Non-destructive assessment of flesh firmness and dietary antioxidants of greenhouse-grown tomato (Solanum lycopersicum L.) at different fruit maturity stages

Abstract

Non-destructive methods have been widely recognized for evaluating fruit quality traits of many horticultural crops and food processing industry. Destructive (analytical) test, and non-destructive evaluation of the quality traits were investigated and compared for 'Red Rose' tomato (Solanum lycopersicum L.) fruit grown under protected environment. Fresh tomato fruit at five distinctive maturity stages namely; breaker (BK), turning (TG), pink (PK), light-red (LR), and red (RD) were labeled and scanned using the handheld near infra-red (NIR) enhanced spectrometer at a wavelength range of 285-1200 nm. The labeled tomato samples were then measured analytically for flesh firmness, lycopene, β-carotene, total phenolic content (TPC) and total flavonoids content (TFC). The results revealed that quality traits could be estimated using NIR spectroscopy with a relatively high coefficient of determination (R²): 0.834 for total phenolic content, 0.864 for lycopene, 0.790 for total flavonoid content, 0.708 for β-carotene; and 0.679 for flesh firmness. The accumulation of Lyco and β-Car rapidly increased in tomatoes harvested between the TG and the LR maturity stages. Harvesting tomatoes at BK maturity stage resulted in significantly higher flesh firmness than harvesting at the later maturity stages. Tomato fruits had the lowest TPC and TFC contents at the earliest maturity stage (BK), while they had intermediate TPC and TFC levels at LR and RD maturity stages. NIR spectroscopic measurements of fruit firmness and lipophilic antioxidants in tomato fruit at various maturity stages were partially in accordance with those estimated by destructive (analytical) methods. Based on these findings, we recommend using non-destructive NIR spectroscopy as an effective tool for predicting tomato fruit quality during harvest stage and postharvest processing.

Keywords: NIR spectroscopy; Postharvest handling; Quality attributes; Red Rose tomato; Solanum lycopersicum; Spectral analysis.

Fig 1

Raw spectra curves of all tomato samples at various stages of fruit maturity (a), NIR measurements of tomatoes (b), and the five stages of fruit maturity in vertical rows (c): Vertical rows from left to right; (1) Breaker, (2) Turning, (3) Pink, (4) Light-red, (5) Red. Fresh tomato fruits were labeled and scanned using the handheld near infra-red enhanced spectrometer (F-750, Produce Quality Mater, Felix Instruments, Camas WA, USA), at wavelength range (285–1200 nm).

Fig 2

Wave-length influence according to the estimation of fruit quality for: (a) firmness; (b) Lycopene; (c) β-Carotene; (d) TPC; and (e) TFC. Fresh tomato fruit were labeled and scanned using the handheld near infra-red enhanced spectrometer (F-750, Produce Quality Mater, Felix Instruments, Camas WA, USA), at wavelength range (285–1200 nm).

Fig 3

Spectra reflectance (in wave length range 350–1200 nm) of tomato fruit at different maturity stages. The arrow shows the direction of ripening in progress. The reflection spectra was initiated with the spectrophotometer (Model: Felix F-750) around the equator (approximately 120°), at three equidistant positions for each fruit.

Fig 4

Absorbance of tomato fruit at different stages of maturity: (a) Absorbance (log (1/R)); (b) Absorbance of the 1st derivative; and (c) Absorbance of the 2nd derivative. The arrow shows the direction of ripening in progress. Fresh tomato fruits were labeled and scanned using the handheld near infra-red enhanced spectrometer (F-750, Produce Quality Mater, Felix Instruments, Camas WA, USA), at wavelength range (285–1200 nm). The statistical details (e.g means and standard errors) of all quality parameters are shown in Table 1.