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) in vestigation at ambient conditions has been undertaken. The observations wer e carried out for dried (oven-dried) and native lair-dried) starch. The obt ained AFM images of the native starch granule surface demonstrated it as no t uniformly smooth and having rough undulating appearance with layers of ad sorbed water which could be removed by oven drying in 130 degrees C. After freezing, the dried starch granule surface still consisted of nodules of ab out 100 nm in diameter. Significant changes in the granule surface appearan ce 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 r evealed a microstructure with distinct ring-like protrusions of about 300 n m in diameter. Our observations tally with the amylopectine "blocket" starc h granule structure model proposed in the literature and allowed to conclud e that freezing may be a useful tool, among other methods, for modifying st arch granule properties. (C) 2000 Elsevier Science B.V. All rights reserved .