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					                                                                              No. 87/2 e


Application Bulletin
Of interest to:   Foodstuffs, Dairy products                                                A E 1, 7




                        Analysis of dairy products

Summary
                  This Bulletin describes potentiometric titration methods for the determination of the
                  acidity in milk and yoghurt, as well as the chloride content in milk, butter and
                  cheese. The determination of the oxidation stability of butter is also described.
                  See Application Bulletin No. 86 for the determination of the pH value in dairy prod-
                  ucts and Application Bulletin No. 235 for the determination of calcium and magne-
                  sium.


Apparatus and accessories

                  •   Titrino or Titrando with Dosino or Dosimat
                  •   Magnetic swing-out stirrer
                  •   Exchange unit(s) (ev. for NaOH with PP reagent bottle 6.1608.040)
                  •   Porotrode (comb. pH glass electrode) 6.0235.100
                  •   Ag Titrode 6.0430.100
                  •   Electrode cable 6.2104.020
                  • Rancimat (for the determination of the oxidation stability of butter)


Reagents
                  These are given for the individual determination methods.




                  1. Determination of acidity (milk, yoghurt)


General
                  Titrate milk and yoghurt to a pH value of 8.3 with NaOH. The results are given as
                  acid number (mL NaOH, c = 0.1 mol/L for 1 L milk), respectively as acid number
                  according to Soxhlet-Henkel - oSH (mL NaOH, c = 0.25 mol/L for 100 mL milk). It is
                  important to titrate quickly.
                                         Application Bulletin                               No. 87/2 e
Analysis of dairy products                                                                      Page 2

Reagents
                    • c(NaOH) = 0.1 mol/L
                    • Demineralised or dist. H2O
                    • Buffer solutions pH = 4.0 and pH = 7.0 (Metrohm 6.2307.100 and 6.2307.110)
                    • Porolyte (electrolyte for Porotrode) 6.2318.000


Analysis
                    First calibrate the Porotrode with the buffer solutions pH = 4.0 and pH = 7.0 on the
                    titrator. Titrate 50 mL milk (or 10 g yoghurt with 40 mL dist. H2O) to pH = 8.3 with
                    c(NaOH) = 0.1 mol/L against the Porotrode and using following parameters on the
                    Titrator:

Determination of the acidity of milk
'pa                                                  'fr
736 GP Titrino          04268   736.0011             736 GP Titrino          04268  736.0011
date 99-11-02       time 09:52         7             date 99-11-02       time 09:52        7
SET pH             Acidity                           pHc(init)      6.74     SET pH Acidity
parameters                                           smpl size        50 ml    id#1     milk
>SET1                                                EP1           7.712 ml             8.30
  EP at pH               8.30                        SZ              154
  dynamics                  1                        'SH             6.2
  max.rate                 10 ml/min                           ============
  min.rate                 25 ul/min
  stop crit:            drift
  stop drift               20 ul/min
>SET2
  EP at pH                OFF
>titration parameters
  titr.direction:        auto
  pause 1                   0 s
  start V:                OFF
  pause 2                   0 s
  extr.time                 0 s
  dos.element:    internal D0
  meas.input:               1
  temperature            25.0 °C
>stop conditions
  stop V:                abs.
  stop V                99.99 ml
  filling rate           max. ml/min
>statistics
  status:                 OFF
>preselections
  conditioning:           OFF
  req.ident:              OFF
  req.smpl size:          OFF
  activate pulse:         OFF
          ============


                    Fig. 1 Parameters and results report on the Titrino.
                           Determination of the acidity in milk.
                                     Application Bulletin                                  No. 87/2 e
Analysis of dairy products                                                                       Page 3

Calculations
                RS1; Acid number (AN) = EP1 * C01 / C00
                RS2; Acidity (oSH) = RS1 / C02
                The acid number is reported without decimal place and the acidity to 1 decimal.
                C00 = sample size in mL
                C01 = 1000 (for 1 L)
                C02 = 25 (conversion factor)

Remarks

                • The determined acid number in milk is given mainly through the absorption of
                  hydroxyl ions via milk proteins and milk salts at a pH value of 8.3. The acid
                  number increases with bacterial acidification and with enzymatic lipolysis.
                • The following values are characteristic in assessing milk samples:
                                                              Acid number            Acidity
                 Normal, fresh milk                            160 - 190             6.5 - 7.5
                 Milk from cows with diseased udders             < 150                 < 6.0
                 Sour or rancid milk                             > 200                 > 8.0

Literature

                • Schweizerisches Lebensmittelbuch, Kapitel 1 „Milch“ (milk).




   2. Determination of chloride / kitchen salt (milk, butter, cheese)


General
                Since the presence of albuminoids interferes with this determination, they must first
                be removed using a precipitation procedure.


Reagents

                • w(aluminium sulphate) = 20 %         200 g/L Al2(SO4)3 * 18 H2O
                • c(NaOH) = 2 mol/L
                • c(HNO3) = 2 mol/L
                • c(AgNO3) = 0.1 mol/L (standardise by titrating against pure NaCl)

Sample preparation

                A) Milk
                Mix 20 mL milk with 150 mL dist. H2O and 7 mL NaOH in a 200 mL graduated
                flask. Now add 10 mL aluminium sulphate, fill up to the mark with dist. H2O and
                shake thoroughly. Allow to settle and filter off the clear blue solution through a
                chloride-free filter paper. (If the solution is not clear, the NaOH concentration is too
                high).
                                       Application Bulletin                                 No. 87/2 e
Analysis of dairy products                                                                      Page 4

                  B) Butter
                  Weigh exactly 1 ... 2 g butter in an Erlenmeyer flask, add 7 mL NaOH and 20 mL
                  hot dist. H2O. Transfer quantitatively the melted mass with approx. 100 mL hot dist.
                  H2O in a 200 mL graduated flask. Allow to cool. Add 10 mL aluminium sulphate, fill
                  up to the mark with dist. H2O and shake thoroughly. Allow to settle for 30 min, then
                  filter through a chloride-free paper filter.
                  C) Cheese
                  Weigh exactly 1 ... 2 g cheese (broken into pieces) in a 200 mL graduated flask,
                  add 7 mL NaOH and 120 mL hot dist. H2O and shake thoroughly to dissolve. Allow
                  to cool. Add 20 mL aluminium sulphate, fill up to the mark with dist. H2O and shake
                  thoroughly. Allow to settle, then filter the upper liquid through a chloride free paper
                  filter.

