Flavour of sourdough wheat bread crumb

This study investigates the effect of adding sourdough to wheat bread dough on the production of flavour compounds in wheat bread crumb. The sourdoughs were fermented with starter cultures of lactic acid bacteria alone and in combination with sourdough yeasts. The volatile compounds in the bread crumb were isolated by a dynamic headspace technique and extraction analysis, analysed by gas chromatography (GC), and identified on the basis of GC retention times for reference compounds and mass spectrometry (MS). The chemical analyses were combined with sensory evaluation. The volume of the loaves increased significantly when the doughs had 5–20% sourdough added compared with the control bread (bread without sourdough). In the sourdough bread, the content of acetic acid, 2-methylpropanoic acid, and 3-methylbutanoic acid was generally higher, and loaves made with the addition of sourdoughs fermented withLactobacillus plantarum, L. delbrueckii, orL. sanfrancisco had a higher content of 2- or 3-methyl-1-butanol than control bread. Interactions were seen between the starter cultures and the sourdough yeasts, and the production of the following compounds was increased depending on the starter culture used and on the sourdough yeast: ethanol, 2-methylpropanol, 2/3-methyl-1-butanol, 2-phenylethanol, benzyl alcohol, acetic acid, 2-methylpropanoic acid, and 3-methylpropanoic acid. Bread made with an addition of 5% to 15% sourdough fermented withL. sanfrancisco had a pleasant, mild and sour odour and taste.L. plantarum bread had a strong, sour and unpleasant odour and a metallic sour taste with a sour aftertaste, but when the sourdough was also supplemented with the sourdough yeastSaccharomyces cerevisiae, the bread attained a more aromatic wheat bread flavour, which may be caused, in part, by a higher content of 2/3-methyl-1-butanol, 2-methylpropanoic acid, 3-methylbutanoic acid and 2-phenylethanol.     

The sourdough microflora Microbiological, biochemical and breadmaking characteristics of doughs fermented with freeze-dried mixed starters, freeze-dried wheat sourdough and mixed fresh-cell starters

Freeze-dried mixed starters, freeze-dried wheat sourdough and mixed fresh-cell starters made withLactobacillus sanfrancisco CBI,L. plantarum DC400 andSaccharomyces cerevisiae 141 and/orS. exiguus M14 were used for leavening wheat doughs, and their microbiological, biochemical and breadmaking characteristics were compared with those of Italian traditional doughs produced by baker's yeast. All the doughs fermented with starters had more balanced microbiological and biochemical characteristics than dough started with baker's yeast in which alcoholic fermentation end-products largely predominated. By using starters, the greatest lactic acid bacteria cell number and acetic acid production, were achieved, along with more complete profiles of volatile compounds and greater structural stability of fermented doughs. Fresh-cell starters showed higher microbial functionality and represented the only way to enrich the doughs withS. exiguus M14, some of which survived the freeze-drying process. No differences were detected between the two different types of freeze-dried starters and the subsequent use (10 times) of doughs initially produced with freezedried starters eliminated initial differences in the microbial functionality with respect to fresh-cell starters.     

Effects of sourdough and enzymes on staling of high-fibre wheat bread

The effects of sourdough and enzyme mixture (α-amylase, xylanase and lipase) on the specific volume, staling and microstructure of wheat pan bread supplemented with wheat bran were studied. Staling of bread was followed for 6 days by measuring the crumb firmness, changes in crystallization of amylopectin (DSC), increase in signal from the solid phase (NMR) and by light microscopy. The most effective treatment in improvement of quality was the combination of bran sourdough and enzyme mixture. During storage the rate of changes in crumb firmness, amylopectin crystallinity and rigidity of polymers were greatest for the white wheat bread. The most pronounced microstructural changes were swelling of starch granules and separation of amylose and amylopectin in the starch granules. Least changes in crumb firmness, amylopectin crystallinity and rigidity of polymers were observed in bran sourdough bread with enzymes. In contrast to white wheat bread, the starch granules were very much swollen in bran sourdough bread with enzyme mixture. This was hypothesized to be due to the higher water content of bran bread, and degradation of cell wall components leading to altered distribution of water among starch, gluten and bran particles during storage.     

