冷冻面团制作的面包在储存期间风味的变化

在冷冻甜面团的研究开发中,通过感官评价小组采用描述性分析对面包样品的风味剖析,同时采用固相微萃取(SPME)技术分别提取样品中的挥发性风味物质,并经气相色谱-质谱(GC-MS)联用法进行鉴定,重点研究了冷冻甜面团在不同冷冻储存阶段所制作的面包的风味变化问题。结果发现,用冷冻甜面团制作的面包与相同配方制得的新鲜面包相比,在冷冻期间21～28d内,烘焙风味的劣化即呈现出来并急速降级,如酸含量明显升高,醇类明显降低,醛类相对较高,酯类、呋喃类有所升高但芳香族化合物却较低,并在长达70d的冷冻储存期间趋于不可逆转的稳定状态。     

Dough and crumb grain changes during mixing and fermentation and their relation with extension properties and bread quality of yeasted sweet dough

Dough and crumb grain evolution of yeasted sweet dough, as affected by the combined effect of mixing (dough development) and fermentation times, and their relation to rheological properties and bread quality was studied. Structural changes of under or optimum developed dough, without fermentation, were related mainly to increments in extensibility (P > 95%), without a noticeable change in pH. At all mixing stages, fermentation duration increased R_m, whereas extensibility and pH decreased. When plotting R_m with bread specific volume, cell area, total cell area fraction or yellow crumb colour parameter (b*) simple mathematical models, with determination coefficients larger than 0.85 were obtained. Bread crumb image analysis showed that crumb cell size was not affected by mixing time, while fermentation duration had a direct influence on this parameter, increasing the proportion of the smallest and the largest crumb cells, without changing cell density, possibly as a result of Ostwald ripening, coalescence and separation‐redistribution mechanisms.     

南瓜粉对小麦粉粉质特性及面团品质的影响

以南瓜粉和小麦粉为原料,考察南瓜粉添加量对小麦粉粉质特性、糊化特性及面团的晶型与结晶度、水分分布、流变学特性的影响。结果表明：随着南瓜粉添加量的增大,面团的稳定时间、公差指数、带宽及糊化特性均显著性下降（P＜0.01）;储能模量和损耗模量先下降后上升,面团弹性先升高后降低;弱结合水含量逐渐增大;当南瓜粉添加量为15%时,面团中淀粉结晶度出现最大值,为23.9%。综上,适量添加南瓜粉可降低面筋蛋白浓度,抑制淀粉的糊化特性,提高面团弹性,从而改善面粉粉质及品质特性。     

甘薯粉丝生产中粉团的触变性研究

针对传统粉丝加工过程中粉团所表现出的流变性质,用动态流变仪对粉团的触变性进行了测定和研究。通过回归分析,建立起粉团在触变条件下的流变模型方程并探讨了粉团含水量、含芡量及温度对粉团触变性的影响。     

Proline accumulation in baker's yeast enhances high-sucrose stress tolerance and fermentation ability in sweet dough

During bread-making processes, yeast cells are exposed to various baking-associated stresses. High-sucrose concentrations exert severe osmotic stress that seriously damages cellular components by generation of reactive oxygen species (ROS). Previously, we found that the accumulation of proline conferred freeze-thaw stress tolerance and the baker's yeast strain that accumulated proline retained higher-level fermentation abilities in frozen doughs than the wild-type strain. In this study, we constructed self-cloning diploid baker's yeast strains that accumulate proline. These resultant strains showed higher cell viability and lower intracellular oxidation levels than that observed in the wild-type strain under high-sucrose stress condition. Proline accumulation also enhanced the fermentation ability in high-sucrose-containing dough. These results demonstrate the usefulness of proline-accumulating baker's yeast for sweet dough baking.     

和面机扭矩与面团和制效果关系的研究

和面过程中面团扭矩变化跟面团形成程度具有一定相关性。以评价面包成品的质构及比容等为指标,分别考察了特定配方、不同配方组成以及不同水温等影响因素下,面团扭矩与面团和制效果的关系。结果表明,在不同和面条件下,单位质量小麦粉扭矩峰值差变化不大,当该峰值差在0.009-0.012 8N·m/g时,所得面团烘焙得到的面包品质最佳。     

Influence of yeast and frozen storage on rheological, structural and microbial quality of frozen sweet dough

The aim of the present study was to investigate the effect of yeast content and frozen storage (9 weeks at −40 °C) on the structural and rheological parameters, and fermentative activity of frozen sweet dough. Two types of dough were studied (to estimate dough shelf life): simple yeasted dough (SY) and double yeasted dough (DY). Fermentative activity (yeast viability, gassing power, and dough volume), rheological and textural parameters were assessed for frozen sweet doughs.These effects were explored by different and complementary methods: Fourier transform infrared (FTIR), dynamic rheology, texture profile analysis (TPA) and differential scanning calorimetry (DSC).The data showed that the longer the frozen storage time at −40 °C, the higher the decreased of frozen sweet dough quality. The rheological attributes such as hardness, ΔS, springiness, tan δ and yeast activity declined significantly during frozen storage. This modification led to lower specific volume of frozen sweet dough during proofing.The observed changes of the frozen sweet doughs rheological properties after thawing may be attributed to the damage on the gluten cross-linking, mainly produced by the ice crystallization during frozen storage. The storage effect was particularly concentrated in the first 27 days of storage.     

