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BACKGROUND RESULTS
A. Samples32 milk samples from genetically distinct goats A/A and O/O at the CSN1S1 locus encoding αs1‐casein were used for this study. The effects of αs1‐casein polymorphisms on goat milk composition and quality have been intensively studied (Martin and Leroux, 2000); however the effects on oligosaccharide synthesis, which occurs within the same cellular compartment (Endoplasmic Reticulum) where lipids are synthesized and casein micelles are built, have not been previously investigated.
The dataset was spilt into: genotype A/A and genotype O/O at the CSN1S1 locus. For both groups, 8 samples were collected in the morning and 8 were from evening milking.
B. Instrumentation
NOVEL BIOACTIVE MILK OLIGOSACCHARIDES IN DIFFERENT GOAT GENOTYPESBarile D.1, Meyrand M.1, Caillat, H. 2, German B.1, Lebrilla C.3, Martin P.4
The authors would like to thank APIS-Gene (a French Scientific Group gathering professional stakeholders) for partly funding this project.
Fig. 1. Solid‐phase extraction
Fig. 2. Agilent 6520 series HPLC‐Chip Q ‐TOF(Agilent Technologies, Santa Clara, CA)
Fig. 3. The microfluidic Chip consists of an enrichment column and an analytical column, both packed with porous graphitized carbon
In this work, the fraction containing mainly the neutral OS was enriched by SPE (Fig. 1) and analyzed by HPLC‐Chip/Q‐TOF MS (Figs. 2‐3), a sensitive and quantitative method for oligosaccharide profiling. Oligosaccharide composition was confirmed by Tandem Mass Spectrometry analysis.
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Martin & Leroux (2000) Le gène caprin spécifiant la caséine αs1 : un suspect tout désigné aux effets aussi multiples qu’inattendus. INRA Prod. Anim., HS2000, 125‐132.Barile, D., N. Tao, et al. (2009). Permeate from cheese whey ultrafiltration is a source of milk oligosaccharides. Int Dairy J 19(9): 524‐530.
Prior to Mass Spectrometric analysis, oligosaccharides were purified by Solid‐Phase Extraction (SPE) (Fig. 1)with Graphitized Carbon cartridges following the protocol described previously (Barile et al., 2009).
[email protected]@jouy.inra.fr
1 Foods for Health Institute, Department of Food Science & Technology, University of California, Davis, Davis 95616, CA, USA 2 Institut National de la Recherche Agronomique (INRA), UR 631, Station d’Amélioration Génétique des Animaux (SAGA), 31326 Castanet-Tolosan, France3 Department of Chemistry, University of California, Davis 95616, USA4 INRA, UMR Génétique animale et Biologie intégrative (GABI), Equipe « Lait, Génome & Santé » (LGS), 78350 Jouy-en-Josas, France
Human milk contains significant quantities of a unique family of complex carbohydrates (oligosaccharides, OS) that are believed to confer unique health benefits to the nursing infants, such as prevention of pathogen colonization, and directly influence the composition of the intestinal microbiota. Mammalian milk OS are commonly divided into two main groups: neutral and acidic. Neutral OS are composed of galactose (Gal), Glucose (Glc) N-Acetyl‐glucosamine (GlcNAc), fucose (Fuc) and a lactose core; acidic OS are characterized by these same monomers but also one molecule of N‐acetyl‐neuraminic acid (NeuAc) is found. At present, the only source of milk OS is human milk, which limits OS research and practical applications. Recent studies have documented that these complex OS are present in most mammalian milks, such as goat and bovine milk. However, previous research has failed to identify a genetic influence on specific OS formation, which is crucial in defining oligosaccharide functions.
The objectives of this project were:i)use advanced mass spectrometry to perform the most complete characterization of OS in goat milk of extreme genotypes at the CSN1S1 locus (A/A and O/O).ii)provide the proof of principle that goat milk represents a genuine source of complex milk OS suitable as a food ingredient.
