Biogenic amine formation and nitrite reactions in meat batter as affected by high-pressure processing and chilled storage

Changes in biogenic amine formation and nitrite depletion in meat batters as affected by pressure-temperature combinations (300 MPa/30 min/7, 20, and 40 degrees C), cooking process (70 degrees C/30 min), and storage (54 days/2 degrees C) were studied. Changes in residual nitrite concentration in raw meat batters were conditioned by the temperature and not by the pressure applied. Cooking process decreased (P < 0.05) the residual nitrite concentration in all samples. High-pressure processing and cooking treatment increased (P < 0.05) the nitrate content. Whereas protein-bound nitrite concentration decreased with pressure processing, no effect was observed with the heating process of meat batters. High-pressure processing conditions had no effect on the rate of residual nitrite loss throughout the storage. The application of high pressure decreased (P < 0.05) the concentration of some biogenic amines (tyramine, agmatine, and spermine). Irrespective of the high processing conditions, generally, throughout storage biogenic amine levels did not change or increased, although quantitatively this effect was not very important.     

Utilization of Oxidized and Cross-Linked Corn Starches in Wheat Flour Batter

Starch is often added to batters to improve the texture and appearance of fried food products. However, comparisons of commercially available starches in terms of batter characteristics are rare. In this study, various corn starches, native or modified, were mixed with wheat flour (20% dry solids basis), and the physical properties of the batters after deep-fat frying were examined. Native corn starches of different amylose contents (high-amylose, normal, and waxy) and chemically modified corn starches (oxidized and cross-linked) were tested. The batter was prepared by adding water to the starch-flour mixtures (42% solids) and deep-fat frying at 180°C for 30 sec. The texture of the fried batter was analyzed using a texture analyzer (TA) with a Kramer shear cell. The pasting viscosity profile of the starch-flour mixtures (7% solids in water) was also measured with a Rapid Visco Analyser. When the native corn starches of different amylose contents were compared, the crispness (peak number before breakage) and hardness (maximum peak force) measured using the instrument were positively correlated with the amylose content in starches but negatively correlated with the residual moisture content of the fried batters. The peak viscosity and breakdown in viscosity profiles of the starch-flour mixtures were also negatively correlated with crispness. The use of high-amylose corn starch was effective not only in increasing the crispness, but also in reducing the oil uptake. However, the fried batter containing high-amylose starch was denser and harder than the batter containing normal starch. Among the modified starches tested, oxidized (0.4% active Cl₂) and cross-linked (4% 99:1 mixture of STMP and STPP) starches showed improvements in the overall properties of the fried batters. With excessive oxidizations (>0.4% Cl₂), however, the crispness was reduced.     

Baking Characteristics of Chiffon Cake as Influenced by Microbial Transglutaminase

Protein modification via covalent bonds by using microbial transglutaminase (TGase) has generated many processing functionality improvements in specific food ingredients. In this study, TGase was added into different cake portions (foam and yolk batter) at levels of 0, 0.5, and 1.0% (w/w, total protein weight basis). The treatment of 0.5% TGase in the yolk batter portion significantly (P ≤ 0.05) increased its emulsion activity. The addition of 1.0% TGase in the yolk batter portion significantly increased both foam stability and emulsion activity of cake batter, whereas the addition in the foam portion only increased the emulsion activity of cake batter significantly (P ≤ 0.05). As the addition of TGase, in foam or in the yolk batter portion, rose from 0 to 1.0%, the specific volume of chiffon cake increased. Cakes with 1.0% TGase in the foam portion had the maximum specific volume, 7.078 mL/g, and the softest texture. SDS‐PAGE was used to analyze the modifications of TGase to the protein fractions from different cake portions. The effect of TGase on protein fractions from the yolk batter portion was more evident than that on protein fractions from the foam portion. However, there was no significant difference between the protein fractions of cake batters with the same level of TGase in the foam and yolk portions, which suggested that the main substrates of TGase were yolk protein and wheat protein, instead of egg white protein.     

