Adaptability of lactic acid bacteria and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava and use of competitive strains as starters

The adaptability of lactic acid bacteria (LAB) and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava was investigated using PCR-DGGE and bacteriological culture combined with rRNA gene sequence analysis. Sourdoughs were prepared either from flours of the cereals wheat, rye, oat, barley, rice, maize, and millet, or from the pseudocereals amaranth, quinoa, and buckwheat, or from cassava, using a starter consisting of various species of LAB and yeasts. Doughs were propagated until a stable microbiota was established. The dominant LAB and yeast species were Lactobacillus fermentum, Lactobacillus helveticus, Lactobacillus paralimentarius, Lactobacillus plantarum, Lactobacillus pontis, Lactobacillus spicheri, Issatchenkia orientalis and Saccharomyces cerevisiae. The proportion of the species within the microbiota varied. L. paralimentarius dominated in the pseudocereal sourdoughs, L. fermentum, L. plantarum and L. spicheri in the cassava sourdough, and L. fermentum, L. helveticus and L. pontis in the cereal sourdoughs. S. cerevisiae constituted the dominating yeast, except for quinoa sourdough, where I. orientalis also reached similar counts, and buckwheat and oat sourdoughs, where no yeasts could be detected. To assess the usefulness of competitive LAB and yeasts as starters, the fermentations were repeated using flours from rice, maize, millet and the pseudocereals, and by starting the dough fermentation with selected dominant strains. At the end of fermentation, most of starter strains belonged to the dominating microbiota. For the rice, millet and quinoa sourdoughs the species composition was similar to that of the prior fermentation, whereas in the other sourdoughs, the composition differed.     

Biodiversity of lactic acid bacteria and yeasts in spontaneously-fermented buckwheat and teff sourdoughs

In this study, four different laboratory scale gluten-free (GF) sourdoughs were developed from buckwheat or teff flours. The fermentations were initiated by the spontaneous biota of the flours and developed under two technological conditions (A and B). Sourdoughs were propagated by continuous back-slopping until the stability was reached. The composition of the stable biota occurring in each sourdough was assessed using both culture-dependent and -independent techniques. Overall, a broad spectrum of lactic acid bacteria (LAB) and yeasts species, belonging mainly to the genera Lactobacillus, Pediococcus, Leuconostoc, Kazachstania and Candida, were identified in the stable sourdoughs. Buckwheat and teff sourdoughs were dominated mainly by obligate or facultative heterofermentative LAB, which are commonly associated with traditional wheat or rye sourdoughs. However, the spontaneous fermentation of the GF flours resulted also in the selection of species which are not consider endemic to traditional sourdoughs, i.e. Pediococcus pentosaceus, Leuconostoc holzapfelii, Lactobacillus gallinarum, Lactobacillus vaginalis, Lactobacillus sakei, Lactobacillus graminis and Weissella cibaria. In general, the composition of the stable biota was strongly affected by the fermentation conditions, whilst Lactobacillus plantarum dominated in all buckwheat sourdoughs. Lactobacillus pontis is described for the first time as dominant species in teff sourdough. Among yeasts, Saccharomyces cerevisiae and Candida glabrata dominated teff sourdoughs, whereas the solely Kazachstania barnetti was isolated in buckwheat sourdough developed under condition A. This study allowed the identification and isolation of LAB and yeasts species which are highly competitive during fermentation of buckwheat or teff flours. Representatives of these species can be selected as starters for the production of sourdough destined to GF bread production.     

