Uv 2550 ultraviolet spectrophotometer

All chemicals and solvents were purchased from commercial providers and used without purifying. FT-IR spectra were measured using a Bruker ALPHA-T spectrometer (KBr, Bruker, Germany). The ¹H NMR and ¹³C NMR spectra were recorded on a Bruker AVANVE 400 MHz system (Bruker, Germany) using CF₃COOD as the solvent. The HRMS was carried out on an FTMS Ultral Apex MS spectrometer (Bruker Daltonics Inc., USA). The ultraviolet–visible (UV-vis) spectra were gained on a UV-2550 ultraviolet spectrophotometer (Shimadzu, Japan). The fluorescence spectra were obtained through the PerkinElmer LS55 fluorescence spectrometer (PerkinElmer, UK). All pH values were made with PHS-3C pH meter (Inesa, China).

The measurement of anthocyanin content was performed as described previously [40 (link)]. Approximately 0.5 g apple skins were finely ground in 5 mL 1% (v/v) HCl-methanol for 24 h at 4 °C in darkness and centrifuged at 13,000× g for 10 min at 4 °C. Analysis was conducted on a high-performance liquid chromatography (HPLC) system equipped with a photo diode array (PDA) detector (Waters, Milford, MA, USA). Separation of anthocyanins was accomplished on a C18 column (5 μ, 250 mm × 4.6 mm internal diameter, Waters, USA) with cyanidin 3-galactoside as a standard (Sigma).
Chlorophyll was extracted with 80% acetone, and the content was determined on a UV-2550 ultraviolet spectrophotometer (Shimadzu Corp., Kyoto, Japan) according as previously described [41 (link)]. Four independent biological replicates were performed for each experiment. Data are expressed as means ± standard deviation and were assessed via one-way analysis of variance (ANOVA) followed by Tukey’s tests (p < 0.05) using SPSS 16.0 software (SPSS Inc., Chicago, IL, USA).

Here, 50 mL supernatant samples were filtered before the analysis. The analyzed chemical index included ammonium, nitrite, and nitrate. The filtration was carried out on filter membranes (Jinteng, Tianjin, China) with a pore size of 0.45 μm. The ammonium, nitrate, and nitrite were analyzed three times in parallel by a colorimetric assay using a UV-2550 ultraviolet spectrophotometer (Shimadzu, Kyodo, Japan). The COD concentrations were detected by a COD analyzer (HACH, Loveland, CO, USA).