A research group including Assistant Professor Sachi Katsumata of the Graduate School of Environmental, Life, Natural Science and Technology (Agriculture) at Okayama University and Associate Professor Daichi Ijiri of the Graduate School of Agriculture, Forestry and Fisheries at Kagoshima University has clarified the relationship between protein degradation levels in chicken muscle and the content of umami components (free glutamic acid) in breast meat after aging. The study demonstrated that the accumulation of free glutamic acid in breast meat involves the degradation of specific myofibrillar proteins and the potential action of Calpain 11, which may function within the living body through the aging process. The findings were published in Poultry Science.
Provided by Okayama University
In poultry slaughtering plants, chickens are fasted for approximately 16 hours before slaughtering to prevent contamination from digestive tract contents. However, fasting is known to promote pre-slaughter protein degradation in the muscle through in vivo protein degradation pathways (such as proteasomes, cathepsins, and calpains).
Previous research by the group clarified that longer fasting periods lead to higher levels of pre-slaughter muscle protein degradation, and these degradation levels are associated with the free glutamic acid content in breast meat after aging, as well as the umami and richness values of chicken soup.
On the other hand, since the free glutamic acid content in breast meat immediately after slaughtering did not increase, it was suggested that the increase in free glutamic acid associated with pre-slaughter muscle protein degradation likely occurs only during the aging period. However, the mechanism and the enzymes that contribute to the increase in free glutamic acid content were not known.
The research group conducted the experiment by standardizing the fasting period to the conventional 16 hours. The results revealed that even with a uniform fasting period, chickens with high protein degradation levels in their muscles showed a greater increase in free glutamic acid content during aging.
Furthermore, when the muscle protein degradation level rose, the mRNA expression levels of the proteasome system and the calpain system (Calpain 11) increased in breast meat immediately after slaughtering. Additionally, the free glutamic acid content in breast meat after aging was associated with ATP-independent calpain systems (Calpain 11 and Calpain 2) and cathepsin systems (Cathepsin L-like and H), but no association was found with the proteasome system.
These results suggest that while the proteasome system is mainly involved in pre-slaughter muscle protein degradation, Calpain 11 may contribute to the accumulation of free glutamic acid in breast meat from the pre-slaughter stage through the postmortem aging period.
Furthermore, electrophoresis analysis of breast meat before and after aging found that the band intensities of three unknown myofibrillar proteins located at approximately 12, 13, and 15 kilodaltons changed before and after aging. The amount of change was associated with the free glutamic acid content and umami after aging, the mRNA expression levels of Calpain 11, Calpain 2, Cathepsin L-like, and Cathepsin H, and the pre-slaughter muscle protein degradation level.
These results indicate that the degradation of specific myofibrillar proteins is likely involved in the accumulation of free glutamic acid during aging. This is expected to contribute to the optimization of rearing management and slaughtering conditions, as well as the advancement of research toward improving the flavor of chicken.
Katsumata stated, "In this study, we demonstrated that the protein degradation occurring in chicken muscle is involved in the accumulation of umami components in breast meat after aging, and we investigated that mechanism. I am deeply grateful to Associate Professor Ijiri of Kagoshima University and all the joint researchers for their great support. The time we spent eating together before and after experiments was also precious. I am truly thankful."
Journal Information
Publication: Poultry Science
Title: Individual pre-slaughter muscle proteolysis levels correlated with postmortem taste-related amino acid concentrations in broiler chickens
DOI: 10.1016/j.psj.2026.106553
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