Use of psychrophilic xylanases provides insight into the xylanase functionality in bread making

The bread-improving potential of three psychrophilic xylanases from Pseudoalteromonas haloplanktis TAH3A (XPH), Flavobacterium sp. MSY-2 (rXFH), and unknown bacterial origin (rXyn8) was compared to that of the mesophilic xylanases from Bacillus subtilis (XBS) and Aspergillus aculeatus (XAA). XPH, rXFH, and rXyn8 increased specific bread volumes up to 28%, 18%, and 18%, respectively, while XBS and XAA gave increases of 23% and 12%, respectively. This could be related to their substrate hydrolysis behavior. Xylanases with a high capacity to solubilize water-unextractable arabinoxylan (WU-AX) during mixing, such as XBS and XPH, increased bread volume more than xylanases that mainly solubilized WU-AX during fermentation, such as rXFH, rXyn8, and XAA. Irrespective of their intrinsic bread-improving potential, the dosages needed to increase bread volume to a similar extent were much lower for psychrophilic than for mesophilic xylanases. The xylanase efficiency mainly depended on the enzyme's temperature activity profile and its inhibition sensitivity.     

Elucidating the mechanism of laccase and tyrosinase in wheat bread making

Cross-linking enzymes generate covalent bonds in and between food biopolymers. These enzymes are interesting tools for tailoring dough and bread structures, as the characteristics of the biopolymers significantly determine the viscoelastic and fracture properties of dough and bread. In this study, the influence of oxidative cross-linking enzymes, tyrosinase from the filamentous fungus Trichoderma reesei and laccase from the white rot fungus Trametes hirsuta, on dough and bread were examined. Oxidation of low molecular weight phenolic model compounds of flour, cross-linking of gluten proteins, dough rheology, and bread making were characterized during or after the enzymatic treatments. In the dough and bread experiments, laccase and tyrosinase were also studied in combination with xylanase. Of the model compounds tyrosine, p-coumaric acid, caffeic acid, ferulic acid, and Gly-Leu-Tyr tripeptide, tyrosinase oxidized all except ferulic acid. Laccase was able to oxidize each of the studied compounds. The phenolic acids were notably better substrates for laccase than l-tyrosine. When the ability of the enzymes to cross-link isolated gliadin and glutenin proteins was studied by the SDS-PAGE analysis, tyrosinase was found to cross-link the gliadin proteins effectively, whereas polymerization of the gliadins by laccase was observed only when a high enzyme dosage and prolonged incubation were used. Examination of large deformation rheology of dough showed that both laccase and tyrosinase made doughs harder and less extensible, and the effects increased as a function of the enzyme dosage. In bread making, interestingly, the pore size of the breads baked with tyrosinase turned out to be remarkably larger and more irregular when compared to that of the other breads. Nevertheless, both of the oxidative enzymes were found to soften the bread crumb and increase the volume of breads, and the best results were achieved in combination with xylanase.     

Reaction kinetics of gliadin-glutenin cross-linking in model systems and in bread making

The gluten proteins gliadin and glutenin are important for wheat flour functionality in bread making, where, during baking, they polymerize through a heat-induced sulfhydryl-disulfide exchange mechanism. A model system was used to study the kinetics of this reaction. Thus, gluten was subjected to hydrothermal treatment with the rapid visco analyzer (RVA) with holding temperatures of 80, 90, and 95 degrees C. At these temperatures, omega-gliadin solubility did not change, but the solubilities of alpha- and gamma-gliadin in 60% ethanol decreased according to first-order reaction kinetics. All reaction rate constants increased with temperature. The activation energies for the heat-induced exchange reaction were 110 and 147 kJ/mol for alpha- and gamma-gliadin, respectively. Starch did not influence the reaction rates of the association of alpha- and gamma-gliadin with glutenin. During gluten-starch model bread baking, glutenin oxidized first, and when the internal crumb temperature reached 100 degrees C, alpha- and gamma-gliadin cross-linked to glutenin, again following first-order reaction kinetics. The experimental findings and similarities in temperature conditions and reaction kinetics suggest that the RVA system can be instrumental in understanding gluten behavior in concentrated food systems, such as bread making.     