Effects of fermentation and rye flour on microstructure and volatile compounds of chestnut flour based sourdoughs

The study is aimed at developing a new cereal-based product, with increased nutritional quality, by using natural fermentation of blends of chestnut and rye flour. In spite of the remarkable similarity, the technological potential of combinations of both flours has never been explored before. Three spontaneous chestnut/rye sourdough fermentations were performed over a period of twelve days with daily back-slopping. Samples taken at all refreshment steps were used for culture-dependent and culture-independent evaluation of the microbiota present. Dominant species basically overlapped to those associated to sourdoughs strengthened with chestnut flour, such as Pediococcus pentosaceus or Weissella paramesenteroides. Microstructures, evaluated by means of Scanning Electron Microscopy, revealed the presence in chestnut sourdoughs of a distinguishable network surrounding starch granules, while rye flour-added sourdoughs showed a less structured matrix. By gas chromatography coupled to mass spectrometry, 51 volatile organic compounds were identified at 24 h and after prolonged fermentation. Within volatile organic compounds, alcohols, esters, acids, aldehydes and ketones, all well-known flavour compounds in sourdough fermentation, appeared as dominant. The PCA discriminated the sourdoughs into three distinct clusters and highlighted a clear influence of fermentation time on the volatile composition of sourdoughs.     

Identification of lactic acid bacteria isolated from oat sourdoughs and investigation into their potential for the improvement of oat bread quality

The use of sourdough in wheat and rye breads has been extensively studied; however, little is known about its potential effect when baking oat bread. Consequently, the impact of sourdough on oat bread quality was investigated. Two different sourdoughs were prepared from wholegrain oat flour without the addition of starter cultures, by continuous propagation at 28 (SD 28) or 37 °C (SD 37) until the composition of the lactic acid bacteria remained stable. The dominant LAB were identified by sequence analysis of the 16S rDNA isolated from pure cultures. LAB from SD 28 belonged to the species Leuconostoc argentinum, Pedicoccus pentosaceus and Weissella cibaria, while Lactobacillus coryniformis dominated SD 37. The isolated LAB were further used as starter cultures for the production of oat sourdoughs. Fundamental rheology revealed softening of the sourdoughs compared to non-acidified and chemically acidified controls, which could not be attributed to proteolytic activity. Incorporation of oat sourdough into an oat bread recipe resulted in significantly increased loaf-specific volume as well as improved texture, independent of addition level or sourdough type. Overall, the results of this study show that sourdoughs containing lactic acid bacteria isolated from oats have the potential to enhance oat bread quality.     

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.     

The bacteriocin producer Lactobacillus amylovorus DCE 471 is a competitive starter culture for type II sourdough fermentations

Type II sourdoughs were prepared using Lactobacillus amylovorus DCE 471, a producer of the bacteriocin amylovorin L. The strain was used as a starter culture for rye and wheat sourdoughs on laboratory scale (10 L), and in rye sourdough on pilot scale (100 L). The sourdoughs were acidified to a pH of around 3.5 within 15 h (laboratory dough) to 25 h (pilot‐scale dough). Final amylovorin L titres of 0.3–0.4 (laboratory scale) and 0.2 (pilot scale) MAU kg^?1 of sourdough were detected. After baking of wheat dough that was supplemented with the pilot‐scale sourdough, no amylovorin L activity was recovered from the breadcrumbs. On laboratory scale, aeration or the addition of complex carbohydrates hardly affected growth or amylovorin L production. Rye and wheat sourdough fermentation were rather similar despite differences in sugar concentrations. The persistence of L. amylovorus DCE 471 during rye sourdough fermentation, both on laboratory and pilot scale, was confirmed by repetitive sequence‐based polymerase chain reaction (rep‐PCR) and by testing isolates towards an amylovorin L‐sensitive organism. Further, rep‐PCR indicated that the background microbiota of the flour—probably responsible for the production of low amounts of acetic acid—grew poorly and were overgrown by L. amylovorus DCE 471 during the pilot‐scale fermentation. Copyright © 2007 Society of Chemical Industry     

Influence of lactic acid bacteria on the oxidation–reduction potential of buckwheat (Fagopyrum esculentum Moench) sourdoughs

