Study of Physico-Chemical Properties of Hom Mali Brown Rice Flour Extract Powder and Optimum Concentration in Aspergillus niger Culture Media

Abstract

The objectives of this research were to determine the physico-chemical properties of Hom Mali brown rice flour (HMBRF) extract powder and the optimal concentration to include in ready-touse media for culturing Aspergillus niger TISTR 3089. The HMBRF extract powder contained reducing sugar (3.45%) and total sugar (31.99%) with water activity, water absorption index and water solubility index being 0.18, 0.11 g/g and 81.75%, respectively. The concentrations of HMBRF extract powder used in liquid media (broth) and solid media (agar) for culturing A. niger were optimized by comparing cell dry weight and colony diameter of A. niger in liquid media and on solid media, respectively, with control media of potato dextrose broth (PDB) and potato dextrose agar (PDA). Results showed that cell dry weight of A. niger after growing for 4 d at 30±2°C in HMBRF extract powder solution at 7.5, 7.6 and 7.7% (w/v) was not significantly different (p>0.05) from the control medium (PDB). Therefore, the optimum concentration of HMBRF extract powder as liquid medium for A. niger was used at 7.5% (w/v) to minimize cost. The colony diameter of A. niger on HMBRF extract solution at 5.0, 5.5 and 6.0% (w/v), each with 1.0% agar, was measured daily for 10 d and was significantly (p≤0.05) larger than that grown on the control medium (PDA) from the first day of measurement. The mycelium of A. niger on agar at these same concentrations of HMBRF extract powder reached the edge of the Petri dish (9.0 cm diameter) after cultivation for 7 d compared with 10 d on the control medium (PDA). Therefore, the optimum concentration for solid medium for A. niger was 5% (w/v) HMBRF extract powder with1.0% agar.