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.