冰温贮藏期间淀粉添加对水滑肉品质的影响

水滑肉是我国传统的菜肴,具有爽滑细嫩、鲜香无比的特点。为了探究水滑肉淀粉外壳变化对水滑肉品质的影响,以质构、剪切力、水分含量、回生程度、淀粉热力学特性等为评价指标,研究了在冰温贮藏期间水滑肉品质的变化情况。结果表明：与水煮肉进行对照,在冰温贮藏期间淀粉的添加显著抑制了水滑肉的硬度、咀嚼性及剪切力的增加;水滑肉在贮藏期品质指标劣化,但感官得分优于对照组。在冰温贮藏期间,水滑肉外壳的水分含量、糊化焓值及R_1047/1022依次增加了7.29%、327.42%、5.17%,增长幅度均低于淀粉组 (P＜0.05);肉的存在显著减缓了水滑肉淀粉外壳的回生(P＜0.05)。在冰温贮藏条件下,淀粉外壳的回生与水滑肉的质构指标呈现显著正相关(P＜0.05),即淀粉外壳的回生会劣化水滑肉的硬度、咀嚼性和剪切力。冰温条件下,肉中水分向淀粉外壳转移可能会延缓淀粉外壳的回生,从而延缓其品质劣化;冰温贮藏第8 天可能为水滑肉品质变化的关键点。研究结果可为水滑肉预制菜肴品质研究提供参考。     

Oil uptake properties of fried batters from rice flour

Batters were prepared, using rice flour as the main component, and analyzed for their oil uptake properties during frying. Rice flour resisted oil absorption better but was less effective as a thickening agent than wheat flour. Of the rice components, increased amylose in the amylopectin/amylose ratio of the starch decreased the batter oil uptake, whereas increased protein content had the opposite effect. Various additives were introduced and investigated for their ability to develop viscosity and other desirable characteristics for the batter. As additives to the rice flour batters, phosphorylated starch and gelatinized rice flour enhanced both the thickening and oil-reducing capacities of the batter. Compared with values for batters from wheat flour, the percent batter oil uptake in the fried crust for the modified rice flour batters was decreased by up to 62%, and the percent total oil uptake for the whole coated drumstick was reduced by up to 59%.     

Effects of Secondary Structures of Heated Egg White Protein on the Binding Between Prime Starch and Tailings Fractions in Fresh Wheat Flour

Dried egg white protein was heated at 120°C for 1 hr, added to a fresh wheat flour (protein 8.6%), and the protein and wheat flour were subjected to acetic acid (pH 3.5) fractionation. The results showed that egg white protein increased the binding between prime starch (PS) and tailings (T) fractions in wheat flour. Several conditions for heating of egg white protein were examined to determine 1) the effect of the amount of water added to the protein before heating; 2) the effect of heating time (hr) on protein at 120°C; and 3) the effect of heating temperature on the binding between PS and T fractions. The amount of protein per 50.0 g of wheat flour was further examined for the maximum binding between PS and T fractions. The heated egg white protein was analyzed by Fourier transform infrared (FT‐IR) spectroscopy, and the changes in the secondary structures (α‐helix, β‐sheets, and others) of the protein caused by heating were studied. When egg white protein was heated at 120°C for 8 hr, 9.0% of the α‐helix structures of egg white protein decreased to 3.0%, and 37.0% of the β‐sheet structures increased to 41.0%. The decrease of α‐helix and increase of β‐sheet structures of heated egg white protein were related to the increase in the binding between PS and T fractions in the same heated egg white protein and wheat flour sample. A relationship between the structural changes in heated egg white protein (180°C, 1 hr) and the binding between PS and T fractions in the heated egg white protein and wheat flour was also observed.     

Myowater dynamics and protein secondary structural changes as affected by heating rate in three pork qualities: a combined FT-IR microspectroscopic and 1H NMR relaxometry study

The objective of this study was to investigate the influence of heating rate on myowater dynamics and protein secondary structures in three pork qualities by proton NMR T2 relaxation and Fourier transform infrared (FT-IR) microspectroscopy measurements. Two oven temperatures at 100 degrees C and 200 degrees C corresponding to slow and fast heating rates were applied on three pork qualities (DFD, PSE, and normal) to an internal center temperature of 65 degrees C. The fast heating induced a higher cooking loss, particularly for PSE meat. The water proton T21 distribution representing water entrapped within the myofibrillar network was influenced by heating rate and meat quality. Fast heating broadened the T21 distribution and decreased the relaxation times of the T21 peak position for three meat qualities. The changes in T21 relaxation times in meat can be interpreted in terms of chemical and diffusive exchange. FT-IR showed that fast heating caused a higher gain of random structures and aggregated beta-sheets at the expense of native alpha-helixes, and these changes dominate the fast-heating-induced broadening of T21 distribution and reduction in T21 times. Furthermore, of the three meat qualities, PSE meat had the broadest T21 distribution and the lowest T21 times for both heating rates, reflecting that the protein aggregation of PSE caused by heating is more extensive than those of DFD and normal, which is consistent with the IR data. The present study demonstrated that the changes in T2 relaxation times of water protons affected by heating rate and raw meat quality are well related to the protein secondary structural changes as probed by FT-IR microspectroscopy.     

