Capsaicin standard

Capsicum oleoresin was provided by Yingchaolabeier Co., Ltd. (Shandong, China). The capsaicin standard was purchased from Sigma (St. Louis, MO, USA). Macroporous adsorption resins (MARs) D101-1, 201 × 7, HZ202, D301, D301G, D201, and ADS-17 were provided by Hebei Huazhong Chemical Industries Co., Ltd. (Hebei, China). HZ816, HZ835, and HZ915MARs were purchased from Shanghai Huazhen Technology Co., Ltd. (Shanghai, China). The reverse-phase resin (SKP-10-4300) was obtained from Jinan Bona Biological (Jinan, Shandong, China). [Emim] [HSO₄] and [Emim] [OAc] were prepared by Lanzhou Greenchem ILS, LICP. CAS. China (Lanzhou, Gansu, China). Polyethylene glycol (PEG1000, PEG2000, PEG4000, PEG6000) was obtained from Shanghai Lingfeng. Sodium citrate were acquired from Tianjin Guangcheng Chemical Company (Tianjin, China). Methanol (MeOH) of HPLC grade, ethyl acetate, and ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The others reagents were analytical grade. Deionized water was employed throughout in the experiment.

The interaction between chitosan and capsaicin was analyzed by Fourier Transformed Infrared Spectroscopy (FT-IR). The spectra were obtained in a Perkin–Elmer FT-IR Spectrum GX (Shelton, CT, USA) with an average of 16 scans within a spectral range of 4000 to 400 cm⁻¹. The analysis was carried out in liquid media. The identification and content of the capsaicinoids in the samples were determined by comparing the retention times of the capsaicin standard (Sigma-Aldrich Co., St. Louis, MO, USA): The experiment was carried out in an Agilent Technologies 1260 Infinity High Performance Liquid Chromatograph equipped with a photodiode detector, a Zorbax Eclipse XDB-C18 semi-preparative column (5 µm particle size, 250 × 9.4 mm i.d.), and a 20 µL injection loop. Column temperature was set at 20 °C. Elution of components was carried out at a flow rate of 2 mL/min using a linear gradient from 50:50 to 0:100 during the first 9 min [27 (link)].