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POTENTIOMETRICANALYSIS OF TOTAL

ACID IN THAI FRUIT

JUICESMongkol Engkalohakul, Nakharin Nebbua,

Paradon Dilekrojanavuti and Weerasak Samee

Natural Product Evaluation Center (NPEC), Department of Pharmaceutical

Chemistry and Pharmacognosy, Faculty of Pharmacy, Srinakharinwirot

University, Nakhon Nayok 26120, Thailand


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ABSTRACT

Organic acids are widely used in cosmetics, these acids are of great significance in plants.

As intermediates in the metabolic processes of the fruit, acid content differs depending on

the particular origin and growth conditions of the original fruits. Twenty Thai fruit juicesamples were investigated with respect to total acid content equivalent to milligram of

citric acid using potentiometry. This method determines the milliliter of the alkaline

consumption of fruit juice at the equivalent point. The method proved to be reliable at the

concentration range between 0.02-0.40 mg/mL. The accuracy of the method was between

97.92-101.38%. The coefficient of variation (%CV) of precision within day was less than1.15 for all concentrations. The correlation coefficient (r2) of the calibration line was

0.9999 with slope of 0.1559 and intercept of 0.0027. The total acid content of twenty

fruit juices was in the range of 0.45-5.94 g/100 ml of fruit juice. Citrus aurantifolia

Swing, Garcinia schombuakiana Pierre, Phyllanthus emblica Linn, Spondias pinnata

Kurz andTamarindus indica Linn are the five most total acid content fruits possessedcitric acid equivalent of 5.94, 3.59, 3.05, 2.71, and 2.19 g/100 mL, respectively. These

results could be used to future development of cosmetic products.


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SWU

Herbal

Facial Cream

INTRODUCTION

The total acid determination of fruit juice is essential for

searching the appropriate fruit in herbal cosmetics and

quality control.


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INTRODUCTION

CHO COOH

CH2

CH2

COOH

COOH

+ 3NaOH CHO COONa

CH2

CH2

COONa

COONa

+ 3 H2O

Potentiometry Potentiometry is commonly used as analternative method to determine the total

acid in fruit juice.Titration curve of citric acid

equivalent

point


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METHOD

Sample preparationFruits

Wash

Cut

Squeeze Extraction

Heat at 96

C for 1 min

Cool down

Centrifuge

Filter

Stored at -5 C

Citrus fruits


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METHOD

Assay

Pipette 1.0 mL of fruit juice

Stirred for 2 min.

Add 250 mL of H2O

Titrated with 0.1 N NaOH

(751 GPD Titrino, Metrohm)


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0

2

4

6

8

10

1214

16

18

0 20 40 60 80 100 120

mg of citric acid

m

Lof0.1

NNaOH

METHOD VALIDATION

Mean recovery = 99.83%

%CV = 1.15

LOQ = 0.02 mg/mL

r2 = 0.9999

Y = 0.1559X 0.0027


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1.19RhamnaceaeZiziphusmauritiana Lamk1.57OxalidaceaeAverrhoa carambola Linn.1.66AnacardiaceaeMangifera indica var. namdokmai2.06SolanaceaeSolanum stramonifolium Jacq.2.14CombretaceaeTerminalia chebula Retz.2.19CaesalpiniaceaeTamarindus indica Linn.2.71AnacadiaceaeSpondias pinnata Kurz.

3.05EuphorbiaceaePhyllanthus emblica Linn.3.59CuttiferaeGarcinia achombuakiana Pierre.5.94RutaceaeCitrus aurantifolia Swing.

(g/100 mL)

Citric acid

equivalentFamilyScientific Name

RESULTS


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0.45RosaceaePyrus spp.0.47VitidaceaeVitis spp.0.49RosaceaePyrus lindteyi Rehd.0.55RutaceaeCitrus grandis Osb.0.69BromeliaceaeAnanas comosus0.76RutaceaeCitrus grandis Osb.0.76RosaceaePyrus spp.

0.78VitidaceaeVitis spp.0.8ElaeocarpaceaeElaecarpus hygrophilus Kurz1.01RutaceaeCitrus reticulata

(g/100 mL)

Citric acid

equivalentFamilyScientific Name

RESULTS


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RESULTS

Candidate fruit

Citrus aurantifolia Swing. Garcinia achombuakiana Pierre.

Phyllanthus emblica Linn. Spondias pinnata Kurz. Tamarindus indica Linn.


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CONCLUSION

Determination of total acid in fruit juices by potentiometry

was rapid, easy, save, and reproducible. Citrus aurantifolia

Swing, Garcinia schombuakiana Pierre, Phyllanthus emblicaLinn, Spondias pinnata Kurz andTamarindus indica Linn are

the candidate fruit juices for cosmetic development.

ACKNOWLEGEMENT

The authors would like to thank Natural Product Evaluation

Center (NPEC), Faculty of Pharmacy, Srinakharinwirot

University for providing research facilities.


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REFERENCES

1. Takamura K, Ohtsuki S, Kusu F. Development of a

new amperometric sensor for probing the total acid ofbeverages. Analytical Sciences 2001; 17(supplement):

737-739.

2. Fernandes JCB, Kubota LT and Neto GO.

Potentiometric biosensor for L-ascorbic acid based on

ascorbate oxidase of natural source immobilized on

ethylenevinylacetate membrane. Analytica Chimica

Acta 1999; 385 (1-3): 3-12.

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