Effects of multi-frequency ultrasonic assisted sodium hypochlorite on the cleaning effect and quality of fresh-cut scallion stems

This study aimed to evaluate the feasibility of multi-frequency ultrasound-assisted sodium hypochlorite (NaClO) on fresh-cut scallion stem (FCS) cleaning. Ultrasonic cleaning parameters (frequency mode, frequency amplitude, and the sample to water ratios) were optimized against cleanliness and microbial biomass as evaluation indexes. Under the optimum conditions, the free chlorine residues and quality attributes of FCS were also investigated. The results showed that the cleanliness of FCS improved significantly (p < 0.05) and the total number of microorganisms, especially Escherichia coli, decreased dramatically under the optimized cleaning condition with the simultaneous ultrasound (US) at the sweep frequency (SF) combination of 20 + 28 kHz, the ultrasonic density of 60 W/L, pulse time of 10 s, which indicated that the shelf life of FCS would be extended. Compared to FCS after the 250 ppm NaClO cleaning, the retention of ascorbic acid (AA), color, and texture structure of FCS had no significant difference after ultrasound-assisted NaClO treatment. Meanwhile, the content of allicin increased by 52.5% under ultrasound-assisted cleaning. The integration of US into the cleaning process resulted in a notably reduction of 68% in NaClO concentration, as well as the weight loss and respiration rate (RR) of the scallion stems. Therefore, ultrasound-assisted NaClO cleaning was regarded as a promising and effective approach for cleaning fresh-cut vegetables.

Microwave-Driven Electrodeless Ultraviolet Lamp Based on Coaxial Slot Radiator

Microwave-driven electrodeless ultraviolet (UV) lamps have the advantages of high efficiency and high power. However, the conventional microwave system is slightly oversized, which restricts the use of the lamp in a narrow space. A miniaturized microwave-driven electrodeless UV lamp based on a coaxial slot antenna was developed in this study. First, the structure of slots was optimized using a finite-difference time-domain algorithm such that high efficiency of radiated energy could be achieved. Second, a complex model based on the Drude model and the electromagnetic theory was established to simulate the interaction between the microwave and UV lamps. The efficiency and uniformity of the UV lamps were analyzed. Finally, an experimental system was built, and the computed results agreed well with the simulation results. The efficiency of the miniaturized microwave-driven electrodeless UV lamp reached 91.8%.