New lignins with antioxidant activity extracted from almond by-products

Lignin, as the most abundant aromatic polymer on the earth, was assessed considering aspects such as sources, type, structure, and isolation processes. Thus, almond shells and almond stems were chosen to aim to represent two different botanical origins, and a study was evaluated to determine their potential properties such as their structural characterization, quantification of their functional groups, and evaluation of thermal properties. A significant difference in the structural characteristics, molecular mass distribution, and thermal properties were observed in each starting material. The almond shells lignin shows a greater content of G-units (66%) than S-units (27%), in contrast to the almond stems lignin, where H-units (60%) are greater than G-units (30%). Therefore, the almond stems lignin has the lowest amount of sugar (15.78%), the highest weight-average molecular weight (9973 g.mol(-1)), the lowest polydispersity index (1.58), and the greatest thermal stability. The antioxidant properties of extracted lignins were evaluated and compared to other commercial products. All the tested lignins exhibit good antioxidant properties that are revealed by the obtained EC50 values, especially for almond stems lignin (EC50=0.485 mg.mL(-1)). As a result of this finding, using lignins extracted from almond by-products as a new antioxidant formulation in textile applications could be very promising. [GRAPHICS]