in dairy productsplace 2 g celite 545 in the digestion vessel 4. add up the appropriate amout of...

Proximate determination in dairy products

Dive into more than 50 years of experience in food analysis

BUCHI develops and offers efficient and reliable techniques for protein, fat, moisture, ash and carbohydrates determination. Explore the guidebook for proximate determination in dairy products and find the solution that fits you best.

BÜCHI Labortechnik AGMeierseggstr. 40, PostfachCH-9230 Flawil 1SwitzerlandT +41 (0)71 394 63 63F +41 (0)71 394 64 64www.buchi.com

Fat determination in Yogurt

Application Note No. 184/2015Extraction Unit E-816 ECE: Fat Determination in Yogurt samples using Twisselmann and Soxhlet extraction

Nitrogen & protein determination in milk powder

Application Note No. 105/2013KjelDigester K-449, KjelMaster K-375 with Kjel-Sampler K-376: Accelerated Nitrogen and Protein Determination in Milk Powder with Kjeldahl Tablets and Hydrogen Peroxide

BUCHI NIR Applications

NIR Pre-calibrated applications for the Milk & Dairy Industry

Application NoteNo. 184/2015

Fat determination in Yogurt

Extraction Unit E-816 ECE:Fat Determination in Yogurt samples using Twisselmann and Soxhlet extraction

www.buchi.com Quality in your hands

Application Note 184/2015 March 2015 2/8

1. Introduction

An effective procedure for fat determination in food according to §64 LFGB L 01.00-20 is

presented [1]. The sample is hydrolyzed with the Hydrolysis Unit E-416. The Twisselmann

extraction is performed with the Extraction Unit E-816 ECE (Economic Continuous Extraction).

This allows the sample to be constantly kept in hot solvent vapor whilst being efficiently rinsed

with freshly distilled solvent. After the extract has been dried to a constant weight the total fat

content is determined gravimetrically.

The results from the Twisselmann extraction were compared to the results from the Soxhlet

extraction method.

2. Equipment

Extraction Unit E-816 ECE

Extraction Unit E-816 SOX

Hydrolysis Unit E-416

Analytical balance (accuracy ± 0.1 mg)

Microwave oven

Drying oven / Vacuum drying oven

3. Chemicals and Materials

Chemicals:

Quartz sand, particle size 0.3-0.9 mm, BUCHI (037689)

Celite 545, Macherey-Nagel (815560)

10 L of 4 M Hydrochloric acid (HCl) are prepared by dilution of 4 L HCl 32 % (Hänseler 20-

2000-5) to 10 L with deionised water

Petroleum ether, boiling range 40-60 °C, analytical grade, ACS, Merck (1.01775.2500)

For a safe handling please pay attention to all corresponding MSDS!

Samples:

Yogurt Mocha, declared fat content: 3.0 g/100g

Yogurt Vanilla, declared fat content: 3.0 g/100g

Yogurt Choco, declared fat content: 4.0 g/100g

Yogurt Greek with honey, declared fat content: 6.5 g/100g

Yogurt Fruits, declared fat content: 3.0 g/100g

Yogurt Apricot, declared fat content: 3.0 g/100g

Yogurt plain, declared fat content: 3.5 g/100g

Yogurt Strawberry, declared fat content: 3.0 g/100g

Yogurt Banana, declared fat content: 3.0 g/100g

Yogurt Greek, plain, declard fat content: 7.0 g/100g

The samples were purchased at a local supermarket.


4. Procedure

The determination of fat includes the following steps:

Homogenization of the sample by stirring

Acid hydrolysis of the sample, using the Hydrolysis Unit E-416

Fat extraction of the sample following Twisselmann extraction and Soxhlet extraction, using

the Extraction Units E-816 ECE and E-816 SOX

Calculation of the fat content

4.1. Homogenization of the sample

The yogurt samples were only homogenized by stirring with a spatula before use

4.2. Acid hydrolysis of the sample, using the Hydrolysis Unit E-416

4.2.1. Preparation of the glass sample tubes

1. Add approx. 20 g of quartz sand to the glass sample tube and compact the sand by gently tapping the glass sample tube onto the table

2. Add approx. 2 g Celite 545 and spread it evenly using a spoon

The sand and the Celite layer should not be mixed together. Otherwise the Celite

phase may breakthrough the frit and affect the results either by increasing the

recovery or by blocking the frit.

