ADV01-05_1-298

• 4 •

www.restekcorp.com

RESTEK Advantage

800-356-1688

Verify Fruit Juice Quality

from Organic Acid Profiles

Using New Allure

™

Organic Acids HPLC Column

By Rebecca Wittrig, Ph.D., Senior Innovations Chemist

✔

One 30cm Allure

™

Organic Acids column replaces two C18 columns in

AOAC methodology.

✔

Stable and reproducible retention, even with 100% aqueous mobile

phases, as in AOAC method 986.13.

✔

Facilitates detection of fruit juice adulteration.

The fruit juice industry in the US alone is worth over

$12 billion per year

and is many times that world-

wide. High-value juices have been replaced or

extended through substitution of sugars for juice

solids, or by dilution with less expensive juices, such

as white grape juice or pear juice. To detect adulter-

ation, investigators examine sugar profiles and sor-

bitol content; minerals; anthocyanin pigments; phe-

nolics; oligosaccharides; carbon stable isotope ratio

for various components; and/or organic acid pro-

files. Because juices are chemically complex, several

complementary analyses should be performed to ver-

ify authenticity. The resolving power of high perform-

ance liquid chromatography (HPLC) is invaluable for

accurately quantifying many of these components.

The organic acids that give fruit products their char-

acteristic tartness vary in combination and in con-

centrations among different juices, and the organic

acid profile can be used to identify a juice or verify

its purity. For example, malic acid is a major com-

ponent of the organic acid content of apple juice. If

apple juice has been diluted, e.g., with sugar water,

the malic acid content will be low. Cranberry juice

contains quinic, malic, and citric acids; grape juice,

on the other hand, contains relatively high levels of

tartaric acid. A “cranberry juice” that contains meas-

urable amounts of tartaric acid should be suspect.

Typically, organic acids in fruit juices are identified

and quantified by using methods such as AOAC

method 986.13.

In this procedure, reversed phase

HPLC is used to separate the acids. Because several

of the analytes are extremely difficult to resolve, a

100% aqueous mobile phase is needed to enhance

interaction between the acids and the C18 stationary

phase, but the C18 chains in conventional columns

collapse in a totally aqueous environment, greatly

reducing the resolving capability of the column. To

compensate, two columns must be used in series.

Now there is a simpler and more reliable approach:

a single 30cm Allure

™

Organic Acids column effec-

tively resolves key organic acids, under the chro-

matographic conditions specified in AOAC method

986.13. Figure 1 shows a separation of typical fruit

juice organic acids: tartaric, quinic, malic, citric,

and fumaric acids. Note the excellent resolution of

tartaric and quinic acids! This superior performance

makes interpretation of the data more reliable.

Similarly, note the distinct organic acid profiles for

grape juice and cranberry juice cocktail in Figure 2.

Analysis of polar organic acids is difficult at best on

conventional reversed phase columns. In contrast,

an Allure

™

Organic Acids column provides excellent

retention and selectivity for these compounds, allow-

ing the separation to be performed on a single col-

umn. Retention is stable and reproducible, even with

a 100% aqueous mobile phase as specified in AOAC

method 986.13. If you are monitoring fruit juice

quality, and want a trouble-free analysis with accu-

rate results, we highly recommend an Allure

™

Organic Acids column.

References

Authenticity of Apple Juice

Technical Bulletin #2 (1996),

Analytical Chemical Services of Columbia, Inc.

Official Methods of Analysis (2000), AOAC International, 17th

edition, method #986.13.

Peak List:

Conc.

1. tartaric acid

1mg/mL

2. quinic acid

1mg/mL

3. malic acid

1mg/mL

4. citric acid

1mg/mL

5. fumaric acid

0.005mg/mL

Sample:

organic acids; for concentrations, see Peak List

Inj.:

10µL

Conc.:

See peak list

Sample Diluent:

purified water

Column:

Allure Organic Acids

Catalog #:

9165585

Dimensions:

300 x 4.6mm

Particle Size:

5µm

Pore Size:

60Å

Conditions:

Mobile Phase:

100mM phosphate buffer, pH 2.5

Flow:

0.5mL/min

Temp.:

ambient

Det.:

UV @ 226nm

Figure 1

– Excellent separation of organic acids, including tartaric and quinic acids,

using one 30cm Allure

™

Organic Acids column.

LC_0238

Organic acids are difficult to analyze

on conventional reversed phase

columns. A 100% aqueous mobile

phase increases interaction between

the acids and the stationary phase, but

C18 chains collapse in a totally aque-

ous environment. The Allure

™

Organic

Acids column was designed to

enhance retention and selectivity for

this challenging application. Novel

binding chemistry ensures the alkyl

groups in Allure

™

Organic Acids

columns remain extended in 100%

aqueous mobile phases; retention is

stable and reproducible.

New organics acids

reference mix listed

on page 5!