Effect of a plant growth regulator on optical properties of kiwifruit during growth in wavelength range of 950-1650 nm

Abstract

The absorption coefficient (μa) and reduced scattering coefficient (μ's) of flesh and skin of kiwifruit samples, which were treated with N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU, a plant growth regulator) at the concentrations of 0, 5, 10, and 15 mg/L, were measured using an integrating sphere system in 950–1650 nm and 4–16 weeks after full bloom. The results showed that at the same growth stage, the flesh's μa of CPPU treated kiwifruit were higher than that of CPPU untreated ones at the absorption peaks of 970 nm, 1190 nm and 1390 nm. Over the whole growth stage, the skin's μa of CPPU treated kiwifruit was higher than that of CPPU untreated ones at the absorption peak of 1440 nm. The μ's of flesh and skin almost increased with the increase of CPPU concentration. Both CPPU concentration and growth stage had significant influence on μa and μ's of kiwifruit's flesh and skin at absorption peaks. Moreover, the CPPU treated kiwifruit had higher soluble solids content and moisture content, lower firmness, and larger cell than untreated ones. The study provides useful information for knowing the influence of CPPU on optical properties of kiwifruit, and suggests that the optical properties has great potential in discriminating CPPU treated kiwifruits from untreated ones and even in identifying CPPU concentration.