Summary:
In this thesis, the first isolation and production of yeast β-glucan from a
completely new and unexplored source, yeast cell walls from winery spent yeast
biomass (winery sludge) was achieved with a sustainable and ‘green’ method
which: 1) is suitable for β-glucan industrial scale production from winery
by-products, 2) is able to treat the huge quantities of wine sludge produced
every year in winery fermentation tanks without producing new wastes but
unlike, the generated wastes can be valorized or reutilized for the recovery of
more products, 3) is able to produce an added value product which is intended
for its incorporation in functional foods and medicines and 4) has a degree of
sustainability with an ecological direction towards the protection of the
environment through the valorization of an industrial waste.
In the first part of this thesis, a technical evaluation of various isolation
and purification methods from yeast was done. The methods were evaluated as to
the required steps and their optimal conditions, the time needed, the required
technical equipment, the drying method of the final product, its solubility or
not in water, its yield and purity, the yeast growth conditions as also the
parallel production of other products during β-glucan production process. The
aim of the evaluation was the enlightenment on which method suits for lab scale
and which one for industrial scale β-glucan production, as the offered methods
for its isolation provide confused technical information. The evaluation
revealed that Method 2 can be used for the purpose of this study.
In the next part, three different production protocols were compiled based on
the information received from the evaluation study of the previous part, which
were experimentally tested in lab. Protocol 3, which was based on Method 2,
gave the best results in β-glucan purity and yield during its production
(purity 64.56 ± 1.25 % of β-glucan in final yeast powder and yield in β-glucan
10.01 ± 0.42 %.
Next, protocol 3 β-glucan production steps were optimized: 1. Yeast cell
autolysis and 2. β-Glucan isolation with the use of hot NaOH. The optimization
was done because in the international bibliography, this method has not been
optimized for its steps. With optimal extraction conditions, the produced β-
glucan was 70.8 ± 1.44 % pure with 12.56 ± 0.24 % yield.
In the next part, this method was used for β-glucan isolation from spent yeast
biomass in wine sludge and more precisely from red and white lees. With optimal
extraction conditions, the produced β-glucan was 32.95 ± 0.30 %, 43.37 ± 0.65 %
pure and yielded 2.45 ± 0.03 %, 11.21 ± 0.17 % for red and white lees
respectively with the proviso that for the max β-glucan purity, its isolation
must take place at the end of alcoholic fermentation.
In the last experimental part, a study of the production of β-glucan in the
cell wall of wine yeast S. cerevisiae during the alcoholic fermentation under
the influence of different glucose concentrations and hyperosmotic stress with
the use of NaCl, of yeast cells salt preconditioning or not before media
inoculation, took place. The results revealed that β-glucan increases during
yeast growth exponential phase and at the end of this reaches to a peak and
then starts to decrease during yeast cell death and lysis phase. The results
confirmed the results of the previous section about the optimum time for wine
lees harvesting and treating for β-glucan production.
Keywords:
β-glucan, Yeast, Winery by-products, Added value products, Winery sustainability
