Spectral shift as advanced index for fruit chlorophyll breakdown

Abstract

The decline of fruit chlorophyll is a valuable indicator of fruit ripeness. Fruit chlorophyll content can be nondestructively estimated by UV/VIS spectroscopy at fixed wavelengths. However, this approach cannot explain the complex changes in chlorophyll catabolism during fruit ripening. We introduce the apparent peak position of the red band chlorophyll absorption as a new qualitative spectral indicator. Climacteric fruit (apple: n = 24, mango: n = 38, tomato: n = 48) were analysed at different ripeness stages. The peak position and corresponding intensity values were determined between 650 and 690 nm of nondestructively measured fruit spectra as well as of corresponding spectra of fruit extracts. In the extracts, individual contents of chlorophyll a, chlorophyll b, pheophytin a and carotenoids were analysed photometrically, using an established iterative multiple linear regression approach. Nondestructively measured peak positions shifted unimodal in all three fruit species with significant shifts between fruit ripeness classes of maximal 2.00 ± 0.27 nm (mean ± standard error) in tomato and 0.57 ± 0.11 nm in apple. Peak positions in extract spectra were related to varying pigment ratios (Rmax = −0.91), considering individual pigments in the pool. The peak intensities in both spectral readings, nondestructive and fruit extracts, were correlated with absolute chlorophyll contents with Rmax = −0.84 and Rmax = 1.00, respectively. The introduced spectral marker of the apparent peak position of chlorophyll absorbance bears the potential for an advanced information gain from nondestructive spectra for the determination of fruit ripeness.