Location of Sites of Reaction Within Starch Granules

Abstract

To observe granular reaction patterns within modified starch granules, starch derivatives were converted to thallium(I) salts and viewed by scanning electron microscopy compositional backscattered electron imaging. Observation of phosphorylated potato and sorghum starches and a hydroxypropyl analog of waxy maize starch revealed that granular patterns of reaction were influenced by both starch and reagent types. In waxy maize and sorghum starches, flow of reagent into the granule matrix occurred from channels (laterally) and cavities (from the inside outward). In potato starch granules, which do not possess channels, reagent diffused inward through exterior granule surfaces. Phosphoryl chloride (highly reactive) reacted to a large extent at granule surfaces, while the propylene oxide analog (less reactive) appeared to diffuse into the granule matrix prior to reacting.

Understanding Starch Structure: Recent Progress

“…The channels are filled with proteins [25,29,83] and also phospholipids were found there [83]. The channels are important sites of penetration of different enzymes, such as α-amylases or glucoamylases, and diverse chemicals during modification of starch in vitro [85,86].…”

Effect of Cross-Linking on Physicochemical and in Vitro Digestibility Properties of Potato Starch

“…The extent of in vitro digestibility can be related to not only the degree of cross-linking but also the swelling factor (Koo et al, 2010). According to Huber and BeMiller (2001), after cross-linking, cereal starch can prevent the penetration of α-amylase through the channels that result in the inside of the starch, leading to decreased enzymatic digestibility. According to Yeh and Yeh (1993), α-amylase finds it very hard to digest highly cross-linked starch because cross-linking stabilizes the starch granules and regulates their swelling.…”

Impact of A/B-type granule ratio on reactivity, swelling, gelatinization, and pasting properties of modified wheat starch. Part I: Hydroxypropylation

“…Purified A-and B-type granule fractions of waxy and normal wheat starch were derivatized with POA using an aqueous-ethanol reaction medium outlined by Huber and BeMiller (2001). The appropriate level of POA reagent was dissolved in a mixture of 0.125 M NaOH, deionized water, and absolute ethanol (Table 1), followed by addition of starch (5.0 g, dry weight basis or d.b.)…”

“…A propylene oxide analog (POA, sodium 3-chloro-2-hydroxy-1-propanesulfonate) was employed to investigate A-and B-type starch granule reactivity, because it: (1) reacts with starch molecules in a manner similar to PO, (2) facilitates straightforward determination of modified starch MS levels (based on the amount of incorporated sulfur), and (3) possesses an anionic group that aids investigation of the locale of reaction sites within granules, accommodating future analysis of granular reaction patterns (Gray & BeMiller, 2004Huber & BeMiller, 2001). To minimize starch leaching from granules during derivatization, an aqueousethanol reaction system was used for POA reactions, as reported by Han and Sosulski (1998), who revealed 5-7 times lesser amounts of starch leachate for an aqueous-ethanol starch cationization process relative to that conducted in an aqueous medium.…”