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。     

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.     

Weight loss of frozen bread dough under isothermal and fluctuating temperature storage conditions

Evaporative weight loss from food leads to both loss of saleable weight and quality deterioration so it need to be minimized. The effect of isothermal and fluctuating conditions on frozen dough weight loss was measured and compared with kinetic, physical and artificial neural network (ANN) models. Frozen dough samples were regularly weighed during storage for up to 112 days in loose-fitting plastic bags. The storage temperatures were in the range of −8 to −25 °C with fluctuations of ±0.1 °C (isothermal), ±1, ±3 or ±5 °C about the mean. For each combination of temperature and fluctuation amplitude, the rate of dough weight loss was constant. The rate of weight loss at constant temperature was nearly proportional to water vapour pressure consistent with standard theories for evaporative weight loss from packaged foods but was also accurately fitted by Arrhenius kinetics. Weight loss increased with amplitude of temperature fluctuations. The increase could not be fully explained by either the physic model based on water vapour pressure differences or the kinetic model alone. An ANN model with six neurons in the input layer, six neurons in hidden layers and one neuron in the output layer, achieved a good fit between experimental and predicted data for all trials. However, the ANN model may not be accurate for product, packaging and storage systems different to that studied.     

冷冻工艺条件对发酵面团中抗冻酵母活性的影响

研究了冷冻面团的冷冻终结温度、冻藏温度、冻藏时间对抗冻酵母活性的影响,得出最有利于抗冻酵母活性保持的冷冻工艺条件：冷冻终结温度-18℃,冻藏温度应与冷冻终结温度保持一致,贮存时间不超过30d为宜。     

冷冻面团馒头品质改良研究进展

为了研究食用碱添加量对不同冷冻杂粮（小麦、荞麦、玉米、绿豆）面团品质的影响,本文设计了0%、1%、2%、3%、4%、5%（以100 g冷冻杂粮面团为基准）食用碱添加量分别加入到小麦面团、荞麦面团、玉米面团、绿豆面团中,在−30 ℃条件下冷冻8 h,在−18 ℃的条件下冷冻1 d,然后在25 ℃下解冻30 min。然后分别测定冷冻面团的失水率、持水率、pH、质构特性、水分分布以及利用扫描电子显微镜（SEM）对冷冻面团表面网络结构和蛋白质结构的变化进行研究。结果表明,食用碱添加量与冷冻面团的失水率呈负相关,可以显著（P<0.05）影响冷冻面团的pH;在食用碱添加量为4%时,各个冷冻杂粮面团的弹性达到最大值,小麦面团、荞麦杂粮面团、玉米杂粮面团、绿豆杂粮面团的A₂₁分别达到48.189±1.509、45.652±2.202、43.585±2.472、43.743±1.155,说明食用碱可以抑制水分迁移,进而保持良好的持水性,且能有效改善冷冻杂粮面团面筋蛋白网络结构和品质,进一步提高冷冻杂粮面团品质。本文研究食用碱对冷冻杂粮面团特性的影响,以期为冷冻杂粮面团的品质改善以及现代化生产提供一定的理论依据。

     

混合试验仪确定冷冻面团馒头复配添加剂最佳配方

利用混合试验仪研究硬酯酰乳酸钠（SSL）、黄原胶、抗坏血酸（VC）对冷冻面团特性的影响。通过单因素试验、正交试验确定了冷冻面团复配添加剂的最佳配方为SSL0.1%、VC0.010%和黄原胶0.3%。用不同复配添加剂配方制作冷冻面团馒头,利用感官品质评分、质构品质测定进行综合评价,最佳结果与Mixolab试验结果一致。     

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.     

冷冻面团原料小麦粉的筛选及各指标的相关性分析

本实验选取了六种不同商业高筋小麦粉,采用粉质仪、拉伸仪和糊化仪对其进行基础成分和流变学特性的测定,并对所得指标数据进行相关性分析,同时对应用各小麦粉制作的冷冻面团的质构特性进行测定分析,筛选出北大荒高筋小麦粉适于制作冷冻面团。各特性指标进行相关性分析结果显示,吸水率与水分含量、蛋白质含量、最大拉伸阻力呈显著正相关(p<0.05),相关系数为0.849、0.789、0.828;形成时间与湿面筋含量、最大拉伸比例呈显著正相关(p<0.05),相关系数为0.900、0.885;形成时间与拉伸阻力、最大拉伸阻力、拉伸比例呈极显著正相关(p<0.01),相关系数为0.986、0.958、0.933;水分含量与最大拉伸阴力呈显著正相关(p<0.05),相关系数达到0.828;蛋白质含量与拉伸阻力、最大拉伸阻力、拉伸比例呈显著正相关(p<0.01),相关系数为0.986、0.958、0.933。      

Isolation of new temperature-sensitive mutants of Saccharomyces cerevisiae deficient in mannose outer chain elongation.