4.2.2. Hydrolyzing the sample matrix

3. Place 2 g Celite 545 in the digestion vessel 4. Add up the appropriate amout of sample1 to the digestion vessel and note the accurate

weight of the sample 5. Add 50 mL hydrochloric acid (4 M) and form a suspension by gently swirling the tube 6. Add another 50 mL hydrochloric acid (4 M) making sure to rinse any remaining sample

off the glass wall 7. Preheat the Hydrolysis Unit for 10 min 8. Insert the samples into the unit and lower the digestion vessels 9. Insert the glass sample tubes into the Hydrolysis Unit 10. Connect the digestion tubes and the glass samples tubes with the aspiration tubes,

reduce the heat to level 3 and start the water-jet pump after boiling begins

Violent foaming can be prevented by adding 4 M hydrochloric acid dropwise.

The degree of foaming depends on the sample and on the preheating time of the

unit. Do not extend preheating excessively.

11. Hydrolyze the sample for 15 min after constant boiling is observed in each position 12. Add 100 mL of warm (40-50 °C) deionised water to each digestion vessel at the end of

the hydrolysis time 13. Switch off the heating and lift the digestion vessels to the top position in order to filter

the hydrolyzate 14. Wash each of the digestion vessels by gradually adding a total of at least 400 mL warm

deionised water, until a neutral pH is reached 15. Check the pH with a pH paper on the bottom of the frit

For maximum efficiency, aspirate all samples/rinsing water at the same time.

16. Stir the Celite layers (without touching the sand layer at the bottom) with a spatula to loosen the pulp

17. Carefully wipe off the spatula with a piece of tissue and add it on the top of the sample

1 The sample weight has to be chosen according to the approximate fat content of the sample. 80-100 %: 0.7-1 g 20-50 % 1.5-3.5 g <10 %: 7- 10 g 50-80 %: 1-1.5 g 10-20 % 3.5-7 g


18. Dry the glass sample tubes in a vacuum oven (≤ 4 h at 100 °C/200 mbar), in a drying oven (≤ 8 h at 100 °C) or in a microwave oven

Using a microwave oven accelerates the drying process. However, its control is more delicate.

This is due to the fact that the sample can easily overheat (> 105 °C) if an inappropriate heating

power is chosen. The following suggestion is valid for the drying of six hydrolyzed samples at the

same time. First step: 15 min at 640 W, second step: 9 min at 480 W, power of microwave oven

800 W (the optimal parameters may depend on the model of microwave).

Faster drying at higher temperatures is not recommended because fat may

decompose at temperatures above 105 °C. Oxidized fat can result in an excessive

recovery.

19. Allow the glass sample tubes to cool down to room temperature in a desiccator 20. Add another layer of quartz sand (20 g). This prevents the Celite from being re-

suspended in the condensed solvent

4.3. Fat extraction of the sample following Twisselmann extraction and Soxhlet extraction, using the Extraction Units E-816 ECE and E-816 SOX

4.3.1. Preparation of the beakers

Always use dry and clean beakers for the Twisselmann extraction. Add a boiling aid (e.g. boiling

stones) to each beaker and dry them for at least 30 min at 102 °C. Let them cool down to ambient

temperature in a desiccator for at least 1 h. Record the exact weight prior to extraction.

4.3.2. Twisselmann extraction

Put the sample tubes into the extraction chamber using the pliers. See Figure 1.

Figure 1: Twisselmann extraction chamber with sample before start

Fill the solvent into the beakers and place them on their corresponding heating plate. Close the

safety shield and lower the rack. Activate the occupied positions, open the cooling water or switch

on the connected chiller and start the extraction according to the parameters listed in Table 1.

