Microwave Drying Kinetics, Hypericin Content, Effective Moisture Diffusivity and Activation Energy ofHypericum perforatumL.

Modelling of drying kinetics and comparison of two processes: forced convection drying and microwave drying of celery leaves (Apium graveolens L.)

“…For microwave drying, the average drying rates evolved from 0.15 kg water/kg dm min at the lowest power level (100 W) to 2.93 kg water/kg dm min at the highest level (1000 W). The same rates observed in this study were observed by many authors, such as Khazaei and Daneshmandi (2007) and Kumar et al (2012), who studied the effect of temperature and Dadalı et al (2007) and Alibas and Kacar (2016) who studied microwave drying.…”

“…These values are also similar to those (31.19 kJ/mol) obtained during the drying of tomato slices at 50-70 ⁰C (Azeez et al, 2017), mango ginger (32.6 kJ/mol) at 40-70 °C (Murthy and Manohar, 2014), unripe Cardaba banana (38.46 kJ/mol) at 50-70 °C (Olawoye et al, 2017), potato variety Golden delicious (35.3 kJ/mol) at 30-60 °C (Cruz et al, 2014) and pumpkin (33.74 kJ/mol) at 30-70 °C (Guiné et al, 2011). On the other hand, the Ea values obtained during microwave drying are different from those reported in the literature for the drying of many products, such as the values ranging from 17.96 to 21.38 W/g for kiwi slices (H. Darvishi et al, 2016) and 28.68087 W/g for Hypericum perforatum L. (Alibas and Kacar, 2016), 5.54 W/g for okra (Dadalı et al, 2007), 14.67 W/g for pepper (Hosain Darvishi et al, 2014), 11.41 W/g for basil leaves (Demirhan and ÖZbek, 2009) and 24.7 W/g for the yam of elephant foot yam (Harish et al, 2014). However, these values are particularly comparable to the Ea reported by Zhu et al (2015), which is about 77.0485 W/g for Ximeng lignite.…”

“…This decrease is fast at the beginning of the drying process and then slows down gradually as the drying process progresses. This can be explained by the fact that during the first phase of the drying process, the water content in the matrix is high, which leads to a large diffusion of moisture from the product (Alibas and Kacar, 2016). However, at an advanced drying process stage, we observed a reduction of the energy absorbed by the product surface.…”

“…Therefore, a modified Arrhenius equation (Eq. (10)), used in previous studies (Hosain Darvishi et al, 2014;Alibas and Kacar, 2016), was applied in this study to calculate the activation energy…”

“…That is why, the use of microwave rays in the drying of products has become widespread because it minimizes the decline in quality and provides rapid and effective heat distribution in the material as well. Furthermore, high quality product is obtained via microwave drying in addition to the decline in drying period and energy conservation during drying (Alibas and Kacar, 2016). Given the very large variability and diversity of food and biological products, the best way to characterize the drying behavior of a product is to experimentally measure its drying kinetics (Bonazzi et al, 2008) which are the most important data required for the design and simulation of dryers (Ratti, 2008).…”