We have isolated two temperature-sensitive Saccharomyces cerevisiae mutants which exhibit a deficiency in mannose outer chain elongation of asparagine-linked oligosaccharide. The size of yeast glycoprotein, secretory form of invertase, of one mutant (och1) was slightly larger than that of the sec18 mutant at the non-permissive temperature, while that of the other mutant (och2) was almost the same as that of the sec18 mutant. Unlike sec mutants, the och mutants were not deficient in secretion of invertase. The och1 mutant showed a 2+:2- cosegregation with regard to the temperature sensitivity and mannose outer chain deficiency, suggesting that a single gene designated as OCH1 is responsible for these two phenotypes. The och1 mutant stopped its growth at the early stage of bud formation and rapidly lost its viability at the non-permissive temperature. The och1 mutation was mapped near the ole1 on the left arm of chromosome VII. The och1 mutant cells accumulated the external invertase containing a large amount of core-like oligosaccharides (Man9-10GlcNAc2) and a small amount of high mannose oligosaccharides (greater than Man50GlcNAc2) at the non-permissive temperature. Production of the active form of human tissue-type plasminogen activator was increased in the och1 mutant compared with the parental strain, suggesting the potential advantage of this mutant for the production of mammalian-type glycoproteins which lack mannose outer chains in yeast.     

胶原抗冻肽的制备及在冷冻面团中的应用

抗冻肽是一类通过抑制冰晶生长使生物有机体免受冰冻伤害的多肽。文中采用酶法制备了高热滞活性的胶原抗冻肽,并考察了该抗冻肽对冷冻面团酵母存活率、发酵时间、馒头比容、质构及感官评分的影响。结果表明:胶原抗冻肽显著改善了冷冻面团的品质,当其添加量为0.3%时,面团经21 d冻藏后,酵母存活率从43%增加到54.5%;醒发时间缩短了33.3%,为60 min;馒头比容从1.74 m L/g增加到2.11 m L/g,上升了27.1%;馒头的硬度和咀嚼性显著减小,其回弹性、黏性、弹性均增加;同时冷冻面团的外观较好,感官总分达到55.5分。     

Lipid deficient extender for bovine spermatozoa: its development and use in measuring freezing-induced lipid loss.

To facilitate the measurement of lipid losses from spermatozoa due to freezing, three low-lipid seminal extenders containing lactose, bovine serum albumin, or soybean protein were evaluated as potential cryoprotectants. All extenders were formulated to have an osmotic pressure within the range of 270 to 330 mosmol and a pH of 6.8 to 7.0. Soybean protein (Promine-D) maintained the highest post-thaw motility of spermatozoa with similar survival for spermatozoa frozen in ampules and straws. The extender derived from testing several components consisted of Tris(hydroxymethyl) aminomethane (245 mM), and citric acid monohydrate (78mM), as the buffering compounds; and fructose (69 mM), glycerol (7% vol/vol), and Promine-D (1.5% wt/vol). Post-thaw sperm motility of approximately 40% was not different from the Tris-egg yolk control. Fertility of fresh rabbit semen treated with the extender was normal. After freeze-thawing, protected spermatozoa contained more lipid (1.61 versus 1.20 mug/10-6 sperm) and lost less glutamic oxaloacetic transaminase enzyme (102 versus 108 Karmen units) than when Promine-D was not incorporated. However, even with protection by soybean protein, spermatozoa lipid content decreased from 2.43 to 1.61 mug/10-6 sperm after one freeze-thawing. The lipid status of spermatozoa frozen and thawed in conventional bull seminal extenders containing large amounts of lipids is unknown.     

