冷冻面团技术的应用和发展

冷冻面团技术因其特殊的优越性成为我国食品工业最具发展潜力的技术之一,可以运用在面包、馒头、包子等面食食品中。面粉、酵母、工艺条件(调粉工艺、前发酵工艺、冷冻系统),以及添加剂等对冷冻面团质量有影响,酵母的耐冻性弱、冷冻过程中面团组分遭到破坏是目前冷冻面团技术中存在的问题。     

Fermentation Process and Grain Structure of Baked Breads from Frozen Dough Using Freeze-Tolerant Yeasts

The fermentation process for frozen doughs using freeze‐sensitive (Saccharomyces cerevisiae, Kyowa for sweet bread; S. cerevisiae, FC for white bread) and freeze‐tolerant (S. cerevisiae, YF for sweet bread) yeasts was traced by magnetic resonance imaging (MRI). Grain network structures of baked breads were also visualized by MRI. Prefermentation before freezing, punching and remolding, or resheeting and molding treatments increased loaf volume by 10 to 110% for the baked breads using freeze‐tolerant yeast, while these treatments decreased loaf volume by 70% using freeze‐sensitive yeast. The first fermentation before freezing and the second fermentation with punching or resheeting after thawing are useful for obtaining good quality breads from frozen dough using freeze‐tolerant yeast.     

木聚糖酶对冷冻面团和馒头品质的影响

本实验研究了木聚糖酶对冻藏1d、7d、14d的冷冻面团和馒头品质特性的影响;并采用差示量热扫描仪(DSC)测定了冷冻面团的可冻结水(冰)含量,讨论了木聚糖酶改善冷冻面团品质的热力学机制。研究结果表明,随着冻藏时间的延长,面团的发酵力、酵母存活率、馒头比容、抗老化能力均呈现一定的下降趋势;在相同的冻藏时间下,木聚糖酶对面团的发酵特性和馒头品质改善作用明显;木聚糖酶含量为80mg.kg_-1时,可冻结水(冰)含量最低;添加木聚糖酶后,冰晶颗粒更加细小均匀。这说明适量的木聚糖酶能够有效地降解水不溶性阿拉伯木聚糖,使更多的水分保留在面筋网络结构中,从而抑制低温面筋网络结构和酵母细胞的破坏作用,改善馒头品质。     

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.     

Characterization of a new set of mutants deficient in fermentation-induced loss of stress resistance for use in frozen dough applications

In frozen dough applications a prefermentation period during the preparation of the dough is unavoidable and might also be important to obtain bread with a good texture. A major disadvantage of the prefermentation period is that it is associated with a rapid loss of the freeze resistance of the yeast cells. A major goal for the development of new baker's yeast strains for use in frozen dough applications is the availability of strains that maintain a better freeze resistance during the prefermentation period. We have isolated mutants that retain a better stress resistance during the initiation of fermentation. Some of these showed the same growth rate and fermentation capacity as the wild type cells. These mutants are called 'fil', for deficient infermentation induced loss of stress resistance. First we used laboratory strains and heat stress treatment, given shortly after the initiation of fermentation, as the selection protocol. The first two mutants isolated in this way were affected in the glucose-activation mechanism of the Ras-cAMP pathway. The fil1 mutant had a partially inactivating point mutation in CYR1, the gene encoding adenylate cyclase, while fil2 contained a nonsense mutation in GPR1. GPR1 encodes a member of the G-protein coupled receptor family which acts as a putative glucose receptor for activation of the Ras-cAMP pathway. In a next step we isolated fil mutants directly in industrial strains using repetitive freeze treatment of doughs as selection protocol. Surviving yeast strains were tested individually for maintenance of fermentation capacity after freeze treatment in laboratory conditions and also for the best performing strains in frozen doughs prepared with yeast cultivated on a pilot scale. The most promising mutant, AT25, displayed under all conditions a better maintenance of gassing power during freeze-storage. It was not affected in other commercially important properties and will now be characterised extensively at the biochemical and molecular level.     

