Scattering Studies of the Internal Structure of Starch Granules

Abstract

Small Angle X-ray Scattering (SAXS) and Small Angle Neutron Scattering (SANS) are applied to the study of the internal supramolecular packing within starch granules. SAXS is able to provide information on the packing of the semicrystalline lamellae and the amorphous growth rings. Using synchrotron radiation it is possible to follow changes in structure at both elevated temperatures within the gelatinisation regime, and at sub-zero temperatures when ice crystallisation can change the packing via compression of the granule. The role of amylose in modifying the response of the granule to these temperature variations has been examined. SANS has been used to examine the distribution of water in different parts of the granule, and quantify the molecular densities in different regions of the granule.

Understanding Starch Structure: Recent Progress

“…Unexpectedly, the amorphous lamellae tend to be thicker in the absence of amylose (i.e., in waxy starches) than in its presence, whereas the crystalline lamellae are thinner [72]. The molecular density in the crystalline lamellae is lower in potato starch (1.10 gcm −3 ) than in waxy maize (1.22 gcm −3 ), probably due to the higher water content in the B-polymorph crystals, whereas the molecular density of the amorphous lamellae was found to be fairly similar in potato and waxy maize (0.52 and 0.46 gcm −3 , respectively, the latter being A-crystalline) [73]. Interestingly, only minor differences appeared to exist between waxy maize and normal maize, as well as between waxy maize and rice or cassava starch, all being A-type crystalline starches [73].…”

“…The rings are semi-crystalline in nature as they contain both the amorphous and the crystalline lamellae [66], but they have also been considered as "crystalline" [74] or "hard" [74,75] shells. The rings are embedded in an amorphous matrix [66] with a lower molecular density in potato (0.49 gcm −3 ) than in waxy maize (0.68 gcm −3 ) and other A-crystalline starches [73]. The matrix was described as an "amorphous background" [66], "semi-crystalline shell" [74], or "soft shell" [74,75].…”

The impact of heat-moisture treatment on the molecular structure and physicochemical properties of normal and waxy potato starches

“…According to this concept, a glass transition of the amorphous regions will precede the melting of crystallites and gelatinizationiscontrolled by the molecular mobility in the anlOrphous phase surrounding crystallites (Biliaderis, 1992;BJanshard,1987). Waigh et al (2000b) proposed a mechanism for gelatinization based on a side chain liquid crystalline polymeric (SCLCP) model of starch (Donald et al, 2001;Jenkins et aI., 1993;Waigh etal., 2000a;Waigh et al, 1998). In this mechanism, depending on the water content and heating rate, gelatinization results from helix-coil transitions and transfomlations from a glassy nematic phase to a plasticized smectic phase of amylopectin helices.…”

Ultrasound irradiation in the production of ethanol from biomass

“…In general, the structure of semi-crystalline native starch granules is found as a hierarchical structural periodicity (Fig. 10), having a layered organization with alternating radial rings of amorphous and semi-crystalline material in thickness of 120-400 nm [73]. Although the amorphous rings are formed by amylose and amylopectin in a disordered conformation, the semi-crystalline rings consist of a lamellar structure of alternating crystalline and amorphous regions with a regular repeat distance of 9-10 nm [9].…”