EFFECT OF (BIO-)TECHNOLOGICAL APPROACHES ON BRAN TO IMPROVE THE QUALITY OF CEREAL PRODUCTS

The design of foods enriched in dietary fiber has recently received great attention among academia and food industry, since in many European countries the daily intake of dietary fiber is much lower than the recommended levels (25 g; EFSA, 2010). Being a staple food category, cereal products may represent a valid resource to satisfy the optimal amount of soluble and insoluble fiber and other bioactive components. Despite the nutritional benefits, the incorporation of fiber into flour negatively affects the textural and sensory properties of bread and pasta products. This PhD project dealt with the application of physical and/or biotechnological strategies to modify the structural properties of peculiar macromolecules (such as non-starch-polysaccharides or proteins) to enhance the quality of fiber-enriched foods. Samples from the outermost layers of cereals and pseudocereals particularly rich in bioactive compounds (e.g. purple wheat and buckwheat) were included in pasta or bread after treatment and evaluated in terms of technological behavior. The first part of the thesis regarded the application of a two-step debranning process to purple wheat that allowed the selective recovery of bioactive compounds, such as fiber and phenolic compounds. Debranned fractions from the first and the second step were used separately to produce fiber-enriched pasta. Bran from conventional milling was also used as a control. Both fractions had higher or comparable content in total and soluble fiber than bran. Moreover, both of them exhibited a higher ferric reducing-antioxidant power (FRAP) than bran, whereas the highest amount of anthocyanins was found in the first fraction. When compared with pasta enriched in bran, the samples enriched either in the first or second fraction had similar FRAP values and higher amount of anthocyanins, while retaining a fair cooking quality. In the second part of the thesis micronization was applied to buckwheat bran to evaluate the effect of granulometry on dough/bread quality. The role of coarse and fine buckwheat bran enrichment on wheat dough was studied at increasing levels (5, 10, 20%). Dough and bread properties were negatively affected by the interplay of bran addition level and particle size. The thermo-mechanical behavior of dough was found to be mainly related to starch phase transitions during heating with no regards of particle size. Front-face fluorescence studies reveled differences in gluten structural arrangement and solvation with a distinct effect of particle size. Despite the better or similar dough rheological properties (e.g. elasticity, resistance to extension, extensibility), bread enriched in fine bran had lower baking quality in comparison with samples enriched in coarse bran, in terms of loaf specific volume and crumb softness. Concerning the texture, the variations in the perceived crumb hardness were mainly related to changes in crumb density. The application of an adapted Ashby-Gibson model to correct hardness values for the variation in density revealed that the mechanical properties of the solid crumb matrix were controlled by the differences in moisture and in bran volume fraction. Buckwheat bran was used also to evaluate the effects of superheated steam (SS) on bran properties. SS is an innovative technology that has allowed drying of many food matrices while limiting collateral effect on the product. After screening the process conditions, the selected treated bran samples (120 °C, 140 °C, or 160 °C; 40 min; 0.7 aw) were incorporated into high-enriched dough (20%) and their influence on the rheological properties and on the baking quality were considered. The treatment deeply affected the chemical/physical properties of buckwheat bran. In particular, changes in water affinity were progressively observed with increasing temperature, also due to the formation of protein aggregates. These modifications influenced the thermo-mechanical properties of high-bran enriched doughs that reflected baking behavior. When appropriate setting was chosen (temperature: 160 °C) SS treatment increased buckwheat bran performances in terms of specific volume and crumb softness in comparison with untreated bran. The last part of the thesis regarded the use of specific enzymatic treatment (i.e. pectinases and cellulases) to decrease the size of non-starch-polysaccharide chains, aiming at mitigating the worsening effects of fiber on enriched products. Either coarse buckwheat bran or SS bran (treated at 140 °C; 40 min; 0.7 aw) were used. From a technological standpoint, the preliminary bran treatment with cellulases could be a feasible solution to produce bread enriched in buckwheat bran. Besides this, no synergistic effect was observed between SS treatment and enzymatic treatment. Future studies will include the assessment of the effects of bran-treatments on the macromolecular structure of fiber, to define not only its rheological performance but also its nutritional functionality.