measurement methods of soil, water, plant and fruit, in berry ... - NJF

Pectins in AIS
The AIS contained in average 26 g/100 g dry weight acid extractable pectins, corresponding
to a content in the fruit of 0.9 g pectins/100 g fresh weight or 11 g pectins/100 g dry weight.
The range noticed among the genotypes (23.0–30.4 g/100 g dry weight) is large and should
make it possible to improve yield through selection of genotypes with high content of pectic
substances.
UA and GalA in pectins
There was a significant difference between the methods for UA/GalA estimates in pectins but
no significant interaction between genotype and method. Thus anyone of the two methods
could be used to estimate uronic acids in pectins.
In pectins, the content of UA was in average 63% dw, and the content of GalA 57% dw. The
reason for the higher estimates obtained by the colorimetric method (about 10%) may be that
the used enzymes were not able to completely degrade the pectins (Massiot and Renard
1997).
GalA in fruits
The combined enzymatic/HPLC method revealed significant differences between genotypes
in content of GalA when homogenized frozen fruit samples were analysed. The ranking of the
genotypes was consistent regardless of whether fresh weight or dry weight estimates were
used. Furthermore, the ranking of genotypes was also consistent with the ranking of
genotypes based on content of acid extractable pectins.
Correlations
Between content of GalA in fruits estimated by the combined enzymatic/HPLC method, and
content of acid extracted pectins, a high correlation (R=0.89) was obtained based on dry
weight. Between estimates based on fresh weight an even higher correlation was obtained
(R=0.93). UA were not assayed colorimetrically in fresh fruit samples because of the presence
of interfering compounds which exclude the colorimetric approach. By contrast, the combined
enzymatic/HPLC method is most useful for this purpose. At the same time other important
organic acids like malic and succinic acids can be analysed with this method, thus enabling
detection of multiple compounds and reducing screening costs.
Selection of a proper column for HPLC separation is most important. The Aminex HPX-87H
column produces highly reproducible results, can be used for years with limited maintenance
and provides good separation for a range of compounds. However, the Aminex HPX-87H
column has one drawback: citric acid elutes close with GalA, which may cause problem if this
compound is present in detectable amount. This problem could be avoided by use of another
analytical column.
It would be interesting to validate the comparatively easy and fast enzymatic/HPLC method
for analysis of other raw materials, e.g. apple. In case of apples, there is no reason why the
combined enzymatic and HPLC method shouldn’t work, since it has been shown that pectins
in Japanese quince are very similar to pectins in apples.
Acknowledgements
I thank Dr Maud Thomas, Dr Jean-Francois Thibault and Nancy Badilas, INRA, Nantes, who
made the validation of the combined enzymatic and HPLC method possible, in a fruitful cooperation.
The cited study was carried out with financial support from the Commission of the
European Communities, Agriculture and Fisheries (FAIR) specific RTD programme, CT 97-
3894, ’Japanese quince (Chaenomeles japonica) - a new European fruit crop for production of
juice, flavour and fibre’. It does not necessarily reflect its views and in no way anticipates the
Commission’s future policy in this area.