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.     

Interaction effects of fermentation time and added asparagine and glycine on acrylamide content in yeast-leavened bread

The interaction effects of fermentation time and added asparagine and glycine on acrylamide precursors (asparagine and reducing sugars) in dough and content of acrylamide in yeast-leavened wheat bread were studied. Two experiments, with low and high levels of added asparagine (0–0.044 and 0.071–0.476 g/100 g flour, respectively), were performed. Glycine was added (0.042–0.380 g/100 g flour) only in the high asparagine addition experiment. The fermentation time, which was varied between 13 and 164 min, showed a reducing effect on acrylamide precursors in the dough in both experiments (p < 0.001). These effects of fermentation were more pronounced in the experiment with low asparagine levels, which resembled levels in ingredients. In contrast, fermentation time did not affect the content of glycine in the dough. Added asparagine increased the levels of asparagine in dough and of acrylamide in bread (p < 0.001). A strong correlation was found between the contents of asparagine in the fermented dough and acrylamide in breads at all levels of asparagine. Glycine significantly increased the colour intensity and reduced the acrylamide in bread (p < 0.001) with the latter effect being dependent on the level of asparagine.     

Effect of addition of protein concentrates from natural and yeast fermented rice bran on the rheological and technological properties of wheat bread

The effect of substituting wheat flour with 0%, 5%, 10% and 15% protein concentrates from natural and yeast fermented rice bran on the rheological properties of their dough and bread properties was studied. Rheological properties of wheat dough were influenced by addition of rice bran protein concentrates. Overall acceptability score and specific loaf volume of 100% wheat bread were not significantly different from composite bread up to 10% rice bran protein substitution, and therefore, the optimised level of substitution was established. The optimised composite bread contained higher total amino acid content, radical scavenging activity and ferric reducing ability power (43.04–48.87 g/100 g, 182.77–201.65   mmol TEAC/100 g and 613.29–637.81 mmol TE/100 g) than control (33.86 g/100 g, 109.43 mmol TEAC/100 g and 540.13 mmol TE/100 g). Springiness, cohesiveness and resilience values of wheat bread were not significantly different from composite bread. Scanning electron microscopy revealed that composite bread had surfaces with embedded granules like protein deposits with small spores.     

Effect of defatted maize germ flour addition on the physical and sensory quality of wheat bread

Maize (Zea mays L.) processing produces large quantities of defatted maize germ (DMG) that is being used mainly for animal feed. The objective of this study was to exploit use of this nutrient-rich by-product in bread by replacing wheat flour at 5-20 g/100 g levels. Breads prepared with wheat-DMG flour blends were analyzed for loaf volume, density, instrumental dough hardness and bread firmness, Hunter color (“L”, “a”, “b”, chroma, and hue angle), and selected sensory attributes. Loaf volumes decreased significantly, from 318.8 ml to 216.3 ml, as the DMG flour supplementation was increased from 0 to 20 g/100 g; a similar effect was observed for bread specific volume. Increase in dough hardness (7.56-71.32 N) was directly related to increase in DMG flour levels. Instrumental firmness values were significantly higher for breads containing DMG flours, 61.58 N in 20 g/100 g DMG bread versus 32.84 N for the control bread, made with wheat flour only. The control bread was lighter in color, as shown by higher “L” values, than those having DMG flour, with chroma and hue angle values significantly higher in treatment breads. In general, no differences were observed for the sensory attributes of crumb color, cells uniformity, aroma, firmness, mouthfeel, and off-flavor in breads with up to 15 g/100 g DMG flour, while the overall acceptability scores showed a mixed pattern. The results of this study demonstrated that acceptable quality bread could be made with DMG flour addition at ≤15 g/100 g.     

Study of the behaviour of Lactobacillus plantarum and Leuconostoc starters during a complete wheat sourdough breadmaking process

The acidification properties, metabolic activity and technological performance of four individual Lactobacillus plantarum or Leuconostoc freeze-dried starters were investigated during a complete wheat sourdough breadmaking process including 0.2 g/100 g baker's yeast. Microbiological contents (lactic acid bacteria and yeasts), acidification characteristics (pH and total titratable acidity), soluble carbohydrates (maltose, glucose and fructose) and fermentative end-products (lactic and acetic acids, ethanol) contents were evaluated during both sourdough and corresponding bread dough fermentation. Biochemical and technological analysis of the resulting bread products are also presented. Some differences among strains in acidification properties and soluble carbohydrates availability were outlined both in sourdough and bread dough. Each individual Leuconostoc or Lb. plantarum starter was able to produce a characteristic fermentation and was found to ensure the production of breads with overall satisfactory acceptance.     

