Relationship of the bulk optical properties in 950–1650 nm wavelength range with internal quality and microstructure of kiwifruit during maturation

Abstract

Investigating the relationship between bulk optical properties and internal quality/microstructure of kiwifruit during maturation is helpful to understand the evolution mechanisms of physiological properties. In this study, absorption coefficient (μa) and reduced scattering coefficient (μ′s) of kiwifruits during maturation, from 44 days after full bloom (DAFB) to 114 DAFB, were obtained using a single integrating sphere and inverse adding-doubling technique over the wavelength range of 950–1650 nm. Relationships of μa and μ′s with internal quality (i.e., soluble solids content (SSC), moisture content (MC) and firmness (FI)) and microstructural parameters (i.e., area and diameter of cells) were investigated. The results showed that the strongest correlations between μa and SSC and MC were observed around the μa peak of 1390 nm, with correlation coefficients (R) of −0.80 and 0.88, respectively. Over the whole wavelength range, the μ′s had stronger correlation with FI (|R| = 0.74–0.87) than with SSC (|R| = 0.49–0.81) and MC (|R| = 0.59–0.80). The areas and diameters of large and small cells of kiwifruit tissue were highly correlated with the μ′s over the whole wavelength range with R of 0.65–0.91. This study suggests that the bulk optical properties could be used to evaluate the internal quality and microstructure of kiwifruits during maturation.