Table 1: Parameters for the extraction with the Extraction Unit E-816 ECE

Method parameters Extraction Unit E-816 ECE

Solvent Petroleum ether2

Extraction step 50 min (Heater 100 %)3

Drying step 10 min (Heater 100 %)4

Total time 60 min

Solvent volume 70 mL

2 Please select the solvent, which is the default in the menu. 3 Choose the heater power between 100 – 120 % so the boiling is sufficient. 4 Choose the same parameter for the heater power that was selected for the extraction step.


4.3.3. Soxhlet extraction

To compare the fat contents determined with the Twisselmann extraction, the samples were also

extracted by the Soxhlet extraction method using the Extraction Unit E-816 SOX.

Put the sample tubes into the extraction chamber using the pliers and adjust the optical sensor to

the correct sample amount. Fill the beakers with solvent and place them on their corresponding

heating plate. Close the safety shield and lower the rack. Activate the occupied positions, open

the cooling water or switch on the connected chiller and start the extraction using the parameters

listed in Table 2.

Table 2: Parameters for the extraction using the Extraction Unit E-816 SOX

Method parameters Extraction Unit E-816 SOX

Solvent Petroleum ether5

Extraction step 120 min (Heater 100 %)6

Rinse step 5 min (Heater 100 %)7

Drying step 25 min (Heater 100 %)8

Total time 150 min

Solvent volume 120 mL

4.3.4. Drying of the extract

Dry the beakers containing the extract in a drying oven at 102 °C until a constant weight is

reached. Let the beakers cool down to ambient temperature for at least 1 h in a desiccator and

record the weight.

Make sure that the cooling down time of the beakers in the dessicator is the same

before and after extraction. Differences in beakers temperature falsify the results.

4.4. Calculation

The results are calculated as percentage of the fat according to equation (1).

%100)

m

m -(mFat %

Sample

BeakerTotal (1)

% Fat : Percentage of fat in the sample

mTotal : Beaker + extract [g]

mBeaker : Empty beaker weight with boiling aid [g]

mSample : Sample weight [g]

5. Results and Discussion

The fat contents of the yogurt samples obtained with the Twisselmann and Soxhlet extraction

method are lower than the declared values however, they are within the guidelines of the

laboratory from the Food control of the Canton of Zug, Switzerland. Importantly, the results

obtained by Twisselmann and Soxhlet extraction are well comparable with low relative standard

deviations.

5 Please select the solvent, which is the default in the menu. 6 Choose the heater power between 100 – 120 % so the boiling is sufficient. 7 Choose the same parameter for the heater power that was selected for the extraction step. 8 Choose the same parameter for the heater power that was selected for the extraction step.


The results are summarized in Tables 3 - 12

Table 3: Yogurt Mocha (Declaration: 3.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 2.20 2.45

Sample 2 2.47 2.49

Sample 3 2.41 2.50

Mean value [g/100g] 2.36 2.48

rsd [%] 6.0 1.1

Table 4: Yogurt Vanilla (Declaration: 3.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 2.73 3.01

Sample 2 2.75 3.01

Sample 3 2.74 3.03

Mean value [g/100g] 2.74 3.01

rsd [%] 0.4 0.3

Table 5: Yogurt Choco (Declaration: 4.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 3.21 3.35

Sample 2 3.26 3.30

Sample 3 3.21 3.33

Mean value [g/100g] 3.23 3.32

rsd [%] 0.9 0.8

Table 6: Yogurt Greek with honey (Declaration: 6.5 g/100g)

E-816 ECE E-816 SOX

Sample 1 5.75 5.86

Sample 2 5.85 5.98

Sample 3 5.86 5.90

Mean value [g/100g] 5.82 5.92

rsd [%] 1.1 1.0

Table 7: Yogurt Fruits (Declaration: 3.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 1.93* 2.31

Sample 2 2.16 2.27

Sample 3 2.16 2.21

Mean value [g/100g] 2.16 2.26

rsd [%] 0.0 2.2

*outlier, not taken for calculation (Dean-Dixon test)


Table 8: Yogurt Apricot (Declaration: 3.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 2.34 2.42

Sample 2 2.42 2.37

Sample 3 2.20 2.45

Mean value [g/100g] 2.32 2.41

rsd [%] 4.7 1.7

Table 9: Yogurt Plain (Declaration: 3.5 g/100g)

