Measuring pH, Color, and Texture in Muscle

Muscle pH was recorded with a pH meter (HI99163, Hanna Instruments Inc., Washington, DC, United States). Calibration of the pH probe was performed using pH 4.0 and 7.0 standard buffers. Color coordinates (lightness, L*; redness, a*; yellowness, b*; hue angle; chroma) were determined at three random locations using a Minolta CR-400 colorimeter, equipped with a D65 illuminator, 8 mm aperture and 2° viewing angle (Konica Minolta Sensing Inc., Osaka, Japan). Chroma ( $\sqrt{{\left(a^{\ast }\right)}^2+{\left(b^{\ast }\right)}^2}$ ) and hue angle ( ${\tan }^{-1}\frac{a^{\ast }}{b^{\ast }}$ ) values were calculated according to Honikel (23 (link)). Pressing loss was calculated as the difference in weight before and after pressing, divided by initial weight, as reported previously (24 (link)). Briefly, a muscle core sample (25 mm diameter, 10 mm thickness) was weighed, pressed for 5 min under a force of 343 N using a dilatometer, then reweighed. Drip loss and cooking loss of psoas major muscles were measured as reported previously (25 (link)). For cooking loss determination, samples were weighed, sealed in bags, heated to center temperature of 70°C in a water bath (80°C), cooled, refrigerated, wiped dry, and reweighed. After determining cooking loss, the Warner-Bratzler shear force was conducted, on the same samples, with 10 strips (10 mm × 10 mm × 20 mm) using an HDP/BSW V-shaped blade attached to a texture analyzer (TA.XT. Plus, Stable Micro Systems, Godalming, United Kingdom).