Abstract
The aim of the present thesis was the valorisation of whey, a major
waste of the food industry. Another objective of the thesis was the study of
simple thermal drying techniques as preservation methods of microorganisms
fermenting lactose and the production of dried starter cultures with potential
for commercialisation.
In the first section of the thesis, a literature review provides:
General information on whey and lactose
Lactose fermenting microorganisms
Preservation methods for microorganisms
Cell immobilization methods and technologies for food production
In the second section, the materials and methods used in the present
thesis are presented. Finally, in the third section, the results are presented
and thoroughly discussed.
Specifically, thermal drying of kefir and Kluyveromyces marxianus, free
and immobilized cells on delignified cellulosic material (DCM) and gluten
pellets, were studied. Three different thermal drying methods (convective
drying, drying unde ...
The aim of the present thesis was the valorisation of whey, a major
waste of the food industry. Another objective of the thesis was the study of
simple thermal drying techniques as preservation methods of microorganisms
fermenting lactose and the production of dried starter cultures with potential
for commercialisation.
In the first section of the thesis, a literature review provides:
General information on whey and lactose
Lactose fermenting microorganisms
Preservation methods for microorganisms
Cell immobilization methods and technologies for food production
In the second section, the materials and methods used in the present
thesis are presented. Finally, in the third section, the results are presented
and thoroughly discussed.
Specifically, thermal drying of kefir and Kluyveromyces marxianus, free
and immobilized cells on delignified cellulosic material (DCM) and gluten
pellets, were studied. Three different thermal drying methods (convective
drying, drying under vacuum, and drying by air stream) were used for drying
of kefir biomass and the effect on cell viability, fermentation rate and other
kinetic parameters of lactose and whey fermentation using these dried culture
were examined. Air drying rate was higher than that of the convective drying
and even higher than that of vacuum drying at all temperatures were studied
(28, 33 and 38oC). Ethanol concentration, productivity and yield were higher in
whey fermentations performed by air dried kefir biomass. However, higher
lactic acid concentration was achieved in batch fermentations performed by
convectively dried kefir. Storage of kefir, air dried at 33oC for 4 months,
without any other precautions, decreased its fermentation activity, ethanol
production by 31% and lactic acid productivity by 20%. Nevertheless, a
significant part of its initial fermentative activity was retained, rendering
thermal drying a promising technology for industrial starter culture production.
Subsequently, air drying of a thermophilic K. marxianus strain was
effectively performed at temperatures 35-60oC, with 35 oC being the most
effective. Volatile analysis of fermented whey using SPME GC-MS revealed
similar volatile profiles with traditional drinks from vegetable raw materials.
Kefir cells were also immobilized on DCM and were air dried at 28, 33
and 38oC. Drying kinetics showed no significant differences among the
applied drying temperatures. The dried immobilized biocatalysts were stored
at 4oC for 4 months and subsequently used for whey fermentation. The results
showed that the air dried biocatalyst can be preserved for 4 months without
significant loss of its fermentation efficiency.
The fermentation efficiency of K. marxianus cells immobilized on DCM
and dried with different thermal drying techniques at various temperatures
was also studied. Firstly, the immobilized biocatalyst was dried by convective,
air, and vacuum drying techniques at 35, 42, 48, 55 and 60oC and the dried
biocatalysts were used for lactose and whey fermentations. Air drying was the
most efficient technique used, and the fermentation efficiency of air dried
immobilized K. marxianus on DCM at the higher temperatures of 70, 80 and
90oC was further studied. The dried biocatalyst showed high tolerance even at
these high temperatures and although fermentation times were higher, they
were within acceptable limits. SPME GC-MS analysis of whey fermented with
the biocatalyst dried at high temperatures showed presence of numerous
aroma-related compounds. In conclusion, high temperature dried K.
marxianus immobilized on DCM retained its fermentation efficiency. However,
the higher energy demand of the high temperature drying is a considerable
disadvantage, but the higher drying rate and lower time required for full
dehydration of the biocatalyst decreases the process cost within reasonable
levels.
Furthermore, kefir and K. marxianus cells immobilized on gluten pellets
were air dried and their lactose and whey fermentation efficiency are reported.
It was concluded that gluten pellets could be used as immobilization support
for the production of active thermally dried starter cultures. The required time
for drying of the immobilized biocatalyst was higher than that of DCM but the
fermentation kinetics were satisfactory.
Finally, the investment cost for dried kefir cells production with thermaldrying
methodology was evaluated aiming at commercial production of starter
cultures for dairy industry. Kefir biomass was produced at pilot plant scale
using a 250 L bioreactor with cheese whey as raw material. Kefir cells were
subsequently dried in an industrial thin layer thermal dryer at 38°C and used
as starter culture at industrially ripened of hard cheeses. This was the basis
for an economic analysis in which the industrial-scale production of thermally
dried kefir starter culture was carried out. The industrial design involved a
three-step process using three bioreactors of 100, 3000, and 30000 L for a
plant daily capacity of 300 kg of thermally dried kefir culture. The cost of
investment was estimated at 238,000 €, which is 46% of the corresponding
cost using freeze-drying methodology. The production cost was estimated at
4,9 €/kg of kefir biomass for a daily plant capacity of 300 kg, roughly equal to
the cost of freeze-dried cells. Finally, the added value within the European
Union is estimated to 10,8×109 €, provided that the total EU whey amount
produced, will be employed.
show more
