8.1
Products for Which Extraction from the Fermented Solid is Not Needed
In these situations the whole fermented solid is used as the product. If a product
is used fresh, it must be used soon after production. Examples include
delignified wheat straw used as a feed supplement for ruminants and novel
fermented foods such as tempe produced from indigenous Ethiopian beans, in
which the fresh fermented product is cooked in a stew [185, 186].
If there is any processing, it is usually relatively simple, such as drying. In this
case it may be stored for some time before use. Relatively little attention has
been given to the drying of fermented materials for use as foods or feedstuffs.
However, it is clear that the drying temperature should not reach levels which
can cause undesirable changes in the material, such as charring. Many of the
issues will be similar to those encountered in drying of food products.
Other examples in which the whole product is used include the production
of animal feeds by the protein enrichment of sweet potato residue, cassava peel,
or whole cassava, or when SSF is used to remove toxic or inhibitory compounds
from feed materials, such as the reduction of phytic acid in canola meal, antidigestive constituents in rye, or caffeine from coffee pulp [187–193]. In these
studies it was not made clear whether the product would be used fresh or dried.
This is because the research addressed the feasibility of the process itself, and
not the use of the product as food or feed. The major consideration as to
whether the product will be dried is the time the product must be kept before
use, and the perishability of the product.
8.2
Methods for Recovery of Fungal Spores
Fungal spores are sometimes the products of SSF processes. They can be
produced in medium-scale processes as inocula for large-scale SSF processes.
They can also be produced as inocula for food fermentations, such as the
production of spores of Penicillium roqueforti for inoculation into curds to
produce blue cheese. Finally, spores may represent the active ingredient in the
final product, as is the case with many fungal biopesticides.
The question of recovery has received most attention in the case of biopesticide production. In some cases the product can be dried and pulverized to
a dust for direct application, or granules can be formulated from the dust [194].
These drying processes are similar to those described above for drying of other
SSF products. In general rapid drying below 30–35 °C is essential to maintain
high spore viabilities for many biopesticide fungi, although temperatures up to
50 °C can be used with Trichoderma harzianum [194, 195]. More recently, Daigle
et al. [36] directly extruded a mixture of the fermented rice flour medium with
various binding agents and then dried the granules at 50 °C in a fluidized bed to
produce biopesticide granules.
In other cases it is desirable to recover the spores separately. This can be done
by vacuuming the spores off directly, or partially drying the solid mass and then
tumbling it to knock off spores which are then recovered by aspiration.
Biochemical Engineering Aspects of Solid State Bioprocessing
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Products for Which Extraction from the Fermented Solid is Not Needed
In these situations the whole fermented solid is used as the product. If a product
is used fresh, it must be used soon after production. Examples include
delignified wheat straw used as a feed supplement for ruminants and novel
fermented foods such as tempe produced from indigenous Ethiopian beans, in
which the fresh fermented product is cooked in a stew [185, 186].
If there is any processing, it is usually relatively simple, such as drying. In this
case it may be stored for some time before use. Relatively little attention has
been given to the drying of fermented materials for use as foods or feedstuffs.
However, it is clear that the drying temperature should not reach levels which
can cause undesirable changes in the material, such as charring. Many of the
issues will be similar to those encountered in drying of food products.
Other examples in which the whole product is used include the production
of animal feeds by the protein enrichment of sweet potato residue, cassava peel,
or whole cassava, or when SSF is used to remove toxic or inhibitory compounds
from feed materials, such as the reduction of phytic acid in canola meal, antidigestive constituents in rye, or caffeine from coffee pulp [187–193]. In these
studies it was not made clear whether the product would be used fresh or dried.
This is because the research addressed the feasibility of the process itself, and
not the use of the product as food or feed. The major consideration as to
whether the product will be dried is the time the product must be kept before
use, and the perishability of the product.
8.2
Methods for Recovery of Fungal Spores
Fungal spores are sometimes the products of SSF processes. They can be
produced in medium-scale processes as inocula for large-scale SSF processes.
They can also be produced as inocula for food fermentations, such as the
production of spores of Penicillium roqueforti for inoculation into curds to
produce blue cheese. Finally, spores may represent the active ingredient in the
final product, as is the case with many fungal biopesticides.
The question of recovery has received most attention in the case of biopesticide production. In some cases the product can be dried and pulverized to
a dust for direct application, or granules can be formulated from the dust [194].
These drying processes are similar to those described above for drying of other
SSF products. In general rapid drying below 30–35 °C is essential to maintain
high spore viabilities for many biopesticide fungi, although temperatures up to
50 °C can be used with Trichoderma harzianum [194, 195]. More recently, Daigle
et al. [36] directly extruded a mixture of the fermented rice flour medium with
various binding agents and then dried the granules at 50 °C in a fluidized bed to
produce biopesticide granules.
In other cases it is desirable to recover the spores separately. This can be done
by vacuuming the spores off directly, or partially drying the solid mass and then
tumbling it to knock off spores which are then recovered by aspiration.
Biochemical Engineering Aspects of Solid State Bioprocessing
125