Solid-State 13C CP/MAS NMR studies on aging of starch in white bread

The effects of storage methods and glycerol on the aging of breadcrumbs were studied using solid-state (13)C CP/MAS NMR. After baking, a shift in C(1) peaks from triplet (A-type) to singlet (V-type) was observed. Addition of glycerol reduced the carbon peak intensities of fresh and aged breads, which correlated well with the DSC amylopectin "melting" enthalpy (r(2) = 0.91). Upon storage of bread with crust in hermetically sealed containers (when moisture migrated from the crumbs to the crust), the (13)C CP/MAS NMR peak intensity increased more rapidly during aging than when the bread was stored without crust. Although addition of glycerol retarded the starch retrogradation, as observed by (13)C CP/MAS NMR and DSC, it accelerated the firming rate. Therefore, bread firming in this case was controlled not only by starch retrogradation but also by other events (such as local dehydration of the matrix or gluten network stiffening).     

Impact of redox agents on the extractability of gluten proteins during bread making

The gluten proteins gliadin and glutenin are important for dough and bread characteristics. In the present work, redox agents were used to impact gluten properties and to study gliadin-glutenin interactions in bread making. In control bread making, mixing increased the extractability of glutenin. The level of SDS-extractable glutenin decreased during fermentation and then further in the oven. The levels of extractable alpha- and gamma-gliadin also decreased during bread baking due to gliadin-glutenin polymerization. Neither oxidizing nor reducing agents had an impact on glutenin extractabilities after mixing. The redox additives did not affect omega-gliadin extractabilities during bread making due to their lack of cysteine residues. Potassium iodate (0.82-2.47 micromol/g of protein) and potassium bromate (1.07-3.17 micromol/g of protein) increased both alpha- and gamma-gliadin extractabilities during baking. Increasing concentrations of glutathione (1.15-3.45 micromol/g of protein) decreased levels of extractable alpha- and gamma-gliadins during baking. The work not only demonstrated that, during baking, glutenin and gliadin polymerize through heat-induced sulfhydryl-disulfide exchange reactions, but also demonstrated for the first time that oxidizing agents, besides their effect on dough rheology and hence bread volume, hinder gliadin-glutenin linking during baking, while glutathione increases the degree of covalent gliadin to glutenin linking.     

Effects of alpha-amylases from different sources on the firming of concentrated wheat starch gels: relationship to bread staling

The firming and carbohydrate fractions of concentrated starch gels supplemented with four alpha-amylases from different sources were evaluated. Correlations were found between the firmness data and results for the carbohydrate fractions extracted from the gels. The thermostable (TBA) and intermediate temperature stability (ISBA) bacterial alpha-amylases were most effective in decreasing the rate of firming. The cereal alpha-amylase at the high level (CAH) was also effective. The CAH produced the largest quantity of dextrins at storage time zero and the thermostable bacterial alpha-amylase at the high level (TBAH) after storage for 5 days. None of the maltooligosaccharides appeared to be responsible for the decreased rate of firming of the gels. The results indicated that the TBA and ISBA most effectively inhibited firming because they degraded the external branches and the intercluster regions of amylopectin during storage. Consideration of previously reported differential scanning calorimetry and X-ray crystallography results leads to the conclusion that the antifirming action of the TBA and ISBA is due to their ability to degrade the amylopectin and amorphous regions of the gels during storage, which inhibits the formation of double helices and decreases the strength of the starch gel matrix. Gels supplemented with the TBA and ISBA were most crystalline but firmed to a lesser extent. These results are similar to those previously reported by other researchers for bread and strongly suggest that starch retrogradation plays a primary role in bread staling.     

红外辐射制备柠檬酸糯米淀粉酯工艺优化及功能特性

为提高柠檬酸淀粉酯制备效率,拓展淀粉在工业领域的应用价值,以糯米淀粉为研究对象、柠檬酸为酯化剂,红外辐射为核心制备技术,取代度为衡量指标,用单因素和响应面法优化柠檬酸淀粉酯的制备工艺条件,并对改性前后淀粉的理化性质、微观结构测定分析.最佳工艺参数为:红外辐射照度2474 W/m2、红外辐射时间7.1 min、pH值为2...     

