Changes in lactic acid levels during thawing of lamb chops

Loins from 20 lambs with an ultimate pH ranging from 5.5 to 6.4 were frozen and stored at -20 °C, then thawed at + 3 °C. During thawing, muscle (m. longissimus lumborum) lactate was measured in samples taken when the meat temperature reached -20, -5, -2, 0, and + 2 °C. At -5 °C, muscle lactate concentration was similar to that at -20 °C, but at -2 °C lactate levels were double those at -20 °C. As the temperature increased to +2 °C lactate concentrations fell from their -2 °C level. Low pH (5.5-5.6) and intermediate pH (5.7-6.1) meat at +2 °C had a higher lactate level than at -20 °C, with the greatest difference occurring in the low pH group (5 mmol lactate kg equating to approximately 0.05 pH unit increase). High pH meat (6.2-6.3) had similar lactate levels at -20 °C and +2 °C. These results demonstrate the importance of measuring the pH of frozen meat immediately rather than thawing the meat before measurement, and also show that meat pH may change on thawing, depending on the ultimate pH of the sample.