Thermal resistance and high-performance microwave decontamination assessment of Bacillus endospores isolated from food-grade herbal extracts

Generally, endospore contamination can occur from different sources during product manufacturing in many industries and therefore lower its quality by affecting physicochemical properties and shelf-life. Bacterial endospores can germinate inside the product and produce several enzymes, which can cause several undesirable changes. This study assessed the spores thermal resistance and applied a microwave decontamination technique toward herbal extracts (Tilia tomentosa and Centella asiatica) containing ethanol or glycerol. Based on 16S rRNA analysis, the detected contaminant endospores belonged to different Bacillus species, namely B. subtilis, B. zhangzhouensis, and B. pumilus. The thermal resistance assessment using inoculated endospores in the actual products revealed B. pumilus T2 as the most resistant endospore to the heat treatments tested in both T. tomentosa and C. asiatica extracts. Finally, a high-performance microwave technique was used to decontaminate T. tomentosa extract against the mixture of Bacillus spores. Results from the microwave technique indicate that the increase of temperature from 100°C to 105°C not only decontaminated the product but also could dramatically decrease the effective thermal treatment time (10 times), which can benefit the product quality. The results provided in this study considerably contribute to improving an original decontamination method for products containing glycerol and ethanol with the most negligible effect on product quality.

High Sensitivity Electrical Properties Measurement of Graphene-based Composites using Interferometric Near-field Microwave Technique

High sensitivity electrical properties measurement of composite materials using an interferometric near-field microwave technique is proposed in this paper. A one-port calibration model is developed to relate the measured transmission coefficient to the local properties of the material. To represent the probe-composite sample interaction, an electrical model based on lumped elements is developed. As a demonstration, complex permittivity and conductivity of composite materials prepared with polyvinyl chloride (PVC) and different concentration of graphene are experimentally determined at 2.45 GHz. The obtained results show that the proposed technique is sensitive for the detection of small contrast of permittivity and conductivity in composite material. When graphene concentration increases from 1 to 30%, the conductivity increases from 0.0061 s/m to 0.056 s/m.

Synthesis, Optical Properties and Applications of Ternary Oxide Nanoparticles by a Microwave Technique

Nanocrystal preparation is in high demand due to the development of nanodevices. Nanostructures or microstructures of binary oxides such as TiO2, ZnO, and Al2O3 have been extensively prepared and studied. Synthesis of ternary oxide nanomaterials with controlled structures, morphologies, and sizes are of interest due to their potential applications in nanodevices caused by tunable energy level, bandgap, and structure. In this work, a solution-based method is used to prepare CaWO4 and LaPO4 ternary oxide nanomaterials by microwave technique. Controlled sizes and morphologies including nanorods and microspheres are synthesized by the microwave method, which is believed to be a facile and low-cost technique for the synthesis of ternary oxide nanomaterials. Furthermore, the (relatively) quick process enables high efficiency of the production. The structural and optical properties of the prepared nanomaterials are also investigated in this work. This work benefits nanomaterial synthesis for nanomanufacturing and applications in lighting and photodynamic activations as well as optical storage.