Study on physicochemical properties, antioxidant and antimicrobial activity of okara soluble dietary fiber/sodium carboxymethyl cellulose/thyme essential oil active edible composite films incorporated with pectin Derong Lin a, ⁎ ,1 , Yan Zheng a,1 , Xiao Wang a,1 , Yichen Huang a,1 , Long Ni a,1 , Xue Chen a,1 , Zhijun Wu b, ⁎ ,1 , Chuanyan Huang a , Qiuju Yi a , Jingwen Li a , Wen Qin a , Qing Zhang a , Hong Chen a , Dingtao Wu a a College of Food Science, Sichuan Agricultural University, Ya'an 625014, China b College of Mechanical and Electrical Engineering, Sichuan Agricultural University, Ya'an 625014, China abstract article info Article history: Received 8 May 2020 Received in revised form 24 September 2020 Accepted 1 October 2020 Available online 09 October 2020 Keywords: Edible films Physicochemical properties Antioxidant and antibacterial activity Active edible films based on okara soluble dietary fiber (SDF), pectin, sodium carboxymethyl cellulose (CMC \\ Na) and thyme essential oil (TEO) were successfully prepared. We aimed to exploit biodegradable edible films and realize the full utilization of waste resources. The effects of different amounts of pectin on the properties and structural characterization of the composite film with or without TEO were studied using a solution casting evaporation method. In general, the addition of TEO can improve the properties of the composite membrane. Pec- tin was homogeneously distributed within the films and exhibited good interaction with the polymer matrix. The addition of pectin led to significantly higher mechanical and optical properties of the composite film, compared with SDF/CMC-Na composite film. The tensile strength reached 21.419 ± 2.22 MPa, and the minimum transpar- ency reduced to 88.9% ± 0.42%, with increasing pectin. Notably, the water resistance and oil resistance were en- hanced. The composite films also possessed satisfactory antioxidant activity, with a DPPH-free radical scavenging rate of 46.33% ± 0.72%, while antibacterial activity against E. coli and S. aureus bacteria was not obvious. Antiox- idant and antibacterial SDF/pectin/CMC-Na composite films with enhanced mechanical, optical and barrier prop- erties are excellent candidates for active edible packaging. © 2020 Elsevier B.V. All rights reserved. 1. Introduction The waste of resources and environmental pollution caused by pack- aging based on petroleum-based synthetic polymers are becoming in- creasingly serious [1]. Therefore, environmentally friendly and renewable active packaging based on natural degradable and renewable materials have attracted much attention due to their low impact on the environment and low production costs [2,3]. Edible films prepared from film-forming edible biomacromolecules by the casting method [4] were used to wrap the surface of food and showed tremendous potential re- garding food safety and environmental friendliness. Ecologically sound methods for the production of biodegradable packaging materials that do not compete with commercial applications (e.g., feeding and food patterns) depend on the use of underutilized nat- ural resources and byproducts, such as residues generated during pro- cessing operations [5]. The scientific community [6–8] has expressed considerable concern for the development of biodegradable coatings and films that are produced from biopolymers, extracted from food res- idues. This study innovatively used waste okara as one of the raw mate- rials. Okara is the main soybean byproduct from soymilk and tofu processing, and it contains about 12.6%–14.6% SDF, 40.2%–43.6% insolu- ble dietary fiber, 20% protein, 8% carbohydrate, 1.2% hemicellulose, 1.4% lignin and 0.07% phytic acid [9]. However, most okara is discarded as fertilizer or waste [10]. Using it as a new biodegradable material is a rel- atively new sustainable use of waste to produce additional nutritional value for food packaging [11]. There were few studies on the application of SDF extracted from okara for biodegradable films. Thus, we consid- ered the preliminary purification, separation, drying and pulverization of SDF for the fabrication of edible films in order to improve the utiliza- tion of okara and provide a theoretical basis for the study of SDF-based biodegradable films. Pectin, one of the byproduct materials of the agricultural and food industries, is an effective biopolymer for edible film production, due to International Journal of Biological Macromolecules 165 (2020) 1241–1249 ⁎ Corresponding authors at: 46 Xinkang Road, Sichuan Agricultural University, Ya'an 625014, China. E-mail addresses: lindr2018@sicau.edu.cn (D. Lin), wzj@sicau.edu.cn (Z. Wu), qinwen@sicau.edu.cn (W. Qin), zhangqing@sicau.edu.cn (Q. Zhang), chenhong945@sicau.edu.cn (H. Chen), DT_Wu@sicau.edu.cn (D. Wu). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.ijbiomac.2020.10.005 0141-8130/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac