Agriculture Reference
In-Depth Information
been associated with the reduction in the content of lignocellulose (associated with loss of
biomass via microbial respiration as carbon dioxide). Although agricultural and food industry
waste materials are percieved as cheap enough to achieve sustanaible microbial conversion
for their protein enrichment pollution potential of applied technology as well as vicinity of
facility where they are generate should be taken into consideration. Ensiling itself hardly
leads to protein enrichment of the biomass except if mineral nitrogen is included [14].
Besides protein enrichment of other agro-food wastes, the possibility of use of sugar beet
shreds as principal carbon and energy sources enriched by microbial biomass protein such as
single cell protein and fungi has also been investigated. Four fungi
Trichoderma viride,
Trichoderma reesei, Fusarium oxisporum
and
Chaetopium cellulolyticum
were cultivated in
submerged and solid-state cultivation using sugar beet shreds as substrate. Products with up
to 27% protein content were obtained in submerged cultivation. Sugar beet shreds could be
upgraded to a product of 31% protein level with 49% product recovery in solid state
cultivation of 5 days while upgrading of 33.8% protein could be achieved in solid-state
cultivation of 3 days. Solid state cultivation with these fungi could be appropriate processing
method for protein enrichment of sugar beet shreds considering their availability and not
producing large volume of effluents [17].
One more fungus was considered for microbial conversion of sugar beet shreds for their
protein enrichment. Conditions of solid state cultivation of
Neurospora sitophila
was
optimized regarding protein enrichment of these lignocellulosic by-product leading to
increase in protein content of untreated sugar beet shreds after 5 days of cultivation on surface
from 15% (w/w) to 30% (w/w) [18]. Obtained results could be very promising for large scale
production of animal feed especially for countries which import animal feed and where such
residues are plentiful. Conversion of sugar beet shreds into microbial protein by
Aspergillus
tamarii
in solid-state cultivation was yielded in protein enrichment of lignocellulosic material
with 22.4% protein content of the product after two-day process [8].
Microbial conversion of sugar beet shreds to single cell protein was studied by four
yeasts of
Candida
spp.
- C. utilis, C. tropicalis, C. parapsilosis
and
C
.
solani
[19].
Candida
utilis
and C.
tropicalis
showed better performances than other investigated yeasts. Maximum
bioconversion efficiency, 46%, was achieved by C.
tropicalis
in two-day batch flask
cultivations. The bioconversion of sugar beet shreds under controlled conditions was also
studied using C.
tropicalis
in a 5 L bioreactor giving 29% and 48% product recovery with
39% and 25% protein level, in a two- and one-stage process, respectively. The one-stage
process (simultaneous saccharification and cultivation) was also run in a larger volume and
gave 50% product recovery with 29% protein content. In addition, solid state cultivation of
Candida tropicalis
was optimized with the purpose of bioconversion of sugar beet shreds into
a protein-rich product. By one-stage process a product having 48% protein content was
obtained when
C. tropicalis
was cultivated for 42h at 30°C and pH 5.0, after 6 hours of
combined action of cellulolytic and pectinolytic enzymes at 40°C and pH 4.8 [20].
Sugar beet shreds showed themselves as good economic substrates for single cell protein
production by yeasts cultivation and the process can be explored on large scale. This not only
solves the disposal problem of these by-products of sugar industry but also produces a protein
enriched product which could be used as a source of protein in various food and feed
applications.
