Lignin-chitosan-based bioplastics from oil palm empty fruit bunches for seed coating

Abstract

Lignin is a hydrophilic-hydrophobic biopolymer known for its antioxidant activity, which could make it a suitable coating material. In this research, a bioplastic based on the combination of alkali lignin from oil palm empty fruit bunches and chitosan was developed for seed coating via a dipping method. Chili seeds were used as a model in this study. The bioplastic was prepared via a modified solvent casting method at lignin:chitosan:glycerol weight ratio of 0.25:1.0:0.2. For the isolated lignin, the antioxidant activity, total phenolic content, methoxyl content, and equivalent weight were measured; for the bioplastic lignin, contact angle, swelling, antioxidant activity, mechanical properties and biodegradability were assessed. The presence of the coating was observed by Cryo-EM while the suitability of lignin-chitosan bioplastics for seed coating was evaluated by the germination rate, root length, height, and dry weight of the sprouts. The results showed that isolated lignin enhances the antioxidant activity of the lignin-chitosan liquid bioplastic by up to 84%. The addition of isolated lignin increased the contact angle and reduced the swelling rate of the bioplastics. The presence of lignin increases the tensile strength and elastic module in the biofilm. The microscopical investigation demonstrated the presence of the coating and no alteration in the seed surface morphology under the coating layer. The application of chitosan-lignin-based bioplastics maintain the quality of the seed during its shelf life. The germination rate of the coated chili seeds increased by up to 100% after one week of storage and 40–80% after five weeks of storage.