Extracted substrate colour as an indicator of fungal growth in solid state fermentation

ABSTRACT

Aims: In solid state fermentation (SSF), estimation of biomass is difficult as fungal mycelium penetrates deep and remains attached to the solid substrate particles. This study examines and evaluates a new technique based on colour changes of fermented substrates during SSF as an indicator for fungal growth. Methodology and Results: SSF refers to microbial fermentation, which takes place in the absence or near absence of free water, thus being close to the natural environment in which the selected microorganisms, especially fungi, are naturally adapted. Although many promising methods are available, the evaluation of microbial growth in SSF may sometimes become difficult, impractical, and inaccurate. Essentially, this remains another critical issue for monitoring growth. In this study, measurements of colour changes of fermented substrates during SSF are used as indicators for growth and this technique has a potential to be used to quantify growth of microbes. For the growth of Aspergillus awamori and A. oryzae on wheat bran, soybean hulls, and rapeseed meal, it was confirmed that colour changes were directly proportional to the fungal growth. This new approach is an important complementation to the existing techniques, especially for basic studies. The advantages of this method are its ease of use, fast, non-destructive, cheap, and requires no special and expensive reagents. The key finding is that the colorimetric technique demonstrated in this study provides good means to estimate growth than that obtained by visual observation or spores counting.