Antifungal activity of sourdough fermented wheat germ used as an ingredient for bread making

This study aimed at investigating the antifungal activity of sourdough fermented (Lactobacillus plantarum LB1 and Lactobacillus rossiae LB5) wheat germ (SFWG). Preliminarily, methanol and water/salt-soluble extracts from SFWG were assayed by agar diffusion towards Penicillium roqueforti DPPMAF1. As shown by hyphal radial growth rate, the water/salt-soluble extract showed the inhibition of various fungi isolated from bakeries. The antifungal activity was attributed to a mixture of organic acids and peptides which were synthesized during fermentation. Formic (24.7 mM) acid showed the highest antifungal activity. Four peptides, having similarities with well known antifungal sequences, were identified and chemically synthesized. The minimal inhibitory concentration was 2.5–15.2 mg/ml. Slices of bread made by addition of 4% (wt/wt) of freeze dried SFWG were packed in polyethylene bags and stored at room temperature. Slices did not show contamination by fungi until at least 28 days of storage and behaved as the calcium propionate (0.3%, wt/wt).     

The effects of low mixing temperature on dough rheology and bread properties

In this research, the effects of a low mixing temperature on dough rheology and the quality of bread were investigated. In the experiments, strong flour samples (Type 550), 1.5% salt, 3% of yeast and 1% additive mixture were used and dough samples were mixed at 17 °C (low temperature), 23 °C (control) and 30 °C (high temperature). Five different periods (0, 30, 60, 90 and 120 min) were applied at the bulk fermentation stage. At the final proofing stage, the dough was fermented until it reached a constant height. It was determined that almost every bread from dough samples mixed at 17 °C resulted in not only the highest bread volume and bread weight, but also the best texture, elasticity and crumb structure. The results of dough samples mixed at 23 °C were worse than those of dough samples mixed at 17 °C. The worst results were obtained from dough samples mixed at 30 °C (high temperature). As a result, it may be concluded that the quality of bread from dough samples mixed at low temperature (17 °C) is superior to those from dough samples mixed at the higher temperatures. Besides these findings, it may also be stated that prolonging the period of bulk fermentation in dough samples mixed at 17 °C positively develops baking performances.     

Effects of wheat sourdough process on the quality of mixed oat-wheat bread

The aim of this work was to study the effects of sourdough fermentation of wheat flour with Lactobacillus plantarum, on the quality attributes of mixed oat-wheat bread (51 g whole grain oat flour and 49 g/100 g white wheat flour). Emphasis was laid both on β-glucan stability as well as bread structure and sensory quality. The variables of the sourdough process were: dough yield (DY), fermentation time, fermentation temperature, and amount of sourdough added to the bread dough. The sourdough process was shown to be a feasible method for mixed oat-wheat bread, and, when optimized, provided bread quality equal to straight dough baking. A small amount (10g/100 g dough) of slack sourdough fermented at high temperature for a long time resulted in the most optimal sourdough bread with the highest specific volume (3.5 cm³/g), the lowest firmness after 3 days storage (0.31 kg), and low sensory sourness with high intensity of the crumb flavour. Wheat sourdough parameters did not affect the content of oat β-glucan in the bread. Additionally, both straight dough and sourdough bread contained 1.4-1.6 g β-glucan/100 g fresh bread. The average molecular weight of β-glucan was 5.5 × 10⁵ in both types of bread, while that of oat flour was 10 × 10⁵. This indicates that a slight degradation of β-glucan occurred during proofing and baking, and it was not affected by variation in the acidity of the bread between pH 4.9-5.8.     

Incorporation of dairy ingredients into wheat bread: effects on dough rheology and bread quality

 Dairy ingredients are used in breadmaking for their nutritional benefits and functional properties. The effects of the traditionally-used whole and skimmed milk powder, sodium caseinate, casein hydrolysate and three whey protein concentrates on dough rheology and bread quality were studied. Whole and skimmed milk powders improved sensory characteristics. Sodium caseinate and hydrolysed casein displayed beneficial functional properties in breadmaking including low proof time, high volume and low firmness. Both ingredients increased dough height measured with the rheofermentometer. Bread with 2% or 4% sodium caseinate added was rated highly in sensory evaluation. Incorporation of whey protein concentrates generally increased proof time, decreased loaf volume and decreased dough height measured with the rheofermentometer. Received: 6 April 1999 / Revised version: 13 July 1999     

Impact of sourdough on the texture of bread

Sourdough has been used since ancient times and its ability to improve the quality and increase the shelf-life of bread has been widely described. During sourdough fermentation, lactic acid bacteria (LAB) produce a number of metabolites which have been shown to have a positive effect on the texture and staling of bread, e.g. organic acids, exopolysaccharides (EPS) and/or enzymes. EPS produced by LAB have the potential to replace more expensive hydrocolloids used as bread improvers. Organic acids affect the protein and starch fractions of flour. Additionally, the drop in pH associated with acid production causes an increase in the proteases and amylases activity of the flour, thus leading to a reduction in staling. While improving the textural qualities of bread, sourdough fermentation also results in increased mineral bioavailability and reduced phytate content. In this review we will be discussing the effect of sourdough on wheat and rye bread as well as the potential of sourdough to improve the quality of gluten-free bread.     

