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EFFECTS OF MILK PROTEIN VARIANTS ON THE PROTEIN RECOVERY IN CHEESE
E. Hallén1, A. Andrén1, T. Allmere1 & A. Lundén2
1Dept Food Science & 2Dept Animal Breeding and GeneticsSwedish University of Agricultural Sciences
”Carrier” 87.7%
Lactose 4.8% Fat 4.2%Protein 3.3%
Casein Whey protein
αs2-casein
αs1-casein
β-casein
κ-casein
Genetic casein variants
β-casein alleles
κ-casein alleles
αs1-casein
αs2-casein
- A1- A2- A3 (rare)- B (rare)
- A- B - E
Questions asked:
What relevance has the cow’s milk protein genotype for milk protein composition?
– and how does this affect quality and yieldof dairy products?
Milk viewed at different magnifications
MILKx 0
Milk viewed at different magnifications
x 500
Milk viewed at different magnifications
x 50 000
”Hairy” casein micelle model
Binding of calcium via serine residues in casein micelles
calcium
casein amino acid chain
Nucleotide sequence of κ-casein A, exon 4
*Exon 4 Y 4921 :::::::::c gctgtgagaa agatgaaaga ttcttcagtg acaaaatagc caaatatatc 4981 ccaattcagt atgtgctgag taggtatcct agttatggac tcaattacta ccaacagaaa 5041 ccagttgcac taattaataa tcaatttctg ccatacccat attatgcaaa gccagctgca 5101 gttaggtcac ctgcccaaat tcttcaatgg caagttttgt caaatactgt gcctgccaag 5161 tcctgccaag cccagccaac taccatggca cgtcacccac acccacattt atcatttatg 5221 gccattccac caaagaaaaa tcaggataaa acagaaatcc ctaccatcaa taccattgct 5281 agtggtgagc ctacaagtac acctaccACC gaagcagtag agagcactgt agctactcta 6-cn B T 6-cn E C 5341 gaaGATtctc cagaagttat tgagAGCcca cctgagatca acacagtcca agttacttca 6-cn B C A 6-cn E A G 5401 actgcagtct aa:::::::: :::::::::: :::::::::: :::::::::: :::::::::: Exon 4 Y*
(Alexander et al., 1988)
Yield of cheese
CheeseCaseins
(Fat)
Milk
Cheese curd
Caseins(Fat)Water
(Whey proteins)Removed ~5%
Removed ~80%Losses:
Whey prot.Caseins
(Fat)
Whey
Water
”Press water”
Losses:Whey prot.
Caseins(Fat)
Water
Step 2
Step 1
100 %
Renneting/chymosin
20 %
10 %
2
Genotyping of milk proteins
Genotyping of the university experimental herd
for β-casein & κ-casein using pyrosequencing
Phenotyping of β-lactoglobulin using FPLC (Fast Protein Liquid Chromatography)
Methods – “micro cheese”
“Micro cheese” – chymosin clotting; analysis of losses at various stages in the process (skim milk, whey, & press water)
Analysis of concentrations of αs1-, αs2-, β- & κ-casein,
α-lactalbumin, and β-lactoglobulin in cheese curd and whey
- Reverse Phase High Performance Liquid Chromatography (HPLC)
Analysis of effects of genetic milk protein variants and other
factors on “cheese protein” composition
M & M – cheese rheology
92 Swedish Ayrshire & Swedish Holstein cows from the university experimental herd
Chymosin is added to skim milk
The coagulation process is studied in a BohlinVOR Rheometer during 30 min
Measure coagulation start time and gel elasticity, G’, at 1500 s (25 min)
M & M – yoghurt rheology
GDL (glucono-δ-lactone) yoghurt – slow acid coagulation of heat treated milk
Measure coagulation start time and gel elasticity, G’, at fixed times
Analysis of effects of genetic milk protein variants and other factors on rheological parameters
Distribution of coagulation start times
0
5
10
15
20
25
3.5 4 4.5 5 5.5 6 6.5 7 7.5 Morenon coag
lnGstart
n
Distribution of curd firmness values
0
10
20
30
-2.9 -2 -1 0 1 2 3 4 5 6lnG1500
n
Genotype effects on rheology
Coagulation start time (s) Curd firmness (Pa)β-cn/κ-cngenotypeA1A2/BBA1B/BBA2A2/BBA1A2/BEA1A2/ABA1A1/ABA1A1/AEA1A2/AAA2A2/ABA1A2/AEA1A1/AAA2A2/AAA2B/AAA2A2/AE
LSMeans (ln)3.94.75.35.35.65.65.55.65.75.96.36.06.06.7
Mean 40150150250274340350386440444488569790900
Mean2352301318010665887578423536180.2
LSMeans (ln)3.62.43.73.03.83.83.13.43.33.52.93.44.6-0.1
N112181923131251321
Non-coagulating milk
Of the six cows that had repeatedly produced non-coagulating milk (i.e. not within 30 min), four carried the κ-casein AE genotype!
Future analyses within the project
Analysing more cows, in the experimental herd at Viken
Effect of β-lactoglobulin genotype on processing properties of acid gels for yoghurt production
Liquid Chromatography/Mass Spectrometry (LC/MS) analyses for identification of protein peptides in whey and cheese curd