Microbial behavior and changes in food constituents during fermentation of Japanese sourdoughs with different rye and wheat starting materials.

Sourdough is a food item made by kneading grain flour and water together and allowing fermentation through the action of lactic acid bacteria (Lactobacillales) and yeast. Typically, Japanese bakeries make sourdough with rye flour, wheat flour, malt extract, and water and allow spontaneous fermentation for 6 days. We compared the microbial behavior and food components, such as organic acids, sugars, and free amino acids, of sourdoughs made using two different rye and wheat flours during the 6-day fermentation period. Comparisons were made for two types of rye and wheat flours, using different production sites and different milling, distribution, and storage conditions. The microbial count was evaluated using different culture media. All sourdough types showed a significant increase in lactic acid levels on fermentation day 2 and a decrease in free amino acid levels on day 4. Low overall lactic acid production and little fluctuation in sugar levels occurred in sourdough made from French ingredients. For sourdough made from Japanese ingredients, sugar levels (chiefly glucose, sucrose, and maltose) declined on fermentation day 1, increased on day 2, and declined by day 5. With the French ingredients, no yeast cells were detected until day 3, and many acid precursors of sourdough flavor components were detected. Yet with the Japanese ingredients, 106/g yeast cells were detected on days 3-5, as well as sourdough-flavor esters and alcohols. Differences in raw material quality affected the microbial behavior and changes in food constituents during the fermentation process and, consequently, the sourdough flavor.

Fujimoto A ，Ito K ，Itou M ，Narushima N ，Ito T ，Yamamoto A ，Hirayama S ，Furukawa S ，Morinaga Y ，Miyamoto T ... -  《-》

Identification of lactic acid bacteria and yeasts, and characterization of food components of sourdoughs used in Japanese bakeries.

Sourdough is a low-pH, fermented product prepared using lactic acid bacteria and yeast mixed with rye flour, wheat flour, and water. It is used and backslopped in bakeries because it enhances texture, flavor, and dough expansion of bread. Various lactic acid bacteria and yeasts have been identified in sourdough, especially in the West. However, microbial and physical characteristics of sourdough from Japan have not been investigated. Here, we characterized the microbial composition and food component characteristics of sourdough from four bakeries in Kansai region, Japan, and performed sensory and quality evaluation of baguettes enriched with 10% sourdough. We detected different species of lactic acid bacteria such as Lactobacillus brevis, Lactobacillus alimentarius, Lactobacillus pentosus, Lactobacillus vaccinostercus, Lactobacillus sanfranciscensis, and Lactobacillus sakei. The identified yeasts primarily included Saccharomyces cerevisiae, with Candida humilis detected in some samples. Components such as amino acids, lactic acid, acetic acid, ethanol, 3-methyl-1-butanol, ethyl acetate, and phenethyl alcohol differed among samples and distinctively affected flavor, quality, and aroma of sourdough-enriched baguettes. The different species of lactic acid bacteria and the ratio of lactic acid bacteria to yeasts possibly affected food components such as free amino acids, sugars, and organic acids via the Maillard reaction, which influences the savory aromas of bread. Future investigation of the effect of lactic acid bacteria will help to improve the overall quality of bread.

Fujimoto A ，Ito K ，Narushima N ，Miyamoto T ... -  《-》

Metabolism of phenolic acids in whole wheat and rye malt sourdoughs.

