The kinetics of the raspberry drying in laboratory conditions

Abstract

For a long time Serbia has been an important producer, processor and exporter of the raspberry. From the point of view of primary production, we could be proud of our success. However, on the question of processing, we are somehow behind. The reason is the typical "line of least resistance". We have always earned enough by exporting frozen raspberry and no one has even tried to explore new products or other attractive useful values of this fruit. Namely, although the raspberry has attractive useful values (which brings high demand), it is known that it has some inviolable chemical engineering characteristics. The raspberry, due to its consistency, is very susceptible to mechanical damage. It is also known for its high breathing warmth, and therefore it can only be preserved for a short time. These characteristics impose upon the producers the necessity to quickly proceed with the conservation and processing. The best way to achieve the turnover of capital is by not processing it completely. When the raspberry is half-processed, investments are smaller and so are risks for the deterioration of the quality of the product. Among products not completely processed, made from raspberries and other types of fruits, the most convenient are certainly frozen or dried fruits. Unfortunately, up to now, little has been done on the drying process of the raspberry because the fruit is very perishable as a raw material and also various problems occur during the drying process. Positive results have, however, been achieved locally in the process of drying by freezing, i.e. lyophilizing. The subject of this paper is the kinetics of drying raspberry in laboratory conditions with the idea of pinpointing at which level of humidity there is a change in the speed of evaporation. The quantity of evaporated water is expressed in relative and absolute units of measure.

Već dosta dugo Srbija je značajan proizvođač, prerađivač i izvoznik maline. Sa stanovišta primarne proizvodnje možda se može i pohvaliti, čak i ponositi dobrim uspesima. Ipak, sa stanovišta prerade nekako zaostajemo. Razlog je klasična "linija manjeg otpora". Uvek se dovoljno dobro zarađivalo izvozom smrznute maline i niko nije ni pokušavao da istražuje nove proizvode i neke druge atraktivne upotrebne vrednosti od ovog voća. Naime, iako malina ima atraktivnu upotrebnu vrednost (time i značajnu potražnju), poznato je da ima veoma nepovoljna tehnološka svojstva. Malina ima zbirnu cvast, a time i zbirni plod te je veoma osetljiva na mehanička oštećenja. Poznata je i po velikoj brzini tj. po visokoj toploti disanja, te stoga ima kratak period mogućeg čuvanja. Takva svojstva zahtevaju od proizvođača da veoma brzo reaguju sa konzervisanjem ili preradom. Najbrži obrt uloženog kapitala se može postići ako se od plodova dobiju poluproizvodi. Tada su ulaganja najmanja, a smanjen je i rizik po kvalitet. Među poluprerađenim proizvodima od maline, ali i ostalih vrsti voća. svakako su najpoželjniji zamrznuti ili osušeni plodovi. Nažalost, do sada se malo radilo na sušenju maline jer je ona veoma osetljiva kao sirovina i problemi pri sušenju su višestruki. Doduše, postoje i u domaćoj praksi pozitivni rezultati za sušenje smrzavanjem tj. liofilizacijom. U ovom radu je izučavana kinetika sušenja malina u laboratorijskoj sušari sa idejom da se uoči pri kojim sadržajima vlage dolazi do promene brzine isparavanja. Količina isparene vode je izražena u relativnim i apsolutnim jedinicama mere.