Figure 2
Tartaric andmalic acids, the primary organic acids in
grape juice, resolved by anAllure
™
Organic Acids column.
The fruit juice industry in theUS alone isworth over $12 billion
per year
1
and ismany times that worldwide.Aswith other indus-
tries inwhich there is a large potential for profit, unscrupulous
juice producers and traders have foundways to replace or extend
more valuable juices. This can be done by substituting sugars for
juice solids, or by diluting higher cost juiceswith less expensive
ones. For example, white grape juice and pear juice have been
used to extend other, more costly juices. To detect these adulter-
ations, a number of laboratories employ fruit juice authenticity
testing.
Because juices are chemically quite complex, several complemen-
tary tests should be performed to verify authenticity. These can
include determining sugar profile and sorbitol content; minerals;
anthocyanin pigments; phenolics; oligosaccharides; carbon stable
isotope ratio for various components; and organic acid profile.
High performance liquid chromatography (HPLC) is a powerful
tool in analyses ofmany of these components.With these com-
plexmatrices, the resolving power of HPLC is invaluable for
accurately quantifying components.
Organic acids give fruit products their characteristic tartness.
Since the organic acids content varies in composition and in con-
centrations among different fruit juices, organic acid content can
be used to identify a product and verify its purity. For example,
malic acid is amajor component of the organic acid profile of
apple juice. If apple juice has been diluted, e.g., with sugar water,
themalic acid content will be low. In grape juice, tartaric acid is
present at relatively high levels. Cranberry juice, on the other
HPLC
Applications
note
Restek Corporation • (800) 356-1688 • (814) 353-1300 •
#59530
HPLC
Single-ColumnMethod for HPLCAnalysisof OrganicAcids
inFruit Juices,Using anAllure
™
OrganicAcidsColumn
Figure 1
Organic acids playmultiple roles in food and beverage sys-
tems: they are important flavor compounds, and they are
indicators of product quality. Organic acid profiles aremoni-
tored to determine the purity of certain fruit juices. In some
food and beverage systems they are added as acidulants, to
control the pH of a product. Certain organic acids also can be
used as antimicrobial agents; for example, propionic acid can
be used to slowmold growth. Malic acid, citric acid, and oth-
ers are found in fruits. Oxalic acid is present in spinach and
rhubarb; grapes contain tartaric acid.
Analysis of polar organic acids can be difficult on conven-
tional reversed phase columns.Ahighly aqueous mobile
phase is needed to increase interaction between the acids and
the stationary phase, but stationary phases in conventional
C18 columns collapse in 100% aqueous mobile phases. The
Allure OrganicAcids columnwas designed to enhance
retention and selectivity in challenging applications such as
this. Polar embedded groups allow the alkyl groups in
Allure OrganicAcids columns to remain extended in 100%
aqueous mobile phases; retention is stable and reproducible.
Excellent separation of tartaric and quinic acids by an
Allure
™
Organic Acids column.
PeakList:
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:
Fruit JuiceOrganicAcidMixture
Inj.:
10µL
Conc.:
see peak list
SampleDiluent: purifiedwater
Column:
Allure
™
OrganicAcids
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
LC_0238
PeakList:
1. tartaric acid
2. malic acid
Sample:
grape juice
Inj.:
10µL
Conc.:
grape juice:water (50:50, v/v)
SampleDiluent: purifiedwater
Column and conditions same as Figure 1
LC_0237
