Estimation of growth in solid state fermentation: A review

Carleysmith and Fox (1984) stated without doubt, the single most vital yet most problematical value sought during fermentation is biomass estimation. Achieving a positive result in determining biomass remains a major challenge in solid state fermentation (SSF). Fungi are well-characterised microorganisms and are widely used in SSF due to their ability to colonise and penetrate into the solid substrate. The compressed structure of the mycelia and the solid substrate does not allow a complete recovery of the biomass, which may not be insurmountable. Since the use of a direct technique such as the dry weight method is impractical, the use of an indirect estimation technique is the only alternative. This review examines strategies that have been used to estimate biomass in SSF. Many promising indirect estimation techniques are available, which can be classified into six categories as follows; (i) measuring cell components not present in the substrate; (ii) measuring biomass component present in both substrate and biomass; (iii) measuring other secondary metabolites; (iv) measuring metabolic activity; (v) measuring images from direct microscopic observation and (vi) measuring biomass from the substrate matrix. New potential technique and future directions are also discussed in this review. Although significant advances have been made with the availability of various techniques; however, progress has been very unsatisfactory. The evaluation of microbial growth in SSF may sometimes become laborious, impractical and inaccurate. Essentially, this remains another critical issue for monitoring growth. The information of the profile of fungal biomass growth throughout any SSF process constitutes an essential parameter in estimation of kinetic variables and subsequently, scale-up of the process.