Because of its high density of negatively charged phosphate groups, phytic acid (PA) forms very stable complexes with mineral ions rendering them unavailable for intestinal uptake. Indeed, the first step in mineral absorption requires that the mineral remains in the ionic state. As the PA content of the diet increases, the intestinal absorption of zinc, iron and calcium decreases. The inhibitory effects of PA on magnesium or copper are more controversial. Nevertheless, PA does not occur alone in foods and is often consumed with various compounds. Phytates are always present in vegetal matrix composed of fibres, minerals, trace elements and other phytomicronutrients. Thus, in order to evaluate mineral absorption from phytate-rich products, all components of diet and food interactions should be considered and it is hard to predict mineral bioavailability in such products by using only the phytate content.

The physiologic importance of ferulic acid (FA), and notably its antioxidant properties, depends upon its availability for absorption and subsequent interaction with target tissues. Because FA is widely present in cereals, the aim of the present study was to investigate its intestinal and hepatic metabolism in rats by in situ intestinal perfusion model (from 10 to 50 nmol/min), and its bioavailability in supplemented diets (from 10 to 250 micromol/d) or in a complex cereal matrix, i.e., whole flours from Valoris (Triticum aestivum) or Duriac (T. durum) cultivars and bran or white flour from the Valoris cultivar. In perfused rat intestine, net FA absorption was proportional to the perfused dose (R2 = 0.997); once absorbed, FA was completely recovered as conjugated forms in plasma and bile secretion (representing 5-7% of the perfused dose). In rats fed FA-enriched semipurified diets, FA absorption was quite efficient because approximately 50% of the ingested dose was recovered in urine. This extensive elimination by kidneys limited FA accumulation in plasma (typically 1 micromol/L in rats fed 50 micromol FA/d). In contrast, in rats fed cereal diets providing 56-81 micromol FA/d, urine excretion was 90-95% lower than in rats fed FA-enriched semipurified diets, and plasma concentrations were approximately 0.2-0.3 micromol/L. Thus, the cereal matrix appears to severely limit FA bioavailability. This inherently low bioavailability of FA in cereals likely reflects FA association with the fiber fraction through cross-linking with arabinoxylans and lignins.

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Bread is one of the most widely consumed staple foods worldwide. White-wheat bread, largely consumed in France, is made from highly refined flour, which leads to a low nutrient density. Due to a highly porous structure and gelatinised starch, it is easily broken down during digestion, leading to a rapid increase of glucose released into the bloodstream. Low glycaemic responses are considered favourable to health, especially against a background of diabetes. Literature reports show that selection of raw material is an essential factor in decreasing the glycaemic index (GI) of white bread. There are two means of decreasing the rate of starch degradation: either (i) slowing gastric emptying rate and/or glucose diffusion-absorption through the intestinal mucosa, which can be achieved by incorporating soluble fibre or organic acid in bread, or (ii) limiting starch accessibility to a-amylase by using high-amylose cereal varieties and/or incorporating intact cereal grains. Studies on cereal products show that preservation of the food structure during digestion seems to be a more important GI-reducing factor than the degree of starch crystallinity or the presence of soluble fibre. Thus, we should look to produce bread with a more compact food structure or higher density, which is the case in leavened wholewheat bread or bread with intact cereal grains. The baking process should also be improved to achieve this goal, by using, for example, a reduced kneading time or less yeast than usual.Breads: Glycaemic index: Food structure

The current study was undertaken to provide solutions to optimize the unsaponifiable antioxidants content of bread. We report a complete description of changes in wheat carotenoids and vitamin E content from grain to bread and highlight the most important processing steps affecting their level in wheat bread. Major carotenoids losses occurred during kneading. A close correlation (r(2) = 0.97; P = 0.05) was found between carotenoid pigment losses and lipoxygenase (LOX) activity, both parameters depending on wheat genotype. The use of wheat species exhibiting high carotenoid contents and low LOX activity was shown to preserve significant carotenoid level in the bread. No relation was found between vitamin E losses during doughmaking and LOX activity. In addition, moderate kneading resulted in higher vitamin E retention in comparison with carotenoids (12% and 66% losses, respectively). It is concluded that carotenoids are more susceptible to oxidation by endogenous lipoxygenase than vitamin E during breadmaking. This study showed that bread nutritional quality, in terms of antioxidant content, could be improved by selecting suitable cereal genotypes, if this potential is preserved by milling and baking processes.