影响冷冻面团的因素及其品质改良研究进展

冷冻面团技术因具有延长货架期、防止老化、便于冷藏和运输等优越性,在国内外食品工业得到了广泛的应用。然而,冷冻面团的生产和储存也会面临诸多困难,例如酵母活性降低、面筋结构破坏和冰晶形成等,这些都会破坏冷冻面团的质量。本文概括总结了影响冷冻面团品质因素的作用机理及研究现状,并总结了提高酵母耐冻性、改善面筋结构和面团特性的有效方法。添加改良剂可以减小由于冻藏或冻融循环致使面筋网络破坏的程度,添加谷氨酰胺转氨酶可改善冷冻面团的粘弹性与面筋网络结构,还可明显增加冷冻面团面包的比容,减小面包芯的硬度。选用优质酵母可提高酵母在冷冻期间的发酵力,改善冷冻面制品的风味和口感,其中高产胞外多糖的乳酸菌可以有效改善冷冻馒头面团品质。冷冻面团技术推动了我国馒头、包子、饺子、月饼等中式面食制品快速发展,具有一定的发展潜力。     

抗冻蛋白的制备及对冷冻面筋蛋白的改良研究进展

冷冻面团在运输储藏过程中,温度波动引起的冰晶生长和重结晶会导致面团品质劣变,致使最终产品感官特性变差,消费性下降,这限制了冷冻面团的大规模应用。面筋蛋白作为冷冻面团的重要组分,在冻藏过程中冰晶对其特性的影响与冷冻面团的品质密切相关。抗冻蛋白（AFPs）能够与冰晶结合,调控冰晶生长行为,对冷冻面筋蛋白有着很好的改良效果。但生物体内的天然AFPs含量少,提取纯化困难,这使AFPs一直以来难以实现工业化生产与应用,因此,探寻合适的制备方法提高AFPs的产量对于AFPs的发展是至关重要的。本文即综述了AFPs的生产现状及对冷冻面筋蛋白的改良研究,以期为AFPs在冷冻面制品中的应用提供理论基础。     

文献导读

<正>冷冻面团法生产面包的关键工艺讨论冷冻面团法在烘焙食品领域中的应用越来越广泛,但也面临着一些技术难题。本文阐述了冷冻面团法生产面包的关键工艺,包括冷冻条件、酵母发酵活力的保持以及解冻工艺条件等。冷冻时降温速率不宜过快或过慢,在-5℃/min时制作的面包品质较好,为了确保酵母的存活率,冷冻温度不宜低于-50℃;冷冻保护剂的加入可以有效防止冷冻过程中酵母的死亡,有利于保持其发酵活力,也可以通过生物工程的途径提高酵母的耐冻力;解冻是冷冻的逆过程,同样要使面团快速地通过最大冰晶生成区,解冻时间     

抗冻蛋白对预发酵冷冻面团发酵流变特性和馒头品质的影响

运用F4发酵流变仪、质构仪等研究冻藏和冻融循环下抗冻蛋白对预醒发冷冻面团发酵流变学特性和馒头品质的影响。结果表明:随着冻藏时间的延长和冻融循环次数的增加,冷冻面团馒头的比容减小,硬度和咀嚼性明显增大,弹性和回复性下降。冷冻面团的最大发酵高度、气体总释放量和气体释放最大高度均明显下降。说明冻藏和冻融循环严重影响了酵母的产气能力和面团的持气性,与冻藏和冻融循环过程中重结晶和大冰晶的形成有关。添加抗冻蛋白的冷冻面团馒头品质得到明显改善,说明抗冻蛋白能够减缓冷冻面团馒头冻藏和冻融循环过程中品质下降。     

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。     

冷冻面团发酵技术在中式食品中的应用II．冰结构蛋白对鲜酵母及包子类冷冻面团流变发酵特性的影响

应用F3 流变发酵仪和动态流变仪研究冰结构蛋白(ISP)对冻藏0、1、2、3、4 周鲜酵母发酵特性和冷冻面团动态流变学特性的影响。结果表明：随着冻藏时间延长,所有酵母样品发酵过程中气体释放曲线最大高度H′m、产生CO2 气体总体积V总及面团最大膨胀高度Hm 均逐渐降低,冷冻面团的弹性模量(G′)和黏性模量(G 〞)逐渐下降,冷冻面团包子比容显著减小。引入冰结构蛋白(ISP)后,冻藏时间相同时,酵母发酵过程中的H′m、V 总及Hm 均有所增大,G′和G 〞下降趋势减缓,冷冻面团包子比容明显大于空白组,说明ISP 能够抑制冻藏过程中冰晶的形成和重结晶,减弱冰晶对酵母及面筋蛋白质网络结构的破坏,同时也说明ISP 能够增强面筋蛋白质网络结构的强度,提高面筋蛋白质对冰晶破坏的抵抗力。     

