Acrylamide–asparagine relationship in baked/toasted wheat and rye breads

Acrylamide in baked and toasted wheat and rye bread was studied in relation to levels of asparagine in flour, dough, bread and toasts. Asparagine was consumed during bread preparation resulting in reduced acrylamide content in the products. In wheat bread, 12% of the asparagine initially present in the flour (0.14 g kg^?1) remained after yeast fermentation and baking; for rye bread, 82% of asparagine remained after sourdough fermentation and baking. Asparagine present in untoasted wheat bread had totally reacted after hard toasting. Toasted wheat and rye bread slices contained 11–161 and 27–205 µg kg^?1 acrylamide, respectively, compared to untoasted wheat and rye bread with <5 and 7–23 µg kg^?1 acrylamide, respectively. The dietary intake of acrylamide from bread (untoasted) of 2 µg day^?1 is relatively low; however, acrylamide exposure from bread increases several fold for people eating toasted bread.     

Acrylamide-asparagine relationship in baked/toasted wheat and rye breads

Acrylamide in baked and toasted wheat and rye bread was studied in relation to levels of asparagine in flour, dough, bread and toasts. Asparagine was consumed during bread preparation resulting in reduced acrylamide content in the products. In wheat bread, 12% of the asparagine initially present in the flour (0.14 g kg(-1)) remained after yeast fermentation and baking; for rye bread, 82% of asparagine remained after sourdough fermentation and baking. Asparagine present in untoasted wheat bread had totally reacted after hard toasting. Toasted wheat and rye bread slices contained 11-161 and 27-205 microg kg(-1) acrylamide, respectively, compared to untoasted wheat and rye bread with <5 and 7-23 microg kg(-1) acrylamide, respectively. The dietary intake of acrylamide from bread (untoasted) of 2 microg day(-1) is relatively low; however, acrylamide exposure from bread increases several fold for people eating toasted bread.     

Mapping of Saccharomyces cerevisiae metabolites in fermenting wheat straight-dough reveals succinic acid as pH-determining factor

Fermenting yeast does not merely cause dough leavening, but also contributes to the bread aroma and might alter dough rheology. Here, the yeast carbon metabolism was mapped during bread straight-dough fermentation. The concentration of most metabolites changed quasi linearly as a function of fermentation time. Ethanol and carbon dioxide concentrations reached up to 60 mmol/100 g flour. Interestingly, high levels of glycerol (up to 10 mmol/100 g flour) and succinic acid (up to 1.6 mmol/100 g flour) were produced during dough fermentation. Further tests showed that, contrary to current belief, the pH decrease in fermenting dough is primarily caused by the production of succinic acid by the yeast instead of carbon dioxide dissolution or bacterial organic acids. Together, our results provide a comprehensive overview of metabolite production during dough fermentation and yield insight into the importance of some of these metabolites for dough properties.     

Yeast leavened banana-bread: Formulation,processing, colour and texture analysis

Banana powder (BP) was added to hard-red spring wheat (HRSW) flour intended for yeast-leavened bread formulation. Five different formulations containing 10%, 15%, 20%, 25%, and 30% BP were prepared with varying amounts of base flour, while vital gluten was maintained at 25% in all blends. Based on the added BP amounts only, the prepared bread could deliver 42.87–128.6 mg potassium/30 g of bread (one regular slice) and 0.33–1.00 g of fibre. Although the dough water absorption was increased, due to BP addition, the dough mixing tolerance (MTI) decreased. The bread loaf volume was significantly higher than the control except for the 30% blend, where the loaf volume was similar to the control. Bread staling increased with BP levels due to the high sugar content but, this effect was limited to the first two days of storage. Blends exhibited darker colour due to the high sugar and protein, while the 25% and 30% blends had the lowest percent of freezable water. The amounts of acetic acid extractable proteins from the dry blends and the dough decreased with increase in BP. The linear rheological properties of the control, 10%, and 30% blends exhibited similar viscoelastic solid behaviour, where both G′ and G′′ had plateaus (G′ > G′′) and they were parallel to each other over three decades of the frequency. Blends showed higher moduli values than the control.     

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).     

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.     

