Antioxidant, antimicrobial, and antimutagenic properties of technical lignins and their applications

At present, more than 70 million tons per year of technical lignins are obtained from cellulose pulping and lignocellulosic refineries (e.g., kraft, lignosulfonates, soda, and organosolv lignin). These lignins are commonly incinerated to produce steam and energy, and only a small part is used as an additive in various low volume and niche applications, such as dispersant, in concrete admixtures, as an adhesive and as a binder. Furthermore, the potential of technical lignins is considered to be beyond that of an inexpensive fuel or raw material to produce low added value products. The technical lignins consist of complex polyphenolic polymers that contain numerous chemical functional groups, such as phenolic hydroxyl, carboxylic, carbonyl, and methoxyl groups. The phenolic hydroxyl and methoxyl groups present in lignin reportedly possess various biological activities. The amount of data describing the biological activities of technical lignins has increased in the last 10 years. This review presents the most relevant research concerning the various biological activities (antioxidant, antimicrobial, antimutagenic, and others) of technical lignins. Additionally, the most promising and relevant applications are highlighted.