Postmortem pH evolution in four muscles and onset, state and resolution of rigor mortis of guinea pigs (Cavia porcellus) carcass
The effect of pH on meat quality is a subject that has been deeply investigated extensively in meat science, and there is a wealth of qualitative knowledge. In the same way, rigor mortis is one of the most important physicochemical changes in skeletal muscles occurring at a relatively earlier postmortem period and then maintaining for a certain period, which results in an increasing toughness of meat. No information exists in the literature about the pH evolution or instauration and resolution of rigor mortis in guinea pig. The objetive of this work was to determine the postmortem evolution of pH in four different muscles of guinea pig, as well as to establish the rigor mortis instauration, rigor state and its resolution. Forty eight guinea pigs, randomly selected from the same production system were divided into four groups of 12 animals as follows: 3 months-aged female, 3 months-aged male, 12 months-aged female, and 12 months-aged male. Four muscles, longissimus dorsii (LD), quadriceps femoris (QF), triceps braquii (TB), and psoas major (PM), were used to measure pH at 15, 30, 45 min, each hour from 1 h to 12 h, 15 h, 18 h, 21 h, and 24 h postmortem. These muscles were selected because of energy metabolism described in other species, which PM displays the lowest and LD the highest anaerobic capacity. Analysis of variance with repeated measures was conducted to test the significance of the two variables muscle and time postmortem. Splitting the data was used to check the effect of age or sex. Least squares means were calculated and considered significantly different if P < 0.05. pH started near 7 in LD and TB, followed by QF, and PM had the lower pH value (6.6) at 15m postmortem. pH decreased during the experimental time until 5 hours in TB and QF, and 6 hours in LD and PM. However, pH decline rate was slower for PM, being higher after 6 h than the other muscles. After 12-15 h postmortem, pH values increased slightly. Rigor mortis was onset after 5-6 h postmortem. After rigor onset, the muscle undergoes a longer period of rigor state, which was resolved after 13-15 h postmortem. No differences were found regardless sex or age. In conclusion, authors recommend at least 15 hours of chilling for guinea pigs carcass, until the rigor mortis was resolved.
Keywords: guinea pig, pH, rigor mortis