nutrient test methods (part 2)7_part_2.pdf · aoac official method 996.06 peaks of known identity...

1

Nutrient Test Methods(Part 2)

1. Sugars2. Sodium 3. Fatty acids (sat fat & trans fat)4. Cholesterol

2

1. Analysis of Sugars in Foods

O

HOOH

OO

HOOH

OH

OHOH

OHO

HOOH

OH

OH

OH

3

Definition of Sugars (Codex)

All monosaccharides and disaccharides in food

OHO

HOOH

OO

HOOH

OH

OHOH

OHO

HOOH

OH

OH

4

Common sugars in foods

Monosaccharides:

Fructose, Glucose, Galactose

Disaccharides:

Lactose, Maltose, Sucrose

5

Common Properties

1. Water soluble

2. Low thermal stability

3. High chemical reactivity

4. Do not have properties of fluorescenceemission and only absorb in UV at very shortwavelenghts

6

Typical analysis

SugarsSugars Preparation/Clean up

Preparation/Clean up

LCLC

DerivatizationDerivatization LC/GCLC/GC

7

Preparation/Clean up

Extraction:Water or water/ethanol mixture

Clean up:Solid phase extraction (e.g. C18, charcoal)

8

LC Analysis

After the clean up step, carbohydrates can be analysed by HPLC without derivatization, using

1. Refractive index detector

2. Light scattering detector

3. UV detector at low wavelengths

9

LC analysis with derivatization

Introduce chromogenic or fluorogenic group tothe saccharide molecules.

Common reagents:p-Aminobenzoic acid (p-AMBA)4-(3-methyl-5-oxo-2-pyrazolin-1-yl) benzoicacid (PMPA).

10

GC analysis with derivatization

Convert carbohydrates into volatile derivativesbefore GC analysis.

Popular derivatives are methyl, trifluoroacetyl,trimethylsilyl and tert-butyldimethylsilyl ethers.

11

AOAC methods

Carbohydrates in soluble (instant) coffee

AOAC 995.13

Glucose, fructose, sucrose and maltose in presweetened cereals

AOAC 982.14

Separation of sugars in honeyAOAC 977.20

Fructose, glucose, lactose, maltose and sucrose in milk

AOAC 980.13

12

AOAC 980.13 with modification

Extraction: Mixture of ethanol and waterSeparation: CentrifugeEquipment: LC with refractive index

detectorColumn: Amine & sugar columnMobile phase: Acetonitrile and water

No derivatization required

13


Extract thesugars fromsample using amixture of ethanoland water

14


Centrifuge themixture after the extraction

15


Clean up the extract by SPE

16


Analyse theextract using LC with refractiveindex detector(No derivatisation)

17


18


19

Proficiency test

FAPAS

LGC

AOAC

20

Points to note

Sugar alcohols (polyols) are not “sugars”

Not all monosaccharides and disaccharides are reducing sugars. Test method for reducing sugar may not be suitable for the analysis of sugars.

21

Points to note

Definition of “0”Sugars ≤0.5 g/100 g

Limit of detection of total sugars should be less than or equal to 0.5 g/100 g.

22

2. Analysis of Sodium in Foods

23

Examples in AOAC

Ca, Cu, Fe, Mg, Mn, P, K, Na and Zn in Infant Formula

AOAC 984.27

Minerals in Infant Formula, Enteral Products and Pet Foods

AOAC 985.35

Sodium and Potassium in Seafood

AOAC 969.23

24

Examples in AOAC

Destroy the organic matrix


Dissolve the analytes

Dissolve the analytes

Analyse the analytes


25


Organic matrix is destroyed by:

1. Dry ashing

2. Wet digestion

26


Sodium in the residue of dry ashing/wet digestion are dissolved in diluted acid and analysed by:

1. Flame atomic absorption spectrometry(FAAS)

2. Inductively coupled plasma atomic emission spectrometry (ICP-AES)

27


Dissolve theresidue of digestion in dilute acid

28


Analyse theelements usingICP-AES

29

Flame atomic absorption spectrometryFlame is used to produce ground-state atoms.

Sodium atoms formed during the atomizationmay be lost by ionization.

Na Na+ + e-

Depression of signal.

30

Flame atomic absorption spectrometry

Ionization suppressor

Large excess of easily ionisable element (e.g.,Cs) can be used to suppress the ionization.

31


Excess Cs in the flame suppresses the Ionization (e.g. Na) by mass action effect

Cs Cs+ + e-

Na Na+ + e-

32


Typical limits of detection: 0.01 – 0.1 mg/L

Linear dynamic range is generally no more than three orders of magnitude (e.g. from 0.01 to 10 mg/L).

33

Inductively coupled plasma atomicemission spectrometry

Plasma instead of flame is the excitation source.

Temperature in plasma is much higher thanthat in flame (7,000 K compared with 2000 to 3000 K).

34


Because of the high temperature most samplesare completely atomized and this techniquesuffers from few chemical interferences compared with the flame.

35


Characterized by low detection limits of theorder of 1 – 100 ng/mL, because of its highexcitation temperature compared with the flame.

It has a larger linear dynamic range comparedwith FAS.

36

Proficiency test

FAPAS

AOAC

LGC

37

Points to note

Addition of Cs can produce higher resultsespecially in the presence of high level ofpotassium in food.

38

Points to note

Definition of “0”Sodium ≤5 mg/100 g.

Limit of detection should be better than 5 mg/100g

39

3. Analysis of Fatty Acids(saturated and trans)

in Foods

40

AOAC Official Method 996.06

Fat (Total, Saturated, and Unsaturated) in Foods

Hydrolytic Extraction GasChromatographic Method

41


The method is supported by interlaboratorystudy for the determination of total, saturated fatand monounsaturated fat in different food stuffs

Wheat-based cerealPeanut butterFish sticksGround beef, etc

42


Fat and fatty acids are extracted from food by hydrolytic method.

Triglyceride, triundecanoin (C11:0), is added as internal standard.

43


Fat is extracted into ether, then methylated to fatty acid methyl esters (FAMEs) using BF3 in methanol.

FAMEs are quantitatively measured by capillarygas chromatography against C11:0 internal standard.

44


FatFat HydrolysisHydrolysis

Methylatedto FAMEs

Methylatedto FAMEs

GC-FID(quantitation)GC-FID

(quantitation)

45

Apparatus

Gas chromatograph equipped with flameionisation detector (GC-FID).

Capillary column (SP2560 100 m x 0.25 mm with 0.25 µm film is suitable).

Mojonnier flasks.

46

Mojonnier flask

47


Hydrolysis

Weigh sampleand pyrogallicacid into the Mojonnier flask

48


Hydrolysis

Add internalstandard, ethanoland 8.3 M HCl.

49


Hydrolysis

Hydrolyse thesample at 70 –80 oC

50


Hydrolysis

Remove flasksfrom water bath.Cool to roomtemperature.

51


Extraction

Add ethanol anddiethyl ether.Shake.

52


Extraction

Add petroleum ether.Shake.

53


Extraction

Centrifuge sampleat 600 rpm.(allow contents tosep. at least 1 h if centrifuge is notavailable)

54


Extraction

Decant the etherlayer into a tube.

55


Extraction

Evaporate etheron water bathusing nitrogenstream to aidin evaporation.

56


Extraction

Dissolve the residue in chloroform.

57


Methylation

Transfer mixture to a glass vial. Evaporate todryness.

58


Methylation

Add 7% BF3

reagent and toluene.

59


Methylation

Seal vials withscrewcap andheat them in 100 oC.

60


Methylation

Allow vials to coolto roomtemperature.

61


Methylation

Add water (5 mL),hexane (1 mL),Na2SO4 (1 g).Shake

62


Methylation

Allow layers to separate and transfer top layer to anothervial containing Na2SO4 (1 g).