E-816 ECE E-816 SOX

Sample 1 2.14 3.10

Sample 2 3.15 3.06

Sample 3 3.16 3.05

Mean value [g/100g] 3.15 3.07

rsd [%] 0.3 0.8

Table 10: Yogurt Strawberry (Declaration: 3.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 2.36 2.29

Sample 2 2.35 2.25

Sample 3 2.36 2.24

Mean value [g/100g] 2.36 2.26

rsd [%] 0.1 1.2

Table 11: Yogurt Banana (Declaration: 3.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 2.41 2.49

Sample 2 2.33 2.53

Sample 3 2.42 2.50

Mean value [g/100g] 2.39 2.50

rsd [%] 1.9 0.7

Table 12: Yogurt Greek, plain (Declaration: 7.0 g/100g)

E-816 ECE E-816 SOX

Sample 1 6.61 6.75

Sample 2 6.51 6.73

Sample 3 6.62 6.22*

Mean value [g/100g] 6.58 6.74

rsd [%] 0.9 0.2

*outlier, not taken for calculation (Dean-Dixon test)

6. Conclusion

The determination of fat in different yogurt samples using the Hydrolysis Unit E-416 and the

Extraction Unit E-816 ECE following Twisselmann extraction method provides results which were

comparable to the results received with the Soxhlet extraction method following Weibull-Stoldt.

The determined fat contents of the yogurt samples are within the acceptance criteria of the


Association of cantonal chemists of Switzerland (Föderation der Schweizerischen

Nahrungsmittel-Industrie)9. The results show low relative standard deviations (rsd).

With the Extraction Unit E-816 ECE the time to results is significantly reduced (60 min) when

compared to the use of the Extraction Unit E-816 SOX (150 min).

7. Acknowledgements

We gratefully acknowledge Mr. Urs Aschwanden from the Food control, Canton of Zug,

Switzerland, for his support in the development of this application note.

8. References

[1] §64 LFGB L 01.00-20 Bestimmung des Gesamtfettgehaltes in Milch und Milchprodukte

Operation Manual of Hydrolysis Unit E-416

Operation Manual of Extraction Unit E-816 ECE

Operation Manual of Extraction Unit E-816 SOX

9 Acceptance criteria of the Association ofcantonal chemists, Switzerland:

Declared fat content: Max. acceptable deviation: ≤ 2 g +/- 50 % > 2 g ≤ 5 g +/- 40 % > 5 g ≤ 10 g +/- 30 % > 10 g ≤ 20 g +/- 25 % > 20 g ≤ 30 g +/- 20 % > 30 g +/- 15 %

Application Note No. 105/2013 Nitrogen & protein determination in milk powder KjelDigester K-449, KjelMaster K-375 with KjelSampler K-376:

Accelerated Nitrogen and Protein Determination in Milk Powder with Kjeldahl Tablets and

Hydrogen Peroxide


Introduction1

An easy and reliable method for the determination of total nitrogen and protein in milk powder by

the use of hydrogen peroxide, according to ISO 8968-3, is introduced below. The samples are

digested using the KjelDigester K-449. The distillation and boric acid titration are performed with

the KjelMaster K-375 with KjelSampler K-376. The combination of the accelerated digestion

method, using the Kjeldahl Tablet Titanium in combination with hydrogen peroxide, and the

KjelMaster system K-375/K-376 increases the sample throughput.

Equipment2

KjelDigester K-449 (the parameters used are also valid for K-446)

Scrubber K-415 TripleScrub ECO

KjelMaster K-375 with KjelSampler K-376

Analytical balance (accuracy ± 0.1 mg)

Safety accessories:

User protection shield, BUCHI (11057889)

Hirschmann bottle top dispenser ceramus® 5-30 mL, VWR (613-3243) with ceramus

®

discharge tube, spiral-shaped, VWR (612-0917)

Figure 1: Safety accessories for the digestion with hydrogen peroxide and Kjeldahl Tablet Titanium


Chemicals and Materials3

Chemicals:

Sulfuric acid conc 98 %, Merck (1007482500)

Titanium, BUCHI Kjeldahl Tablet (11057980)

Hydrogen peroxide, 30 %, Fluka (95302)

