Kinetics of transglutaminase-induced cross-linking of wheat proteins in dough

The effects of TGase in dough after 15, 30, 45, and 60 min of resting time after mixing were studied with a Kieffer test. The resistance to stretching of control dough did not change greatly during the 60 min time period after mixing. In dough, TGase decreased extensibility and increased resistance to stretching and this change was already observed after the first 15 min (first measurement). The higher the enzyme dosage was, the higher the magnitude of the rheological change was. All of the doughs that contained TGase 3.8 or 5.7 nkat/g flour had a higher resistance to stretching and lower extensibility than control dough 15 min after mixing. Resistance to stretching clearly increased at a dosage of 5.7 nkat/g flour during the 15-60 min period after mixing. Extensibility increased in the control dough and in the doughs with a low enzyme dosage almost at the same rate. The evolution of air bubbles during proofing was determined with bright field microscopy and image analysis. In the presence of 5.7 nkat/g TGase, the fermented dough contained more of the smallest and less large air bubbles in comparison to the control dough. The effect of TGase and water content on the specific volume of the conventional and organic wheat bread was studied. Water did not have a significant effect on the specific volume of bread. TGase increased the specific volume of breads baked from organic flour only, when additional water (+10% of farinogram absorption) and a small enzyme dosage were used. Microstructural characterization showed that bread baked without TGase from conventional flour had a stronger protein network than that baked from organic flour. TGase improved the formation of protein network in breads baked from either normal or organic flour but at higher dosage caused uneven distribution.     

Effect of Mixing Time and Speed on Experimental Baking and Dough Testing with a 200 g Pin Mixer

Undermixing or overmixing the dough results in varied experimental loaf volumes. Bread preparation requires a trained baker to evaluate dough development and determine the stop points of the mixer. Instrumentation and electronic control of the dough mixer would allow for automatic mixing. This study used a 200 g mixer that provided an output signal during dough mixing to evaluate potential mixing stop points. The effect of varied mixing time on the baked loaf volume was tested by using three flours with protein contents of 10.6, 12.4, and 13.8%. Dough samples were undermixed, mixed to peak, and overmixed. Overmixing by 0.6 min reduced the loaf volume in all flours tested, by 16–50 cm³ at 90 rpm and by 29–68 cm³ at 118 rpm. When the high‐protein flour sample was undermixed, the largest baked loaves were produced, with an average volume of 922 cm³. A second objective studied the similarities and differences between a 200 g mixer and a 35 g mixograph. The same flours were mixed on both units. The mixing peaks for the 200 g mixer were normalized with the 35 g mixograph peaks. When flour and water were used, the mixing times for the 200 g mixer averaged 0.7, 1.2, and 1.6 min shorter than the 35 g mixograph, at 90, 104, and 118 rpm, respectively. Although both the 200 g mixer and the 35 g mixograph system look mechanically similar, they both have unique mechanical motion, speeds, and sample sizes. Their results may show similar trends, but their measured values are usually different. However, when other baking ingredients were included in the 200 g mixer at 90 rpm, the mixing times were within 0.2 min of the 35 g mixograph times for three of four flours.     

Competition for Oxygen Among Oxidative Systems During Bread Dough Mixing: Consequences of Addition of Glucose Oxidase and Lipoxygenase on Yeasted Dough Rheology

The effect on O₂ uptake during the mixing of yeasted dough, either unsupplemented or supplemented with glucose oxidase (GOX), horsebean flour (HB), soybean flour (SB), or combinations thereof, was studied using an airtight mixer. Two wheat flours with a low (flour A) and a high (flour B) content of free polyunsaturated fatty acids were used. Addition of HB or SB provokes a similar increase of O₂ uptake for both wheat flours, whereas addition of GOX causes a larger increase for flour A than for flour B. When the wheat flours were supplemented with HB or SB, addition of GOX caused a small but significant increase of O₂ uptake for flour A. This increase was not observed for flour B. The mixing tolerance of dough A, determined with the Chopin Consistograph, is increased by GOX addition. However, this effect is less pronounced when flour A is supplemented with HB or SB. Similarly, the relaxation index of dough B is decreased by GOX addition, but the decrease is less distinct in the presence of HB or SB. These results can be explained by a competition among yeast, GOX, and lipoxygenases (present in wheat, HB, and SB flours) for the O₂ uptake by dough, which likely decreases the amount of hydrogen peroxide produced by GOX during dough mixing. This competition for O₂ consequently also modifies the rheological properties of dough.     

