Abstract: To achieve the high-value utilization of apple pomace, pectin (PE) was extracted from apple pomace using an ultrasonic-assisted deep eutectic solvent extraction method. Two fractions, designated PE30 and PE80, were obtained by gradient ethanol precipitation using 30% and 80% (V/V) ethanol, respectively. This study systematically compared the differences in the physicochemical properties of PE30, PE80 and commercial pectin (CP). Furthermore, using PE and sodium alginate (SAG) as composite wall materials, Lactiplantibacillus plantarum (Lp) capsules (SAG-PE-Lp, SAG-PE30-Lp, SAG-PE80-Lp, and SAG-CP-Lp) were prepared by an extrusion method. Their physicochemical properties, structural characteristics, and stability were analyzed. The results showed that ethanol fractionation effectively separated pectin fractions, and the yield of PE30 (57.45%) was significantly higher than that of PE80 (18.11%). PE30 exhibited the highest galacturonic acid content along with a highly linear chain structure, whereas PE80 was characterized by a low molecular mass, a high total sugar content, and a branched conformation. Notably, CP was identified as a low-methoxyl pectin, while PE, PE30, and PE80 were all high-methoxyl pectin. Rheological analysis indicated that all four pectins exhibited non-Newtonian pseudoplastic fluid behavior. The encapsulation efficiency of all four types of capsules was approximately 80%. All capsules exhibited a regular spherical shape with a particle size of approximately 2 mm. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) characterizations confirmed that PE and sodium alginate formed a stable composite gel network through hydrogen bonding, electrostatic interactions, and calcium ion crosslinking, with L. plantarum successfully embedded in the matrix. Stability evaluation demonstrated that the capsules significantly enhanced the freeze-drying tolerance of L. plantarum and its stability during simulated gastrointestinal digestion and storage at 4 ℃. Among the four capsules, SAG-CP-Lp exhibited the best protective effect during gastrointestinal digestion, while SAG-PE-Lp showed the optimal freeze-drying stability. The viable cell counts of all capsules remained above 7 (lg(CFU/g)) after 28 days of storage. This study provides a theoretical basis and technical support for the fractional utilization of pectin derived from apple pomace and the construction of probiotic encapsulation systems.

Key words: apple pomace; pectin; gradient ethanol precipitation; Lactiplantibacillus plantarum; capsules