Mathematical modeling of the drying kinetics of the leaves of lemon grass (Cymbopogon citratus Stapf) and its effects on quality

Abstract

The aim of this study was evaluate the drying of the lemon grass plant (Cymbopogon citratus Stapf) at different air temperatures (40 °C, 50 °C, 60 °C and 70 °C) to adjust the experimental data obtained with different mathematical models and assess the quality of the plant after drying. A completely randomized design (CRD) was used with three drying replications for each speed and temperature of the drying air. The essential oil content extracted from the dried plant at 0.8 m s -1 and 1.3 m s -1 with manual control system was not affected by the drying process; the temperature of the drying air had a negative influence on the levels of the essential oil of the plant; drying with automatic control decreased the essential oil content for all velocities studied compared to the fresh plant; increments in the temperature of the drying air significantly reduced drying time. The mathematical model of Two Terms is adequate to describe the drying process of lemon grass plant (Cymbopogon citratus Stapf); diffusion values increased with increasing temperature of the drying air, while the value of activation energy was 62.84 kJ mol -1 .Key words: air, control, plant, velocity, temperature. RESUMEN El objetivo de este estudio fue evaluar el secado de la planta de hierba de limón (Cymbopogon citratus Stapf) a diferentes temperaturas de aire (40 °C, 50 °C, 60 °C y 70 °C) para ajustar los datos experimentales obtenidos con diferentes modelos matemáticos y evaluar la calidad de la planta después del secado. Un diseño completamente al azar (DCA) se utilizó con tres repeticiones para

Thin‐layer drying behavior of West Indian lemongrass (Cymbopogan citratus) leaves

“…The loss of quality in oven-dried leaves, especially at higher temperatures, can be attributed to browning reactions at higher temperatures, a decrease in chlorophyll content and essential oils (Coradi et al, 2014;Chen & Patel, 2008;Kassem et al, 2006;Sanmeema et al, 2012). With respect to the effect of air velocity on quality of dried leaves, Coradi et al (2014) found that increasing the air velocity from 0.8 to 1.3 m/s did not negatively affect the essential oil content of lemongrass leaves when compared with fresh leaves; however, further increasing the velocity to 1.8 m/s resulted in a statistically significant reduction in oil content. They noted the works of Buggle et al (1999) who dried lemongrass leaves at 30-90°C and found that the highest oil content of 1.43% was found in leaves dried at 50°C.…”

“…Oven (cabinet) drying still remains an attractive option for bulk drying of fragrant leaves such as coriander, olive mint, basil, thyme, bay leaves, and olive leaves (Ahmed, Shivhare, & Singh, 2001;Erbay & Icier, 2010;Cakmak, Kumcuoglu, & Tavman, 2013;Rodríguez, Clemente, Sanjuán, & Bon, 2014;Doymaz, 2014). A review of the work performed on lemongrass reveals studies which focus on different aspects of the drying process, including quality and essential oil content (Lonkar, Chavan, Pawar, Bansode, & Amarowicz, 2013;Martinazzo et al, 2009), drying efficiency (Kassem, El-Batawi, & Sidky, 2006), effect of pretreatments (Lonkar et al, 2013), drying curves (Coradi, Melo, & Rocha, 2014;Fudholi et al, 2012;Ibrahim, Sopian, & Daud, 2009;Rahman, Tasirin, Razak, Mokhtar, & Muslim, 2013), and mathematical modeling of drying data (Coradi et al, 2014;Ibrahim et al, 2009;Kemat, Rahman, & Wahit, 2008;Waewsak, Chindaruksa, & Punlek, 2006). However, with respect to the drying method employed, there are limited studies on lemongrass which include conventional cabinet drying (Kassem et al, 2006;Lonkar et al, 2013).…”

“…However, with respect to the drying method employed, there are limited studies on lemongrass which include conventional cabinet drying (Kassem et al, 2006;Lonkar et al, 2013). Previous works have instead focused on the drying of leaves in a solar dryer well as other dryers such as fluidized bed dryer, heat pump dryer, constant temperature and humidity chamber, biomass dryer, and a fixed bed dryer (Kassem et al, 2006;Waewsak et al, 2006;Kemat et al, 2008;Ibrahim et al, 2009;Fudholi et al, 2012;Sanmeema, Poomsa-ad, & Wiseet, 2012;Rahman et al, 2013;Coradi et al, 2014). The effect of drying parameters (such as temperature and velocity) on the behavior of leaves has not been reported for leaves dried in conventional ovens.…”

“…With respect to drying rates, no information has been presented on the effect of drying parameters on moisture curves and drying rate curves for leaves dried in conventional ovens. Drying curves were presented by some authors (Ibrahim et al, 2009;Fudholi et al, 2012;Coradi et al, 2014). Rahman et al (2013) calculated drying rate of leaves dried in a fluidized bed dryer in units of g/g min.…”

“…Rahman et al (2013) calculated drying rate of leaves dried in a fluidized bed dryer in units of g/g min. Lastly, with respect to mathematical modeling of drying data, modeling has been performed for methods other than conventional drying, with limited drying variables and using selected thin-layer models, which vary in their method of model assessment (Coradi et al, 2014;Ibrahim et al, 2009;Kemat et al, 2008;Waewsak et al, 2006).…”