Starch Granule-Associated Proteins and Polypeptides: A Review

Abstract

This paper reviews current information regarding the (non-gluten) proteins which are naturally located in and on starch granules, and which are termed starch granule associated proteins (SGAPs). At least ten major SGAPs can be extracted from most starches and have molecular weights in the range of approximately 5 to 149 kDa. A substantial number of these proteins are located at the starch granule surface, where their presence in association with that of other minor granule components (such as lipids), appears to significantly influence the overall properties of both starch granules and starchy products. The different extraction conditions which can be exploited to selectively remove SGAPs are detailed. Although some SGAPs may serve as supplementary storage proteins, the majority of SGAPs are believed to be starch biosynthetic enzymes, a proportion of which remain trapped within the growing granule structure. The identity and quantities of the biosynthetic enzymes varies with botanical source, genetic variety and even with time. Current knowledge regarding the identities, compositions, locations, properties and functions of several of the more common SGAPs (e.g. the ~15 kDa friabilin/puroindoline proteins, the ~30 kDa protein, and the ~60 kDa starch granule-bound starch synthase (SGBSS) protein) are reviewed in detail.

Effects of surface proteins and lipids on molecular structure, thermal properties, and enzymatic hydrolysis of rice starch

“…Starch is synthesized as granules in higher plants and composed of two major components, amylose and amylopectin, and some minor components such as proteins and lipids (Baldwin, 2001;Jaiswal & Kumar, 2015;Xia et al, 2015). The proteins and lipids within starch granules are normally classified into two types: starch surface and interior proteins and lipids.…”

“…The proteins and lipids within starch granules are normally classified into two types: starch surface and interior proteins and lipids. The starch surface proteins stem from the storage proteins and some matrix proteins that remain absorbed to the surface of starch granules during starch development or after starch extraction, whereas the starch interior proteins stem from the starch biosynthetic or degradative enzymes, which remain following the starch synthesis and are entrapped within starch granules (Baldwin, 2001). The starch surface lipids are loosely attached or absorbed into the surface layers of starch granules in the endosperm, whereas the starch interior lipids are inclined to form a complex with amylose (Morrison, 1995).…”

“…The contents of protein and lipid in isolated starch depend on both botanical source and isolation method of starch. In general, grain starch of cereals contains approximately 0.25% protein and 1.0% lipid, and root or tuber starches have approximately 0.05% protein and 0.1% lipid (Swinkels, 1985;Baldwin, 2001;Wang et al, 2014). Although on a quantitative scale, the proteins and lipids within starch granules are considered negligible, there is increasing awareness that their presence, especially surface proteins and lipids, has significant effects on starch properties and applications.…”

The influence of non-starch polysaccharide on thermodynamic properties of starches from facultative wheat varieties

“…To determine the effect of AX adsorbed to the surface of starch granules in the process of washing out from flour, on the susceptibility of starch to gelatinization and hydrolysis by α-amylase, the AX were extracted with water and then with saturated Ba(OH) 2 . This enabled to remove separately the water extractable arabinoxylans (WEAX) and water unextractable arabinoxylans (WUAX).…”

“…Substances inherently associated with starch granules, like lipids and proteins, either attached to the surface or located inside, affect swelling and gelatinization of starch [1][2][3]. Particularly potent effectors are lipids that either bind to the surface or are incorporated into amylose-lipid inclusion complexes (AML) [4][5][6][7].…”