Sodium hydroxide 32 %, Brenntag (81980-452)

Boric acid 4 %, 400 g boric acid, Brenntag (80948-155) diluted to 10 L with deionized water,

pH adjusted to 4.65

Sulfuric acid 0.05 mol/L, Fluka (35358)

Neutralization solution for the Scrubber: 600 g sodium carbonate, calcined, technical,

Synopharm (0179420) about 2 mL ethanol and a spatula tip of bromthymol blue, Fluka (18460)

diluted to 3 L with distilled water

D/L tryptophan, assay 99 %, Fluka (162698)

For a safe handling please pay attention to all corresponding MSDS!

Samples:

Skimmed milk powder I with a protein content of 32 g/100 g

Skimmed milk powder II with a protein content of 32 g/100 g

Whole milk powder I with a protein content of 25 g/100 g

Whole milk powder II (reference material) with a declared protein content of 26.44 g/100 g

The reference material was purchased at LVU, Herbolzheim (Germany).

Procedure4

The determination of nitrogen and protein in milk powder includes the following steps:

Digestion of the sample, using K-449 (K-446 respectively)

Distillation and titration of the sample, using KjelMaster system K-375/K-376 4.1 Digestion method – tryptophan (verification of the method)

1. Start the KjelDigester K-449 according to the parameters listed in Table 1 2. Place 0.1 g tryptophan in a 300 mL sample tube 3. Add 1 Titanium tablet and 10 mL of sulfuric acid (conc. 98 %) 4. Prepare additional blanks, chemicals without sample 5. Connect the Scrubber K-415 to the K-449 for absorbing the acid fumes created during

digestion 6. Place the rack under the fume hood and affix the user protection shield

7. Slowly add 8 mL hydrogen peroxide (30 %) with the dispenser down the glass wall of the sample tube, wait until the fuming stops and the reaction subsides.

8. Insert the rack containing the user protection shield and the samples into the cooling position and mount the suction module onto the samples, immediately start the digestion according to the parameters listed in Table 1.

9. Let the samples cool down when the digestion is completed.


4.2 Digestion method – samples

1. Start the KjelDigester K-449 according to the parameters listed in Table 1 2. Place 0.25 g of each sample in a 300 mL sample tube 3. Add 1 Titanium tablet and 10 mL of sulfuric acid (conc. 98%) to each tube 4. Prepare additional blanks, chemicals without sample 5. Connect the Scrubber K-415 to the K-449 for absorbing acid fumes created during digestion 6. Place the rack under the fume hood and affix the user protection shield

7. Slowly add 8 mL hydrogen peroxide (30 %) with the dispenser down the glass wall of the sample tube, wait until the fuming stops and the reaction subsides.

8. Insert the rack containing the user protection shield and the samples into the cooling position and mount the suction module onto the samples, immediately start the digestion according to the parameters listed in Table 1.

Table 1: Temperature profile for digestion with the K-449

Step Temperature [°C] Time [min]

1 330 0

2 420 60

Cooling – 25

NOTE: If the liquid inside the sample tube is not clear and blue-green, digest for additional 15 min at 420 °C. NOTE: The samples should be clear-green immediately after the digestion. A darkening of the clear liquid samples during the cooling down process is possible but does not affect the results.

9. Let the samples cool down when the digestion is completed.


4.3 Distillation and titration Distill the samples according to the parameters listed in Table 2.

Table 2: Distillation and titration with the KjelMaster system K-375/K-376

Method parameters KjelMaster K-375

H2O volume 50 mL Titration solution H2SO4 0.05 mol/L

NaOH volume 45 mL Sensor type Potentiometric

Reaction time 5 s Titration mode Online

Distillation mode Fixed time Titration start time 90 s

Distillation time 180 s Measuring mode Endpoint pH

Stirrer speed distillation 5 Endpoint pH 4.65

Steam output 100 % Stirrer speed titration 7

Titration type Boric acid Titration start volume 0 mL

Receiving solution vol. 60 mL Titration algorithm Optimal

NOTE: The sample throughput for this application was increased by using the Titration mode “Online”.

