Changes in microstructure of native starches and starch acetates of different botanical origin during retrogradation

Water 2% starch suspensions prepared from native cereal starches (wheat, corn) and tuber ones (potato, tapioca) as well as their acetates were cooked at 100°C for 1 h. The obtained pastes were cooled to 25°C and stored at 4°C for 56 days. Retrogradation of 2% pastes was determined in two ways: as actual changes in the turbidity development, and as relative rates of turbidity between gels during 56 days of storage. The obtained results showed that the development of turbidity of the native and consequently acetylated starches followed the order: wheat > corn starch > potato > tapioca. Retrogradation evoked significant changes in microscopic pictures of pellets and supernatants obtained by LM and SEM examinations. The pictures varied considerably in amylose distribution. These alternations were unique for each botanical source of starch as well as starch acetates. The native cereal starches were characterized by a strong association of amylose particles with amylopectin fraction. While the tuber starches showed a weaker interaction between granule remnants and precipitated amylose. Changes in the microstructure of the native and acetylated starch granules were in accordance with turbidometric analysis. Des suspensions d'amidon a 2% dans l'eau preparees a partir de cereales (ble, mais) ou de tubercules (pomme de terre, manioc) et leurs acetates ont ete chauffee a 100° pendant 1 heure, puis refroidies a 25° et entreposees pendant 56 jours a 4°.La retrogadation a ete determinee et les differents gels ont ete classes en fonction de leur turbidite decroissante: Amidon de ble, de mais ,de pomme de terre et de manioc.La retrogradation provoque des modifications structurales des granules d'amidons ainsi que des changements dans la distribution de l'amylose.