Chlorogenic acid

According to the previous study on the composition of the exudate droplets of Sclerotinia, eight related organic acids were selected as reference. The reference compounds were oxalic acid (o2si, Charleston, SC, USA), gallic acid, ferulic acid, vanillic acid, chlorogenic acid, tannic acid (ANPEL, Shanghai, China), cinnamic acid (CNW, Duesseldorf, Germany), and caffeic acid (Dr. Ehrenstorfer GmbH, Augsburg, Germany). The purity of these ingredients was >98% as determined by HPLC. For the oxalic acid component of the sample, the chromatographic system was controlled by an Agilent 1260 series HPLC chromatograph equipped with an Athena C₁₈-WP column (2.1 × 150 mm, 3 µm). After diluting the sample 10 times, 5 µL sample was injected. The sample was separated using 0.1% phosphoric acid as the mobile phase (flow rate, 1.0 mL/min) for 15 min at a column temperature of 35 °C. The wavelength of the UV–visible detector was set at 210 nm. To detect the other seven compounds, the sample was passed through an Agilent 1260 series HPLC chromatograph equipped with an Innoval ODS 2 column (4.6 × 150 mm, 5 µm). Separation was carried out under the following chromatographic conditions: injection volume, 10 µL; column temperature, 35 °C; UV detection wavelengths, 265 nm and 323 nm; mobile phase, 0.1% phosphoric acid and acetonitrile with gradient elution at a flow rate of 1.0 mL/min.

Leucine enkephalin was purchased from Waters Corporation (Milford, MA, USA). Chromatography-grade methanol, mass-spectrometry-grade acetonitrile, and formic acid were purchased from Thermo Fisher Scientific (Waltham, MA, USA). Folin & Ciocalteu phenol reagent was bought from Sigma-Aldrich, Co., Ltd. (St. Louis, MO, USA). Ferrous sulfate, ferric chloride, and analytical-grade ethyl alcohol were procured from Tianjin Xinbo Chemical Co., Ltd. (Tianjin, China). Analytical-grade anhydrous sodium carbonate (Na₂CO₃), aluminum chloride (AlCl₃), potassium acetate, and gallic acid monohydrate (purity 99.0%) were obtained from Tianjin Yongsheng Fine Chemical Co., Ltd. (Tianjin, China). The phenolic standards such as rutin, quercetin, ferulic acid, caffeic acid, isorhamnetin, kaempferol 3-O-beta-rutinoside, p-coumaric acid, chlorogenic acid, and isoquercetin were purchased from Anpel Laboratory Technologies Inc. (Shanghai, China). Hydrochloric acid was purchased from Xi’an Chemical Reagent Factory (Xi’an, China). The 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,4,6-tris (2-pyridyl)-s-triazine (TPTZ), and sodium acetate were provided by Beijing Solarbio Science & Technology Co., Ltd. (Beijing, China). Ultrapure water was purchased from Watsons Group Ltd. (Hong Kong, China).

Jujube fruit (Ziziphus jujuba Mill. cv. Junzao) was harvested in December 2020 in Hotan, Xinjiang province (latitude, 79°18′22″; longitude, 37°13′9″). The local climate is temperate continental desert with a high temperature and dry climate, and the annual average rainfall is <50 mm. Approximately 10 kg of dry mature jujube fruit (wet base moisture content, 21%) was collected in foam boxes covered with ice. The samples were sent to the laboratory at Xinjiang Shihezi University within one day. The screened samples were cleaned with double-distilled water (ddH₂O), and stored in a dry and odorless cold storage at 4 °C until drying and analysis were complete.
Caffeic acid, ferulic acid, phloroglucinol, cinnamic acid, chlorogenic acid, p-hydroxybenzoic acid, p-coumaric acid, vanillic acid, gallic acid, catechin, protocatechuic acid, epicatechin, rutin, quercetin, and procyanidins B1 and B2 were obtained from Anpel Co. (Shanghai, China). A total of 37 fatty acid mixed standards, 17 amino acid mixed standards, asparagine, glutamine, citrulline, valine, tryptophan, and 21 hydroxyproline and sarcosine standards were obtained from Sigma Aldrich (St. Louis., Mo, USA).