Milk somatic cell count (SCC) - implications for cheese

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					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
   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:

   Milk composition
   Microbial activity of milk
   Somatic cell count (SCC)
   Enzymatic activity of milk
   Chemical residues
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.
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
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
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
Effect of somatic cell count (SCC) on the moisture-
adjusted (to 37%) Cheddar cheese yield


             Moisture-adjusted cheese yield (kg/100 kg milk)
                                                               9.4


                                                               9.2


                                                               9.0


                                                               8.8


                                                               8.6


                                                               8.4


                                                               8.2
                                                                     100

                                                                           200

                                                                                 300

                                                                                       400

                                                                                             500

                                                                                                   600

                                                                                                         700

                                                                                                               800

                                                                                                                     900

                                                                                                                           1000

                                                                                                                                  >1000
                                                                                 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
   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 >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
       4.3 % reduction in the percentage yield efficiency Cottage cheese
Effect of SCC on milk processing
   The negative impact of SCC on yield and
    recoveries are mainly due to:
       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
            plasmin
            plasminogen
            plasminogen activator in the milk
High SCC - Slower curd-firming rate
   Lower concentration of αs- and β-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
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.
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 <
    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
   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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posted:12/10/2011
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