| Abstract | Istraživanje kinetike sušenja jabuke sorte „ Gold Rush“ provedeno je upotrebom laboratorijskog tunelskog sušionika pri različitim temperaturama sušenja, različitim brzinama strujanja zraka, te različitim vrstama prethodne obrade svježih uzoraka. Uzorci jabuke su rezani pomoću modelnog sjekača u oblik valjka promjera 20 mm i visine 5 mm. Temperatura sušenja neobrađenih uzoraka iznosila je 50, 60 i 70 °C, a brzina strujanja zraka 1, 5 i 2, 64 m/s. U cilju ubrzavanja kinetike sušenja i sprječavanja enzimskog i neenzimskog posmeđivanja uzoraka jabuke tijekom procesa sušenja, primjenjeni su različiti fizikalno-kemijski postupci prethodne obrade uzoraka. Sušenje prethodno obrađenih uzoraka (blanširanje u vodi temperature 85 °C, uranjanje u 0, 5 %-tnu otopinu askorbinske kiseline ; uranjanje u 0, 3 %-tnu otopinu L– cisteina ; uranjanje u 0, 1 %-tnu otopinu 4– heksil– resorcinola ; uranjanje u 1 %-tnu otopinu natrij– metabisulfita, uranjanje u kombinaciju 0, 3 %-tne otopine askorbinske kiseline i 0, 05 %-tne otopine 4– heksil– resorcinola, te uranjanje u 0, 3 %-tnu otopinu cimeta) provedeno je pri temperaturi 70 °C i brzini strujanja zraka 1, 5 m/s. Cilj istraživanja bio je dobivanje osušenih uzoraka jabuke s prosječnim udjelom vode od 10 %, dobrom sposobnošću rehidratacije i prihvatljivom bojom. Za praćenje utjecaja pojedinih procesnih parametara, primijenjene su standardne analitičke metode: termogravimetrija, rehidratacija i kolorimetrija. Za matematičku obradu eksperimentalnih podataka korišten je Page – ov eksponencijalni matematički model koji je pokazao dobra slaganja s eksperimentalnim podacima. Najbolji rezultati u kojima se uočava skraćivanje ukupnog vremena sušenja i visoke vrijednosti rehidratacionog omjera dobiveni su u slučaju prethodne obrade svježih uzoraka 0, 1 %-tnom otopinom 4-heksil-resorcinola i 1 %-tnom otopinom natrij-metabisulfita, dok je najmanja ukupna promjena boje dobivena u slučaju prethodne obrade svježih uzoraka s 0, 5 %-tnom otopinom askorbinske kiseline. Prethodna obrada uzoraka jabuke postupkom blanširanja, u vreloj vodi temperature 85 °C tijekom 3 minute, rezultirala je povećanjem ukupne brzine sušenja, kao i većim vrijednostima rehidratacionog omjera, dok je s druge strane ukupna promjena boje, tako obrađenih uzoraka, bila značajno smanjena. |
| Abstract (english) | The drying characteristics of Gold Rush apple were investigated using a laboratory tray drier at different drying temperatures, different airflow velocities and different pre treatments. Fresh apple samples were cut into discs, diameter 20 mm and height 5 mm. Temperatures of drying for non - treated samples were 50, 60, and 70 °C, and airflow velocities 1.5 and 2.64 m/s. To speed-up drying rates and to prevent enzymatic and non enzymatic browning during dehydration process, different physical and chemical pre treatments of samples were applied. Prior to drying at temperature of 70 °C and at airflow velocity of 1.5 m/s, apple samples were treated as follows: blanching in hot water at temperature of 85 °C; dipping in 0.5% ascorbicacid solution; dipping in 0.3 % L-cysteine solution; dipping in 0.1% 4-hexyl resorcinol solution; dipping in 1% sodium metabisulfite solution, mixture solution of 0.05% 4-hexyl resorcinol and 0.3% ascorbicacid and finally dipping in 0.3% cinnamon solution. The aim was to obtain apple with approximately 10% water content, good rehydration ability and suitable color. The effect of drying temperatures, airflow velocities and different pre-treatments on the properties of dried materials were performed using standard analytical methods: thermo-gravimetric, rehydration, colorimetric. The drying kinetic equations were estimated using Page's mathematical model. The results of the estimation showed a good agreement with the experimental data. High rehydration ratio and the most reduced drying time were obtained in the case of the previous treatment of fresh samples with 4-hexyl-resorcinol and sodium metabisulfite, while the minimum color change was achieved when samples were pre - treated with 0.5% ascorbicacid solution. Apple samples pre - treated with blanching in hot water at 85 °C temperature has resulted infaster drying rate and higher rehydration ratio, but unacceptable change in color appearance. |
