Ice in Prefermented Frozen Bread Dough—An Investigation Based on Calorimetry and Microscopy

The amount, morphology, and distribution of ice in prefermented frozen bread dough were investigated by differential scanning calorimetry (DSC) and cryoscanning electron microscopy (cryo‐SEM). Bread dough was frozen after proofing, stored frozen at ‐22 ± 3°C and analyzed without previous thawing. At constant storage conditions, the ice fraction amounted to 53% of the total water and remained constant even over a period of 56 days. Unlike other frozen food foams, ice crystals were observed in the gas pores of the dough. Ice crystals were already present at 1 hr after freezing. Crystal growth and rounding off by recrystallization was observed after 1 day of frozen storage. After 149 days, crystal size reached several 100 μm. It is concluded that growth of ice crystals leads to a redistribution of water in the dough mix in the form of ice, which in turn affects the properties of polymeric compounds in dough and reduces the baking performance of prefermented frozen doughs.     

复合改良剂对后发酵馒头冷冻面团冻藏品质的影响

冷冻面团加工技术作为一种面食生产新工艺,是目前较先进的面制品保鲜技术。冷冻处理会对酵母活力、面团品质、面团面筋结构等产生不良影响。为了提高冷冻面团品质,明确不同食品改良剂对后发酵冷冻面团馒头品质的影响,该研究优化了复配增稠剂(卡拉胶、瓜尔豆胶、海藻酸钠)、复配乳化剂(双乙酰酒石酸单双甘油酯、羧甲基纤维素)、复配酶制剂(谷氨酰胺转氨酶、葡萄糖氧化酶)和海藻糖对后发酵冷冻面团馒头品质的作用,通过单因素和响应面试验设计,考察了不同复合改良剂对冷冻面团馒头比容、质构和感官品质的影响。研究表明:海藻糖、酶制剂对冷冻面团馒头比容的影响极其显著(p0.01)。在添加量为0.4%乳化剂、0.8%增稠剂、45 mg/kg酶制剂、2%海藻糖的复配工艺下,冷冻面团馒头的比容达到最佳水3.15 mL/g,其硬度和弹性也达到较优值,分别为926.832 g、0.912 8。同时对未添加和添加复合改良剂冻藏0～2.5个月的冷冻面团进行扫描电镜观察,发现未添加复配改良剂的冷冻面团中大多数小淀粉颗粒裸露在外,颗粒分明,内部组织结构不均匀,而添加复合改良剂的冷冻面团淀粉颗粒镶嵌在面筋网络之间,蛋白网络结构清晰完整,冷冻面团内部组织结构均匀紧密,面团的抗冻性较强。     

Effect of Formulation and Processing Treatments on Viscosity and Solubility of Extractable Barley β‐Glucan in Bread Dough Evaluated Under In Vitro Conditions

β‐Glucan shows great potential for incorporation into bread due to its cholesterol lowering and blood glucose regulating effects, which are related to its viscosity. The effects of β‐glucan concentration, gluten addition, premixing, yeast addition, fermentation time, and inactivation of the flour enzymes on the viscosity of extractable β‐glucan following incorporation into a white bread dough were studied under physiological conditions, as well as, β‐glucan solubility in fermented and unfermented dough. β‐Glucan was extracted using an in vitro protocol designed to approximate human digestion and hot water extraction. The viscosity of extractable β‐glucan was not affected by gluten addition, the presence of yeast, or premixing. Fermentation produced lower (P ≤ 0.05) extract viscosity for the doughs with added β‐glucan, while inactivating the flour enzymes and increasing β‐glucan concentration in the absence of fermentation increased (P ≤ 0.05) viscosity. The physiological solubility of the β‐glucan concentrate (18.1%) and the β‐glucan in the unfermented dough (20.5%) were similar (P > 0.05), while fermentation substantially decreased (P ≤ 0.05) solubility to 8.7%, indicating that the reduction in viscosity due to fermentation may be highly dependent on solubility in addition to β‐glucan degradation. The results emphasize the importance of analyzing β‐glucan fortified foods under physiological conditions to identify the conditions in the dough system that decrease β‐glucan viscosity so that products with maximum functionality can be developed.     

