Convective and microwave drying of coriander leaves: Kinetics characteristics and modeling, phenolic contents, antioxidant activity, and principal component analysis

Abstract

AbstractIn this study, coriander leaves were subjected to two different drying techniques: convective (40, 80, and 120°C) and microwave (100, 500, and 1,000 W). The effects of both processes on the kinetic parameters variation, modeling, and phytochemical quality were studied. Kinetic parameters variation showed that time reduction (2.53 min), high drying rate (3.08 kg water/kg dm min), and high diffusivity (1.21 × 10−10 m2/s) were obtained during microwave drying. For energy consumption, an opposite trend was observed between the variation in the specific electrical energy consumption (SECe), which is significant during convective drying (208.33 × 10+07 MJ/kg H2O), and the energy efficiency (EE), which is obtained during microwave one (12.16 × 10−03%). The kinetic data modeling done on 23 empirical models allowed us to choose the Sledz model as the best describing the drying kinetics of coriander since it presented better predictive performances with .9947 < adjusted R2 < .9995, 0.0001 < χ2 < 0.0005, and 0.0070 < RMSE<0.0228 values. In relation to the bioactive compounds, the highest values of the total phenolic content (TPC) and antioxidant activities (ABTs and DPPH) were observed during microwave drying with 0.37 mg GAE/mL, 83.33, and 71.94%, respectively. Correlations between kinetic parameters, energy consumption as well as phytochemical quality were established using principal component analysis (PCA). As a result, the innovative microwave process proved to be the best method for drying coriander leaves.Practical applicationsThe evolution of technological conservation processes has led to the development of a wide range of modern drying processes. The success of these processes can be explained by the many advantages attributed to them: shorter drying times, high drying rate, high energy efficiency, and product quality. The most difficult is the appropriate choice of a drying method with highly energy efficient and consumes less energy while maintaining the best quality. Fresh coriander leaves are widely used to flavor foods. However, they are highly perishable and require immediate processing or preservation. Thus, the objective of this study is to compare two drying processes, convective and microwave drying of coriander leaves based on kinetic data, modeling, calculation of moisture diffusivity and energy consumption, as well as evaluation of the dried powders quality. The results obtained will be useful for the technological design of convective or microwave drying for coriander leaves preservation.