Date

2014

Author

Übeyitoğulları, Ali

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Dry apricot is one of the most exported fruits in Turkey. However, there are some quality problems faced with sulfuring before drying. Sulfuring is a chemical method that is used to prevent/delay oxidation and fungal-bacterial growth. Indeed, sulfuring is harmful to human health. Therefore, alternatively to sulfuring, hemicellulose coating was investigated. In this study, hemicellulose was extracted from hazelnut shells by using alkaline peroxide solutions. The extraction conditions were optimized with respect to temperature (40, 50 and 60 °C), alkaline concentration (10, 15 and 20 %) and extraction time (4, 8 and 12 h) and the highest hemicellulose purity was found as 64.24 % (w/w) by Box-Behnken response surface methodology at optimum conditions (10 % NaOH at 40 °C for 4 h). Hemicellulose coated apricots were dried in a tray dryer with various conditions; hemicellulose concentration (1-3 %), air velocity (0.5-1.5 m/s) and air temperature (60-80 °C). The effects of hemicellulose coating on apricot during drying was evaluated by color parameters (ΔE* and Δb*) and final moisture content. The optimum drying conditions were found as 1 m/s of air velocity, 80 °C of air temperature, and 3 % (w/v) hemicellulose coating which gave experimental values of 15.2, -8.3 and 26 % for ΔE*, Δb* and final moisture content, respectively. The models prediction of the responses were successful with close values of 13.2, -8.3 and 24.9 % for ΔE*, Δb* and final moisture content. Comparison of color values of dried apricots indicated that hemicellulose coated apricots had significantly better color values than uncoated and chitosan coated apricots. Apricot drying kinetics was evaluated by four models: Newton, Page, Henderson and Pabis and Logarithmic model. The best drying kinetics model for 2 % hemicellulose coated apricots at 60 and 70 °C was found as Logarithmic model. Page model described best the drying kinetic model for 2 % hemicellulose coated apricots at 80 °C. Effective diffusion coefficients increased with increasing temperature and ranged at 2.499-5.742 x 10-9. Arrhenius type equation used for description of the temperature dependency of effective diffusion coefficient was resulted in 33.78 kJ/mol of activation energy during apricot drying. Comparison of dried apricots with respect to rehydration rates revealed that hemicellulose coated dried apricots had slightly higher rehydration rate (0.011 min-1) than the uncoated dried apricots (0.010 min-1). In conclusion, this study shows that hazelnut shell is an effective feedstock for the hemicellulose extraction and hemicellulose coating has promising results to be used prior to apricot drying.

Subject Keywords

Apricot., Apricot, Hazelnuts., Hemicellulose., Edible coatings.

URI

http://etd.lib.metu.edu.tr/upload/12617701/index.pdf
https://hdl.handle.net/11511/23831

Collections

Graduate School of Natural and Applied Sciences, Thesis