4.4 Calculation The results are calculated as a percentage of nitrogen. In order to calculate the protein content of the sample, the nitrogen content is multiplied with a sample-specific protein factor. The following equations (1), (2), and (3) are used to calculate the results. For the reference substance, the purity of the tryptophan is considered in equation (4).

1000 m

Mfc z V-(Vw

Sample

NBlankSampleN

) (1)

%N = wN ∙ 100 % (2)

%P = wN ∙ PF ∙ 100 % (3)

P

100 •%N=%NTry (4)

wN : weight fraction of nitrogen

VSample : amount of titrant for the sample [mL]

VBlank : mean amount of titrant for the blank [mL]

z : molar valence factor (1 for HCl, 2 for H2SO4)

c : titrant concentration [mol/L]

f : titrant factor (for commercial solutions normally 1.000)

MN : molecular weight of nitrogen (14.007 g/mol)

mSample : sample weight [g]

1000 : conversion factor [mL/L]

%N : percentage of weight of nitrogen

%NTry : percentage of weight of nitrogen corrected for the purity of reference substance

tryptophan [%]


%P : percentage of weight of protein

P : purity of the reference substance tryptophan [%]

PF : sample-specific protein factor (6.38 for dairy products)

Results5

5.1. Recovery of tryptophan

The results of nitrogen determination and recovery for tryptophan analysis (assay > 99 %) are presented in Table 3. The nominal value of tryptophan is 13.72 % nitrogen. The recoveries are within the specification of 98 – 100 % [1] Table 3: Results of the recovery of nitrogen in tryptophan

Tryptophan mSample [g] VSample [mL] %NTry Recovery [%]

Sample 1 0.0991 9.933 13.54 98.7

Sample 2 0.1075 10.704 13.50 98.4

Sample 3 0.1058 10.720 13.74 100.1

Sample 4 0.0988 9.923 13.57 98.9

Average [%] – – 13.58 99.0

Rsd [%] – – 0.8 0.8

The mean blank volume (VBlank) was 0.449 mL (n = 4).

5.2 Protein determination in dairy products The results of the determination of nitrogen and protein contents in different milk powders are presented in Tables 4 – 7. Table 4: Results of the determination of nitrogen and protein in skimmed milk powder(protein content 32 g/100 g)

Skimmed milk powder I

mSample [g] VSample [mL] %N %P

Sample 1 0.2470 9.242 4.986 31.8

Sample 2 0.2496 9.372 5.007 32.0

Sample 3 0.2523 9.398 4.982 31.7

Average [%] – – 4.987 31.8

Rsd [%] – – 0.4 0.4

The mean blank volume (VBlank) was 0.449 mL (n = 4). Table 5: Results of the determination of nitrogen and protein in skimmed milk powder (protein content 32 g/100 g)

Skimmed milk powder II


Sample 1 0.2519 8.180 5.067 32.3

Sample 2 0.2730 7.799 5.045 32.2

Sample 3 0.2456 7.706 5.057 32.3

Average [%] – – 5.056 32.3

Rsd [%] – – 0.2 0.2

The mean blank volume (VBlank) was 0.449 mL (n = 4).


Table 6: Results of the determination of nitrogen and protein in whole milk powder (protein content 25.2 g/100 g [4])

Whole milk powder I


Sample 1 0.2483 7.602 4.035 25.7

Sample 2 0.2687 8.143 4.011 25.6

Sample 3 0.2576 7.823 4.010 25.6

Average [%] – – 4.019 25.6

Rsd [%] – – 0.4 0.4

The mean blank volume (VBlank) was 0.304 mL (n = 4). Table 7: Results of the determination of nitrogen and protein in whole milk powder (declared protein content 26.44 g/100 g)

Whole milk powder II


Sample 1 0.2625 8.180 4.125 26.32

Sample 2 0.2506 7.799 4.108 26.21

Sample 3 0.2456 7.706 4.139 26.41

Average [%] – – 4.124 26.31

Rsd [%] – – 0.4 0.4

The mean blank volume (VBlank) was 0.449 mL (n = 4). The whole milk powder was purchased at LVU, Herbolzheim. It has a declared protein content of 26.44 %, the protein content was verified by an interlaboratory test. Comparing the declared protein content with the one determined by this Kjeldahl method showed comparable results.

