Effect of Near-infrared Scanning Angle in Prediction of Tenderness and Sensory Attributes in Longissimus Thoracis Steaks

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Variation in beef tenderness is a primary concern of the U.S. beef industry. In order to maintain uniform quality, near-infrared (NIR) is used as a rapid, accurate tool; however, there has been inconsistency in the ability of NIR to accurately predict beef tenderness. The objective of this study was to test the effects of scanning angle on longissimus thoracis steaks from Certified Angus Beef (CAB) and USDA Select ribs. Steaks, aged for either 0 or 14 d (24 steaks/aging period), were randomly assigned to one of three treatments in which the scanning angle of NIR and Warner-Bratzler shear force (WBSF) angle were varied. Steaks in the first two treatments were scanned with the light source and optical sensor perpendicular to the surface, and WBSF angle parallel and perpendicular to muscle fiber orientation, whereas, steaks in the third treatment were scanned with light source, optical sensor, and WBSF angle parallel to muscle fiber orientation. In addition, steaks were scanned at random 10° angles. Results indicated obvious amplitude differences, as evidenced by reflectivity values of approximately 0.349, 0.342, and 0.261at 811 nm for 10, 20 and 30° angles respectively. Because there was differences in amplitude with respect to the angle of scanning, chemometric modeling WBSF values with steak reflectance using partial least squares (PLS) resulted in coefficient of determination of 0.17, 0.23, and 0.18 (visible spectrum), and 0.14, 0.01, and 0.16 (NIR spectrum) for treatments 1, 2, and 3 respectively. Shear force values did not (P > 0.10) differ among treatments; however, 14-d aged steaks from CAB ribs had lower WBSF values than CAB steaks aged 0 d and USDA Select steaks aged 0 or 14 d (quality grade × aging time interaction; P < 0.01). Near- infrared spectroscopy may be an accurate tool to predict moisture, fat, and protein content of meat, but results of this study indicate that steaks may not be accurately classified into tenderness categories unless the scanning angle is standardized.