The surface chemistry of starch granules studied by time-of-flight secondary ion mass spectrometry

This paper reports the novel application,of time-of-flight-secondary ion mass spectrometry (TOF-SIMS) to the investigation of starch granule surface chemistry and composition. TOF-SIMS spectra were recorded from five different starch samples, and were interpreted by applying standard mass spectrometry rules. The chemical identity of the majority of peaks in the spectra have thus been assigned, and allow the identification of ions arising from granule surface carbohydrates, lipids and surface contamination. The remaining peaks, which could not be assigned to the above species; have been tentatively assigned as arising from granule-surface proteins. The TOF-SIMS spectra reveal significant information regarding the types of lipids present at the starch granule surface and the identities of their acyl R chains. TOF-SIMS analysis of chlorinated starch samples lead to the conclusion that neither direct addition of chlorine to starch polymers, nor oxidation of the C2 and C3 hydroxyls to carbonyl groups, occurs following chlorination. The TOF-SIMS spectra reveal however, that the phosphocholine group of starch surface phospholipids is modified following chlorination, and furthermore, that chlorination may cause starch depolymerization. (C) 1997 Academic Press Limited.