Aeration and Foam Control in Baker's Yeast Production: Mapping Patents

A key ingredient in the baking industry, baker's yeast must be produced under strict controlled conditions. High yields of baker's yeast cannot be attained unless a huge quantity of air is injected into fermentation vats. This review of 245 patent specifications shows that inventors have paid much attention to the distribution of fine air bubbles in order to optimize oxygen transfer to the yeast cells. Technical solutions to reduce energy costs associated with aeration are also proposed. Intense aeration caused foaming problems, so mechanical destruction of foam was first proposed until inventions on specific chemical antifoams were patented. In recent years, the development of cheaper and more efficient foam control techniques has remained an issue. Aeration during yeast growth in tanks impairs its fermentative activity in anaerobic bread dough. Since the beginning of the 20th century, massive adoption of air‐grown fed‐batch baker's yeast probably encouraged sugar addition to stimulate yeast gassing activity in pan bread characterized by high loaf volume, especially those prepared under short dough fermentation conditions.     

Loading ofSaccharomyces cerevisiaewith glycerol leads to enhanced fermentation in sweet bread doughs

Addition of exogenous glycerol to yeast coupled with a period of storage under refrigerated conditions allowed for influx of the polyol and equilibration of its intra- and extracellular concentrations. Glycerol-added yeast exhibited greater fermentation activity when inoculated into sweet bread doughs than yeast to which no exogenous glycerol was added. This effect was found for all yeast strains investigated. Glycerol addition also resulted in significantly greater maintenance of the sweet dough fermentation activity of yeast when stored for up to three weeks at 4°C. Improvements were manifested when yeast were in aqueous or in compressed form. The effect of glycerol was dose- and equilibration-time dependent.     

A Novel Bread Making Process Using Salt-Stressed Baker's Yeast

ABSTRACT:  By adjusting the mixing order of ingredients in traditional formula, an innovative bread making process was developed. The effect of salt-stressed Baker's yeast on bread dough of different sugar levels was investigated. Baker's yeast was stressed in 7% salt solution then mixed into dough, which was then evaluated for fermentation time, dough fermentation producing gas, dough expansion, bread specific volumes, and sensory and physical properties. The results of this study indicated that salt-stressed Baker's yeast shortened fermentation time in 16% and 24% sugar dough. Forty minutes of salt stress produced significant amount of gas and increased bread specific volumes. The bread was softer and significantly improved sensory properties for aroma, taste, and overall acceptability were obtained.     

Improving freeze tolerance of yeast and dough properties for enhancing frozen dough quality - A review of effective methods

BackgroundFrozen dough technology could effectively extend the shelf life of bread to ensure the freshness, which is widely used and gradually replace the traditional bread production. However, during the production and storage of frozen dough, a series of problems could take place, such as inhibition of yeast activity, damage of the structure of the dough, leading to the deterioration of dough quality.Scope and approachThis review summarizes the factors that affect the final quality of frozen dough, including yeast activity, dough structure and dough properties. Some effective methods for improving freeze tolerance of yeast, dough structure and dough properties are discussed, including addition of various additives, use of genetic engineering technique, optimization of freezing and storage conditions, and employment of novel freezing technology.Key findings and conclusionsThe addition of additives can not only improve the freeze tolerance of yeast but also maintain the rheological and thermophysical properties of dough. Through the modification of gene, freeze tolerance and fermentation ability of yeast can be improved. Optimizing freezing and storage conditions ensures the activity of yeast as well as dough network structure so that freezing damage due to ice crystals can be minimized. In addition, novel freezing technology such as ultrasound-assisted freezing can simultaneously accelerate the freezing process as well as generate fine and uniform ice crystals, thus protecting dough network structure.     