Mineral balance in milk heated using microwave energy

Milk heated to 75 and 85 degrees C in a water bath or in a microwave oven was assayed for changes in salt partitioning after cooling to room temperature. To properly to assess differences and draw valid comparisons, the two heating methods used in the experiment were applied to samples for identical exposure times, and the samples were heated to attain the same final temperatures. Although the soluble Ca and P(i) contents were lower in the heated milk samples, no significant differences in salt partitioning were found between microwave and conventional heating. Ionic calcium levels in the milk samples pasteurized using microwave energy were very close to the levels in the samples heated in a conventional water bath (approximately 90% of the level in the untreated milk samples). The microwave heating-induced changes were completely reversed after storage at 20 degrees C for 24 h. The coagulation properties of the heated milk samples were also examined, and the coagulation time was longer and the curd formation rate slower in the microwave-heated milk than in the raw milk. Still, the experimental results demonstrated that microwave heating was no more detrimental to the milk than conventional heating and could thus be used for pasteurization purposes.     

Influence of Sodium Chloride on Color Development of Cereal Model Systems Through Changes in Glass Transition Temperature and Water Retention

Research efforts aim to enhance fundamental understanding about the role of salt in cereal products. Such knowledge may open new strategies for salt reduction in respective product categories. A model system, containing pregelatinized starch, glucose, and amino acids heated at 230°C for up to 10 min demonstrated that NaCl leads to darker products compared with the same model heated without NaCl (P < 0.05). The same trend was observed in wheat breakfast cereal flakes toasted at 230°C. The present study investigated two hypotheses how salt may influence color formation through Maillard Reaction: 1) hygroscopic behavior of salt may change the retention of water during heating and encourage Maillard reactions by improving mobility of reactants; 2) salt has a plasticizing effect and the presence of salt might keep the product in a rubbery state longer while heating, hence improving mobility and Maillard reactions of reactants. The same models (pregelatinized starch, glucose, and amino acids) mixed with several types of plasticizers (NaCl, KCl, or trehalose) and a blank without plasticizer were made and heat‐treated under controlled conditions. The presence of plasticizers always led to darker products but no correlation was found between color formation, the hygroscopic behavior of the system, and its glass transition temperature as measured by phase transition analyzer.     

Comparison of changes in the secondary structure of unheated, heated, and high-pressure-treated beta-lactoglobulin and ovalbumin proteins using fourier transform raman spectroscopy and self-deconvolution

Changes in protein secondary structure and conformation of ovalbumin and beta-lactoglobulin (15% protein w/w) were investigated by Fourier transform Raman spectroscopy and self-deconvolution. The amounts of alpha-helix, beta-sheets, random coil, and beta-turns in native beta-lactoglobulin were 15, 54, 6, and 25%, respectively, and those for ovalbumin (41, 34, 13, and 12%) compared well with published values obtained by X-ray crystallography. The proteins were heated at 90 degrees C for 30 min and high-pressure-treated at 600 MPa for 20 min. Heating increased beta-sheet structures in both proteins at the expense of alpha-helix; for beta-lactoglobulin beta-sheet structures increased from 54 to 70% and for ovalbumin, from 34 to 54%. Random coil increased from 6% in the native protein to 30% in high-pressure-treated beta-lactoglobulin. However, for ovalbumin, the contribution from beta-turns doubled in high-pressure-treated samples, with little change in random coil. Further examination of the deconvoluted amide I band in heated samples revealed several component bands. Bands at 1626 and 1682 cm(-1) for ovalbumin and at 1625 and 1680 cm(-1) for beta-lactoglobulin were observed and are associated with aggregated, intermolecular beta-sheet (beta-aggregation), indicative of heat denaturation. The band seen at 1632-1640 cm(-1) corresponded to intramolecular beta-sheet structures, whereas the band at 1625 cm(-1) is associated with exposed beta-sheets (for example, beta-strands with strong hydrogen bonding that are not part of the core of beta-sheets). In high-pressure-treated samples bands were also observed at 1628 and 1680 cm(-1) for ovalbumin and at 1626 and 1684 cm(-1) for beta-lactoglobulin, suggesting involvement of beta-sheet structures in protein aggregation. Raman bands were observed at 1665-1670 cm(-1) for ovalbumin and at 1663-1675 cm(-1) for beta-lactoglobulin due to random coil structures. The bands at 1650-1660 cm(-1) due to alpha-helices were observed in both heated and high-pressure-treated samples. In addition, in heated samples of both ovalbumin and beta-lactoglobulin, peak intensity increased for beta-sheet in the amide III region, 980-990 cm(-1), and decreased for helix structures (900-960 cm(-1)). In contrast, there was no peak at 1240 cm(-1) (amide III beta-sheet structures) in either high-pressure-treated ovalbumin or beta-lactoglobulin, suggesting that high-pressure denaturation at 600 MPa for 20 min is less extensive than heat denaturation at 90 degrees C for 30 min.     

