Crude fermentation extract showed to be rich in low molecular weight compounds and since its plasticization action, freeze-drying the crude fermentation extract resulted in a collapsed system with glass transitions (Tg) of negative values where a-amylase was susceptible to be inactivated by heat-treating for 2h at 90°C. Dry enzyme instability was consequence of the presence of solutes of MW lower than 10kDa. Due to its elimination, 70 % of the enzyme activity could be retained after heat-treatments at high moisture content. Enzyme stability was related to the presence of solutes of a molecular weight (MW) range from 50 to 300 kDa. We found that a stabilization mechanism in which amorphous dextrines, pectines, and/or cellulose or its fungal metabolized products is involucrate. No relationship was found between Tg and hygroscopic properties of the ultrafiltrated systems with the enzyme stabilization. However, the stabilization associated to the ultrafiltration of the crude fermentation extract could be related to the heterogeneity of the system aroused from the elimination of low molecular weight plasticizers that allowed the formation of a separate phase between a-amylase and the stabilizer, promoting the enzyme and amorphous polymeric matrix interactions that extremely improved the stability of the enzyme.