Microbial cell-free extracts affect the biochemical characteristics and sensorial quality of sourdough bread.

This study aimed to improve the sensorial quality of sourdough wheat bread by the addition of cell-free enzyme extracts (CFEs) from Lactobacillus sanfranciscensis (SF), Hafnia alvei (HF) and Debaryomyces hansenii (DH). CFEs were suitable sources of peptidases, glutamate dehydrogenase and cystathionine γ-lyase. The concentration of free amino acids (FAA) in the sourdoughs containing CFEs was higher than the control sourdough, produced without addition of CFEs. The community-level catabolic profiles showed that the highest number of carbohydrates, polymers and carboxylic acids were consumed in the SF sourdough. Breads produced with CFEs were characterized by higher specific volume than the control. The use of CFEs impacted on the profile of volatile organic compounds. Overall, positive correlations were found between some key-aroma compounds and enzyme activities/precursor FAA. The SF bread, characterized by highest level of alcohols, received the highest score for aroma and sweetness in the sensory analysis.

The lactic acid bacteria and yeast microbiota of eighteen sourdoughs used for the manufacture of traditional Italian sweet leavened baked goods.

The lactic acid bacteria and yeast microbiota of eighteen sourdoughs used for the manufacture of some traditional Italian sweet leavened baked goods were studied through culture-dependent method and pyrosequencing. Flours used for back slopping and sourdoughs were also biochemically characterized. Principal component analysis was applied to explore eventual correlations between process parameters applied during back slopping, some flour nutrients, profile of microbiota, and biochemical characteristics of sourdoughs. The median values of the cell density of lactic acid bacteria and yeasts were 8.05 and 7.03 log CFU/g, respectively. As shown by culture-dependent method, Lactobacillus sanfranciscensis was identified in all the sourdoughs, except for Panaredda and Torcolo di San Costanzo. For eleven sourdoughs, all the lactic acid bacteria isolates were allotted to this species. For Buccellato di Lucca, Mbriagotto, Pandoro, and Nadalin sourdoughs, at least 80% of the isolates was allotted to this species. Other lactic acid bacteria isolated with a relatively high frequence were Lactobacillus plantarum and Leuconostoc citreum. Pyrosequencing confirmed and complemented the culture-dependent approach, detecting L. sanfranciscensis also in Panaredda and Torcolo di San Costanzo sourdoughs. Saccharomyces cerevisiae was identified in all the sourdoughs, except for Mbriagotto, Ciambella di Mosto and Pandolce Genovese. These latter sourdoughs harbored strains of Candida humilis, whereas five sourdoughs combined the presence of both yeast species. Positive correlations were found between time of back slopping and cell density and main metabolites of lactic acid bacteria. Percentage of sourdough used as inoculum was mainly correlated with the cell density of yeasts and the concentration of ethanol. This study provided a comprehensive and comparative approach to highlight the dominant microbiota of Italian sourdoughs, which could be exploited further to guarantee a highly reproducible quality of the Italian sweet goods studied, while preserving their traditional trait.

Lactic acid bacterium and yeast microbiotas of 19 sourdoughs used for traditional/typical italian breads: interactions between ingredients and microbial species diversity.

The study of the microbiotas of 19 Italian sourdoughs used for the manufacture of traditional/typical breads allowed the identification, through a culture-dependent approach, of 20 and 4 species of lactic acid bacteria (LAB) and yeasts, respectively. Numerically, the most frequent LAB isolates were Lactobacillus sanfranciscensis (ca. 28% of the total LAB isolates), Lactobacillus plantarum (ca. 16%), and Lactobacillus paralimentarius (ca. 14%). Saccharomyces cerevisiae was identified in 16 sourdoughs. Candida humilis, Kazachstania barnettii, and Kazachstania exigua were also identified. As shown by principal component analysis (PCA), a correlation was found between the ingredients, especially the type of flour, the microbial community, and the biochemical features of sourdoughs. Triticum durum flours were characterized by the high level of maltose, glucose, fructose, and free amino acids (FAA) correlated with the sole or main presence of obligately heterofermentative LAB, the lowest number of facultatively heterofermentative strains, and the low cell density of yeasts in the mature sourdoughs. This study highlighted, through a comprehensive and comparative approach, the dominant microbiotas of 19 Italian sourdoughs, which determined some of the peculiarities of the resulting traditional/typical Italian breads.

Use of sourdough lactobacilli and oat fibre to decrease the glycaemic index of white wheat bread.

This work was aimed at decreasing the glycaemic index (GI) of white wheat bread. Breads made with wheat flour (WF) or wholemeal flour (WMF) and fermented with baker's yeast had similar values of resistant starch (RS; 1.4-1.7 %, starch basis). Sourdough Lactobacillus plantarum P1 and Lactobacillus brevis P2 favoured the highest formation of RS (approximately 5 %) when fermented with WF and WMF. The mixture (1:1) of WF and WMF (WF/WMF) was selected. The effect of dietary fibres, chemical or sourdough acidification on the hydrolysis index (HI) of WF/WMF bread was determined. Among fibres, only the addition of oat fibre (5 %) decreased the HI to 90.84 %. Lactic acid determined the lowest HI, and the effect was related to the decrease of pH. For the same decrease of pH, breads fermented with L. plantarum P1 and L. brevis P2 (sourdough WF/WMF) showed values of HI lower than chemical acidification. The glucose response and GI of WF bread or sourdough WF/WMF bread enriched with oat fibre was determined by using fifteen healthy volunteers. Anhydrous glucose was used as reference. The area under the glucose response curve and the value of GI (72 %) of WF bread were significantly (P < 0.05) higher than sourdough WF/WMF bread enriched with oat fibre (GI = 53.7 %). The decrease of GI of the sourdough WF/WMF bread may be due to both fibre content and decreased pH. Compared to WMF bread, sourdough WF/WMF bread, enriched with oat fibre, had higher specific volume, better cell crumb structure and more appreciated acidulous smell, taste and aroma.