Analysis
                  Place 100 mL filtrate into a beaker and add 2.5 mL HNO3.
                  Titrate with c(AgNO3) = 0.1 mol/L against the Ag Titrode.
Determination of chloride in milk                   'fm
'pa                                                 736 GP Titrino          04268   736.0011
736 GP Titrino          04268   736.0011            date 99-11-02       time 14:39        11
date 99-11-02       time 14:39        11            DET U              Cl- Milk
DET U              Cl- Milk                         >calculations
parameters                                          Chloride=EP1*C01*C02*C03/C00;0;mg/dl
>titration parameters                               C00=                  20
  meas.pt.density           4                       C01=              3.5453
  min.incr.              10.0 ul                    C02=                 100
  titr.rate              max. ml/min                C03=                   2
  signal drift             30 mV/min                          ============
  equilibr.time            32 s                     'fr
  start V:                OFF                       736 GP Titrino          04268   736.0011
  pause                     0 s                     date 99-11-02       time 14:39        11
  dos.element:    internal D0                       U(init)         131 mV DET U    Cl- Milk
  meas.input:               1                       smpl size        20 ml
  temperature            25.0 °C                    EP1           2.784 ml             11 mV
>stop conditions                                    Chloride         99 mg/dl
  stop V:                abs.                       stop V reached
  stop V                    6 ml                              ============
  stop U                  OFF mV                    'cu
  stop EP                   9                       736 GP Titrino          04268   736.0011
  filling rate           max. ml/min                date 99-11-02       time 14:39        11
>statistics                                         start V      0.000 ml DET U     Cl- Milk
  status:                 OFF                       2.0 ml/div      dU=50.0 mV/div
>evaluation
  EPC                       5
  EP recognition:    greatest
  fix EP1 at U            OFF mV
  pK/HNP:                 OFF
>preselections
  req.ident:              OFF
  req.smpl size:          OFF
  activate pulse:         OFF
          ============




                                                                 ============
                  Fig. 2 Parameters and results report on the Titrino.
                         Determination of the chloride content in whole milk.
                                      Application Bulletin                               No. 87/2 e
Analysis of dairy products                                                                   Page 5

Calculations
                1 mL c(AgNO3) = 0.1 mol/L = 3.5453 mg Cl- resp. 5.8443 mg NaCl

                The results are given in mg chloride / 100 mL without decimal place in milk and in
                % NaCl in butter and cheese.
                Milk
                mg/100 mL chloride = EP1 * C01 * C02 * C03 / C00
                C00 = sample size in mL
                C01 = 3.5453
                C02 = 100 (for 100 mL)
                C03 = 2 (half of the initial sample is titrated)
                Butter/cheese
                % NaCl = EP1 * C01 * C02 * C03 / C00
                C00 = sample size in g
                C01 = 5.8443
                C02 = 0.1 (for %)
                C03 = 2 (half of the initial sample is titrated)


Remarks

                • Contrary to the original specification, AgNO3 is used instead of the toxic
                  Hg(NO3)2.
                • The chloride content in milk lies between 90 and 110 mg / 100 mL.
                • The NaCl content in unsalted butter lies under 0.1 %, in salted butter between
                  0.5 % and 2 %.
                • The NaCl content in cheese can vary within wide limits.




                           3. Oxidation stability (butter)


General
                Susceptibility to rancidness can be tested with the oxidation stability. Certain in-
                formation concerning storage stability or deterioration during storage is also possi-
                ble. The analysis regulation corresponds with the following generally acknowl-
                edged methods:
                AOCS Cd 12b-92 (1992)
                Sampling and analysis of commercial fats and oils. Oil Stability Index (OSI)


Analysis
                First test the temperature with the GLP Test Set according to the instructions for
                use (Rancimat) and enter the temperature difference on the instrument.
                Weigh out 3 g sample into the reaction vessel (melting beforehand if necessary)
                taking care that none of the sample touches the sides of the vessel.
                                                  Application Bulletin                               No. 87/2 e
Analysis of dairy products                                                                              Page 6

                         Fill each absorption vessel with 60 mL dist. H2O. The induction times are usually
                         determined by 120 oC and 20 L/h air throughput. (See instructions for use of the
                         Rancimat).

        25
                                                                    11.30




        20




        15
µS/cm




        10




        5




        0
             0   1   2   3    4   5   6       7   8   9   10   11    12
                                          h


                             Determination        Tempera-          Induction time   Block Channel
butter                        04.01.2000           120°C               11.30 h         B      4

                         Fig. 3 Report Rancimat 743 for cooking butter


Remarks

                         • The induction times are reduced approx. to the half through a temperature in-
                           crease of 10 oC,.
                         • Pay heed that the reaction vessels are meticulously clean! Dirt particles (also
                           e.g. residue from a washing agent) catalyse the reaction.

				
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Description: No. 87/2 e Application Bulletin