STAND OUT
TECHNOLOGY
57
DEC 2017 FOOD FOCUSTHAILAND
thecavityquicklyfillswithcirculating laser light.A fast photodetector
senses the small amount of light leaking through one of themirrors
toproducea signal that isdirectly proportional to the intensity in the
cavity. (Figure 1)
Identify theAdditionof C4Sugars
A “normal” plant—one that doesn’t havephotosyntheticadaptations
to reducephotorespiration—iscalledaC3plant.Thefirst stepof the
Calvin cycle is the fixation of carbon dioxide by rubisco, and plants
that useonly this “standard”mechanismof carbonfixationarecalled
C3 plant for the three-carbon compound (3-PGA) the reaction
produces. InC4Plant, the light-dependent reactions and theCalvin
cycle are physically separated, with the light-dependent reactions
occurring in themesophyll cells (spongy tissue in themiddle of the
leaf) and theCalvin cycle occurring in special cells around the leaf
veins. These cells are called bundle-sheath cells.
C4Sugar is generated fromC4 plant like corn and sugar which
significantly have different ratio of
13
C/
12
C (
δ
13
C,‰) when compared
with C3 plant (such as coconut in this study) which can detect
adulteration from ratio
13
C/
12
C. For pure coconut water, the range
of
13
C/
12
C. should be different from sucrose sugar (C4 sugar).
(Figure 2)
Comparisonof CRDS and IRMSAnalysis for
CoconutWaterAuthentication
IsotopeRatioMassSpectrometry (IRMS) isaspecializationofmass
spectrometry in which methods are used to measure the relative
abundance of isotopes in a specific sample. Cavity Ring-Down
Spectroscopy (CRDS) is a form of laser absorption spectroscopy.
Numerous journal articles have validated that CRDS is as precise
and accurate as IRMS for isotopic analyses in a range of natural
science applications. This application note compares CRDS with
IRMS for the specific purpose of organic beverage authentication,
specifically, thedetectionof sugar adulteration incoconutwater that
is indicated to be pure. Coconut water samples provided by a
commercial producer were analyzed to validate the linearity,
reproducibility, and accuracy of the CM-CRDS. The system was
calibrated using primary and secondary standards. Unadulterated
coconut water andC4 sugar end-members (
δ
13
C) were determined
using respective referencematerial,anda linearmixingdiagramwas
established (Figure 3). The R2 value of the dataset was 0.999.
Analyzing a second commercial sampleof coconut water, known to
beadulterated, confirms that~40%of its total sugarcontent isadded
fructose. Measurements of the
δ
13
C composition of both coconut
waters (pure and adulterated) using CRDS were compared to
independent IRMSdataprovided by a coconut water producer, and
theywere found tobe identicalwithin±0.1permil (Table1).Precision
for an individual measurement, obtained from three replicates, was
±0.3 permil.
The study demonstrates that CM-CRDS is a high-performance
system that provides accurate isotopic measurements over a wide
rangeofcoconutwateradulteration (4 to100%). Itmaintainsexcellent
precision, linearity, and minimal drift, with no need for any post
correction to thefinal dataset.Acomparisonof samplesprovidedby
acommercial coconutwater producer illustratesaclear difference in
the
δ
13
C compositionof thepureand theadulterated coconut water.
It also illustrates the validity of theCM-CRDS datawhen compared
to themore costly, difficult, and time-consuming IRMSanalyses.
Additional Information
Referencesand technical informationofPICARRO,pleasecontactThaiUniqueCo.,Ltd.
