Agriculture Reference
In-Depth Information
The most often type of cultivation for microbial conversion of sugar beet shreds to
pectinolytic enzymes is solid state one, no metter if bacteria or fungi are producers. Besides
many advantages of solid state cultivation over the submerged one [34, 35, 36] there is
always a step of enzyme extraction from solid waste materials. An interesting approach was
made by cultivation of fungus
Polyporus squamosus
in aqueous two-phase system containing
sugar beet shreds [28]. Generally, cultivation of microorganisms in aqueous two-phase
systems for the purpose of production of extracellular enzymes are based on the idea of
separationg cells from enzymes by partitioning them into opposite phases, thus avoiding
conventional step of mechanical separation. The basic idea of study was the production of
pectinases by
P. squamosus
and their simultaneous separation from biomass in aqueous two-
phase system containing sugar beet shreds as cheap pectin source.
During the whole time course of cultivation, fungal growth was restricted to the bottom
phase and the amounts of biomass and exo-pectinase activity produced were superior to the
ones in control homogeneous cultivation (Figure 1). The partition coefficients for two
produced pectinolytic enzymes - endo-pectinase and exo-pectinase as a measure of their
distribution between the top and the bottom phase, were 4.26 and 2.78, respectively. The top
phase yields in the single extraction step were about 90% for both pectinolytic enzymes.
Moreover, besides from showing themselfs as suitable substrate for pectinase production,
sugar beet shreds did not caused any detrimental effect on partitioning of enzymes in aqueous
two-phase system.
2.5. Biogas and Methane
Microbial conversion of agricultural and food industry waste can be exploited for biogas
and methane production by anaerobic methanogenic bacteria. Obtained biogases could be
valuable supplemantation as an alternative energy source for industry and farms.
However, limited number of investigation has been done with sugar beet shreds. One of
these concerned anaerobic treatment of sugar beet shreds at conditions of high organic load,
low retention time and high specific production of biogas and methane and indicated this
waste material as very suitable substrate. The energy content of methane was approximately
35 MJ/m
3
(for natural gas it is 38 MJ/m
3
) so produced biogas might be a significant
alternative source of energy [37].
In another study, microbial conversion of sugar beet shreds by mesophilic or
thermophilic mixed bacterial cultures taken from anaerobic digestor was assessed in relation
to, among others, biogas and methane production [38]. Thermophilic digestion of sugar beet
shreds showed performance advantages over mesophilic one including higher specific
methane production and operation stability at investigated organic loading rates with more
than 68% recovery of the calorific value as methane.
2.6. Miscellaneous
High-value chemicals are usually synthesized by chemical methods but biological
synthesis through microbial conversion of agri-food wastes adds market value. Ferulic acid
which is component of sugar beet cell walls was biotransformed using
Enterobacter soli
and
