Determination of acetyl in pectin and in acetylated carbohydrate polymers

Author(s): McComb EA, McCready RM


Heat processing results in softening of carrots, changing the pectin structure. The effect of heat processing on pectin was studied, showing that the amount of pectin in water soluble solids (WSS) and chelating agent soluble solids (ChSS) increased substantially upon heat processing of the carrots. Pectin in WSS from both unprocessed and heat processed carrot had a degree of methyl-esterification (DM) of ≈60% and a degree of acetylation (DA) of ≈20%. Enzymatic degradation released methyl-esterified galacturonic acid oligomers of degree of polymerisation ≥6 carrying acetyl groups. Mass spectrometry confirmed acetylation in highly methyl-esterified homogalacturonan (HG) regions, next to known rhamnogalacturonan (RG-I) acetylation. ChSS HGs were un-acetylated.

RG-I levels of both heat processed carrot WSS and ChSS increased. Digestion of WSS with RG-I degrading enzymes showed that WSS arabinan became more linear upon heat processing resulting in the release of oligosaccharides, while in ChSS galactan became more linear.

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