茶多糖对面包粉及其淀粉糊化和老化特性的影响

为探索茶多糖作为添加剂在面包制品中应用的可行性,该文利用差示扫描量热法(DSC)、X-衍射分析了1%～5%茶多糖的添加对面包粉及其淀粉糊化、老化的影响,结果表明:随茶多糖浓度的增加,面包粉及其淀粉糊化的吸热焓(ΔH1)、峰温不断增加。面包粉及其淀粉胶在4℃下贮藏20d的老化过程中,随贮藏时间的延长,吸热焓、老化速率不断增加;随茶多糖浓度的增加,老化热焓(ΔH2)、老化速率、结晶速率不断减少,但玻璃化温度随茶多糖浓度的增加而不断提高。综合结果表明,面包粉添加1%～2%的茶多糖而面包淀粉添加2%～3%的茶多糖,具有明显抑制样品的老化热焓、老化速率和结晶速率的作用。     

Effect of alpha-amylases from different sources on the retrogradation and recrystallization of concentrated wheat starch gels: relationship to bread staling

Concentrated starch gels were supplemented with four alpha-amylases from different sources. The retrogradation and recrystallization of the gels were evaluated using differential scanning calorimetry (DSC) and X-ray crystallography. Correlations between the retrogradation data and the carbohydrate fractions extracted from these gels were determined. The thermostable (TBA) and intermediate temperature stability (ISBA) bacterial alpha-amylases were most effective in decreasing the rate of retrogradation of the starch in the gels. The cereal alpha-amylase at the high level (CAH) was also effective. Supplementation with the alpha-amylases increased the crystallinity of the gels. Gels supplemented with TBA or ISBA were most crystalline and retrograded to a lesser extent. The results indicated that DSC gives not only a measure of recrystallized amylopectin but also a measure of total order (recrystallized amylopectin and double-helical content). The maltooligosaccharides produced by the enzymes did not appear to be responsible for the reduced rates of retrogradation, but they appeared to be an expression of the degree of starch modification that was responsible for the inhibition of retrogradation. The crystallinity and retrogradation data were similar to results reported for bread and strongly suggest that bread staling is caused by the retrogradation of starch. The results also indicate that alpha-amylases decrease the rate and extent of retrogradation of starch gels by inhibiting the formation of double helices.     

Assignments of proton populations in dough and bread using NMR relaxometry of starch, gluten, and flour model systems

Starch-water, gluten-water, and flour-water model systems as well as straight-dough bread were investigated with (1)H NMR relaxometry using free induction decay and Carr-Purcell-Meiboom-Gill pulse sequences. Depending on the degree of interaction between polymers and water, different proton populations could be distinguished. The starch protons in the starch-water model gain mobility owing to amylopectin crystal melting, granule swelling, and amylose leaching, whereas water protons lose mobility due to increased interaction with starch polymers. Heating of the gluten-water sample induces no pronounced changes in proton distributions. Heating changes the proton distributions of the flour-water and starch-water models in a similar way, implying that the changes are primarily attributable to starch gelatinization. Proton distributions of the heated flour-water model system and those of fresh bread crumb are very similar. This allows identifying the different proton populations in bread on the basis of the results from the model systems.     