Effects of Yeast Freezing in Frozen Dough

The effects of freezing and frozen storage of bread dough and compressed yeast on bread quality were studied. Besides, the effects of compressed yeast freezing on cell viability, gas production and release of substances by the yeast cells were examined. Freezing and frozen storage of dough made with fresh yeast had more negative effects on baking quality than the addition of frozen yeast to dough. When the compressed yeast is frozen and stored at ‐18°C, the CO₂ production decreased, while the amount of dead cells, the total protein, and the total reducing substances leached from the yeast increased as the length of yeast frozen storage increased. SDS‐PAGE showed that the substances leached from frozen yeast caused an increase in the solubility of some gluten proteins. On the other hand, size‐exclusion chromatography (SEC) pointed out that the relative amount of two protein fractions of low molecular weight leached from frozen yeast increased for longer yeast frozen storage periods. The yeast leachates had an adverse effect on loaf volume.     

酵母对冷冻面团发酵特性及馒头品质的影响

为了找出使冷冻面团和馒头综合品质较稳定的酵母产品,采用动态流变仪和F3发酵仪对低糖型国光高活性干酵母(1#)、英联马利苹果即发高活性干酵母(2#)、品一高活性干酵母(3#)、高糖型马利即发高活性干酵母(4#)、高糖型丹宝利即发高活性干酵母(5#)和耐高糖安琪高活性干酵母(6#)冷冻面团冻藏35 d过程中的流变学特性和发酵特性进行研究,并对由此面团制作馒头的质构、色泽、比容和感官品质进行分析。结果表明:不同市售酵母冷冻面团在不同冻藏时间下的流变学特性和发酵特性不同。不同酵母冷冻面团制作馒头后硬度、弹性、回复性、咀嚼性、亮度、红度、黄度、比容和感官品质分别差异显著,不同冻藏时间下同种酵母冷冻面团馒头的质构、色泽、比容和感官品质也分别差异显著。6种酵母在冻藏35 d内,1#和2#酵母冷冻面团的发酵活力始终较大,6#酵母冷冻面团的发酵特性参数始终最稳定;1#、5#和6#酵母冷冻面团的弹性模量与黏性模量较大,其中面团流变学特性最稳定的是5#;1#和6#酵母冷冻面团制作馒头的感官品质较好的同时,比容较高,色泽品质较好,质构品质也较好。因此整个冻藏期间,使冷冻面团和馒头综合品质较好较稳定的是1#,其次是6#。研究结果为冷冻面团馒头工业化生产中酵母的选择提供参考。     

Impact of Sodium Alginate and Xanthan Gum on the Quality of Steamed Bread Made from Frozen Dough

The impact of freezing on dough rheology, fermentation performance, and final steamed bread quality was investigated in this study. Also, the incorporation of sodium alginate and xanthan gum into the frozen dough formulation, in comparison with 0.1% salt, was studied to test their suitability as frozen dough improvers. Incorporating these hydrocolloids into steamed bread revealed their totally different characteristics from those in baked bread. Freezing of dough led to diminished specific volumes of proofed dough and steamed bread, and it also caused higher crumb firmness for steamed bread. The incorporation of sodium alginate and xanthan gum did not improve the quality of the steamed bread but led to further reduction in specific volume and increase in crumb firmness at the higher levels of 0.3, 0.5, and 1.0% and 0.07 and 0.1%, respectively. Xanthan gum and sodium alginate showed dough strengthening effects by increasing resistance to uniaxial deformation, bubble burst stress, and declining dough weakening coefficients at these levels, but decreased dough extensibility and bubble burst strain were revealed at these concentrations tested.     

