Isolation and characterisation of cell wall polysaccharides from cocoa (Theobroma cacao L.) beans

Cell wall material (CWM) was prepared from sun-dried cocoa (Theobroma cacao L.) bean cotyledons before and after fermentation. The monosaccharide comp osition of the CWM was identical for unfermented and fermented beans. Polys accharides of the CWM were solubilised by sequential extraction with 0.05 M trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), 0.05 M Na2 CO3, and 1 M, 4 M and 8 M KOH. The non-cellulosic sugar composition for eac h fraction was similar For unfermented and fermented samples. indicating th at fermentation caused no significant modification of the structural featur es of individual cell wall polysaccharides. Pectic polysaccharides accounte d for 60% of the cell wall polysaccharides but only small amounts could be solubilised in solutions of CDTA, Na2CO3, and 1 M and 4 M KOH. The bulk of the pectic polysaccharides were solubilised in 8 M KOH and were characteris ed by a rhamnogalacturonan backbone heavily substituted with side-chains of 5-linked arabinose and 4-linked galactose. Linkage analysis indicated the presence of additional acidic polysaccharides, including a xylogalacturonan and a glucuronoxylan. Cellulose, xyloglucan and a galactoglucomannan accou nted for 28%, 8% and 3% of the cell wall polysaccharides. respectively. It is concluded that the types and structural features of cell wall polysaccha rides in cocoa beans resemble those found in the parenchymatous tissue of m any fruits and vegetables rather than those reported for many seed storage polysaccharides.