甘氨酸和淀粉膜对面包中丙烯酰胺的协同控制作用

研究面包配料中添加甘氨酸和在面团表面涂刷淀粉膜对面包表皮中丙烯酰胺的协同控制作用。甘氨酸对丙烯酰胺的抑制效果非常显著,当甘氨酸的添加量为面粉的0.1%时,对丙烯酰胺的抑制率达到80.5%;当甘氨酸添加量为面粉的3%时,能将丙烯酰胺含量减少到检测限（＜1?μg/kg）以下。在对面团进行焙烤前,将面团表面涂刷不同的淀粉膜,能够抑制面包中的丙烯酰胺20%以上;抑制效果由高到低分别为：混合淀粉膜＞马铃薯淀粉膜＞玉米淀粉膜。将两种方法结合,甘氨酸在低添加量（0.1%）时结合玉米淀粉膜,对丙烯酰胺的抑制率增加到85.1%,同时还能较好地保持面包的外观颜色。甘氨酸与天冬酰胺竞争底物和淀粉膜中限制性前体物质天冬酰胺的大量减少,是面包中丙烯酰胺的生成量显著降低的主要原因。     

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.     

Influence of size distribution of proteins,thiol and disulfide content in whole wheat flour on rheological and chapati texture of Indian wheat varieties

The influence of protein composition, as measured by size-exclusion high performance liquid chromatography (SE-HPLC), on rheological properties and chapati texture was investigated in the whole wheat flours of eight Indian wheat cultivars grown at a single location. Proteins were extracted using two-step procedure: extraction with buffer containing 0.5% SDS (SDS buffer), followed by sonication. The results showed that SDS buffer extracted 72–90% of the total flour protein in different varieties and 7–11% protein was extracted from the remaining residues by sonication. The proteins extracted were fractionated by SE-HPLC into large polymeric proteins (>130 kDa), small polymeric proteins (80–130 kDa) and monomeric proteins (10–80 kDa). Total polymeric protein content in the flour protein showed a significant positive correlation with dough hardness (r = 0.71, p < 0.05) and positive correlation with chapati texture (r = 0.58, p < 0.05). Of the SDS extractable polymeric proteins, large polymeric protein in flour protein had significant positive correlation to dough hardness (r = 0.89, p < 0.05) and chapati cutting force, which reflects the chapati texture (r = 0.70, p < 0.05). Protein disulfide content showed positive correlation to dough hardness (r = 0.66, p < 0.05) and texture of chapati (r = 0.58, p < 0.05) while protein thiol content showed significant negative correlation to chapati texture (r = −0.77, p < 0.05). Thus, the results indicate that high proportion of SDS extractable large polymeric protein in flour protein increases the toughness of chapati texture while flours having high thiol content decrease the toughness of chapati.     

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.     

Monitoring the dynamic density of dough during fermentation using digital imaging method

A simple and new method was developed for monitoring the dynamic density of dough during fermentation process. In this method digital imaging was applied to determine volume of dough sample in actual proofing conditions, i.e., temperature and relative humidity of the fermentation oven. The method resulted that the volume increasing profile affected by temperature and relative humidity conditions of the fermentation oven. As when temperature and relative humidity was increased, volume expansion rate was higher. The data also demonstrated that dough density decrease with the investigated proofing temperatures of 25, 30 and 35 °C more significantly (p < 0.01) than proofing relative humidity of 65%, 75% and 85% (p < 0.05). The new imaging method have the advantage of being low cost and measuring dough density in actual proofing conditions as used in bread making.     

A survey of acrylamide precursors in Irish ware potatoes and acrylamide levels in French fries

Reducing sugars (glucose and fructose) and asparagine levels in three varieties of Irish ware potatoes (Rooster, Record and Oilean) on sale in a local supermarket were monitored over an 11-month period. Samples were processed into French fries using conditions similar to those used for home preparation of fries and acrylamide levels in a selection of samples were measured. A wide range of total reducing sugar levels (fructose+glucose) were observed over the course of the study with values ranging from 152-12,286, 301-8812 and 279-7881 μg/g FW for the Rooster, Record and Oilean varieties, respectively. This resulted in high levels of acrylamide in some samples (up to 2970 μg/kg). In comparison to reducing sugars, asparagine contents were relatively constant for the three varieties and no particular trend in asparagine levels was noted. Both fructose and glucose contents of the tubers were positively correlated with acrylamide content (r=0.809, 0.776, respectively, P<0.001). A negative relationship between Hunter L values and acrylamide content of the French fries was observed (r=−0.712, P<0.001) indicating that L values could serve as a convenient and reliable indicator of acrylamide levels in French fries.     

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.     