市售面包酵母冷冻过程发酵性能研究

为了研究市售的面包生产用酵母产品的品质,收集了6种活性干酵母和1种压榨酵母共7种市售酵母产品,在评价其初始活力后进行了预发酵、冷冻、冻藏等处理,并对比研究了处理前后的发酵力、起酵时间、酵母存活率及酵母形态等特征。结果表明不同品牌、状态的产品在发酵力、起酵时间、酵母形态学特征和低温敏感性等方面均有较大差异,不同酵母产品在冷冻和冻藏过程中的酵母活力受产品本身及加工过程影响较大。研究为相关面包及面制品等发酵食品生产企业应根据自身需要选择和正确使用合适的酵母产品提供了依据。     

Characterization of a Torulaspora delbrueckii diploid strain with optimized performance in sweet and frozen sweet dough

Torulaspora delbrueckii is a baker's yeast that is highly tolerant to freeze-thaw stress, making it suitable for frozen dough technology. The T. delbrueckii strain PYCC5321, isolated from traditional bread dough, combines this tolerance with a high degree of ionic and osmotic stress resistance. However, the industrial use of this strain for frozen and sweet frozen baking is hampered by its small cell size, which causes clogging problems at the filtering stage. Here, we report the construction of a stable diploid strain of T. delbrueckii PYCC5321, which we named Td21-2n. The new strain was more than 2.7-fold bigger than their haploid counterpart, whereas biomass yield, stress resistance and sweet dough leavening ability were found to be similar in both strains. Moreover, the gassing power of the diploid after dough freezing also remained unaltered. Thus, Td21-2n meets the requirements necessary for industrial production and is suitable for application in frozen sweet baking products.     

Image analysis of structural changes in dough during baking

The bakery market is developing new technologies based on dough partial baking and the study of the changes that dough undergoes through the whole baking process could help in the selection of baking times. The aim of this work was to study the changes of dough structure and their relationship with dough temperature, mass loss and loaf height during baking by applying image analysis techniques. Results showed that during baking, bubble coalescence was presented, observing a maximum at the first stages of baking (<250 s). This phenomenon was associated with an increment in dough height without a significant change in dough centre temperature. Fractal dimension of texture of crumb, fractal dimension of contour of cells and crumb grain features were useful indicators of coalescence as well as to distinguish the baking time needed for crumb features remain invariable.     

玉米油在油条煎炸过程中的品质变化

以玉米油在190℃下连续煎炸油条32h,每2h取一次煎炸油样,对其感官、理化指标、VE、脂肪酸等指标进行检测,研究玉米油煎炸油条过程中的品质变化。结果表明:连续煎炸32h后,玉米油的吸光度OD448nm由0.028上升到0.673,酸价从0.33mg KOH/g增大至2.40mg KOH/g,羰基价由7.78 meq/kg增大至97.40 meq/kg,极性组分由3.81%增加至30.16%。依据GB 7102.1—2003中的相关规定,玉米油在190℃下连续煎炸油条不宜超过18h。     

Structural changes in the wheat dough and bread with the addition of alpha-amylases

The influence of fungal and bacterial -amylases on the texture and microstructure of dough and bread was investigated. Loaf specific volume, crumb porosity and texture properties were accepted as bread structure and texture characteristics. The microstructure analysis of dough and bread using light and scanning microscopy methods was performed.The changes in loaf specific volume, crumb porosity and texture properties showed different anti-staling activity of the enzymes used. The simultaneous action of enzyme addition and the fermentation process evoked significant changes in the microstructure of dough. The character of these changes depended on the kind of enzyme used. A substantial effect of both amylases on starch behaviour during bread baking and staling was also observed.     

抗冻性面包酵母选育及其在冷冻面团中应用

冷冻面团技术代表了当今世界面包生产的主流,它的应用得到了人们的广泛关注。控制冷冻面团的质量需要从多方面考虑,其中选择抗冻性面包酵母为问题的关键。研究发现,面包酵母的抗冻性可能与耐酒精度相关联,本文通过耐酒精度实验,选育出了抗冻性面包酵母S.cerevisiae X—003,并对其在冷冻面团中的应用进行了研究。     

面筋含量与面筋指数在面团熟化过程中的变化

以高筋粉、中筋粉、低筋粉为原料粉.三种原料粉在温度为30℃,湿度为70%的条件下,分别选取熟化0min,18min,36min,54min,72min,90min为熟化点来制取样品.采用手洗法测定各熟化时间点上的湿面筋含量;利用干面筋仪与面筋指数仪测定各熟化时间点上的干面筋含量及面筋指数.得到面筋含量与面筋指数在面团熟化过程中的变化规律,从而为制面行业根据产品要求,制定最佳熟化时间提供了理论上的依据.     

