小麦面筋蛋白酶法改性研究

本研究采用中性蛋白酶水解小麦面筋蛋白,就几种因素对水解程度的影响、酶解条件及酶解物的功能性质进行了系统研究,并分析了酶解前后巯基含量的变化,酶解后的小麦面筋蛋白功能性质显著提高。     

Functional properties of microwave-treated wheat gluten

In this study, the effects of microwave treatments on solubility, foaming and emulsifying properties of gluten were investigated. The solubility of microwave-heated gluten proteins gradually decreased as the treatment time increased, at all power levels applied. The highest solubility values were obtained for gluten samples microwave treated at 50% power level. The lowest emulsifying capacity values were obtained with the samples heated at 100% power level at all treatment times. The emulsifying stability values of microwave-heated gluten samples were found to be slightly higher than those of the control sample. However, there were no significant differences among the microwave power levels at all treatment times in terms of the emulsifying stability values. The foam volumes of the samples treated at 80 and 100% energy levels were slightly higher than those of the control gluten. The foam stability values of microwave-heated gluten samples gradually increased with treatment time at all power levels, which were more pronounced at 100% power level. Generally, microwave treatment did not cause major changes on the protein electrophoretic patterns of gluten samples at the power levels used.     

谷朊粉与其制备蛋白膜性能的相关性研究

选取国内10种市售谷朊粉分别制备蛋白膜,分析谷朊粉的主要品质及蛋白膜的性能,通过相关性分析及逐步回归分析研究谷朊粉与蛋白膜品质之间的相关关系。相关分析表明:谷朊粉的巯基含量、溶解性、麦醇溶蛋白含量、吸水率、粗蛋白含量、水分含量、泡沫稳定性与膜的透光率、水溶性、阻氧性、水蒸气透过率及拉伸强度呈显著(P0.05)或极显著相关(P0.01)。逐步回归分析得出谷朊粉的粗蛋白含量、巯基含量、麦醇溶蛋白含量、溶解性、吸水率及起泡性对膜性能的影响较大。     

Influence of soy protein on rheological properties and water retention capacity of wheat gluten

A better understanding of the physicochemical and rheological changes in soy/wheat composite dough may lead to overcome the problems caused by the incorporation of high levels of soy products on bread formulation. The effects of commercial soy protein isolate (SPI) on uniaxial extension and creep behavior, microstructure and free water of hydrated gluten were studied. Different solid:moisture ratios were used. Results showed that the substitution of wheat protein by soy protein negatively affected the gluten-SPI mixture rheological properties due to network weakening. It was demonstrated that gluten was weakened as a consequence of the interference effect of soy proteins on their structure, and the smaller availability of water to the build-up of the gluten network. A greater amount of moisture could partially improve the rheological performance of the gluten-SPI mixture.     

Aggregative and structural properties of wheat gluten during post-harvest maturation

Wheat post-harvest maturation induced baking and technological quality improvement through a series of biochemical and colloidal changes. Weak-, middle-, and strong-gluten wheat displayed varying gluten network structures that determined the flour ingredient formulations and processing conditions. However, the aggregation and structural properties of wheat with different gluten strengths post-harvest remain largely unexplored. In this study, we investigated changes in the aggregative properties of gluten protein, gluten composition, S–S content, network structure, and secondary structures of weak-, middle-, and strong-gluten wheat during post-harvest maturation. The results indicated that the macromolecular aggregation of gluten proteins was impaired in weak-gluten wheat, while it was enhanced for middle- and strong-gluten wheat during storage. Post-harvest maturation resulted in an increase in glutenin content and a decline in the gliadin and gliadin/glutenin ratio in middle- and strong-gluten wheat as well as a decreased glutenin content in weak-gluten wheat. Moreover, additional gluten subunits were observed in middle- and strong-gluten wheat, but no substantial change was observed in weak-gluten wheat with long storage times. The disulfide bond content of gluten protein for middle-gluten and strong-gluten gradually increased but declined for weak-gluten wheat. Secondary structure analysis of gluten indicated that post-harvest maturation caused the conversion of α-helix to random coil for weak-gluten wheat, β-turn and random coil to α-helix for middle-gluten wheat, and β-turns to α-helix for strong-gluten wheat, which led to a disordered structure for weak gluten and an ordered stable gluten network for middle- and strong-gluten. Thus, the increased S–S and α-helix content induced by post-harvest maturation enhanced the aggregation of gluten proteins for middle- and strong-gluten wheat, resulting in a denser network structure. Conversely, the decrease in the content of α-helix resulted in the existence of a looser gluten network structure for weak-gluten wheat during post-harvest maturation.     