63


Methylation

Top layer shouldcontain FAMEsand internal standard.

64


GC Determination

Transfer to autosampler vialfor GC analysis.

65


Peaks of unknown identity should not be included in the summation when quantifying fat in the test portion.

66


Peaks of known identity with relative retention times are given the method (more than 50 FAMEs).

The FAME are ranging from butyric acid (C4:0)To docosahexaenoic acid (C22:6).

Relative retention time of several trans and cis-FAMEs are also provided in the method.

67

FAME standards (saturated fat)

C15:0 Methyl pentadecanoate

C14:0 Methyl myristate

C12:0 Methyl laurate

C10:0 Methyl decanoate

C8:0 Methyl octanoate

C6:0 Methyl hexanoateC4:0 Methyl butyrate

68

FAME standards (saturated fat)

C24:0 Methyl tetracosanoate

C22:0 Methyl docosanoate

C20:0 Methyl eicosanoate

C18:0 Methyl stearate

C17:0 Methyl heptadecanotate

C16:0 Methyl palmitate

69

FAME standards (trans fat)

C18:2TT (9,12-trans) Methyl trans-9,12-octadecadienoate

C18:1T (11-trans) Methyl trans-11-octadecenoate



C16:1T (9-trans) Methyl trans-9-hexadecenoate

C14:1T(9-trans) Methyl trans-9-tetradecanoate

70

FAME standards (trans fat)

C22:1T (13-trans) Methyl trans-13-docosenoate

C18:2T (9-cis,11-trans) Methyl cis-9, trans-11-octadecadienoate

C20:1T (11-trans) Methyl trans-11-eicosenoate

C18:2T (9-trans,12-cis) Methyl trans-9, cis-12-octadecadienoate

C18:2T (9-cis,12-trans) Methyl cis-9, trans-12-octadecadienoate

71

Standard FAMEs

min25 30 35 40 45 50 55

pA

20

40

60

80

100

120

140

FID1 A, (090116\PMQ6F.D)

Area

: 519

.32

Area

: 240

.455

Area

: 226

.64 A

rea: 2

51.94

5 A

rea: 2

24.63

Area

: 245

.512

Area

: 233

.893

Area

: 254

.705

Area

: 239

.542

Area

: 243

.066

Area

: 246

.059

Area

: 254

.488

Area

: 259

.112

Area

: 247

.221

Area

: 246

.985

Area

: 262

.943

Area

: 254

.781

Area

: 103

.284

Area

: 136

.183

Area

: 252

.828

Area

: 251

.662

Area

: 24

25.

194

- C

11:0

34.

833

- C

14:1

(9-

cis)

37.

172

- C

15:1

(10

-cis

)

39.

110

- C

16:1

(9-

cis)

41.

255

- C

17:1

(10

-cis

)

43.

041

- C

18:1

(6-

cis)

43.

146

- C

18:1

(9-

cis)

43.

326

- C

18:1

(11

-cis

)

45.

073

- C

18:2

(9,

12-

cis)

46.

491

- C

18:3

(6,

9,12

-cis

) 4

6.85

7 -

C20

:1 (

8-ci

s) 4

7.01

0 -

C20

:1 (

11-c

is)

47.

257

- C

18:3

(9,

12,1

5-ci

s)

48.

830

- C

20:2

(11

, 14

-cis

)

50.

162

- C

20:3

(8,

11,1

4-ci

s) 5

0.61

2 -

C22

:1 (

13-c

is)

50.

886

- C

20:3

(11

,14,

17-c

is)

51.

192

- C

20:4

(5,

8,11

,14-

cis)

52.

368

- C

22:2

(13

, 16

-cis

) 53.

432

- C

20:5

(5,

8,11

,14,

17-c

is)

54.

237

- C

24:1

(15

-cis

) 5

4.52

3 -

C22

:3 (

13,1

6,19

-cis

) 5

5.16

1 -

C22

:4 (

7,10

,13,

16-c

is)

56.

