Noncontact assessment of oxymyoglobin changes in beef during retail display using diffuse reflectance spectroscopy in a new configuration

Discoloration of meat costs the US beef industry approximately $3.73 billion annually. Currently, hand-held colorimeters are used to assess meat color in three scales, including L* (light vs. dark), a* (red vs. green), and b* (yellow vs. blue). These scales represent sensory perceived color but indirectly represent the myoglobin redox forms that determine the color. We recently used a contact DRS having a 3mm source-detector-separation (SDS) to measure the changes of myoglobin oxygenation of beef during retail display. The reduction of oxymyoglobin (OxyMb) and increase of metmyoglobin (MetMb) resolved by contact DRS were consistent with color changes and metabolic profiles. This study reports the measurements of myoglobin forms of beef in retail display assessed by noncontact DRS, by referencing those assessed with contact DRS and colorimeter. A LED-synthesized broad-band light source was branched to a reference DRS channel configured with the contact probe of 3mm SDS. The light from the synthesized broad-band light source was also branched into a non-contact DRS channel configured in a centerilluminated- area-detection (CIAD) geometry of ~4mm in diameter. Colorimetry, contact-DRS, and non-contact DRS were conducted daily over 6 days on seven USDA Choice longissimus lumborum muscles sliced into ~2.54-cm thick steaks and displayed under controlled LED lighting. Increase in MetMb from <5% to >40% over the 6 days of retail display was consistent across the three methods. The OxyMb and DeoxyMb proportions were consistent between the contact and non-contact DRS. Myoglobin estimation by colorimeter following the American Meat Science Association guidelines potentially significantly overestimated the OxyMb for day0-day3.