Spectral evaluation of apple fruit ripening and pigment content alteration

Abstract

The aim of this study was to study spectral-based investigation methods of apple fruit quality parameters for the evaluation of ripeness, water content, and quality monitoring of certain species by rapid, non-invasive way.The research site which is located in North East part of Hungary is an intensive apple orchard with micro irrigation. Considering ripening characteristics, two anthocyanin containing (Gala Galaxy, Gala Must) and two anthocyanin-free (Early Gold, Golden Reinders) apple species were studied. Considering the fruit ripening process of the four apple species, spectral properties, chlorophyll, carotenoid and moisture changes of the skin and the pulp of the fruits were investigated.Conforming to the results, carotenoid–chlorophyll ratio is appropriate for the characterization of ripening process in anthocyanin free species. Based on the spectral data, 678nm wavelength is sensitive for low chlorophyll content, therefore RED interval (678nm) is suitable for examining the ripeness and ripening process. Though reflectance at 678nm±30nm wavelength showed greater variability for high chlorophyll content, therefore reflectance, measured on 700nm can be applicable for monitoring the early stage of ripening and the pigment content changes. New ripening monitoring spectral indices were set up, which are feasible for surveying pigment changes within the ripening process of anthocyanin-free species. The water-content and the Water Band Index (WBI) are not suitable for monitoring the ripening, but it can be applied for surveying the moisture content changes during the postharvest period.