ORIGINAL Determination of the drying kinetics and energy efficiency of purple basil (Ocimum basilicum L.) leaves using different drying methods Kadriye Altay 1,2 & Ali Adnan Hayaloglu 2 & Safiye Nur Dirim 1 Received: 30 August 2018 /Accepted: 18 January 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract In this work, the effects of different drying methods, namely sun, freeze, convective and microwave oven drying on the drying time, rate and kinetics were investigated in purple basil leaves. Additionally, the energy efficiencies of the driers were determined. All the drying processes took place mainly in the falling-rate period. Comparatively, higher drying rates were obtained from microwave oven drying of the samples. Eleven thin-layer drying models, (Lewis, Page, Modified Page I, Henderson and Pabis, Modified Henderson and Pabis, Logarithmic, Midilli, Modified Midilli, Two-Term, Two-Term Exponential, and Wang and Singh) were fitted to the experimental moisture ratio data. Handerson and Pabis for freeze drying, logarithmic for sun drying and Page for convective and microwave oven drying were found to be the best models for explaining the drying behavior of the purple basil leaves with the highest R 2 and lowest RMSE values. The effective moisture diffusivity (D eff ) values of the dried purple basil leaves were calculated with Fick’s diffusion model and ranged from 1.62 × 10 −9 to 7.09 × 10 −8 m 2 /s. The energy efficiency of microwave oven drying was higher than the other methods. 1 Introduction The genus Ocimum basilicum L. belonging to Lamiaceae hav- ing 65 to 150 annual and perennial species in subtropical regions of Asia, Africa and South America [1]. Both the fresh and dried leaves are extensively used to add a distinctive aro- ma and enhance the flavor of salads, pasta, tomato products, vegetables, pizza, meat, soup, marine foods, confectioneries, and other food products [2, 3]. Basil also has medicinal ben- efits in the treatment of headache, cough, diarrhea, worm, intestinal disorder, warts, pain, and kidney and heart problems [1]. Drying is one of the preservation methods ensuring mi- crobial safety and extending shelf-life of foods. The main purpose of this process is to inhibit the increase in biolog- ical deterioration. It is well-known that the choice of drying method and applied drying conditions are critical for the herbs and spices [4]. To date, different methods have been employed for the drying of herbs and spices. For example, sun drying has been used since ancient times to dry grains, vegetables, fruits and other agricultural products because of its simplicity and low investment cost. However, this meth- od also has many disadvantages, such as the lack of ability to control the drying operation properly, exposure to envi- ronmental contamination, weather uncertainties, difficulty in achieving consistent quality standards, long drying time during the falling-rate period, high labor cost, and large area requirement. Moreover, quantity and quality losses occur in the dried product related to contamination by dirt, dust and infestation by insects, rodents and animals [4, 5]. These problems have led to the development of industrial drying methods [4], one of which is freeze drying that pro- vides a porous structure combined with small or negligible shrinkage, superior flavor and aroma retention, and im- proved rehydration behavior. Freeze drying method has al- so been used to dry several herbs. Most of the deterioration and microbiological reactions are prevented due to the ab- sence of liquid water and the low temperature required for the drying and the method gives the final product with an excellent quality [6]. The disadvantages of this method are high operating cost and long processing time [7]. Another method commonly used for drying food is convective dry- ing which is a fundamental technology for postharvest * Kadriye Altay kadriye_ergun555@hotmail.com 1 Department of Food Engineering, Engineering Faculty, Ege University, 35100 Bornova, Izmir, Turkey 2 Department of Food Engineering, Engineering Faculty, Inonu University, 44280 Malatya, Turkey Heat and Mass Transfer https://doi.org/10.1007/s00231-019-02570-9