dc.description.abstract | Phloridzin is member of chemical class of dihydrochalcones, phenylpropanoids with
structure similar to chalcones, immediate flavonoid precursors, hence it is often classified
as flavonoid glucoside [1,2]. It is usually extracted from Malus species since it is very
abundant in young apple leaves and twigs. Due to its phenolic structure, phloridzin has
significant antioxidant activity and anti-UV properties, which makes it interesting for
application in food and cosmetics. Major limitation to wider application of phloridzin is its
low solubility in hydrophobic environment, which can be circumvented by synthesis of
physiologically active compounds derivatives by acylation of phloridzin. Synthesis of acyl
esters can be catalyzed by inorganic catalysts or enzymes, but chemical esterification is
not regioselective and results with unwanted functionalization of phenolic hydroxyl
groups responsible for antioxidative properties.
Therefore, in our study enzymatic esterification of phloridzin was performed using
immobilized lipase from Candida antarctica (Novozyme® 435). Several organic solvents
were tested and acetonitrile was proved to be the most adequate medium for this
reaction. Different acyl-donors were used with respect to chain length and saturation
level. Potential physiological activity of obtained esters was evaluated by determination of
their antioxidant activity using DPPH assay, so acyl donors were compared with respect to
both, product yields and antioxidant activity. After comparison of results of preliminary
study, phloridzyl oleate was selected as derivative with the best prospects and it used in
further experimental series for optimization of key experimental factors. Response surface
methodology was applied as statistical tool for optimization of product concentration (in
mM) as output and analyzed factors were: reaction time, temperature, enzyme
concentration, substrate molar ratio, and phloridzin concentration. After statistical
analysis each of examined experimental factors was found significant and second order
regression model was obtained. It was established that highest product concentration can
be expected at 68 oC, with 0.17 M of phloridzin, 2,5 % (w/v) of enzyme, 19-fold molar
excess of oleic acid after 7 days of reaction. | sr |