Ultrasonic technology was applied for extraction of polyphenols and antioxidants from the rice bran using ethanol as a food grade solvent. Response surface methodology (RSM) was used to optimize experimental conditions for extraction of polyphenols and antioxidants. Three independent variables such as solvent percentage (%), temperature (°C) and time (min) were studied. Effect of ethanol concentration was found to be significant on all responses. Total phenolic content (TPC) varied from 2.37 to 6.35mg gallic acid equivalent/g of dry sample. Antioxidant activity of the extracts was determined by the ferric reducing antioxidant power (FRAP) assay and scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. FRAP and DPPH values varied from 31.74 to 57.23μmol Fe(2+)/g of dry sample and 16.88% to 55.61% inhibition, respectively. Extraction yields ranged from 11 to 20.2%. Optimal ultrasonic-assisted extraction (UAE) conditions were identified as 65-67% ethanol, 51-54°C, 40-45min. The experimental values agreed with those predicted by SRM models, thus indicating suitability of the model employed and the success of RSM in optimizing the extraction conditions.

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Highly luminescent nitrogen-doped graphene quantum dots (N-GQDs) were prepared from glucose and ammonia as carbon and nitrogen sources, respectively. The N-GQDs showed a strong emission at 458 nm with excitation at 360 nm. The N-GQDs exhibited analytical potential as sensing probes for silver ions determination. Factors affecting the fluorescence sensing of Ag(+) ions such as pH, N-GQDs concentration and incubation time were studied using Box-Behnken experimental design. The optimum conditions were determined as pH 7, N-GQDs concentration 1 mg/mL and time 60 min. It suggested that N-GQDs exhibited high sensitivity and selectivity toward Ag(+). The linear range of N-GQDs and the limit of detection (LOD) were 0.2-40 μM and 168 nM, respectively. The N-GQDs-based Ag(+) ions sensor was successfully applied to the determination of Ag(+) in tap water and real river water samples.

The antioxidant and antibacterial activities of six edible plants were evaluated. The active constituents of the edible plants were extracted using boiling water or 80% methanol. Results demonstrated that extraction of antioxidants by boiling water was more efficient. Lycium depressum and Berula angustifolia had the highest antioxidant activities and, therefore, could be rich sources of natural antioxidants. The antibacterial activities of the extracts were tested against Staphylococcus aureus, Escherichia coli, Entrococcus faecalis and Proteus mirabilis. Further research is needed to isolate, characterize, and identify the bioactive compounds present in these plants.

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