The effects of low temperatures on starch granule structure

Simultaneous small angle X-ray scattering, wide angle X-ray scattering and differential scanning calorimetry have been used to study the effects of su b-zero temperatures on the structure of hydrated starch granules. Results i ndicate that completely reversible compression of the starch lamellar struc ture occurs upon the freezing of water and ice formation. It is proposed th at this compression, caused by the expansion of water upon freezing, result s in preferential compression of the more 'open' amorphous lamellae which a ct as 'shock absorbers'. The lamellar repeat distance is reduced whilst per iodicity is maintained. For solvents other than water, which do not expand on freezing, the behaviour is qualitatively different since no compression occurs. Freezing behaviour-as well as providing information about the micro mechanical properties of starch granules-also has implications for cryo-mic roscopy studies of starch. (C) 2000 Elsevier Science Ltd. All rights reserv ed.