Application of a Micro Z‐Arm Mixer to Characterize Mixing Properties and Water Absorption of Wheat Flour

This study applied the use of a new small‐scale apparatus, the micro Z‐arm mixer, which has analogous mixing action to that of the traditional valorigraf and farinograph. A novel methodology has been developed for prediction of water absorption replacing the traditional titration method. The basis of this technique is a common characteristic of wheat flour samples: a reasonably constant slope (20–25.7 BU%) of the relationship between dough resistance and the amount of water present during mixing. Using an average slope value, prediction of water absorption was possible from a single measurement using a simple equation and with a standard error of 1.65%. Applications of the new mixer to cereal research are highlighted, including investigation of the effects of flour protein content and protein composition on mixing properties and water absorption. When protein content and protein composition have been systematically altered by the addition of isolated proteins into the flour, both dough development time (DDT) and water absorption increased when protein content was increased by glutenin addition and decreased when protein content was decreased by starch addition. Gliadin addition decreased DDT; gluten addition slightly increased DDT; glutenin addition significantly increased DDT. Water absorption was not affected by altering the glutenin‐to‐gliadin ratio, but it changed in proportion to the amount of protein added. The effect of HMW‐GS composition on the mixing requirement obtained with the micro Z‐arm mixer and with the 2‐g mixograph was also investigated using a set of single‐, double‐, and triple‐null lines for HMW‐GS coding genes. While subunits coded on the GluD1 locus were most important for determining the mixing requirement in both cases, the sample ranking was different in the two mixing actions. A better differentiation ability of the micro Z‐arm mixer was established for triple‐ and double‐null lines.     

Studies on proofing of yeasted bread dough using near- and mid-infrared spectroscopy

Dough proofing is the resting period after mixing during which fermentation commences. Optimum dough proofing is important for production of high quality bread. Near- and mid-infrared spectroscopies have been used with some success to investigate macromolecular changes during dough mixing. In this work, both techniques were applied to a preliminary study of flour doughs during proofing. Spectra were collected contemporaneously by NIR (750-1100 nm) and MIR (4000-600 cm(-1)) instruments using a fiberoptic surface interactance probe and horizontal ATR cell, respectively. Studies were performed on flours of differing baking quality; these included strong baker's flour, retail flour, and gluten-free flour. Following principal component analysis, changes in the recorded spectral signals could be followed over time. It is apparent from the results that both vibrational spectroscopic techniques can identify changes in flour doughs during proofing and that it is possible to suggest which macromolecular species are involved.     

Determining Wheat Dough Mixing Characteristics from Power Consumption Profile of a Conventional Mixer

A Hobart mixer with a pin‐type attachment was used to mix soft wheat flour dough. Power consumption profiles were measured continuously during mixing for 20 min using a current transducer and a data logging system. Experimental variables were quantity of flour (500, 1,000, and 1,500 g of dry wheat flour), water content (43, 45, and 47%, wb), and mixer speed setting (low, medium, and high). The power consumption profiles were evaluated by moving average and spectral analysis. Peaks in the power consumption profiles were located to determine the optimal mixing time. The optimal mixing times were then compared with storage and viscous moduli measured using a dynamic rheometer to assure the maximum strength of wheat dough at the optimal mixing time. Tolerance was determined using the signal amplitude and phase angle data from spectral analysis. Optimal mixing times of various doughs at medium speed ranged from 510 to 850 sec; low and high flour quantities required longer mixing times than medium quantity of flour. The optimal mixing time increased when the moisture content was lowered. Tolerance was affected by mixing speed and moisture content of flour     

