Uv 550

The light absorption properties were measured using UV–vis diffuse reflectance spectrophotometer (DRS, JASCO, UV-550) with a wavelength range of 200–900 nm. A 300 W xenon lamp (λ > 290 nm, PLS-SXE300CUV, Perfectlight Instruments Co. Ltd., Beijing) was used as light source, and the average light intensity was 78.5mw/cm − 2 (UV-A radiation meter). LC-MS data were measured with Thermo Scientific ISQ QD. ¹HNMR and ¹³CNMR were recorded on a Bruker Avance II 500 spectrometer in CDCl₃ unless stated otherwise, using tetramethylsilane as an internal reference, operated at 500.13 MHz for ¹H, and 125 MHz for ¹³C. J values are given in Hz. Penicillin and intermediate concentrations were measured via HPLC (Dionex and Agilent) with an UltimateR XB C18 column (4.6 × 250 mm, 5 μm) at a flow rate of 1.0 mL min-1, column temperature of 30 °C, mobile phase of methanol and phosphate (0.1 M potassium dihydrogen phosphate, pH 3.5) at a ratio of 50:50, injection volume of 20 μL, and detection wavelength of 225 nm.

The X-ray diffraction (XRD) patterns were performed by an X-Ray diffractometer with Cu Kα radiation (Rigaku Corporation D/max-2400, Japan). The surface morphology of the samples was characterized by using a field emission scanning electron microscope (FESEM, Hitachi SU8010, Japan). The transmission electron microscopy (TEM) images were captured by using a FEI Tecnai G20 (USA). In addition, the chemical states and surface elements compositions were conducted by X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250XI). The UV-Visible diffuse reflection spectra (DRS) were recorded by using an absorption spectrophotometer (JASCO, UV-550) from 200 to 800 nm. The specific surface area and pore distribution were investigated by nitrogen adsorption/desorption isotherms using an automated gas sorption analyzer (Autosorb-IQ, USA).

A 10^–3 M aqueous solution of TPPS (tetrakis(4-sulfonatonphenyl)porphine, Dojindo Laboratories) was prepared and divided into several aliquots in which the as-prepared lipid gels were added. The mixtures were gently shaken for a while and settled overnight under ambient conditions for full absorption of TPPS on the surface of the nanostructures. The excess TPPS in the aqueous solutions was removed using a centrifuge (Anke TGL-16C, Shanghai) at 6000 rpm for 5 min. The green sediments were dispersed in water and re-centrifuged several times until the supernatant liquid was colourless. After that, the sediments were dispersed into 3 mL of aqueous hydrochloric acid (0.1 M) and then centrifuged to remove residual acid. Finally, the sediments were re-dispersed into methanol for UV/Vis and CD spectral measurement on a JASCO UV-550 and J-815 CD spectrophotometer, respectively.

The total polyphenolic content (TPC) compounds in the tea samples were quantified by the Folin-Ciocâlteu colorimetric method as previously described [30 ], with appropriate modifications. The fermented tea sample (0.1 mL) was transferred in an amber glass vial and was added by 2 mL of distilled water, 0.5 mL of the Folin-Ciocâlteu reagent (diluted 1:10 with distilled water), and 0.4 mL of a 7.5% sodium carbonate solution (Na₂CO₃), up to a final volume of 3 mL. The mixture was shaken under constant magnetic stirring for 30 min, at room temperature in the dark. The absorbance was measured at 760 nm using a spectrophotometer Jasco UV-550. Three analyses were carried out for each sample. Gallic acid was used as the standard in order to plot the calibration curve. For the linearity study, an eight-point calibration curve was constructed using different concentrations of gallic acid stock solutions (range 0.5–0.01 mg mL⁻¹). A linear correlation was found between absorbance of the blue complex at 760 nm and concentration of gallic acid in the range 0.5–0.01 mg mL⁻¹ (y = 3.6607x − 0.0036). The coefficient (R²) obtained from the linear regression was 0.9998, indicating an excellent linear correlation between the data. The total phenolic content (TPC) was expressed as µg equivalents of gallic acid (µg GAE) per mL of kombucha.

The scavenging activity on DPPH radical was determined by the colorimetric method previously described [25 ] with slight modification. To different volumes of each sample (10, 50, 100, 200 µL), 0.1 mL of DPPH solution (1 mM) and 2.8 mL of MeOH were added. After an incubation time of 30 min, under magnetic stirring, at room temperature and in the dark, the reduction of DPPH free radical was measured by reading the absorbance at 517 nm using a spectrophotometer Jasco UV-550. The experiments were carried out against a blank (3 mL of MeOH) and a control (2.9 mL of MeOH, 0.1 mL DPPH solution). Each sample was tested in triplicate. The antioxidant activity was given as a percentage of free radical inhibition (%I_DPPH), according to the formula:
%I_DPPH = [(absorbance of the control − absorbance of the sample)/absorbance of the control)] × 100.
The results were expressed also as µg of Trolox equivalents per mL of tea samples (µg TE mL⁻¹).

Total flavonoid content (TFC) was determined by a colorimetric method as described previously [32 (link)]. Briefly, 0.30 mL of the sample solution were diluted with 1.68 mL of distilled water. Then, 0.9 mL of MeOH, 0.06 mL of a 10% AlCl₃ solution, and 0.06 mL of 1 M solution of potassium acetate were added to the solution. The mixture was allowed to stand for 30 min at room temperature, under constant magnetic stirring, in the dark, and then the absorbance was measured against the blank at 420 nm using a spectrophotometer Jasco UV-550. Three analyses were carried out for each sample. Quercetin was used as the standard in order to plot an eight-point calibration curve. The linearity range of calibration curve was 10–0.001 µg mL⁻¹ (y = 0.084x − 0.0019). The coefficient (R²) obtained from the linear regression was 0.9984, indicating a good linear correlation between the data. The results were expressed as µg of quercetin equivalents (µg QE) per mL of kombucha [31 (link)].