Development of Chinese steamed bread enriched in bioactive compounds from barley hull and flaxseed hull extracts

Hull from cereal and oilseed grains represent low-cost agricultural materials that have not be fully explored as functional food ingredients. The objectives of the present study were to investigate the phytochemical profile and antioxidant activity of Chinese steamed bread (CSB) containing extracts of barley hull and flaxseed hull. HPLC and LC–MS/MS analyses showed that the phytochemical profile of CSB containing barley hull extract was enriched in ferulic and p-coumaric acids. The flaxseed hull extract introduced secoisolariciresinol diglucoside (SDG), ferulic acid glucoside (FeAG) and coumaric acid glucoside (CouAG) into CSB. All the major phenolic compounds originating from the two types of hulls were found in CSB when barley–flaxseed hull co-extracts were added to the formulation. The total phenolic content was improved by 83.1, 138.3 and 70.3%, respectively when barley, flaxseed, and barley–flaxseed hull extracts were added. The antioxidant activity of CSB containing hull extracts was increased by 34.5–90.7% compared to the control. CSB containing hull extracts had significantly higher (p < 0.05) DPPH radical scavenging activity compared to the control. However, barley–flaxseed hull co-extracts resulted in the highest enhancement of ORAC values of the CSB, although no significant differences were found (p < 0.05). The findings indicate that extracts from barley hull, flaxseed hull and barley–flaxseed can be targeted for development as functional food ingredients that can enhance the phytochemical content of refined flour products, such as steamed bread.     

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.     

Application of Kluyveromyces marxianus, Lactobacillus delbrueckii ssp. bulgaricus and L. helveticus for sourdough bread making

The application of Kluyveromyces marxianus (IFO 288), Lactobacillus delbrueckii ssp. bulgaricus (ATCC 11842) and Lactobacillus helveticus (ATCC 15009) as starter cultures for sourdough bread making was examined. Production of lactic and acetic acids, bread rising, volatile composition, shelf-life and organoleptic quality of the sourdough breads were evaluated. The amount of starter culture added to the flour, the dough fermentation temperature and the amount of sourdough used were examined in order to optimise the bread making process. The use of mixed cultures led to higher total titratable acidities and lactic acid concentrations compared to traditionally made breads. Highest acidity (3.41 g lactic acid/kg of bread) and highest resistance to mould spoilage were observed when bread was made using 50% sourdough containing 1% K. marxianus and 4% L. delbrueckii ssp. bulgaricus. The use of these cultures also improved the aroma of sourdough breads, as shown by sensory evaluations and as revealed by GC–MS analysis.     

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.     

Evaluation of Leuconostoc citreum HO12 and Weissella koreensis HO20 isolated from kimchi as a starter culture for whole wheat sourdough

Leuconostoc citreum HO12 and Weissella koreensis HO20 isolated from kimchi were evaluated as starter cultures in the making of whole wheat sourdough bread. After 24 h of fermentation at 25 °C, both lactobacilli grew to the final cell numbers of ca. 10⁹ cfu/g dough, and both doughs had similar pHs and total titratable acidities. In addition, the fermentation quotient of the dough with Lc. citreum HO12 was slightly lower than that of the dough with W. koreensis HO20 (1.6 versus 2.8). Sourdoughs and bread with 50% sourdough produced with the starter cultures exhibited consistent ability to retard the growth of bread spoilage fungi (Penicillium roqueforti and Aspergillus niger) and rope-forming bacterium (Bacillus subtilis). Sourdough breads underwent a significant reduction in bread firming during storage. It seems that both lactobacilli have the potential to improve the shelf-life of wheat bread. The results indicate that the selected lactobacilli have unique fermentation characteristics and produce sourdough breads with overall satisfactory quality.     

The in vitro protein digestibility,microbiological quality and gelatinization behaviour of macaroni as affected by cowpea flour addition

Cowpeas were germinated, fermented, cooked, ground to flour and added to standard durum wheat semolina at 20% (w/w) level for macaroni production. Macaroni samples were analysed for in vitro protein digestibility, microbial count (total bacteria, mould and yeast) and gelatinization behaviour over a 6-month storage period at room temperature (<25 °C). Starch gelatinization behaviour of the samples was analysed using differential scanning calorimetry. Supplementing semolina with cowpea flour did not have a significant affect on in vitro protein digestibilities or aerobic plate counts of macaroni samples (p < 0.05). There was a small but significant increase in mold and yeast counts after 6 months of storage in cowpea treated samples. Two endothermic peaks were observed with significant differences in ΔH values of control and cowpea treated macaroni samples. The transition peak (T_p) temperatures were in the range of 66.9–67.9 and 86.9–100.4 °C for the first and second peaks, respectively. The transition enthalpies (ΔH) were in the range 2.41–4.21 and 1.71–3.86 J/g for the first and second peaks, respectively.     

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.