Effect of Batter Solids and Starch Type on the Structure of Baked Starch Foams

The effects of starch type on the properties of baked starch foams were investigated. Starch types used for baking were normal corn, normal potato, waxy corn, high-amylopectin potato, wheat, and tapioca. Solids content of the starch batters used to bake foam trays ranged from 25 to 45%. Processing parameters and physical properties of the foams were examined. Starch-foamed trays were formed by heating a starch batter inside a closed mold. Scanning electron micrographs showed that the thin-walled foamed trays have a dense outer skin and a less dense interior with large cells. The weight of the foamed trays and density of the foam depended on the amount of batter cooked inside the mold, the percent solids of the batter, and the type of starch used. The high-amylopectin starches made the lightest trays, while the normal cereal starches made the heaviest trays. Baking time depended on percent solids of the batter, the batter volume added to the mold, and starch type. The normal cereal starches had the longest baking times and the high-amylopectin starches had the shortest baking times Strength and flexibility of the trays are correlated with tray weight and foam density. Heavier trays had greater strength and less flexibility than did lighter trays. Physical properties of the trays can be tailored to meet specific criteria by changing the starch type used and the batter solids.     

解冻方式对调理猪肉饼品质的影响

为探索不同解冻方式对猪肉饼品质和蛋白质氧化程度的影响,本试验将-18℃冻藏的调理猪肉饼分别采用室温解冻、冷藏解冻、流水解冻以及盐水解冻4种方式进行解冻,通过测定解冻后肉饼的保水性(解冻损失率、离心损失率)、pH值、TBARS值、TVB-N值,并测定猪肉饼肌原纤维蛋白羰基含量、巯基含量、蛋白溶解等,分析不同解冻方式对其蛋白氧化程度的影响。结果表明,解冻对调理猪肉饼保水性有较大影响,其中空气解冻与冷藏解冻组的保水性最好,解冻损失维持在5.03%~5.75%之间,离心损失率在31.02%~32.19%之间;同时与新鲜肉饼组相比,空气解冻、盐水解冻和流水解冻组猪肉饼TVB-N值显著上升(P<0.05),盐水解冻组TVB-N值上升至3.17 mg·100g^-1;但解冻对调理肉饼pH值、TBARS值、色泽的影响均不显著(P>0.05);通过对肌原纤维蛋白氧化程度的测定发现,解冻会引起肌原纤维蛋白羰基含量上升、巯基含量和溶解度下降,SDS-PAGE试验也证明解冻会引起蛋白质发生不同程度的降解。本研究为实际生产中冻结肉制品解冻工艺的选择与优化提供了一定的理论依据。     

Rheological Properties of Soft Wheat Flour Doughs: Effect of Salt and Triglycerides

The small deformation rheological properties of wheat flour doughs in relation to their structure and hydration were studied by dynamic mechanical thermal analysis, differential scanning calorimetry, and electron spin resonance. The effect of salt and triglycerides was also examined and compared with results we obtained previously on starch dispersions. Moisture content was adjusted to 48 or 60% (w/w, wb). Samples contained 0–16% NaCl (g/100 g of flour‐water) and 0–18% triolein or lard (g/100 g of flour‐water). The obtained results suggested that starch has an active role in determining the evolution of dough rheological characteristics during heating. The main factors controlling rheological behavior during thermal treatment are the volume fraction and deformability of starch granules. Gluten changes the viscoelasticity of the continuous phase and competes with starch for water. The addition of sodium chloride to flour dispersions shifted the structural disorganization and rigidity increased during heating to higher temperatures. At >7% NaCl, the reverse effect was observed. The mechanism controlling the effect of salt on dough rheological behavior was explained in terms of effect on water properties and on starch structure and hydration. Triglycerides had a lubricant effect (i.e., lowering G′ modulus) on the wheat flour dough system. These effects are of great importance for production and quality of bakery products.     

