| The lactation period is an essential factor in changes in milk composition,physicochemical properties,and other characteristics,particularly concerning lipids,proteins,and other nutrients.However,variations in lactation traits during camelid lactation have been less well studied.In this thesis,milk samples from six healthy Bactrian camelids on days 1,7,21,35,and 90 after parturition,labeled as colostrum(group C=1 day,group S=7 days),transition(group T),regular(group M)and final(group L),was used as test material.Subsequently,patterns of change during the lactation period were explored by measuring physicochemical properties and thermal stability to investigate changes in the phenotypic properties of camel milk.Combined with multi-omics techniques,the expression patterns of camel milk during different lactation were comprehensively on the protein,metabolite,and lipid levels.The extraction of key functional information used to provide theoretical guidance for the comprehensive assessment and analysis of the nutritional value of camel milk and its efficient and rational application.The main results of this study are as follows.1.Study on the general physicochemical properties,composition,and thermal stability of camel milk at different lactation stages(1)Among the basic components,the protein,milk fat,and total solids(TS)contents were 3.86-5.29%,2.11-6.59%,and 12.26-17.88%,respectively,decreasing with lactation;while the,non-milk fat solids(SNF),lactose,and ash contents were 10.37-11.36%,5.596.23%and 0.83-0.92%respectively,decreases with lactation,then rises to a maximum and then decreases again.A total of 17 amino acids(AA)were measured in camel milk,with Glu being the highest and Cys and Gly being the lowest;all AA levels decreased with lactation;the AA scores all meet the ideal protein criteria,making it a high quality,ideal protein for consumption.A total of 23 camel milk fatty acids were measured,mainly C18:ln9c,C16:0,C14:0,and C18:0;PUFA,MUFA,and health indicators such as HFA/UFA,n-6 FA/n-3 FA,AI,and TI showed a negative trend during lactation,while SFA,h/H,PUFA/SFA,and SFA:MUFA:PUFA were in contrast,which was all within the FAO/WHO recommended values.(2)Among the physicochemical properties,refractive index(1.3481-1.3705)and density(1.0362-1.0399 g/cm3)fluctuated and decreased overall with lactation;pH(6.166.63)increased at 21 days postpartum and then decreased.The thermal stability of camel milk was negatively correlated with temperature and positively to pH overall;colostrum stability(especially thermal stability)was the worst and increased significantly with lactation until it increased to a maximum at the end of lactation.2.Changes in the content of immunoglobulin G in camel milk at different lactation stages and its structural characterizationThe IgG isoforms IgG1,IgG2,and IgG3 were successfully purified from camel milk at different lactation stages by Protein A/G affinity chromatography,and purity was high,as indicated by SDS-PAGE electrophoresis and SEC-HPLC-UV.The molecular mass of IgG1 was 146.04kDa,IgG2 was 86.92kDa,and IgG3 was 81.79kDa,and each IgG isoform was mainly β-sheet(36.0-37.1%),which further identified the purified protein as the target protein.The concentrations of total IgG and its isoforms decreased sharply within one week of lactation and then tapered off after one week,gradually approaching mature and late milk;IgG1:HCAbs(IgG2+IgG3)was relatively stable at approximately 1:3 during lactation.3.Proteomic analysis of camel milk at different lactation stagesA total of 987 proteins were quantified,of which 104 were up-regulated,465 were down-regulated and 98 were fluctuating,out of 667 differentially expressed proteins(FC>1.2,p<0.05).The up-regulated proteins with lactation are mainly whey proteins,IgGbinding protein Fc and glycosylation-dependent cell adhesion molecule 1,which are involved in the processes,such as stress,immune response,exercising catalytic,enzymatic,and peptidase regulatory activities.Significantly down-regulated proteins include PGRP1,1-acid glycoprotein and Igγ-3 chain C region,MHC-Ⅱ,and other proteins involved in the construction and regulation of the immune system.During lactation,differential lactation proteins are involved in immune inflammation pathways,hypertension,cardiac remodeling,ECM deposition,and cardiovascular-related pathways.4.Metabolomic analysis of camel milk at different lactation stagesA total of 361 metabolites were identified using a non-targeted metabolomics technique based on UHPLC-Q-TOF MS,with 5,27,51,and 66 metabolites differing between the S,T,M,L,and C groups,respectively.The up-regulated metabolites in colostrum were mainly amino acids and dipeptide analogs,sugars,lipids,and nucleotides.They are involved in the metabolic pathways of ABC transport,galactose metabolism,ether lipid metabolism,arginine,proline metabolism,and other nutrient transport pathways,providing essential raw materials for the early survival of camel camb.The metabolites significantly up-regulated in the final milk are mainly energy substances such as NAD,betaine,and citric acid.These metabolites are involved in energy-related pathways,such as glyoxalate and dicarboxylic acid metabolism,the glucagon signaling pathway,and the TCA cycle,providing energy for the body’s vital activities.5.Combined proteomic and metabolomic analyses of camel milk at different lactation stagesIntegrative analysis of proteomics and metabolomics used to find key metabolites and proteins.Metabolites contain 1-palmitoyl lysophosphatidylcholine,linoleic acid,inosine,Lys-Leu,hydroxy quinoline,allopurinol nucleoside,etc.The proteins contain alphalactalbumin,xanthine dehydrogenase,fructose-6-phosphate 2-kinase,and olfactory receptor 2W6.These differentials are mainly involved in nutrient-related pathways such as glycolysis/gluconeogenesis,metabolism of galactose,glycerophospholipids,arachidonic acid,and amino acid.These differential proteins and metabolites are directly related to the changes in nutrients during lactation.Colostrum provides a more source of raw materials for immune protection,growth,and development of young animals.The mature and late milk provide energy for the vital activities.6.Non-targeted lipidomics analysis of camel milk at different lactation stagesThe non-targeted quantitative lipidomics based on mass spectrometry system was used to systematically compare the lipid composition of different lactations.24 subclasses and 980 lipid compounds were identified,including glycerophospholipids(12),sphingolipids(8),glycerol esters(2)and fatty acyl esters(2),with the highest content of TG,followed by DG and PE.Triglycerides(TG)mainly contain long-chain unsaturated fatty acids.Camel milk is rich in TG52:2(16:0/18:1/18:1)+NH4 and TAG composed of long chain unsaturated fatty acids,similar to human milk,making it suitable as a lipid raw material for infant formula milk powder.During lactation,the differential lipids between groups S,T,M,and L and C were 21,347,202,and 263,respectively(VIP>1,P<0.05).TG,phospholipids and sphingolipids such as TG(52:7)+NH4,TG(54:8)+NH4,Cer(d44:2)+HCOO were highly expressed in colostrum.High expression of DG,lysophospholipids,and sphingomyelin such as PE(39:1)-H,PC(28:2p)+H,So(d17:0+pO)+H,LPE(18:3)-H in normal final milk.Camel colostrum has potential functions in promoting early brain development and neurotransmitter production in newborn camel lambs,as well as antibacterial,hypocholesterolemic,and carcinogenic properties,and also provides a research direction for identifying potential indicators of camel lactation.The above results initially reveal the phenotypic differences in camel milk and the differences in the composition of protein,metabolite,and lipid molecules in different lactation stages.The analysis enables us to understand the differential expression of protein,metabolite,and lipid metabolic pathways and their related physiological functions during lactation and provides practical information for the development of camel milk and screening potential biomarkers. |
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