Effect of Glutamate Accumulation During Sourdough Fermentation with Lactobacillus reuteri on the Taste of Bread and Sodium‐Reduced Bread

NaCl is an important contributor to the taste and texture of bread; therefore, it is challenging to reduce NaCl in bread without compromising quality. This study investigated sensory properties of bread with sourdough fermented with Lactobacillus reuteri accumulating glutamate or γ‐aminobutyrate (GABA). Sourdough was fermented with the GABA‐producing L. reuteri 100‐23 and LTH5448 as well as the glutamate‐accumulating L. reuteri 100‐23ΔgadB and TMW1.106. A consumer panel detected significant differences in the taste of bread with 6% addition of sourdough fermented with glutamate‐ or GABA‐producing L. reuteri. Remarkably, this difference was also detected when GABA‐producing L. reuteri 100‐23 was compared with its glutamate‐producing isogenic mutant L. reuteri 100‐23ΔgadB. The intensity of the salty taste of sourdough bread produced with 1% (flour basis) salt was equivalent to the intensity of the salty taste of reference bread produced with 1.5% salt. A trained panel found that sourdough breads (1 or 2% NaCl flour base) had a higher sour and umami taste intensity when compared with reference bread with the same salt content. Bread produced with sourdough fermented with L. reuteri 100‐23ΔgadB consistently had a higher umami taste intensity when compared with other sourdough breads. Neither sourdough addition nor NaCl level influenced bread volume or texture. In conclusion, the use of sourdough fermented with glutamate‐accumulating lactobacilli allowed reduction of NaCl without adverse effects on the taste or other quality attributes of bread.     

Neutral Lipids in Free,Bound, and Starch Lipid Extracts of Flours,Sourdough, and Portuguese Sourdough Bread Determined by NP‐HPLC‐ELSD

A detailed analysis was developed, focused on the neutral lipids (NL) in free (FL), bound (BL), and starch lipid (SL) extracts of maize and rye flours, sourdough, and broa (a traditional bread manufactured in Portugal). Selective sequential extraction of said lipids with hexane at 20°C, water‐saturated n‐butanol at 20°C, and n‐propanol‐water (3:1, v/v) at 100°C was performed to clean the lipid extracts from extraneous impurities, and isolation thereof from glyco‐ and phospholipids was by solid phase extraction of NL; these classes were then quantitatively assayed by HPLC, using evaporative light scattering detection, with calibration curves prepared with standard mixtures of NL. The BL and SL contents in the original flours increased and that of FL decreased throughout the fermentation and baking processes. The dominant NL class was not the same in all lipid extracts; the highest concentrations of triacylglycerols and the lowest concentrations of free fatty acids were detected in FL—with the former accounting for 82, 76, and 71% of the total FL in flours, sourdough, and bread, respectively. Triacylglycerols and free fatty acids also accounted for the highest concentrations found in BL: these, together with diacylglycerols, contributed up to 84% of the total neutral BL. High levels of free fatty acids and low levels of the remaining NL classes were typically found in SL: free fatty acids, triacylglycerols, sterol esters, and diacylglycerols accounted for ≈90% of the total SL.     

Quality Requirements of Soft Red Winter Wheat for Making Northern‐Style Chinese Steamed Bread

Flours of 19 soft red winter (SRW) wheat varieties having protein contents of 6.6–9.9% were used to determine the suitability of SRW wheat for making northern‐style Chinese steamed bread (CSB) and the influences of flour characteristics on the quality attributes of CSB. Fourteen varieties produced CSB of acceptable to good quality with a total score greater than 70. Both protein content and dough strength‐related parameters, including sodium dodecyl sulfate sedimentation (SDSS) volume, wet and dry gluten contents, and midline peak time (MPT), were significantly associated with the quality attributes of CSB. The rapid viscosity analyzer setback value exhibited significant negative correlations with specific volume, smoothness, crumb structure, and total score of CSB. Stepwise multiple regression analysis indicated that 89% of variability in total scores of CSB could be predicted from SDSS volume, wet gluten content, and MPT. Contributions of high‐molecular‐weight glutenin subunits 7*+8 and 5+10 to flour characteristics, specific volume, stress relaxation score, and total score of CSB were greater than those of their counterpart allelic variations. Absence of the 1B/1R translocation in SRW wheat varieties was desirable for the production of CSB.     