Frozen Bread Dough Properties Modified by Thermostable Ice Structuring Proteins Extract from Chinese Privet (Ligustrum vulgare) Leaves

Thermostable ice structuring proteins (TSISPs) extracted from Chinese privet (Ligustrum vulgare) leaves were used in frozen dough. TSISPs extract thermal hysteresis activity ranged from 0 to 0.27°C based on different ice fractions in solution. The effects of the TSISPs extract on melting enthalpy of ice (ΔH), water molecular state, microstructure, rheofermentation capacity, and baking properties of doughs during frozen storage were investigated by differential scanning calorimetry, thermal gravimetric analysis, scanning electron microscopy, rheofermentometer, and texture analyzer. The addition of TSISPs in frozen dough caused a decrease in freedom of water molecules and ΔH, which resulted in improved microstructure, fermentation capacity, and baking properties of frozen doughs. Residual gluten fibril increased, exposed starch granules decreased, and gas production and retention of frozen doughs was enhanced. These effects resulted in an increase in specific volume and a decrease in crumb hardness of baked frozen dough.     

Mathematical model of sugar uptake in fermenting yeasted dough

Fermentation prior to freezing significantly reduces the shelf life of frozen dough, measured as a decline in proofing power. Changes during fermentation caused by yeast metabolism have previously been described empirically on a dough weight basis and have not been mathematically modeled. In this work, yeast metabolites were quantified in fermenting dough and their concentrations were estimated in the aqueous environment around yeast cells. The osmotic pressure in the aqueous phase increases by 23% during 3 h of fermentation, which depresses the freezing point by 1 degrees C. The rise in osmotic pressure and the accumulation of ethanol may affect phase equilibria in the dough, baking properties, and the shelf life of frozen dough. Predictive modeling equations fitted sugar concentration data accurately. It was found that the preference of baker's yeast for glucose over fructose was stronger in fermenting dough than in liquid fermentations. The usefulness of the model in industrial bakery formulation work was demonstrated.     

Centrifuged Liquid and Breadmaking Properties of Frozen‐and‐Thawed Bread Dough

Breadmaking properties (bread height, mm, and specific volume, cm³/g ) showed marked deterioration when bread dough was frozen and stored at ‐20°C for one day. However, these properties of bread dough baked after storage for three to six days were not further deteriorated as compared with that baked after one day of storage. A large amount of liquid was oozed from the frozen‐and‐thawed bread dough. The liquid was separated from the bread dough by centrifugation (38,900 × g for 120 min at 4°C), and collected by tilting the centrifuge tube at an angle of 45° for 30 min. There was a strong correlation between the amount of centrifuged liquid and breadmaking properties (bread height and specific volume). The mechanism responsible for the oozing of liquid in frozen‐and‐ thawed bread dough was studied. The presence of yeast and salt in bread dough was suggested to be closely related to the amount of centrifuged liquid, and fermented products particularly had a large effect on the amount of centrifuged liquid.     

Changes in Phytate Content in Whole Meal Wheat Dough and Bread Fermented with Phytase‐Active Yeasts

The degradation of inositol hexakisphosphate (IP6) was evaluated in whole meal wheat dough fermented with baker's yeast without phytase activity, different strains of Saccharomyces cerevisiae (L1.12 or L6.06), or Pichia kudriavzevii with extracellular phytase activity to see if the degradation of IP6 in whole meal dough and the corresponding bread could be increased by fermentation with phytase‐active yeasts. The IP6 degradation was measured after the dough was mixed for 19 min, after the completion of fermentation, and in bread after baking. Around 60–70% of the initial value of IP6 in the flour (10.02 mg/g) was reduced in the dough already after mixing, and additionally 10–20% was reduced after fermentation. The highest degradation of IP6 was seen in dough fermented with the phytase‐active yeast strains S. cerevisiae L1.12 and P. kudriavzevii L3.04. Activity of wheat phytase in whole meal wheat dough seems to be the primary source of phytate degradation, and the degradation is considerably higher in this study with a mixing time of 19 min compared with earlier studies. The additional degradation of IP6 by phytase‐active yeasts was not related to their extracellular phytase activities, suggesting that phytases from the yeasts are inhibited differently. Therefore, the highest degradation of IP6 and expected highest mineral bioavailability in whole meal wheat bread can be achieved by use of a phytase‐active yeast strain with less inhibition. The strain S. cerevisiae L1.12 is suitable for this because it was the most effective yeast strain in reducing the amount of IP6 in dough during a short fermentation time.     

