Investigating the influence of pore size, pore fluid and wavelength on backscattering images with sintered glass filter matrices as experimental models

Abstract

Laser backscattering imaging (LBI) is an economic, energy-saving method, which can be applied to characterise bio-organisms in postharvest processes. When applying LBI to horticultural crops, scientists seldom report the cell size of their samples, and often consider the scattering coefficient as constant. The objective of this research was to investigate the influence of pore size, the pore filling for different solutes and concentrations, and wavelength under controlled conditions. Porous glass discs with five different pore diameters from 1 to 160 µm were used as reproducible experimental models for the experiment. NaCl aqueous solutions (0, 1, 2, 3 and 4 mol/L) and NaH2PO4 aqueous solutions (0, 0.8, 1.6, 2.4 and 3.2 mol/L) were applied as pore fills. The LBI system used laser modules at three wavelengths (405, 635, 780 nm). The results revealed that three of the four investigated experimental factors influence LBI, specifically: (i) the pore diameter, (ii) the solutes and (iii) their concentrations. In contrast, the three wavelengths applied did not show clear differences in the LBI patterns. Thus, when applying LBI on fruit for example, the cell size at different depths from the fruit surface needs to be carefully considered.