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