Feasibility of a simplified handheld optical system to evaluate fresh-cut Valerianella locusta Laterr

Fresh-cut fruit and vegetable sector could be greatly helped by new analytical methods that are accurate, rapid and integrated into production process to meet consumer demand. The aim of this work was to study the feasibility of a simplified handheld and low-cost optical device, based on measurement and processing of diffuse reflectance at a few wavelengths appropriately selected. This study was focused on identifying the most significant wavelengths able to discriminate freshness levels during shelf life of fresh-cut Lamb’s lettuce (Valerianella locusta Laterr.). For this aim vis/NIR spectra, in the range 340-1000 nm, were acquired for Lamb’s lettuce stored at 4 °C and 20 °C up to 7 and 5 days respectively. A total of 140 samples were analyzed and divided into two categories: before (C1) and after (C2) commercial expiration date. Principal Component Analysis (PCA) highlighted two principal spectral bands (at 680 nm and 740 nm) in which differences between C1 and C2 samples spectra were maximized. Reflectance values at these wavelengths were used to define specific normalized spectral ratios. Based on these relations, a simple classification index was proposed. Results demonstrated the feasibility of a simplified and low-cost handheld device, based on the use of only three wavelengths (680 nm, 740 nm and 850 nm), able to quickly monitoring shelf life of fresh-cut Lamb’s lettuce.