Process effectiveness assessment by modeling the kinetics of lotus seed drying combining air‐borne ultrasound and microwave vacuum

Abstract

This study presents the effects of ultrasound (US) on the drying kinetics of lotus seeds in a hybrid dryer equipped with constant microwave power in combination with airborne US at vacuum degree (USMVD) and atmospheric pressure (USMD) from 120 to 440 W of five US power levels. Water‐borne US pretreatment before microwave drying (US + MD) or microwave vacuum drying (US + MVD) was simultaneously performed to compare their effectiveness in drying lotus seeds under the same US power. USMD and USMVD techniques reduced the drying time up to 26.19% and 14.29% while reducing energy consumption by up to 10.42% and 23.02% when compared with MVD and MD (without US), respectively, and with relatively high ultrasonic power density. The US + MD and US + MVD drying also reduced the processing time and energy consumption compared to MD and MVD process, respectively, but was less effective than USMVD and USMD. In addition, with higher US power applied, drying occurred more rapidly with less energy consumption. The newly proposed model showed the best fit to the drying curve based on model with the highest regression coefficient, lowest root mean square error, sum square error, and chi‐square. Furthermore, the enhanced effectiveness by USMVD and USMD could be attributed to the respective “heating” and “synergistic” effects generated by microwave and US. Therefore, US in combination with MVD or MD could be used jointly owing to the enhanced process effectiveness. Practical applications Drying process is one of the most complex and energy‐consuming processes. The drying kinetics model was applied in drying equipment engineering. The drying kinetic model studies the law of moisture changes during the drying process and provides a theoretical basis for the adjustment of the lotus seed drying equipment parameters. In order to improve the quality of drying products and optimize the drying process, it is necessary to use mathematical model to simulate the drying process under different drying conditions. This study provides data support for equipment selection, energy saving, and consumption reduction and industrial design of lotus seeds drying process.

Research progress and application of ultrasonic‐ and microwave‐assisted food processing technology

“…In the study of Xu et al (2022), the USMD process reduced the drying time of T. fuciformis by up to 42.86% compared to the ultrasonic pretreatment-assisted microwave drying method, and effective moisture diffusivity increased from 1.72 × 10 −5 to 2.28 × 10 −5 m 2 /s. When the microwave power is constant, the increase of ultrasonic power can improve drying efficiency (Wang, Lei, et al, 2021). It is due to the facilitated drying by reduced mass transfer resistance in the food materials on both surfaces and their internal regions, with the increased ultrasonic power (Kowalski et al, 2016).…”

“…The reduction in drying time by USMD inhibits the degradation and oxidation of these nutrients. Lei et al (2021) reported that the USMD method significantly reduced the loss of total sugar, total phenols, and total antioxidants in dried mushrooms. Similarly, Xu et al (2022) reported that the USMD samples showed maximum protein and total sugar content.…”

“…At present, the USMD technology has been reported for drying apple slices (Şen & Aydin, 2020), Tremella fuciformis (Xu et al., 2022), lotus seed (Wang, Lei, et al., 2021), raspberries (Kowalski et al., 2016), green pepper (Szadzinska et al., 2017), and Chinese hickory (Zhang et al., 2021). The USMD drying method improves the drying efficiency, color, and nutrient content of the samples.…”