Sequential Extraction and Physicochemical Property Analysis of Cell Wall Polysaccharides from the Passion Fruit Peels

This study sequentially extracted five cell wall polysaccharides from passion fruit peels using water, cyclohexane-trans-1,2-diamine tetra-acetate (CDTA), Na₂CO₃, and NaOH at varying concentrations. The composition, structure, and physical properties of these polysaccharides were investigated. The results demonstrated that water-extracted polysaccharides yielded the highest content, accounting for 9.04% of the dry weight of the peel's alcohol-insoluble residue. This was followed by polysaccharides extracted with 4 mol/L NaOH (8.15%), 0.05 mol/L CDTA (7.38%), 0.05 mol/L Na₂CO₃ (5.36%), and 1 mol/L NaOH (3.89%). Water-extracted and 0.05 mol/L CDTA-extracted polysaccharides were dominated by homogalacturonan, with molecular weights of 198.46 kDa and 73.67 kDa, respectively. The 0.05 mol/L Na₂CO₃-extracted polysaccharides had a high percentage of rhamnogalacturonan (53.47%) and the most negligible molecular weight (30.29 kDa). The polysaccharides extracted with 1 mol/L NaOH and 4 mol/L NaOH were hemicellulosic in nature, primarily composed of xylose, glucose, mannose, and galactose. All polysaccharides exhibited shear-thinning flow behaviors in aqueous solutions. The 0.05 mol/L Na₂CO₃-extracted polysaccharides showed the highest apparent viscosity and demonstrated elastic behavior, with the elastic modulus G′ exceeding the viscous modulus G″. The water-extracted polysaccharides and the 0.05 mol/L CDTA-extracted polysaccharides exhibited a gel-to-sol transition at angular frequencies near 1.10 and 0.43 rad/s, respectively. The 0.05 mol/L Na₂CO₃-extracted polysaccharides displayed relatively excellent emulsifying ability and emulsion stability. Hemicellulosic polysaccharides exhibited lower viscosity and higher thermal stability. Thus, passion fruit peels contained abundant cell wall polysaccharides, with different polysaccharides showing varied potential for emulsification and food texture improvement. This study provides valuable insights for the in-depth development of the extraction and use of peel polysaccharide fractions.