常温和冷冻面团披萨中的挥发性风味物质分析

采用气相色谱和质谱联用(GC-MS)技术分析了常温和冷冻面团披萨中的挥发性风味物质。研究表明,披萨中主要的挥发性物质是(Z,Z)-9,12-十八碳二烯酸、三十碳六烯、十六酸、邻苯二甲酸二丁酯和D-柠檬烯,这些物质可能是常温和冷冻面团披萨的主要风味物质。冷冻面团和常温面团制作的披萨在风味物质组成上有很大的相似性,低温冷冻过程对面团品质没有产生太大的影响。     

Selection and properties of Streptococcus thermophilus mutants deficient in urease

Natural variations of the urea content of milk have a detrimental effect on the regularity of acidification by Streptococcus thermophilus strains used in dairy processes. The aim of the present study was to select urease-deficient mutants of S. thermophilus and to investigate their properties. Using an improved screening medium on agar plates, mutants were selected from 4 different parent strains after mutagen treatment and by spontaneous mutation. Most mutants were stable and had a phage sensitivity profile similar to that of their parent strain. Some of them contained detrimental secondary mutations, as their acidifying activity was lower than that of the parent strain cultivated in the presence of the urease inhibitor flurofamide. The proportion of this type of mutant was much lower among spontaneous mutants than among mutants selected after mutagen treatment. Utilization of urease-deficient mutants in dairy processes may have several advantages, such as an increase in acidification, an improved regularity of acidification, and a lower production of ammonia in whey.     

Simultaneous accumulation of proline and trehalose in industrial baker's yeast enhances fermentation ability in frozen dough

Freeze tolerance is a necessary characteristic for industrial baker's yeast because frozen-dough baking is one of the key technologies for supplying oven-fresh bakery products to consumers. Both proline and trehalose are known to function as cryoprotectants in yeast cells. In order to enhance the freeze tolerance of yeast cells, we constructed a self-cloning diploid baker's yeast strain with simultaneous accumulation of proline, by expressing the PRO1-I150T allele, encoding the proline-feedback inhibition-less sensitive γ-glutamyl kinase, and trehalose, by disrupting the NTH1 gene, encoding neutral trehalase. The resultant strain retained higher tolerance to oxidative and freezing stresses than did the single proline- or trehalose-accumulating strain. Interestingly, our results suggest that proline and trehalose protect yeast cells from short-term and long-term freezing, respectively. Simultaneous accumulation of proline and trehalose in industrial baker's yeast also enhanced the fermentation ability in the frozen dough compared with the single accumulation of proline or trehalose. These results indicate that baker's yeast that accumulates both proline and trehalose is applicable for frozen-dough baking.     

Isolation and characterization of Kluyveromyces marxianus mutants deficient in malate transport

In malic acid-grown cells of the strains ATCC 10022 and KMS3 of Kluyveromyces marxianus the transport of malic acid occurred by a malate-proton symport, which accepted l-malic, d-malic, succinic and fumaric acids, but not tartaric, malonic or maleic acids. The system was inducible and subjected to glucose repression. Mutants of the strain KMS3, unable to grow in a medium with malic acid, were isolated and checked for their capacity to utilize several carbon sources and to transport dicarboxylic acids by the malate-proton symport. Two distinct clones affected on malate transport were obtained. Both were able to grow on a medium with glycerol or ethanol but not with dl-malic, succinic, oxoglutaric and oxaloacetic acids as the sole carbon and energy sources. However, while one of the mutants (Mal7) displayed activity levels for the enzymes malate dehydrogenase, isocitrate lyase, and phosphoenolpyruvate carboxykinase similar to those of the wild strain, in the other mutant type (Mal6) the activities for the same enzymes were significantly reduced. Plasma membranes from derepressed cells of the wild strain and of the mutants Mal6 and Mal7 were isolated and the protein analysed by SDS–PAGE. The electrophoretic patterns of these preparations differed in a polypeptide with an apparent molecular mass of about 28 kDa, which was absent only in the mutant Mal7. The results indicated that Mal7 can be affected in a gene that encodes a malate carrier in K. marxianus. © 1998 John Wiley & Sons, Ltd.     

