How pH causes paleness or darkness in chicken breast meat

Chicken breasts (Pectoralis) at a low-pH (5.91 ± 0.12, n = 10) were compared with breasts at a high-pH (6.36 ± 0.25, n = 10, P < 0.001). Low-pH breasts had the highest reflectance (P < 0.001 from 400 to 700 nm). High-pH breasts had the greatest transmittance into their depth and across individual muscle fibres (P < 0.001). The differences in refractive index between ordinary and extraordinary rays across individual muscle fibres were greater in low-pH than in high-pH breasts (P < 0.001). Light at low wavelengths had greater reflectance and lower transmittance than light at long wavelengths (P < 0.001). Myofibrillar refraction contributed to differences in light scattering between PSE (pale, soft, exudative) and DFD (dark, firm, dry) chicken meat, as it does in pork and beef.