Improved physicochemical and fermentation properties of frozen dough with bacterial cellulose

Effects of a novel category of hydrocolloid (Bacterial cellulose, BC) on physicochemical and fermentation properties of frozen dough were studied to address the reduction in baking performance due to refrigeration. The addition of BC reduced free thiol content and inhibited the de-polymerisation degree of glutenin macropolymers, resulting in enhanced emulsifying activities of frozen dough, when the amount was added up to 0.1 g 100 g⁻¹of wheat flour (dry basis). Further supplement hurt these attributes due to competition for water molecules. However, increasing the addition of BC significantly enhanced its protective effect on yeast activity, which in turn improved the fermentation properties of frozen dough. After 8 weeks of storage at −18 °C, 31% of yeast survived in with the protection of BC. When BC was added at a ratio of 0.1 g 100 g⁻¹ of wheat flour, the improved frozen dough showed maximum volume of gas which was 2.7 times higher than that of the control after 3 h of fermentation. Baking performances confirmed the effect of BC as bread crumbs containing intermediate addition of BC rose optimally during proofing and baking, which contributed to the higher specific volume, less firm and more tender crumb texture of bread. These results suggested that BC might act as an effective additive to improve the shelf-life stability of frozen food during long periods of frozen storage.     

Enzymatic Reduction of Phytate in Whole Wheat Breads

The presence of phytate in flour may be responsible for reduced bioavailability of iron, magnesium, zinc, and calcium from bread. The effect of various concentrations of commercial phytase or phosphatase added to whole wheat flour-yeast doughs on their phytate and nonphytate phosphorus content has been investigated. By using 2.0% (flour basis) of phytase and 0.11% phosphatase the initial phytate phosphorus concentration of the dough was reduced to 1/8 and 1/12 of its initial values, respectively. Storage of the whole wheat breads for up to 96 hr at room temperature showed further significant reduction of phytate phosphorus. The phytate phosphorus content of yeast leavened whole wheat breads decreased during 2 hours of dough fermentation, baking and the subsequent 48 hours of storage at room temperature from 24 mg/100g dough (dry matter) to 1.7 mg/100g bread (dry matter); the phytate phosphorus continued to decrease and after 96 hours storage it was 0.6 mg/100g bread.     

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.     

Selenium concentration and speciation in biofortified flour and bread: Retention of selenium during grain biofortification,processing and production of Se-enriched food

The retention and speciation of selenium in flour and bread was determined following experimental applications of selenium fertilisers to a high-yielding UK wheat crop. Flour and bread were produced using standard commercial practices. Total selenium was measured using inductively coupled plasma-mass spectrometry (ICP-MS) and the profile of selenium species in the flour and bread were determined using high performance liquid chromatography (HPLC) ICP-MS. The selenium concentration of flour ranged from 30 ng/g in white flour and 35 ng/g in wholemeal flour from untreated plots up to >1800 ng/g in white and >2200 ng/g in wholemeal flour processed from grain treated with selenium (as selenate) at the highest application rate of 100 g/ha. The relationship between the amount of selenium applied to the crop and the amount of selenium in flour and bread was approximately linear, indicating minimal loss of Se during grain processing and bread production. On average, application of selenium at 10 g/ha increased total selenium in white and wholemeal bread by 155 and 185 ng/g, respectively, equivalent to 6.4 and 7.1 μg selenium per average slice of white and wholemeal bread, respectively. Selenomethionine accounted for 65–87% of total extractable selenium species in Se-enriched flour and bread; selenocysteine, Se-methylselenocysteine selenite and selenate were also detected. Controlled agronomic biofortification of wheat crops for flour and bread production could provide an appropriate strategy to increase the intake of bioavailable selenium.     

Effect of dietary fiber from sugarcane bagasse and sucrose ester on dough and bread properties

The suitability of an emulsifier, sucrose ester, to enhance the proportion of dietary fiber in white pan bread was examined. The substitution of dietary fiber from sugarcane bagasse and a commercial dietary fiber (Solka Floc^® 900) were varied from 0 to 15 g/100 g of wheat flour mass. Expansion and stickiness of dough, volume, specific volume, firmness and springiness of bread, including sensory evaluation all decreased as each of dietary fiber increased. Bread properties improved with sucrose ester addition. Bread made by 10 g/100 g of each dietary fiber substitution, was scored favorable by consumer when sugar ester was added at 1.5 g/100 g as wheat flour mass.     

