analysis of organic acids - cfs.gov.hk · maleic acid malonic acid ... recalculated after oa...
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Analysis of Organic Acids
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Definition of Organic Acids
No definitions from Codex
Broadly speaking, all organic compounds having at least one carboxylic acid functional group
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Important OAs in FoodCitric acid Malic acid
Lactic acid Acetic acid
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Other OA can be found in FoodsOther OA can be found in Foods
Formic acidFumaric acidMaleic acidMalonic acidOxalic acidQuinic acid Shikimic acidSuccinic acid Tartaric acid
No exhaustive list
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Relevancy of OAs in NLRelevancy of OAs in NL
May contribute in energy calculationNot a core nutrient but voluntary labeled value must be correct
energy (kcal in 100g) = carbohydrate x 4 +protein x 4 +total fat x 9 +ethanol x 7 +organic acid x 3
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Analytical MethodsAnalytical Methods
Q : Can I determine the “organic acids”content by titration?
A : Not recommended since titration might:(1) over-estimate due to common additives
such as benzoic acid, sorbic acid,sulphur dioxide, erythoric acid, etc. and
(2) no suitable conversion factor for calculation
LC methods are preferred
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Analytical MethodsAnalytical Methods
Quinic, Malic, and Citric Acids in Cranberry Juice Cocktail and Apple Juice
AOAC 986.13
食品中有机酸的測定
Determination of Organic Acid in FoodsGB/T 5009.157-2003
TitlesOfficial method
… and any other suitable methods for the food matrix concerned.
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FRL Method WorkflowFRL Method Workflow
sample homogenization
solvent extraction
centrifuge& filter HPLC
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EquipmentEquipment
HPLC
homogenizer centrifuge
nitrogen evaporator
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Protocol for Liquid SamplesProtocol for Liquid Samples
mixing or blending
aliquot, add buffer, make up
centrifuge 3000 rpm 10 min
filter supernatant, HPLC
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Protocol for Solid SamplesProtocol for Solid Samples
10 g homogenized sample + 20 ml 80% EtOH
extract 2x with 80% EtOH, combine supernatants
aliquot, dry by N2 (50°C), add buffer, make up
filter supernatant, HPLC
homogenize, 3000 rpm 10 min, collect supernatant
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HPLC ConditionsHPLC Conditions
20 µLInjection vol:
40 min + 10 min post-runRuntime:220 nmUV (λ):
0.5 mL/minFlow:25 °CTemp:MeSO3H & NaSO4 buffer (pH 2.8)Mobile phase:C18 (7mm)Guard column:two C18 (15cm, 25cm) + one Dionex OAColumn:HPLC-DAD/PDAInstrument:
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ChromatogramChromatogram
All 13 OAs separatedFrequent interferences :ascorbic acid and some anions
100 ppm
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Calculation of Available Carbohydrate Calculation of Available Carbohydrate when when OAsOAs is of concernis of concern
Carbohydrate = 100 g – ( water + ash + DF(available) + protein + fat + ethanol +
organic acid )
Q : How would energy content be affected?A : (1) Due to different conversion factors for
carbohydrates & OA (i.e. 4 vs 3)
(2) The extent depends on cases
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Example 1 Example 1 –– Thousand Island SauceThousand Island Sauce
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Example 1 Example 1 –– Thousand Island SauceThousand Island Sauce
11.312.3Carbohydrate
45.545.5Fat
462
0.0
1.0
1.1
revised
463Energy (kcal/100ml)
0.0Ethanol
Not determinedOrganic acid
1.1Protein
originalNutrient (g/100 ml)
Difference = 0.2 %
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Example 2 Example 2 –– Grapefruit JuiceGrapefruit Juice
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Example 2 Example 2 –– Grapefruit JuiceGrapefruit Juice
12.813.5Carbohydrate
0.00.0Fat
53.3
0.0
0.7
0.0
revised
54Energy (kcal/100ml)
0.0Ethanol
Not determinedOrganic acid
0.0Protein
originalNutrient (g/100 ml)
Difference = 1.3 %
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Example 3 Example 3 –– Chinese Red VinegarChinese Red Vinegar
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Example 3 Example 3 –– Chinese Red VinegarChinese Red Vinegar
5.010.0Carbohydrate
0.00.0Fat
35
0.0
5.0
0.0
revised
40Energy (kcal/100ml)
0.0Ethanol
Not determinedOrganic acid
0.0Protein
originalNutrient (g/100 ml)
Difference = 12.5 %
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Points to NotePoints to Note
HPLC method is preferred for OA analysis
Carbohydrate content should be recalculated after OA analysis
OA analysis is only important for samples of low energy content or with high level of OA
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THANK YOUTHANK YOU