Deep-freezing of potato starch.

Samples of oven-dried, air-dried, and moisturised potato starch (5, 13, and 24% w/w moisture content, respectively) were frozen in liquid nitrogen. Samples after thawing were studied by means of cross-polarised light beam microscope (CLBM), Fourier Transformation Infrared Spectroscope (FT-IR), powder X-ray diffractometer, and non-contact Atomic Force Microscope (nc-AFM). Rapid deep-freezing followed by thawing produced changes on the granule surface. They were accompanied by internal alteration manifested by FT-IR spectra and powder X-ray diffractograms. The results depended on the water content in the sample. Deep-freezing of moistened starch resulted in increased crystallinity of granules. It had minor effect on the granule aqueous solubility and characteristics of gelation.