Comparison of viscoelastic properties of gluten from spelt and common wheat

Rheological properties of gluten from spelt and common wheat were studied. The mechanical spectra of gluten samples were registered over a frequency range of 0.001–200 rad/s. Retardation tests were performed to keep all measurements within a linear regime. The mechanical spectra were fitted with Cole–Cole functions to calculate the viscoelastic plateau modulus G _N ⁰, the central frequency of the upper dissipative loss peak ω ₀, and the spread parameter n. Steady state compliance J _e ⁰ and Newtonian viscosity η ₀ were determined from the retardation tests results. Recovery data were converted from time to frequency domain using the Kaschta method and combined with dynamic data; this enabled the extension of the gluten mechanical spectra down to 10⁻⁶ rad/s, revealing the lower dissipative peak loss. The width of the viscoelastic plateau τ _m ⁰/τ ₀ was calculated, and substantial qualitative and quantitative differences were found in spelt and common wheat gluten. All differences in gluten rheological properties were related to spelt and common wheat flour baking quality and protein composition.     

Continuous production of wheat gluten peptide with foaming properties using immobilized enzymes

Gluten peptides are prepared using limited hydrolysis of wheat gluten, resulting in improved solubility and physico-chemical properties. In general, the hydrolysis is performed using a batch-wise process. In this study, we developed a bioreactor system that can continuously produce gluten peptides with foaming properties. Two kinds of acid protease, pepsin and rapidase, were immobilized on porous chitosan beads. The partial deamidation of gluten in advance increased initial velocity of hydrolysis by immobilizing protease and also worked to enhance foaming properties. A packed-bed reactor filled with immobilized protease was designed, and operating parameters were optimized. The optimized conditions were as follows: pH, 3.0; temperature, 40 °C; substrate concentration, 40 mg/ml; and space velocity, 2.0 h^–1. Based on these results, a bench-scale reactor was manufactured to determine the stability of continuous operation. The half-life of the reactor was approximately 45 days, and both productivity and quality were stable and excellent.     

Analysis of wheat gluten and starch matrices during deep-fat frying

An important quality parameter of fried food is the amount of oil uptake, which is incompatible with recent consumer trends towards healthier food. The oil penetration mechanism is not fully understood but study of formulated products is a good way to elucidate the role of the food matrix in oil absorption.     

Pyrolytic acrylamide formation from purified wheat gluten and gluten-supplemented wheat bread rolls

Recent studies have revealed different acrylamide formation mechanisms, e. g. from carnosine (N-beta-alanyl-L-histidine) and aminopropionamide as additional precursors. The occurrence of acrylamide in food matrices devoid of common precursors such as meat supports an additional formation pathway. Gluten was recovered from wheat flour by water extraction. Starch, reducing sugars and amino acids were removed using alpha-amylase and NaCl solution and were completely absent in the purified gluten fraction. The gluten was dry heated at temperatures ranging from 160 to 240 degrees C for 8 to 12 min and analyzed for acrylamide and cinnamic amide using liquid chromatography-tandem mass spectrometry. Acrylamide could be detected up to 3997 microg/kg gluten dry weight. Cinnamic amide was detected and unambiguously identified in the gluten samples, thus confirming the proposed formation of acrylamide from proteins. After gluten addition to bread roll dough, protein pyrolysis to form acrylamide in the complex food matrix was assessed. Contents of asparagine and reducing sugars were diminished due to the addition of the gluten. In contrast to the expectation with respect to the well-established common formation mechanism of acrylamide, it increased from 53.4 to 63.9 microg/kg (+20%), which was in good correlation with the higher proportion of gluten. As demonstrated by the t-test, the increase in acrylamide was significant when comparing 0 and 15% gluten addition. Additionally, cinnamic amide could be found in crusts of bread rolls. Thus, evidence for pyrolytic formation of acrylamide from wheat gluten was provided.     