Structural Modifications of Gluten Proteins in Strong and Weak Wheat Dough During Mixing

The network‐forming attributes of gluten have been investigated for decades, but no study has comprehensively addressed the differences in gluten network evolution between strong and weak wheat types (hard and soft wheat). This study monitored changes in SDS protein extractability, SDS‐accessible thiols, protein surface hydrophobicity, molecular weight distribution, and secondary structural features of proteins during mixing to bring out the molecular determinants of protein network formation in hard and soft wheat dough. Soft wheat flour and dough exhibited greater protein extractability and more accessible thiols than hard wheat flour and dough. The addition of the thiol‐blocking agent N‐ethylmaleimide (NEM) resulted in similar results for protein extractability and accessible thiols in hard and soft wheat samples. Soft wheat dough had greater protein surface hydrophobicity than hard wheat and exhibited a larger decrease in surface hydrophobicity in the presence of NEM. Formation of high‐molecular‐weight (HMW) protein in soft wheat dough was primarily because of formation of disulfides among low‐molecular‐weight (LMW) proteins, as indicated by the absence of changes in protein distribution when NEM was present, whereas in hard wheat dough the LMW fraction formed disulfide interaction with the HMW fraction. Fourier transform infrared spectroscopy indicated formation of β‐sheets in dough from either wheat type at peak mixing torque. Formation of β‐sheets in soft wheat dough appears to be driven by hydrophobic interactions, whereas disulfide linkages stabilize secondary structure elements in hard wheat dough.     

Understanding and Modeling the Processing‐Mechanical Property Relationship of Bread Crumb Assessed by Indentation

Measuring fundamental mechanical parameters such as Young's modulus and critical stress is a straightforward and valid approach to evaluating the physical texture of breadcrumb. The objectives of this study were to evaluate whether such fundamental mechanical properties could be measured by indentation techniques such as the AACC crumb firmness method, and then to alter breadmaking conditions so as to model the relationship between these indentation mechanical properties as a function of crumb moisture content and crumb density. Bread was baked according to a short dough process using Canadian western red spring (CWRS) wheat flour. Factors considered in the design of experiments were proofing time, water absorption, crosshead speed, and indenter diameter. Young's modulus and critical stress, measured with 12‐ and 20‐mm cylindrical indenters, were well covalidated with those obtained from a standard compression test. With increases in proofing time and water absorption, a more porous and compliant bread texture led to decreasing Young's modulus and critical stress. Our results revealed a good mapping of mechanical properties to crumb moisture content and density that were correlated to breadmaking conditions, thus permitting more precise prediction of the mechanical properties that determine bread texture.     

Effects of Genotype and Environment on Glutenin Polymers and Breadmaking Quality

Six genotypes of hard red spring (HRS) wheat were grown at seven environments in North Dakota during 1998. Effects of genotype and environment on glutenin polymeric proteins and dough mixing and baking properties were examined. Genotype, environment, and genotype‐by‐environment interaction all significantly affected protein and dough mixing properties. However, different protein and quality measurements showed differences for relative influences of genotype and environment. Total flour protein content and SDS‐soluble glutenin content were influenced more by environmental than genetic factors, while SDS‐insoluble glutenin content was controlled more by genetic than environmental factors. Significant genotypic and environmental effects were found for the size distribution of SDS‐soluble glutenins and between SDS‐soluble and SDS‐insoluble glutenins as well as % SDS‐insoluble glutenins. With increased flour protein content, the proportions of monomeric proteins and SDS‐insoluble glutenin polymers appeared to increase, but SDS‐soluble glutenins decreased. Flour protein content and the size distribution between SDS‐soluble and SDS‐insoluble glutenin polymers were significantly correlated with dough mixing properties. Environment affected not only total flour protein content but also the content of different protein fractions and size distributions of glutenin polymers, which, in turn, influenced properties of dough mixing. Flour protein content, % SDS‐insoluble glutenin polymers in flour, and ratio of SDS‐soluble to SDS‐insoluble glutenins all were highly associated with dough mixing properties and loaf volume.     

