Valorization of Spanish lime (Melicoccus bijugatus) shell waste: optimized pectin recovery and preliminary evaluation in edible film formation

Abstract

Valorizing agro-industrial by-products into high-value materials aligns with the growing emphasis on circular bioeconomy strategies. In this study, shell waste from Spanish lime (Melicoccus bijugatus) was investigated as a novel source of pectin, with subsequent development of an edible film as a potential sustainable packaging application. Response surface methodology was used to optimize the yield and viscosity-average molecular weight of the pectin obtained through hot acid extraction. The pectin was characterized for its physico-chemical and techno-functional properties and then used to develop an edible film. Optimal conditions for maximizing pectin yield (16.37%) were 180 minutes extraction time, a solid–liquid ratio of 1 : 50, and a solvent pH of 1.5 while maximum molecular weight (37 445.18 Da) was achieved at 60 minutes extraction time, a solid–liquid ratio of 1 : 30, and a solvent pH of 3.5. The extracted pectin had an equivalent weight of 1744.66 g mol⁻¹ and was classified as high methoxyl pectin, with a degree of esterification of 80.4%. Notably, the pectin exhibited significantly higher antioxidant activity than commercial citrus pectin, with a 20% greater DPPH radical scavenging capacity and a 6.5-fold higher FRAP value. Preliminary testing of the film made from the extracted pectin showed that the film had a DPPH scavenging rate of 25.6%, a FRAP value of 224.65 and had significantly lower oxygen permeability than both PET and HDPE controls. These results demonstrate that the Melicoccus bijugatus shell wastes are a promising source of antioxidant-rich pectin suitable for edible film applications.