Gelation of mixed myofibrillar/wheat gluten proteins treated with microbial transglutaminase

Gluten (Glu) and an acid-extracted protein fraction (AF) from wheat flour were mixed (1:1 ratio) with myofibrillar protein (MP) and treated with microbial transglutaminase (MTGase) to observe the effect on heat-induced gelation. Dynamic rheological properties and thermal denaturation patterns of treated samples were measured, respectively, with an oscillatory rheometer and a differential scanning calorimeter. The storage modulus (G′) of control MP sample (no MTGase), with a value of 533 Pa at end of heating (77 °C), was not affected (P > 0.05) by Glu nor by AF. However, mixed protein samples after the MTGase treatment produced higher gel elasticity values that differed (P < 0.05) between samples (1355, 1700 and 1875 Pa at 77 °C for MP, MP/AF, and MP/Glu, respectively). The MP sample underwent three endothermic transitions (peaking at 61.5, 68.0, and 78.5 °C) during thermal scan. The treatment with MTGase and/or addition of Glu or AF tended to lower the temperature for the first transition but raised the temperature for the third transition, suggesting possible interactions of the muscle with non-muscle proteins.     

Comparative investigations of gluten proteins from different wheat species I. Qualitative and quantitative composition of gluten protein types

In contrast to the hexaploid common (bread) wheat, little information is available on the qualitative and quantitative compositions of gluten proteins from other cultivated wheat species. Therefore, representatives of hexaploid spelt, tetraploid durum wheat and emmer, and diploid einkorn were compared with three classes of common wheat (winter wheat, spring wheat, wheat rye hybrid). The flours were extracted to yield total endosperm proteins and the gluten protein fractions (gliadins and glutenin subunits). The extracts were characterised using sodium dodecyl sulfate polyacrylamide gel electrophoresis and reversed-phase HPLC; both methods revealed that gluten protein groups and types known from common wheat (ω-, α-, γ-gliadins, HMW and LMW subunits of glutenin) were present in all species. The HPLC platterns of gliadins and glutenin subunits from species with the same genome composition (common wheat/spelt or durum wheat/emmer) were related, and those of einkorn quite different. According to the quantities determined by reversed-phase HPLC, α-gliadins were predominant in most cases, followed by γ-gliadins and LMW subunits; ω-gliadins and HMW subunits were generally minor components. Common wheats were characterised by the highest proportions of total glutenins and HMW subunits, which are known to be important for breadmaking quality. Moreover, the lower ratio of gliadins to glutenins was typical. Emmer had the lowest proportions of total glutenins and of HMW and LMW subunits, together with einkorn the highest proportion of α-gliadins, and, by far, the highest ratio of gliadins to glutenins. The values for spelt and durum wheat were mostly in a medium range between common wheats, emmer, and einkorn, respectively. Amongst common wheats, spring wheat was characterised by more balanced quantities of α- and γ-gliadins, and wheat rye hybrid by the highest proportions of ω-gliadins. Received: 26 November 1999     

Degradation of gluten proteins by Fusarium species and their impact on the grain quality of bread wheat

The protein quality of wheat, the most important crop worldwide, is affected by the presence of fungi, mainly those belonging to the Fusarium genus. The aim of this study is to analyze the effects of Fusarium spp. on ground wheat grains quality by measuring gluten strength and quantifying the gliadin/glutenin content. A total of 23 Fusarium spp. isolates and two bread wheat (Triticum aestivum L.) genotypes with contrasting baking quality were used in the investigation. The results of SDS sedimentation test (SDSS) revealed that the presence of Fusarium species significantly affected the gluten strength negatively; while F. pseudograminearum and F. graminearum are the species that predominantly affected the SDSS values. Principal component analysis of gluten composition showed that the effect of Fusarium species on gluten composition depended on the wheat genotypes analyzed. Cluster analysis revealed that all the Fusarium species used as inoculum produced severe effects on grain quality and gluten composition on both the genotypes. In summary, our results showed that the presence of Fusarium spp. impaired storage proteins affecting the wheat dough properties. Therefore, constant monitoring is necessary to reduce the presence of Fusarium in the food chain for reducing the negative potential impact on bread quality.     

