Restoration of thiamine status with white or whole wheat bread in a thiamine-depleted rat model.

Long-term thiamine deficiency has been largely documented, whilst little is known about effects of short-term depletion/repletion periods on thiamine vitamers status. Rats were submitted to short-term depletion (8 days) followed by different durations of repletion (3 or 14 days) with thiamine from bread (whole wheat bread or white bread, whole B and white B respectively) or corresponding controls. Short-term depletion drastically decreased plasma thiamine (-97%) and its urinary excretion (-77%). TDP (thiamine diphosphate) was strongly affected in liver (-67%) but less affected in cerebellum (-38%) or kidneys (-45%). Short-term repletion (3 days) with whole B diet or its control restored TDP at initial values in cerebellum and kidneys. A longer repletion (14 days) was required to restore liver TDP. Comparison of the diet groups indicates that thiamine status in tissues of rat fed whole B or white B diet was comparable to that of rats fed purified thiamine. Plasma thiamine concentration could not be restored at initial values in the bread groups or respective controls. In conclusion, thiamine in whole wheat bread appears effective in preventing marginal deficiencies and plasma thiamine is a less reliable indicator of thiamine status than tissue TDP levels.

Genetic analysis of bread-making quality scores in bread wheat using a recombinant inbred line population.

Bread-making quality has been evaluated in a progeny of 194 recombinant inbred lines (RILs) from the cross between the two French cultivars Récital and Renan, cultivated in three environments. These cultivars have been previously identified as having contrasting grain protein content and dough rheology properties, although they achieve similar scores for the official bread-making test used for cultivar registration in France. However the progeny displayed a wide range of variations, suggesting that favourable alleles at several loci are present in the two parental lines. Correlation analyses revealed that bread-making scores are poorly correlated among environments, as they are poorly predicted by multiple regression on dough rheology parameters and flour-protein content. However, loaf volume was the most heritable and predictable trait. A total of seven QTLs were found for bread scores, each explaining 5.9-14.6% of trait variation and six for the loaf volume (10.7-17.2%). Most bread-making QTLs, and particularly those detected in all environments, co-located with QTLs for dough rheology, protein content or flour viscosity due to soluble pentosans (Fincher and Stone 1986; Anderson et al. in J Cereal Sci 19:77-82, 1994). Some QTL regions such as those on chromosome 3A and chromosome 7A, which display stable QTLs for bread-making scores and loaf volume, were not previously known to host obvious genes for grain quality.

Structure of Acetobacter cellulose composites in the hydrated state.

The structure of composites produced by the bacterium Acetobacter xylinus have been studied in their natural, hydrated, state. Small-angle X-ray diffraction and environmental scanning electron microscopy has shown that the ribbons have a width of 500 A and contain smaller semi-crystalline cellulose microfibrils with an essentially rectangular cross-section of approximately 10 x 160 A(2). Incubation of Acetobacter in xyloglucan or pectin results in no changes in the size of either the microfibrils or the ribbons. Changes in the cellulose crystals are seen upon dehydration of the material, resulting in either a reduction in crystal size or an increase in crystal disorder.

In vitro synthesis and properties of pectin/Acetobacter xylinus cellulose composites

Pectin and cellulose are major components of most primary cell walls, yet little is known about the way in which they interact either during assembly or in subsequent functional performance of the wall. As a mimic of cell wall assembly, we studied the formation of molecular composites formed by deposition of cellulose from Acetobacter xylinus into pectin/calcium systems, and the molecular, architectural and mechanical properties of the composites obtained. The formation of interpenetrating cellulose/pectin composite networks (as envisaged in current models for primary cell walls) required a pre-existing, but not too strong, pectin network. For pectin either in solution or strongly networked, phase separation from cellulose occurred, providing two physical models for the formation of middle lamellae. Composite networks showed no evidence of direct molecular interaction between the components, but pectin networks became more aggregated following deposition of cellulose into them. The shear strength under small deformation conditions for cellulose/pectin composites was very similar to that of cellulose alone. In contrast, under uniaxial tension, extensibility was greatly increased and stiffness decreased. These major changes were due to the effect of pectin on cellulose network architecture at deposition, as they were maintained upon removal of the pectin component. These results show that the presence and physical state of pectin at the time of cellulose deposition in muro may be a significant determinant of subsequent extensibility without compromising strength.