Quantitative Assessment of Gas Cell Development During the Proofing of Dough by Magnetic Resonance Imaging and Image Analysis

The structure of bread crumb is an important factor in consumer acceptance of bakery products. The noninvasive monitoring of the gas cell formation during the proofing of dough can aid in understanding the mechanisms governing the crumb appearance in the baked product. The development of gas cells during the proofing of dough was monitored in a noninvasive manner using magnetic resonance imaging (MRI) at 4.7‐T. The acquired MRI time series were analyzed quantitatively using image analysis (IA) techniques. The effects of both kneading temperature and mechanical damage by molding were studied. When additional rheological stress was introduced during molding, a more heterogeneous (coarse) gas cell size distribution was observed, and the dough had a smaller specific volume (as measured by MRI). These characteristics were preserved in the bread crumb structure after baking. The fast‐deformation during molding also resulted in an isotropic growth of the dough during proofing, whereas slow‐deformation during molding resulted in anisotropic growth. This can be related to a better conservation of stress in the dough under a moderate molding operation. A higher temperature during kneading also resulted in a coarser distribution of the gas cells and a smaller MRI specific dough volume. No effect of kneading temperature on the growth anisotropy could be detected, however. This indicates that temperature has a smaller effect on the conservation of stress in the dough than molding. The current work illustrates the capability of MRI/IA for understanding and predicting the influence of food processing parameters on consumer‐relevant features in a food product (bread).     

Investigation of a Small‐Scale Asymmetric Centrifugal Mixer for the Evaluation of Asian Noodles

A high throughput centrifugal mixer capable of using smaller amounts of flour (50 g) was evaluated for the production of oriental alkaline noodles. The unit requires a small footprint on a laboratory bench and offers variable speed mixing (300–3,500 rpm) for 5–60 sec. Three different mixing bowls, plain, pin, and paddle, were evaluated for the small‐scale production of alkaline noodles using straight‐grade flour derived from Canada Western Red Spring (CWRS) and Canada Prairie White Spring (CPSW) wheat. Under optimized mixing conditions (3,000 rpm for 30 sec), the pin and paddle bowls produced noodle dough with crumb size distribution and adhesion characteristics consistent with commercial requirements. The plain bowl produced dough with larger undesirable dough chunks and showed excessive heat buildup. Noodle sheets produced from this dough were not comparable in color characteristics to conventionally produced noodle sheets. Noodles prepared using the paddle mixer also displayed some significantly different color and texture characteristics than conventionally prepared noodles. However, raw noodle sheets or cooked noodles of either wheat class, prepared using the pin bowl mixer, displayed color values (L*, a*, and b*) at 2 and 24 hr and cooked noodle texture characteristics (bite, chewiness, resistance to compression, and recovery) comparable to a conventional laboratory‐scale Hobart type mixer. In addition to the very short mixing time and small equipment footprint for the centrifuge mixer, rapid throughput is enhanced by the ability to rapidly clean or interchange bowls and to potentially vary sample size to as little as 5 g. These attributes should be particularly useful in earlier generation breeder programs where large numbers of samples require rapid screening.     

