TÓM TẮT NỘI DUNG:

Phytase supplementation has been found to increase not only the growth rate of onogastric animals but also the efficiency of phosphate utilization in feeds, which signifi-cantly reduces phosphorus excretion and the chances of environmental pollution. Thus, the objectives of this study were to optimize medium composition and conditions of fermentation semi-solid state for extracellular phytase by Aspergillus niger YD with the aim to increase yields to make it economical as a commercial product. With the experimental results achieved, medium composition include: corn starch (73%) and soybean meal (24.44%); and fermentation coditions optimum such as: temperature is 37 0C, fermention time is 5 days and relative humidity of media is 70%. With these parameters in both surveys, along and other parameters has been studied before, the extracellular phytase activity of fermentation was 917.40 ± 13.48 U/g.