Effects of Fermentation and Baking of Whole Wheat and Whole Rye Sourdough Breads on Cereal Alkylresorcinols

Alkylresorcinol (AR) content was determined in multiple-stage whole wheat and whole rye flour sours, as well as in whole wheat and whole rye flour doughs and breads. AR content decreased considerably during fermentation and baking. AR content was reduced by 20 and 46%, respectively, at the end of sourdough starter fermentation of whole wheat and whole rye flour sours. AR content, which was 512 and 210 μg/g in whole rye and whole wheat flour doughs, respectively, was 30 and 0 μg/g, respectively, after baking of breads. Synthetic AR added at different levels to doughs was also greatly reduced during fermentation and baking.     

Evidence for formation of heterooligosaccharides by Lactobacillus sanfranciscensis during growth in wheat sourdough

Lactobacillus sanfranciscensis is a key organism of the lactic microflora in traditional and industrial sourdough fermentations. In this paper we provide evidence for the formation of heterooligosaccharides (HeOS) by L. sanfranciscensis during growth in sourdough. To identify the HeOS based on HPAEC-PAD analysis, HeOS standards were synthesized by enzymatic reactions with L. sanfranciscensis levansucrase in a chemically defined system in the presence of raffinose, maltotriose, maltose, xylose, or arabinose as acceptor carbohydrates. The oligosaccharides known to originate from the corresponding acceptor reactions, 1(F)-beta-fructosylraffinose, 1(F)-beta-fructofuranosylmaltotriose, erlose (1(F)-beta-fructofuranosylmaltose), xylsucrose, 1(F)-beta-fructosylxylsucrose, and arabsucrose, were identified by HPAEC-PAD. Evidence for the formation of further tri-, tetra-, and pentasaccharides was provided. Wheat doughs with sucrose were fermented with L. sanfranciscesis TMW 1.392 or the isogenic, levansucrase-negative strain TMW 1.392Deltalev, and the analysis of dough extracts or invertase-treated dough extracts provided evidence for the formation of arabsucrose and erlose in sourdough in addition to 1-kestose and nystose.     

Proteolysis and bioconversion of cereal proteins to glutamate and γ-Aminobutyrate (GABA) in Rye malt sourdoughs

This study aimed to achieve the conversion of cereal proteins to the alternative end products glutamate or γ-aminobutyrate (GABA). Rye malt, fungal proteases, and lactobacilli were employed to convert wheat gluten or barley proteins. Glutamate and GABA formations were strain-dependent. Lactobacillus reuteri TMW1.106 and Lactobacillus rossiae 34J accumulated glutamate; L. reuteri LTH5448 and LTH5795 accumulated GABA. Glutamate and GABA accumulation by L. reuteri TMW1.106 and LTH5448 increased throughout fermentation time over 96 h, respectively. Peptides rather than amino acids were the main products of proteolysis in all doughs, and barley proteins were more resistant to degradation by rye malt proteases than wheat gluten. However, addition of fungal protease resulted in comparable degradation of both substrates. Glutamate and GABA accumulated to concentrations up to 63 and 90 mmol kg(-1) DM, respectively. Glutamate levels obtained through bioconversion of cereal proteins enable the use of hydrolyzed cereal protein as condiment.     

Formation of Oligosaccharides and Polysaccharides by Lactobacillus reuteri LTH5448 and Weissella cibaria 10M in Sorghum Sourdoughs

