Tailoring hydrophobic alginate amino acid derivatives for food packaging films and coatings

The growing demand for sustainable alternatives to petroleum-based plastics has increased interest in bio-based materials for food packaging. Alginate, a seaweed-derived polysaccharide, is renewable and film-forming but has poor water resistance, limiting its applications. To address this, we synthesized hydrophobic, chemically functionalized alginate–amino acid derivatives and investigated a novel use of these derivatives as coating materials for food packaging applications. Alginate derivatives were synthesized through amidation reactions. Using 2-chloro-1-methylpyridinium iodide (CMPI) activator can improve the degree of substitution compared to 1–3-dimethylaminopropyl-3-ethylcarbodiimide hydrochloride (EDC-HCl). Among the various amino acids tested in their ester forms, including phenylalanine, alanine, lysine, glutamic acid, tyrosine, and serine, only the phenylalanine functionalized alginate compound (Alg-Phe) exhibited water insolubility, making it a promising material for packaging purposes. The chemical structures of the modified alginates were confirmed using DOSY NMR, and FTIR. The hydrophobic Alg-Phe compound was further developed into films and coating materials. Mechanical properties were evaluated to optimize film formulation. Results showed that increasing the polymer concentration in the Alg-Phe films enhanced tensile strength, flexibility, and stiffness. In contrast, increasing the amount of glycerol plasticizer reduced tensile strength and stiffness but improved flexibility as indicated by a higher elongation at break. Additionally, Alg-Phe was applied as a coating on paper, and the modified films and coated surfaces demonstrated strong resistance to water. The coated paper exhibited excellent liquid repellency against substances such as ketchup, cola, coffee, milk, hot water, and laundry detergent. These findings highlight the potential of Alg-Phe as a promising and effective material for packaging applications. • Hydrophobic amino alginate was designed and synthesized. • CMPI yielded a higher degree of substitution than EDC-HCl in the synthesis. • Chemically functionalized Phenylalanine can improve alginate's hydrophobicity. • Alg-Phe (phenylalanine functionalized alginate) coatings showed excellent liquid repellency (ketchup, coffee, etc.). • Biopolymer Alg-Phe can be used as a packaging material.