Proanthocyanidins (PACs) are present as monomers and oligomers in cocoa beans and have been reported to have anti-inflammatory and digestive-enzyme-inhibitory effects. Previous studies have suggested that high temperature roasting can cause PAC polymerization. It is difficult to characterize these polymers by direct quantification using LC-MS due to lack of available standards and chromatographic challenges due to increased PAC polymerization. This study compared three LC-MS-based methods to characterize PACs, one of which is applied to cocoa for the first time.  The goal was to compare the information provided by each method to study the effect of roasting on PAC composition.  Cocoa beans were roasted under different time-temperature combinations. Method 1 used six cone voltages to fragment oligomers of increasing size.  PAC-terminal and extension units were identified by their unique fragmentation in the MS. The terminal-to-extension-units ratio was used as an indicator of chain length. Method 2 used thiolytic cleavage of PAC chains into monomers and thiolytic derivatives, and the ratio of these products, to compute the mean degree of polymerization (mDP). Method 3 was a direct quantification of PACs using standards upto (DP)5. Method 1 showed that some roasting treatments had a lower ratio of terminal-to-extension units than the unroasted control indicating greater PAC polymerization.  Higher cone voltages could fragment larger PAC chains more effectively as indicated by the increased mDP with increasing cone voltage. Method 2 showed that the mDP increased (~27%) for some roasting treatments compared to unroasted control, confirming findings from method 1.  Method 3 revealed a decrease (50-70%) in oligomer (DP2-5) concentration and an increase in monomer concentration (~100%) with longer roasting treatments.  Oligomer concentrations were unaffected by shorter roasting treatments at the temperatures studied. Each method gave unique structural information about the effect of roasting on cocoa PACs in addition to validating findings from other methods.

Structural characterization of cocoa proanthocyanidins using three LCMS-based methods

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