不同酵母对冷冻面团发酵特性及馒头品质的影响

对市场上4种活性干酵母进行了无糖和低糖面团发酵活力及冷藏1周后发酵力的变化进行测定。结果表明:不同酵母在无糖面团和低糖面团中的发酵力存在差异,酵母Y2基本无差别,Y1、Y3和Y5发酵力都有不同程度的提高。冷藏7d后相对发酵力的测定表明:Y1、Y3和Y4在无糖面团中相对发酵力较高;Y2和Y3在低糖面团中的相对发酵力较高。通过无糖冷冻面团馒头感官评价及质构特性的测定,用酵母Y3来发酵的冷冻面团馒头品质较好。     

Frozen Sangak dough and bread properties: Impact of pre-fermentation and freezing rate

The impact of pre-fermentation time and freezing rate on Sangak frozen dough and bread quality were studied. The pre-fermented doughs for 0, 30, 60, 90, or 120 min were frozen under –20, –25, or –30°C in air blast freezer. After 24 h storage at –18°C, dough samples were baked after final fermentation. The yeast viability, gassing power, and dough development for fresh and frozen Sangak doughs were determined. Crust color, density, and shear stress of bread obtained from fresh and frozen Sangak dough were evaluated. The results showed that yeast survival initially increased and then decreased with increasing freezing rate. The maximum yeast survival was observed at short pre-fermentation (30 min). A direct relationship was observed between gassing power, dough development, and yeast viability. From bread quality point-of-view, short pre-fermentation and higher freezing rate led to a more desirable bread.     

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.     

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.     

基于模糊数学综合感官评价的甘薯淀粉面包的工艺优化

为了提高面包营养价值,改善滋味,降低面包老化速度,延长保质期,将甘薯淀粉添加到面包当中,采用单因素和正交实验,考察配方(甘薯淀粉、黄油、干酵母的添加量)及加工工艺(一次醒发时间、醒发温度和烘焙时间)对面包感官性状和质构的影响。基于模糊数学的评价方法评价甘薯淀粉面包的品质,对甘薯淀粉面包的形状、色泽、松软度、香味、滋味进行感官性质的分析。结果表明:最佳配方为混合粉(小麦粉+甘薯淀粉)150 g,甘薯淀粉的含量为15 g、黄油15 g、干酵母5.5 g;最优加工工艺为一次醒发时间为60 min、醒发温度为25 ℃、烘焙时间为9 min;最优条件下其硬度为27.95 N,弹性为15.18 mm,咀嚼性为228.30 mJ,胶粘性为15.05 N。按此条件制作的甘薯淀粉面包色泽金黄,外形饱满,柔软适口具有甘薯淀粉面包特有的风味,为甘薯淀粉面包工业化生产提供理论指导,同时丰富面包种类,拓宽甘薯淀粉用途。     

发酵型速冻油条制作工艺条件的优化

为了优化发酵型速冻油条的制作工艺,考察影响发酵型速冻油条品质的主要因素,在单因素试验的基础上,采用响应曲面法,研究酵母添加量、发酵时间、膨松剂添加量对发酵型速冻油条比容的影响规律。结果表明,发酵型速冻油条制作的最佳工艺条件为：酵母添加量1.0%(以面粉质量计)、膨松剂添加量3.0%(以面粉质量计)、发酵时间2.4h,－35℃速冻20min,在此最佳工艺条件下制得油条的比容为(4.54±0.03)mL/g。     

Study of the behaviour of Lactobacillus plantarum and Leuconostoc starters during a complete wheat sourdough breadmaking process

The acidification properties, metabolic activity and technological performance of four individual Lactobacillus plantarum or Leuconostoc freeze-dried starters were investigated during a complete wheat sourdough breadmaking process including 0.2 g/100 g baker's yeast. Microbiological contents (lactic acid bacteria and yeasts), acidification characteristics (pH and total titratable acidity), soluble carbohydrates (maltose, glucose and fructose) and fermentative end-products (lactic and acetic acids, ethanol) contents were evaluated during both sourdough and corresponding bread dough fermentation. Biochemical and technological analysis of the resulting bread products are also presented. Some differences among strains in acidification properties and soluble carbohydrates availability were outlined both in sourdough and bread dough. Each individual Leuconostoc or Lb. plantarum starter was able to produce a characteristic fermentation and was found to ensure the production of breads with overall satisfactory acceptance.     