205

- C

22:5

(4,

7,10

,13,

16-c

is)

57.

720

- C

22:5

(7,

10,1

3,16

,19-

cis)

58.

939

- C

22:6

(4,

7,10

,13,

16,1

9-ci

s)

72

Standard FAMEs

min10 15 20 25 30 35 40 45 50

pA

20

40

60

80

100

120

140

FID1 A, (090106\Q5F.D)

Area

: 216

.944

Area

: 260

.661 A

rea: 3

24.52

7

Area

: 393

.621

Area

: 527

.329

Area

: 359

.293

Area

: 379

.854

Area

: 117

.608

Area

: 381

.531

Area

: 392

.303

Area

: 90.3

693

Area

: 343

.03 A

rea: 3

74.96

8

Area

: 93.2

559

Area

: 90.7

685

Area

: 100

.41 A

rea: 9

2.264

7 A

rea: 3

72.71

6

Area

: 92.5

985 A

rea: 1

40.66

2

Area

: 141

.343

Area

: 379

.466

Area

: 93.4

157

Area

: 386

.3

12.

361

- C

4:0

14.

403

- C

6:0

17.

896

- C

8:0 22.

658

- C

10:0 2

5.26

4 -

C11

: 0

27.

871

- C

12:0

32.

931

- C

14:0

34.

278

- C

14:1

T (9

-tra

ns)

35.

328

- C

15:0

37.

627

- C

16:0

38.

700

- C

16:1

T (9

-tra

ns)

39.

823

- C

17:0

41.

934

- C

18:0

42.

758

- C

18:1

T (6

-tra

ns)

42.

832

- C

18:1

T (9

-tra

ns)

42.

941

- C

18:1

T (1

1-tr

ans)

44.

286

- C

18:2

TT (

9, 1

2-tr

ans)

45.

901

- C

20:0

46.

718

- C

20:1

T (1

1-tr

ans)

47.

636

- C

18:2

T (9

-cis

, 11

-tra

ns)

47.

930

- C

18:2

T (1

0-tr

ans,

12-

cis)

49.

569

- C

22:0

50.

331

- C

22:1

T (1

3-tr

ans)

53.

112

- C

24:0

73

Real sample

min10 20 30 40 50

Norm.

20

30

40

50

60

70

80

90

FID1 A, (GC-FTIR\FA09~1\090409\751DF.D)

Area: 6

5.8292 A

rea: 49.2763

Area: 3

1.2856 Area: 7

3.2028

Area: 1

01.161

Area: 0

.409949

Area: 3

3.6879 A

rea: 880.722

Area: 2

0.0957 A

rea: 328.499

Area: 1

2.6639 Area: 5

7.6488 A

rea: 4.25208

Area: 3

.56204 A

rea: 2.33197

12.

048

- C

4:0

14.

015

- C

6:0

17.

405

- C

8:0

22.

070

- C

10:0

24.

647

- C

11: 0

27.

224

- C

12:0

32.

259

- C

14: 0

33.

583

- C

14:1

T (9

-tra

ns)

34.

616

- C

15:0

36.

967

- C

16:0

37.

998

- C

16:1

T (9

-tra

ns)

39.

075

- C

17:0

41.

223

- C

18: 0

41.

902

- C

18:1

T (6

-tra

ns)

42.

079

- C

18:1

T (9

-tran

s) 4

2.21

1 -

C18

:1T

(11-

trans

)

45.

112

- C

20:0

46.

802

- C

18:2

T (9

-cis

, 11

-tra

ns)

47.

112

- C

18:2

T (1

0-tr

ans,

12-

cis)

48.

779

- C

22:0

52.

276

- C

24:0

74

Proficiency test

FAPAS

AOAC

LGC

75

Points to note

Availability of FAME standards is crucial tothis test method.

Insufficient FAME standards wouldunderestimate the level of sat or trans fat.

