Hyperspectral FTIR imaging of olive fruit for understanding ripening processes

A combination of micro-FTIR hyperspectral imaging and chemometrics is proposed to better understand biochemical changes in olive fruit during the ripening process without the need for fractionation and related analytical methods. Principal component analysis was used for the study of the spatial distribution of vibrational spectroscopic signatures in flesh, hypodermis and epidermis tissues. Partial least squares discriminant analysis was then employed to highlight the main spectral changes related to ripening. Modifications in cell wall polysaccharides were identified as the major processes taking place during ripening in both the flesh and the hypodermis whereas olive oil accumulation was characteristic in the flesh of the fruit. Evidence of solubilization and depolymerization of cell wall polysaccharides as well as demethylation with the subsequent formation of carboxylate groups were found. Spectral features attributed to polyphenols and sugars also change during the ripening process. No clear temporal trends were observed in the epidermal tissues.