Osmotic treatment of nettle leaves-optimization of kinetics and antioxidant activity

The presented paper describes an investigation of nettle leaves kinetics during osmotic treatment in two different osmotic solutions (sugar beet molasses and ternary solution, was made from sucrose in quantity of 1,200 g/kg water, NaCl in quantity of 350 g/kg water and distilled water), at temperature of 20, 35 and 50ºC, during 90 min process. The main objective of this study was to examine the influence of type of different osmotic agents, process temperature and immersion time on the mass transfer phenomena during osmotic treatment, as well as the antioxidant activity. Water loss and solid gain were monitored. Antioxidant activity of osmotically treated nettle leaves was measured using a novel assay based on decrease of DC polarographic anodic current of hydroxo-perhydroxo mercury (II) complex [Hg(O2H)(OH)] (HPMC) formed in alkaline solution of H2O2 at potential of mercury oxidation. In order to get an insight into agreement between HPMC assay and common spectrophotometric assay, DPPH (2.2- diphenyl-1-picrylhydrazyl) analysis has been included in this study. Strict correlation between HPMC with commonly used DPPH assay was observed.