Back to the Wastes: The Potential of Agri-Food Residues for Extracting Valuable Plant Cell Wall Polysaccharides.

The agro-industrial sector generates large volumes of fruit waste each year, leading to environmental concerns and sustainability challenges. In this study, we evaluate the potential of fruit residues-apple, pear, blueberry, tomato, papaya, and a mixed fruit juice blend-as alternative sources of high-value polysaccharides, including pectins, hemicelluloses, and cellulose. Additionally, white strawberry, included as a reference from fresh fruit rather than agro-industrial waste, was analyzed to expand the comparative framework. These biopolymers, naturally derived from the plant cell wall, are renewable and biodegradable, and they possess physicochemical properties suitable for applications in food, pharmaceutical, cosmetic, textile, and bioenergy industries. Using a combination of cell wall fractionation, biochemical characterization, and immunodetection of specific structural domains, we identified significant variability in polysaccharide composition and structure among the samples. Blueberry, pear, and apple residues showed high levels of rhamnogalacturonan-I (RG-I) with extensive branching, while variations in rhamnogalacturonan-II (RG-II) dimerization and the degree of methylesterification of homogalacturonan were also observed. These structural differences are key to determining the gelling properties and functional potential of pectins. In the hemicellulose fractions, xylans and xyloglucans with distinct substitution patterns were especially abundant in apple and pear waste. Our findings demonstrate that fruit processing waste holds significant promise as a sustainable source of structurally diverse polysaccharides. These results support the reintegration of agro-industrial residues into production chains and emphasize the need for environmentally friendly extraction methods to enable industrial recovery and application. Overall, this study contributes to advancing a circular bioeconomy by transforming underutilized plant waste into valuable functional materials.