Characteristics of Noodles and Bread Prepared from Double‐Null Partial Waxy Wheat

Double‐null partial waxy wheat (Triticum aestivum L.) flours were used for isolation of starch and preparation of white salted noodles and pan bread. Starch characteristics, textural properties of cooked noodles, and staling properties of bread during storage were determined and compared with those of wheat flours with regular amylose content. Starches isolated from double‐null partial waxy wheat flours contained 15.4–18.9% amylose and exhibited higher peak viscosity than starches of single‐null partial waxy and regular wheat flours, which contained 22.7–25.8% amylose. Despite higher protein content, double‐null partial waxy wheat flours, produced softer, more cohesive and less adhesive noodles than soft white wheat flours. With incorporation of partial waxy prime starches, noodles produced from reconstituted soft white wheat flours became softer, less adhesive, and more cohesive, indicating that partial waxy starches of low amylose content are responsible for the improvement of cooked white salted noodle texture. Partial waxy wheat flours with >15.1% protein produced bread of larger loaf volume and softer bread crumb even after storage than did the hard red spring wheat flour of 15.3% protein. Regardless of whether malt was used, bread baked from double‐null partial waxy wheat flours exhibited a slower firming rate during storage than bread baked from HRS wheat flour.     

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.     

Formation of Enzyme‐Resistant Starch in Bread as Affected by High‐Amylose Wheat Flour Substitutions

High‐amylose wheat flour was used to substitute for normal wheat flour in breadmaking and formation of resistant starch (RS) in bread during storage was determined. Substitution with high‐amylose wheat flour (HAF) decreased peak and final viscosities, breakdown, and setback. Doughs with HAF substitutions were weaker and less elastic, and absorbed more water than those of the normal wheat flour. After baking, RS contents in breads with 10, 30, and 50% HAF substitutions were 1.6, 2.6, and 3.0% (db), respectively, higher than that of the control (0.9%, db). The levels of RS increased gradually during storage for one, three, and five days. With substitutions of 30 and 50% HAF, the total levels of dietary fiber (DF) and RS in bread after five days of storage were 15.5 and 16.8% (db), respectively, as compared to 13.0% (db) in bread from the normal wheat flour. The loaf volumes and appearances of bread crumbs made from HAF substitutions of 10 and 30% were not significantly different from those of the control, whereas the substitution with 50% HAF decreased loaf volume and resulted in inferior appearance of breadcrumbs. The firmness of breadcrumbs increased along with increase in the level of HAF substitutions after baking. During storage, the firmness of breadcrumb with 10% HAF substitutions was higher than that of the control, whereas breads with 30 and 50% HAF substitutions had similar firmness to the control. As a result, HAF might be used to substitute for up to 50% normal wheat flour to make bread with acceptable bread quality and significantly high amount of RS.     

Effects of Bran Fermentation on Quality and Microstructure of High‐Fiber Wheat Bread

We compared the effects of spontaneous fermentation of the bran fraction and fermentation with added yeast or added yeast and lactic acid bacteria (Lactobacillus brevis) on the quality of wheat bread supplemented with bran. Prefermentation of wheat bran with yeast or with yeast and lactic acid bacteria improved the loaf volume, crumb structure, and shelf life of bread supplemented with bran. The bread also had added flavor and good and homogenous crumb structure. Elasticity of the crumb was excellent. Spontaneous fermentation of the bran fraction did not have the same positive effects on bread quality. The microstructure of the breads was characterized by light microscopy. The positive effect of fermentation of bran on bread quality was evident when comparing the well‐developed protein network structure of the breads baked with fermented bran with the control bread. Prefermentation of the bran with yeast and lactic acid bacteria had the greatest effect on the structure of starch. The starch granules were more swollen and gelatinized in the breads made with prefermented bran. The pretreatments of the bran fraction had no detectable effect on the microstructure of the cell wall particles in the test breads.     

Comparison of Near‐Infrared Reflectance Spectroscopy and Texture Analyzer for Measuring Wheat Bread Changes in Storage

Bread staling affects bread texture properties and is one of the most common problems in bread storage. Bread firmness, as measured in compression mode by a texture analyzer (TA) has been commonly used to measure bread staling. This study investigated the potential of visible and near‐infrared reflectance spectroscopy (NIRS) to detect bread changes during storage by comparing NIRS results with those obtained by TA. Twenty‐five loaves of commercial wheat white pan bread from one batch were studied over five days. NIRS and TA measurements were made on the same slice at approximately the same time. The experiment was repeated five times using the same kind of commercial samples from five different batches. NIRS measurements of slices, loaf averages, and daily averages were compared with TA measurements. NIRS spectra had a high correlation to TA firmness. NIRS measurements correlated better with the actual storage time and had smaller standard deviations than the TA measurements. The batch differences had less effect on NIRS measurements than on the TA measurements. The results indicate that NIRS could follow bread changes during storage more accurately than the TA. NIRS is probably based on both physical and chemical changes during bread staling, unlike the TA method that only measures bread firmness, which is only one aspect of the staling phenomenon.     

