Lignin as a Natural Antioxidant: Property-Structure Relationship and Potential Applications
Lignin, as one of the most abundant natural polymer compounds in wood and annual plants, has a complex chemical structure. It is fundamentally an aromatic polymer, composed of many aromatic rings with methoxyl and hydroxyl functional groups. Because of it
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Lignin as a Natural Antioxidant: Property-Structure Relationship and Potential Applications Zhao Qin, Hua-Min Liu, Ling-Biao Gu, Run-Cang Sun, and Xue-De Wang
Abstract Lignin, as one of the most abundant natural polymer compounds in wood and annual plants, has a complex chemical structure. It is fundamentally an aromatic polymer, composed of many aromatic rings with methoxyl and hydroxyl functional groups. Because of its multifunctional side groups, lignin can act as a free radical scavenger, thus acting as a natural antioxidant agent. However, extraction conditions, source species and structure affect the antioxidant activity of lignins. As a relatively safe and natural antioxidant, lignin can be used in foods, pharmaceuticals, cosmetics, and industrial materials. In this chapter, the correlation of lignin between structural characteristics and its radical scavenging capabilities, the relationship between antioxidant capacity and potential cytotoxicity, and the advances in commercial applications of lignin as an antioxidant were reviewed and analyzed. Keywords Composite · Cytotoxicity · Modification · Structure-activity relationship
Z. Qin · H.-M. Liu (*) · X.-D. Wang (*) College of Food Science and Technology, Henan University of Technology, Zhengzhou, China e-mail: [email protected] L.-B. Gu School of Biological and Food Engineering, Anyang Institute of Technology, Anyang, China R.-C. Sun Center for Lignocellulose Science and Engineering, College of Light Industry and Chemical Engineering, Dalian Polytechnic University, Dalian, China © Springer Nature Switzerland AG 2020 T. J. Gutiérrez (ed.), Reactive and Functional Polymers Volume One, https://doi.org/10.1007/978-3-030-43403-8_5
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5.1 Introduction Antioxidant agents can prevent or delay oxidation, thus improving the stability of products and prolonging their shelf life. They can be divided into natural and synthetic antioxidants. Synthetic antioxidants, such as butylated hydroxytoluene (BHT), butylhydroxyanisole (BHA), propyl gallate (PG) and tert-butylhydroquinone (TBHQ), represent an important part of the antioxidant market (Yang et al. 2018c). However, the potential toxicity of synthetic antioxidants has been recognized (André et al. 2010). For this reason, more and more attention has been given to natural antioxidants. Natural antioxidants compared to synthetic antioxidants, in particular, polyphenols are biodegradable and non-toxic. Nonetheless, due to their low molecular weight (Mw) and instability at prolonged high temperatures, natural antioxidants cannot prevent oxidation under conditions of thermal stress. Lignin is a natural phenolic polymer with relatively higher thermal stability, thus it has relatively more applications as an antioxidant (Gutiérrez et al. 2016; Gutiérrez and Alvarez 2017). In this sense, interest in the use of lignin is growing. Figure 5.1 clearly illustrates this trend in research publications, while Fig. 5.2 shows the many areas in which lignin research is conducted.
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