Gluten‐free breads, which are composed of gluten‐free flours, starch, and hydrocolloids, differ from wheat and rye breads in relation to texture, volume, and crumb structure. Moreover, the dietary fiber content is lower compared with wheat or rye breads. Cereal isolates of lactic acid bacteria frequently produce oligo‐ and homopolysaccharides from sucrose, which can improve the nutritional and technological properties of gluten‐free breads as prebiotic carbohydrates and hydrocolloids, respectively. Sorghum sourdough was fermented with Lactobacillus reuteri LTH5448 or Weissella cibaria 10M, which synthesize fructooligosaccharides (FOS) and levan, and isomaltooligosaccharides and dextran, respectively. The gluten‐free bread was produced with 14% sourdough addition. L. reuteri LTH5448 formed FOS and 1.5 g of levan/kg DM in quinoa sourdoughs. FOS were digested by the baker's yeast during proofing, and the levan could be qualitatively detected in the bread. W. cibaria 10M produced >60 g of isomaltooligosaccharides/kg DM and 0.6 g of dextran/kg DM, which could still be detected in the bread. Breads prepared with W. cibaria 10M were less firm compared with breads prepared with L. reuteri LTH5448 or a FOS and levan‐negative mutant of L. reuteri LTH5448. The addition of sourdoughs fermented with oligo‐ and polysaccharide forming starter cultures can increase the content of prebiotic oligosaccharides in gluten‐free breads.     

Glucan and fructan production by sourdough Weissella cibaria and Lactobacillus plantarum

After a large screening on sourdough lactic acid bacteria, exopolysaccharide (EPS)-forming strains of Weissella cibaria, Lactobacillus plantarum, and Pediococcus pentosaceus were selected. After 6 days of incubation at 30 degrees C, the synthesis of EPS in MRS-based broth ranged from 5.54 to 7.88 mg mL-1. EPS had an apparent molecular mass of ca. 104 Da. As shown by carbohydrate consumption, the synthesis of EPS was found from sucrose only. Two types of homopolysaccharides were synthesized: glucans simultaneously with growth and fructans after 1 day of incubation. Two protein bands of ca. 180-200 kDa were in situ detected on SDS-PAGE gels incubated with sucrose. PCR products of ca. 220 bp were found for L. plantarum PL9 (100% of identity to putative priming glycosyltransferase of L. plantarum WCFS1) and W. cibaria WC4 (80% of identity to putative glycosyltransferase, epsD, of Bacillus cereus G9241) by using hybrid primers for the priming gtf genes. Degenerated primers DexreuR and DexreuV showed a unique PCR product, and the predicted amino acid sequences were identical for W. cibaria WC4 and L. plantarum PL9. The sequence had similarity with polysaccharide biosynthesis glycosyltransferases. W. cibaria WC4 or L. plantarum LP9 synthesized ca. 2.5 g kg-1 EPS during sourdough fermentation with sucrose added. Compared to the sourdough started with an EPS-negative strain, the sourdough started with W. cibaria WC4 or L. plantarum LP9 increased the viscosity, and the resulting bread had higher specific volume and lower firmness. The synthesis of EPS by selected sourdough lactic acid bacteria could be considered as a useful tool to replace the additives for improving the textural properties of baked goods.     

Combined effect of sourdough lactic acid bacteria and additives on bread firmness and staling

The effect of various sourdoughs and additives on bread firmness and staling was studied. Compared to the bread produced with Saccharomyces cerevisiae 141, the chemical acidification of dough fermented by S. cerevisiae 141 or the use of sourdoughs increased the volume of the breads. Only sourdough fermentation was effective in delaying starch retrogradation. The effect depended on the level of acidification and on the lactic acid bacteria strain. The effect of sourdough made of S. cerevisiae 141-Lactobacillus sanfranciscensis 57-Lactobacillus plantarum 13 was improved when fungal alpha-amylase or amylolytic strains such as L. amylovorus CNBL1008 or engineered L. sanfranciscensis CB1 Amy were added. When pentosans or pentosans, endoxylanase enzyme, and L. hilgardii S32 were added to the same sourdough, a greater delay of the bread firmness and staling was found. When pentosans were in part hydrolyzed by the endoxylanase enzyme, the bread also had the highest titratable acidity, due to the fermentation of pentoses by L. hilgardii S32. The addition of the bacterial protease to the sourdough increased the bread firmness and staling.     

