The formation mechanism and solution for the black bone syndrome of deep-fried chicken legs

The black bone syndrome (BBS) in deep-fried chicken legs, characterized by abnormal browning of bones and adjacent tissues, significantly impacts flavor and consumer acceptance. This study investigated the formation mechanism of BBS in deep-frying process and proposed an industrial solution to mitigate the issue. The results showed that the main cause of BBS lying in the marrow leakage and darkening during deep-frying process. The severity of BBS quantified by the rate of deep extravasation (DEB) increased with the increase of deep-frying temperature (120-180°C) and time (12-18 min), ranging from 0.12% to 16.91%. NMR&MRI analysis indicated that the marrow leakage driven by the thermal expansion of gas micropores and water evaporation. CT and SEM revealed that decreased bone density (0.4565 to 0.3987) and microstructure damage provided channels for the marrow migration. XPS revealed the iron ion-mediated thermal denaturation of hemoglobin led to darkening of marrow. Therefore, the precise marrow separation equipment was designed to remove marrow by drilling and negative pressure extraction. This solution effectively solved the BBS issue without changing the key flavor of deep-fried chicken legs. This work provided important insights into the impact of hot processing on chicken legs and established a new strategy for quality control in chicken processing.