Agriculture Reference
In-Depth Information
studies showed that after extraction of sucrose carbohydrate composition of sugar beet shreds
based on dry matter is 20 - 30% cellulose, 17.5 - 34% hemicellulose and 23 - 32% pectins,
while lignin content is low, 1 - 4.4% [4, 7, 8, 9, 10]. Composition of carbohydrates in sugar
beet shreds might be expressed through components of polymeric sugars as 22.7% glucan,
5.14% xylan, 5.92% galactan, 23.73% arabinan and 1.85% mannan [10].
To date, sugar beet shreds have mainly been used as animal feed or, in regions with no
livestock farming, dumped in landfill [2, 3, 11, 12]. However, it is possible to extract
components from sugar beet shreds and modify them by some physico-chemical treatment in
order to modulate the nutritional effects and/or to improve their functional properties in this
way increasing their value [13]. It is also possible to utilize them as substrate for microbial
and enzymatic conversion in order to produce alternative uses of higher value products of
biotechnology. Bioconversion reactions, based on the use of (immobilized) microbial
biocatalysts (cells or enzymes) have many advantages over the chemical synthesis which are
based on so-called sustainable-related properties. In such way obtained products are derived
from renewable agro-substrates and agro-industrial residues under mild reaction conditions,
they are biodegradable and posses desired chirality; bioconversion reaction generaly have
positive environmental impact which relates them to “green chemistry” [13].
2.
M
ICROBIAL
C
ONVERSIONS OF
S
UGAR
B
EET
S
HREDS
2.1. Ensiling
Ensiling is a way to conserve forage with high water content by microbial fermentation in
the absence of air (oxygen) for use in animal (predominantly ruminant) feeding. Efficient
fermentation should ensure a palatable and digestible feed. During ensiling, some bacteria are
able to degrade cellulose and hemicellulose to their component sugars which are subsequently
metabolized to low molecular weight acids, mostly lactic acid. This can also be encouraged
by the use of appropriate mix of enzymes and microbial (lactic acid bacteria) silage
inoculants. The lactic acid bacteria are also believed to produce bacteriocins that discourage
the growth of and spoilage by unwanted populations.
Ensiling is a multiphase process which starts with the impounding of the forage and is
initiated by aerobic microbial populations. During this stage the aerobic organisms consume
and exhaust oxygen which leed to anaerobic conditions. This phase is undesirable, because
the aerobic bacteria consume soluble carbohydrates that should otherwise be available for the
beneficial lactic acid bacteria. It also leads to the production of moisture, and heat generation
which if not properly managed are capable of destroying the process. Proteinaceaous
materials may also be rapidly broken down during this phase and this can lead to loss of
nutrients and the accumulation of ammonia [14].
In the anaerobic phase of ensiling, a mixed population of lactic acid bacteria
predominates and metabolizes fermentable sugars, producing lactic acid and reducing the pH
of the mass to acidic levels. Production of good quality silage requires that anaerobiosis is
achieved quickly to enable development and predomination of lactic acid bacteria and
consequent decreasing of pH in the forage. This discourages spoilage of the silage and
ensures the retention of the most nutrients in the final product. To encourage rapid