Correlations between the amounts of free asparagine and saccharides present in commercial cereal flours in the United Kingdom and the generation of acrylamide during cooking

A range of commercially available cereals (mainly rye and wheat) used to manufacture U.K. bakery products were obtained, and the levels of free amino acids and sugars were measured. Selected samples were cooked as flours and doughs to generate acrylamide and the data compared with those obtained from a model system using dough samples that had been additionally fortified with asparagine (Asn) and sugars (glucose, fructose, maltose, and sucrose). In cooked flours and doughs, Asn was the key determinant of acrylamide generation. A significant finding for biscuit and rye flours was that levels of Asn were correlated with fructose and glucose. The results suggest that for these commercial cereals, selection based on low fructose and glucose contents, and hence low asparagine, could be beneficial in reducing acrylamide in products (e.g., crackers and crispbreads) that have no added sugars.     

Fermentation Reduces Free Asparagine in Dough and Acrylamide Content in Bread

Free asparagine is an important precursor for acrylamide in cereal products. The content of free asparagine was determined in 11 milling fractions from wheat and rye. Whole grain wheat flour contained 0.5 g/kg and whole grain rye flour 1.1 g/kg. The lowest content was found in sifted wheat flour (0.2 g/kg). Wheat germ had the highest content (4.9 g/kg). Fermentation (baker's yeast or baker's yeast and sourdough) of doughs made with the different milling fractions was performed to investigate whether the content of free asparagine was reduced by this process. In general, most of the asparagine was utilized after 2 hr of fermentation with yeast. Sourdough fermentation, on the other hand, did not reduce the content of free asparagineas efficiently but had a strong negative impact on asparagine utilization by yeast. This indicates that this type of fermentation may result in breads with higher acrylamide content than in breads fermented with yeast only. The effect of fermentation time on acrylamide formation inyeast‐leavened bread was studied in a model system. Doughs (sifted wheat flour with whole grain wheat flour or rye bran) were fermented for a short (15+15 min) or a long time (180+180 min). Compared with short fermentation time, longer fermentation reduced acrylamide content in bread made with whole grain wheat 87%. For breads made with rye bran, the corresponding reduction was 77%. Hence, extensive fermentation with yeast may be one possible way to reduce acrylamide content in bread.     

Rheological Changes in Wheat Sourdough During Controlled and Spontaneous Fermentation

The changing rheological characteristics of wheat doughs during fermentation at 30°C for 72 hr were measured using a controlled stress rheometer. Dynamic oscillation tests were performed at frequencies ranging from 0.01 to 10 Hz. Wheat sourdoughs (dough yield 200) were prepared with a mixed starter culture containing typical hetero- and homofermentative sourdough lactic acid bacteria. Results from the controlled fermentation process were compared to results from spontaneous fermentation. Maximum phase angle values, especially at low frequencies, were closely related to total gas production in the doughs. Complex viscosity decreased during fermentation and reached lower final values for doughs without starter culture. Heating characteristics of doughs after various fermentation times were measured at temperatures ranging from 30 to 80°C. The highest values for complex viscosity were found at ≈65°C. When heated, fermented doughs produced weaker gels than fresh doughs. The temperatures at which these maxima occurred increased significantly with fermentation time for spontaneously fermented dough.     

Effect of Single Strain and Traditional Mixed Strain Starter Cultures on Rheological Properties of Wheat Dough and on Bread Quality

Investigations were made to test the effect of two different sourdough starter culture types on wheat dough and bread quality. Two single‐strain starter cultures consisting of well‐defined strains of lactic acid bacteria (Lactobacillus plantarum, L. brevis) and a traditional mixed‐strain sourdough culture (containing L. crispatus, L. pontis, and Saccharomyces cerevisiae) were evaluated for their effects on the rheological characteristics of wheat dough using both fundamental rheological and standard baking tests. Two other doughs were also evaluated, one which was chemically acidified to a comparable pH value by the addition of lactic acid, and a control which was not acidified. Dynamic oscillation tests were performed using a controlled stress rheometer. The phase angle and the absolute value of the complex dynamic modulus were measured for all doughs at frequencies of 0.1–10 Hz. The addition of sourdough prepared using single‐strain or mixed‐strain cultures significantly increased the phase angle and reduced the complex modulus of the doughs at all frequencies (P < 0.05). Significant differences were found between the dough which was chemically acidified and those doughs which were biologically acidified. The addition of sourdough effected an increase in loaf specific volume relative to both the chemically acidified and the nonacidified doughs.     

