Effects Of Chlorogenic Acid On Meat Quality And Lipid Metabolism Of Ningxiang Pigs

Chlorogenic acid(CGA),as one of the most abundant polyphenols in Lonicera macranthoides,has been demonstrated to exert variable biological functions including antimicrobial,anti-inflammatory and antioxidant properties,as well as hypolipidemic and immunomodulatory activities.The present study evaluated the effects of dietary CGA on carcass traits,meat quality and lipid metabolism of Ningxiang pigs.A total of 36 castrated female pigs with a similar initial weight(43.25 ± 0.56 kg)were randomly assigned to two treatments(with six pens per treatment and three pigs per pen).Pigs were fed a basal diet,unsupplemented(Control group)or supplemented with 100 mg/kg CGA(CGA group)for 56 days.The results were as follows:(1)Dietary CGA decreased the average daily intake(P = 0.064)of Ningxiang pigs slightly.No significant differences in carcass traits including slaughter yield,straight/oblique length and loin muscle area were observed between control and CGA-treated groups,as were p H value,marbling score,drip and cooking loss.However,supplementation of CGA into diets significantly altered muscle colors(i.e.,L*,a*,and b*)(P < 0.05),and had a tendency to reduce average backfat thickness(P = 0.080)of Ningxiang pigs.The oleic acid(C18:1n9c,P = 0.043)proportion in the longissimus dorsi muscle,as well as the total monounsaturated fatty acid(MUFA,P = 0.075)percentage was increased in pigs that were fed the CGA diet compared with those of the control diet.In contrast,the arachidonic acid(C20:4n6,P =0.016)and the total polyunsaturated fatty acid(PUFA,P = 0.087)proportions were decreased after CGA supplementation.Ningxiang pigs fed with diets containing CGA exhibited lower hydrolytic Met concentration(P = 0.092)in the longissimus dorsi muscle compared with the control group.These results suggested dietary CGA supplementary has beneficial effects on meat quality via decreasing average backfat thickness and modifying long-chain fatty acid profiles(especially the ratio of both C18:1n9c and C20:4n6 in the muscle were improved,respectively),but impairing muscle colors of Ningxiang pigs to some extent.(2)Compared with those of the control group,The concentrations of serum urea nitrogen(UN,P = 0.001),albumin(ALB,P = 0.069),total cholesterol(TC,P = 0.065)and low density lipoprotein-cholesterol(LDL-C,P = 0.089),and some free amino acids such as Asp(P = 0.023)and Phe(P = 0.037)of pigs fed the diet with CGA were decreased,while serum Ala(P < 0.001),Gly(P = 0.018),His(P < 0.001),Met(P = 0.009),Leu(P < 0.001),Arg(P = 0.090)and Ile(P = 0.071)of this group were increased.However,CGA exhibited down-regulated expression levels of the sodium-dependent neutral amino acid transporter 2(SNAT2,P < 0.001)gene in the longissimus dorsi muscle,Slc7a1(P = 0.009)in the duodenum and Slc1a5(P = 0.074)gene in the jejunum of Ningxiang pigs.These findings indicated that CGA could improve amino acid and lipid metabolism of Ningxiang pigs.(3)Subcutaneous and visceral adipose tissues with different anatomical locations showed specific development and deposition,especially in de novo synthesized long-chain fatty acids due to desaturation and elongation.Thus,the effects of dietary CGA on fatty acid profiles in adipose tissues of Ningxiang pigs also showed in a tissue-specific manner.Our finding presented greater alternation of PUFAs in subcutaneous adipose tissues than those in perirenal adipose(PA)or mesenteric adipose when added CGA in the diets.Moreover,?-linolenic acid(C18:3n3,P = 0.039)proportion in dorsal subcutaneous adipose(DSA),as well as total PUFA(P < 0.05)(particularly linoleic acid(C18:2n6c,P < 0.05))in DSA and abdominal subcutaneous adipose(ASA)tissues was increased in the pigs that were fed the CGA diet compared with those fed the control diet.Dietary CGA exhibited down-regulated expression levels of acetyl-Co A carboxylase ?