Organic Acids Copigmentation With Hibiscus syriacus Flower (Hibiscus syriacus L.) Anthocyanins: Thermal Stability,...

Hibiscus syriacus flowers are not only aesthetically pleasing but also palatable. However, their vibrant colors tend to fade easily due to the high concentration of anthocyanins. In this work, three organic acids (malic, tartaric, and citric) were employed to copigment H. syriacus flowers. This investigation systematically examined the effects of these acids on the chromatic properties and thermostability of anthocyanins, with particular emphasis on elucidating the molecular mechanisms underlying copigmentation phenomena. Nontargeted metabolomic analysis revealed the presence of 34 distinct anthocyanins in desiccated H. syriacus flowers. Notably, treatment with organic acids significantly enhanced both the compositional diversity and abundance of anthocyanins relative to untreated controls. All three organic acids demonstrated chromatic effects, enhancing the thermal stability of the anthocyanin extracts and preventing browning at pH 2.2. After being heated at 90°C for 4 h, the retention rates of anthocyanins in the malic, tartaric, and citric acid treatment groups increased by 13.67%, 23.05%, and 13.32%, respectively, compared with the control group. Among the three acids, tartaric acid exhibited the most pronounced stabilization effect. Thermal degradation kinetics of H. syriacus anthocyanins followed first-order reaction models (R² > 0.9). Furthermore, combined spectroscopic and computational analyses-including Fourier-transform infrared spectroscopy (FTIR), molecular docking, and molecular dynamics simulations-demonstrated that organic acids form stable complexes with anthocyanins via intermolecular hydrogen bonding and hydrophobic interactions. Thus, the H. syriacus flowers treated with organic acids exhibited enhanced color and thermal stability compared to untreated anthocyanins, making them suitable for further development into jam products.