Heterologous expression of type I antifreeze peptide GS-5 in baker's yeast increases freeze tolerance and provides enhanced gas production in frozen dough

The demand for frozen-dough products has increased notably in the baking industry. Nowadays, no appropriate industrial baker's yeast with optimal gassing capacity in frozen dough is, however, available, and it is unlikely that classical breeding programs could provide significant improvements of this trait. Antifreeze proteins, found in diverse organisms, display the ability to inhibit the growth of ice, allowing them to survive at temperatures below 0 degrees C. In this study a recombinant antifreeze peptide GS-5 was expressed from the polar fish grubby sculpin (Myoxocephalus aenaeus) in laboratory and industrial baker's yeast strains of Saccharomyces cerevisiae. Production of the recombinant protein increased freezing tolerance in both strains tested. Furthermore, expression of the GS-5 encoding gene enhanced notably the gassing rate and total gas production in frozen and frozen sweet doughs. These effects are unlikely to be due to reduced osmotic damage during freezing/thawing, because recombinant cells showed growth behavior similar to that of the parent under hypermosmotic stress conditions.     

Properties of Arabinoxylans in Frozen Dough Enriched with Wheat Fiber

The global market for frozen bread dough is rising; however, its quality could deteriorate during extended storage. Our previous study indicated that undesirable changes caused by freezing could be reduced by adding arabinoxylan‐rich fiber sources. The present study investigated the changes in arabinoxylan properties of yeasted dough during frozen storage. Dough samples made from refined, whole, and fiber‐enriched (15% either wheat aleurone or bran) flours were stored at –18°C for nine weeks, and structural properties of arabinoxylan were probed during storage. Water‐extractable arabinoxylan (WEAX) content in dough samples increased by about 19–33% during the first three weeks of storage. Prolonged storage of dough (weeks 6 and 9), however, correlated with a decline in WEAX content. Average molecular weight and intrinsic viscosity of WEAX decreased during storage for all frozen dough samples. Arabinose‐to‐xylose ratios also decreased by 11 and 6% for control and composite dough samples, respectively. There was a significant positive correlation (r = 0.89, P < 0.0001) between WEAX content of dough and bread quality throughout the storage period. The results demonstrated that changes in dough quality during frozen storage were related to changes in the content and structure of WEAX that took place during frozen storage.     

Effects of Mutant Thermostable α‐Amylases on Rheological Properties of Wheat Dough and Bread

Thermostable mutant α‐amylases (21B, M111, and M77) with various degrees of thermostability were purified from Bacillus amyloliquefaciens F and used as improvers for breadmaking. Test baking with the mutant enzymes was conducted using the long fermentation sponge‐dough method. Addition of an appropriate amount of mutant α‐amylases to the ingredients distinctly increased the specific volume of the bread and improved the softness of breadcrumb as compared with the addition of Novamyl (NM), an exo‐type α‐amylase. M77 was the most effective in retarding the staleness of breadcrumb. The softness of breadcrumb during storage, however, was not correlated with the thermostability. All mutant α‐amylases weakened the mixing property of the dough, whereas they strengthened the property of fermented dough. Especially, M77 and NM had different effects on the dough properties, but their bread qualities were similar to each other. The strong tolerance of M77 dough to the long baking process might be due to the production of hydrolyzed starches, oligosaccharides in the range of maltopentaose to maltohexaose, as compared with NM. Therefore, in the light of present findings, these mutant α‐amylases are possible substitutes for NM as bread improvers.     

