Drying kinetics and shrinkage analysis of Valeriana officinalis roots

Abstract

Drying kinetics and shrinkage of valerian plant root (Valeriana officinalis) was investigated during the convective hot air dryer with forced convection mode. Whole root without cutting, root cut into quarters, and root cut into 2 mm thin slices were used in drying experiments. Initial moisture content of roots was 51.2±0.3% and roots were considered to be dry when they lost 68% of the fresh weight and reached the moisture content of 10%. Drying air temperature was set to be 40 and 50°C, air velocity at 1 m/s. The relative humidity of drying air was not controlled and it depended on surroundings. The experimental results were fitted to the five thin layer drying models and according to the non-linear regression analysis Page model was most suitable to describe the drying kinetics. The characteristic drying curves were created for each experimental set and they showed that the samples' preparation strongly influenced the drying process and drying time. Experiments to determine shrinkage of different cell structures of valerian root were carried out for raw material, as well as for dried samples, by using optical and electron microscopy observations and measurements. It was observed that shrinkage processes are significantly dependent of the type of cell tissue and drying air temperature.

Istraživanje kinetike sušenja i analiza skupljanja biomaterijala korenja lekovitog bilja Valeriana officinalis izvršeno je na konvektivnoj sušari sa vrućim vazduhom kao agensom sušenja. U eksperimentima su korišćeni uzorci: ceo koren, koren sečen na četvrtine i koren sečen na uzorke debljine 2 mm. Početni sadržaj vlage u uzorcima iznosio je 51.2±0.3%, a uzorak se smatrao suvim onda kada sadržaj vlage opadne na 10%. Temperatura vazduha u sušari iznosila je 40 i 50oC, sa brzinom strujanja od 1 m/s. Relativna vlažnost vazduha koji dospeva na materijal nije kontrolisana i zavisila je od spoljnih uslova. Eksperimentalni rezultati su analizirani kroz pet najčešće korišćenih modela za opisivanje promene bezdimenzionog sadržaja vlage u vremenu kod sušenja u tankom sloju, pri čemu je ustanovljeno da se kinetika sušenja najbolje opisuje modelom Page-a. Postupcima optičke i elektronske mikroskopije izvršeno je posmatranje uzoraka svežeg i osušenog korenja pri različitim režimima sušenja u cilju praćenja skupljanja materijala. Ustanovljeno je da proces skupljanja bitno zavisi od vrste ćelijskog tkiva u posmatranom poprečnom preseku materijala i od temperaturnog režima sušenja.