4.7. AIS production
Fresh tomato pericarp (40 g) was skinned, cubed and boiled at
80 C in 95% EtOH (100 ml) for 30 min. The sample was cooled to
room temperature, homogenised using a coffee grinder then
filtered through miracloth and washed successively with hot 85%
EtOH (200 ml), chloroform:methanol (1:1 v/v) (200 ml) and 100%
acetone until a run through became clear. Samples were then air
dried overnight.
4.8. Cell wall analysis
Pectinwas extracted from the AIS by incubating in 50 mMCDTA
for 6 h at room temperature. The liquid fraction was removed and
the residue treated with 50 mM Na2CO3 overnight at 2 C, after
which the second liquid fraction was removed. Both liquid fractions,
containing the ionic and covalent pectin fractions, respectively
were then subjected to an uronic acid assay as described by
Filisetti-Cozzi and Carpita [39] and the results pooled. The
remaining residue was fractionated into “cellulose” and “hemicellulose”
rich fractions using 1:20 residue to 4 M KOH ratio, for 2 h at
room temperature or 25 C. The residue was washed to neutral pH
and dried to give the cellulose rich fraction. The KOH extracted
material was adjusted to pH5.5 using acetic acid, precipitated with
80% acetone and dried to give the hemicellulose rich fraction. Recovery
of each of these fractions was assessed gravimetrically.
4.9. Monomeric composition
The hemicelluloses or cellulose rich fraction (30 mg) was subjected
to a two stage acid hydrolysis: initially with 12 M sulphuric
acid for 1 h at 37 C followed by 1Msulphuric acid diluted from the
12 M concentrate for 2 h at 100 C. The sugar monomers content of
the supernatant was determined by HPAEC-PAD (Dionex, UK) using
a CarboPac PA20 column with a 50 mM NaOH isocratic system and
flow rate of 0.5 ml/min at 30 C. Glucose, xylose, arabinose and
galactose were used as standards with mannitol as internal
standard.
4.10. Determination of degree of esterification of pectin by titration
Degree of esterification was measured by the reductive method
[40]. AIS (200 mg) was incubated overnight in 20 ml 10 mg ml1
NaBH4 dissolved in a 1:1 mixture of ethanol and 0.5% NaOH.
Samples were then dried and washed 5 times with acetic acid and
methanol at a ratio of 1:9 respectively and then 2 washes of
methanol. Samples were dried and then dissolved in 67% H2SO4 and
the unesterified pectin determined by the method of Filisetti-Cozzi
and Carpita [39].
4.11. Statistical analysis
Statistical analysis on cell wall composition time points and
esterification time points was performed using students T-test with
significance taken at p values below 0.05. Statistical analysis of the
monomeric composition was done using GenStat 14th Edition, by