Impact of RN genotype and ageing time on colour characteristics of the pork muscles longissimus dorsi and semimembranosus.

The effect of RN genotype on pH decline, ultimate pH, pigment content, blooming and colour stability during 6 days of display at 5°C was studied in two pig muscles, M. longissimus dorsi (LD) and M. semimembranosus (SM), and furthermore the effect of anaerobic storage time (2 days vs. 9 days of ageing) on the same parameters was examined. The postmortem pH decline was faster and the ultimate pH lower in LD and SM of the RN(-) genotype compared with corresponding muscles from the rn(+) genotype. Pork of the RN(-) genotype was initially lighter and more red and yellow than pork of the rn(+) genotype due to a higher degree of blooming, which might be explained by the faster pH decline and/or lower ultimate pH. The level of oxymyoglobin (MbO(2)) was decisive for the redness of both muscles during display in air despite a higher presence of metmyoglobin (MetMb). Pork of the RN(-) genotype was thus redder than that of the rn(+) genotype throughout display in air despite higher oxidation to MetMb. Ageing for 9 days in chill improved the blooming potential in pork of both genotypes compared with 2 days of ageing, resulting in superior meat colour. However, only in pork from the RN(-) genotype, the colour was not negatively affected by ageing time upon display in air.