Structural and ultrastructural changes in yeast cells during autolysis in a model wine system and in sparkling wines

This study shows the changes that occur during the autolysis of yeast in a model wine medium and in a sparkling wine after 12 months of aging, using Nomarsky Light Microscopy and Low Temperature Scanning Electron Microscopy (LTSEM). The size of the yeasts after 24 h of autolysis in a model medium is much smaller than when they are in the growth stage. With LTSEM. a large number of folds can be observed on the surface of the yeast and practically empty cells. Greater morphological changes, both structural and ultrastructural, can be observed in the yeast after 12 months of aging in wine than in the yeast after 24 h of induced autolysis. However, less of the cytoplasmic content of the yeast that has undergone autolysis in the wine was solubilized than that of the yeast after 24 h of autolysis in the model wine system. These findings indicate that autolysis of yeast in wine is a long-lasting process, which continues for at least 12 months.     

Effects of oxidizing agents and defatting on the electrophoretic patterns of flour proteins during dough mixing

3 ) or ascorbic acid at levels of 50, 100 and 150 mg/kg. The effects of mixing, lipid extraction and additives on dough proteins were studied using electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis results for the 50 % 1-propanol insoluble fractions of both varieties showed that the relative band intensities of the flours were more intense than those of the optimum mixed control doughs. KBrO₃ did not affect the extractability of protein in optimum mixed dough, while ascorbic acid reduced the extractability. Generally, overmixing caused a decrease in relative band intensities. The reductions in the relative band intensities were especially noticeable in the oxidant-added doughs. The relative band intensities of the defatted samples were more intense than those of the undefatted ones. Received: 7 December 1999 / Revised version: 14 February 2000     

Energetical and rheological approaches of wheat flour dough mixing with a spiral mixer

Wheat flour dough was mixed in a spiral mixer for different operating conditions, at a speed ranging from 80 to 320 rpm, for a period of 7-15 min. The specific mechanical energy E_s delivered and the dough temperature T_d were continuously recorded and varied from 7 to 82 kJ/kg and T_d of 13.5 to 36 °C, respectively. E_s and T_d were strongly correlated because of viscous dissipation but variations of ingredients initial temperature allowed to uncouple them. The energy balance during mixing process was set through a simple model assuming constant heat transfer (h = 75 W/(m² °C)) which took into account thermal losses. Shear viscosity curves of the dough were determined by correlating volumic power to angular speed; by comparison to typical dough shear flow curve, a constant characteristic of the mixer geometry (K_s = 1.55) was determined like for models of mixer power consumption. The impact of mixing on small deformation rheological properties was assessed by DMA and the variations of the ratio, of maximum (75 °C) to minimum (50 °C) elastic modulus, was interpreted in relation with gluten network development.     

揉面过程中面团面筋蛋白结构的变化

研究了手工揉面过程中面团面筋蛋白结构的变化。结果表明:揉面过程中,揉面初期(2 min)面团游离巯基下降10.69%,二硫键增加4.48%,随后缓慢增长或下降;氢键显著增多(P<0.05),疏水作用力显著下降(P<0.05);二级结构中的无规则卷曲初始骤降56.52%,β-折叠初始增加32.34%,随后小幅增长或下降,α-螺旋和β-转角无明显变化;面筋蛋白、麦醇溶蛋白、麦谷蛋白的SDS可萃取率均有不同程度下降;B/C-LMW-GS峰面积分别增加4.56%,2.61%,4.11%,6.73%,3.18%,0.81%,α-麦醇溶蛋白亚基峰面积分别降低22.42%,10.87%,11.59%,12.87%,9.22%,4.35%。手工揉面促进了面筋蛋白的交联聚合反应,使其蛋白构象朝着更为有序和稳定方向发展,进而增强了面团的黏弹性。     

Growth of Salmonella enterica and Staphylococcus aureus in no-knead bread dough during prolonged yeast fermentation

A convenient bread making method involving prolonged fermentation of no-knead (nonkneaded) dough has become popular in recent years. In the present study, the microbial safety of no-knead dough made with a 375:325:5:1 weight ratio of flour, water, salt, and bread yeast was investigated. Three brands of dehydrated yeast were used for this study. The growth of inoculated Salmonella enterica and Staphylococcus aureus in no-knead dough during fermentation was significant (P<0.05), regardless of yeast brand. The multiplication rates of S. enterica in the initial 12 h and S. aureus over the entire 24 h of fermentation were positively correlated with fermentation temperatures of 21 to 38°C (P<0.005; r≥0.996). Mean counts of S. enterica increased by 0.5, 1.5, 1.9, and 2.4 log CFU/g, respectively, after 6, 12, 18, and 24 h of fermentation at 21 °C. The level of S. aureus increased by 0.4, 1.1, 1.7, and 2.2 CFU/g, respectively, after 18 h of fermentation at 21, 27, 32, and 38 °C. Because prolonged fermentation permits substantial growth of infectious and/or toxin-producing foodborne pathogens, the making of slow-rise, no-knead bread may compromise consumer kitchen sanitation and food safety.