Non-contact AFM investigation of influence of freezing process on the surface structure of potato starch granule

To assess the influence of the freezing process on the surface structure of a potato starch granule, a non-contact Atomic Force Microscopy (NC-AFM) investigation at ambient conditions has been undertaken. The observations were carried out for dried (oven-dried) and native lair-dried) starch. The obtained AFM images of the native starch granule surface demonstrated it as not uniformly smooth and having rough undulating appearance with layers of adsorbed water which could be removed by oven drying in 130 degrees C. After freezing, the dried starch granule surface still consisted of nodules of about 100 nm in diameter. Significant changes in the granule surface appearance can be seen for dried starch samples frozen with some excess of water as well as for native starch samples frozen with its original water. Then the aggregation and polishing of the granules was observed and their surface revealed a microstructure with distinct ring-like protrusions of about 300 nm in diameter. Our observations tally with the amylopectine "blocket" starch granule structure model proposed in the literature and allowed to conclude that freezing may be a useful tool, among other methods, for modifying starch granule properties. (C) 2000 Elsevier Science B.V. All rights reserved.