Study On The Effects Of Protein Oxidation Of Soybean Meal On Digestive Function,Antioxidant Status And Meat Quality In Broilers

The soybean meal(SBM)is the most frequently used protein source in diet formulations for broiler chickens,and the good-quality of SBM proteins is needed for maintaining growth and health.Transportation,storage and processing can cause oxidative modification of protein in soybean and soybean meal,however,information regarding the effect of oxidative modification of SBM in feed on its quality of protein and broilers are sparse.Therefore,current study evaluated the effects of heat treatment in vitro on protein oxidation in SBM,and the effects of protein oxidized SBM on growth performance,digestive function,antioxidant status,meat quality and intestinal transporter of broilers.This study was composed of 5 trials as below:Trail 1 aimed to evaluate the proteins oxidative modification and lipid peroxidation of soybean meal(SBM)after exposed to different heating times.The SBM was heated at 100℃ for 1,2,4 and 8 h,respectively,and non-heated SBM was defined as control group(CON).Compared with CON,the peroxide value(PV)of heated SBMs and the thiobarbituric acid reactive substances(TBARS)value of SBM heated for 8 h increased(P<0.05).The decrease of nitrogen solubility index(NSI,P<0.05)of SBM were observed in all treatments(P<0.05).The carbonyl content increased while the total sulthydryl content in SBMs decreased after heat for 2 h(P<0.05).Compared with CON and SBM heated for 1 h,the sulfhydryl content of SBM heated for 8 h decreased(P<0.05).The decreases in in vitro digestibility of crude protein(CP)and dry matter(DM)in the SBMs were observed in all treatments(P<0.05).SDS-PAGE analysis suggested that proteion oxidation caused the degradation of polypeptide chain in SBMs as evidenced by decreased β,B and α,α’ bands.The PV and TBARS value,carbonyl content in the SBMs were linearly increased as heating time increased(Linear,P<0.05).The NSI,sulfhydryl,total sulfhydryl,free amino groups,the contents of Thr,Ala,Met,Lys and His,and in vitro digestibility of CP and DM in the SBMs were linearly decreased as heating time increased(Linear,P<0.05).Trail 2 was conducted to evaluate the effects of protein oxidized SBM on growth performance and digestive function of broilers.A total of 400 one-day-old Arbor Acres broilers(initial weight is 47.45±0.15g)were randomly divided into 5 treatments with 8 replicates of 10 birds each.The Arbor Acres broilers of 5 treatments were fed with basal diet(CON),1 h,2 h,4 h and 8 h heated SBM diet(Hl,H2,H4,H8),for 42 days,respectively.Compared with CON,H8 increased feed to gain ratio(F:G)of broilers during d 22-42 and d 1-42(P<0.05);broilers fed H4 and H8 at d 21,and broilers fed H8 at d 42 showed higher serum urea nitrogen(UN)content;broilers fed H2,H4 and H8 showed lower serum glucose(GLU)content at d 42(P<0.05);broilers fed H8 showed higher relative pancreas weight,lower activity of trypsin in anterior intestine content at d 42 and lower the apparent total digestibility of CP and DM during d 16-18 and d 37-39(P<0.05).The average daily gain(ADG)during both d 22-42 and d 1-42 of study,the serum GLU contents at both d 21 and 42,the activity of trypsin in anterior intestine content and apparent total digestibility of CP and DM were linearly decreased in broilers as heating time of dietary SBM increased(Linear,P<0.05).The F:G during both d 22-42 and d 1-42 of study,serum UN contents at both d 21 and 42,and the relative weight of pancreas at d 42 linearly increased in broilers as heating time of dietary SBM increased(Linear,P<0.05).Trail 3 aimed to evaluate the effects of the protein oxidized SBM on intestinal development,mucosal morphology and intestinal nutrients transporter of broilers.A total of 400 one-day-old Arbor Acres broilers(initial weight is 39.60±0.18g)were randomly divided into 5 treatments with 8 replicates of 10 birds each,and fed with basal diet(CON),1 h,2 h,4 h and 8 h heated SBM diet(H1,H2,H4,H8),for 42 days,respectively.Compared with CON and H1,ADG of broilers in H8 was decreased during d 22-42(P<0.05).Broilers fed H8 showed higher F:G than that of CON during d 22-42(P<0.05).Compared with CON and H1,H4 and H8 decreased ADG while increased F:G during d 1-42(P<0.05).At d 42 broilers fed H8 showed lower villus height of jejunum than that in H1(P<0.05),higher crypt depth of jejunum than those in CON and H1(P<0.05),and lower villus height to crypt depth ratio(V/C)of jejunum than those in CON,H1 and H2(P<0.05).The villus height and V/C of jejunum decreased linearly while the crypt depth of jejunum increased linearly at both d 21 and 42(P<0.05).At d 42,ASCT1,b0+AT and PepT1 mRNA expressions of jejunum in broilers in H8 was lower than those in CON and H1(P<0.05).CAT1 mRNA expression of jejunum in broilers in H8 was lower than those in CON,H1 and H2 at d 42(P<0.05).The