Oat Bran Fermentation by Rye Sourdough

Hydration of oat bran including fermentation by rye sourdough was studied. Three types of oat bran suspensions were prepared (a control, one with whole meal rye flour added, and one with rye starter added). The suspensions were incubated for 1, 2, 3 and 4 hr. β‐Glucan content and solubilities of protein and β‐glucan were analyzed. Viscosity of the supernatants of oat bran suspensions was determined. Neither the rye sourdough nor the rye flour alone had a significant effect on the total β‐glucan content of oat bran suspensions. However, the addition of rye, either as whole meal rye flour or as sourdough starter, markedly increased the solubility of β‐glucan and proteins and simultaneously decreased the viscosity of the water‐soluble fraction of oat bran suspension. This suggests that a hydrolysis of β‐glucan had occurred that could change the rheological properties of oat bran in baking and the physiological potential of oat bran in nutrition.     

Influence of thiol metabolism of lactobacilli on egg white proteins in wheat sourdoughs

In wheat sourdoughs, the degradation of gluten proteins is favored by acidification and reducing conditions. This study aimed to determine the proteolytic degradation of egg white proteins in wheat sourdoughs acidified with lactobacilli differing in their thiol metabolism. Ovotransferrin was the only major egg white protein that degraded during sourdough fermentations. An extensive degradation of ovotransferrin required a heterofermentative lactobacilli starter, Lactobacillus sanfranciscensis, with glutathione reductase activity. Ovotransferrin was more resistant to breakdown when sourdoughs were acidified with homofermentative lactobacilli or a mutant strain of L. sanfranciscensis lacking the glutathione reductase. Its susceptibility to proteolysis in L. sanfranciscensis sourdoughs is thus attributable to thiol accumulation by L. sanfranciscensis, which apparently altered the structure of ovotransferrin through a reduction of disulfide bonds. Proteolytic degradation of ovotransferrin was attributable to wheat aspartic proteinases. In addition to the susceptibility to proteolysis, other functional properties of egg proteins may be influenced by thiol-exchange reactions.     

Degradation of HMW Glutenins During Wheat Sourdough Fermentations

Bakeries use sourdoughs to improve bread properties such as flavor and shelf life. The degradation of gluten proteins during fermentation may, however, crucially alter the gluten network formation. We observed changes that occurred in the HMW glutenins during wheat sourdough fermentations. As fermentation starters, we used either rye sourdough or pure cultures of lactobacilli and yeast. In addition, we incubated wheat flour (WF) in the presence of antibiotics under different pH conditions. The proteolytic activities of cereal and sourdough‐derived proteinases were studied with edestin and casein. During sourdough fermentations, most of the highly polymerized HMW glutenins degraded. A new area of alcohol‐soluble proteins (≈30.000 MW) appeared as a result of the proteolytic breakdown of gluten proteins. Very similar changes were observable as WF was incubated in the presence of antibiotics at pH 3.7. Cereal and sourdough‐derived proteinases hydrolyzed edestin at pH 3.5 but showed no activity at pH 5.5. An aspartic proteinase inhibitor (pepstatin A) arrested 88–100% of the activities of sourdough enzymes. According to these results, the most active proteinases in wheat sourdoughs were the cereal aspartic proteinases. Acidic conditions present in sourdoughs create an ideal environment for cereal aspartic proteinases to be active against gluten proteins.     

