Objective At present, the extraction methods of hemicellulose from corn cobs are showing a diversified development trend. Among them, the alkaline solution extraction method is the most fundamental and commonly used one. However, the traditional alkaline solution extraction method has disadvantages such as large consumption of alkaline solution, long reaction and extraction time, and low yield. In this study, corn husk powder, an agricultural waste, was used as the raw material. The Box-Behnken response surface method was employed to optimize the ultrasound-assisted extraction process of corn husk hemicellulose using dilute alkali (KOH).

Methods The single-factor experiments and response surface methodology were combined to systematically optimize the extraction parameters of corn husk hemicellulose, in which the hemicellulose extraction rate was used as the response value while the independent variables selected were KOH concentration, liquid-solid ratio (the ratio of KOH solution volume to corn cob powder mass), ultrasonic time and extraction temperature. A mathematical model was established for optimization analysis, and the structure of the extracted product was characterized through infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy.

Results The results showed that the extraction rate of hemicellulose from corn husks by the ultrasound-assisted dilute alkali was higher than that without ultrasonic treatment. However, the influence of ultrasonic treatment time was the least among the four factors, indicating that ultrasonic wave had played an auxiliary role for the dilute alkaline extraction of hemicellulose from corn cobs. Compared with the traditional alkaline extraction process, the ultrasound-assisted dilute alkaline extraction method used in this work can effectively reduce the concentration of alkali solution, decrease the amount of alkali solution, and significantly shorten the extraction time. The influencing factors, such as KOH concentration, extraction temperature, liquid-solid ratio, and ultrasonic treatment time, had a decreasing impact in sequence on the extraction rate of hemicellulose from corn cobs. Among them, the KOH concentration was the main influencing factor. Its mechanism of action lies in disrupting the hydrogen bonds and ester bonds that connect hemicellulose with lignin and cellulose, significantly enhancing the solubility of hemicellulose in alkaline systems. Based on the quadratic regression model, the optimal extraction conditions obtained through optimization are as follow: KOH concentration of 6.69%, liquid-solid ratio of 17.68 mL/g, ultrasonic treatment time of 34.62 min, and extraction temperature of 63.42 ℃.

Conclusions Under the optimal conditions, the theoretical maximum extraction rate was 34.22%, while the extraction rate obtained from the verification test was 33.88%. The relative error between them was only 0.34%, indicating that the established model has a good fitting effect and predictive ability. The extraction method used in this study has shown excellent results in the extraction of hemicellulose from corn husks. The present ultrasound-assisted dilute alkaline extraction technology provides a new idea for the resource utilization of agricultural waste, and demonstrates good prospects for industrial application in terms of reducing production costs and improving extraction efficiency. It is of great value in promoting the green and efficient utilization of biomass resources.