Identification of the connecting linkage between homo- or xylogalacturonan and rhamnogalacturonan type I

Pectin is of interest both as cell wall component and as food additive. The precise chemical structure of pectin remains under debate, although the structural elements of pectin are rather well described. In order to get more insight in the inter linkage between the various structural elements, apple pectin modified hairy regions were degraded by controlled acid hydrolysis. From the degradation products oligomeric fragments were selected which could represent interconnection points, and these oligomers were characterized using LC–MS and NMR approaches. It was shown that the oligomers GalA 3Rha 1, GalA 4Rha 2, and GalA 5Rha 3 consisted out of a homogalacturonan and a rhamnogalacturonan type I segment connected via a GalA pα-(1 → 2) Rha p linkage. In addition, a GalA 6Rha 3Xyl 1 oligomer was identified, which consisted out of a xylogalacturonan and a rhamnogalacturonan type I segment. These oligomers indicated that in apple pectin both homogalacturonan and xylogalacturonan were covalently linked to rhamnogalacturonan type I. With these new insights, currently used pectin models were refined.