Synthesis of angiotensin I-converting enzyme (ACE)-inhibitory peptides and gamma-aminobutyric acid (GABA) during sourdough fermentation by selected lactic acid bacteria

This article aimed at investigating the synthesis of angiotensin I-converting enzyme (ACE)-inhibitory peptides and gamma-aminobutyric acid (GABA) during sourdough fermentation of white wheat, wholemeal wheat, and rye flours. Sourdough lactic acid bacteria, selected previously for proteinase and peptidase activities toward wheat proteins or for the capacity of synthesizing GABA, were used. The highest ACE-inhibitory activity was found by fermenting flour under semiliquid conditions (dough yield 330) and, especially, by using wholemeal wheat flour. Fourteen peptides, not previously reported as ACE-inhibitory, were identified from the water/salt-soluble extract of wholemeal wheat sourdough (IC 50 0.19-0.54 mg/mL). The major part of the identified peptides contained the well-known antihypertensive epitope VAP. The synthesis of GABA increased when the dough yield was decreased to 160. The highest synthesis of GABA (258.71 mg/kg) was found in wholemeal wheat sourdough.     

Gluten hydrolysis and depolymerization during sourdough fermentation

Hydrolysis and depolymerization of gluten proteins during sourdough fermentation were determined. Neutral and acidified doughs in which microbial growth and metabolism were inhibited were used as controls to take into account the proteolytic activity of cereal enzymes. Doughs were characterized with respect to cell counts, pH, and amino nitrogen concentrations as well as the quantity and size distribution of SDS-soluble proteins. Furthermore, sequential extractions of proteins and analysis by HPLC and SDS-PAGE were carried out. Sourdough fermentation resulted in a solubilization and depolymerization of the gluten macropolymer. This depolymerization of gluten proteins was also observed in acid aseptic doughs, but not in neutral aseptic doughs. Hydrolysis of glutenins and occurrence of hydrolysis products upon sourdough fermentation were observed by electrophoretic analysis. Comparison of sourdoughs with acid control doughs demonstrated that glutenin hydrolysis and gluten depolymerization in sourdough were mainly caused by pH-dependent activation of cereal enzymes.     

Effect of Baking Method and Fermentation on Folate Content of Rye and Wheat Breads

The effect of baking method on folates of rye and wheat breads, as well as the effect of sourdough fermentation of rye, were examined. Sourdough fermentations were performed both with and without added yeast, and samples were taken throughout the baking process. Samples were analyzed microbiologically for their total folate content after trienzyme extraction. Individual folate vitamers were determined by HPLC after affinity chromatographic purification. The lowest folate contents for both rye and wheat breads were found from breads baked without added yeast. Total folate content increased considerably during sourdough fermentation due to increased amounts of 10‐HCO‐H₂folate, 5‐CH₃‐H₄folate, and 5‐HCO‐H₄folate. Baker's yeast contributed markedly to the final folate content of bread by synthesizing folates during fermentation. Proofing did not influence total folate content but changes in vitamer distribution were observed. Folate losses in baking were ≈25%. The variety of sourdoughs and baking processes obviously lead to great variation in folate content of rye breads. The possibilities to enhance natural folate content of rye bread by improving folate retention in technological processes and by screening and combining suitable yeasts and lactic acid bacteria should be further investigated.     

Influence of peptide supply and cosubstrates on phenylalanine metabolism of Lactobacillus sanfranciscensis DSM20451(T) and Lactobacillus plantarum TMW1.468

Bread spoilage is mainly due to the growth of filamentous fungi, and metabolites produced during sourdough fermentation by lactobacilli can inhibit fungal growth. One of these metabolites is phenyllactic acid (PLA), which is a catabolite from phenylalanine. In this work, the influence of peptide supply and cosubstrates was determined on PLA formation from phenylalanine by Lactobacillus plantarum TMW1.468 and Lactobacillus sanfranciscensis DSM20451(T). Transport of single amino acids is not efficient in lactobacilli, and only 1% of the offered phenylalanine was converted to PLA. PLA yields were increased 2-4-fold when peptides instead of single amino acids were used as a substrate. The accumulation of phenylalanine after peptide addition indicated that, after transport, transamination was the second limiting factor. In L. plantarum TMW1.468, PLA yields were increased from 5 to >30% upon the addition of alpha-ketoglutarate. In L. sanfranciscensis DSM20451, a combination of both citric acid and alpha-ketoglutarate increased PLA formation. The combined effect of citric acid and alpha-ketoglutarate can be attributed to changes in the NAD/NADH ratio.     

