Effects of Hom Mali Brown Rice Flour Extract on Aspergillus niger Growth

Abstract

The objectives of this study were to determine the optimum extraction process for Hom Mali brown rice flour (HMBRF) and to investigate the growth of Aspergillus niger using the extract as a culture medium. A completely randomized design (CRD) factorial experiment was used to assess the effects of α-amylase, BAN^® 480L, concentrations (0.025, 0.050, 0.075 and 0.100 % v/w) and digestion time (15, 20, 25, 30 and 35 min). The optimum conditions for HMBRF extraction involved mixing HMBRF with distilled water (1:3.7), adding α-amylase at 0.05 % v/w of HMBRF, digesting for 30 min at 75°C in a water bath, then cooling down rapidly in an ice bath, boiling for 10 min to stop enzyme activity and separating the supernatant by centrifuging at 5,000 rpm for 30 min. HMBRF extracted solution contained total soluble solids (TSS) with 16.80°Brix and 6.78% reducing sugar. The growth of A. niger in the extract at 6°Brix was not significantly different (p>0.05) from growth in the control medium (PDB, commercial). There was high correlation between TSS and the growth of A. niger. This study revealed that HMBRF extract contained nutrients suitable for growing A. niger. Therefore, processing of the culture medium in dry form should be subjected to further study.