(ACC?,P = 0.040),stearoyl-Co A desaturase(SCD,P = 0.025),malic enzyme(ME,P = 0.076)and fatty acid desaturase 1(FADS1,P =0.076)m RNA in DSA,Adipo Q(P = 0.024)and fatty acid transport protein 4(FATP4,P =0.063)m RNA in ASA,and elongase of very long chain fatty acid 2(Elovl2,P = 0.071)and Elovl5(P = 0.071)m RNA in PA of Ningxiang pigs.These data indicated that CGA probably inhibited the related gene expressions of long-chain fatty acid synthesis,and thus optimize the long-chain fatty acid profiles in DSA and ASA of Ningxiang pigs.(4)A liquid chromatography coupled mass spectrometry-based untargeted metabolomics approach was developed to characterize the key endogenous metabolic modifications induced by CGA treatment in the liver of Ningxiang pigs.Out of 27 significant variables in livers between groups,16 metabolites such as glucose-6-phosphate(G-6-P),indole-3-carboxylic acid and many phospholipids were found at higher concentrations following CGA intervention,but linoleic acid,lysine and choline were at lower concentration,which were closely related to amino acid metabolism,sugar metabolism,aminoacyl-t RNA biosynthesis and lipid metabolism.Among 18 metabolic pathways,linoleic acid and lysine metabolic pathways were noticed due to the low P-value and high pathway impact calculated by the Metabo Analyst.Furthermore,the gene expressions of hepatic3-hydroxy-3-methylglutaryl-Co A reductase(HMGCR,P = 0.001)and SCD(P = 0.017)were significantly up-regulated by CGA,whereas Elovl5(P = 0.008)was markedly down-regulated compared with those pigs receiving the control diet.These observations indicated that CGA may strengthen hypolipidemic effects possibly through multidirectional metabolites such as amino acid,fatty acid,and the related genes.(5)CGA significantly changed 16 species of cecal microbiota in Ningxiang pigs.Based on the COG classification system,dietary CGA had a tendency to decrease the relative abundance of RNA processing and modification.The concentrations of acetic acid and propionic acid in the cecum were decreased in the pigs that were fed the CGA diet compared with those fed the control diet,which may be related to the decrease of Prevotella,Lactobacillus and Ruminococcus.These changes of microecological environment were beneficial to the improvement of lipid metabolism.In addition,the present study also determined the responsiveness of dietary linseed oil(LO)on fatty acid profiles in longissimus dorsi muscle and three different adipose tissues of Ningxiang pigs,and then investigate the underlying lipogenesis mechanisms.Thirty castrated female pigs with a similar initial weight(43.21±0.64 kg)were randomly allocated into two treatments(with 5 pens per treatment and 3 pigs per pen)consisting of a basal diet,unsupplemented or supplemented with 2% LO for a 56-d period.Dietary LO increased C20:1,C18:3n3 and C18:3n6(P < 0.05),and decreased C20:4n6(P < 0.05)in longissimus dorsi muscle;the fatty acid profiles of adipose tissue fractions influenced by LO were analogous to those found from the muscle.The increments in polyunsaturated fatty acids(PUFA)including C18:2n6c,C18:3n6,C18:3n3,C20:3n6(P < 0.05)in DSA,ASA and PA were accompanied by a corresponding decrease in C18:1n9c(P < 0.05),C20:4n6(P < 0.10)in DSA and APA,as well as C18:0(P < 0.05)in PA.Furthermore,ACC?,PPAR?,FADS2(P< 0.05)and PPAR?(P < 0.10)gene expressions in DSA also were down-regulated with LO intake.These observations indicate that after dietary inclusion of 2% LO,the content of C18:3n3 is increased and the average n-6/n-3 PUFA ratio in three different adipose tissues of Ningxiang pigs reduce to 5.92,in accordance with the recommended value(4-6)of Dietary Guidelines for Chinese Residents(2016).LO may reduce the de novo synthesis and cell differentiation by modifying gene expression involved in lipogenesis.In aggregate,dietary CGA supplementation improved amino acid and nitrogen metabolism,inhibited the deposition of back fat of Ningxiang pigs by regulating the expressions of related genes,and decreasing serum TC and LDL-C.CGA also optimized the long-chain fatty acid profiles in different tissues such as DSA and ASA,activated the hepatic metabolism pathways including lysine degradation and linoleic acid metabolism,improved microecological environment in the cecum.But it also had a certain adverse effect on meat colors.