Using fluorescence spectra to quantitatively evaluate the constituent content and functionality of hydroponically grown Fragaria × Ananassa

Strawberry leaves contain polyphenolic compounds such as elagitannins and flavonoids and are thought to possess antioxidant and amyloid-β (Aβ) aggregation inhibitory properties. However, strawberry leaves are usually discarded because their functional components vary with growth stages and environmental factors, and a method that immediately evaluates such functional strawberry leaf components in the field has not yet been developed. In this study, the fluorescence spectra obtained by irradiating strawberry leaves with excitation light were used to analyze strawberry leaves during hydroponic cultivation. Standard methods that assess the functional components (chlorophyll, total polyphenol and flavonoid content, ellagic acid, ferulic acid, naringenin) and functionality (free radical–scavenging activity, ferric reducing antioxidant power, oxygen radical absorptivity, and Aβ aggregation inhibition activity) of plants were performed. The correlations between fluorescence spectra and these parameters were analyzed using spectral indices analyses. The correlation between each spectral index and component amount and functionality of the obtained predictive model was 0.84 ≥ R ≥ 0.61. This new method facilitates the simultaneous and nondestructive prediction of both component content and functionality of strawberry leaves and allows the determination of optimal strawberry leaves for utilization as a source of functional foods and medicinal material.