The influence of lactic acid bacteria (LAB) growth on oxidation–reduction potential (ORP) of buckwheat sourdoughs was investigated. Sourdough fermentations are widely used for the production of bread and other bakery products. Until now the pH value is the most used control parameter taken into account during sourdough technology and no information is available about the influence of sourdough microbiota on the ORP or the use of redox potential (E _h7) measurements as a fermentation control parameter. The influence of growth and metabolism of lactobacilli on the oxidation–reduction potential of buckwheat (Fagopyrum esculentum Moench) sourdoughs was investigated. Upon inoculation with LAB, ORP changes were observed. Each strain exhibits a different ORP time course curve. The E _h7 after 8?h using Lactobacillus plantarum, Lactobacillus sakei, Weissella cibaria and Pediococcus pentosaceus reached 89.2?±?4, 104.5?±?15.3, 30.2?±?4 and 181.5?±?2.6?mV, respectively. W. cibaria showed the highest reducing activity and P. pentosaceus the lowest one. The maximal reduction rate was neither correlated with the highest acidification rate nor with the maximal growth rate. Nevertheless, the reduction rate shows a similar trend like the acidification rate during the time course of fermentation. The ORP changes occurred concomitantly with the acidification, and the acid production decreased after 2?h from the reducing step. These results showed the possibility to carry out ORP measurements in dough system. As strains exhibit very characteristic ORP curves, this parameter can be used as real-time control tool to monitor the time course of fermentation and metabolic activity. This enables an evidence-based determination of fermentation end and/or (intermediate) harvesting point, which is especially helpful in the development of new cereal fermentation types as in gluten-free sourdoughs.     

Microbiological and technological characterization of sourdoughs destined for bread-making with barley flour

The aim of the present study was the microbiological and technological characterization of laboratory- made sourdoughs for use in barley-flour-based bread-making. A defined multi-strain starter culture consisting of selected lactic acid bacteria (LAB) and yeasts from wheat sourdoughs was inoculated into three flour–water mixtures, composed of: (i) 100% wheat flour (ii) 50% wheat flour and 50% hull-less barley flour (composite flour); (iii) 100% hull-less barley flour. After two months of continuous propagation, the chemical characteristics of the three sourdoughs were investigated by measuring: pH, total titratable acidity and concentrations of various microbial metabolites by HPLC (i.e. lactic, acetic, phenyllactic and butyric acids and diacetyl). The microbial traits were studied through viable counts, isolation and typing of LAB and yeasts and PCR-DGGE analyses. Only Saccharomyces cerevisiae and Lactobacillus plantarum were detectable in the sourdoughs together with other lactobacilli species which were different depending on the type of flour blend used. The molecular typing of the isolates highlighted that only a few strains among those initially inoculated prevailed. The volume increases of the three types of sourdough were also investigated and a correlation was seen between an increase in the barley flour content and a reduction in the dough volume.     

Lactic acid bacteria ecology of three traditional fermented sausages produced in the North of Italy as determined by molecular methods

In this study the bacterial biodiversity during the maturation process of three traditional sausages produced in the North of Italy (Salame bergamasco, Salame cremonese and Salame mantovano) was investigated by using culture-dependent and -independent methods. Eleven plants, in the three provinces considered here, were selected because starter cultures were never used in the production. The bacterial ecology, as determined by plate counts, was dominated by lactic acid bacteria (LAB), with minor contribution of coagulase negative cocci and yeasts. After molecular identification of 486 LAB strains, the species more frequently isolated were Lactobacillus sakei and Lactobacillus curvatus. This evidence was also confirmed by PCR-Denaturing Gradient Gel Electrophoresis (DGGE). All the samples analyzed were characterized by the constant presence of L. sakei and L. curvatus bands. A richer biodiversity was only detected at the beginning of maturation. The results obtained by the molecular characterization of the L. sakei and L. curvatus and by the cluster analysis of the DGGE profiles highlighted a plant-specific population, rather than a geographic characterization of the products, underlining how the environmental and processing conditions are able to select specific microbiota responsible for the main transformations during the fermentation and ripening of the sausages.     