减少玉米粗淀粉挤出物中抗性淀粉的工艺参数优化

为减少玉米粗淀粉经过挤压蒸煮后,在室温下冷却而产生的抗性淀粉Ⅲ,以降低其对挤出物制备糖化液葡萄糖当量值的影响,需要对挤压参数进行优化选择。该文以玉米粗淀粉为原料,采用五因素五水平二次正交旋转组合试验设计,研究挤压参数对挤出物中抗性淀粉Ⅲ质量分数的影响,得出产生抗性淀粉Ⅲ质量分数最小的挤压条件为：套筒温度60.0℃,原料含水率27.0%,模孔直径11.0 mm,螺杆转速200.0 r/min,轴头间隙10.0 mm,抗性淀粉Ⅲ质量分数可降低到1.48%。     

Browning indicators in bread

Bread is the most important food in the Spanish household and represents the largest proportion of products produced by commercial bakeries. The browning indicators furosine, hydroxymethylfurfural (HMF), and color were determined to evaluate heat effects induced during manufacture of these foods. The breads analyzed were common, special, sliced toasted, and snack breads. Identical sample preparation and HPLC conditions were used to determine HMF in all breads. The precision tested at high and low HMF concentration in breads was 2.60% and 1.57%, respectively. Recovery of HMF was 96.2%. The HMF values ranged from 2.2 to 68.8 mg/kg. Color index (100 - L) ranged from 17.0 to 38.2. The linear correlations (r(2)) between 100 - L/HMF were above 0.70 for common, special, and snack breads. Similar correlation was obtained between 100 - L/HMF in a dough baking at different times. The furosine content in common bread ranged between 125 and 208 mg/100 g of protein. No linear correlation was found between furosine and HMF. Moreover, HMF and furosine were also determined in crumb and crust. Levels of HMF had a wide range (0.9-1.76 mg/kg) and furosine was between 43 and 221 mg/100 g of protein.     

Optimizing dough proofing conditions to enhance isoflavone aglycones in soy bread

Native beta-glucosidase activity in soy bread can convert isoflavone glucosides to aglycones during proofing, and this study determined the time-temperature dependence of this process. Samples were taken every hour for 4 h during proofing at 22, 32, and 48 degrees C to determine beta-glucosidase activity and isoflavone profiles of the dough. After 1-2 h, the beta-glucosidase activity increased 43-84% achieving a plateau value at 22 degrees C but declining when proofed beyond 2 h at 32 degrees C and 48 degrees C. Large increases in aglycones and corresponding decreases in the simple glucosides were observed during proofing. The level of malonyl-glucosides decreased 3-15%, and acetyl-glucosides were fairly constant. The two higher temperatures drove more rapid conversion: 70-73% of simple glucosides in 2-4 h. The extent of conversion in the early proofing periods corresponded to beta-glucosidase activity. The optimum time-temperature protocol was 2 h at 48 degrees C resulting in a rapid, high conversion.     

乡镇淀粉工业存在的问题及优化模式的确定

阐述了乡镇淀粉工业在国民经济中的地位与作用，论述了乡镇淀粉工业发展带来的问题以及面临的国内外形势，同时指出应建立适合我国乡镇淀粉工业的生产模式，并提出今后乡镇淀粉工业的发展方向。     

A bayesian approach to crop Model calibration under unknown error covariance

Bayesian methods seem well adapted to dynamic system models in general and to crop models in particular, because there is in general prior information about parameter values. The usefulness of a Bayesian approach has often been pointed out, but actual applications are rather rare. A major difficulty is including the elements of the covariance matrix of model errors in the treatment. We treat the specific case of balanced data and an unstructured covariance matrix. In our particular case this is a 3 × 3 matrix. We illustrate two methods for deriving a sample from the joint posterior density for the crop model parameters and the error covariance matrix parameters. The first method is based on importance sampling, the second on Metropolis within Gibbs sampling. We derive an instrumental density for the former and a proposal density for the latter which are adapted to this type of model and data. Both algorithms work well and they give very similar results. The example concerns a model for sunflowers during rapid leaf growth. The ultimate goal is to use the model as a decision aid in predicting disease risk.     

Utilization of enzyme mixtures to retard bread crumb firming

The influence of enzyme mixtures containing amylase and lipase activities on straight dough bread staling was studied. Amylopectin retrogradation, crumb firming, amylose-lipid complexes, and dextrin production were analyzed in bread samples supplemented with two enzyme mixtures. The addition of enzyme mixtures to bread formula causes a beneficial effect on bread keeping properties and the formation of a more thermostable amylose-lipid complex than the one found in control bread. Amylopectin retrogradation was inhibited by the use of the enzyme; the effect was accompanied by reduced crumb-firming rates. The enzymatically generated water-soluble dextrins (maltose and DP3, DP4, DP5, and DP6 dextrins) are the most effective in preserving crumb softness during bread storage.     