Prolamin hydrolysis in wheat sourdoughs with differing proteolytic activities

The prolamins of wheat, rye, and barley contain structures that are harmful to gluten-sensitive people, and an extensive degradation of these prolamins during food processing might eliminate this problem. Sourdough fermentation is a cereal food process during which some protein degradation occurs. In this study, the prolamin hydrolysis that occurred in a high-proteolytic-activity germinated-wheat sourdough (GWSD) was compared with that of wheat sourdough systems which contained moderate or no proteolytic activities. Virtually all of the wheat prolamins (gliadins and glutenins) were degraded during the GWSD fermentation. Quantification of its prolamin levels confirmed that extensive prolamin hydrolysis had occurred in the GWSD. This hydrolysis was attributed to the cysteine proteinase activities of the germinated wheat. The use of high-proteolytic sourdoughs in baking could make it possible to prepare new low-prolamin cereal-based products for use by gluten-sensitive people, who could then diversify their diets by including these whole-grain containing products into their every-day diets.     

Fluorescence labeling of wheat proteins for determination of gluten hydrolysis and depolymerization during dough processing and sourdough fermentation

This study was undertaken to enable the determination of hydrolysis and functionality of proteins in situ during fermentation of wheat doughs. Wheat proteins were fractionated and labeled with fluorescein-isothiocyanate (FITC). Fluorescent proteins were incorporated into wheat sourdoughs inoculated with lactobacilli and into neutral and acid control doughs. Doughs containing fungal protease were furthermore evaluated. Doughs were analyzed by extraction and size exclusion chromatography analysis of sodium dodecyl sulfate soluble proteins. Labeled proteins exhibited characteristics comparable to native proteins, with respect to proteolytic degradation and polymerization. Proteolytic breakdown of proteins was enhanced at low pH. Glutenin subunits were incorporated into the gluten macropolymer at neutral pH. Polymerization of FITC proteins was not observed at low pH. Sourdoughs were comparable to acid control doughs, major effects were attributed to changes of pH, rather than microbial metabolism. A synergistic effect with respect to proteolytic activity was observed between fungal protease and L. pontis.     

Influence and Interactions of Processing Conditions and Starter Culture on Formation of Acids,Volatile Compounds,and Amino Acids in Wheat Sourdoughs

The aim of this work was to study the influence of process parameters and the starter culture on the characteristics of wheat sourdough by using response surface methodology. Influence of fermentation temperature (16–32°C), ash content of flour (0.6–1.8%), and fermentation time (6–20 hr) were considered as independent factors and their effects were studied in sourdough fermented with Lactobacillus plantarum, L. brevis, Saccharomyces cerevisiae, or with a combination of yeast and lactic acid bacteria. Formation of acidity, free amino acids, and volatile compounds were considered the main responses. A possibility to enhance formation of potential flavor compounds and precursors without excessive acidity formation in wheat sourdoughs was established. The total amount of amino acids increased by 25–50%, depending on the strain and fermentation conditions. The total amount of volatile compounds increased seven‐ to 100‐fold, depending on the strain and fermentation conditions. Sourdough started with S. cerevisiae was an effective way to optimize the amount of volatile compounds without excessive acidity formation in appropriate processing conditions. Ash content of flour and fermentation time were the most significant factors to modify metabolic activity of wheat sourdoughs. Frequent interactions between the studied factors were observed on the formation of acidity, amino acids, and volatile compounds with most of the strains studied. Possibility to improve current industrial fermentation processes and control flavor attributes of breads by using optimized sourdough was established.