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

PROTOCOL FOR SCREENING OF PECTINS IN FRUITS OF
JAPANESE QUINCE (CHAENOMELES JAPONICA)
Kimmo Rumpunen
Balsgård - Department of Horticultural Plant Breeding, Swedish University of
Agricultural Sciences, Fjälkestadsvägen 123-1, 291 94 Kristianstad, Sweden.
Tel.: +46-44-75533; fax: +46-44-75530.
E-mail address: kimmo.rumpunen@hvf.slu.se (K. Rumpunen)
Abstract
An important component of fruit dietary fibre is pectins, which have well documented health
benefits and industrial applications. Estimating content of pectins in plant material is,
however, difficult because of their complex composition and because of their association with
other cell wall materials. In this paper a combined enzymatic and HPLC method is presented,
that recently was validated for analysis of galacturonic acid (GalA) in alcohol-insoluble solids
(AIS), and in pectins, extracted from fruits of Japanese quince (Chaenomeles japonica). The
enzymatic/HPLC method proved to be useful as a simple and efficient screening method since
a very high correlation was obtain between GalA estimates of the fruit and the AIS content of
acid extracted pectins in Japanese quince.
Keywords: Alcohol-insoluble solids; Galacturonic acid; Pectins; Screening method; Uronic
acids
Introduction
Pectins are widely used in various foods as gelling or thickening agents, and are at present
commercially extracted by hot dilute acid, mainly from citrus fruits. Pectins are considered as
valuable components of dietary fibres since they are able to reduce blood plasma cholesterol
levels and provide other health benefits to humans (Sungsoo Cho and Dreher 2001). Fresh
fruits are a valuable source of pectins. The content of pectins in fruits is therefore important,
and should be considered also in plant breeding.
In breeding, efficient screening methods are needed to enable analysis of large number of
genotypes. Quantitative extraction of pectins in plant material is, however, difficult because
of their complicated chemical nature and because of their association with other cell wall
materials. The extraction method as such affects the yield and composition of pectins and
therefore also presents problems and may induce artefacts. In those pectins, which are
composed mainly of GalA polymers, e.g. apple pectins (Voragen et al. 1995), analysis of the
GalA monomers may be a method to estimate the total amount of pectins present in the
sample. Furthermore, the content of GalA appears to be more stable during fruit ripening than
the content of extractable pectins (e.g. in apple, Fischer and Amadò 1994). GalA is usually
analysed colorimetrically after acid hydrolysis (Thibault 1979). The colorimetric method can
only be used for analysis of purified samples, which make it less efficient as a screening
method in plant breeding, and therefore enzymatic methods have been advocated.
In this paper a combined enzymatic and HPLC method is described. The method has
recently been validated for analysis of galacturonic acid (GalA) in alcohol-insoluble
solids (AIS), and in pectins, extracted from fruits of Japanese quince (Chaenomeles
japonica) and for screening of pectins (Rumpunen et al. 2002). Japanese quince is
presently studied and developed as a commercial crop in a joint north-European plant
breeding program. Japanese quince is a dwarf shrub belonging to Maloideae