Deuterium-labelled (methyl-d(3)) pectin was prepared by esterifying a
lemon peel pectin with methanol-h. A pure powder sample and multicompo
nent model confectioneries containing the labelled pectin and various
amounts of water were studied by solid-state H-2 NMR spectroscopy. In
the pure sample the broad H-2 NMR lineshape indicates that the only fa
st motion occurring on the NMR timescale is reorientation of the methy
l-d3 group about its C-3 axis. In contrast, in systems of 50% water co
ntent the H-2 NMR lineshape is much narrower, indicating significant m
otional averaging. As the percentage water in the confectionery system
s is reduced to <40% the main effect is the appearance of a broad comp
onent in the spectrum associated with a more static motional environme
nt. As the water content decreases further the proportion of labelled
pectin in this region increases and the amplitude of the motions decre
ases, until for systems of <10% water content motions are now slow on
the NMR timescale, except for the methyl-d(3) group reorientation abou
t its C-3 axis, and H-2 NMR lineshapes are identical to those observed
in the pure powder sample. The evolution of the two component linesha
pe indicates that the removal of successive amounts of water does not
simply 'stiffen' the entire system but rather initially restricts moti
on in certain regions and eventually 'crystallizes' distinct domains w
ithin the sample. (C) 1998 Elsevier Science Ltd. All rights reserved.