Effect of Select Parameters of the Sourdough Rye Fermentation on the Activity of Some Mixed Starter Cultures

The effect of select parameters (i.e., rye flour ash content, temperature, and dough yield) of the sourdough fermentation on the fermentation activity of different starter cultures (lactic acid bacteria Lactococcus lactis ssp. Lactis, Weissella confusa, Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus helveticus, and yeast Kluyveromyces marxianus subsp. Marxianus) was determined. The major metabolic end products of fermentation (D, L-lactic acid, acetic acid, ethanol and glycerol) and the evolution of total phenolic content and folic acid during bread making were measured. Lactobacillus helveticus and Kluyveromyces marxianus allowed obtaining sourdoughs with the highest lactic acid/acetic acid ratios. The mixed starter culture with Lactococcus lactis and Saccharomyces cerevisiae generated the most important quantities of D/L lactic acid. The maximum values of ethanol concentration were obtained in case of the sourdoughs from whole rye flour fermented at lower temperature (30°C) with mixed starter cultures containing Sacchomyces cerevisiae. The fermentation process and type of starter culture are also tools to increase the bioactive compounds, enabling the increase of the phenolic content of the sourdough.     

Fundamental study on the effect of hydrostatic pressure treatment on the bread-making performance of oat flour

The use of sourdough in wheat and rye breads has been extensively studied; however, little is known about its potential effect when baking oat bread. Consequently, the impact of sourdough on oat bread quality was investigated. Two different sourdoughs were prepared from wholegrain oat flour without the addition of starter cultures, by continuous propagation at 28 (SD 28) or 37 °C (SD 37) until the composition of the lactic acid bacteria remained stable. The dominant LAB were identified by sequence analysis of the 16S rDNA isolated from pure cultures. LAB from SD 28 belonged to the species Leuconostoc argentinum, Pedicoccus pentosaceus and Weissella cibaria, while Lactobacillus coryniformis dominated SD 37. The isolated LAB were further used as starter cultures for the production of oat sourdoughs. Fundamental rheology revealed softening of the sourdoughs compared to non-acidified and chemically acidified controls, which could not be attributed to proteolytic activity. Incorporation of oat sourdough into an oat bread recipe resulted in significantly increased loaf-specific volume as well as improved texture, independent of addition level or sourdough type. Overall, the results of this study show that sourdoughs containing lactic acid bacteria isolated from oats have the potential to enhance oat bread quality.     

Functional properties of Lactobacillus strains isolated from kimchi

The objective of this study was to evaluate the functional properties of lactic acid bacteria (LAB) from kimchi, a traditional Korean fermented vegetable product generally consumed raw as a side-dish with practically every meal.Twelve mild acid producing facultatively heterofermentative Lactobacillus strains were selected for their potential as starter cultures for fermentation of kimchi, and evaluated for their functional properties. Eleven strains were identified as Lactobacillus sakei and one as Lactobacillus plantarum. The strains identified as L. sakei differed in some physiological features; of particular interest was the fact that 9 of these strains produced L(+) lactic acid from glucose in presence of acetate.All strains were able to survive gastrointestinal conditions simulating stomach and duodenum passage. In addition, they showed higher adherence to HT-29 cells than Lactobacillus rhamnosus GG, a commercial probiotic strain used worldwide. These strains also showed antimicrobial activity against a number of food-borne pathogens. Their ability to lower cholesterol was demonstrated by BSH (bile salt hydrolytic) activity, and cholesterol assimilation tests in vitro. The results suggest the probiotic potential of these strains for use in kimchi fermentation.     

Analysis of volatile compounds produced by different species of lactobacilli in rye sourdough using multiple headspace extraction

Profiles of volatile organic compound (VOC) produced by nine individual lactic acid bacteria (LAB) during rye sourdough fermentation were compared by automated SPME and GC/MS‐Tof. The dough samples were inoculated with individual strains, placed inside the headspace vials and incubated during next 24 h. The production or loss of VOC‐s was followed by adsorbing volatiles onto 85‐m Car/PDMS fibre in every 4 h. Volatile profiles differed among LAB species and divided LAB into two main groups – hetero‐ and homofermentative. Hetrofermentative LAB (Lactobacillus brevis; Leuconostoc citreum; Lactobacillus vaginalis, Lactobacillus panis) showed high production of acetic acid, CO₂, ethanol, ethylacetate, producing also hexyl acetate, ethyl hexanoate and isopentyl acetate. Whereas homofermentative LAB species (Lactobacillus helveticus; Lactobacillus casei; Lactobacillus sakei; Lactobacillus curvatus) produced a considerable amount of 2,3‐butanedione. Production of l ‐leucine methyl ester was unique for Lb. sakei, Lb. casei and Lb. curvatus strains. Lb. helveticus was the only LAB that produced benzaldehyde.     

