Chemical and Microscopic Characterization of the Yellow Passion Fruit Peel

Passion fruit (<i>Passiflora edulis</i> f. <i>flavicarpa</i>), commonly known as yellow passion fruit, is widely grown across tropical and subtropical regions worldwide, with Brazil as one of the top producers. Mexico also produces a significant amount of this variety, mainly for juices, jams, or flavoring in desserts. Since this fruit is highly perishable with a short shelf life, it needs to be consumed or used quickly. Although different preservation methods have been suggested, no structural analyses of the peel have been performed to improve these processes. This study aimed to analyze the structural and chemical properties of the peel's cuticular matrix to better understand water loss. CPMAS ¹³C NMR analysis revealed a matrix containing polysaccharides, a small amount of aliphatics, and a notable group of aromatic signals that may indicate lignin presence. This was supported by alkaline hydrolysis, which achieved only 30% hydrolysis. Soluble compounds identified included hexoses, palmitic acid, stearic acid, and derivatives of ferulic and caffeic acids, the latter being parts of lignin monomers. MCL and SEM analyses showed features similar to cutans, including pores along the structures. The BET surface area measurement indicated that the insoluble cuticular material (ICM) has a significant specific surface area. The lignin in the yellow passion fruit peel gives the shell toughness, which, along with its pores, may contribute to dehydration and a short shelf life.