Previously, research adopted an ultrasound-assisted extraction method to isolate crude polysaccharide from blackened jujube, followed by preliminary structural identification of the purified polysaccharide (BJP). This manuscript analyzed the accurate structure and immunomodulatory activity of BJP. Further structural identification indicated that BJP was mainly composed of →3)-α-L-Araf-(1→, →3,5)-α-L-Araf-(1→, →3)-β-D-GalpA-(1→, →2,4)-β-D-Galp-(1→, →4)-β-D-GalpA-(1→, →3)-α-L-Rhap-(1→ and →3,4)-α-L-Rhap-(1→. The immunomodulatory effects of BJP were examined using a mouse model with immunosuppression induced by cyclophosphamide. The findings suggested that BJP could relieve the condition of immunosuppressed mice. BJP could inhibit decreases in the body weight and organ index of mice, and HE staining showed that BJP could alleviate the harm to spleen and thymus tissues. BJP enhanced the secretion of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), interleukin-2 (IL-2), interleukin-6 (IL-6), immunoglobulin A (IgA), and immunoglobulin G (IgG) in serum. It also reduced liver oxidative stress by increasing superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) activities, while lowering malondialdehyde (MDA) levels. Moreover, BJP contributed to the maintenance of gut homeostasis by stimulating the generation of short-chain fatty acids in the cecal contents. The study aims to establish a solid basis for the comprehensive development of blackened jujube and furnish a theoretical framework for its polysaccharides’ role in immune modulation.

α-Glucosidase inhibitors (AGIs) significantly regulate blood glucose by delaying carbohydrate digestion and slowing glucose absorption, thus playing a critical role in glycemic control. Structurally, dihydromyricetin (Unless otherwise stated, the term dihydromyricetin used throughout this manuscript refers to trans-(2R,3R)-(+)-dihydromyricetin.) differs from myricetin in that the C2=C3 double bond in the C-ring is saturated, resulting in a dihydroflavonol instead of a flavonol. This study investigated the inhibition mechanism of α-glucosidase by the C2=C3 double bond structure using a set of integrated and multi-perspective approaches combining enzyme kinetics, multi-spectroscopic methods, molecular docking, isothermal titration calorimetry (ITC), and surface plasmon resonance (SPR). Myricetin (IC₅₀ = 13.648 ± 0.157 μM) was found to be a more potent α-glucosidase inhibitor than dihydromyricetin (IC₅₀ = 453.922 ± 1.643 μM). Enzyme kinetics indicated that myricetin acted as a competitive inhibitor, whereas dihydromyricetin functioned as a non-competitive inhibitor. To further examine these interactions, multi-spectroscopic analysis demonstrated that binding of myricetin caused significant changes in the microenvironment around fluorescent amino acids (such as tyrosine and tryptophan) in α-glucosidase, resulting in slight unfolding of the enzyme structure. Additionally, molecular docking provided a detailed molecular perspective, identifying hydrogen bonding and hydrophobic interactions as the primary forces driving the binding of two flavonoids to α-glucosidase. Delving deeper into the binding mechanism, ITC analysis provided thermodynamic evidence that myricetin (K_D = 6.215 ± 0.022 μM) exhibited a stronger binding affinity to α-glucosidase than dihydromyricetin (K_D = 232.648 ± 1.236 μM), with both interactions being enthalpy-driven and primarily mediated by hydrogen bonds. Building on this, SPR analysis offered additional insights into the binding process, showing that myricetin not only had a higher binding affinity (K_D = 3.416 ± 0.015 μM) but also a faster association rate (k_a = 1668 ± 23 M⁻¹ s⁻¹) compared to dihydromyricetin (K_D = 11.539 ± 0.056 μM, k_a = 339.7 ± 17.1 M⁻¹ s⁻¹). In conclusion, this study demonstrated that the C2=C3 double bond plays a key role in enhancing α-glucosidase/inhibitor interactions, providing a theoretical basis for the design of novel AGIs and proposing a new set of multi-perspective methods for elucidating these inhibition mechanisms.

Polysaccharides are important bioactive components of dried tangerine peel, exhibiting antioxidant, anti-inflammatory, and hypoglycemic activities. However, the ability of dried tangerine peel polysaccharides to alleviate gastric injury remains insufficiently understood. Therefore, the structure and alleviation of gastric injury induced by dried tangerine peel polysaccharides were explored in this study. Firstly, DTPP-4 was purified from dried tangerine peel. As shown in the HPLC chromatogram, DTPP-4 is a homogeneous polysaccharide with a mean molecular weight of 1.35 × 10³ kDa. DTPP-4 was mainly composed of L-Rha, L-Ara, D-Gal, and D-GalpA with percentages of 10.56%, 9.15%, 4.83%, and 75.45%, respectively. Methylation and NMR results suggested that DTPP-4 was a pectic polysaccharide with →4)-α-D-GalpA-6-OMe-(1→ and →4)-α-D-GalpA-(1→ as the backbone. The alleviation of gastric injury of dried tangerine peel polysaccharide was evaluated in ethanol-induced acute gastric injury mice. Based on the macroscopic images of gastric tissues and the area of gastric tissue injury in mice, the dried tangerine peel polysaccharide can reduce the mouse gastric lesion area and alleviate gastric tissue pathological damage. Histopathological analysis of H&E and PAS staining revealed that the dried tangerine peel polysaccharide could ameliorate the disordered arrangement and necrosis of epithelial cells, reduce inflammatory cell infiltration, and thus alleviate gastric injury. Dried tangerine peel polysaccharide confers gastroprotection by modulating MPO and PGE2 levels, reducing MDA accumulation, enhancing SOD and CAT antioxidant activities, suppressing IL-1β and TNF-α secretion, and upregulating IL-10 expression. These findings provide a theoretical foundation for subsequent structure–activity relationship investigations and provide empirical support for the subsequent development and practical application of this polysaccharide.