Fluorescent properties of surface tissues of apples of different varieties in the green area of spectrum

Abstract

Background: Traditional methods of the content and composition of fruits nutrients determining are labor-intensive and material-intensive, require grinding and special processing of biological material. The fluorescent method is one of the most modern and promising. It allows determining physiological and metabolic parameters without plant tissues destruction. Therefore, the patterns and causes of differences identification of the different apple varieties fluorescent properties is an important task, which will solve the problem of non-invasive determination of the composition and content of useful substances in fruits. Objectives: The determination of the surface tissues fluorescent properties in the green area of the fluorescence spectrum of apple varieties with different coloring of exocarp is the purpose of the work. Materials and methods: The object of the study is apples of four popular winter varieties, close in maturity, with different coloring of exocarp. The method of fluorescence spectroscopy of the apples surface tissues was used. The excitation was made by a semiconductor laser with a wavelength of 405 nm and a power of 36 mW, operating in a continuous mode. The apples coloring is defined as the coordinate a of the CIELAB color mapping system. Results: It was found that the wavelength of the maximum in the green area of the fluorescence spectrum of different apple varieties surface tissues differs by approximately 8–18 nm. At the same time, the difference of wavelengths of the maximum in the red area for different apple varieties does not exceed 5 nm. It was found that wavelength of the maximum in the green area of the fluorescence spectrum differs in different varieties in accordance with the coloring of the exocarp. If green color prevails in the exocarp coloring the fluorescence maximum in the green area has a longer wavelength, and if red prevails it has a shorter wavelength, while if yellow prevails, the wavelength occupies an intermediate position. Conclusions: The pigment composition of the surface tissues of apples affects on their fluorescence in the green area of the spectrum. Possible reasons for the differences of the maximum wavelength in the green area of the fluorescence spectrum are the variability of flavonols composition depending on the apple variety and the influence of red pigments.