Enhanced flavonoids and antibacterial function in Houttuynia cordata with different organic fertilizers

Houttuynia cordata, or fish mint, is an important plant in traditional Chinese food culture. Traditional Chinese herbal medicine books also record H. cordata being used to heal wounds and treat diseases, including dysentery and pulmonary abscesses. However, little is known about factors affecting the nutritional or bioactive contents of H. cordata. Therefore, we sought to investigate how three common household wastes (pomegranate peel, eggshell, and citrus peel) used as organic fertilizers might affect the nutrient composition and antibacterial effect of H. cordata. We hypothesized that adding organic fertilizers to H. cordata would: (1) increase nutritional contents, including plant flavonoids and lysine, and (2) enhance antibacterial function, as measured by inhibition of E. coli growth. We further hypothesized: (3) orange peels would increase nutritional contents and enhance antibacterial function more than the other fertilizer treatments since previous research found the pH of orange peel-amended soils was closest to fish mint’s preferred conditions. We found the overall impact on H. cordata nutritional contents and E. coli inhibitory effect varied by organic fertilizer. Although orange peel powder did increase the plant flavonoid concentration most, pomegranate peel powder enhanced the E. coli inhibitory effect most, and lysine content was not significantly impacted by any treatment. These findings raise the possibility of developing more sustainable H. cordata cultivation, particularly by utilizing relatively inexpensive, widely available, and environmentally friendly organic fertilizers to improve the nutritional and medical value of this important crop.