Time-resolved reflectance spectroscopy for non-destructive assessment of food quality

In the majority of most food and feed, visible, and near infrared light undergoes multiple scattering events and the overall light distribution is determined more by scattering rather than absorption due to the microscopic spatial changes in the refractive index. Conventional steady state reflectance spectroscopy can provide information on light attenuation, which depends both on light absorption and light scattering, but cannot separate these two effects. In contrast, time-resolved reflectance spectroscopy (TRS) allows more detailed optical characterization of diffusive media in terms of their absorption coefficient and reduced scattering coefficient. From the assessment of the absorption and reduced scattering coefficients, information can then be derived on the composition and internal structure of the medium. The main advantages of the technique are the absolute non-invasiveness, the potentiality for non-contact measurements and the capacity to probe internal properties with no influence from the skin. In this work we review the physical and technical issues related to the use of TRS for non-destructive quality assessment of fruit and vegetable. A laboratory system for broadband TRS, based on tunable mode-locked lasers and fast micro-channel plate photomultiplier and a portable set-up for TRS measurements, based on pulsed diode lasers and compact metal-channel photomultiplier, are described. Results on broadband optical characterization of fruits and applications of TRS to the detection of internal defects in pears and to maturity assessment in nectarines are presented. Conference: SPIE OPTICS EAST, 9–12 September 2007, Seaport World Trade Center, Boston, MA USA; Session: Optics for Natural Resources, Agriculture, and Foods II; Conference Chairs: Yud-Ren Chen, USDA Agricultural Research Service; George E. Meyer, Univ. of Nebraska/Lincoln; Shu-I Tu, USDA Agricultural Research Service.