| In China,pork belly is used to make red braised pork belly and Dongpo pork in China(sweet and sour pork is made with pork fillet).Pork belly,referring to the five-layered pork belly meat with the skin-on,is an essential raw material for making bacon in western countries.It has indispensable edible and important economic value in the world.However,the quality or grade of pork belly has not been regarded as one of important indicator of meat quality,and it is often ignored in the pig breeding selection for meat quality.If belly quality or grade could be measured or evaluated in live pigs using B-ultrasound,which can be used in direct breeding selection on meat quality of belly in pig breeding farms.This study investigated the method of determining the grade of belly in live pigs by B-ultrasound.The correlations between the indicators of pork belly quality and its layer number and thickness of fat and muscle layers were analyzed.The accuracy of determining the layer number and thickness of fat and muscle layers in pork belly by B-ultrasound was investigated.The method of determining belly quality by B-ultrasound live pigs was discussed and a scoring system for evaluation on pig belly grade has been established.1.Correlation analysis between the indicators of meat quality and the layer number and thickness of fat and muscle layers in pork bellyThe purpose of this experiment was to analyze the correlation between the indicators of meat quality and the number of layers and the thickness of each fat and muscle layer in pork belly.Thirty-three samples of pork belly(from the front of abdomen to the ribs on the back)with a width of 3 cm were selected from the market in Nanjing,Jiangsu Province,China.Each sample runs along the ribs,and 3 cm wide strips were taken at the 8-9th rib from last,the 3-4th rib from last and the 2-3th lumbar vertebrae.Each sample was equally divided into three parts.The layer number and the thickness of each layer including skin,fat and muscle were recorded.Then each small samples were divided into three parts for determination of drip loss,cooking loss,and sensory scoring of meat quality.Pearson correlation analyses and canonical correlation analyses(CCA)between the indicators of belly composition(the number of layers and the thickness of each fat and muscle layer)and indicators of meat quality of pork belly were carried out.Pearson correlation analyses showed that the ratio of accumulative thickness fat layer to the total thickness of belly(TFT)was negatively correlated with hue angle(H)(r=-0.376;P<0.05).The number of layers(Num)was correlated with H(r=0.485;P<0.01).Num was negatively correlated with redness(a value of Minolta colorimeter)(r=-0.363;P<0.05).There was a significant negative correlation between the ratio of accumulative thickness muscle layer to the total thickness of belly(TMT)and chroma(C)(r=0.431;P<0.05).TMT was correlated with the score of taste(r=0.431;P<0.05)and palatability(r=0.438;P<0.05).A canonical correlation analysis(CCA)between the indicators of belly composition and indicators of meat quality of pork belly was carried out(r=0.751;P<0.05).Among them,TMT,TFT,and TFTM have larger correlation coefficients.The results of CCA showed that palatability,taste and chroma of belly have higher correlation coefficients with these three indicators,which can be used for determination of the pork belly quality.Based on the linear and grading scoring on pork belly meat quality indicators,the formula for calculating the comprehensive pork belly meat quality index was formulated as follows:In the formula,Imq represents the comprehensive meat quality index of the sample,Xi represents the i-th meat quality index of the sample,and σx represents the standard deviation of the i-th meat quality index.The 10 meat quality indicators are drip loss(X1),cooking loss(X2),meat color(X3),pH value(X4),taste/taste(X5),flavor/scent(X6),juiciness(X7),Chewiness(X8),palatability(X9)and total score(X10).A significant correlation was found between the comprehensive meat quality index of pork belly and TMT(r=0.63,P<0.001).But no significant correlation was found between the meat quality index and the number of layers(P>0.05)of pork belly.The above results show that the meat quality indicators of pork belly are mainly related to TMT,TFT and TFTM,but not significantly related to Num.These three indicators can be used to evaluate pork belly quality by using a B-ultrasound instrument.2.Accuracy analysis of the thickness of each layer of pork belly measured by ultrasoundTo study the accuracy and feasibility of B-ultrasound in determining each layer thickness of pork belly,correlation analyses between layer thicknesses of pork belly measured by B ultrasound and those measured by venire caliper were carried out.In this study,160 pig carcasses in a market at Nanjing were selected and measured by a B-ultrasound instrument.The scan depth of B-ultrasonic instrument was 15 cm and the frequency was 3.6 Hz.The B-ultrasonic images were taken at the anterior,middle,and posterior of belly in the carcasses.At the same time,a venire caliper was used to measure the thickness of each layer.The results show that linear regression relationships were found(P<0.001)between B-ultrasound and vernier caliper in determining 13 indicators,such as the thickness of the 1st,2nd,and 3rd fat layers(F1,F2,and F3),the thickness of the 1st,2nd,and 3rd muscle layers(M1,M2,and M3),the number of layers(Num),the total thickness of belly sample(Total),the accumulated thickness of muscle layers(TM),the accumulated thickness of fat layers(TF),TFT,TMT