Drying kinetics and quality characteristics of green apple peel (Mallus communis L. var. "Granny Smith") used in herbal tea production

Abstract

Green apple peels, (25.06 +/- 0.06 g) with the moisture content of 3.05 +/- 0.02 [kg (moisture) kg(-1) (dry matter)], were dried using two dehydration methods, microwave, and natural drying until moisture content of apple peels was reduced to 0.092 +/- 0.001 [kg (moisture) kg(-1) (dry matter)]. Microwave drying periods at 1,000, 800, 600, and 400 W lasted for 17, 21, 27, and 33 min, respectively; whereas, natural drying lasted for 66 hr. The scope of this study, a comparison of measurements of moisture with that of the predicted results was made, obtained from 21 thin layer drying models. For both 600 and 800 W microwave drying, Modified Henderson and Pabis's model; whereas, at 1,000 W, Alibas's model, and at 400 W, Modified Jena and Das's model were considered to be the most appropriate models. The most suitable drying process according to color parameters, chlorophyll content, and nutrients was obtained at 400 W microwave drying. Practical applications The herbal tea industry is growing globally and it is constanrly looking for new flavors that can attact consumers' attention. Herbal teas, in addition to being delicious, are required to meet the daily nutritional needs of the consumers. One of the drawbacks of drying is the loss of aroma and nutrients, moreover, drying operations carried out in open fields, such as sun drying, leads to contamination and can cause more harm than benefit. Thus, for food safety, it is very essential for herbal tea production facilities to use appropiriate methods to produce high-quality products. The present study on drying of apple peels for herbal tea contains important data on the selection of the most suitable drying method for the preservation of nutrients.