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Verify Fruit Juice Quality
fromOrganic Acid Profiles
UsingNewAllure
™
Organic Acids HPLCColumn
By RebeccaWittrig, Ph.D., Senior Innovations Chemist
✔
One 30cmAllure
™
Organic Acids column replaces two C18 columns in
AOACmethodology.
✔
Stable and reproducible retention, evenwith 100% aqueousmobile
phases, as in AOACmethod 986.13.
✔
Facilitates detection of fruit juice adulteration.
The fruit juice industry in the US alone is worth over
$12 billion per year
1
and ismany times that world-
wide. High-value juices have been replaced or
extended through substitution of sugars for juice
solids, or by dilutionwith 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 quantifyingmany 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 amajor com-
ponent of the organic acid content of apple juice. If
apple juice has been diluted, e.g., with sugar water,
themalic 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 containsmeas-
urable amounts of tartaric acid should be suspect.
Typically, organic acids in fruit juices are identified
and quantified by usingmethods such as AOAC
method 986.13.
2
In this procedure, reversed phase
HPLC is used to separate the acids. Because several
of the analytes are extremely difficult to resolve, a
100% aqueousmobile 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 columnsmust be used in series.
Now there is a simpler andmore reliable approach:
a single 30cm Allure
™
Organic Acids column effec-
tively resolves key organic acids, under the chro-
matographic conditions specified in AOACmethod
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 datamore 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, evenwith
a 100% aqueousmobile phase as specified in AOAC
method 986.13. If you aremonitoring fruit juice
quality, andwant a trouble-free analysis with accu-
rate results, we highly recommend an Allure
™
Organic Acids column.
References
1
Authenticity of Apple Juice
Technical Bulletin #2 (1996),
Analytical Chemical Services of Columbia, Inc.
2
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:
purifiedwater
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 30cmAllure
™
Organic Acids column.
LC_0238
Organic acids are difficult to analyze
on conventional reversed phase
columns. A 100% aqueousmobile
phase increases interaction between
the acids and the stationary phase, but
C18 chains collapse in a totally aque-
ous environment. The Allure
™
Organic
Acids columnwas 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%
aqueousmobile phases; retention is
stable and reproducible.
Neworganicsacids
referencemix listed
onpage5!
