cally with 81 mM NaOH and 480 mM NaOH, respectively. Carboxylic acids and inorganic an-
ions were separated by a gradient of 0.5 – 38.25 mM NaOH for 18 min. Phytic acid was eluted
with a gradient of 23 – 60 mM NaOH for 1 min. The injected sample volume was 20 ml and the flow
rate usually 1 mlmin. Standards of sugars, oligosaccharides, sugar alcohols, carboxylic acids
and inorganic anions were from Sigma St. Louis, MO except stachyose tetrahydrate which was
from Extrasynthe`se Genay, France. All results represent the mean of three repetitions.
3. Results
Concentrations of glucose, fructose and sucrose evolved in a very similar way during maturation
for both Arabica and Robusta grains Fig. 1. At the earliest stages of maturity examined Arabicas:
12 WAF; Robustas: 18 and 24 WAF until ap- proximately the halfway stage of maturation, glu-
cose and fructose were usually the major free sugars of young coffee grains, glucose being con-
sistently approximately twice the concentration of fructose. Levels of glucose were higher in the
Arabica varieties studied between 8 and 12 DW than in Robusta 2 to 4 DW. By the end
of grain development 30 WAF for Arabica, 36 to 40 WAF for Robusta concentrations of glucose
and fructose had decreased for both species to 0.03 and 0.04 DW, respectively. The decrease in
these two sugars was accompanied by an increase in sucrose, which approached 100 of total free
sugars in mature grains, again being higher on average in Arabica from 5 to 12 DW than
Robusta 4 – 5 DW. A more refined analysis of free sugars in one variety of Arabica Caturra
2308, in which maternal perisperm tissues were dissected from endosperm and analysed sepa-
rately, explains the maturation profile of these components Fig. 2. Higher concentrations of glu-
cose and fructose the former being approximately twice that of the latter, compared to sucrose, are
specifically associated with perisperm tissue. Su- crose is always the dominant sugar in endosperm
tissue even at the earliest stages of maturation of this tissue.
The results of the analysis of other sugars and sugar alcohols are presented in Table 1. Stachyose
content was normally within the range 0.1 – 0.25 DW, although for one variety Robusta COM
higher levels of 0.32 and 0.56 were observed for two of the four stages. Despite the variability of
levels noted for this one variety, no overall ten- dency indicating a fundamental modification of
the metabolism of this sugar during maturation was discernible. Concentrations of galactose simi-
larly tended to be low at all levels, although a transient increase may be noted to levels of 0.2 –
0.3 DW at the halfway stage of development, this corresponding to the period of rapid en-
dosperm expansion. The levels of free arabinose decreased during grain maturation from 0.10 to
Fig. 1. Changes in concentrations of sucrose, fructose and glucose in whole grains separated from pericarp and locules from two varieties of Coffea canephora Robusta, A Dormilon, B ROM, and two varieties of C. arabica Arabica, C Caturra
Commercial Arabica COM, D CRM during grain maturation.
W .J
. Rogers
et al
. Plant
Science
149 1999
115 –
123
Table 1 Content of free sugars, sugar alcohols and inorganic anions gg DW in whole grains of two varieties of Robusta and two varieties of Arabica during grain maturation
a
Stachyose WAF
b
Raffinose Maltose
Melibiose Xylose
Mannitol Chloride
Sulphate Nitrate
Phosphate Sample weight g
Arabinose Galactose
Isomaltose 0.14
0.00 0.00
0.12 0.1
0.14 0.27
0.04 0.25
0.25 0.44
0.81 0.35
0.130 18
Robusta ROM 0.24
0.04 0.03
0.12 0.0
0.01 0.13
0.06 Robusta ROM
0.03 24
0.57 0.423
0.07 0.28
0.07 0.11
0.03 0.00
0.00 0.0
0.04 0.05
0.04 0.03
0.500 0.00
0.09 0.10
0.02 Robusta ROM
30 0.04
36 0.13
0.00 0.00
0.00 0.0
0.01 0.11
0.02 0.01
0.11 0.506
0.03 0.04
Robusta ROM 24
0.32 0.56
0.04 0.15
0.12 0.0
0.09 0.31
0.22 0.62
1.09 0.274
0.21 Robusta COM
0.15 0.10
0.03 0.04
0.01 0.0
0.01 0.08
0.05 0.05