Comparison to ISO 8968-36

This application note is based on the standard method ISO 8968-3 with minor differences. These differences are shown in Table 8. Table 8: Differences to AOAC ISO 8968-3

Application note ISO 8968-3 Notes/Impact

Catalyst 1 × 3.7 g Tablets Composition 94.4 % K2SO4 2.8 % TiO2 2.8 % CuSO4*5H2O

2 × 3.7 g Tablets Composition 94.4 % K2SO4 2.8 % TiO2 2.8 % CuSO4*5H2O

Just one tablet to lower the risk of crystallisation

Hydrogen peroxide

8 mL (Conc. 30 %)

5 mL (Conc. 30 %)

Higher volume of hydrogen peroxide instead of two Titanium Tablets to speed up the digestion.

Boric acid 60 mL 50 mL In the conducted experiments a higher amount of boric acid was used then de-scribed in standard methods as the tip of the condenser outlet and the elec-trode hve to be immersed in the solution.


Conclusion7

The determination of nitrogen and protein in milk powder using the KjelDigester K-449 and

Kjeldahl sampler system K-375/K-376 provides reliable and reproducible results. These results

correspond well to the labelled values of the different milk powders and with the results of the

standard Kjeldahl method Application Note 104/2013 with low relative standard deviations (rsd),

but the digestion time is reduced to 60 min. The recovery with tryptophan was 99.0 %

(rsd = 0.8 %), which was within the specification of 98 - 100 % [1].

In combination with the accelerated digestion method using the KjelDigester K-449, Kjeldahl

Tablet Titanium and hydrogen peroxide, the time needed for sample analysis is significantly

reduced and therefore throughput increased.

With the KjelDigester K-449 the digestion process (including preheating, digestion and cooling) is

very fast and is fully automated. Together with the fully-automatic KjelMaster system

K-375/K-376, the time to result is significantly reduced and it offers fully walk-away convenience.

References8

[1] ISO 8968-3 Milk-Determination of nitrogen content Part 3: Block-digestion method [2] Kessler, H.-G.: Lebensmittel- und Bioverfahrenstechnik, Molkereitechnologie, Verlag A. Kessler, Freising, 4. Auflage 1996 KjelCalc App Application Note 104/2013, Nitrogen and Proten Determination in Milk Powder according to Kjeldahl Method Operation Manual of KjelDigester K-446/K-449 Operation Manual of Scrubber K-415 Operation Manual of KjelMaster system K-375/K376

You need fast and reliable information about your samples in order to make far-reaching deci-sions. We support you in overcoming your daily challenges, from incoming goods inspection to finished product release, with more than 15 years experience in supplying laboratory and at-line NIR analytical solutions for milk and dairy industry.

BUCHI NIR ApplicationsMilk & Dairy

NIR Pre-calibrated applicationsMilk & Dairy Industry

Time savings ∙ Shorter time to routine use. Measure parameters such as moisture, fat, protein, lactose and much more from day one

∙ Measure all parameters simultaneously ∙ Control the value chain at each critical point, from incoming goods to finished product release

Reliability ∙ Deliver the same accuracy in the production as in the laboratory ∙ Get accurate results from a robust spectral database spanning geographical and seasonal variations

Precision and accuracy ∙ Our NIR technology provides unparalleled measurement reproducibility and spectrometer performance

∙ Intimate knowledge and experience with reference methods like Kjeldahl, Dumas and Extraction have been implemented into applications development

Your most important benefits

Your «NIRSolutions Laboratory» Your «NIRSolutions At-line»

Based on our NIRFlex® N-500 spectrometer ∙ Flexible, with various measurement cells and

add-ons to accommodate any sample matrix

Based on our NIRMasterTM spectrometer ∙ Hygienic, representative sampling ∙ Practical, ingress-protected design ∙ Simple operator interface

“BUCHI NIRSolution convince us for quality of fast screening solution provided as well as forthe quality of Service support.”Fromagers de Thiérache Quality Contol

