Non-contact diffuse reflectance spectroscopy using center-illuminated-area-detection modeled by a simple formula for assessing myoglobin.

A convenience that is desirable in diffuse reflectance spectroscopy (DRS) is to recover the spectral absorption by direct model inversion to facilitate decomposition of spectrally significant chromophores. Attaining such convenience that requires a simple forward model has been challenging in non-contact DRS, for assessing myoglobin forms, which is important to the evaluation of discoloration of meat. This work demonstrates that non-contact DRS configured in a center-illuminated-area-detection (CIAD) geometry [Appl. Opt.61, 9143 (2022) APOPAI0003-693510.1364/AO.468342] may be modeled by an exceptionally simple formula. This simple forward model for DRS in the CIAD geometry on a homogeneous medium has been examined by using Monte Carlo simulations, over a radius of the area of CIAD ranging from 1.5 to 10 mm, for the absorption coefficient to vary five orders of magnitude over , and the reduced scattering coefficient to vary two orders of magnitude over while limited to one scattering phase function. When compared to a previous cumbersome model for the same geometry, the simple model markedly outperforms at high absorption, e.g., . The simplicity of this model facilitates that, with knowledge of the spectral scattering, analytical operation could directly recover the spectral absorption to subsequently use linear inversion to resolve the chromophore proportions. Non-contact DRS in the CIAD geometry of in diameter using this simple forward model has been applied to seven steaks over 6 days of retail display. The progressive changes of myoglobin, including the decrease of oxymyoglobin and increase of metmyoglobin, over 6 days estimated by the simple model of non-contact DRS in CIAD are consistent with those assessed concurrently by a contact DRS using 3 mm source-detector separation [Meat Muscle Biol.5, 1 (2022)10.22175/mmb.12562].