Effect of CPPU on bulk optical properties of kiwifruit during storage in near-infrared range

Abstract

Background: Investigating the effect of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) on the bulk optical properties of postharvest kiwifruit is helpful in understanding the mechanism of identification of CPPU-treated kiwifruit using spectroscopy and to develop effective optical sensing techniques. In this study, the absorption coefficient μ_a and reduced scattering coefficient ${\mu }_s^{\text{'}}$ of flesh and skin of kiwifruit treated with CPPU solutions at CPPU concentration levels (CCLs) of 0, 5, 10 and 15 mg L^-1 were measured by using a single integrating sphere setup over the range 950-1650 nm during 12 weeks' storage.

Results: Generally, at the same storage period, there was no significant difference (P ≤ 0.05) on flesh's μ_a among the kiwifruit treated with different CCLs at absorption peaks of 970, 1190, and 1390 nm. The average flesh's ${\mu }_s^{\text{'}}$ of kiwifruit treated with higher CCLs at 1190 nm were larger than those treated with lower CCLs, and there was a significant difference (P ≤ 0.05) between the kiwifruit treated with 0, 5 and 15 mg L^-1 CPPU solutions except for week 6. Contrasted with the μ_a and ${\mu }_s^{\text{'}}$ of kiwifruit flesh, the μ_a and ${\mu }_s^{\text{'}}$ of skin had bigger standard deviations and larger fluctuations with storage time. Additionally, the CPPU-treated kiwifruit had higher moisture content, lower firmness, and larger cells than CPPU-untreated kiwifruit.

Conclusions: This study indicates that the ${\mu }_s^{\text{'}}$ of flesh has potential in identifying kiwifruit treated with different CCLs during storage. © 2020 Society of Chemical Industry.

Keywords: CPPU; absorption coefficient; kiwifruit; reduced scattering coefficient; storage period.