乳酸菌发酵豆渣酸面团对馒头面团特性和馒头品质的影响

为促进大豆副产物资源利用,开发新型营养面制品,本试验以豆渣为原料,利用柠檬明串珠菌E12为发酵剂制作豆渣酸面团,探究不同豆渣酸面团添加量(0%、20%、30%和40%)对馒头面团(对应编号分别为S0、S20、S30和S40)发酵活力、动态流变特性、抗氧化特性以及膳食纤维含量的影响,并研究豆渣酸面团馒头(对应编号分别为CS0、CS20、CS30和CS40)的感官品质,以及在贮藏期间馒头质构和水分含量的变化。结果表明,添加豆渣酸面团会降低馒头面团的弹性、黏性和综合黏弹性。馒头面团的抗氧化特性以及膳食纤维含量随着豆渣酸面团添加量的增加而显著增加;当添加量为40%时,S40馒头面团的1,1-二苯基-2-三硝基苯肼(DPPH)自由基清除率和2,2-联氮-二(3-乙基-苯并噻唑-6-磺酸)二铵盐(ABTS)自由基清除率分别达到15.61%和79.59%,比S0增加了5.10和15.02个百分点,总膳食纤维含量达到3.91 g·100g^-1,比S0增加了138.79%。豆渣酸面团的添加量为20%时,CS20馒头的比容和延展率与CS0相比无显著差异,但对馒头的外观、色泽、风味和口感产生了积极影响,整体可接受度达到7.8。在贮藏5 d后,CS0的硬度、咀嚼性和胶着性分别增加了180.85%、69.62%和98.08%,而CS40分别增加了76.19%、30.88%和33.96%,与CS0相比增加量显著减小,且在贮藏期间CS40的水分含量始终高于CS0,表明豆渣酸面团有利于减缓馒头的老化。本研究为实现豆渣资源的合理化应用以及新型营养的酸面团产品开发提供了一定的理论基础。     

Network Formation in Gluten‐Free Bread with Application of Transglutaminase

One of the main problems associated with gluten‐free bread is obtaining a good structure. Transglutaminase (TGase), an enzyme that catalyzes acyl‐transfer reactions through which proteins can be cross‐linked could be a way to improve the structure of gluten‐free breads. The objective of this study was to evaluate the impact of TGase at different levels (0, 0.1, 1, and 10 U of TGase/g of protein) on the quality of gluten‐free bread. The recipe consisted of white rice flour (relative amount: 35), potato starch (30), corn flour (22.5), xanthan gum (1), and various protein sources (skim milk powder [SMP] [12.5], soya flour, and egg powder). The influence of the various proteins in combination with the different addition levels of TGase on bread quality (% bake loss, specific volume, color, texture, image characteristics, and total moisture) was determined. Confocal laser‐scanning microscopy (CLSM) was used to evaluate the influence of TGase on the microstructure of the bread. Baking tests showed that TGase had an effect on the specific volume of the bread. For instance, the SMP bread with 10 U of enzyme contained the most compact structure, which was reflected in the crumb texture profile analysis results (highest values) (P < 0.05), digital image analysis (highest level of cells/cm²) (P < 0.05), and CLSM micrographs (network formation). Finally, it can be concluded that it is possible to form a protein network in gluten‐free bread with the addition of TGase. However the efficiency of the enzyme is dependent on both the protein source and the level of enzyme concentration.     

Environmental Effects on Developing Wheat as Sensed by Near‐Infrared Reflectance of Mature Grains