Effect of sourdough fermentation on stabilisation,and chemical and nutritional characteristics of wheat germ

Lactic acid bacteria strains were identified from wheat germ by 16S rRNA partial sequencing, subjected to RAPD-PCR typing and screened. Lactobacillus plantarum LB1 and Lactobacillus rossiae LB5 were used as starters to produce sourdough fermented wheat germ (SFWG). The chemical and nutritional characteristics of SFWG were compared to those of the raw wheat germ (RWG). Lipase activity in SFWG was ca. 2.6-fold lower than that found in RWG. As shown by SPME/GC/MS analysis, most of the volatile compounds derived from lipid oxidation during storage (40 days) were at markedly lower levels in SFWG compared to RWG. Fermentation of wheat germ increased of ca. 50% the concentration of free amino acids. Glu markedly decreased in SFWG, due to its conversion in GABA. The concentration of the anti-nutritional factor raffinose also decreased in SFWG. The in vitro protein digestibility, the concentration of total phenols, phytase and antioxidant activities were increased by fermentation.     

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.     

Production of microbial exopolysaccharides in the sourdough and its effects on the rheological properties of dough

Exopolysaccharides (EPS) are exogenous microbial metabolites which are secreted mainly by bacteria and microalgae during growth. In addition to natural polysaccharides present in cereal grains flour and dough, microbial flora is usually involved in production of polysaccharide on sourdough fermentation. Total polysaccharides (microbial and flour) were extracted from sourdough and dough samples dehydrated and were added at the rate of 0%, 0.25%, 0.5%, 1%, 1.5%, 2% and 2.5% (w/w flour based) on the dough to investigate its effects on the rheological properties of the dough. Addition of polysaccharides to the dough increased the water absorption and decreased the dough softening after 20 min. Resistance to extension after 45, 90 and 135 min resting time was decreased by increasing the percentage of the added polysaccharides. Longer fermentation time for each level of polysaccharides led to greater stability. No significant differences were observed in the extensibility of dough. The overall effects of different levels of added polysaccharides resulted in a decrease in resistance to extension ratio of the samples. Energy input decreased in all cases. It seems therefore that addition of polysaccharides may be useful when bread is to be made with stronger flour and longer fermentation time is needed.     

Effect of extruded wheat bran on dough rheology and bread quality

Bran extrusion is mainly under study and works should be performed to know the effect on dough and bread. This study was designed to investigate the effect of bran extrusion (addition of 2.5 g/100 g to 20 g/100g bran) on the rheological characteristics of bread dough, behaviour during fermentation, and bread quality. Extruded bran increased dough development time and tenacity to a greater extent than non-extruded bran, and minimized the loss of stability if over-mixing occurred. Extruded bran, due to its greater gas production, also reduced loss of dough height during fermentation to a greater extent than untreated bran. However, breads with extruded bran showed a higher volume and lower initial firmness than breads with normal bran if improver was added. However, no differences were found in the organoleptic evaluation. Bran extrusion therefore modified dough rheology but did not negatively affect bread quality. It could even improve the quality of breads with bran when improvers are added.     

The use of sourdough fermented by antifungal LAB to reduce the amount of calcium propionate in bread

Addition of sourdough is a common practice in the bakery industry to improve, among other quality parameters, the shelf life of bread. In this study, sourdough fermented by antifungal Lactobacillus plantarum strains was investigated for the ability to inhibit growth of common bread spoilage fungi. In both in vitro and sourdough wheat bread system, the antifungal sourdoughs significantly affected the outgrowth of Aspergillus niger, Fusarium culmorum, or Penicillium expansum spores, however on wheat bread outgrowth of Penicillium roqueforti spores was not affected. In an attempt to reduce the amounts of chemical additives in bread, the antifungal sourdoughs were used in combination with calcium propionate (CAP) and possible synergistic effects were evaluated. Presence of 3000 ppm CAP in the bread did not affect the outgrowth of P. roqueforti, whereas outgrowth of the other fungi was retarded. A strong synergistic effect was observed when CAP and antifungal sourdoughs were combined into the bread formulation, and outgrowth of P. roqueforti was affected. The use of reduced CAP amount (1000 ppm) showed significant inhibition only when antifungal sourdough was added. Remarkably, the increase in shelf life achieved was higher than that obtained using 3000 ppm of CAP alone. In conclusion, the results of this study clearly show that the addition of antifungal sourdough has the potential to reduce the levels of chemical additives needed in the bakery industry to ensure the microbiological safety of bread.     