Hard Red Spring wheat/C-TRIM 20 bread: Formulation,processing and texture analysis

C-TRIM, a β-glucan-rich fraction, was added to Hard Red Spring wheat (HRSW) flour to increase soluble fiber content of bread, and to obtain a minimum of 0.75 g/bread serving (0.75 g/30 g or 2.5%) required by FDA for health claim. Three treatments or blends FGT0 (100% wheat flour – control), FGT1 (58% flour, 25% gluten and 17% C-TRIM) and FGT2 (60% flour, 22.5% gluten, and 17% C-TRIM) were used in the study. The total amount of soluble fiber from C-TRIM in FGT1 and FGT2 was 4.07–4.17% which was more than the amount required by FDA. The presence of C-TRIM increased both, the Farinograph water absorption and the arrival time. The dough mixing tolerance index (MTI) was also increased by C-TRIM. The FGT1 had higher stability than FGT2, whereas, the loaf volume of FGT1-B was also significantly higher than FGT0-B control and FGT2-B bread. The DSC results indicated that the amount of freezable-water in C-TRIM treated bread (FGT1-B and FGT2-B) was significantly higher than the control wheat flour bread (FGT0-B). This may be attributed to the higher amount of water absorbed by C-TRIM during bread dough (FGT1-D and FGT2-D) preparation and trapped or bound within the bread matrix after baking as compared to the control. After storage of FGT0-B, FGT1-B, and FGT2-B breads 2, 5, and 7 days storage at 25 °C, 4 °C, and −20 °C, the texture of bread were measured with a Texture Analyzer and the data analyzed statistically. The FTG0-B control bread firmness was significantly higher than FGT1-B and FGT2-B C-TRIM treated breads after 7 days storage at 25 °C. The amount of 0.1 M acetic acid-extractable protein was lower in FGT1-B than the control wheat flour (FGT0-B) sample. In addition, more protein was extracted at pH 7.0 than pH 4.5 because of less charges at neutral pH than pH 4.5. The free zone capillary electrophoresis analysis showed obvious differences in the protein charge and size between the dough and bread.     

Properties of yeast free bread produced by supercritical fluid extrusion (SCFX) and vacuum baking

A novel technology, supercritical fluid extrusion (SCFX), allows for continuous production of yeast-free dough leavened via incorporation of supercritical carbon dioxide (SC-CO₂). In this study, an optimum dough formulation, SCFX leavened dough production and baking procedures were developed. A premixed dough was leavened by 1% (feed basis) SC-CO₂ injection in a twin screw extruder at 37 °C. Specific mechanical energy input was 18 kW h/ton. SCFX leavened dough and bread density, moisture content, bake loss, texture profile analysis (TPA) and stress relaxation were evaluated and compared to conventional yeast leavened breads throughout 5-day storage. A combination of vacuum and conventional baking yielded the lowest SCFX leavened bread density of 0.19 g/cm³ and crumb hardness comparable to conventional yeast leavened and commercial products. This approach could be beneficial for a continuous production of consistent ready-to-bake dough and breads having equivalent quality to commercial products but produced in shorter time and without ethanol emission issues.

Industrial relevance

The dough leavening process in conventional bread production is an industrial hurdle for a number of reasons. First, it is very time consuming. Dough leavening through yeast fermentation can take up to eight hours, which is not conducive to high production rates. This long waiting period also means a great deal of storage space is required to produce a large amount of dough. This storage environment must be carefully controlled in terms of temperature, humidity, and air conditions in order to maintain optimal yeast fermentation, which can also be very costly. Finally, the emission of ethanol, a significant byproduct of yeast fermentation, must be controlled according to the EPA clean air act. Expensive catalytic converters must be installed and maintained in commercial bread production facilities.Bread produced by super critical fluid extrusion (SCFX) overcomes these problems. Total dough production time is less than an hour, and with the proper baking equipment, the entire process can be made continuous. This means constant output, less downtime, and none of the costly storage space used for conventional dough proofing. Furthermore, since there is no yeast being used, there is no ethanol being produced. This means no harmful volatile organic emissions and no expensive catalytic converter. Coupled with vacuum baking, this process results in bread with qualities similar to commercially produced bread in significantly less time.     

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 butter content and baking condition on characteristics of the gluten‐free dough and bread

This study aimed to investigate effect of butter content (0–30 g/100 g flour) and baking conditions hot air baking (HA), microwave baking (MW) and hot air‐microwave baking (HA‐MW) on quality of the rice flour dough and bread. The increased butter (up to 15 g butter/100 g flour) enhanced elastic modulus (G′) and viscous modulus (G″) of dough and specific volume of bread. Additionally, the increased butter improved crust colour and reduced hardness of the bread. The HA‐MW and MW conditions were useful for the gluten‐free bread by reducing baking time and predicted glycemic index (GI), regardless of butter content. However, enthalpy of retrogradation and crystallinity in the HA‐MW and MW bread stored at 4 °C for 7 days were increased and higher than those of the HA bread, indicating a faster staling. The predicted GI of both MW and HA‐MW bread remained at a medium level during storage.     

