Marie-Ann Ha

The impact of a school-based nutrition education intervention on dietary intake and cognitive and attitudinal variables relating to fruits and vegetables

OBJECTIVE To assess the impact of a school-based nutrition education intervention aimed at increasing the consumption of fruits and vegetables. DESIGN The intervention programme increased the provision of fruits and vegetables in schools and provided a range of point-of-purchase marketing materials, newsletters for children and parents, and teacher information. Curriculum materials at age 6-7 and 10-11 years were also developed and utilised. Evaluation was undertaken with groups of younger (aged 6-7 years) and older (aged 10-11 years) children. Methods included 3-day dietary records with interview and cognitive and attitudinal measures at baseline, with follow-up at 9 months, in intervention and control schools. SETTING The work was undertaken in primary schools in Dundee, Scotland. SUBJECTS Subjects comprised 511 children in two intervention schools with a further 464 children from two schools acting as controls. RESULTS Children (n=64) in the intervention schools had an average increase in fruit intake (133+/-1.9 to 183+/-17.0 g day(-1)) that was significantly (P<0.05) greater than the increase (100+/-11.7 to 107+/-14.2 g day(-1)) estimated in children (n=65) in control schools. No other changes in food or nutrient intake were detected. Increases in scores for variables relating to knowledge about fruits and vegetables and subjective norms were also greater in the intervention than in the control group, although taste preferences for fruits and vegetables were unchanged. CONCLUSIONS It is concluded that a whole school approach to increasing intakes of fruits and vegetables has a modest but significant effect on cognitive and attitudinal variables and on fruit intake.

Molecular Rigidity in Dry and Hydrated Onion Cell Walls

Solid-state nuclear magnetic resonance relaxation experiments can provide information on the rigidity of individual molecules within a complex structure such as a cell wall, and thus show how each polymer can potentially contribute to the rigidity of the whole structure. We measured the proton magnetic relaxation parameters T2 (spin-spin) and T1p (spin-lattice) through the 13C-nuclear magnetic resonance spectra of dry and hydrated cell walls from onion (Allium cepa L.) bulbs. Dry cell walls behaved as rigid solids. The form of their T2 decay curves varied on a continuum between Gaussian, as in crystalline solids, and exponential, as in more mobile materials. The degree of molecular mobility that could be inferred from the T2 and T1p decay patterns was consistent with a crystalline state for cellulose and a glassy state for dry pectins. The theory of composite materials may be applied to explain the rigidity of dry onion cell walls in terms of their components. Hydration made little difference to the rigidity of cellulose and most of the xyloglucan shared this rigidity, but the pectic fraction became much more mobile. Therefore, the cellulose/xyloglucan microfibrils behaved as solid rods, and the most significant physical distinction within the hydrated cell wall was between the microfibrils and the predominantly pectic matrix. A minor xyloglucan fraction was much more mobile than the microfibrils and probably corresponded to cross-links between them. Away from the microfibrils, pectins expanded upon hydration into a nonhomogeneous, but much softer, almost-liquid gel. These data are consistent with a model for the stress-bearing hydrated cell wall in which pectins provide limited stiffness across the thickness of the wall, whereas the cross-linked microfibril network provides much greater rigidity in other directions.

A definition for dietary fibre

The objective of this paper is to present a definition for dietary fibre based on recent advances that have taken place not only in human nutrition but also in plant cell-wall science and animal nutrition. We propose a physiologically based framework definition but, recognizing the diversity of dietary fibre, we have proposed further classifications within this framework. We also suggest that dietary fibre be removed from the carbohydrate group of nutrients because some compounds defined as dietary fibre are not chemically carbohydrates. The definition and classification system clearly highlight areas where further studies are needed.European Journal of Clinical Nutrition (2000) 54, 861–864

CP-MAS NMR of highly mobile hydrated biopolymers: Polysaccharides of Allium cell walls

The most highly mobile polysaccharides of hydrated Allium cepa (onion) cell walls were not visible in cross-polarisation magic-angle spinning (CP-MAS) 13C spectra recorded using a conventional CP contact time of 0.5 ms. These polysaccharides showed very slow CP and thus did not appear in the 3C spectrum until the contact time was extended to 2 ms or more. A spectrum of this slow-CP material was obtained by subtracting the signal intensities obtained in a delayed-contact experiment from those obtained in an experiment with long, variable contact times. It showed motional line-narrowing compared with the more rigid portion of the cell wall and corresponded to a mixture of β(1,4′)-d-galactan and methyl-esterified α(1,4′)-d-galacturonan, polymers known to be flexible in solution. The CP time constant TCH was approximately 1 ms and the proton T2, measured in a hybrid delayed-contact/long-contact experiment with a variable delay inserted before proton spin-locking, was a few hundred μs. These values were an order of magnitude greater than was observed for the rigid polymers in the same sample. The proton T2 was intermediate between typical values for the solid and solution states. Thus approach should be applicable to other soft, hydrated plant and animal tissues.

Structure of cellulose-deficient secondary cell walls from the irx3 mutant of Arabidopsis thaliana

In the Arabidopsis mutant irx3, truncation of the AtCesA7 gene encoding a xylem-specific cellulose synthase results in reduced cellulose synthesis in the affected xylem cells and collapse of mature xylem vessels. Here we describe spectroscopic experiments to determine whether any cellulose, normal or abnormal, remained in the walls of these cells and whether there were consequent effects on other cell-wall polysaccharides. Xylem cell walls from irx3 and its wild-type were prepared by anatomically specific isolation and were examined by solid-state NMR spectroscopy and FTIR microscopy. The affected cell walls of irx3 contained low levels of crystalline cellulose, probably associated with primary cell walls. There was no evidence that crystalline cellulose was replaced by less ordered glucans. From the molecular mobility of xylans and lignin it was deduced that these non-cellulosic polymers were cross-linked together in both irx3 and the wild-type. The disorder previously observed in the spatial pattern of non-cellulosic polymer deposition in the secondary walls of irx3 xylem could not be explained by any alteration in the structure or cross-linking of these polymers and may be attributed directly to the absence of cellulose microfibrils which, in the wild-type, scaffold the organisation of the other polymers into a coherent secondary cell wall.

Rigid and flexible pectic polymers in onion cell walls

Abstract The amount of thermal motion occurring in individual polymers of a composite material like a plant cell wall can be determined using NMR relaxation methods. This methodology can be used to indicate of the rigidity of each polymer and its contribution to the rigidity of the cell wall as a whole. We have applied this approach to onion cell walls. The proton T 2 is used to identify individual polymer chains differing in rigidity whereas the proton T 1ρ discriminates between spatial locations within which the average amount of motion differs. Through a T 2 -based spectral editing procedure we reconstructed sub-spectra corresponding to a mobile, largely pectic fraction of the cell wall and a rigid microfibrillar fraction which also included a pectic component. There was a third extremely mobile pectic component consisting of a of β(1,4)-linked galactan and highly esterified galacturonan. These highly mobile, hydrated polymers are not represented in a CP-MAS 13 C spectrum obtained under normal conditions. We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a 13 C spectrum of the cell-wall components that are normally too mobile to be visible. Through a T 1ρ -based spectral editing procedure we found some pectic material spatially located near cellulose. This included some ‘eggbox’ pectin. Pectic material was also located more than 2nm away from cellulose. These results show that, within a single cell wall, pectic polymers are very heterogeneous in rigidity as well as in composition, and are not distributed uniformly within the cell wall structure.