ABSTRACTŠimoniová A., Rohlík B.-A., Škorpilová T., Petrová M., Pipek P. (2013): Differentiation between fresh and thawed chicken meats. Czech J. Food Sci., 31: 108-115.Adulteration of fresh meat and its possible substitution with frozen and thawed meat represents a problem, since thawed meat has not only lower sensory qualities than fresh meat but also a lower price. Commercial enzymatic kits seem to be a solution to reveal such unfair practises and were applied to detect the activity of specific enzymes, citrate synthase, mitochondrial enzymes that are released from the organelles destroyed by frost. We determined, whether the meat of slaughtered chicken was fresh or frozen/thawed, and to provide convincing results. The absolute results vary with the type of meat and depend on the enzyme used. However, the enzyme activity in the exudates of frozen/ thawed meat is always higher than in fresh meat. This value further increases with each subsequent freezing cycle. The determination of citrate synthase activity was done only in the exudate released from the examined meat samples. However, to determine the enzymes activity directly in unpacked meat, which have not released any exudate, is the subject of further research.

AbstractŠkorpilová T., Šimoniová A., Rohlík B.-A., Pipek P. (2014): Differentiation between fresh and thawed chicken meat by the measurement of aconitase activity. Czech J. Food Sci., 32: 509-513.The presence of mitochondrial enzymes in the exudate of meat might indicate former freezing procedures. Based on this hypothesis, a method was developed to distinguish fresh meat from frozen/thawed meat. Another goal of this study was to compare the activity of mitochondrial enzyme aconitase in meat under different storage conditions. Despite the theory, the detected enzyme was despite the theory also found in the exudate of fresh meat. However, comparing the enzyme activity measured in fresh meat towith that measured in thawed meat, it is obvious that the enzyme activity in frozen/thawed meat is significantly higher. It was further found that the values of aconitase activity also vary in different anatomical parts of chicken meat. This might be caused by slightly different chemical composition of breasts and thighs and by the presence of bone and skin in the samples of chicken thighs