Specific audible sound waves improve flavonoid contents and antioxidative properties of sprouts

Abstract

Recent studies have suggested that sound waves regulate the growth, phytochemical contents, and stress responses of plants. Here, we investigated the effect of different frequencies of sound waves (0.25, 0.8, 1 and 1.5 kHz) on the flavonoid contents and antioxidative properties of 1–6 day treated sprouts, including red radish (Raphanus sativus), lettuce (Lactuca sativa), and Chinese cabbage (Brassica rapa subsp. pekinensis). These sprouts were treated with each sound wave for 2 h per day for either consecutive (long term [LT]) or three alternating (1st, 3rd, and 5th) days (short term [ST]). The flavonoid contents of the sprouts were found to vary according to the sound frequency, exposure time, species, and growth conditions. A 25–88% increase in flavonoid content could be induced in the sprouts under specific conditions. Quantitative RT-PCR (qPCR) based analysis showed that the expression patterns of the flavonoid biosynthesis-related genes were correlated with the flavonoid contents observed in each treatment suggesting that sound waves regulate the flavonoid biosynthesis pathway. In addition, DPPH and FRAP assays indicated that the antioxidative effects of the sprouts were significantly higher under certain sound wave treatments. Furthermore, the flavonoid accumulation was positively correlated with the antioxidative properties of the sprouts. Therefore, sound waves with a particular frequency could be used to improve the phytochemical contents of crops for functional products.