Drying Kinetics, Microstructure and Antioxidant Properties of Basil Treated by Ultrasound

Abstract

The current study is one of the first provided data on both the quality changes and the drying kinetics of herbal material affected by ultrasound (US). The aim of this study was to investigate the influence of US prior to microwave–convective drying on the drying kinetics, water diffusivity, total phenolic content, antioxidant activity and microstructure of basil leaves. The US pretreatment was applied at different frequencies (21, 35 kHz) for variable time (20, 30 min). Application of US significantly reduced the drying time up to 20% and decreased the total specific energy consumption maximally by 26.2% in the case of 35 kHz 20 min US‐treated basil. Sonication modified the microstructure of basil, which was manifested in larger and elongated cellular spaces. Nonetheless, US did not alter the antioxidant activity and resulted in even significantly higher phenolic content in leaves treated by US at 21 kHz 20 min and at 35 kHz 30 min, compared with untreated sample. Drying coefficients of the model proposed to describe the dehydration kinetics indicated the process intensity due to the significant correlation between the drying rate and effective water diffusivity. Practical Applications Basil is a seasoning herb widely cultivated and distributed in a dried form to nearly every part of the world. Nowadays, the dried leaves are produced for consumption purpose and are intended for pharmaceutical industry, especially due to an antioxidative potential of basil. Ultrasound (US) is a nonthermal, emerging technology which intensifies the highly energy‐consuming drying process and reduces its cost. The current study is one of the first that provided data on both the quality changes and the drying kinetics of herbal material, affected by US treatment. This paper revealed the possibility of industrial utilization of US prior to the drying of herbs. Application of the recommended herein US treatment parameters results in a significant reduction of drying expenditures and improvement of the quality of herbs. It should be emphasized that both investment and operating costs of US pretreatment are negligible compared with benefits associated with decrease of drying energy consumption.

The effect of microwave and convective dryer with ultrasound pre‐treatment on drying and quality properties of walnut kernel

“…The values of SEC are in agreement with the reported values for raspberries from 96.75 to 214.77 kWh/kg in ultrasound pre‐treatment and combined convective‐microwave drying (Kowalski et al, ), for basil leave drying from 36.09 to 52.59 MJ/kg in MIC–CON with US pre‐treatment at different frequencies (21 and 35 kHz) and variable time (20 and 30 min) (Sledz et al, ), and for raspberries, highest SEC (0.8 MJ/g) at convective dryer and lowest SEC (0.37 MJ/g) at combined convective microwave with ultrasound pre‐treatment 200W (Szadzinska et al, ).…”

“…Hence, Midilli et al model was chosen as the best model to describe the thin layer drying characteristics of walnut. Sledz et al () investigated the drying characteristics of basil in a MIC‐CON drying dryer with ultrasound pre‐treatment and were fitted their experimental data to 11 mathematical model Sledz et al models are superior to the other models for explaining the drying kinetics of Basil.…”

“…Numerous studies have been conducted on drying agricultural products through microwave and convection dryers with ultrasound pre‐treatment apple (Mothibe, Zhang, Mujumdar, Wang, & Cheng, ), green pepper (Szadzinska et al, ), basil (Sledz, Wiktor, Nowacka, & Witrowa‐Rajchert, ), garlic (Tao et al, ), sweet potato (Lagnika et al, ), lemon (Deepika & Sutar, ) and raspberries (Szadzinska, Łechtańska, Pashminehazar, Kharaghani, & Tsotsas, ).…”

The effect of ultrasound pre‐treatment on quality, drying, and thermodynamic attributes of almond kernel under convective dryer using ANNs and ANFIS network

“…The results of the investigations show that the hot air temperature and the ultrasonic duration have a positive effect on moisture exits during drying process. The decreasing of drying time with increasing of hot air temperature using ultrasonic pre-treatment has been reported using many agricultural products such as apple (Nowacka et al, 2012), thyme (Rodriguez et al, 2013), apple (Mothibe et al, 2014), parsley leaves (Sledz, Wiktor, Rybak, Nowacka, & Witrowa-Rajchert, 2016), passion fruit (Do Nascimento et al, 2016), and Basil (Sledz, Wiktor, Nowacka, & Witrowa-Rajchert, 2017).…”

“…The maximum value for the SEC was obtained 561.72 kW hr/kg at 40 C and control sample, and minimum value was 169.88 mJ/kg at 70 C for the ultrasonic duration of 40 min. These findings are in agreement with the documented values of 196.75-214.77 kW hr/kg applied for raspberries in ultrasound to enhance convective and combined convective-microwave drying (Kowalski, Pawłowski, Szadzi nska, Łechta nska, & Stasiak, 2016), 5.44 to 24.65 mJ/kg for fluidized bed with ultrasound pretreatment drying of Paddy (Jafari & Zare, 2017), 36.09-52.29 MJ/kg for microwaveconvective drying with ultrasound pretreatment dryer at different frequencies (21 and 35 kHz) for variable time (20 and 30 min) of basil(Sledz et al, 2017).…”