Antimicrobial Activity of Thinned Strawberry Fruits at Different Maturation Stages

Among the phenolic compounds that is generally present in strawberry fruits, five simple phenolics, three flavonoids, and a stilbene were tested for their antimicrobial activity against seven fungi and one oomycete. trans-Cinnamic acid showed strong antimicrobial activity, and the antimicrobial effect of the simple phenolics decreased with an increase in the number of hydroxyl groups. Phytophthora capsici was the most susceptible to the phenolic compounds tested in this study. trans-Cinnamic acid, p-hydroxybenzoic acid, and kaempferol were mainly detected in 'Seolhyang' strawberry fruits, and the total phenolic contents of the fruits decreased during their development. Extracts of the green (1-10% red color) and red (above 90% red color) strawberry fruits reduced the mycelial growth and zoospore germination rate of P. capsici, and the extract of red strawberry fruit showed strong antimicrobial activity against the zoospore germination of P. capsici. These results indicate that strawberry fruits contain antimicrobial phenolic compounds and that strawberry fruit extract can be used as a natural fungistat.