竹笋膳食纤维对冻藏过程中面团加工特性、水分分布及微观结构的影响

竹笋膳食纤维由于其具有独特的理化特性,可显著改善冷冻面制品的品质。采用流变仪、低场核磁和扫描电镜等手段,研究了竹笋膳食纤维对面团恒温冻藏过程中蒸煮特性、流变特性、水分分布和微观结构的影响。结果表明:随着冻藏时间的延长,竹笋膳食纤维的添加减少了面团的蒸煮损失率,且在21 d时蒸煮损失率的减少最大,为6.58%;竹笋膳食纤维的添加增加了面团的吸水率,且在14 d时吸水率的增加最大,为24.82%;竹笋膳食纤维的添加使得冷冻面团的弹性模量和黏性模量提高;竹笋膳食纤维改变了冷冻面团的水分分布,主要体现为强结合水的先上升后下降和弱结合水的下降。扫描电镜研究发现,竹笋膳食纤维改变了冷冻面团的微观结构,使其淀粉颗粒与面筋网络排列更加细腻。研究发现,在冻藏过程中,在面制品中添加膳食纤维可以通过改善面团的水分分布和微观结构,从而影响了面团的蒸煮特性及流变学特性。     

复配品质改良剂对南方馒头冷冻面团冻藏品质的影响

为提升和改善冷冻面团南方馒头的品质,分析冻藏过程中复配品质改良剂(海藻糖添加量4%、磷酸二氢钠添加量0.15%、黄原胶添加量0.05%、羧甲基纤维素钠添加量0.04%)对冷冻面团南方馒头比容、硬度、感官品质的影响,并从面团拉伸特性、动态流变特性、微观结构、蛋白质二级结构等方面探究复配品质改良剂在南方馒头冷冻面团中的作用机理。结果表明:冻藏过程中,冰晶会对淀粉颗粒、面筋蛋白及网络结构造成伤害,导致面团品质下降。复配品质改良剂可以保护面团中的面筋结构,减少面筋蛋白二级结构的变化,进而延缓弹性模量和黏性模量的降低速度,改善面团最大拉伸阻力和延伸度劣变,提升南方馒头硬度、比容和感官品质等品质,保持南方馒头松软的风味。     

冷冻面团的研究与发展

冷冻面团是面包生产的一种新工艺，本文对冷冻面团开发的背景、现状和主要技术问题作了简要的介绍，探讨了酵母耐冷冻性的研究。可通过两种途径提高酵母的耐冷冻性：一方面利用改良剂来保护酵母细胞；另一方面通过生物技术培养发酵良好的耐冻藏酵母，最后对我国冷冻面团的发展前景作了展望。     

冷冻面团的研究与发展

冷冻面团是面包生产的一种新工艺，本文对冷冻面团开发的背景、现状和主要技术问题作了简要的介绍。探讨了酵母耐冷冻性的研究。可通过两种途径提高酵母的耐冷冻性：一方面利用改良剂来保护酵母细胞：另一方面通过生物技术培养发酵良好的耐冻藏酵母，最后对我国冷冻面团的发展前景作了展望。     

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.     

Effects of freezing treatments on the fermentative activity and gluten network integrity of sweet dough

The effect of freezing treatments on sweet dough was studied. The dough was frozen at ?20 °C, ?30 °C and ?40 °C in air-blast freezer cabinet and by immersion in liquid nitrogen. The yeast viability, gassing power, dough volume and dough network integrity from fresh and thawed sweet doughs were assessed. The results showed that both parameters depend on the freezing rate, which controls ice crystals size and location. Dough volume loss after freezing was attributed to reduced yeast fermentative activity and gluten network alteration in frozen dough. Fermentative activity reduced significantly in frozen dough using liquid nitrogen, causing 70% decrease on yeast population. Gluten integrity seemed to be affected by slow freezing treatment, i.e. ?20 °C and ?30 °C. Gas loss was also evaluated as a decrease of 25% ± 2 in dough volume. A correlation was observed between the freezing rate and osmotic pressure effects which influence strongly the yeast viability.     

