Non-destructive approach for the characterization of the in situ carotenoid deposition in gac fruit aril

Abstract

Carotenoid deposition in gac fruit aril, carrot root, and tomato fruit was investigated in situ using a combination of light microscopy, UV/Vis transmission spectroscopy, and diffuse reflectance spectroscopy. Reflectance data was transformed to absorbance data using the Kubelka-Munk function. As shown by light microscopy, carotenoids of gac fruit aril were deposited in round-shaped chromoplasts, whereas tomato and carrot were characterized by needle-shaped, crystalloid chromoplasts. Crystalline carotenoid deposition in tomato and carrot could be confirmed via polarized light microscopy. By identical means, crystalline deposition of lycopene and β-carotene in gac fruit aril was revealed, most likely in form of microcrystalline aggregates. This hypothesis was supported by a simple solubility estimation based on carotenoid and lipid contents in gac fruit aril. By comparison of UV/Vis absorption spectra recorded from aggregated genuine carotenoid extracts, authentic standards, and transformed reflectance spectra, an H-aggregated form of lycopene in tomato, J-aggregated forms of carotenoids in carrot, and a combination of H-aggregated lycopene, J-aggregated β-carotene, and possibly lipid-dissolved carotenoids in gac fruit aril was confirmed. The present approach was used to gain insights into the aggregate forms of carotenoids in planta, representing a low-cost, non-destructive in situ-characterization method.