For 30 years, near‐infrared (NIR) spectroscopy has routinely been applied to the cereal grains for the purpose of rapidly measuring concentrations of constituents such as protein and moisture. The research described herein examined the ability of NIR reflectance spectroscopy on harvested wheat to determine weather‐related, quality‐determining properties that occurred during plant development. Twenty commercial cultivars or advanced breeding lines of hard red winter and hard white wheat (Triticum aestivum L.) were grown in 10 geographical locations under prevailing natural conditions of the U.S. Great Plains. Diffuse reflectance spectra (1,100–2,498 nm) of ground wheat from these samples were modeled by partial least squares one (PLS1) and multiple linear regression algorithms for the following properties: SDS sedimentation volume, amount of time during grain fill in which the temperature or relative humidity exceeded or was less than a threshold level (i.e., >30, >32, >35, <24°C; >80%, <40% rh). Rainfall values associated with four pre‐ and post‐planting stages also were examined heuristically by PLS2 analysis. Partial correlation analysis was used to statistically remove the contribution of protein content from the quantitative NIR models. PLS1 models of 9–11 factors on scatter‐corrected and (second order) derivatized spectra produced models whose dimensionless error (RPD, ratio of standard deviation of the property in a test set to the model standard error for that property) ranged from 2.0 to 3.3. Multiple linear regression models, involving the sum of four second‐derivative terms with coefficients, produced models of slightly higher error compared with PLS models. For both modeling approaches, partial correlation analysis demonstrated that model success extends beyond an intercorrelation between property and protein content, a constituent that is well‐modeled by NIR spectroscopy. With refinement, these types of NIR models may have the potential to provide grain handlers, millers, and bakers a tool for identifying the cultural environment under which the purchased grain was produced.     

White Pan Bread and Sugar‐Snap Cookies Containing Wheat Starch Phosphate,A Cross‐Linked Resistant Starch

Pup‐loaf bread was made with 10, 30, and 50% substitution of flour with wheat starch phosphate, a cross‐linked resistant starch (XL‐RS4), while maintaining flour protein level at 11.0% (14% mb) by adding vital wheat gluten. Bread with 30% replacement of flour with laboratory‐prepared XL‐RS4 gave a specific volume of 5.9 cm³/g compared with 6.3 g/cm³ for negative control bread (no added wheat starch), and its crumb was 53% more firm than the control bread after 1 day at 25°C, but 13% more firm after 7 days. Total dietary fiber (TDF) in one‐day‐old bread made with commercial XL‐RS4 at 30% flour substitution increased 3–4% (db) in the control to 19.2% (db) in the test bread, while the sum of slowly digestible starch (SDS) plus resistant starch (RS), determined by a modified Englyst method, increased from 24.3 to 41.8% (db). The reference amount (50 g, as‐is) of that test bread would provide 5.5 g of dietary fiber with 10% fewer calories than control bread. Sugar‐snap cookies were made at 30 and 50% flour replacement with laboratory‐prepared XL‐RS4, potato starch, high‐amylose (70%) corn starch, and commercial heat‐moisture‐treated high‐amylose (70%) corn starch. The shape of cookies was affected by the added starches except for XL‐RS4. The reference amount (30 g, as‐is) of cookies made with commercial XL‐RS4 at 30% flour replacement contained 4.3 g (db) TDF and 3.4 g (db) RS, whereas the negative control contained 0.4 g TDF and 0.6 g RS. The retention of TDF in the baked foods containing added XL‐RS4 was calculated to be >80% for bread and 100% for cookies, while the retention of RS was 35–54% for bread and 106–113% for cookies.     

Accumulation of High‐Molecular‐Weight Glutenin Subunits in Superior and Inferior Grains of a Winter Wheat,Yangmai 158

The difference in accumulation of high‐molecular‐weight glutenin subunits (HMW‐GS) in superior (basal) and inferior (distal) grains results in the nonuniformity of grain quality in a winter wheat (Triticum aestivum L. ‘Yangmai 158’). The HMW‐GS accumulation and glutenin macropolymer (GMP) content were studied in superior and inferior grains during the grain‐filling period. Compared with inferior grains, HMW‐GS was formed earlier and total accumulation amount was higher in superior grains. The total HMW‐GS content was higher in superior grain than inferior grain, except at maturity. For individual HMW‐GS types, the accumulation and content of subunit 7 were the highest, followed by subunit 12, and those of subunit 8 were the lowest, followed by subunit 2 in superior grain. In contrast, the accumulation and content of subunit 7 at maturity were significantly higher than subunit 8 but similar between subunit 2 and subunit 12 in inferior grain. Moreover, the accumulation of subunit 7 and 12 in superior grain was significantly higher than in inferior grain. However, compared with the inferior grain, the GMP accumulation was higher but content was lower in superior grain at maturity.     

