A Preliminary Approach to Assess Peach Fruit Texture by Time-Resolved Spectroscopy (Trs)

Abstract

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 nondestructively 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 pigments and flesh constituents produce characteristic spectral features, so that absorption spectra determination gives information concerning the chemical composition. Light scattering inside the medium is due to local variation of the refractive index, and thus scattering spectrum provides information concerning the structural characteristics of the fruits. 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 MilanoDepartment of Physics, was exploited. At least two cultivars for each peach flesh phenotypes (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 higher chlorophyll content corresponds to a less ripe fruit). With the exception of the cultivar 'Iride', particularly rich in anthocyanins, and 'Ghiaccio', a cultivar totally depigmented, the absorption spectra of all the samples are similar. Concerning the scattering properties of peaches, by considering the equivalent density and the scatter power Mie parameters, it is 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.

Emerging nondestructive techniques to quantify the textural properties of food: A state‐of‐art review

“…There is an inverse relationship between reduced scattering with firmness (Rizzolo et al, 2014). The change in the reduced scattering coefficient can be utilized to monitor change in the firmness of the fruits as a virtue of cultivar difference, storage, and processing as well as the development of internal defects and associated biochemical changes in the fruits (Attanasio et al, 2013; Lurie et al, 2011; Rizzolo, Vanoli, Cortellino, Spinelli, & Torricelli, 2011; Rizzolo, Vanoli, Spinelli, & Torricelli, 2010; Vanoli et al, 2014). However, most of the studies are concentrated on the evaluation of texture of apples for their manifestation with aforesaid quality parameters (Table 4).…”