A problem with measuring components of the biomass is that the relationship between biomass and the component measured may change over time.
This has been noted for protein, glucosamine, and ergosterol contents within
fungal biomass [180–182]. Also the indirect methods of biomass estimation
must be calibrated to establish the relationship with biomass, which can only be
done in systems allowing direct measurement of the biomass. Some workers
have calibrated indirect methods of biomass estimation using liquid culture;
however, there is no guarantee that the biomass will have the same composition
in the different environment in SSF. Membrane culture methods, where the
fungus grows on a membrane overlaid on an artificial medium and in which the
biomass can be readily removed, mimics SSF more closely, and can be used as
the system for calibration [183].
8
Downstream Processing and Waste Disposal from SSF Processes
To date the downstream processing steps in SSF have received relatively little
attention, due to the relatively few successful large-scale operations. Many of the
studies of SSF simply show that the product can be produced within the
fermented solid mass and do not consider recovery of the product. Although
the product is often extracted for analysis, the objectives of extraction for
analysis and extraction for product purification are different, and many
processes used to extract products for analysis would not be economic. One
current commercial product are microbial enzymes, and more attention has
been given to enzyme recovery from SSF processes than has been given to the
recovery of other products.
A review of downstream processing steps in SSF was written by Lonsane and
Kriahnaiah in 1992 [184]. There has been relatively little progress since that
time. This review briefly summarizes the main points of this earlier review,
updating where appropriate. Since the purification of biotechnology products
has already received extensive attention, this review concentrates only on
aspects that are specific to solid-state fermentation, especially the step of
extraction of product from the solids, a step which is not needed in submerged
liquid fermentations, but is crucial in those SSF processes in which the product
must be separated from the fermented material. In this extraction step there are
two important criteria of success, which can have great effects on the economic
performance of the process:
1. The percentage of the product that is extracted from the solid substrate. This
is important because any product remaining in the solid residues represents
a loss of potential income. This will be referred to below as the leaching efficiency, equal to the amount of product in the final extracted solution
divided by the amount of product originally present in the solids.
2. The concentration of the product after extraction. Higher concentrations
reduce the costs of further processing steps by reducing the costs of water
removal.
124
D.A. Mitchell et al.
This has been noted for protein, glucosamine, and ergosterol contents within
fungal biomass [180–182]. Also the indirect methods of biomass estimation
must be calibrated to establish the relationship with biomass, which can only be
done in systems allowing direct measurement of the biomass. Some workers
have calibrated indirect methods of biomass estimation using liquid culture;
however, there is no guarantee that the biomass will have the same composition
in the different environment in SSF. Membrane culture methods, where the
fungus grows on a membrane overlaid on an artificial medium and in which the
biomass can be readily removed, mimics SSF more closely, and can be used as
the system for calibration [183].
8
Downstream Processing and Waste Disposal from SSF Processes
To date the downstream processing steps in SSF have received relatively little
attention, due to the relatively few successful large-scale operations. Many of the
studies of SSF simply show that the product can be produced within the
fermented solid mass and do not consider recovery of the product. Although
the product is often extracted for analysis, the objectives of extraction for
analysis and extraction for product purification are different, and many
processes used to extract products for analysis would not be economic. One
current commercial product are microbial enzymes, and more attention has
been given to enzyme recovery from SSF processes than has been given to the
recovery of other products.
A review of downstream processing steps in SSF was written by Lonsane and
Kriahnaiah in 1992 [184]. There has been relatively little progress since that
time. This review briefly summarizes the main points of this earlier review,
updating where appropriate. Since the purification of biotechnology products
has already received extensive attention, this review concentrates only on
aspects that are specific to solid-state fermentation, especially the step of
extraction of product from the solids, a step which is not needed in submerged
liquid fermentations, but is crucial in those SSF processes in which the product
must be separated from the fermented material. In this extraction step there are
two important criteria of success, which can have great effects on the economic
performance of the process:
1. The percentage of the product that is extracted from the solid substrate. This
is important because any product remaining in the solid residues represents
a loss of potential income. This will be referred to below as the leaching efficiency, equal to the amount of product in the final extracted solution
divided by the amount of product originally present in the solids.
2. The concentration of the product after extraction. Higher concentrations
reduce the costs of further processing steps by reducing the costs of water
removal.
124
D.A. Mitchell et al.