METHODS
CONCLUSION
A. Goat milk oligosaccharides profilingThe typical Base Peak Chromatogram (BPC) obtained for goat milk OS extraction (neutral fraction) is presented in Fig. 4. No differences between genotypes were observed by visual of the BPC in the 32 samples analyzed.
B. Goat milk oligosaccharide Library of compositions validated by Tandem Mass spectrometryThe mass lists obtained from the profile were deconvoluted using the Molecular Feature Extractor from Mass Hunter Qualitative Analysis Version B.03.01 (Agilent Technologies) and OS compositions were established using an in‐house program, Glycan Finder, written in Igor Pro version 5.04B (WaveMetrics Inc., Portland, OR). OS compositions were determined using mass error ≤5 ppm . Compositions were then confirmed by tandem mass spectrometry (fragmentation) that allows the identification of individual constituents of the OS molecules (Table 1).
22 different OS are presented in the table (against). Fucosylated molecules are highlighted in pink, acidic in green, neutral containing N‐acethylhexosamine in blue, and the polymer of hexoses (Glc, Gal) in grey.
C. Genotypes may influence oligosaccharides compositionOligosaccharides presented similar abundance in all samples, with the same five OS representing the majority of the BPC signal measured (Fig.5). However, a meticulous data analysis enabled us to identify a marker discriminating between genotypes :
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MW 530.208
The OS composed of: 1 Hexose, 1HexNAc and1 Fucose (in green) was consistently detected in significant amount in the milk from O/O genotype, whilst it was completely absent from the A/A genotype. Its tandem profile is shown in Fig. 6.
This project constitutes the first comprehensive effort to profile and elucidate the structures of milk OS in goat milk and simultaneously study the correlation between OS expression and different genotypes. We demonstrated similarities and differences between genotypes. The complexity of the OS common to both genotypes detailed in the library, make goat milk a genuine source of fucosylated bioactive OS to improve human health.
D. New fucosylated oligosaccharides discoveredEight novel OS never reported in the literature have been discovered in the present work; their composition has been confirmed by tandem mass spectrometry. Three of them are fucosylated : a) 1Hex, 1HexNAc, 1Fuc ; b) 4Hex, 2HexNAc, 1Fuc; c) 3Hex, 3HexNAc, 1Fuc (highlighted in pink in Table 1). OS a) and c) seem to be present only in genotype O/O for the CSN1S1 locus.
Fig 6.Fragmentation of the OS 1 Hexose, 1HexNAc and 1 Fucose. (Neutral mass 529.201)
Fig. 4
Hex HexNAc Fuc NeuAc NeuGcneutral mass
abbrev.
1 2 1 488.174 2'FL2 3 504.169 3‐GL3 3 504.169 6‐GL4 1 1 1 529.201 ‐5 2 1 545.196 NAL6 2 1 633.212 6‐SL7 2 1 633.212 3‐SL8 2 1 649.206 NGL9 4 666.222 GOS(4)10 1 1 1 674.238 ‐11 3 1 707.248 NAHL12 2 2 748.275 DNAL13 3 1 811.259 SNGHL14 5 828.275 GOS(5)15 3 1 1 853.306 ‐16 4 1 869.301 NADHL17 6 990.327 GOS(6)18 4 2 1072.381 LNH19 3 3 1113.407 ‐20 2 4 1154.434 ‐21 4 2 1 1218.438 ‐22 3 3 1 1259.465 ‐
Table 1: Library of confirmed goat milk OS.
Fig. 5. Extracted ion chromatogram (EIC) of the most abundant OS (genotype O/O).circle, hexose (Hex); square, N‐acetylhexosamine (HexNAc); triangle, fucose (Fuc); diamond, sialic acid (NeuAc).
H2O= 18.010
Fucose= 146.058Hexose
= 162.053HexNAc= 203.079
Institut National de la Recherche AgronomiqueInstitut National de la Recherche Agronomique