Preparation of cellulose nanocrystals from purple sweet potato peels by ultrasound-assisted maleic acid hydrolysis

Abstract

This study aimed at realizing high value utilization of purple sweet potato (PSP) peels. Firstly, ultrasonic assisted ethanol method was used to extract anthocyanins from PSP peels, and the individual anthocyanin composition and antioxidant activity were analyzed. Then the technological parameters of preparing cellulose nanocrystals (CNCs) by ultrasonic-assisted maleic acid hydrolysis were optimized, and Zeta-potential, chemical structure, thermal stability and crystallinity of CNCs were analyzed. Results showed the optimal technological parameters were as follows: the ratio between PSP peel residues and 75 wt% maleic acid was 1:10 (g/mL, W/W), and ultrasonic-assisted hydrolysis was carried out at 60℃ for 1 h, followed by 120℃ for 2.5 h. The yield and Zeta-potential of CNCs were 8.17 % and -57.7 mV, respectively. The chemical structure and physical properties of CNCs were similar to those of commercial CNCs. In conclusion, ultrasound-assisted maleic acid hydrolysis has great potential to realize the industrialization of CNCs.

Keywords: Cellulose nanocrystals; Chemical structure; Crystallinity; Thermal stability; Ultrasound-assisted maleic acid hydrolysis; Zeta potential.