Structural reorganization and enhancing the functional properties of pumpkin seed protein isolate by conjugation with...

Protein-polysaccharide conjugates were prepared via dry-heated Maillard reaction using pumpkin seed protein isolate (PSPI) and cherry gum exudate (CGE) in a 1:1 weight ratio. The mixture was placed in sealed glass containers with a saturated potassium chloride (KCl) solution to maintain 79 % relative humidity and incubated in a laboratory oven maintained at 60 °C for one week. The conjugated sample (PSPI-CGE CG) exhibited a 32.61 % grafting degree and a decrease in free amino groups from 0.87 to 0.74 mM/mL, confirming successful conjugation. The solubility increased from 16.26 % to 22.38 %, while emulsifying activity index (EAI) and emulsion stability index (ESI) improved from 52.48 m²/g to 98.35 m²/g and 53.55 min to 87.59 min, respectively. The DPPH radical scavenging activity enhanced significantly from 34.20 % to 48.50 %. Circular dichroism revealed a reduction in α-helix content (7.80 → 5.70 %) and an increase in random coils (34.30 → 49.50 %), indicating greater structural flexibility. Thermal analysis showed improved denaturation enthalpy (47.87 → 59.75 J/g), while the zeta potential became more negative (-11.47 → -19.77 mV), reflecting enhanced colloidal stability confirmed moderate crystallinity from Maillard-induced covalent bonding, forming a denser matrix in grafted PSPI. Morphological analysis showed a porous, rough structure, while HPSEC and rheological studies verified covalent linkage and enhanced molecular cross-linking in PSPI-CGE CG. Overall, Maillard-type conjugation effectively improved the functional, structural, and thermal properties of PSPI, suggesting its potential as a multifunctional ingredient for food applications.