| 口試日期：2026 |
| 學位類別：碩士 |
| 指導教授：譚發瑞 |
| 研究生：賴穆樺 |
| 摘要 |
| Wooden breast (WB) is one of the more prevalent meat quality abnormalities, or myopathies, observed in the pectoralis major muscle of modern commercial broilers. It is characterized by muscle hardening, abnormal muscle fiber arrangement, connective tissue proliferation, and altered water holding capacity, all of which may affect the appearance, processing properties, texture, and sensory quality of chicken breast meat. Because WB meat often presents processing-related challenges, including reduced marinade uptake, increased firmness, and abnormal tissue structure, evaluating the effects of suitable processing treatments on its quality characteristics is of practical importance. The objective of this study was to investigate the effects of different ultrasonic treatment durations on the quality, tenderness, and microstructure of WB meat. Samples were collected from the pectoralis major muscles of 35-day-old broiler carcasses and classified as normal breast meat or WB meat based on appearance, texture, and tactile characteristics. The experiment consisted of five groups: untreated normal breast meat (NR, 0 min), untreated WB meat (U0, 0 min), WB meat subjected to short-duration ultrasonic treatment (U1, 60 min), WB meat subjected to medium-duration ultrasonic treatment (U2, 80 min), and WB meat subjected to long-duration ultrasonic treatment (U3, 100 min). Among these groups, only NR consisted of normal breast meat, whereas U0, U1, U2, and U3 were all WB samples. After weighing, the samples were combined with 5% sodium chloride solution at a chicken breast-to-brine ratio of 3:1 (w/w), and the meat and brine were placed together in vacuum packaging bags for vacuum packaging. After packaging, the samples were allowed to stand for 30 min and then treated in an ultrasonic water bath for the designated durations. The ultrasonic treatment conditions were 40 kHz, 400 W, and 20 °C. The analyses included color, pH, marinade uptake, cooking loss, water holding capacity, shear force, texture profile analysis, thiobarbituric acid reactive substances, myofibrillar fragmentation index, histological observation, and sensory evaluation. The results indicated that WB meat differed from normal breast meat in several quality attributes, and that the effects of ultrasonic treatment on WB meat varied depending on treatment duration and the parameter measured. In terms of color, the L* and b* values of raw meat did not differ significantly among groups, suggesting that the treatments had limited effects on the color of unheated meat. However, cooked meat color varied with treatment duration, with the cooked L* and a* values of the U2 group being closer to those of the NR group. Regarding pH, the raw meat pH values of the WB groups (U0, U1, U2, and U3) were generally higher than those of the normal group (NR), suggesting that WB meat may inherently have a higher pH. After heating, pH values increased in all groups, possibly because heat-induced denaturation of muscle proteins altered the pH-related status of the meat system. Differences in cooked meat pH among ultrasonic treatment durations may be associated with varying degrees of ultrasonic effects on muscle tissue structure and water status. With respect to processing properties, the WB groups (U0, U1, U2, and U3) had lower marinade uptake than the normal group (NR), while the U2 group exhibited relatively better marinade uptake. Cooking loss did not differ significantly among groups and showed only a decreasing-then-increasing trend; therefore, the results were insufficient to confirm that ultrasonic treatment significantly reduced water loss during heating. In terms of water holding capacity, U1 and U2 improved the water holding capacity of raw meat, while U2 showed better water holding capacity in cooked meat. When the treatment duration was extended to U3, some water holding capacity indicators declined, suggesting that prolonged treatment may impair moisture retention. Regarding tenderness and tissue structure, the U3 group had a lower shear force value, indicating that longer ultrasonic treatment may help reduce the shear resistance of WB meat. Texture profile analysis showed that different treatment durations affected hardness and springiness, whereas chewiness and cohesiveness showed no obvious differences. The myofibrillar fragmentation index results revealed that the MFI values of the ultrasonic treatment groups were higher than those of the untreated group, indicating that ultrasonic treatment promoted disruption of the myofibrillar structure. Histological observations showed that WB samples exhibited irregular muscle fiber arrangement and increased inter-fiber spaces. As ultrasonic treatment duration increased, the spaces between muscle fibers expanded and structural connections weakened. In terms of lipid oxidation, the malondialdehyde content of the WB groups (U0, U1, U2, and U3) in cooked samples was generally higher than that of the normal group (NR), suggesting that WB meat may be more susceptible to lipid oxidation after heating. In addition, different ultrasonic treatment durations affected the extent of lipid oxidation in cooked meat, although the changes did not increase linearly with treatment duration. Sensory evaluation showed that the U0 group scored lower than the NR group in juiciness, textural attributes, and tenderness, whereas some texture-related sensory attributes improved after ultrasonic treatment. Taken together, ultrasonic treatment affected the quality, tenderness, and microstructure of WB meat. These effects may be related to loosening of the muscle fiber structure, increased myofibrillar fragmentation, changes in inter-fiber spaces, and redistribution of water. However, the responses of individual quality attributes to treatment duration were not consistent. The U2 group performed more favorably in marinade uptake, cooked meat water holding capacity, and certain cooked meat color attributes, whereas the U3 group exhibited more pronounced effects in reducing shear force and promoting tissue loosening. Therefore, ultrasonic treatment may be considered a potential processing strategy for improving certain quality characteristics of WB meat. Nevertheless, for practical application, treatment conditions should be optimized according to the targeted quality attributes. |