2.1 Experimental Materials
The raw materials used in the experiment were corn cobs discarded from agricultural fields surrounding the school. The main chemical reagents included D-xylose (AR), lichen phenol (AR), ferric chloride (AR), hydrochloric acid (AR), and anhydrous ethanol (AR), with deionized water used for all aqueous solutions.
2.2 Experimental Method
The corn cob raw materials were cleaned with tap water to remove dust, dried at 60 ℃, cut into segments, ground with a grinder, sieved through a 100-mesh screen, and the solid powder was placed in a porcelain boat and dried at 102 ℃. The solid powder was mixed with water at a liquid-to-solid ratio of 75:1 mL/g to prepare a slurry, stirred evenly with a glass rod, and then subjected to water bath oscillation at a temperature of 50 ℃, oscillation time of 120 min, and oscillation rate of 180 r/min to obtain the extract. 10 mL of the supernatant was taken and mixed with 10 mL of hydrochloric acid solution (4 mol/L), placed in a 25 mL stoppered test tube, hydrolyzed in a boiling water bath for 120 min, cooled, and then filtered through filter paper to collect the filtrate for later use (it can be appropriately diluted by n times). The filtrate was vacuum concentrated at 40 ℃, then 3 times the volume of 80% anhydrous ethanol was added to precipitate the xylan product, filtered to obtain the filter cake, which was then freeze-dried under vacuum at -56 ℃ and − 0.095 MPa to obtain the xylan solid.
The calculation of the xylan extraction yield refers specifically to NY/T 2335 − 2013 "Determination of Xylan Content in Grains - Spectrophotometric Method".
2.3 Single-Factor Experiments
Single-factor experiments[21, 22, 23] primarily considered the effects of three factors on the extraction rate of xylan: extraction temperature, extraction time, and liquid-to-solid ratio. The liquid-to-solid ratios were tested at five levels: 10:1 mL/g, 25:1 mL/g, 50:1 mL/g, 75:1 mL/g, and 100:1 mL/g, under conditions of a water bath temperature of 40 ℃ and a water bath time of 120 min. Extraction times were tested at five levels: 30 min, 60 min, 120 min, 180 min, and 240 min, under conditions of a liquid-to-solid ratio of 50:1 mL/g and an extraction temperature of 40 ℃. Extraction temperatures were tested at five levels: 30 ℃, 40 ℃, 50 ℃, 60 ℃, and 70 ℃, under conditions of a liquid-to-solid ratio of 75:1 mL/g and a water bath time of 120 min. The suitable range of extraction conditions was determined through response surface optimization experiments.
2.4 Characterization Methods
Characterization was performed using SEM[24, 25, 26] with a Hitachi SU5000 scanning electron microscope (EHT = 20 KV), FTIR[27, 28, 29] with a PerkinElmer Spectrum Two infrared spectrometer (spectral range 4000 − 400 cm^-1, resolution of 0.5 cm^-1), and UV-VIS[30, 31, 32] with a PerkinElmer LAMBDA 365 UV-Vis spectrophotometer (wavelength 200–700 nm), to analyze the structure of the extract.