Abstract
This work represents an experimental study and mathematical modeling of convective apple slice drying. The influence of multiple process parameters such as temperature, air humidity, air velocity and slice thickness on process kinetics, product water activity and parameters of empirical models has been investigated. Drying characteristics of apple slices were monitored at temperatures of 40, 45 and 50 °C, air velocities of 0.6, 0.85 and 1.1 m/s., slice thicknesses of 4, 6, 8, 10 and 12 mm, and in relative air humidity ranges of 25–28, 35–38 and 40–45%. During the process, samples were dried from an initial moisture content of 86.7% to that of 20% (w.b), corresponding to product water activity of 0.45 ± 0.05. By increasing the temperature from 40 to 50 °C, the time for reaching the required product water activity decreased by about 300 min. Sample thickness is the most significant parameter; by increasing the slice thickness from 4 to 12 mm, the time required to achieve the required water activity increased by more than 500 min. For all experimental runs, parameters of five different thin-layer empirical models were estimated. A thin-layer model sensible to process conditions such as temperature, air velocity, layer thickness and air relative humidity was developed and statistically analyzed.
Highlights
Agricultural products such as fruits and vegetables are considered perishable foods because of their high moisture content [1]
This work aims to investigate convective thin-layer drying of apple slices at temperatures ranging from 40 to 50 ◦ C, ambient air relative humidity from 25% to 45%, air velocity from 0.6 to 1.1 m/s, slice thickness from 4 to 12 mm at an average ambient pressure of 82 kPa, typical of geographical locations with an altitude of 1800 to 2000 m above sea level
Up to 96% of the total water content in apples evaporated during the experiment
Summary
Agricultural products such as fruits and vegetables are considered perishable foods because of their high moisture content [1]. Preservation for off seasonal time and prevention from microbial spoilage and enzymatic reactions can be accomplished by removing free water from the foods [2]. Drying is a well-known method of free water removal and preservation, extending shelf-life, and decreasing transportation weight and space requirements for storage [3,4,5,6]. Convective drying usually requires hot air circulation; high temperature and long times required in hot air-drying adversely affect the texture, flavor, and color of products [7,8]. Many parameters affect the drying process; temperature, air relative humidity, air velocity, and particle sizes of dried material can significantly influence the required drying time, cost as well as product quality
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