Citric acid-based microwave and ultrasonic extractions of lemon peel pectin and their effects on the properties of pectin films.

This study investigated the valorization of agro-industrial lemon peel waste via microwave- and ultrasonic-assisted extractions with organic acid (citric acid). The resulting pectin samples were designated as CMP and CUP, respectively. The microwave extraction yield was higher and required a shorter processing time than the ultrasonic process. Physicochemical characterization revealed that, while both pectins had similar high degrees of methylation, CUP possessed a substantially higher molecular weight than CMP and a more compact, globular hydrodynamic shape. Pectin films were subsequently prepared, and their functional properties were evaluated. Despite its lower molecular weight, the CMP film exhibited markedly superior mechanical performance, achieving a tensile strength 2.7 times that of the CUP film and a better water contact angle. This counterintuitive result in strength is attributed to the more efficient packing of the flexible small random coils of CMP molecules, resulting in a more cohesive network. Conversely, the CUP film was more transparent and smoother, with a lower oxygen transfer rate compared to the CMP film. These findings demonstrate that extraction methodology can be tuned to tailor pectin functionality: MAE is preferable for mechanically robust films, while UAE is suited for applications requiring high transparency.