Robusta COM 0.07
0.29 0.02
0.09 0.383
30 0.32
0.06 0.02
0.01 0.0
0.01 0.11
0.03 0.01
0.08 Robusta COM
36 0.501
0.01 0.04
0.03 0.15
0.02 0.02
0.01 0.0
0.02 0.03
0.01 0.04
0.01 40
0.13 0.519
Robusta COM 0.21
0.05 12
0.61 0.16
0.23 0.00
0.17 0.0
0.58 0.25
0.17 0.48
0.33 0.120
0.24 Arabica CRM
0.04 18
0.32 0.21
0.05 0.17
0.17 0.0
0.30 0.46
0.29 0.40
1.03 0.175
0.31 Arabica CRM
0.23 0.20
0.03 0.00
0.04 0.0
0.03 0.20
0.08 0.07
Arabica CRM 0.01
0.50 0.24
0.05 0.499
24 0.18
0.02 0.00
0.00 0.0
0.05 0.05
0.03 0.00
Arabica CRM 0.10
30 0.497
0.02 0.20
0.12 0.23
0.00 0.31
0.03 0.0
0.12 0.15
0.02 0.10
0.200 0.34
0.33 0.15
0.40 Arabica COM
12 18
0.07 0.18
0.11 0.08
0.01 0.0
0.02 0.23
0.12 0.02
0.78 0.283
0.14 Arabica COM
0.14 Arabica COM
0.18 24
0.02 0.01
0.01 0.0
0.03 0.17
0.00 0.01
0.02 0.502
0.04 0.28
0.04 0.18
0.02 0.02
0.00 0.0
0.03 0.06
0.02 0.00
0.04 0.08
Arabica COM 30
0.507 0.03
0.06
a
Results are means of triplicate experiments.
b
WAF, weeks after flowering.
Fig. 2. Changes in concentrations of free sugars in grains of Arabica variety Caturra 2308 during maturation. After being separated from pericarp and locules, grains were divided into perisperm mainly in the young grains up to 20 WAF and
endosperm tissues for analysis.
0.30 DW in young grains to trace levels 0.02 – 0.04 DW between 30 and 36 WAF. Mannitol
decreased towards the end of grain maturity to levels of between 0.01 Robusta ROM and 0.05
DW Arabica CRM. No evidence for the pres- ence of free arabitol, sorbitol, dulcitol, xylitol or
scyllo-inositol was found data not shown.
The concentration of myo-inositol decreased during grain development Fig. 3 from between 3
and 4 Robustas, 0.7 and 1.08 DW Arabicas in the perisperm-dominated stages to approxi-
mately 0.05 for the mature Robustas and be- tween 0.08 and 0.14 DW for mature Arabicas.
In contrast, phytic acid increased during grain maturation, reaching higher levels in mature Ro-
busta 0.4 – 0.6 DW than in Arabica 0.1 – 0.3 DW.
Data for the free carboxylic acids analysed that were above trace levels are given in Fig. 4. The
content of citric acid was very low at the begin- ning of grain development 0.04 – 0.19 DW but
increased substantially during the development of the grain, reaching levels of between 1.28 and
1.58 DW at the latest maturity stages tested. Malic acid content was either maintained rela-
tively high or tended to increase during the first half of development, before declining to lower
levels 0.4 – 0.5 DW in the mature grains. How- ever, malic acid was consistently the second most
abundant carboxylic acid following citric acid. During grain development, concentrations of ox-
alic and acetic acid decreased and were very low towards the end of maturity 0 – 0.03 DW.
Formic acid remained constantly at a trace level. Quinic acid was found to form a significant part
of the dry matter content of young coffee grains
Fig. 3. Changes in concentrations of A myo-inositol and B phytic acid in whole grains of two varieties of Robusta and
two varieties of Arabica during maturation.
Fig. 4. Concentrations of organic acids during maturation of whole grains of two varieties of Robusta and two varieties of Arabica. Grains were separated from pericarp and locules before analysis.
Fig. 5. At the earliest developmental stages ex- amined, its content varied between 6 and 16
DW, respectively, for the Arabica and Robusta coffees. Towards the end of grain development
levels decreased to much lower levels 0.34 DW for Robusta and 0.67 DW for Arabica.
Concentrations of chloride, sulphate and nitrate ions decreased during grain maturation Table 1.
The contents of sulphate and nitrate were between undetectable and 0.03 DW at the end of grain
development. Phosphate concentrations were rela- tively high between 0.7 and 1.1 DW in young
grains in both species until the halfway stage of development before decreasing to concentrations
of around 0.10 DW at the end of grain development.
4. Discussion
