Uv vis 2700 spectrophotometer

The diluted extracts were mixed with 2.5 mL of DPPH methanolic solution (0.06 mM) and allowed to react for 1 h in the dark. Measurements were performed at 515 nm with a Shimadzu UV-VIS 2700 spectrophotometer (Nakagyo-ku, Kyoto, Japan). The analysis was performed in triplicate. The decline in the DPPH radical absorbance concentration caused by the extracts was compared to a Trolox standard. The results were expressed as μmol Trolox equivalent (TE) g⁻¹ dry weight of the samples.^{29,30 (link)}

An initial aqueous solution (50 mg/10 mL) of each soluble dried Arabica coffee extract was prepared. Then, three dilutions of these solutions, with aliquots of 10, 50 and 100 μL, were added to 2 mL of ultrapure water (these solutions also were used for measurement of antioxidant activity, except ORAC).
The total phenolic content of the extracts was determined according to the Folin–Ciocalteu method, as described by Hudáková et al.^{28 (link)} From each of the dilutions, in triplicate, 500 μL was retrieved and added to 2.5 mL of Folin–Ciocalteu reagent and 2.0 mL of 4% sodium carbonate solution. The mixture was allowed to rest for 2 h in the dark. Measurements were performed at 750 nm in triplicate, in a Shimadzu UV-VIS 2700 spectrophotometer (Nakagyo-ku, Kyoto, Japan). Gallic acid, in the concentration range of 0–100 mg mL⁻¹, was used for the calibration curve. The concentration of total phenolic compounds of the extracts was expressed as gallic acid equivalents, which reflect the phenolic content as the amount of gallic acid in mg 100 g⁻¹ dry weight of the samples.

The produced ammonia during NRR was spectrophotometrically detected by the indophenol blue method on a UV-Vis 2700 spectrophotometer (Shimadzu, Japan). In detail, 5.0 mL of sample was diluted with 5.0 mL of deionized water. Subsequently, 500 μL of 0.55 M NaOH coloring solution (5.0 wt.% salicylic acid and 5.0 wt.% sodium citrate), 100 μL of catalyst solution (0.1 g Na₂[Fe(CN)₅NO]·2H₂O diluted to 10 mL with deionized water), 100 μL of oxidizing solution (sodium hypochlorite (ρCl = 4~4.9) and 0.75 M sodium hydroxide) were added respectively to the measured sample solution. After standing at room temperature for 1 h, the UV-Vis absorption spectrum was measured at a wavelength of 697.5 nm. The concentration-absorbance curves were calibrated using standard NH₄Cl solutions with a series of concentrations in 0.1 M Na₂SO₄ solution (pH = 10.5) with and without AgNDs incorporation and the obtained calibration curve (y = 0.013 + 0.811x, R² = 0.999) was used to calculate the produced ammonia concentration.