Use of optical absorption and scattering properties to monitor the change of chemical characteristics, particle structure and viscoelasticity during apple puree processing.

This work explored the optical absorption (μ) and reduced scattering (μ') properties at 400-1050 nm (Vis-NIR) and 900-1650 nm (SWIR) of apple puree at different heating times to evaluate their changes in composition and structure. The optical absorption and scattering coefficients of μ and μ' decreased with increasing heating time. The specific μ' coefficients at 432 nm, 455 nm, 1183 nm and 1304 nm were related to particle structural changes. The partial least squares regression (PLSR) models based on μ' coefficients in the combined Vis-NIR and SWIR regions provided satisfactory estimations of puree particle area (R = 0.90) and particle perimeter (R = 0.85), whereas the μ' coefficients in the Vis-NIR region predicted puree viscosity (R = 0.83), elasticity modulus (R = 0.81) and viscous modulus (R = 0.78). Consequently, optical properties can be a potential tool to determine structural and rheological changes of apple puree.