Drying kinetics and thermodynamic properties of boldo (Plectranthus barbatus Andrews) leaves

Abstract

Boldo leaves are used as medicinal plants by the Brazilian population. Among several factors that contribute to the proper storage of this product, we highlight the drying process, which is fundamental to reduce its moisture content, aiming to maintain phytotherapic characteristics. Different works involving the drying of leaves were carried out in the last years. However, there is not much information related to the drying process related to boldo leaves. This work evaluates drying kinetics at temperatures of 20, 40 and 60 °C, as well as determines thermodynamic properties: enthalpy, entropy and Gibbs free energy. Forced air circulation ovens were used for thin layer drying of leaves. The leaves, uniformly cut rectangular, were weighed periodically until hygroscopic equilibrium. Several mathematical models were fitted to the experimental data to characterize the drying processes, using the following statistical criteria: coefficient of determination (R²), mean standard error (SE), chi-square (χ²), and residue distribution. According to the criteria used, Modified Henderson and Pabis was the model that best represented the drying kinetics of boldo leaves. The activation energy for the drying of boldo leaves was 17.969 kJ mol-1. Both enthalpy and entropy decreased with increasing drying air temperature, while Gibbs free energy increased.

Drying kinetics and thermodynamic properties of Uzun pistachios dried by convective drying

“…Values for ΔG of in hull and in-shell pistachio samples ranged from 137.85 to 141.78 kJ/mol and 135.43 to 140.25 kJ/ mol over the range of 50-65°C, respectively. ΔG increased as the temperature increased and the ΔG values were positive, which means the drying of pistachio samples was not spontaneous under the conditions of this study (Silva et al, 2019). Additionally, this is an endothermic reaction, requiring an additional energy source to raise the energy level and convert the reagents to the vapor state (Ong et al, 2013;Silva et al, 2020).…”

“…Additionally, this is an endothermic reaction, requiring an additional energy source to raise the energy level and convert the reagents to the vapor state (Ong et al, 2013; Silva et al, 2020). With increasing the temperature, the decrease in Δ H and Δ S and increase in Δ G have been observed in various agricultural products such as jabuticaba peel (Costa et al, 2016), boldo leaves (Silva et al, 2019), bacaba pulp (Morais et al, 2019), bitter lemon (Silva et al, 2020), trapia residues (Moura et al, 2021), and baru almond flours (Alves et al, 2021).…”

“…Thermodynamic parameters are of importance for understanding the characteristics of water and determining the energy required for heat and mass transfer in biological systems (Dalgıç et al, 2012; Iglesias et al, 1976). To calculate the required energy, examine the features of the adsorbed water, and evaluate the food microstructure and physical events happening on its surface, understanding the thermodynamic properties of agricultural crops is crucial (Correa et al, 2010; Silva et al, 2019). Additionally, knowledge of thermodynamic properties is critical for predicting the end point at which agricultural products must be dried to obtain a product that can be stored for an extended period of time while consuming the least amount of energy possible to remove the moisture to suitable storage levels (Resende et al, 2017).…”

Secado de hojas de muña (minthostachys mollis): Modelado, cinética y propiedades termodinámicas

“…A temperaturas más bajas, el tiempo necesario para eliminar el agua de la superficie del producto es mayor que a temperaturas más altas, debido a que, a menor temperatura, la contribución a la remoción de agua presente en la superficie es baja. Este comportamiento de menor tiempo de secado a mayores temperaturas puede explicarse por la estructura de las hojas, las condiciones de secado, el aumento de los coeficientes de transferencia de masa y el incremento de la gradiente de presión de vapor entre el aire de secado y el aire dentro de las hojas (Bensebia & Allia, 2015;Da Silva et al, 2019).…”

Comparación de métodos sensoriales descriptivos: perfil flash y preguntas CATA para caracterizar infusiones de muña (Minthostachys mollis)

“…Este comportamiento de menor tiempo de secado a mayores temperaturas puede explicarse por la estructura de las hojas, condiciones de secado, aumento de los coeficientes de transferencia de masa y el gradiente de presión de vapor que aumenta entre el aire de secado y el aire dentro de las hojas. Por el contrario, a temperaturas más bajas, el tiempo necesario para eliminar el agua presente en la superficie del producto es mayor a temperaturas más altas, debido a que a menor temperatura la contribución a la remoción de agua presente en la superficie es baja (Bensebia y Allia, 2015;Da Silva et al 2019). Por lo que, una mayor temperatura favorece al incremento de percepción de los atributos sensoriales por parte de los consumidores, a diferencia del proceso de secado a bajas temperaturas, donde tiempos largos de exposición reduce los componentes volátiles disminuyendo la selección y descripción de los atributos sensoriales por parte de los participantes.…”