Proteins Extracted by Water or Aqueous Ethanol During Refining of Developed Wheat Dough to Vital Wheat Gluten and Crude Starch as Determined by Capillary‐Zone Electrophoresis (CZE)

Fluids applied to large‐sale, technical separation of wheat starch and protein also extract soluble proteins. The degree and rate of extraction and the specific components extracted depend on the flour, the flour hydration and development, the starch‐displacing fluid composition, the temperature, and the mechanical processing method. This study sought to identify major extracted protein groups using high‐performance capillary zone electrophoresis (CZE) applied directly to fluids obtained during laboratory‐scale technical separations. A dough‐ball or compression separation method was applied using a Glutomatic system and a batter or dispersion method was applied using a a McDuffie mixer and Pharmasep vibratory separator. Process fluids were water at 22°C to model commercial practice and 70 vol% ethanol in water at ‐13°C to model the cold ethanol process being developed here. Data were referenced to use of 70 vol% ethanol in water at 22°C in the Glutomatic compression method. The dough processed by each method was developed by mixing to a separable state. When flooded with excess water, this dough immediately released starch and water‐soluble or albumin proteins. When flooded with excess cold aqueous ethanol, neither the albumin nor gliadin proteins appeared in significant amounts until the bulk of the starch had been displaced, regardless of the mechanical method. Even with extraction and manipulation well beyond that necessary for starch displacement, the net amount of gliadin proteins dissolved was only ≈10% of that available from wet developed dough using 70 vol% ethanol at 22°C. There was more gliadin protein in the fluids at earlier stages of processing when the batter dispersion method was applied using cold ethanol. The most common soluble proteins revealed in the electrophoresis patterns for the batter compression method using cold aqueous ethanol were initially albumins and later γ‐gliadins. Albumins not appearing as soluble in cold 70 vol% ethanol were found in the insoluble crude starch, suggesting their precipitation in the dough fluids during the change from free water to cold aqueous ethanol. These results establish that some protein is dissolved during starch displacement by cold aqueous ethanol, but that the amounts may be limited by control of the mechanical working of the dough in the presence of the displacing fluids.     

Effect of Mixing Time on Gluten Recovered by Ultracentrifugation Studied by Microscopy and Rheological Measurements

The effect of mixing time on gluten formation was studied for four commercial flour mixtures. The gluten phase was separated from dough using a nondestructive ultracentrifugation method. Small deformation dynamic rheological measurements and light and scanning electron microscopy were used. The recovered gluten was relatively pure with a small amount of starch granules embedded. The protein matrix observed by microscopy became smoother with prolonged mixing. No effect of overmixing was observed on the storage modulus (G′) of gluten for any of the flours. The amount of water in gluten increased from optimum to over‐mixing for most of the flours. Increased water content during prolonged mixing was not related to an effect on G′. The Standard flour resulted in the highest water content of gluten, which increased considerably with mixing time. The Strong flour had the lowest G′ of dough, a high G′ of gluten, and no increase in gluten water content from optimum to over‐mixing. The Durum flour did not show gluten development and breakdown similar to the other flours. The differences in gluten protein network formation during dough mixing are genetically determined and depend on the flour type.     

Changes in Distribution of Isoflavones and β‐Glucosidase Activity During Soy Bread Proofing and Baking

Bread made partially with soy may represent a viable alternative for increasing soy consumption in populations consuming Western diets. The potential health‐promoting activity of soy isoflavones may depend on their abundance and chemical form. The objective of this study was to characterize the changes in isoflavone distribution and β‐glucosidase activity during the soy breadmaking process. Soy bread ingredients were combined and mixed to form a dough that was subsequently proofed at 48°C for 1–4 hr and baked at 165°C for 50 min to produce breads. The isoflavone composition and β‐glucosidase activity in bread ingredients, doughs, and breads were monitored. Soy ingredients and wheat flour (not bread yeast) were the major contributors of the β‐glucosidase activity in bread. No degradation of isoflavones was observed during breadmaking but the isoflavone distribution was largely altered. Proofing and baking have important but different roles in changing the isoflavone distribution. Proofing converted isoflavone β‐glucosides to aglycones by highly specific β‐glucosidase activity. Thermal treatment during baking significantly decreased the isoflavone malonylglucosides and increased isoflavone β‐glucosides. Enzyme activity during proofing and the balance between formation and deconjugation of isoflavones during baking determine the isoflavone content and composition in the final product.     