冷冻华夫面团保质期内品质提升的研究

研究了冷冻华夫面团冻藏期间的水分质量分数、水分分布、酵母含量、产气能力、持气能力等指标的变化,阐明冷冻面团品质变化的机制。实验表明,冷冻华夫面团冻藏时间对产品品质具有显著影响,当冻藏时间为3个月时,酵母含量、产气能力、持气能力分别下降了28%、23%和36%。通过研究不同类型添加剂(谷朊粉、黄原胶、羟丙基甲基纤维素、结冷胶)对冷冻面团冻藏期间品质的影响,发现适量加入添加剂对于产品品质的提升具有一定效果,其中谷朊粉和黄原胶在降低冰晶体机械损伤、提高面团发酵能力方面效果显著。与对照相比,谷朊粉提升酵母含量131%,发酵能力210%,黄原胶提升酵母含量107%,发酵能力181%。     

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.     

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.     

Intracellular concentration of exogenous glycerol inSaccharomyces cerevisiaeprovides for improved leavening of frozen sweet doughs

Addition of glycerol to baker's yeast coupled with an incubation period under conditions of refrigeration to allow equilibration of the polyol across the yeast membrane, resulted in improved frozen sweet (10% sugar) dough leavening and keeping, relative to doughs made with yeast containing no added glycerol. Glycerol-loaded yeast showed smaller proof time increases after initial freezing and thawing. Also, glycerol treatment led to slower deterioration of the frozen sweet doughs during storage at −21°C for up to 8 weeks (proof time increases were significantly lower in stored frozen doughs made with glycerol-added yeast). Benefits of glycerol loading of yeast for the purpose of production of frozen plain (unsugared) doughs were less significant. The glycerol treatment effects became more significant as the yeast was stored refrigerated prior to mixing and freezing of doughs, i.e. shelf-life of yeast for use in frozen dough manufacture was improved by addition of glycerol. The improvements were dependent on glycerol concentration.     

冻藏时间对冷冻面团馒头品质的影响

为探究冻藏时间对冷冻面团馒头品质的影响,本文通过采用酵母菌活性测定、馒头质构特性测定、面筋蛋白二级结构测定、扫描电镜观察等方法,从宏观和微观的角度上分析了冻藏时间的延长对冷冻面团馒头品质的影响。结果表明,随着冻藏时间的延长,酵母菌数量及存活率均呈下降趋势,其中冻藏1周后,表面和内芯的酵母菌数量均减少5.8 lg CFU/g;经过5周冻藏后,冷冻面团馒头的硬度、咀嚼性、胶着性分别增大74.6%、75.7%、75.6%;面筋蛋白二级结构中α-螺旋也随着冻藏时间的延长呈下降趋势,蛋白二级结构稳定性逐渐下降;经过扫描电镜观察发现,面筋网络结构逐步减少,淀粉颗粒与面筋结构分离,部分淀粉颗粒完全裸露。因此表明冻藏时间的延长,会导致冷冻面团馒头品质下降。本研究结果为后续提高冷冻面团馒头品质应用研究提供理论依据。     

冷冻面团专用流态起酥油及其对冷冻面团微结构影响研究

为了生产冷冻面团专用流态起酥油并考察流态起酥油对冷冻面团微结构影响,在二次冷却法生产流态起酥油基础上应用中心组合设计,采用响应面分析法,研究搅拌速度,急冷温度,老化时间对流态起酥油相稳定性和流动性影响,使用扫描电子显微镜观察使用流态起酥油后冷冻面团微结构,结果表明:(1)使用二次冷却程序制作流态起酥油过程中急冷程序对产品稳定性影响很大,必须严格控制急冷温度和速度;急冷对流态起酥油流动性影响不大,当搅拌速度为70 rpm,老化时间为1．5 h,急冷温度为5℃时,流态起酥油离心分离率为1％,粘度为500 cp。(2)使用流态起酥油后冷冻面团经30 d冷冻储存后面筋结构比使用普通塑性起酥油、大豆色拉油、添加SSL大豆色拉油的冷冻面团面筋结构好,淀粉分布均匀,面筋网络细腻,面包心纹理好。从冷冻面团微结构可看出,使用流态起酥油可较好弥补冷冻面团在冷冻储存过程中因冷冻所造成烘焙潜力降低。