花生油炸制油条香气物质的分析鉴定

采取同时蒸馏萃取制备样品,气相色谱-质谱联用(GC-MS)、稀释法气相色谱-嗅闻(GC-O)对花生油炸制油条香气成分进行分析鉴定。基于检索NIST14质谱库、保留指数,气-质联机鉴定出83种化合物,包括醛类、酮类、醇类、酯类、酸类、含硫化合物、含氮杂环、含氧杂环、烃类、其他类,含量最高的是醛类,其中己醛、壬醛、(E)-2-癸烯醛、(E,Z)-2,4-癸二烯醛的含量远高于鉴定出的所有其它化合物。基于GC-MS鉴定结果、嗅闻的保留指数、嗅闻的气味特征及标准品,GC-O分析鉴定出30种香气活性物质,其中3-羟基-2-丁酮、3-乙基-2,5-二甲基吡嗪、糠醇、(E,E)-2,4-癸二烯醛、2,3-二甲基吡嗪、己醛、庚醛、(E)-2-壬烯醛、(E)-2-癸烯醛、(E)-2-十一烯醛、3-甲基丁醛、3-甲硫基丙醛、丙醛、辛醛、壬醛、(Z)-2-癸烯醛、1-辛烯-3-醇等17种化合物具有较高的稀释因子(log₂FD≥5)。通过本实验研究发现,花生油炸制油条中挥发性化合物种类丰富,构成了花生油条独特的油脂香、焦香、甜香等风味,其中醛类、含氧杂环化合物及含氮杂环化合物含量较高,是花生油炸制油条风味物质的主要成分。     

Characterization of a Schizosaccharomyces pombe mutant deficient in UDP-galactose transport activity.

In fission yeast, Schizosaccharomyces pombe, the carbohydrate components of the cell wall consist of galactomannan, unlike in Saccharomyces cerevisiae. We previously found that the disruption of gms1+, a gene encoding the UDP-galactose transporter required for the synthesis of galactomannan, led to the complete defect of cell surface galactosylation in Sz. pombe. The Deltagms1 strain is therefore useful for the analysis of physiological properties of galactose residues in Sz. pombe. The deletion strain of gms1+ was viable; however, itshowed an aberrant cell morphology and increased sensitivities to digestion with beta-glucanase and to various drugs, such as hygromycin B, sodium orthovanadate and Calcofluor white. A reduction of galactomannan layers of the cell wall in the Deltagms1 strain was observed by scanning and transmission electron microscopic analyses. The addition of osmotic stabilizer suppressed the morphologic defect of the Deltagms1 cells, while other phenotypes were weakly suppressed. The Deltagms1 (h90) strain was incapable of sexual conjugation during nutritional starvation. These results suggest that the cell surface galactosylation is required not only for non-sexual flocculation but also for sexual conjugation in Sz. pombe.     

Effect of freezing and frozen storage on the gelatinization and retrogradation of amylopectin in dough baked in a differential scanning calorimeter

Frozen and non-frozen dough were baked in a differential scanning calorimeter (DSC) pan (heated in the calorimeter at temperatures similar to those of the center of the crumb during baking) and were aged at different temperatures. Gelatinized dough (DSC-baked dough) was heated again in the DSC. This methodology permitted us to study the effects of dough freezing and frozen storage on gelatinization and retrogradation of starch. During storage of frozen doughs at −18 °C an increase in the gelatinization enthalpy after 150 day of storage was observed. At 230 days of frozen storage a decrease in the onset temperature and an increase in the gelatinization temperature range was also detected. An increase of starch retrogradation with time of storage in frozen conditions was observed. During the aging of dough baked in DSC, a higher retrogradation temperature range was detected together with a faster retrogradation of starch at low temperature of aging.     

Quantitative fit of a model for proving of bread dough and determination of dough properties

The early stages of bread dough proving were modeled following the diffusion theory and using a newtonian constitutive equation to account for dough rheology. The model was fitted, by constrained minimization of the sum of squared errors function, to experimental growth curves of common dough formulations. Values for the dough viscosity, a first order fermentation rate constant and the bubble size at the beginning of proving were chosen as the degrees of freedom in the fitting procedure. The viscosity value obtained for a plain dough formulation was 30 × 10⁶ Pa s, this value is in the range of viscosity values determined by Rouillé et al. (2005), for wheat dough through creep-recovery and lubricated squeezing flow tests. The results obtained were plotted as a function of dough formulation composition and the trends were observed and analyzed. The observed tendencies and correlations between dough properties and dough formulation follow the trends observed in experimental data reported in the literature for dough systems.