engleski

Influence of process parameters and pre-treatments on quality and drying kinetics of organic apple samples

The drying characteristics of "Florina" apple were investigated using a laboratory tray drier at different drying temperatures, different airflow velocities and different pre – treatments. Fresh samples of apple were cut into tube-shaped samples, 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 2.75 ms-1. To speed-up drying kinetics 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 60 °C and at airflow velocity of 2.75 ms-1, apple samples were treated as follows: blanching in hot water at temperature of 85 °C ; dipping in 0.5 % ascorbic acid solution ; dipping in 0.3 % L– cysteine solution ; dipping in 0.1 % 4– hexyl resorcinol solution ; dipping in 0.5 % sodium metabisulfite solution and finally dipping in mixture solution of 0.05 % 4– hexyl resorcinol and 0.5 % sodium metabisulfite. The aim was to obtain apple with approximately 12 % water content, good texture, good rehydration ability and suitable color. The effect of drying temperatures, airflow velocities and different pre-treatment methods 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. The best results (reduced drying time, high rehydration ratio and minimum color change) were achieved when samples were pre–treated with 4–hexyl resorcinol. Apple samples pre–treated with blanching in hot water at temperature of 85 °C has resulted in faster drying rate and higher rehydration ratio, but unacceptable change in color appearance.

drying kinetics; convection drying; organic apple; pre– treatment; rehydration; color

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