Plant Science 149 1999 115 – 123
Changes to the content of sugars, sugar alcohols, myo-inositol, carboxylic acids and inorganic anions in developing grains from
different varieties of Robusta Coffea canephora and Arabica C. arabica coffees
William John Rogers , Ste´phane Michaux, Maryse Bastin, Peter Bucheli
Department of Plant Science, Nestle´ Research Centre,
101
A6enue Gusta6e Eiffel, Notre Dame D
’
Oe´, BP
9716
,
37097
Tours Cedex
2
, France Received 4 March 1999; received in revised form 2 July 1999; accepted 20 July 1999
Abstract
Changes in concentration of mono- and oligosaccharides, sugar alcohols, myo-inositol, carboxylic acids and inorganic anions in coffee grains were analysed during grain development in three cultivars of Coffea arabica L Arabica and two of C. canephora
L var. Robusta Robusta by high performance anion exchange chromatography coupled to pulsed electrochemical detection HPAE-PED. The majority of the components analysed either decreased in concentration during the first half of the development
period or accumulated steadily during the latter half of the period. The profiles are taken to indicate relationships between the perisperm, the principal tissue in the young grain and the endosperm during maturation. While most of the free sugar in the
mature grain is accounted for by sucrose, fructose and glucose are both at higher concentrations in the perisperm. Considerable amounts of myo-inositol 3 – 4 dry weight DW are found in young grains, while only the phosphorylated form phytic acid
occurs in mature grains 0.3 – 0.6 DW. Quinic acid, which is present in very low amounts in mature endosperm, represents between 6 and 16 DW in young grains, this possibly being the major precursor pool for the high amounts of chlorogenic acids
5 – 10 DW which are a characteristic of mature coffee grains. Of the other organic acids analysed, citric and malic acids are dominant in the mature grain, with higher concentrations in Arabica than Robusta. The results are discussed with respect to the
potential implications for transport mechanisms in developing coffee grains and also the importance of the compounds analysed for industrial quality and flavour. © 1999 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Coffea arabica; Coffea canephora; Seed development; Endosperm; Perisperm www.elsevier.comlocateplantsci
1. Introduction
Analysis of the levels of some of the principal free components occurring in mature coffee grains
are available in the literature [1 – 7]. The content and forms of chlorogenic acids, which occur at
high concentrations in the grains, have received particular attention [8]. The great majority of the
studies have considered the components in mature grains from an industrial perspective as precursors
of coffee beverage flavour and aroma. Information regarding the evolution and accumulation of com-
pounds during coffee grain maturation is more scarce. Some exceptions to this include the work
done on caffeine biosynthesis and transport [9 – 12], attempts to correlate grain maturity to the
generation of components in the final beverage [13,14] and some measurements of enzyme activi-
ties during fruit ripening [15]. Such developmental
Abbre6iations
:
WAF, weeks after flowering. Corresponding author: Tel.: + 33-2-47628383; fax: + 33-2-
47491414. E-mail address
:
john.rogersrdto.nestle.com W.J. Rogers 0168-945299 - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 9 9 0 0 1 4 7 - 8
information is, however, an essential biochemical base for the elucidation of mechanisms of trans-
port and metabolism in the grains and should provide targets for the improvement of the
technological and agronomic character of the species.
In this study we describe changes in concentra- tions during grain maturation of a limited number
of components free sugars, sugar alcohols, car- boxylic acids and inorganic anions likely to be
implicated in final beverage quality in the two main commercial coffee species, Coffea arabica
Arabica and C. canephora Robusta. Sucrose, while being significantly degraded during roasting,
remains in roasted grains at concentrations of 0.4 – 2.8 dry weight DW and is likely to con-
tribute to beverage sweetness [16]. It is also the main contributor of reducing sugars which are
implicated in Maillard reactions occurring during roasting. Inorganic, chlorogenic and carboxylic
acids contribute to the final beverage acidity [3], acidity being associated with better flavour and
aroma [17].
The principal interest of this study is the rela- tionship between concentration profiles in the
young grain and the more mature stages in an attempt to begin to identify biochemical mecha-
nisms of transport and accumulation for a range of components. The grain of Coffea species is
dominated
by a
well developed
maternal perisperm tissue up to approximately the halfway
stage of maturation from the ‘pinhead’ stage until approximately 15 weeks after flowering WAF,
following which the locular space is progressively filled with endosperm up to full grain maturity at
between 20 and 30 WAF.
The mature coffee grain has been convincingly identified as endosperm [18] and not perisperm as
suggested previously [19]. This identification has been supported by more recent studies [20 – 22].
Wormer [23] also observed the role of the perisperm, during the expansion occurring during
the first half of the maturation period, in defining the final size of the locular space. Although virtu-
ally nothing is known about the characteristics of metabolism and transport in the fruits and grains
of coffee species, the relatively large size of the two principal tissues and the duration of the matura-
tion period provide an interesting model for the study of relationships between them during grain
development.
2. Materials and methods