Optimization of sourdough process for improved sensory profile and texture of wheat bread

The aim of the study was to determine optimum sourdough process conditions for improved flavour and texture of wheat bread. The influence of process conditions and the starter culture on the characteristics of wheat sourdough bread was established by using response surface methodology. Influence of fermentation temperature (16-32 °C), ash content of flour (0.6-1.8 g/100 g), and fermentation time (6-20 h) were considered as independent factors and their effects were studied in sourdough bread fermented with Lactobacillus plantarum, Lactobacillus brevis, Saccharomyces cerevisiae or with a combination of yeast and lactic acid bacteria. Intensity of sensory attributes, specific volume and bread hardness were considered as the main responses. Ash content of flour and fermentation time were the main factors determining the intensity of sensory attributes. The possibility to enhance intensity of overall flavour, aftertaste and roasted flavour without excessive pungent flavour and without reduced fresh flavour in wheat bread containing 20 g sourdough/100 g of wheat dough was demonstrated by choosing e.g. Lb. brevis for a starter and by utilization of high ash content of flour, long fermentation time and reduced temperature. Bread specific volume was improved 0.2-0.5 ml/g and hardness was reduced (after 4 days of storage) up to 260 g by using low ash content of flour and by optimizing fermentation time according to the microbial strain. Lactic acid fermentation had more profound influence on both desired and undesired flavour attributes, as well as textural features of bread in comparison with yeast fermentation.     

Effect of selected autochthonous starter cultures on processing and quality characteristics of Greek fermented sausages

Selected autochthonous starter (SAS) cultures (i.e. Lactobacillus sakei 8416, Lactobacillus sakei 4413, and L. sakei 8426, L. plantarum 7423 and L. curvatus 8427) were used as starter cultures in addition to a control treatment in the production of fermented sausages. The SAS cultures had a rapid growth and dominated the fortuitous population of LAB during the whole fermentation and ripening process improving the sensory attributes in comparison to control. Apart from the treatment produced with L. sakei 8416, all other SAS cultures prevented the lipid oxidation to values lower than 1 mg malonaldehyde/kg. The Micrococcaceae count and the redness of the sausages was not affected by the smoking and the acidification during the fermentation in the treatments produced with L. sakei 8416 and L. sakei 4413. The treatment of L. sakei 4413 had the lowest (*P < 0.05) content of all biogenic amines. In comparison to the control, the reduction of tyramine was 13%, tryptamine 55%, cadaverine 60% and putrescine 72%. Sausages produced with SAS cultures L. sakei 4413 and L. sakei 8416 had the highest scores for all sensory attributes. The results indicated that the SAS culture of L. sakei 4413 is the best autochthonous starter culture for fermented sausages.     

A review on traditional Turkish fermented non-alcoholic beverages: Microbiota,fermentation process and quality characteristics

Shalgam juice, hardaliye, boza, ayran (yoghurt drink) and kefir are the most known traditional Turkish fermented non-alcoholic beverages. The first three are obtained from vegetables, fruits and cereals, and the last two ones are made of milk. Shalgam juice, hardaliye and ayran are produced by lactic acid fermentation. Their microbiota is mainly composed of lactic acid bacteria (LAB). Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus paracasei subsp. paracasei in shalgam fermentation and L. paracasei subsp. paracasei and Lactobacillus casei subsp. pseudoplantarum in hardaliye fermentation are predominant. Ayran is traditionally prepared by mixing yoghurt with water and salt. Yoghurt starter cultures are used in industrial ayran production. On the other hand, both alcohol and lactic acid fermentation occur in boza and kefir. Boza is prepared by using a mixture of maize, wheat and rice or their flours and water. Generally previously produced boza or sourdough/yoghurt are used as starter culture which is rich in Lactobacillus spp. and yeasts. Kefir is prepared by inoculation of raw milk with kefir grains which consists of different species of yeasts, LAB, acetic acid bacteria in a protein and polysaccharide matrix. The microbiota of boza and kefir is affected from raw materials, the origin and the production methods.     