Association Between % SDS‐Unextractable Polymeric Protein (%UPP) and End‐Use Quality in Chinese Bread Wheat Cultivars

Trial I, with 33 spring cultivars, and trial II, with 21 winter cultivars, sown in four environments in the northwestern China spring wheat region and northern winter wheat region, respectively, were used to study the effect of genotype and environment on the size distribution of polymeric proteins. Association between quantity and size distribution of polymeric protein and dough properties (both trials) and northern‐style Chinese steamed‐bread (CSB) (trial I) and pan bread (trial II) qualities were also investigated. In trial I, all protein attributes, such as flour protein content, SDS‐extractable polymeric protein in the flour (EPP), SDS‐unextractable polymeric protein in the flour (UPP), and percent UPP in total polymeric protein (%UPP), were largely determined by environment, whereas variation in dough strength resulted from variation in UPP and %UPP across environments. In trial II, EPP was largely determined by environment, and UPP and %UPP were largely determined by genotype. These differences might result from different levels of protein content and dough strength in the two trials. The EPP was positively correlated with dough extensibility and was generally negatively correlated with dough stability and maximum resistance in both trials. However, %UPP was significantly positively correlated with dough stability and maximum resistance and end‐use quality in both trials. In trial I, correlation coefficients between %UPP and maximum resistance and CSB score were r = 0.90 and 0.71, respectively, whereas in trial II, the correlation coefficients between %UPP and maximum resistance and pan bread score were 0.96 and 0.87, respectively. Therefore, selection for high %UPP together with high‐quality glutenin subunits should lead to improved dough strength and end‐use quality in Chinese wheats.     

Effects of Mutant Thermostable α‐Amylases on Rheological Properties of Wheat Dough and Bread

Thermostable mutant α‐amylases (21B, M111, and M77) with various degrees of thermostability were purified from Bacillus amyloliquefaciens F and used as improvers for breadmaking. Test baking with the mutant enzymes was conducted using the long fermentation sponge‐dough method. Addition of an appropriate amount of mutant α‐amylases to the ingredients distinctly increased the specific volume of the bread and improved the softness of breadcrumb as compared with the addition of Novamyl (NM), an exo‐type α‐amylase. M77 was the most effective in retarding the staleness of breadcrumb. The softness of breadcrumb during storage, however, was not correlated with the thermostability. All mutant α‐amylases weakened the mixing property of the dough, whereas they strengthened the property of fermented dough. Especially, M77 and NM had different effects on the dough properties, but their bread qualities were similar to each other. The strong tolerance of M77 dough to the long baking process might be due to the production of hydrolyzed starches, oligosaccharides in the range of maltopentaose to maltohexaose, as compared with NM. Therefore, in the light of present findings, these mutant α‐amylases are possible substitutes for NM as bread improvers.     

Application of Response Surface Methodology in the Development of Gluten‐Free Bread

The formulation of gluten‐free (GF) bread of high quality presents a formidable challenge as it is the gluten fraction of flour that is responsible for an extensible dough with good gas‐holding properties and baked bread with good crumb structure. As the use of wheat starch in GF formulations remains a controversial issue, naturally GF ingredients were utilized in this study. Response surface methodology was used to optimize a GF bread formulation primarily based on rice flour, potato starch, and skim milk powder. Hydroxypropylmethylcellulose (HPMC) and water were the predictor variables. Analyses of the treatments from the design were made 24 hr after baking. Specific volume and loaf height increased as water addition increased (P < 0.01). Crumb firmness decreased as water levels increased (P < 0.01). Significant interactions (P < 0.01) between HPMC and water were found for the number of cells/cm². The number of large cells (>4 mm²) decreased with increasing levels of HPMC and water. Optimal ingredient levels were determined from the data obtained. The optimized formulation contained 2.2% HPMC and 79% water flour/starch base (fsb) and measured responses compared favorably to predicted values. Shelf‐life analysis of the optimized formulation over seven days revealed that, as crumb firmness increased, crust firmness and crumb moisture decreased.     

REVIEW: Aroma of Wheat Bread Crumb

Bread aroma is an important parameter for bread quality, and this review aims to provide an overview of aroma compounds identified in bread crumb and how these compounds are formed. More than 150 volatile compounds were identified in bread crumb, and they mainly originated from the fermentative activity of yeast, from oxidation of flour lipids, and to a lower extent from Maillard reactions. Of those volatile compounds, 45 compounds can be characterized as aroma compounds, because they most likely can be sensed when the bread is eaten because of their high odor activity values and flavor dilution factors. The influence of ingredients and mixing conditions on bread aroma has scarcely been investigated. The fermentation conditions (yeast level and strain as well as fermentation temperature and time) were found to significantly influence the aroma of bread crumb. Yeast level and strain mainly influence formation of compounds directly related to the fermentative activity of yeast, whereas fermentation temperature and time also influence formation of compounds from oxidation of flour lipids.     

