Milk somatic cell count (SCC) - implications for cheese manufacture - PowerPoint PPT Presentation

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Milk somatic cell count (SCC) - implications for cheese manufacture

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... and thereby, prevent or reduce inflammation (mastitis) ... increase in proteolysis of s- and -caseins to products soluble in the serum and not recovered ... – PowerPoint PPT presentation

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Title: Milk somatic cell count (SCC) - implications for cheese manufacture


1
Milk 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

2
Cheese 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

3
Quality 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

4
Somatic 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.

5
Dilution 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

6
SCC 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

7
Increase 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

8
Effect 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
9
Further 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

10
Effect 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

11
High 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

12
High 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.

13
SCC 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

14
In 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
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