Dairy products - I

Product

Yogurt and fresh

cheese

N555-505

Hard, semi-hard and

soft cheese

N555-507

Processed cheese

N555-506

Moisture [%] 14.6 – 93.5* 26.6 – 68.4*

Moisture in fat-free cheese [%] 39.7 – 90.0**

Dry matter [%] 44.1 – 61.0*

Fat [%] 0.02 – 48.60* 6.2 – 37.5*

Fat in dry matter [%] 13.6 – 72.7** 41.2 – 48.9*

Protein [%] 0.4 – 19.1* 4.5 – 51.1*

Lactose [%] 0.03 – 4.30**

Total sugar [%] 0.6 – 54.9* 0.3 – 7.4**

Ash [%] 0.2 – 2.0* 0.8 – 18.1**

pH 4.1 – 6.3* 4.1 – 6.4** 5.6 – 6.0*

Salt [%] 0.04 – 1.99** 0.1 – 4.0* 1.6 – 2.3*

Sample compatibility Yoghurt, quark, sour

cream, fresh cheeses,

mascarpone measured

with sample cup in

diffuse reflectance

mode

Cheeses like Emmental,

Gruyeres, St. Paulin,

Raclette, Appenzell,

Tilsiter and cream

cheese measured with

sample cup in diffuse

reflectance mode

Processed cheese

measured with sample

cup in diffuse reflectance

mode

* BUCHI Pre-calibrations; ** Pre-calibrations in developmentIf not indicated otherwise, the pre-calibrations listed are compatible with both the NIRFlex® Solids and the NIRMasterTM spectrometers

Milk

Pre-calibrated application

Milk transflectance

N555-509 Milk flow cell**

Dry matter [%] 7.8 – 15.5* 11.5 – 13.2

Fat [%] 0.05 – 9.80* 1.99 – 6.85

Protein [%] 1.1 – 6.5* 2.9 – 3.6

Lactose [%] 0.08 – 5.50** 4.22 – 4.98

Saturated fatty acids [%] 0.03 – 4.68**

Mono+ Poly unsaturated

fatty acids [%]0.01 – 2.34**

Casein 2.3 – 3.1

Sample compatibility Homogenized milk measured with

sample cup in transflectance mode

Raw milk measured after

homogenization with flow cell in

transflectance mode

Dairy products - II

Product Butter**

Milk creams

transflectance** Milk powders**

Moisture [%] 11.3 – 23.8 1.4 – 7.9

Dry matter [%] 17.5 – 50.9

Fat [%] 74.5 – 88.4 7.5 – 46.0 0.1 – 33.0

Protein [%] 2.0 – 4.5 1.7 – 91.2

Lactose [%] 36.5 – 55.0

Ash [%] 2.0 – 8.5

pH 3.7 – 7.1

Salt [%] 0.03 – 2.60

Sample compatibility Butter measured with

sample cup in diffuse

reflectance mode

Milk-based creams


cup in transflectance

mode

Full and skimmed milk

powder, whey powder


cup in diffuse reflectance

mode

*BUCHI Pre-calibrations; **Pre-calibrations in developmentIf not indicated otherwise, the pre-calibrations listed are compatible with both the NIRFlex® Solids and the NIRMasterTM spectrometers

Milk

&D

airy

NIR

Ap

plic

atio

n en

160

3 B

/Te

chni

cal d

ata

are

sub

ject

to c

hang

e w

ithou

t not

ice/

Qua

lity

Sys

tem

s IS

O 9

001

.T

he E

nglis

h ve

rsio

n is

the

orig

inal

lang

uage

ver

sion

and

ser

ves

as b

asis

for

all t

rans

latio

ns in

to o

ther

lang

uage

s.

NIRMaster™IP54FT-NIR spectroscopy with ingress protection

www.buchi.com/nir Quality in your hands

NIRMaster™ Pro IP65FT-NIR spectroscopy with maximum protection

LIMS Software InterfaceAutomated result datamanagement

NIRFlex® N-500Versatile laboratory FT-NIR spectrometer

For more information please contact your local BUCHI representative.

www.buchi.com/worldwide

in dairy productsplace 2 g celite 545 in the digestion vessel 4. add up the appropriate amout of...

Documents