Isolement et caractérisatioin de souches levuriennes amylolytiques à partir de sol saharien algerien.

Abstract

The isolation of yeasts realized on saharian soil from Biskra , allowed to index 5 strains . They were tested on PDA medium with 1% of starch . On 5 strains , one (S5), presented a high amylolytic activity compared to the others . The microscopic, physiological and biochemical studies of this strain , allowed to identify its kind : Lipomyces. In addition, culture medium , based on flour date rejects, was used at 1.5% for the production of α-amylase with fermentation of selected yeast Lipomyces sp. The ammonium sulphate (at 0.2%) and yeast extract (at 0.5%) were added respectively as source of nitrogen and growth factors, with starch at 1% as inductive substrate, in order to constitute a favourable medium to yeast development and production of α-amylase. The kinetic study for production of α-amylase realized on this medium, revealed that the production reached its maximum (6582 U ) at 78 hour of fermentation. Partial purification of enzyme by ammonium sulphate, gave a maximum yield in enzyme (77.3%) for the fraction 50% . The α- amylase partially purified, has an optimal pH of 6 and an optimal temperature of 55°C. The study of the thermostability of α-amylase of Lipomyces sp, revealed that enzyme is thermostable. The half-life of the enzyme at 80°C, is of 150 min and at 90°C, it is of 130 min .