Effect of Enzymatic Tempering of Wheat Kernels on Milling and Baking Performance

This study examined the effect of cell‐wall‐degrading enzymes added to temper water on wheat milling performance and flour quality. An enzyme cocktail consisting of cellulase, xylanase, and pectinase and five independent variables (enzyme concentration, incubation time, incubation temperature, tempered wheat moisture content, and tempering water pH) were manipulated in a response surface methodology (RSM) central composite design. A single pure cultivar of hard red winter wheat was tempered under defined conditions and milled on a Ross experimental laboratory mill. Some treatment combinations affected flour yield from the break rolls more than that from the reduction rolls. However, a maximum for flour yield was not found in the range of parameters studied. Though treatments did not affect the optimum water absorption for breadmaking, enzyme‐treated flours produced dough exhibiting shorter mixing times and slack and sticky textures compared with the control. Regardless of differences in mixing times, specific loaf volumes were not significantly different among treatments. Crumb firmness of bread baked with flour milled from enzyme‐treated wheat was comparable to the control after 1 day but became firmer during storage up to 5 days.     

Influence of Milk,Corn Starch,and Baking Conditions on the Starch Digestibility,Gelatinization, and Fracture Stress of Biscuits

Dough for nontraditional semisweet biscuits—prepared with wheat flour or replacing part of the wheat flour with corn starch, with or without skim milk—was baked at two oven temperatures, 120 or 170°C, until reaching moisture content and water activity lower than 6% and 0.5, respectively. Assays of fracture stress, differential scanning calorimetry, X‐ray diffraction, and starch digestibility were performed. Results showed that biscuits containing milk had the highest fracture stress, and biscuits baked at low temperature were harder than biscuits baked at high temperature. The degree of starch gelatinization during baking was higher when dough was baked at 170°C, compared with dough baked at 120°C. The decrease in gelatinization coincides with the decrease in the height and surface of peaks at 15 and 23° in the X‐ray diffraction patterns. Milk and corn starch did not affect the starch digestibility of biscuits, but biscuits baked at 170°C presented lower fracture stress and higher starch digestibility than biscuits baked at 120°C.     

HPLC Determination of Stability and Distribution of Added Folic Acid and Some Endogenous Folates During Breadmaking

Bread flour was spiked with folic acid (1.40 mg/lb or 3.08 μg/g of flour) and processed into bread by the sponge and dough method. Changes that occurred to added folic acid and endogenous folate contents through different processing stages, including sponge formation, proofing, and baking, were assessed by reversed‐phase ion‐pair HPLC combined with UV and fluorometric detection. Sample extraction required α‐amylase and rat plasma deconjugase digestion, and sample preparation required purification by solid‐phase extraction. Added folic acid was measured by monitoring UV absorption at 280 nm. Four selected forms of endogenous folates including tetrahydrofolate (THF), 5‐formyl‐THF, 10‐formylfolate, and 5‐methyl‐THF were identified and quantified throughout the bread processing using a fluorescence excitation wavelength of 290 nm and emission wavelength of 350 or 450 nm. Data indicate a relatively good stability of added folic acid and native folates to the baking process, and increased endogenous folate contents in dough and bread as compared with the flour from which they were made.     

Effects of Different Salts on Mixing and Extension Parameters on a Diverse Group of Wheat Cultivars Using 2‐g Mixograph and Extensigraph Methods

