COMPARATIVE SPECTROSCOPIC CHARACTERIZATION OF DIFFERENT PECTINS AND THEIR SOURCES

The results of atomic absorption spectrometry (AAS) analyses and Fouri er transform infrared (FTIR) spectroscopic studies of several pectins obtained from pumpkin and sugar beet, as well as of their vegetable so urces, are compared and discussed. Special emphasis is put on the stat e of carboxylic groups of the polymer backbone and the mineral composi tion of both the sources and the resulting pectins, including the cont ent of alkaline (Na, K) and alkaline-earth metals (Mg, Ca), as well as traces of heavy metals (V, Fe, Cu, Pb). The pectins were obtained fro m dried pumpkin pulp by extraction with dilute hydrochloric add or usi ng a biotechnological process involving the multi-enzyme cell-free cul ture supernatant from the bacterium Xanthomonas campestris; commercial sugar beet pectin extracted by the standard method of acid treatment was obtained from a sugar beet processing plant in Krasnodar (Russia). For comparison, a sample of commercial acid-extracted citrus pectin ( Copenhagen, Denmark) was also studied. The results obtained show that potassium seems to occur as a relatively free constituent, whereas a m ore specific interaction between sodium ions and pectic substances may be assumed depending on the origin of the pectin and obviously on its properties. Much higher amounts of Mg and, especially, Ca found in pu mpkin biopectin as compared to all of the three pumpkin, sugar beet an d citrus acid-extracted products correlate with a relatively well exhi bited capability of pectins to bind these two cations, which is notice ably suppressed in acidic media. The increased content of Ca (and, pro bably, Mg) may in principle contribute to poorer gelling properties of pumpkin pectin and, in general, of biopectins as compared to the corr esponding acid extracts. The results on the mineral fraction of the sa mples are compared considering the FTIR spectroscopic data for the pec tins studied as well as for their sources featuring, in particular, th e state of carboxylic groups responsible for metal binding. It has als o been found that lead and copper essentially accumulate in pectins up on extraction, whereas iron does not, being relatively more weakly bou nd by pectic substances (which may, however, depend on its oxidation s tate) than other heavy metals; the accumulation process is slightly (f or Fe and Pb) or not at all (for Cu) suppressed during acid extraction . Comparing the content of vanadium in the pectins and their sources, it may be concluded that this element occurring in plant tissue obviou sly in different chemical forms may be partly transferred to pectin du ring its extraction in a proportion similar to that in which it is bou nd to pectic substances in the plant cell wall, thus indicating its st rong binding not affected by acid treatment. (C) 1998 Published by Els evier Science Ltd. All rights reserved.