Antioxidant and antiinflammatory properties of germinated and hydrolysed Brazilian soybean flours

The effect of germination in combination with Alcalase hydrolysis of Brazilian soybean cultivar BRS 133 on the production of soybean flours with bioactive peptides as modulators of oxidative stress and markers of inflammation was monitored. The electrophoretic profile showed a weak protein breakdown during germination. However, a strong breakdown of the proteins can be observed after the first hour of hydrolysis with Alcalase. MALDI-TOF-MS analysis of the protein extracts showed differences in the intensity and profile of peptide mass fingerprint due to germination and hydrolysis. Germinated flour showed higher soluble protein concentration and antioxidant capacity. All soybean protein extracts and protein hydrolysates produced (G0, G18 and G72) showed a significant (p < 0.05) inhibition on inflammatory markers such as nitric oxide (20.5–69.3%), iNOS (22.8–93.6%), PGE₂ (64.0–88.3%), COX-2 (36.2–76.7%), and TNF-α (93.9–99.5%) in LPS-induced RAW 264.7 macrophages. However, protein extracts of flours with 18 h of germination were more potent in inhibiting pro-inflammatory responses when compared to 72 h. It can be concluded that a combination of 72 h of soybean BRS 133 germination and 1 h Alcalase hydrolysis resulted in the formation of bioactive compounds with more potent antioxidant activity, and improvement in the reduction of some of the markers of inflammation.     

Incorporation of several additives into gluten free breads: Effect on dough properties and bread quality

The objective of this work was to assess the effect of emulsifiers, hydrocolloids and enzymes on gluten-free dough rheology and thermal properties and bread quality, while relating dough properties parameters to bread technological quality. Breads were based on rice flour, cassava starch and full-fat active soy flour, with 65% or 75% (flour-starch basis) of water incorporation. Additives used were emulsifiers (diacetyl tartaric acid ester of monoglycerides – DATEM and sodium stearoyl lactylate – SSL), enzymes (glucose oxidase and α-amylase) and hydrocolloids (xanthan gum, carboxymethylcellulose, alginate and carrageenan). Results showed that additive incorporation modified dough behavior, evidenced by different calorimetric and rheological properties. Besides, the electrophoretic pattern of dough extracted proteins changed with glucose oxidase addition. These modifications resulted in breads with different characteristics, such as specific volume, firmness and firming rate, and crumb structure. Nonetheless, they did not necessarily show better quality parameters than the control bread. The control dough displayed good performance for obtaining gluten-free breads of acceptable volume, crumb structure and, principally, with lower hardening rate during storage. Contrary to widespread opinion, this work shows that the presence of additives is not essential for gluten-free bread production. This fact provides new perspectives to the gluten free market at the moment of selecting raw materials and technological parameters, reducing production costs and facilitating gluten free products development.     

The interaction between water-insoluble pentosan and gluten of the whole wheat

The water-insoluble pentosan (WIP) and gluten were extracted, and the interactions of WIP and gluten at different water level and ionic strength were measured by small amplitude oscillation tests and atomic force microscopy (AFM), and visualized by scanning electron micrographs (SEM). The results showed that the viscoelasticity of gluten and gluten-WIP mixtures greatly increased with the increase of water level, and decreased when water level was higher than 50%. The WIP significantly (p < 0.0001) improves viscoelasticity of gluten. The G′ and G″ of gluten and gluten-WIP mixtures were significantly (p < 0.0001) increased with the increase of NaCl concentration, and reached maximum when NaCl concentration was 4.0%. The SEM observations showed that the network of gluten-WIP mixtures was homogeneous and rather dense with a regular structure compared with that of gluten. From AFM detection, it was found that the single-molecule bond rupture force between the WIP and gluten proteins was strengthened with the increase of NaCl concentration, which can partly explain the rheological property and microstructure changes of WIP-gluten mixtures.     

Microstructure, mechanical properties, and starch digestibility of a cooked dough made with potato starch and wheat gluten

Processed starch-protein foods may exhibit a variety of microstructures, hence different mechanical properties and starch digestibility but the relation between these parameters is yet to be resolved. This paper reports on the effect of three processing factors (extent of mixing, cooking temperature and cooking time) on the microstructure of a model dough system consisting of potato starch, wheat gluten and water, and the in vitro digestibility of starch in the matrix as well as the relationship between microstructure and starch digestibility. Samples subjected to a high mixing level showed lower rupture stress and rupture strain (decreased by 54% and 46%, respectively), a higher residual gelatinization enthalpy of starch (ΔH), and a higher amount of birefringent starch granules (increased by 25%). Additionally, at higher mixing level the in vitro starch digestibility resulted in 24% less slowly available glucose whereas the rapidly available glucose increased by 25%. These findings were related to the original microstructure of the dough examined by confocal scanning laser microscopy.     

