A preliminary approach to assess peach fruit texture by time-resolved spectroscopy (TRS)

Most fruits can be modeled for their internal composition as a diffusive medium at visible and near-infrared wavelengths. The low absorption in this spectral range allows exploiting VIS/NIR spectroscopic techniques to probe non-destructively the internal food properties. Time-resolved reflectance spectroscopy (TRS), in particular, allows the separate, but simultaneous estimation of absorption and scattering coefficients. Absorption and scattering properties give very different information about the medium investigated. The possibility of applying TRS to assess the texture type of peach fruit was tested. To this purpose, an instrument for TRS developed at Politecnico di Milano-Department of Physics, was exploited. At least two cultivars for each peach flesh phenotype (melting, non-melting, stony hard and slow melting) and a total of 30 fruits for each cultivar were analyzed over the spectral range 540-940 nm. The absorption spectra exhibit high values around 550 nm due to the anthocyanins' absorption features. Furthermore, an absorption peak is visible at 670 nm, linked to the chlorophyll a content and then gives an idea about the fruit ripeness (a high chlorophyll content corresponds to a less ripe fruit). With the exception of the cultivar 'Iride', particularly rich in anthocyanins, and 'Ghiaccio', anthocyaninless, the absorption spectra of all of the samples were similar. Concerning the scattering properties of peaches, by considering the equivalent density and the scatter power Mie parameters, it was possible to discriminate between three out of four texture types (melting, slow melting and stony hard). Further improvements may lead to a full discrimination in the future.