The thermal reaction between cysteine and furfural was investigated at 65 degrees C in five-component food grade oil/water (O/W) microemulsions of R-(+)-limonene/ethanol, EtOH/water/propylene glycol, PG/Tween 60 as apart of a systematic study on the generation of aroma compounds by utilizing structured W/O and O/W fluids. The furfural-cysteine reaction led to the formation of unique aroma compounds such as 2-furfurylthiol (FFT), 2-(2-furanyl)thiazolidine (main reaction product), 2-(2-furanyl)-thiazoline, and N-(2-mercaptovinyl)-2-(2-furanyl)thiazolidine. These products were determined and characterized by GC-MS. Enhancement in flavor formation is termed "microemulsion catalysis". The chemical reaction occurs preferably at the interfacial film, and therefore a pseudophase model was assumed to explain the enhanced flavor formation. The product internal composition is dictated by process conditions such as temperature, time, pH, and mainly the nature of the interface. Increasing water/PG ratio leads to a dramatic increase in the initial reaction rate (V0). V0 increased linearly as a function of the aqueous phase content, which could be due to the increase in the interfacial concentration of furfural. Microemulsions offer a new reaction medium to produce selective aroma compounds and to optimize their formation.

The use of L-cysteine modified silver nanoparticles (Cys-capped AgNPs) as a colorimetric probe for determination of vitamin B1 (thiamine) is described in the present work. This method is based on the measurement of red shift of localized surface plasmon resonance (LSPR) band of Cys-capped AgNPs in the region of 200–800 nm. The color of Cys-capped AgNPs was changed from yellow to colorless by the addition of vitamin B1. The mechanism for detection of vitamin B1 is based on the electrostatic interaction between positively charged vitamin B1, which causes the red shift of LSPR band from 390 nm to 580 nm. The interaction between Cys-capped AgNPs and vitamin B1 was theoretically explored by density function theory (DFT) using LANL2DZ basis sets with help of Gaussian 09 (C.01) program. The morphology, size distribution and optical properties of Cys-capped AgNPs were characterized by transmission electron microscope (TEM), UV-Visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) techniques. The method is linear in the range of 25–500 μg mL⁻¹ with correlation coefficient (R²) 0.992 and limit of detection of 7.0 μg mL⁻¹. The advantages of using Cys-capped AgNPs as a chemical sensor in colorimetry assay are being simple, low cost and selective for detection of vitamin B1 from food (peas, grapes and tomato) and environmental (river, sewage and pond) water samples.

A novel green solvent-based ultrasonic assisted dispersive liquid–liquid microextraction (GS-UADLLME) method was developed for the preconcentration of cadmium and lead ions in various real samples prior to determination by graphite furnace atomic absorption spectrometry (GFAAS). In order to extract trace amounts of cadmium and lead ions, 2-amino-3-sulfhydrylpropanoic acid (l-cysteine) (as a green ligand), tetrafluoroborate ion (BF₄⁻) (as an ion pair agent) and 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄] (as acceptor phase) were used. Different effective factors in the microextraction procedure such as pH of the sample solution, sample solution volume, acceptor phase volume, l-cysteine and tetrafluoroborate concentrations, centrifugation conditions and salting addition were thoroughly optimized. Under the optimum conditions, the calibration graphs were linear in the range of 0.8–180 and 2.5–190 ng L⁻¹ with a correlation coefficient (r²) higher than 0.9967 for the measurement of cadmium and lead ions, respectively. The limits of detection for the determination of Cd(ii) and Pb(ii) for the proposed method were 0.2 and 0.7 ng L⁻¹, respectively. The relative standard deviations (n = 5) for the analyte determination were lower than 3.4%. In order to investigate the method’s accuracy, cadmium and lead contents of a certified reference material, SRM 1643e (NIST), were determined and the results from the proposed method were in very good agreement with the certified values. The suggested method was successfully applied to the determination of cadmium and lead ions in real samples such as real water, soil, rice and tea samples.