Investigation of ultrasound pretreatment time and microwave power level on drying and rehydration kinetics of green olives

Alev Yüksel Aydar

doi:10.1590/fst.15720

Abstract

In this study, the effect of ultrasound (US) combined microwave (MW) drying of green olive slices was studied. Olive samples were exposed to ultrasound (5 and 10 minutes; 32 KHz) at room temperature before dried at microwave at 3 different power level (180W, 450 W and 800 W). The drying and rehydration characteristics and quality parameters of olives were determined by comparing with obtained by non-ultrasound pretreated MW dried samples. Midilli et al and Diffusion models were the most suitable models for US-MW drying with the highest R2, and lowest RMSE and chi square values. Total phenolic compounds (TPC) of olive slices reduced during drying in all treatments, however TPC of ultrasound pretreated samples were relatively higher those non treated samples dried at same microwave. Increasing of microwave level and ultrasound time decreased the total drying time up to %42.5. This study showed that US-MW can be a useful combine drying method for olive slices which decreased the drying time and improved the qualitative properties of olives.

Highlights

Olive (Olea Europea) is one of the most consumed fruits in Mediterranean countries with its superior properties such as high concentration of vitamin E and phenolic compounds including oleuropein, tyrosol and hydroxytyrosol (Aydar et al, 2017a)
The total drying time for olive slices was 849 second at microwave level of 180W and when 10 minutes of sonication applied before drying at 800W microwave level it was reduced to 488 seconds
According to the evaluation criteria (R2, χ2 and root mean square error (RMSE)), most of models well fitted with the thin layer drying characteristics (R2>0.9746, RMSE

Summary

Introduction

Olive (Olea Europea) is one of the most consumed fruits in Mediterranean countries with its superior properties such as high concentration of vitamin E and phenolic compounds including oleuropein, tyrosol and hydroxytyrosol (Aydar et al, 2017a). It is evaluated and consumed mostly as table olive and olive oil after harvesting. Hot air drying is one of the commonly used methods for drying of fruits and vegetables, but, it has many disadvantages, such as long drying time, loss in nutritional content, undesirable product deterioration and low energy efficiency (Horuz et al, 2017). Freeze drying obtains high quality products, it associates with high energy consumption and long drying time. It is necessary to develop new combine drying methods or pretreatments to attain improved drying process and enhanced product quality (Rawson et al, 2011)

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Conclusion