Assessment of the gluten toxicity of wheat and naan in Xinjiang Uyghur Autonomous Region,China

Xinjiang is a high-risk area for celiac disease (CD) regardless of genetic or environmental factors. However, no case has been reported yet in people living in Xinjiang. This study aims to explore the potential connection between diet and occurrence of CD in the Xinjiang population. To this end, the levels of T-cell stimulatory epitopes in 164 accessions of Xinjiang wheat were tested by using Western blot with monoclonal antibodies against α-gliadin epitopes Glia-α9 and Glia-α20. Three wheat varieties with remarkably low amounts of T-cell stimulatory epitopes were obtained. Western blot and R5 competitive ELISA were performed for the assessment of potential toxicity related to CD of naan. Results showed a reduction of gluten toxicity after wheat flour was processed into naan, suggesting it may have the potential to help to reduce the risk of CD for the genetically predisposed individuals.     

Chemistry of gluten proteins

Gluten proteins play a key role in determining the unique baking quality of wheat by conferring water absorption capacity, cohesivity, viscosity and elasticity on dough. Gluten proteins can be divided into two main fractions according to their solubility in aqueous alcohols: the soluble gliadins and the insoluble glutenins. Both fractions consist of numerous, partially closely related protein components characterized by high glutamine and proline contents. Gliadins are mainly monomeric proteins with molecular weights (MWs) around 28,000-55,000 and can be classified according to their different primary structures into the alpha/beta-, gamma- and omega-type. Disulphide bonds are either absent or present as intrachain crosslinks. The glutenin fraction comprises aggregated proteins linked by interchain disulphide bonds; they have a varying size ranging from about 500,000 to more than 10 million. After reduction of disulphide bonds, the resulting glutenin subunits show a solubility in aqueous alcohols similar to gliadins. Based on primary structure, glutenin subunits have been divided into the high-molecular-weight (HMW) subunits (MW=67,000-88,000) and low-molecular-weight (LMW) subunits (MW=32,000-35,000). Each gluten protein type consists or two or three different structural domains; one of them contains unique repetitive sequences rich in glutamine and proline. Native glutenins are composed of a backbone formed by HMW subunit polymers and of LMW subunit polymers branched off from HMW subunits. Non-covalent bonds such as hydrogen bonds, ionic bonds and hydrophobic bonds are important for the aggregation of gliadins and glutenins and implicate structure and physical properties of dough.     

Morphology and structural properties of high-amylose rice starch residues hydrolysed by amyloglucosidase

High-amylose starches are attracting considerable attention because of their potential health benefits and industrial uses. Enzyme hydrolysis of starch is involved in many biological and industrial processes. In this paper, starches were isolated from high-amylose transgenic rice (TRS) and its wild type rice, Te-qing (TQ). The morphological and structural changes of starch residues following Aspergillus niger amyloglucosidase (AAG) hydrolysis were investigated. AAG hydrolysed TQ starch from the granule surface, and TRS starch from the granule interior. During AAG hydrolysis, the content of amorphous structure increased, the contents of ordered structure and single helix decreased, and gelatinisation enthalpy decreased in TQ and TRS starch residues. The A-type polymorph of TRS C-type starch was hydrolysed faster than the B-type polymorph. The short-range ordered structure and B-type polymorph in the peripheral region of the subgranule and the surrounding band of TRS starch increased the resistance of TRS starch to AAG hydrolysis.     

Model studies for wheat sourdough systems using gluten,lactate buffer and sodium chloride

Model studies were conducted in order to study the influence of acid and NaCl, as occurring in wheat sourdough bread, on fundamental rheological properties of wheat gluten. Gluten was divided into pieces and subjected to a swelling period in lactate buffer of pH 3.9, with or without added NaCl (3 g/100 ml). The respective controls were unbuffered NaCl solution and pure water. The microstructure of the gluten pieces was studied by laser-scanning confocal microscopy and the recombined pieces were examined using fundamental rheology. The combination of buffer (pH 3.9) and NaCl in comparison to unbuffered NaCl solution caused a denser, but partially dissolved fibrillar microstructure. Further to this, swelling of the gluten was reduced (62.0% versus 65.9% moisture) and an increase in firmness and elasticity was observed: in comparison with unbuffered NaCl solution, the absolute value of the complex dynamic modulus (|G*|) was higher, while the phase angle was lower in dynamic oscillatory measurements at 30 °C and dynamic temperature sweeps (30–95 °C), while in creep tests at 30 °C and 95 °C strain values were lower and relative recovery higher. In contrast, pH 3.9 buffer without added NaCl caused softer rheological behaviour than water and a film-like microstructure.