The Interaction Between Sour Jujube Kernel Peptide and Pea Starch and Its Effects on Starch Properties and In Vitro Digestibility

In this study, we systematically investigated the concentration-dependent effects of peptides derived from sour jujube kernel peptide (SJKP) on the multiscale structure, physicochemical properties, in vitro digestibility, and antioxidant activity of a complex formed between pea starch (PS) and SJKP. At an optimal SJKP content of 7.5% (w/w, based on starch dry basis), the slowly digestible starch (SDS) and resistant starch (RS) increased by 23.00% and 49.80%, respectively. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT–IR) verified the formation of complexes and enhanced the short-range structural order of starch. Thermal analysis showed that the gelatinization enthalpy increased to 11.73 J/g, accompanied by an elevated gelatinization temperature and improved thermal stability. Conversely, at 15% SJKP content, RDS rebounded to 58.3% due to phase separation and structural collapse of the starch matrix. Intermolecular force analysis revealed that hydrogen bonding dominated at SJKP concentrations ≤ 7.5%, while hydrophobic interactions prevailed at concentrations ≥ 10%. SJKP incorporation also endowed the complexes with antioxidant capacity. These findings illustrate that SJKP interacts with pea starch via non-covalent bonds, forming a mixed gel network. Moderate SJKP levels can effectively modulate starch digestibility and functionality via regulating intermolecular interactions and multi-scale structure, offering promising potential for developing low-glycemic index (LGI) functional foods, including baked snacks, nutritional beverages, and diabetic-specific staple foods.