Structural and Physical Changes in Ultrasound‐Assisted Frozen Wet Gluten

Ultrasound‐assisted freezing is a novel food‐freezing technique which is of benefit to frozen food quality. Studies of the structural and physical changes in the ultrasound‐assisted frozen wet gluten system illustrate how the ultrasound irradiation improves the frozen dough quality. The microtopography of ice crystals in frozen wet gluten was observed indirectly by scanning electron microscopy; the ice crystals were smaller and more uniform in wet gluten frozen using the ultrasound‐assisted technique than in wet gluten frozen without ultrasound. Fourier transform infrared spectroscopy was used to monitor the changes in the secondary structure of a frozen gluten heavy water system during frozen storage. It was determined that there were no noticeable changes in the structure of the wet gluten frozen using the ultrasound‐assisted technique. However, the structure of the wet gluten frozen without ultrasound became unordered. The freezable water content in the frozen wet gluten was determined by differential scanning calorimetry. Compared with conventional freezing, more water was frozen using ultrasound‐assisted freezing. Furthermore, the freezable water content in the wet gluten frozen using the ultrasound‐assisted technique did not increase during frozen storage. Ultrasonic cavitation promoted the primary and secondary nucleation of ice in the wet gluten and loosened the weak interactions between the gluten and the water. Consequently, the existence of a microstructure with small and uniform ice crystals was noted, which was determined to be beneficial with regard to reducing the deterioration of the gluten network and, hence, improving the quality of the frozen food.     

Rheology,Microstructure, and Baking Characteristics of Frozen Dough Containing Rhizopus chinensis Lipase and Transglutaminase

The beneficial effects of a new recombinant lipase (Rhizopus chinensis lipase [RCL]) and transglutaminase (TG) were investigated on frozen dough systems and their breadmaking quality. Rheological properties and microstructure of doughs were measured using a dynamic rheometer, rheofermentometer F3, and scanning electron microscopy (SEM). Measurements of viscoelastic properties showed that both G′ and G″ of dough containing RCL and TG were greater than those of the control after 35 days of frozen storage. The SEM micrographs showed that dough containing RCL and TG had the most starch granules embedded in or attached to the gluten network, and the gluten seemed more powerful and resilient than for the control dough after 35 days of frozen storage. Results of the gas production and dough development tests indicated that RCL and TG improved the rheofermentative characteristics of frozen dough. RCL and TG could improve water‐holding capacity and significantly increase the glycerol content of the control dough. Image analyses showed that bread crumbs containing RCL and TG had a more open network and uniform crumb structure, which resulted in higher specific volume. This combination also yielded a product with higher sensory scores for test breads.     

Long‐Term Storage Effect in Frozen Dough by Spectroscopy and Microscopy

Storage of dough at low temperatures (‐20°C) has a considerable effect on the final quality of baked bread; this is most obviously reflected in lowered specific volumes. In this study, a suite of structural characterization techniques is applied to examine the underlying mechanism of storage damage at the molecular, microstructural, and macroscopic level. By using infrared spectroscopy, the dehydration of the gluten component could be established at the molecular level, and its kinetics could be monitored in time. Time‐domain nuclear magnetic resonance (NMR) showed increased water mobility, which could be attributed to a release of water from the gluten matrix. At the microstructural level, the growth of ice crystals could be monitored by means of cryogenic scanning electron microscopy (cryo‐SEM). These ice crystals are preferably formed in gas cells with kinetics that are slower than those during infrared spectroscopy but similar to those in time‐domain NMR. At the macroscopic level, ice crystals are not evenly distributed over the molded dough, nor are the gas cells homogeneously distributed over the dough. This has implications for the macroscopic water distribution during frozen storage, which could be substantiated by magnetic resonance imaging (MRI) measurements.     