Viscoelastic properties of wheat gliadin and glutenin suspensions

Linear and non-linear rheological properties of wheat gliadin and glutenin suspensions were investigated at various concentrations. Linear dynamic viscoelastic properties for both gliadin and glutenin were strongly dependent on concentration. For gliadins, the storage moduli (G′), loss moduli (G″), and phase shifts dramatically changed within a narrow concentration range, indicating that gliadin suspension properties changed from viscous to viscoelastic. Glutenins exhibited viscoelastic solid behaviour at all measured concentrations. The non-linear shear viscoelastic properties of gliadin and glutenin also depended on concentration. Viscosities of gliadins displayed shear-thinning behaviour; viscosities for glutenins showed shear-thickening behaviour at low shear rates, and shear-thinning behaviour at higher shear rates. Our results indicate that gliadin’s structure in suspension changes over a small concentration range, and suggest that gliadin is important in adjusting and controlling gluten’s viscoelastic behaviour, and not only as a diluent of gluten’s functional properties.     

Experiments on dough rheology to improve screening of bread wheat cultivars

The bread‐making potential of flour may be roughly estimated by dough rheology, especially its tolerance to over‐mixing as determined with the farinograph. The objective of this study was to identify the relative effects of experimental conditions likely to affect dough mixing stability: mixer speed, temperature, salt, yeast and bread additives such as ascorbic acid and preservatives. The addition of 1–2% salt or ascorbic acid (50 mg kg^?1 flour) improved dough mixing stability and counteracted the negative effect of bread preservatives. Mixing salted dough at slow speed (63 rpm) and 25 °C might be a more realistic bread‐making procedure for performing dough rheology assays with equipment such as the farinograph, compared to official methods (only flour and water, no salt; 30 °C). Amongst five bread wheat cultivars, differences existed in dough strengthening response to both salt and ascorbic acid, a property that may find application in wheat breeding and screening.     

Characteristics of bread making doughs: influence of sourdough fermentation on the fundamental rheological properties

The proofing process is an essential step in the bread making technology in providing a link between the bubble structure created in the mixer and the final baked loaf structure. This research was carried out to test the effect of two different types of fermentation on bread making dough properties. Fundamental rheological tests were used to evaluate and compare doughs prepared by using compressed yeast and only natural yeast. Dynamic oscillation tests were performed using a controlled stress--strain rheometer; the phase angle (δ) and the value of the storage modulus (G′) were measured for all samples. Significant differences were found between the doughs which were made using commercial compressed yeast (baker's yeast (BY)) and those prepared using sourdough (SD). In particular SD was less elastic, less firm and easily extensible having higher phase angle and lower G′.     

Interactive effects of flour, starter and enzyme on bread dough machinability

 Dough machinability of samples formulated with the enzyme principles glucose-oxidase, lipase, amylase and pentosanase/hemicellulase, and fermented with different microbial starters, was assessed by texture profile analysis and dough stickiness measurements. The individual and interactive effects of flour, enzyme and starter on the primary and secondary mechanical and surface-related parameters were evaluated, and the suitability of enzyme mixtures added to started doughs to improve dough handling characteristics and minimize adhesiveness and stickiness in flours was established. The general improving effect of the mixture of α-amylase, pentosanase and hemicellulase on most dough texture properties is particularly relevant when high-grade and/or sourer-started systems are used, because of their strong effect in decreasing hardness and adhesiveness respectively. Individual additions of glucose-oxidase and lipase cancelled out the excessive stickiness/adhesiveness of started and enzyme-supplemented doughs while the simultaneous presence of glucose-oxidase and lipase improved cohesiveness, chewiness and gumminess. The extent of the effects of this binary combination on dough mechanical characteristics was comparable to that obtained with the ternary mixture of α-amylase, pentosanase and hemicellulase, but avoided the deleterious effect of the latter enzyme combination on stickiness. In well-defined flour-starter systems, the enzyme supplementation of doughs constitutes a useful alternative to chemical improvers for enhancement of dough plasticity. Reveived: 16 February 1998