Catechin nucleophilic depolymerization of Aronia melanocarpa polyproanthocyanidins by different physical field assistance: Process optimization, product structure characterization and biological activity evaluation in vitro.

The High-polymeric proanthocyanidins (PPC) derived from Aronia melanocarpa (AM) are prone to inducing digestive discomfort, restricting the development of related products. Meanwhile, traditional nucleophilic depolymerization requires high-cost monomers, underscoring the urgent need for improved methods. Herein, we employed response surface methodology optimizing the process of ultrasonic waves, a pulsed electric field (PEF), and electron beam irradiation for catechin nucleophilic depolymerization, further screening optimal depolymerization conditions for PPC. The structures of the depolymerization products were characterized by spectroscopy, chromatography, mass spectrometry, and thermodynamic analysis. The antioxidant activity was evaluated using the ABTS, DPPH, and hydroxyl radical scavenging assays, as well as mitochondrial membrane potential assays. Under optimal conditions, oligomers with lower average degrees of polymerization (DP) were produced: ultrasound+catechin (DP = 2.39 ± 0.15), PEF + catechin (DP = 2.20 ± 0.17), and electron beam+catechin (DP = 1.94 ± 0.15). For antioxidant activity, ABTS scavenging and cell protection followed the order: irradiation of electron beam combined with nucleophilic depolymerization of proanthocyanidin products (INPC) > electric field combined with nucleophilic depolymerization of proanthocyanidin products (ENPC) > ultrasound combined with nucleophilic depolymerization of proanthocyanidin products (UNPC) > nucleophilic depolymerization products (NPC) > PPC. Vitamin C (Vc) outperformed others in hydroxyl radical scavenging. All products were non-toxic to Caco-2 cells. This study indicates that the physical field-nucleophilic depolymerization system can effectively reduce the DP of PPC and enhance its antioxidant activity at a low catechin dosage, providing a new strategy for the economical and efficient depolymerization of PPC and boosting the development of the deep-processing industry for AM.