Gelling properties of heat-denatured beta-lactoglobulin aggregates in a high-salt buffer

Thermal denaturation, rheological, and microstructural properties of gels prepared from native beta-lactoglobulin (beta-LG) and preheated or heat-denatured beta-LG (HDLG) aggregates were compared. The HDLG was prepared by heating solutions of 4% beta-LG in deionized water, pH 7.0, at 80 degrees C for 30 min and then diluted to the desired concentration in 0.6 M NaCl and 0.05 M phosphate buffer at pH 6.0, 6.5, and 7.0. When reheated to 71 degrees C, HDLG formed a gel at a concentration of 2% protein. At pH 7.0, 3% HDLG gelled at 52.5 degrees C and had a storage modulus (G') of 2200 Pa after cooling. beta-LG (3%) in 0.6 M NaCl and 0.05 M phosphate buffer, pH 7.0, did not gel when heated to 71 degrees C. The gel point of 3% HDLG decreased by 10.5 degrees C and the G' did not change when the pH was decreased to 6.0. The HDLG gel microstructure was composed of strands and clumps of small globular aggregates in contrast to beta-LG gels, which contained a particulate network of compacted globules. The HDLG formed a gel at a lower concentration and lower temperature than beta-LG in the high-salt buffer, suggesting an application in meat systems or other food products prepared with salt and processed at temperatures of < or =71 degrees C.     

In situ imaging highlights local structural changes during heating: the case of meat

Understanding and monitoring deformation and water content changes in meat during cooking is of prime importance. We show the possibilities offered by nuclear magnetic resonance imaging (MRI) for the in situ dynamic measurement of deformation fields and water content mapping during beef heating from 20 to 75 °C. MRIs were acquired during heating, and image registration was used to calculate the deformation field. The temperature distribution in the sample was simulated numerically to link structural modifications and water transfer to temperature values. During heating, proton density decreases because of a magnetic susceptibility drop with temperature and water expulsion due to muscle contraction. A positive relationship was found between local cumulative deformation and water content. This new approach makes it possible to identify the deformation field and water transfer simultaneously and to trace thermal history to build heuristic models linking these parameters.     

Tracking Arabinoxylans Through the Preparation of Pancakes

Arabinoxylans (AX) are well known to have a wide‐ranging influence on wheat (Triticum aestivum L.) end‐use quality and are associated with health benefits. There is little information on the effects of processing on AX properties in high‐water‐content batter‐based products and on the associations between AX properties and end‐use quality in such products. The objective of this study was to track total and water‐extractable AX (TAX and WEAX, respectively) contents and determine changes in AX characteristics throughout the baking process of pancakes, a batter‐based wheat product. The TAX and WEAX contents along with the arabinose‐to‐xylose (A/X) ratio were quantified in refined flour and wholemeal as well as batter and pancakes from two soft and three hard wheat varieties. ANOVA F values indicated that the variation in TAX content was influenced most by sample type differences (flour versus batter versus pancakes), whereas varietal differences were responsible for the greatest differences in WEAX. In separate analyses on refined and wholemeal flours, the highest F values were for variety WEAX, largely attributed to the higher WEAX content of the three hard varieties. WEAX levels generally increased slightly from flour to batter to pancakes in refined flour. The WEAX content in flour, batter, and pancakes of both refined flour and wholemeal was highly correlated with pancake volume. These observations suggest moderate changes in wheat AX characteristics during processing and a positive association of WEAX levels with end‐product volume in a batter‐based product.     

Sequential Acid,Alkaline, and Enzymatic Modifications of Chickpea and Lentil Flours Impacted Batter Physical Properties

The effect of sequential acid, alkaline, and enzymatic treatment of chickpea and lentil flours on batter rheological properties was investigated. Substitution of wheat with disrupted chickpea and lentil flours significantly (P < 0.05) increased water‐holding capacity from 66.8% in wheat flour to more than 70.0% based on the disruption treatment, indicating an improved adhesion of coated batter. Flow behavior index of batter treatments of partially replaced wheat flour with various ratios of disrupted chickpea and lentil flours ranged from 0.88 to 1.36 and was significantly (P < 0.05) lower than the flour (i.e., 2.15) and nondisrupted control (i.e., 1.28–1.38 for chickpea and 1.22–1.28 for lentil) flours. Consistency coefficients of disrupted chickpea and lentil flours were significantly (P < 0.05) greater when replacing wheat control, indicating a best fit for the shear‐thickening model. Flour disruption decreased the treatment's pasting properties, except the setback, providing support for the significant role of proteins in dictating the pasting characteristics of batter flour treatments. Results of this study suggested a potential use for treated chickpea and lentil flours in enhancing batter rheological properties including adhesion and water‐holding capacity.     