Effects of Varying Weight Ratios of Large and Small Wheat Starch Granules on Experimental Straight‐Dough Bread

One commercial bread wheat flour with medium strength (11.3% protein content, 14% mb) was fractionated into starch, gluten, and water solubles by hand‐washing. The starch fraction was separated further into large and small granules by repeated sedimentation. Large (10–40 μm diameter) and small (1–15 μm diameter) starch fractions were examined. Flour fractions were reconstituted to original levels in the flour using composites of varying weight percentages of starch granules: 0% small granules (100% large granules), 30, 60, and 100% (0% large granules). A modified straight‐dough method was used in an experimental baking test. Crumb grain and texture were significantly affected. The bread made from the reconstituted flour with 30% small granules and 70% large granules starch had the highest crumb grain score (4.0, subjective method), the highest peak fineness value (1,029), and the second‐highest elongation ratio (1.55). Inferior crumb grain scores and low fineness and elongation ratios were observed in breads made from flours with starch fractions with 100% small granules or 100% large granules. As the proportion of small granules increased in the reconstituted flour, it yielded bread with softer texture that was better maintained than the bread made from the reconstituted reference flour during storage.     

Changes in Phytate Content in Whole Meal Wheat Dough and Bread Fermented with Phytase‐Active Yeasts

The degradation of inositol hexakisphosphate (IP6) was evaluated in whole meal wheat dough fermented with baker's yeast without phytase activity, different strains of Saccharomyces cerevisiae (L1.12 or L6.06), or Pichia kudriavzevii with extracellular phytase activity to see if the degradation of IP6 in whole meal dough and the corresponding bread could be increased by fermentation with phytase‐active yeasts. The IP6 degradation was measured after the dough was mixed for 19 min, after the completion of fermentation, and in bread after baking. Around 60–70% of the initial value of IP6 in the flour (10.02 mg/g) was reduced in the dough already after mixing, and additionally 10–20% was reduced after fermentation. The highest degradation of IP6 was seen in dough fermented with the phytase‐active yeast strains S. cerevisiae L1.12 and P. kudriavzevii L3.04. Activity of wheat phytase in whole meal wheat dough seems to be the primary source of phytate degradation, and the degradation is considerably higher in this study with a mixing time of 19 min compared with earlier studies. The additional degradation of IP6 by phytase‐active yeasts was not related to their extracellular phytase activities, suggesting that phytases from the yeasts are inhibited differently. Therefore, the highest degradation of IP6 and expected highest mineral bioavailability in whole meal wheat bread can be achieved by use of a phytase‐active yeast strain with less inhibition. The strain S. cerevisiae L1.12 is suitable for this because it was the most effective yeast strain in reducing the amount of IP6 in dough during a short fermentation time.     

Volatile Compounds in Crumb of Whole‐Meal Wheat Bread Fermented with Different Yeast Levels and Fermentation Temperatures

The influence of fermentation temperatures (8, 16, and 32°C) and yeast levels (2, 4, and 6%) on the formation of volatile compounds in the crumb of whole‐meal wheat bread was investigated. Volatile compounds were extracted by dynamic headspace extraction and analyzed by gas chromatography–mass spectrometry. Results were evaluated with multivariate data analysis and ANOVA. Bread fermented at a high temperature (32°C) had higher peak areas of the Maillard reaction products 2‐furancarboxaldehyde, 2‐acetylfuran, 2‐methylpyrazine, and phenylacetaldehyde compared with bread fermented at lower fermentation temperatures. Bread fermented at low temperatures (8 and 16°C) was characterized by having higher peak areas of the fermentation products 3‐methylbutanal, 2‐methylbutanal, ethyl acetate, ethyl hexanoate, ethyl propanoate, and 3‐methylbutanol. Fermentation of bread with 6% yeast resulted in a higher peak area of the important fermentation product 2‐phenylethanol. It also reduced the peak areas of important lipid oxidation products. The peak area of 2,3‐butanedione was also relatively higher in bread fermented with 6% yeast compared with lower yeast levels; however, an interaction was seen between the high yeast level and all three fermentation temperatures. In contrast, fermentation with a low yeast level (2%) resulted in bread with relatively higher peak areas of 2‐ and 3‐methylbutanal, as well as (E)‐2‐nonenal and (E,E)‐2,4‐decadienal, which are important lipid oxidation compounds in bread.