Title: Milk somatic cell count (SCC) - implications for cheese manufacture
1Milk somatic cell count (SCC) - implications for
cheese manufacture
- B. OBrien and T. Guinee
- Animal and Grassland Research and Innovation
Centre, Moorepark - and
- Teagasc Food Research Centre, Moorepark
- Moorepark Milk QualityWorkshop
2Cheese facts
- 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
3Quality of raw milk for cheese manufacture
- Is largely defined by
- Milk composition
- Microbial activity of milk
- Somatic cell count (SCC)
- Enzymatic activity of milk
- Chemical residues
4Somatic cells
- 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 - sub-clinical mastitis,
- advance in stage of lactation,
- lactation number,
- stress and poor nutrition.
5Dilution of high SCC milk
- Milk from infected (mastitic) quarters - SCC
200-5,000 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
6SCC and milk characteristics
- 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
7Increase in SCC 100 x 103 to 1,000 x 10 3
cells/mL
- reduced
- 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
- 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
8Effect of somatic cell count (SCC) on the
moisture-adjusted (to 37) Cheddar cheese yield
Increasing SCC in the range 100 x 103 to 600 x
103 6 reduction in moisture-adjusted
Cheddar cheese yield
9Further SCC studies
- Increasing SCC from 100 x 103 to 200 x 103
cells/mL - reduction in yield (i.e. 0.4 kg/100 kg milk)
- Increasing SCC from gt300 x 103 to gt500 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
- 4.3 reduction in the percentage yield
efficiency Cottage cheese
10Effect of SCC on milk processing
- The negative impact of SCC on yield and
recoveries are mainly due to - increase in proteolysis of as- and ß-caseins to
products soluble in the serum and not recovered
in the cheese (?-caseins, proteose peptones and
other peptides) - proteolysis arises from the elevated activity of
- plasmin
- plasminogen
- plasminogen activator in the milk
11High SCC - Slower curd-firming rate
- Lower concentration of as- and ß-caseins results
- 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
- 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
12High SCC - Reduces firmness at cutting
- 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
- 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.
13SCC legislation
- 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 lt 200 x 103 cells/mL - It is considered by some research that milk
constituents abandon their physiological ranges
at SCC gt100 x 103 cells/mL and that infection
is present at SCC gt 100 x 103 cells/mL
14In conclusion
- 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
- 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