76

Points to note (1)

Definition of “0”Saturated fatty acids ≤0.5/100 gTrans fatty acids ≤0.3/100 g

Limit of detection of saturated fatty acids and trans fatty acids should be better than 0.5 g/100 g and 0.3 g/100 g respectively

77

Points to note (2)

For prepackaged product with “Free of sat fat”claim:

Sum of sat and trans fat ≤0.1/100 g

Limit of detection of saturated fatty acids and trans fatty acids should be better than 0.05 g/100 g respectively

78

4. Analysis of Cholesterol in Foods

79

Properties

Waxy alcohol

Low solubility in water

High boiling point (360 oC)

High chemical reactivity

Absorb in UV at very short wavelength

80

Examples

Cholesterol in Multicomponent Foods

AOAC 976.26

Cholesterol in FoodsAOAC 994.10

81

AOAC 976.26

Cholesterol in Multicomponent FoodsGas Chromatographic Method

Similar to method 944.10Benzene instead of toluene is used to extractthe cholesterol.

82

AOAC 994.10

The method has been used in interlaboratoryfor the determination of cholesterol in differenta variety of foods, e.g.,

butter cookies, vegetable bacon baby food,vegetable chicken baby food, commercialpowdered eggs, etc.

83

Analysis

LipidLipid Preparation(Saponified)

Preparation(Saponified)

Saponifiablefraction

Saponifiablefraction

Unsaponifiablefraction

Unsaponifiablefraction

GC-FIDGC-FID

84

AOAC 994.10

Reagents:

TolueneKOHHexamethyldisilane (HMDS)Trimethylchlorosilane (TMCS)Internal standard (5α-cholestane)

85

AOAC 994.10

Saponify thesample athigh temperaturewith ethanolicKOH (70 min)

86

AOAC 994.10

Turn of heat.Add ethanol.Remove flaskfrom condenserand allow to cool.

87

AOAC 994.10

Add toluene.Pour solutioninto a 500-mLseparatory funnel.

88

AOAC 994.10

Add 1 M KOHand shake.Discard aqueouslayer.Wash toluenelayer with water.

89

AOAC 994.10

Pour toluenelayer throughfunnel containingplug of glass wooland Na2SO4.(Flask contains ~2 g Na2SO4)

90

AOAC 994.10

Evaporate extractto dryness (40 oC).

91

AOAC 994.10

Add acetone andevaporate todryness again.Dissolve residuein DMF.

92

AOAC 994.10

Pipet 1.0 mL testportion into a centrifuge tube.Add HMDS andTMCS.

93

AOAC 994.10

Shake and let solution standundisturbed for 15 min.

94

AOAC 994.10

Add 5α-choletaneinternal standardand water.Stopper tube,shake.

95

AOAC 994.10

Centrifuge thetube ~2 minutes.

96

AOAC 994.10

Transfer upperlayer to a GCinjection vial.

97

AOAC 994.10

Analyse the upper layer by gaschromatograph

98

AOAC 994.10

Column:

25 m x 0.32 mm x 0.17 µm film thickness,cross-linked 5% phenyl-methyl silicone ormethyl silicone gum.

99

AOAC 994.10

100

AOAC 994.10

1. Six standard solutions 2. Concentration: 0.0025 – 0.2 mg/mL3. 5α-cholestane: 0.1 mg/mL in n-heptane

101

Proficiency Tests

FAPAS

AOAC

102

Points to note

Centrifuge tubes have to be silanized.

i. Fill tubes with 10% HF (stand 10 min). ii. Rinse with water and anhydrous methanol.iii. Dry tube under nitrogen.iv. Fill tubes with 10% HMDS in toluene and

let stand 1 h. v. Rinse with toluene and methanol.vi. Dry tubes in 100 oC before use.

103

Points to note

Definition of “0”Cholesterol ≤5 mg/100 g.

Limit of detection of cholesterol should be better than 5 mg/100 g.

104

Thank You

nutrient test methods (part 2)7_part_2.pdf · aoac official method 996.06 peaks of known identity...

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