γ-聚谷氨酸对全麦冷冻面团烘焙特性的影响

将γ-聚谷氨酸(γ-PGA)添加至全麦冷冻面团中,通过全麦粉持水率、酵母存活率研究γ-PGA的保水性和抗冻活性;以面包比容和质构等作为评价指标,研究γ-PGA对冷冻面团制作的全麦面包烘焙品质的影响。结果表明,添加γ-PGA可提高冷冻全麦面团的酵母存活率和发酵高度,增大全麦面包比容,减小面包硬度,促进面包芯中形成大气孔;贮藏3 d后,添加γ-PGA的全麦面包硬度和老化率显著降低(P<0.05),且γ-PGA的最佳添加量为1%。     

Effects of hydrophilic hydrocolloids on dough and bread performance of samples made from frozen doughs

ABSTRACT:  The objective of this study was to determine the effects of hydrocolloids in dough (xanthan 0.02%, 0.06%, and 0.1%; κ-carrageenan and carboxymethylcellulose 0.2%, 0.6%, and 1.0%) and duration of frozen storage on the quality of finished bakery product. Doughs were prepared with different concentrations of gums, stored at −18 °C and analyzed after 0, 7, 14, and 30 d for fermentation activity of yeast and rising time of dough. At the end of each frozen storage interval, bread was prepared and characterized for specific volume, crumb firmness, and crumb structure. The addition of the gums had significant effects on dough performance and quality of the final product. Gums at all tested concentrations reduced fermentation activity of yeast and prolonged the rising time of dough, which was similar to the effects of frozen storage. However, specific volume of bread for the control sample significantly decreased on the 30th d of frozen storage. Addition of hydrocolloids resulted in higher specific volume of loaves compared to the specific volume of control sample loaves. With the increase of the duration of frozen storage the specific volume of bread decreases in all analyzed samples. This decrease is less in the samples with hydrocolloids compared to the decrease in the control sample. The addition of 0.1% xanthan accomplished the same or higher values for specific fermentation activity, specific volume, and penetrometric's number compared to the values accomplished by the addition of 1% carboxymethylcellulose and κ-carrageenan, respectively.     

萌发玉米粉在冷冻面团中的应用研究

本实验研究了影响冷冻面团中酵母发酵活力的因素,确定酵母菌的发酵活力随着冷冻时间的延长而降低,在萌发玉米粉添加量10%以下,酵母菌的发酵活力随着添加量的增加而增加,超过10%后,酵母的发酵活力逐渐下降。以比容为指标,冷冻面团的最佳配方为:萌发玉米粉添加量10%,酵母菌2%,食盐0.4%,水65%,以弹性为指标,冷冻面团的最佳配方为:萌发玉米粉添加量5%,酵母添加量为3%,盐添加量为1.2%,水添加量为60%。与普通冷冻面团相比,萌发玉米粉使冷冻面团面包品质得到改善。     

鲢鱼酶解产物和鱼胶原肽对冷冻面团品质的影响

通过对比分析经0～6次冻融循环处理后面团的酵母菌存活率、发酵力保存率、醒发时间以及焙烤性质研究了鲢鱼酶解产物和鱼胶原肽对冷冻面团品质的影响。结果表明:添加鲢鱼酶解产物和鱼胶原肽的面团经6次冻融循环后,酵母菌的存活率分别为78.95%和61.80%,发酵力保存率分别为59.06%和46.67%,面团醒发时间分别为330 min和318min,均明显优于空白组;冻融后的面团与新鲜面团相比,焙烤的面包比容和弹性减小,添加了鲢鱼酶解产物和胶原肽不仅可缓解冷冻面团这一缺陷,还可改善面包色泽。结果证明了鲢鱼酶解产物和鱼胶原肽具有良好的酵母菌抗冻保护活性。