Structural and rheological characterisation of heteropolysaccharides produced by lactic acid bacteria in wheat and sorghum sourdough

Hydrocolloids improve the volume, texture, and shelf life of bread. Exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) during sourdough fermentation can replace hydrocolloids. It was the aim of this study to determine whether heteropolysaccharides (HePS) synthesized intracellularly from sugar nucleotides by glycosyltransferases are produced in wheat and gluten-free sorghum sourdough at effective levels. The HePS-producing strains Lactobacillus casei FUA3185, L. casei FUA3186, and Lactobacillus buchneri FUA3154 were used; Weissella cibaria 10M producing no EPS in the absence of sucrose served as control strain. Cell suspensions of L. buchneri in MRS showed the highest viscosity at low shear rate. Glycosyltransferase genes responsible of HePS formation in LAB were expressed in sorghum and wheat sourdough. However, only HePS produced by L. buchneri influenced the rheological properties of sorghum sourdoughs but not of wheat sourdoughs. Sorghum sourdough fermented with L. buchneri exhibited a low |G^∗| compared to the control, indicating a decrease in resistance to deformation. An increase in tan δ indicated decreased elasticity.The use of LAB producing HePS expands the diversity of EPS and increases the variety of cultures for use in baking.     

On-farm implementation of a starter culture for improved cocoa bean fermentation and its influence on the flavour of chocolates produced thereof

Cocoa bean fermentations controlled by means of starter cultures were introduced on several farms in two different cocoa-producing regions (West Africa and Southeast Asia). Two starter culture mixtures were tested, namely one composed of Saccharomyces cerevisiae H5S5K23, Lactobacillus fermentum 222, and Acetobacter pasteurianus 386B (three heaps and one box), and another composed of L. fermentum 222 and A. pasteurianus 386B (seven heaps and one box). In all starter culture-added cocoa bean fermentation processes, the inoculated starter culture species were able to outgrow the natural contamination of the cocoa pulp-bean mass and they prevailed during cocoa bean fermentation. The application of both added starter cultures resulted in fermented dry cocoa beans that gave concomitant milk and dark chocolates with a reliable flavour, independent of cocoa-producing region or fermentation method. The addition of the lactic acid bacterium (LAB)/acetic acid bacterium (AAB) starter culture to the fermenting cocoa pulp-bean mass accelerated the cocoa bean fermentation process regarding citric acid conversion and lactic acid production through carbohydrate fermentation. For the production of a standard bulk chocolate, the addition of a yeast/LAB/AAB starter culture was necessary. This enabled an enhanced and consistent ethanol production by yeasts for a successful starter culture-added cocoa bean fermentation process. This study showed possibilities for the use of starter cultures in cocoa bean fermentation processing to achieve a reliably improved fermentation of cocoa pulp-bean mass that can consistently produce high-quality fermented dry cocoa beans and flavourful chocolates produced thereof.     

Free D- and L-Amino Acid Evolution During Sourdough Fermentation and Baking

The evolution of free D- and L-amino acids in sourdoughs started with various lactic acid bacteria (LAB) and yeasts was studied. Lactobacillus brevis subsp. lindneri CB1 and Lactobacillus plantrum DC400 had high proteolytic activity. During sourdough fermentation, Saccharomyces cerevisiae 141 and Saccharomyces exiguus M14 sequentially utilized free amino acids produced by bacterial activity. Due to increased cell yeast autolysis, more S. exiguus M14 inocula caused more free amino acids which were partially utilized by LAB without causing hydrolysis of wheat flour protein. D-alanine, D-glutamic acid and traces of other D-isomers were observed in sourdoughs fermented with L. brevis subsp. lindneri CB1 and S. cerevisiae 141. Free total D- and L-amino acid content decreased by more than 44% after baking the sourdoughs. No abiotic generation of new D-amino acid isomers was detected in the baked sourdoughs.