ADG of broilers,the ADFI of broilers during d 22-42,the villus height and V/C of jejunum in broilers decreased(Linear,P<0.05)while F:G,and the crypt depth in broilers increased when heating time of dietary SBM increased(Linear,P<0.05).Trail 4 was conducted to determine the effects of the protein oxidized SBM on antioxidant status in broilers.The experimental design was the same as that of trial 3.Broilers fed H8 had higher ROS level,MDA and carbonyl contents in serum(P<0.05),lower T-AOC,T-SOD,and GSH-Px activity in serum than those in CON(P<0.05),lower CAT activity in serum than those in CON and H1,and lower GSH content in serum than those in H1(P<0.05).Broilers fed H8 had higher ROS level and carbonyl content,lower T-SOD and GSH-Px activity and Nrf2 mRNA expressions in the liver than those in CON(P<0.05),lower CAT activity and total sulfhydryl content in the liver than those in H1(P<0.05),lower GSH content in the liver than those in CON and H1,and lower hydroxyl radical scavenging capacity in the liver than those in CON,H1 and H2 at d 42(P<0.05).Broilers fed H8 had higher ROS levels and carbonyl content and lower superoxide anion radical scavenging capacity,T-AOC,T-SOD,and GSH-Px activity,and Nrf2 mRNA expression in the jejunum than those in CON(P<0.05),they also had lower CAT activity in the jejunum than those in H1 at d 42(P<0.05).Linear decreases were noted in the following:CAT activity in the liver and GSH content in the duodenum at d 21 and T-AOC,T-SOD,GSH-Px,CAT activity and GSH content in the serum and jejunum,T-SOD,GSH-Px,and CAT activity,GSH content,and hydroxyl radical scavenging capacity in the liver,and the superoxide anion radical scavenging capacity in the jejunum at d 42(Linear,P<0.05).The ROS levels in serum,liver,and jejunum linearly increased at d 42 in broilers when the heating time of dietary SBM increased(Linear,P<0.05).Trail 5 aimed to evaluate the effects of the protein oxidized SBM on meat quality,antioxidant status and breast muscle development of broilers.Experimental design was the same as that of trial 3.Broilers fed H8 showed lower yield of breast muscle than those in CON and H1(P<0.05).Broilers fed H8 showed lower Myf5 mRNA expression of breast muscle than that in H1(P<0.05),lower MyoG mRNA expression of breast muscle than that in H2(P<0.05),lower MRF4 and higher MSTN mRNA expressions of breast muscle than those in CON,H1 and H2(P<0.05).Broilers fed H8 showed lower pH24h of breast muscle than those in CON,H1 and H2(P<0.05),higher cooking loss of thigh muscle than those in CON(P<0.05).Broilers fed H2,H4 and H8 showed higher cooking loss and ROS level of breast muscle that those in CON and H1(P<0.05).Broilers fed H8 showed lower T-SOD activity and higher carbonyl content of breast muscle than those of CON(P<0.05),lower GSH-Px activity and total sulfydryl content of breast muscle than those in H1(P<0.05).Broilers fed H4 and H8 showed lower CAT activity of breast than that in H1,higher MDA content of breast muscle than those in CON(P<0.05).Broilers fed H8 showed lower Nrf2 and GSTK1 mRNA expressions of breast muscle than those in CON and H1(P<0.05),lower GPX1 mRNA expression of breast muscle than those in H1 and H2(P<0.05),lower SOD 1 mRNA of breast muscle expression than that in CON(P<0.05).The pH24h,T-SOD,GSH-Px,CAT activities and sulfydryl content of breast muscle decreased linearly(Linear,P<0.05)while the cooking loss of breast and thigh muscle,the 24 h drip loss of breast muscle and 48 h drip loss of thigh muscle,and the ROS level,carbonyl content and MDA content of breast muscle increased when heating time of dietary SBM increased(Linear,P<0.05).It can be concluded as follows:1.Heat treatment causes lipid peroxidation and protein oxidation in SBM,leading to reduced solubility and in vitro digestibility of protein in SBM.2.Protein oxidation of SBM resulting from heat treatment induces compromised growth performance and digestive function of broilers.Dietary SBM heated for 8 h,which has the highest protein oxidation level,showed the most serious effects in broilers.3.Protein oxidation of SBM has a negative effect on the intestinal development of jejunum,and reduces amino acids and peptide transporters mRNA expressions of jejunum.4.Protein oxidation of SBM resulting from heat treatment induces the compromised antioxidant status of broilers,resulting in accumulation of ROS,lipid peroxidation and protein oxidation products in serum and tissues,causing oxidative damage to broilers.Dietary SBM heated for 8 h,which has the highest protein oxidation level,showed the most serious effects in broilers.5.Protein oxidation of SBM resulting from heat treatment induces the compromised antioxidant status,meat quality and muscle development of breast muscle in broilers.Dietary SBM heated for 8 h,which has the highest protein oxidation level,showed the most serious effects in broilers.