• sourdough
• bread
• baker's yeast.
• byproducts
• sensory analysis
• shelf life
• phenols
• purple potato
• Citrus albedo
• fortification
• flaxseed

In recent years, consumers health- and wellness-consciousness has led to a growing demand for high value functional products. Bread is eaten worldwide, therefore its enrichment through the incorporation of a great variety of value-added compounds as extra ingredients is a growing practice to improve the nutritional status of the population.
Any modifications of the bread making process or recipe leads to changes in the quality of the final product and the challenge in fortified cereal food actually lies in the ability to combine nutritional benefits with good sensory quality. Moreover, while different research papers dealing with bread fortification were recently published, few researchers have posed their attention on the effects induced on fortified bread by the use of different leavening agents (sourdough vs baker’s yeast).
In this context, this PhD research project aimed at developing new bakery products by the fortification of bread with different natural sources, especially taking in account the valorization of food-industry by-products. In particular, the focus was threefold: i) to improve the nutraceutical and sensorial features of sourdough bread by the addition of flaxseed cake (0, 5, 7.5 and 10 %); ii) to study the effect of the leavening agent on the compositional and sensorial characteristics of bread fortified with flaxseed cake; iii) to evaluate the effect of the use of purple potatoes and Citrus albedo in bread making.
The chemical composition of raw materials, dough and final fortified breads were determined together with changes in the nutraceutical properties and sensory profile of breads.
Results showed a significant improvement of nutraceutical profile of the bread fortified with flaxseed cake in a dose-dependent manner. Regardless the leavening agent, the fortification determined a decrease of n-6:n-3 ratio, reaching the recommended value (< 3 ) already at 7.5% level. Furthermore, under the same fortification level, sourdough breads showed a higher level of total phenols and antiradical activity than baker’s yeast ones. Sensory profiles were instead deeply influenced by both the fortification percentage and the leavening agents. In conclusion, flaxseed cake proved to be a viable alternative for the production of fortified bread based on sourdough technology. Moreover, considering both nutritional and sensory results, the best formulation as a function of leavening agent utilized was defined: 5% and 7.5% when sourdough and baker’s yeast were used respectively.
Also the use of purple potatoes turned out to be an efficient strategy to formulate novel products, enhancing the nutraceutical and sensory profile of bread, as well as its shelf life, especially when sourdough was used as leavening agent. These results were further improved by the addition of Citrus albedo, although the percentage considered in this study negatively affected the hedonic perception of fortified bread and needs to be further optimized in this respect.
As a result of preliminary shelf life tests, a significant impact of both the fortification and the choice of the leavening agent on bread staling was also detected for all the bread produced in this research project. In addition, aware of the complexity and the environmental impact of bread preservation, a critical review of the recent literature about the main factors affecting bread shelf life was also discussed, focusing in particular on the effect induced by the use of biological leavening agents (baker’s yeasts and sourdough) as well as by the fortification on the kinetics of bread staling.