Milk somatic cell count (SCC)
- implications for cheese
manufacture
B. O’Brien and T. Guinee
Animal and Grassland Research and Innovation Centre,
Moorepark
and
Teagasc Food Research Centre, Moorepark
Moorepark Milk QualityWorkshop
Cheese facts
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Estimated yield of 1 kg Cheddar cheese/10 kg milk
Total milk used for cheese is ~25%
~70 - 90% in some European countries (Italy,
France, Denmark and Germany) to ~0.5% in China.
Production has increased consistently over the last
two decades at an annual average rate of ~1.5%.
Greater emphasis on improved quality and
consistency (fat, protein, calcium and sodium),
physical properties (texture and cooking attributes),
sensory characteristics and processability
Quality – milk – competitive advantage
Quality of raw milk for cheese
manufacture
Is largely defined by:
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Milk composition
Microbial activity of milk
Somatic cell count (SCC)
Enzymatic activity of milk
Chemical residues
Somatic cells
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Released from the blood to combat udder
infection, and thereby, prevent or reduce
inflammation (mastitis)
Factors that contribute to increases in SCC of
bulk manufacturing milk include:
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sub-clinical mastitis,
advance in stage of lactation,
lactation number,
stress and poor nutrition.
Dilution of high SCC milk
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Milk from infected (mastitic) quarters - SCC 2005,000 x 103 cells/mL.
Excluded from the commercial milk supply
The initial stage of mastitic infection (subclinical) not
detectable by visual examination - part of bulk herd
milk and bulk manufacturing milk
Bulking dilutes high SCC milk, but also contributes
to an increased SCC of manufacturing milk
Managing bulk milk SCC
SCC and milk characteristics
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Increasing SCC in milk is
associated with marked changes
in the:
concentrations of milk constituents,
 state (degree of hydrolysis) of the
milk components
 cheesemaking properties
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Increase in SCC 100 x 103 to 1,000 x 10 3 cells/mL:
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reduced
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lactose, fat and casein contents in milk
casein as a percentage of true protein
gel firmness
recoveries of protein from milk to cheese
cheese yield
increased
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milk pH
levels of chloride, whey protein and non-protein nitrogen
curd fines in cheese whey
cheese moisture
rates of primary /secondary proteolysis during maturation
Increased fat and protein losses during cheese manufacture
9.4
9.2
9.0
8.8
8.6
8.4
>1000
1000
900
800
700
600
500
400
300
200
8.2
100
Moisture-adjusted cheese yield (kg/100 kg milk)
Effect of somatic cell count (SCC) on the moistureadjusted (to 37%) Cheddar cheese yield
Somatic cell count (x 103 cells/mL)
Increasing SCC in the range 100 x 103 to 600 x 103 : ~ 6 %
reduction in moisture-adjusted Cheddar cheese yield
Further SCC studies
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Increasing SCC from 100 x 103 to 200 x 103 cells/mL
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reduction in yield (i.e. ~0.4 kg/100 kg milk)
Increasing SCC from >300 x 103 to >500 x 103 cells/mL
in late lactation (220 DIL) results in:
 9.3 % decrease in moisture-adjusted (to 35.5 %) yield
of Cheddar cheese and
 decreases in the recovery of fat (90.1 to 86.6 %) and
protein (78.3 to 74.4 %)
Increasing SCC 83 x 103 to 872 x 103 cells/mL
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4.3 % reduction in the percentage yield efficiency Cottage cheese
Effect of SCC on milk processing
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The negative impact of SCC on yield and
recoveries are mainly due to:
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increase in proteolysis of αs- and β-caseins to
products soluble in the serum and not recovered in the
cheese (γ-caseins, proteose peptones and other
peptides)
proteolysis arises from the elevated activity of
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plasmin
plasminogen
plasminogen activator in the milk
High SCC - Slower curd-firming rate
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Lower concentration of αs- and β-caseins results:
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a slower curd-firming rate
a lower degree of casein-casein interaction in the gel
following cutting (at a given firmness) and during the
early stage of stirring
Such a gel has :
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a greater susceptibility to shattering during cutting and the early
stages of stirring, resulting in higher losses of curd fines and fat
and
an impaired syneretic capacity, with a consequent increase in
moisture level
High SCC - Reduces firmness at cutting
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High SCC can inhibit activity of some strains of lactococci which
further impairs curd firming rate and reduces firmness at cutting
Large modern factories, cannot test curd firmness
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of cheese vats from separate milk silos because of the large scale
of operation and
the use of pre-programmed vats with limited operator access
In commercial practice, the gel is generally not cut on the basis
of firmness, but rather on the basis of a pre-set renneting time
In such operations, the effects of increases in SCC may be
increased as the slower-than-normal curd firming rate is
conducive to lower-than-optimum firmness at cutting.
SCC legislation
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The EU has set the legislative limit of ≤400 x 103
SCC/mL
The permitted SCC limit varies internationally, but
pressure to reduce SCC further, e.g. Bonus for <
200 x 103 cells/mL
It is considered by some research that milk
constituents ‘abandon their physiological ranges’ at
SCC >100 x 103 cells/mL and that ‘infection’ is
present at SCC > 100 x 103 cells/mL
In conclusion
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High SCC detrimental to cheese yield and cheesemaking
profitability
Monetary loss resulting from a 2 % reduction in cheese yield on
increasing the SCC from 100 x 103 to 500 x 103 cells/mL would
be ~€4000 per day for a Cheddar cheese plant processing 1 M
litres milk per day (at a fresh curd value of ~€ 2.0/kg)
Must reduce SCC through the use of:
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good on-farm practices e.g., reducing the percentage of animals in herds
with sub-clinical mastitis,
meeting regulations,
introduction of payment incentives for lower SCC
Milk quality will increasingly contribute to competitive advantage
for the Irish dairy industry – MQ vital to successfully compete in
international markets