Semicarbazide formation in flour and bread

Azodicarbonamide, an approved food additive, is commonly used as a flour additive and dough conditioner in the United States and Canada. A number of researchers have clearly established a link between the use of azodicarbonamide and semicarbazide contamination in commercial bread products. However, all of these studies have primarily focused on the final baked product and have not extensively investigated the processing and conditions that affect the final semicarbazide levels. In this study, a previously developed method for measuring free semicarbazide in bread was applied to dough samples during the mixing and kneading process. Additionally, flour and bread samples were spiked with biurea or azodicarbonamide to help elucidate semicarbazide formation pathways. The results showed that semicarbazide was not formed as a byproduct of azodicarbonamide decomposition to biurea, which occurs upon the addition of water. Indeed, semicarbazide was not detected after room temperature or elevated temperature dough maturation, but only after baking. It was concluded that although azodicarbonamide is the initial starting material, semicarbazide formation in bread occurs through a stable intermediate, biurea.     

Water uptake mechanism in crispy bread crust

Crispness is an important quality characteristic of dry solid food products such as crispy rolls. Its retention is directly related to the kinetics of water uptake by the crust. In this study, a method for the evaluation of the water sorption kinetics in bread crust is proposed. Two different sorption experiments were used: an oscillatory sorption test and a sorption test in which the air relative humidity (RH) was increased stepwise. These two experiments had different time scales, which made it possible to get a better understanding of the mechanisms involved. Results show that the adsorption and desorption dynamics of the oscillatory sorption test could be described by a single exponential in time. The water uptake rate ( k) was one of the fitting parameters. A maximum in the water uptake rate was found for a RH value between 50 and 70%. The rate parameters of the experiment where RH was increased stepwise were around a factor 10 lower than those derived from oscillatory sorption experiments. This is an important factor when designing experiments for the determination of water uptake rates. In addition, also a parameter describing the time dependence of the rate parameters of the oscillatory sorption experiment was calculated (C), again by fitting a single exponential to the rate parameters. C was in the same range as the rate parameter of the isotherm experiment. This indicates that different (relaxation) processes are acting at the same time in the bread crust during water uptake.     

Gas chromatographic determination of calcium propionate added as preservative to bread

A simple and rapid gas chromatographic procedure was developed for determining low concentrations of propionate added as a preservative to bread. A bread sample to be analyzed was ground in a meat grinder with a 3 mm hole plate and finely divided by rubbing through a No. 8 sieve. The propionate was then extracted into 0.050M formic acid in a blender at low speed for 5 min, and an aliquot of a filtrate was analyzed directly by gas chromatography. Chromatographic separation was accomplished on a Carbopack C column coated with 0.3% (w/w) Carbowax 20M and 0.1% (w/w) phosphoric acid. Less than 0.2 ppm propionic acid could be detected in the aqueous extract. Over the range of 0.03-0.23% calcium propionate, average relative error was -1.20% with an average coefficient of variation of 2.02%.     

Mango starch degradation. II. The binding of alpha-amylase and beta-amylase to the starch granule

During mango ripening, soluble sugars that account for mango sweetening are accumulated through carbon supplied by both photosynthesis and starch degradation. The cultivar Keitt has a characteristic dependence on sugar accumulation during starch degradation, which takes place during ripening, only a few days after detachment from the tree. Most knowledge about starch degradation is based on seeds and leaves currently used as models. However, information about the mango fruit is scarce. This work presents the evaluation of alpha- and beta-amylases in the starch granule surface during fruit development and ripening. Extractable proteins were assayed for amylase activity and detected by immunofluorescence microscopy and correlated to gene expression. The results suggest that both amylases are involved in starch degradation during mango ripening, probably under the dependence of another signal triggered by the detachment from the mother-plant.