Changes in the microstructure of wheat, corn and potato starch granules during extraction of non-starch compounds with sodium dodecyl sulfate and mercaptoethanol

Abstract

Wheat, corn and potato starches were subjected to multiple extractions with 1% sodium dodecyl sulfate and mercaptoethanol (SDS/ME) in order to remove non-starch compounds from the starch granule. Molecular mass distribution of the extracted material determined using the column chromatography (Sepharose CL-2B) showed two distinct peaks of 200–800 kDa for high- (HMW) and 100–120 kDa for low molecular weight material (LMW). Only in wheat starch extract (onefold extraction) analysed using 1H- and 13C NMR spectroscopy, in phospholipid area, the main component of LMW was lysophosphatidylcholine (LPC). The residual starch pellets after fifteenfold extraction with SDS/ME were examined by the column chromatography, X-ray diffraction, and light microscopy. Amylopectin insoluble in solvent used was the main component of starch granules residue after extraction. The extraction of non-starch compounds did not affect changes in A-type and B-type crystallinity of cereal and tuber starches, respectively. The starch pellets were characterised by higher relative crystallinity compared to native ones. The removal of non-starch compounds resulted in different behaviour of starch pastes during heating at gelatinisation temperatures. A solvent mixture of n-propanol: water (3:1, v/v) was also used in order to extract surface lipids (cold extraction) as well as lipids present in the starch granule interior (hot extraction). The highest amount (58.8%) of surface lipids was found in wheat starch, while the lowest—in potato starch (9.9%).