Kinetics of Stone Fruit Drying

Abstract

The results of the investigation of technical and technological parameters in the low temperature drying processes of stone fruit (plum and apricot) under both laboratory conditions and in a universal prototype dryer have been presented in the paper. The measurements comprised flow and thermal measurement, technological and kinetic drying parameters and energy consumption. Major emphasis has been on temperature and relative humidity of the drying agents and humidity and temperature of the drying material. According to results, the preheating period has been found to be approx. 2-3 hours being affected by the type of the material and the drying regime, i.e. by the state of drying agents. Maximal plum drying rate has been after 2 h and amounted to about 1.15 kg w/kg d.b.h. In the case of apricot drying, maximal drying rate has been approx. 0.45 kgw/kg d.b.h. and was registered after 4 hours from the very beginning of the drying process. In addition, the curve of apricot drying kinetics has been differed from the curve of plum drying kinetics. The quality of dry fruit under low temperature drying conditions has been found to meet standard requirements primarily respecting sugar and acid loss and the fact that there was no odour or contamination of fruit. In addition to the technical solutions, the fruit drying process was found to be affected by how the process itself is being managed the duration of which may be shortened contributing to the quality of the products, energy production and profitability.

U radu su prikazani rezultati istraživanja tehničko tehnoloških parametara procesa niskotemperatuskog sušenja plodova koštičavog voća (šljiva i kajsija). Eksperimentalna istraživanja sprovedena na laboratorijskoj instalaciji i na prototipskoj univerzalnoj sušari namenjenoj za sušenje biljnih materijala, obuhvatila su strujnotermička merenja, parametre kinetike procesa i tehnološke parametre sušenja. Posebno su analizirani temperatura i relativna vlažnost agensa sušenja, vlažnost i temperatura materijala za sušenje kao i brzina sušenja. Rezultati pokazuju da period predgrevanja materijala iznosi od 2-3 h, što je uslovljeno vrstom materijala i režimom sušenja tj. stanjem agensa sušenja. Maksimalna brzina sušenja plodova šljive nastaje nakon 2 h i iznosi oko 1,15 kg w/kg s. m. h. Kod sušenja plodova kajsija maksimalna brzina sušenja iznosi približno 0,45 kgw/kg s.m.h. i pojavljuje se tek nakon 4 časa od početka procesa u čemu se razlikuje od brzine sušenje plodova šljive za približno isti režim sušenja. Pored toga, kriva kinetike sušenja kajsija ima drugačiji oblik u odnosu na krivu sušenja šljiva. Ostvaren kvalitet obe vrste osušenih plodova sa navedenim niskotemperaturskim režimima u velikoj meri odgovara standardima, pre svega u pogledu gubitka šećera i kiselina, kao i odsustva bilo kakvih mirisa i zagađenosti plodova. Dobijeni rezultati ukazuju da, pored tehničkih rešenja sistema za sušenje, na uspeh procesa značajan uticaj ima i samo vođenje procesa čije se trajanje može redukovati.