This work aimed to study the phenolic acid metabolism of sourdough lactic acid bacteria (LAB) in laboratory media, and in sourdough fermentation with single cultures and in co-fermentations. Lactobacilli were selected from isolates obtained from 35 sourdough samples. Isolates (114 strains) were screened for phenolic acid decarboxylase gene pdc and EPS production. Ferulic acid metabolism of the 18 pdc positive strains was evaluated in mMRS; all pcd positive strains converted ferulic acid by decarboxylation and/or reduction. Single whole wheat and rye malt dough fermentation fermented with lactobacilli or yeasts were characterized with respect to free, conjugated, or bound phenolic acids. Concentrations of free, conjugated, or bound phenolic acids were not altered substantially in chemically acidified sourdoughs, or in yeast fermented doughs. L. plantarum metabolized free ferulic acid in wheat and rye malt sourdoughs; L. hammesii DSM 16381 metabolized syringic and vanillic acids and reduced levels of bound ferulic acid in wheat sourdoughs. Co-fermentation of L. hammesii and L. plantarum achieved release of bound ferulic acid and conversion of the resultant free ferulic acid to dihydroferulic acid and volatile metabolites. Phenolic acid metabolism in sourdoughs was enhanced by co-fermentation with strains exhibiting complementary metabolic activities. Results may enable improvement of bread quality by targeted conversion of phenolic acids during sourdough fermentation.

Ripari V ，Bai Y ，Gänzle MG 《-》

Lactic acid bacteria community dynamics and metabolite production of rye sourdough fermentations share characteristics of wheat and spelt sourdough fermentations.

Four spontaneous rye sourdough fermentations were performed over a period of ten days with daily back-slopping. Samples taken at all refreshment steps were used for culture-dependent and culture-independent characterization of the microbiota present. Furthermore, an extensive metabolite target analysis was performed through a combination of various chromatographic methods, including liquid chromatography coupled to mass spectrometry (LC/MS) and gas chromatography coupled to mass spectrometry (GC/MS). Spearman's rank correlation coefficients were calculated and a principal component analysis (PCA) was performed on the data obtained in this study combined with data obtained previously for wheat and spelt sourdoughs. In general, the establishment of a stable microbial ecosystem occurred through a three-phase evolution, with mainly Lactobacillus plantarum and Lactobacillus fermentum dominating the rye sourdough ecosystems. PCA revealed that ornithine and mannitol were positively correlated with rye sourdoughs, contributing to bacterial competitiveness at the onset of sourdough production. Wheat and spelt sourdoughs showed a high degree of similarity, although certain compounds (e.g. indolelactic acid) appeared to be specific for spelt sourdoughs. The production of amino acid metabolites, mainly hydroxy acids (e.g. phenyllactic acid) and alcohols (e.g. 3-methyl-1-butanol), contributed to the equilibration of the redox balance and further enhanced the competitiveness of dominant species in stable sourdoughs.

Weckx S ，Van der Meulen R ，Maes D ，Scheirlinck I ，Huys G ，Vandamme P ，De Vuyst L ... -  《-》

Impact of starter culture, ingredients, and flour type on sourdough bread volatiles as monitored by selected ion flow tube-mass spectrometry.

This study deals with the detection of volatile compounds originating from the crumb of breads made with sourdoughs obtained through starter culture-initiated fermentations, which differed in flour type (wheat and teff), ingredients (citrate and malate), fermentation time (24h or 72h), and starter culture strains (homo- and heterofermentative lactic acid bacteria species and acetic acid bacteria species) applied. Therefore, selected ion flow tube-mass spectrometry (SIFT-MS) was used. SIFT-MS is an easy-to-use and promising technique in the field of food and flavor analysis. Volatile compounds of crumb samples from the breads with sourdough were measured and compared with those of reference bread crumb samples. In general, sourdough addition had a positive effect on the concentrations of the volatile compounds measured by SIFT-MS. Furthermore, a trend toward higher concentrations of several volatiles was seen upon the addition of sourdoughs that were fermented up to 72h, compared to the addition of sourdoughs that were fermented for a shorter time. Ethanol was the major volatile compound identified tentatively, next to alcohols, aldehydes, esters, terpenes, and heterocyclic compounds. Also acetoin/ethyl acetate could be identified, but these compounds could not be distinguished. Higher alcohols showed an increase upon the use of sourdough fermented for a long time. High concentrations of acetic acid were found in breads made with Gluconobacter oxydans IMDO A845-initiated sourdough, indicating its potential for sourdough production. Breads made with teff sourdoughs were distinct from wheat-based sourdough breads as to their volatile compound profiles.

Van Kerrebroeck S ，Comasio A ，Harth H ，De Vuyst L ... -  《-》