Cell wall polysaccharides of bush butter (Dacryodes edulis (G Don) HJ Lam)fruit pulp and their evolution during ripening

Cell wall material was isolated as alcohol-insoluble solids (AIS) from bush butter endocarp tissue at different stages of ripeness. AIS were then extr acted with 0.05 M CDTA followed by increasing concentrations of KOH (0.05, 1 and 4M respectively). The chemical extractions solubilised a total of 51. 6-60.6% of AIS, the yields of CDTA extracts accounting for approximately 9. 6-12.2% of AIS. The extracts as web as the residues were analysed for their sugar composition and protein and starch contents. CDTA extracted the bulk of uronic acid in AIS, but the uronic acid content (after dialysis) of the se extracts showed a significant decrease as the fruits ripened (from 439 t o 252 mg g(-1) between the first and the last degree of ripeness). Analysis of the CDTA extracts by anion exchange and size exclusion chromatography s howed a gradual appearance of new pectic populations at low degrees of meth ylation and low molecular weights, indicating that CDTA-soluble pectins are demethylated and depolymerised during ripening. The dilute alkali (0.05 M KOH) extracts were essentially composed of proteins in addition to a minor quantity of pectin. The 1 M KOH and principally 4M KOH treatments led to th e extraction of hemicelluloses, mainly xyloglucan-like and mannan-like poly mers. These extracts also contained substantial amounts of protein and star ch. No variation related to the degree of ripeness was visible in the sugar composition of the alkali extracts. The molecular weight distribution of t he hemicelluloses did not change with the degree of ripeness. The final res idues accounted for 21.4-27.3% of AIS and were mostly composed of glucose ( 827-908 mg g(-1)). All these results suggested that only CDTA-soluble pecti ns were involved in bush butter fruit softening. (C) 2001 Society of Chemic al Industry.