Prediction Models for Assessing Lycopene in Open-Field Cultivated Tomatoes by Means of a Portable Reflectance Sensor: Cultivar and Growing-Season Effects

Abstract

Reflectance spectroscopy represents a useful tool for the nondestructive assessment of tomato lycopene, even in the field. For this reason, a compact, low-cost, light emitting diode-based sensor has been developed to measure reflectance in the 400-750 nm spectral range. It was calibrated against wet chemistry and evaluated by partial least squares (PLS) regression analyses. The lycopene prediction models were defined for two open-field cultivated red-tomato varieties: the processing oblong tomatoes of the cv. Calista (average weight: 76 g) and the fresh-consumption round tomatoes of the cv. Volna (average weight: 130 g), over a period of two consecutive years. The lycopene prediction models were dependent on both cultivar and season. The lycopene root mean square error of prediction produced by the 2014 single-cultivar calibrations validated on the 2015 samples was large (33 mg kg) in the Calista tomatoes and acceptable (9.5 mg kg) in the Volna tomatoes. A more general bicultivar and biyear model could still explain almost 80% of the predicted lycopene variance, with a relative error in red tomatoes of less than 20%. In 2016, the in-field applications of the multiseasonal prediction models, built with the 2014 and 2015 data, showed significant ( P < 0.001) differences in the average lycopene estimated in the crop on two sampling dates that were 20 days apart: on August 19 and September 7, 2016, the lycopene was 98.9 ± 9.3 and 92.2 ± 10.8 mg kg FW for cv. Calista and 54.6 ± 13.2 and 60.8 ± 6.8 mg kg FW for cv. Volna. The sensor was also able to monitor the temporal evolution of lycopene accumulation on the very same fruits attached to the plants. These results indicated that a simple, compact reflectance device and PLS analysis could provide adequately precise and robust (through-seasons) models for the nondestructive assessment of lycopene in whole tomatoes. This technique could guarantee tomatoes with the highest nutraceutical value from the production, during storage and distribution, and finally to consumers.

Comparison of lycopene changes between open‐field processing and fresh market tomatoes during ripening and post‐harvest storage by using a non‐destructive reflectance sensor

“…The directional reflectance spectra of whole tomatoes were measured in the 400–758 nm range using the LED‐based spectrometers described early …”

“…Lycopene was predicted by the previously defined multi‐seasonal (2014–2015) single‐cultivar PLS models applied to the reflectance spectra of each fruit. The prediction models were explained and characterized in Ciaccheri et al .…”

“…The directional reflectance spectra of whole tomatoes were measured in the 400-758 nm range using the LED-based spectrometers described early. 29,30,35 For the in-field experiment, the marked side of each tomato was measured once for each temporal detection. During storage, for both first and second experiments, the same side of each tomato was measured twice on two adjacent spots and the average of the two reflectance spectra was calculated.…”

“…Alternatively, reflectance spectroscopy and chemometrics can be employed as a non‐destructive technique . We recently developed a prediction model of tomato lycopene by using spectral reflectance detection and partial least square (PLS) analysis and evaluated its robustness against the cultivar and growing season …”

“…27,28 We recently developed a prediction model of tomato lycopene by using spectral reflectance detection and partial least square (PLS) analysis and evaluated its robustness against the cultivar and growing season. 29 The reflectance spectra of tomatoes in the 400-758 nm range were acquired by a low-cost, compact light-emitting diode (LED)-based sensor 30 that can be used directly in the field. This represented a significant advantage with respect to more precise but more expensive laboratory multispectral imaging systems used for lycopene estimation.…”