• yeast
• sourdough
• pro-technological
• lactic acid bacteria
• functional

Sourdough is a mixture of cereal flour and water, fermented by a complex microbiota, consisting of lactic acid bacteria (LAB) and yeasts, which interact among themselves, often establishing stable associations and contributing to the peculiar properties of sourdough breads (Gobbetti, 1998). In particular, such autochthonous microorganisms produce a large variety of compounds, originating diversified flavours, increasing shelf-life and enhancing nutritional and nutraceutical value of fermented goods. Worldwide, the selection of commercial yeast strains suitable for baked goods has mainly been made according to their leavening and technological traits, while disregarding any functional features able to enhance the nutritional and nutraceutical properties of the derived end-products.
In a previous study the selection of three potential functional yeast starters was performed by using 3 different wholegrain wheat flours.
The aim of this thesis, which was conducted in collaboration with Prof. Kati Katina, Dr. Rossana Coda and Dr. Prabin Koirala of the Department of Food and Environmental Sciences of the University of Helsinki, was to pro-technological and functional characterize doughs obtained using the 3 above wholegrain flours singly inoculated with the best performing yeasts. In particular, Saccharomyces cerevisiae IMA D20Y, S. cerevisiae IMA L22Y and S. cerevisiae IMA L6Y strains were used to ferment a conventional red-grained variety (cv Aubusson), a yellow-grained variety rich in carotenoids (cv Bona Vita) and a blue-grained variety rich in anthocyanins (cv Skorpion), respectively. Moreover, doughs individually inoculated with Kazachstania humilis IMA G23Y, Lactobacillus sanfranciscensis IMA D22LAB and S. cerevisiae ZEUS IBA were also analysed.
The leavening performance and the total titratable acidity (TTA) of each fermented dough were assessed as the main pro-technological traits. For all the three flours, fermented doughs inoculated with the S. cerevisiae selected strains showed the same leavening performance of the commercial baker’s yeast. Moreover, the fermentation process led to a slight decrease of pH and an increase of acidity in all fermented doughs. The L. sanfranciscensis strain was able to acidify all the three wheat doughs, showing a good rate of acidification compared to the not inoculated doughs. TTA values ranged from 13.42±0.07 to 17.85±0.10 mL NaOH 0.1 M.
Among functional properties, the antioxidant activity was determined by the DPPH radical scavenging activity. All the selected yeast and LAB strains singly inoculated in doughs showed radical scavenging activity. In particular, the two enriched flours (Bona vita and Skorpion) fermented with the S. cerevisiae selected strains showed a significantly higher antioxidant capacity than the commercial baker’s yeast. DPPH value was 21.43±0.06 and 11.43±0.09 for Bona Vita and Skorpion doughs, respectively. Moreover, the fermentation with the L. sanfranciscensis strain showed differences of the DPPH inhibitory effect depending of the flour varieties used. In particular, the antioxidant activity of doughs obtained using the two enriched flours singly inoculated with the selected LAB strain resulted significantly higher (21.89±0.11 and 33.05±0.06 for Bona Vita and Skorpion doughs, respectively) than the spontaneously fermented doughs (14.02±0.06 and 24.00±0.05 for Bona Vita and Skorpion doughs, respectively).
In conclusion, the selected yeast strains revealed an interesting leavening ability and antioxidant capacity representing valuable potential functional starters for biotechnological applications.