超高压处理对低盐牛肉乳化肠品质的影响

为探究超高压(UHP)处理对低盐牛肉乳化肠品质的影响,本试验以低盐牛肉乳化香肠(食盐添加量1.4%)为研究对象,以未经UHP处理的C1组(食盐添加量2.8%)和C2组(食盐添加量1.4%)为对照,比较了不同压力(100、200、300、400 MPa)对低盐牛肉乳化肠感官品质、理化指标和微生物指标的影响。结果表明,UHP处理降低了处理组乳化肠的菌落总数(TVC)和挥发性盐基氮(TVB-N)值,当压力≥200 MPa时,乳化肠的TVC和TVB-N值均显著低于C1和C2组(P<0.05);随着压力的增大,蒸煮损失先减小后增大,100和200 MPa处理组乳化肠蒸煮损失最低,分别为3.00%和3.97%,且均显著低于C2组(P<0.05);与C2组相比,UHP处理使低盐乳化肠的硬度、弹性、咀嚼性、内聚性都有所增加,并提高了产品的咸味分数,对多汁性、总体风味及总体可接受性具有改善作用;UHP处理促进了脂质氧化,当压力为300 MPa时,硫代巴比妥酸反应产物(TBARS)值最高;亚硝酸盐含量不受UHP处理的影响,且符合肉制品亚硝酸盐残留量要求。综上,UHP处理能够改善低盐牛肉乳化香肠的品质特性,这为低盐肉制品的开发提供了技术支持和理论依据。     

肉蛋白-畜产源非肉蛋白互作的物理化学研究

为了研究典型畜产源非肉蛋白与肌原纤维蛋白(MP)的相互作用,建立了模拟肉制品加工条件下二者等比例用量的溶液及热致凝胶模型,将血浆蛋白(PPP)、鸡蛋白分离蛋白(EPI)和酪蛋白酸钠 (SC)分别与MP 按照1∶1比例混合,以各单一蛋白为对照,利用流变仪、质构仪和低场核磁等仪器测定各蛋白粘度、加热过程的动态粘弹性、凝胶强度和水分子状态等指标。结果表明,PPP和EPI在加热过程中自身可形成凝胶,但与MP相比,储能模量(G')较弱,SC在加热过程中未能形成凝胶。将PPP和EPI分别与MP混合时,流变结果显示,PPP+MP、EPI+MP相互作用指数均大于零,与单独的MP相比,其G'无显著差异;加入PPP未能显著改变MP的凝胶强度,但加入EPI显著提高了MP的凝胶强度(P<0.05);PPP、EPI的加入均能使凝胶保水性显著提高,不易流动水比例增大(P<0.05)。SC会对MP产生一定不利影响,二者相互作用指数小于零,其G'、凝胶强度及凝胶保水性显著降低(P<0.05)。总体而言,PPP、EPI与MP之间在加热后均产生正向相互作用,而SC对MP产生不利影响。本研究结果为凝胶乳化类肉制品中非肉蛋白的应用提供了一定的理论借鉴。     

Gluten-free sorghum bread improved by sourdough fermentation: biochemical, rheological, and microstructural background

This study was conducted to improve the quality and theoretical understanding of gluten-free sorghum bread. The addition of 2% hydroxypropyl methylcellulose improved bread based on 105% water, 70% sorghum flour, and 30% potato starch. Nevertheless, a flat top and tendency toward a hole in the crumb remained. Sourdough fermentation of the total sorghum flour eliminated these problems. Size-exclusion high-performance liquid chromatography demonstrated that during sourdough fermentation, proteins from the dough liquid were degraded to peptides smaller than kafirin monomers (<19 kDa). Laser scanning confocal microscopy showed aggregated protein in bread crumb without sourdough fermentation, whereas with sourdough fermentation, only small isolated patches of protein bodies embedded in matrix protein remained. In oscillatory temperature sweeps, sourdough fermentation caused a significantly higher resistance to deformation (|G*|) after gelatinization of the above batter relative to batters without sourdough. Results suggest that a strong starch gel, without interference of aggregated protein, is desirable for this type of bread.