Structure of A-amylose: A Revisit from Synchrotron Microdiffraction Analysis of Single Crystals

“…33 In addition, the lower stability of B-versus A-sample toward heating is further enlightened when starch granules, such as those of potato, which present a B-crystal X-ray diagram, get irreversibly converted into the A-type after heating at low moisture for several hours. 34 A similar conversion, but much faster, occurs when the hydrothermal treatment is directly applied to the crystalline fraction of potato starch recovered after partial acid hydrolysis of the granules. 35 Quite interestingly, the preparation of A-amylose crystals requires conditions where the crystallization takes place in aqueous mixtures containing a small percentage -typically of the order of 10 to 15% -of a low polarity precipitant such as ethanol or acetone.…”

Hydration and the phase diagram of acid hydrolyzed potato starch

“…There is some debate in the literature about what the term gelatinization includes (Karapantsios, et al, 2002, Lelièvre and Liu, 1994, Vermeylen, et al, 2006b, but generally it is considered the process where the starch granules swell, lose their long-order structure, and, at least partially, dissolve. Starch gelatinization has been widely studied by means of, e.g., differential scanning calorimetry (DSC), X-ray and neutron scattering techniques, and microscopy (Donovan, 1979, Jenkins and Donald, 1998, Karlsson and Eliasson, 2003, Lelièvre and Liu, 1994, Morikawa and Nishinari, 2000, Vermeylen, et al, 2006a, Vermeylen, et al, 2006b, Waigh, et al, 2000. After the gelatinization A c c e p t e d M a n u s c r i p t 5 process starch can undergo retrogradation upon storage below the gelatinization temperature (Karlsson and Eliasson, 2003).…”