Effect of glucose levels on the rheo-fermentation properties of dough during fermentation

In this study, recombinant dough and simulated dough medium were used to study the effect of different glucose levels on quality of dough. With the increase of glucose levels (3, 6, 9, 12 and 15 g/100 g mixed flour) in recombinant dough, the water absorption and extensibility of the dough decreased significantly. Compared with the sugar-free medium, the maximum height of the dough added with glucose gradually increased, and the CO₂ retention rate decreased slightly. The glucose levels in the dough changed the water mobility and distribution. Compared with 3% glucose levels, yeast produced much more glycerol content and ethanol content in 6% and 15% glucose medium, which affected rheological properties of dough. Different glucose levels affected the fermentation state of yeast and metabolites significantly, 3% glucose medium was more suitable for the dough fermentation and growth of yeast during dough fermentation.     

Cooperation of phosphatidylcholine with endogenous lipids of wheat flour for an increase in dough volume

Phosphatidylcholine (PC) increases the gas-retaining ability of dough, the dough volume on fermentation and the loaf volume of bread. The cooperation of wheat flour endogenous lipids with PC was examined. More than 90% of the total wheat flour lipids were extracted with chloroform, the extracted lipids comprising glycolipids (33 wt%), non-polar lipids (56 wt%), and phospholipids (11 wt%). The increase in the specific volume of dough with delipidated wheat flour by the addition of PC was smaller than the increase in the specific volume of dough with native wheat flour. The addition of the extracted lipids to delipidated wheat flour restored the increase in dough volume by the addition of PC. The glycolipid fraction of the extracted lipids was most effective for enhancing the action of PC. The results suggest that interaction of PC with wheat flour glycolipids may synergistically increase foam stability to enhance the gas-retaining stability of dough.     

Dynamics of γ-aminobutyric acid in wheat flour bread making

The dynamics of the health-improving non-protein amino acid γ-aminobutyric acid (GABA) during bread making were studied. Wheat flour contains trace levels of GABA (<15 ppm) and ca. 160–175 ppm of its precursor, glutamic acid (GA). During dough mixing, the levels of both GA and GABA largely increased. While wheat flour endogenous glutamic acid decarboxylase (GAD) performs some minor conversion of GA into GABA, yeast is the main contributor to GABA formation. Comparison of amino acid levels of dough samples, without or with yeast, indicated that yeast favours both GA and GABA formation already during mixing. Fermentation decreased both GA and GABA contents, due to amino acid consumption by the yeast, which used more GA than GABA. Proofing and baking resulted in large GABA losses, the latter probably in Maillard browning reactions during baking. Thermal loss of GA was less pronounced than that of GABA. Breads contained only trace levels of GABA and ca. 90–130 ppm of its precursor. Exogenous supplementation of recombinantly produced GAD of Yersinia intermedia decreased GA levels in mixed and fermented dough and increased GABA levels. The highest GAD dosage used resulted in fermented doughs with ca. 300 ppm of GABA, i.e. three times higher than the level present in the reference sample (no GAD added). After baking, a significant GABA level was left in the bread samples (ca. 115 ppm) and GABA-enriched breads were obtained. Addition of sodium glutamate (100–380 ppm) to a bread recipe containing no added GAD clearly indicated that its precursor was not the limiting factor for GABA conversion during bread making since the resulting breads contained no GABA, or only trace levels (ca. 20 ppm).     

香菇面包的制作工艺研究

以面粉和香菇茵柄粉为原料,通过对面团配比、发酵、醒发以及烘烤等工艺参数的研究,研制出一种新型的营养面包。结果表明,香菇面包的生产工艺条件为：高筋面粉：香菇菌柄粉：糖：酵母为100：2．0：18：1．2,发酵温度为30℃,发酵时间为100min,醒发温度为32℃,醒发时间为130min,烘烤温度为上火190℃,底火200℃,烘烤时间为12min。对香菇面包进行品质评价,产品具有香菇特有的香气,膳食纤维丰富,营养价值高于普通面包。     

Reduction of rutin loss in buckwheat noodles and their physicochemical characterisation

Tartary buckwheat was subjected to hydrothermal treatments for minimising rutin loss in buckwheat-based foods by water addition. When native buckwheat flour was mixed with water for 60 min, the rutin content was distinctly reduced from 3.74 g/100 g to 0.31 g/100 g, increasing the amount of quercetin. However, the rutin content remained constant and quercetin was hardly detected in hydrothermally-treated buckwheat flour. Also, when noodles were prepared with wheat and buckwheat flours (7:3, w/w), the noodle samples containing hydrothermally-treated buckwheat flour, showed higher amounts of rutin (more than 0.83 g/100 g) than the control noodle with native buckwheat flour (0.27 g/100 g). In addition, the use of hydrothermally-treated buckwheat flour gave less pasting parameters and lower viscoelastic properties. The noodle dough with hydrothermally-treated buckwheat flour also had greater water absorption and development time during mixing while the elongation stress of the noodle dough was reduced.     

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.