Medicinal Plant Research 2024, Vol.14, No.4, 196-209 http://hortherbpublisher.com/index.php/mpr 198 2.3 Seasonal and geographical variation in phytochemical content The phytochemical composition of loquat varies depending on seasonal and geographical factors. Studies have shown that the concentration of bioactive compounds in loquat fruit changes during different ripening stages and across various production locations. For instance, one study evaluated the bioactive compounds in loquat fruits during the ripening process from three different production areas in northeastern Peru. The results indicated significant differences in the total phenolic and flavonoid content among loquat fruits from different regions, with the highest levels found in ripe fruits. In some cases, the phenolic compound content in fruits from certain areas was up to five times higher in ripe fruits compared to unripe ones (Castillo-Chuquizuta et al., 2023). Another study assessed the dynamic changes in phytochemical composition and antioxidant activity in loquat fruits at different ripening stages. It was found that ripe loquat fruits had significantly higher levels of phenolic and flavonoid compounds than unripe fruits, particularly antioxidant components like chlorogenic acid, which were present in higher concentrations during the early stages of fruit development. The study also revealed significant differences in these compounds' levels depending on the growing location, indicating that geographical factors play a crucial role in the accumulation of bioactive compounds in loquat fruits (Zhang et al., 2023). Additionally, the genotype, harvest date, and storage conditions of loquat significantly affect its phytochemical properties. Research has shown that different loquat varieties (such as 'Karantoki' and 'Morphitiki') exhibit significant variations in mechanical properties, storage performance, and phytochemical attributes (including free and bound phenolic compounds and antioxidant capacity) depending on the harvest date. Fruits harvested early displayed higher flesh firmness and phenolic content, while late-harvested fruits showed a significant decrease in titratable acidity and an increase in maturity index (SSC/TA) (Hadjipieri et al., 2020). The study also noted that the harvest date had no significant impact on bound phenolic content, but the contribution of bound phenolics to total phenolics varied between 21.6% and 37.5% under different varieties and storage conditions. 3 Pharmacological Mechanisms of Loquat Bioactive Compounds 3.1 Antioxidant activity Loquat leaves contain various bioactive compounds, including flavonoids and sesquiterpene glycosides, which exhibit significant antioxidant properties. These compounds act by scavenging free radicals, reducing lipid peroxidation, and enhancing the activity of antioxidant enzymes such as superoxide dismutase (SOD) (Jian et al., 2018; Jian et al., 2020a; Chen et al., 2021). For instance, sesquiterpene glycoside 3 (SG3) from loquat leaves has been shown to alleviate oxidative stress by inhibiting cytochrome P450 2E1 (CYP2E1) and enhancing SOD activity (Figure 1) (Chen et al., 2021). Similarly, total flavonoids (TF) from loquat leaves inhibit oxidative stress by downregulating CYP2E1 and upregulating SOD-2 expression (Jian et al., 2020a). In vitro studies have demonstrated that loquat leaf extracts can significantly reduce oxidative stress markers in cell models. For example, SG3 and total sesquiterpene glycosides (TSG) from loquat leaves were found to decrease malondialdehyde (MDA) levels and increase SOD activity in HepG2 cells (Jian et al., 2018; Chen et al., 2021). In vivo studies using animal models, such as db/db mice and cigarette smoke (CS)-induced COPD mice, have shown that loquat leaf extracts can reduce oxidative stress and improve antioxidant enzyme activities (Jian et al., 2020a; 2020b; Chen et al., 2021). These findings suggest that loquat bioactive compounds have potent antioxidant effects both in vitro and in vivo. 3.2 Anti-inflammatory effects Loquat leaves contain bioactive compounds such as triterpene acids and flavonoids that exhibit strong anti-inflammatory properties. These compounds act by inhibiting pro-inflammatory cytokines and signaling pathways. For instance, triterpene acids (TAs) from loquat leaves suppress the generation of pro-inflammatory cytokines like interleukin 1β (IL-1β), IL-6, and tumor necrosis factor α (TNF-α) by regulating AMP-activated protein kinase (AMPK)/nuclear factor erythroid-2-related factor-2 (Nrf2) and nuclear factor kappa B (NFκB) pathways (Figure 2). Similarly, TF from loquat leaves inhibit inflammation by downregulating transient receptor potential vanilloid 1 (TRPV1) and NFκB signaling pathways (Jian et al., 2020b).
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