沙蒿籽粉和谷朊粉对燕麦全粉食品加工品质的影响

为了探讨全燕麦粉面包、馒头加工品质及燕麦粉冷冻面团品质特性，以燕麦全粉为原料，研究了添加沙蒿籽和谷朊粉对燕麦全粉食品(含冷冻面团食品)加工品质改良效果。试验结果表明，谷朊粉对面包制作影响较大；沙蒿籽粉对馒头制作影响较大；沙蒿籽粉和谷朊粉共同使用的效果优于两者单独使用；加入2.5%沙蒿籽粉和8%谷朊粉对燕麦全粉面包和馒头品质改善效果最好。对冷冻面团加工而言，随着冷冻时间的延长面团品质不断下降，冻藏4 d后燕麦全粉冷冻面团面包、馒头品质显著降低。     

Effect of freezing and frozen storage of doughs on bread quality

The effects of freezing and storage in frozen conditions on bread quality, crumb properties, and aggregative behavior of glutenins were analyzed. The effect of different additives on bread quality was also studied. The results obtained showed that freezing and storage at -18 degrees C decreased the bread quality. Samples stored in frozen conditions supplemented with diacetyl-tartaric acid ester of monoglycerides, gluten, and guar gum produced breads of greater volume and more open crumb structure than those prepared with the base formulation (without additives). All additives analyzed increased the proof time. Crumb firmness increased with dough frozen storage and bread aging time at 4 degrees C. A decrease in the amount of glutenin subunits of high molecular mass was observed by electrophoresis analysis of the SDS-soluble proteins aggregates extracted from the frozen dough. This result suggested that the protein matrix of bread underwent depolymerization during storage in frozen conditions.     

Effect of Dough Processing Conditions and DATEM on Norwegian Hearth Bread Prepared from Frozen Dough

The objective of this study was to examine treatments that directly influence Norwegian lean doughs destined to be frozen. Therefore a strip-block experimental design with four dough treatment factors (wheat flour blend, diacetyl tartaric acid esters of monoglycerides [DATEM], water absorption, and dough temperature) and two storage factors (frozen storage time and thawing time) was used. Four levels were selected for frozen storage time and two levels were selected for the remaining factors. After frozen storage (2–70 days), the doughs were thawed and baked. Principal component analysis showed that to obtain a high loaf volume and bread score after freezing, a high dough temperature after mixing (27°C) was essential. The highest form ratio (height/width) level was obtained after 28 days of frozen storage and with a short thawing time (6 hr). Analysis of variance (ANOVA) of dough treatments showed that an increase in dough temperature from 20 to 27°C after mixing resulted in a significant increase in loaf volume (1,653 to 2,264 mL), form ratio (0.64 to 0.69), and bread score (1.7 to 3.2), and a reduction in loaf weight (518.4 to 512.5 g) and crumb score (7.9 to 5.9, i.e., a more open bread crumb). Also, the addition of DATEM significantly increased loaf volume (1,835 to 2,081 mL), form ratio (0.64 to 0.69), and bread score (2.2 to 2.6). Frozen dough storage time significantly affected loaf volume, loaf weight, bread score, and crumb score. Increasing thawing time from 6 to 10 hr significantly increased loaf volume (1,855 to 2,121 mL), and reduced the form ratio (0.69 to 0.63) and loaf weight (516.8 to 511.4 g). ANOVA of the interaction between dough treatment and frozen storage time showed that decreasing water absorption significantly increased the loaf volume.     

Improvement of texture properties and flavor of frozen dough by carrot (Daucus carota) antifreeze protein supplementation

The effects of concentrated carrot protein (CCP) containing 15.4% (w/w) carrot (Daucus carota) antifreeze protein on texture properties of frozen dough and volatile compounds of crumb were studied. CCP supplementation lowered the freezable water content of the dough, resulting in some beneficial effects including holding loaf volume steadily and making the dough softer and steadier during frozen storage. Furthermore, SPME-GC-MS analysis showed CCP supplementation did not give any negative influences on volatile compounds of crumb and gave a pleasant aroma felt like Michelia alba DC from trans-caryophyllene simultaneously. Combining our previous results that CCP supplementation improves the fermentation capacity of the frozen dough, CCP could be used as a beneficial additive for frozen dough processing.