Comparison Of Muscle Fibers,Meat Quality And Heat Treatments Of Two Distinct Broiler Breeds

Commercial broilers?CB?also known as Arbor Acres are commonly raised and consumed globally as well as in China whereas Yellow-feathered chicken?YFC?are mostly found in Asia,predominantly in China.The population CB and YFC are nearly 4 billion heads constituting the major proportion of meat demands of China.This thesis contained the four steps of experiments to evaluate the meat quality of both breeds in pre and post processing conditions.The first trial was conducted to develop the correlations between muscle fiber characteristics and meat quality attributes in the biceps femoris muscle of CB and YFC.A total of forty as experimental pure breed birds of CB?n=20?and YFC?n=20?were used.After slaughtering at their respective market age of slaughtering:CB 40 d and YFC 120 d,samples were collected for meat quality attributes and myosin ATPase staining for fiber types analyses.Meat quality attributes and muscle fiber characteristics i-e;diameter,cross-sectional area?CSA?and density of CB were significantly different from the YFC?p<0.05?.The percentage of type I fibers were significantly higher in YFC than CB,whereas CSA and fiber diameter were higher in CB?p<0.05?.Negative correlations were obtained between lightness?L*?and type I fiber number percentage in CB?p<0.05?.In YFC fiber number percentage,CSA and diameter of type IIA were negatively correlated with Warner-Bratzler Shear Force.Taken together,muscle fibers characteristics of CB and YFC differ in both breeds and have influenced the meat quality attributes.The second trial of experiment establishes the correlations between meat quality traits and type IIB fibers characteristics of pectoralis major muscle of CB and YFC.Results demonstrated that meat quality traits of pectoralis major muscles were significantly different?p<0.05?in both breeds.Histochemical analysis of fiber density,diameter and CSA of type IIB fibers from each breed?n=20?was performed and compared.The YFC has a smaller fiber diameter?46.41?m?than CB?57.12?m??p<0.05?.Furthermore,fiber diameter and CSA were significantly bigger in CB than YFC whereas fiber density was higher in the latter.Fiber diameter has strong negative correlations between lightness?L*?and strongly positively correlated with redness?a*?in CB chickens.YFC has demonstrated the strong inverse correlations among fiber diameter,CSA and pH₂₄.Hence,type IIB fibers characteristics have varying impact on the meat quality traits of both breeds of chicken.In the third trial,cooking meat at different temperatures resulted in loss of fluids and alterations in its textures.This work signifies the effect of different cooking temperatures on the dimensional changes and biophysical properties of breast meat blocks obtained from CB and yellow-feather chicken YFC.Shrinkage in the length and volume of meat blocks of CB were higher,whereas YFC showed an increase in CSA.At each cooking temperature?60,70,80,90 and 100°C?,mostly there were significant differences?p<0.05?found between meat blocks dimensions of both breeds.Results from the biophysical properties indicated that the cooking of CB meat below 80°C increases its hardness,the opposite was observed for YFC.Cooking at 100°C produced more hardness?34.15 N vs 26.80 N?in YFC meat than CB?p<0.05?.Moreover,cooking at higher temperature produced early gel properties in CB than YFC meat.SDS-PAGE results revealed a similar trend for both breeds except cooking at100°C where CB have more band intensities than YFC.LF-NMR?low-field nuclear magnetic resonance?and MRI?magnetic resonance imaging?data suggested that after cooking at each temperature YFC reserved more water than CB.Physical meat quality traits have correlations with dimensional changes and cooking temperatures.Cooking of YFC meat at 90 and 100°C has demonstrated similar correlation patterns with physical quality traits.Overall,cooking at 100°C caused more undesirable changes in YFC than CB meat blocks.Therefore,it is suggested that cooking at 90°C could be better temperature for YFC meat.In the fourth trial,dimensional changes and water migration of individual muscle fibers and meat blocks of pectoralis major muscle obtained from CB and YFC were affected by early cooking temperatures?30,40,50 and 60°C?.At early heating temperatures?30-60°C?the maximum shrinkage in the volume of meat blocks was higher?10-29%?than the individual extracted fiber fragments?7-19%?.The maximum changes in the width and cross sectional area were significantly higher than the length at each heating temperature in both breeds muscle fibers fragments and meat blocks.However,mostly the maximum changes in dimensions while heating were recorded in CB than YFC.Taken together,these all shrinkages in the muscle fibers and meat blocks are governed by the denaturation of myosin and actin with the rising heating temperature.The results of low field-nuclear magnetic resonance and proton density images demonstrated that CB has a higher tendency to loss water that YFC during heat treatments.SEM?scanning electron microscopy?results showed more damages in CB muscle than YFC by formation of cracks which act as drip channels in the muscle structural architectures.Additionally,CB muscle were harder?64-52 N?than YFC?52-37 N?as affected by heat treatment?30-60°C?.Hence,it is plausible that CB has a lower tendency of water holding capacity due to its higher structural deformations than YFC.