Production, physicochemical characterization and rheological properties of the polysaccharide kefiran (Doctoral thesis)

Εξαρχόπουλος, Στυλιανός


Kefiran, an exocellular heteropolysaccharide was produced using kefir grains of household origin as a starter culture and Ultra High Temperature-Treated skimmed bovine milk as the substrate. The multiplication of kefir grains was carried out in three production stages for scaling up purposes. Initially, the kefir grains were produced in 1 L capacity fermenters, testing various fermentation conditions such as percentage of grain inoculum and incubation temperature. Following process conditions optimization, the fermentation was carried out in a 12 L capacity fermenter to collect a quantity of grains sufficient for utilization as starter culture material in a larger fermenter of 428 L capacity, achieving the total production of 30 kg grains out of an initial quantity of starter culture of 80 g.Kefiran isolation from kefir grains and the subsequent purification process involved the following steps; heating at 80°C of the aqueous suspension of kefir grains followed by homogenization, addition of perchloric acid, centrifugation to separate kefiran from proteins, repeated washings with surplus of ethanol, followed by centrifugation and freeze drying of the precipitate to obtain kefiran in powder form. Conformational studies using techniques such as capillary viscometry, size exclusion chromatography, multi angle laser light scattering, dynamic light scattering and zeta potential revealed that kefiran molecule in aqueous solutions behaved as a random coil having a weight average molecular weight of approximately 7 x 105. Water was found to be a good solvent for kefiran whose molecule was slightly negative charged. Hydrodynamic studies employing various aqueous environments of different ionic strengths, pH values, presence of organic acids, sugars, urea and ethanol affected the conformation of kefiran molecule in various degrees. Rheological studies of kefiran aqueous solutions (0.25 to 4%) indicated that kefiran in solution was a pseudoplastic material. Samples of 1 to 4% kefiran concentration which were frozen and then thawed exhibited higher viscosity values than their counterparts which did not undergo the freeze-thaw cycle. Squeeze flow experiments of kefiran systems which underwent the freeze-thaw cycle, revealed that the elongation viscosity exhibited, was concentration dependent, at the range of 4 to 7% concentration, whereas, the sample with 10% kefiran concentration exhibited the behavior of a true gel. Rheological studies of kefiran-milk proteins systems revealed that the influence of the kefiran’s presence on mechanical properties of the systems was almost negligible. Confocal laser scanning microscopy confirmed that the structure of these kefiran systems was dominated by the presence of milk proteins and to a lesser extent by the presence of kefiran.The findings of the present study indicated that kefiran containing food systems subjected to freeze-thaw treatment, will acquire a very stable, cohesive structure ideal for various food applications as far as consumer acceptance is concerned.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
Subject classification: Πολυσακχαρίτες
Keywords: Κεφιράνη,Πειράματα ζυμώσεων,Απομόνωση,Μοριακή διαμόρφωση,Ρεολογικές ιδιότητες,Κρυοπηκτές,Kefiran,Fermentation,Isolation,Conformational characterization,Rheological properties,Cryogels
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/29223
Appears in Collections:Διδακτορικές Διατριβές

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