Use of response surface methodology for selection of nutrient levels for culturing Paecilomyces variotii in eucalyptus hemicellulosic hydrolyzate

Eucalyptus hemicellulose was hydrolyzed by treating eucalyptus wood chips with sulfuric acid. The hydrolyzate was used as the substrate to produce single-cell protein by growing Paecilomyces variotii IOC-3764 for 72 or 96 h. The influences of rice bran, ammonium sulfate and fermentation time were verified by a 23 full-factorial central composite design. At the optimum process conditions, the cell concentration was 12.06 g/l, which was obtained when the microorganisms were cultivated for 89 h in a medium composed of 10 g/l rice bran, 2.0 g/l nitrogen and 1.1 g/l sodium phosphate. The mathematical model Y=10.65+2.40X2+2.36X3+1.16X2X3−2.10X22−1.06X32 describes biomass production by P. variotii in eucalyptus hemicellulosic hydrolyzate with a determination coefficient of R2=0.9561, where X2 and X3 are ammonium sulfate and fermentation time, respectively.