Eco-Friendly Algicidal Potential of Zanthoxylum bungeanum Leaf Extracts: Extraction Optimization and Impact on Algal Growth

<i>Zanthoxylum bungeanum</i> leaves were regarded as a waste byproduct for a long period of time, yet their functional components presented potential as novel antimicrobial agents. However, their effectiveness in controlling algal blooms remains unexplored. In this study, the inhibition effect of <i>Z. bungeanum</i> leaf extracts on algal blooms was firstly demonstrated, and the flavonoid profiles of the leaf extract were identified using non-targeted metabolomics analysis. Then, response surface methodology was performed for extraction to further evaluate the feasibility of industrial application. Specifically, the effects of extracts on the cell density, photosynthetic efficiency, and antioxidant activity of <i>Tetrodesmus obliquus</i> was investigated. The results showed that the extraction yield of flavonoids from <i>Z. bungeanum</i> leaves reached 6.85% under the optimized conditions of an ultrasonic power of 600 W, an LSR of 20:1 mL/g, an ethanol concentration of 77.5%, an ultrasonic duration of 18 min, and an ultrasonic temperature of 80 °C, which significantly decreased the Fv/Fm and PIabs values by 54.60% and 98.22%, respectively, after exposure of <i>T. obliquus</i> to 40.0 mg/L <i>Z. bungeanum</i> leaf extract for 66 h. Meanwhile, treatment with <i>Z. bungeanum</i> leaf extract at a dose of 40.0 mg/L generated T-AOC values that were 4.0 times higher than the control without the addition of <i>Z. bungeanum</i> leaf extracts. These results suggest that <i>Z. bungeanum</i> leaf extracts could be used in the development of potentially effective biological algicides. Our study provides data to support the development of algicides and realizes the resource application of <i>Z. bungeanum</i> leaf waste, achieving a synergistic outcome of both economic and ecological benefits.