Cacao (Theobroma cacao L.) hulls were physically
separated into vascular bundles (VBs) and nonvascular
bundles (NVBs) to investigate their chemical
compositions and the structural features of abundant
polyphenolic compounds. Glucose content was determined
to be 21.4% for VBs and 17.5% for NVBs, together
with xylose content as 13.1% for VBs and 2.8% for NVBs.
In addition, uronic acid in NVBs (12.9%) was much
higher than that in VBs (5.2%). The content of total
(poly)phenolic compounds (35.9%–39.1%) quantified as
Klason residues (KRs) and acid-soluble phenolic compounds
(ASPs) were similar in both cell types, although
there were great differences in the structural characteristics
of polyphenolic compounds. The pyrogram of
VBs clearly showed high intensities of guaiacol and 4-
vinylguaiacol together with low intensities of catechol and
4-methylcatechol. On the other hand, that of the NVBs
showed opposite trends. These results were confirmed by
alkaline nitrobenzene oxidation based on total yields of
vanillin and syringaldehyde. Therefore, the accumulation
of various polyphenolic compounds in cacao hulls relies
strongly on the cell type and is correlated with the development
of a secondary wall.