and TFTM.The correlation coefficients(r)were 0.540,0.812,0.847,0.809,0.727,0.907,1.000,0.811,0.729,0.839,0.757,0.757,0.760,respectively.At the anterior belly,in addition to skin thickness(Skin),F1,F2,M1,M2,Num,Total,TF,TM,TFT,TMT,the mean of TM(MM),the mean of TF(MF),the standard deviation of TM(SDM)and the standard deviation of TF(SDF)were significantly correlated between B-ultrasound and vernier caliper measurements(P<0.001);at the middle belly,all indicators were significantly correlated between B-ultrasound and vernier caliper measurements(P<0.001);at the posterior belly,except for Skin,other indicators were significantly correlated between B-ultrasound and vernier caliper measurements(P<0.001).Num has the highest correlation coefficient among all the indicators in the anterior,middle and posterior belly(r=1.000).In addition,the correlation coefficients of TFT(r = 0.848),TMT(r=0.848)and TFTM(r=0.851)between B-ultrasound and vernier caliper measurements were the greatest in the anterior belly.The above results show that the thickness measurement on each layer of pork belly using a B-ultrasound instrument had a certain accuracy.Among them,the B-ultrasound has the highest accuracy for measuring the number of pork belly layers,followed by the accuracy of measuring the thickness of the muscle layer,and the least accurate for measuring the thickness of the skin.The accuracy of TFT,TMT and TFTM at the anterior belly measured by B-ultrasound was higher than those at the middle and posterior belly.3.Establishment and feasibility analysis of a program for determination of belly grade index using B-ultrasound in live pigsIn order to establish a program for the determination of belly grade index using B-ultrasound in live pigs,TMT,TFT and TFTM were used in the evaluation index of belly grade index based on the previous results of this study.The CCA coefficients obtained in the previous results of this study were used as the coefficients in the formula of belly grade index.The grade index(IB)of belly measured by B-ultrasound in pigs was:IB=0.564×TMT-0.335×TFT-0.189×TFTMThe grade index(x)of the anterior belly measured by B-ultrasound and the mean(y)of the grade index of the anterior,middle and posterior belly measured by a vernier caliper showed a linear regression(y=0.842x+0.0201;R2=0.723;P<0.001).From April to June 2019,58 pigs were subjected to ultrasound measurement at a pig farm.The measurement positions were anterior,middle and posterior belly.The correlation between different measurement positions showed that:except for F2,Num and Total,other indicators were significantly correlated between the anterior and middle belly(P<0.05);except for F1,F2,M2,Num and Total,other indicators were significantly correlated between the anterior and posterior belly(P<0.05);except for Skin,F2,M2,Num and TFTM,other indicators were significantly correlated between the middle and posterior belly(P<0.05).The correlation coefficients of M1 between the anterior and middle belly(r=0.734)and between the middle and posterior belly(r=0.565)were the highest.In addition,three indexes TFT,TMT and TFTM in the formula of grade index were significantly correlated between the anterior,middle,and posterior belly(P<0.01).A linear regression was found between B-ultrasound grade index(y)of the anterior belly and the average B-ultrasound grade index(x)of the anterior,middle,and posterior belly(y=0.6184x+0.0934;R2=0.6932,P<0.001).It can be seen that there was a strong linear regression relationship between the belly grade index composed of TMT,TFT and TFTM and the mean of grade indexes at the anterior,middle and posterior belly measured by vernier calipers.The on-site measurement results on a pig farm also showed that the B-ultrasonic determination on the grade index of anterior belly in live pigs is feasible and representative,and can be used as a technical solution for on-site belly quality measurement in pig breeding.In summary,this study developed a comprehensive index(Imq)of belly meat quality,which can be used as an index to measure the quality of pork belly,and has a significant positive correlation with TMT.The CCA also shows that the palatability,taste and color of pork belly were significantly related to TMT,TFT and TFTM.It can be seen that the meat quality of pork belly is mainly related to the ratio of the thickness of muscle layer to fat layer.Correlation analyses between the thickness of each layer measured by B-ultrasound and those measured by vernier caliper showed that the accuracy of the B-ultrasound for measuring the number of layers of pork belly was the best,the accuracy of measuring the thickness of the muscle layer was the second best,and the accuracy of measuring the thickness of the skin is the worst.The accuracy of measuring TFT,TMT and TFTM in the anterior belly was the highest.Therefore,the three indexes of TMT,TFT and TFTM were formulated as the formula for the grade index(IB)in live pigs:IB=0.564×TMT0.335×TFT-0.189×TFTM.The B-ultrasound grade index of the anterior belly and the mean of the grade index of the anterior,middle and posterior belly measured by a vernier caliper had a strong linear regression,which suggests that the B-ultrasonic grade index of the anterior belly is well representative.The on-site measurement results in a pig farm also showed that the program of using a B-ultrasound instrument to determine the grade index of pork belly in live pigs was representative and can be used as a technical program for on-site belly quality determination in pig breeding. |
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