Effect of Low Temperature and Long Duration Scalding on Feather Removing and Breast Meat Over Heated of Spent Laying Hens

The purpose of this study was to reduce the loss of spent laying hens during slaughtering by adjusting the parameters of scalding. The research object of this study was the spent laying hens with a rearing age of more than 400 days. The research meant to explore the effect of scalding methods on feather removing and muscle overheating. Three scalding parameters were set as follow: 65 ℃-3 min (high temperature scalding, HS), 60 ℃-4 min 20 s (medium temperature and slow scalding, MSS), and 58 ℃-4 min 20 s (low temperature and slow scalding, LSS). Broilers without scalding were set as the control group. The defeathering effect was characterized by measuring the feather retention force (FRF) and counting the number of feathers remaining after defeathering. The overheating degree of breast muscle was characterized by measuring meat color, depth of overheating area, DSC scanning and Raman spectrum scanning. The results showed that no significant difference in feather removal effects between HS treatments and LSS treatments, while the feather retention force and residual feather number of MSS treatment were significantly lower than those of the other two groups (P<0.05). Residual feather counting results showed that the number of feather roots could be reduced by using long time scalding. The L* value of chicken breast after scalding was significantly higher than that of control group (P<0.05), and the L* value in HS treatments was 5.33 and 4.75 significantly higher than that in LSS and MSS treatments (P<0.05), respectively. When the breast meat was cut along the direction of muscle fiber, it was found that the cross section was significantly stratified (white meat and normal meat). The thickness of white meat in HS treatments was significantly higher than that in LSS and MSS treatments, indicating that the two slow scalding treatments could significantly reduce the degree of breast meat overheating. DSC results showed that although all three scalding treatments resulted in denaturation of myosin, HS treatment induced more denaturation degree of sarcoplasmic protein, collagen and actin compared to the other two treatments. The protein secondary structure relative content showed that the protein denaturation of breast in HS group was the highest. Based on the results of feather removal and breast meat overheating, the optimal scalding parameter combination for laying hens was 60℃-4 min 20 s. This study not only reduced the degree of overheating of breast muscles, but also improved the effect of feather removing, which provided technical reference for enterprises to slaughter spent laying hens.