Cations of differing chaotropic capacities (LiCl, NaCl, and KCl) were used in small‐scale mixing and extensigraph studies to assess functional changes in dough behavior of wheat cultivars varying in total protein content and HMW glutenin composition. Salt addition, regardless of cationic type, caused an increase in dough strength and stability. The smaller (hydrated) and least chaotrophic cations (Li⁺<Na⁺<K⁺) effected the greatest increase in mixing time (MT) and resistance to extension (R_max) and produced the most stable resistance breakdown (RBD). The effects of different cations on mixing and extensions indicated strong intercultivar variation; differential responses to salt addition were further shown when the cultivars were grouped according to protein content and Glu‐1D or Glu‐1B genome composition. Increases in dough strength parameters due to the addition of salt were consistently more significant for cultivars showing an overexpression of Bx7 (>12% protein). In the absence of genotypic variation, a significant interactive effect of cultivar type, protein amount, and salt addition was found for all functional dough parameters except extensibility. During mixing, there was a decrease in the amount of apparent unextractable polymeric protein (%UPP) in the dough. This phenomenon was ameliorated by the presence of salt in doughs formed from weaker flours and was most pronounced early on in the mixing process (t = 100–200 sec). Results show the importance of refining 2‐g mixograph studies to include salt in the “flour and water” dough formula.     

Development of a Benchtop Baking Method for Chemically Leavened Crackers. I. Identification of a Diagnostic Formula and Procedure

A benchtop baking method has been developed to predict the contribution of gluten functionality to overall flour performance for chemically leavened crackers. To identify a diagnostic cracker formula, the effects of leavening system (sodium bicarbonate, monocalcium phosphate, and ammonium bicarbonate), sugar concentration (%S), and total solvent (TS) on cracker‐baking performance were explored. From preliminary experiments to establish a production procedure, 10 min of dough‐mixing time, a cord‐weave baking mesh, and a 500°F oven temperature were selected. For the leavening system, increasing ammonium bicarbonate (ABC) level at constant sodium bicarbonate (soda) and monocalcium phosphate (MCP) levels resulted in increased cracker height. For the diagnostic formula, 1.25 g of soda, 1.25 g of MCP, and 1.25 g of ABC were selected, based on 100 g of flour. As the sugar concentration in the cracker formula, at constant total solvent (38 TS), decreased to <20%, the resulting cracker dough became softer, and the baked cracker exhibited an increased blistering tendency because of a too‐high formula water level. In contrast, a cracker dough formulated with >40% sugar concentration was too crumbly to handle and sheet. As the total solvent in the cracker formula increased at constant sugar concentration (≈23.7%S), the resulting dough became softer. A dough with 34 TS was too crumbly to handle, while doughs with 42 and 46 TS were too soft to handle and resulted in blistering. Therefore, 38 TS and 23.7%S were identified for the diagnostic formula. Crackers baked with a hard wheat flour, a soft wheat flour, and blends validated the utility of the developed method.     

Effect of Exogenous Lipase on Dough Lipids During Mixing of Wheat Flours

In control dough, endogenous wheat lipase was inactive, because the triacylglycerol (TAG), 1,2-diacylglycerol (DAG_1,2), and 1,3-diacylglycerol (DAG_1,3) fractions of nonpolar lipids were not affected by mixing. Conversely, the free fatty acid (FFA) and monoacylglycerol (MAG) fractions decreased, mainly due to the oxidation of polyunsaturated fatty acids (PUFA) catalyzed by wheat lipoxygenase. Addition of exogenous lipase to flour (15 lipase units [LU] per gram of dry matter) resulted in substantial modification of nonpolar lipids during dough mixing. Due to the 1,3 specificity of the lipase used in this experiment, the TAG and DAG_1,3 fractions decreased, whereas the MAG and FFA fractions increased. The DAG_1,2 fraction increased at the beginning of mixing and decreased after 40 min of mixing. Moreover, part of the PUFA released by lipase activity was oxidized by wheat lipoxygenase, resulting in major losses of PUFA. Conversely, the net content of the saturated and monounsaturated fatty acids (SMUFA) remained constant, because the free SMUFA content increased primarily at the expense of the esterified forms. For a constant mixing time of 20 min, increasing the amount of lipase added to dough (from 2.5 to 25 LU/g of dry matter) resulted in a linear decrease in the TAG fraction and a linear increase in the SMUFA content in the FFA fraction. At the same time, the PUFA content of the FFA fraction increased only for additions of lipase to flour of >5 LU/g of dry matter, due to partial oxidation by wheat lipoxygenase.