Effect of bran on bread staling: Physico-chemical characterization and molecular mobility

High fibre breads were produced with the addition of durum wheat bran fractions (regular bran and a fraction extracted from the most internal bran layer) and their physico-chemical properties and water status were characterised during storage. Bran enriched breads exhibited similar properties during storage, they were harder, less springy and less cohesive than the control. Water status was strongly affected by bran addition, independently of bran composition: water activity, moisture and frozen water content (measured by Differential Scanning Calorimetry) were generally higher in the bran samples than in the control bread during storage. Amylopectin retrogradation was significantly larger in the presence of bran fractions. ¹H NMR mobility (T₂ number of populations and relaxation times) was different in the high fibre breads as compared to the control sample. The changes in protons mobility observed upon storage indicated an influence of bran on water/gluten/starch molecular domains and their dynamics, that may have affected the development of the gluten network resulting in different textural properties.     

Volume, texture, and molecular mechanism behind the collapse of bread made with different levels of hard waxy wheat flours

Physico-chemical properties of bread baked by partially replacing normal wheat (Triticum aestivum L.) flour (15, 30, and 45%) with two hard waxy wheat flours were investigated. Substitution with waxy wheat flour resulted in higher loaf volume and softer loaves. However, substitution at >30% resulted in excessive post-bake shrinkage and a ‘key-hole’ shape with an open crumb structure. Bread crumb microstructure indicated a loss of starch granule rigidity and fusing of starch granules. The cells in the interior of the bread did not become gas-continuous and as a result, shrunk as the loaf cooled. Soluble starch content was significantly higher in bread crumb containing waxy wheat flour than in control bread. Debranching studies indicated that the soluble starch in bread made with 30-45% hard waxy wheat flour was mostly amylopectin. Incorporation of waxy wheat flour resulted in softer bread immediately after baking but did not retard staling upon storage.     

Impact of the chilling conditions on the kinetics of staling of bread

Breads were chilled at room temperature or using a vacuum chilling process. The staling rate was studied after partial baking and after the final baking. Vacuum chilled breads (VCBs) exhibited a higher moisture loss than conventionally chilled bread (CCB). A higher enthalpy of melting of amylopectin crystals was observed for VCB in comparison to CCB.VCB had a negative effect on the texture of the bread. The hardness of the crumb of VCB was increased by 20% at the end of staling and the kinetics of staling was 10% faster for VCB in comparison to CCB. After 12 days of storage at 4 °C, a second and final baking was applied to the bread. The staling rate of VCB was almost two times that of CCB. The staling rate of CCB was unchanged in comparison to the staling rate after partial baking. Data on the enthalpy of melting of amylopectin showed that the same amount of amylopectin was formed at the end of staling for CCB after part baked process and after full baking process. Beside, the VCB showed a higher amount of recrystallized amylopectin (10%) at the end of the staling which followed the partial baking.     

Effect of flaxseed flour on rheological properties,staling and total phenol of Iranian toast

Effect of adding flaxseed flour (10%, 20% and 30% w/w) to wheat flour on rheological properties of dough, including water absorption, stability and development time, extensibility and resistance to extension, was studied at 45, 90 and 135 min proving time. Qualitative properties of toast regarding staling (after 24 and 72 h) were determined. Phenolic compounds, peroxide values, sensory characteristics and color indices of the breads were evaluated. The results indicated that water absorption and development time increased as the proportion of flaxseed increased in dough. Stability decreased with the increment of flax flour compared to control sample (100% wheat flour). Extensibility and resistance to extension of flaxseed samples respectively decreased and increased comparing to those of control sample. Staling in toast with 20% flaxseed flour was seen to be lower than that of the control. Adding flax flour caused phenolic compounds to increase, however it decreased peroxide value. Bread color parameters L and a reduced by adding flax flour, while parameter b did not show significant different compared to the control (p < 0.05). Results of sensory evaluation indicated that brightness of the toasts decreased with increasing flaxseed flour and that 30% flaxseed toast had the lowest score for overall acceptability.     

Staling of frozen partly and fully baked breads. Study of the combined effect of amylopectin recrystallization and water content on bread firmness

Partly baked (PB) and fully baked (FB) breads were frozen at −18 °C for 7, 21, 63, 92, 126 and 188 d and were analysed after its thawing (FB) or thawing and final baking (PB). The starch retrogradation, the moisture content and the firmness were measured as properties closely related to the aging of bread. The temperature of glass transition of the maximally freeze-concentrated state, T_g′, was also measured and established in (−18 ± 0.8) °C. This value cannot ensure molecular immobility in both types of bread during its frozen storage at (−18 ± 2) °C. Consequently, the rearrangements of starch component molecules, needed for its recrystallization and for the diffusion of water during frozen storage, could take place and could justify the changes observed in the bread. PB bread showed a significant decrease in firmness with frozen storage, while the firmness of the FB bread did not change significantly, although an increase when compared with the control, not frozen bread, was detected. A regression study led to the conclusion that the combined effect of starch component crystallization and water loss could explain the firming evolution and that both variables exerted an effect of similar intensity on crumb firmness.     

Staling of fresh and frozen gluten-free bread

The difficulty in finding gluten-free bread and its high price make it necessary to prolong its shelf life to facilitate its availability. Freezing is an interesting alternative. The storage of bread at over zero temperatures, 20 °C and 4 °C, showed faster staling at refrigerator temperatures. A good relationship between crumb firmness and the extent of starch recrystallization was obtained, although the effect of water loss was also detected. The study of freezing and frozen storage at −14 °C and −28 °C for 7 days showed a substantial effect of the storage temperature on gluten-free bread quality and shelf life. Breads stored at −28 °C retained a quality similar to that of fresh breads while a marked deterioration of the breads stored at −14 °C was observed. This effect, the strongest on bread texture, was a result of starch recrystallization. The glass transition, T_g’ and onset of ice melting, T_m’ of the maximally freeze-concentrated bread crumb were −37.1 ± 0.6 °C and −19.3 ± 0.2 °C respectively. The higher amount of unfrozen water at −14 °C could explain the acceleration of reactions responsible for bread staling during frozen storage. The use of storage temperatures below T_m’ is recommended to retain high quality of the gluten-free bread during frozen storage.     

Impact of baking conditions and storage temperature on staling of fully and part-baked Sangak bread

Bread staling involves a combination of physico-chemical phenomena that leads to a reduction of quality. This study aims at evaluating the impact of baking conditions (280 °C, 8 min; 310 °C, 5.5 min; 340 °C, 4 min), baking type (of fully baked (FB) and part-baked (PB)) and storage temperature (−18, 4 and 20 °C) on the staling of Sangak bread. Results showed that lower baking temperature with longer baking time produced drier bread with higher firmness. In FB Sangak breads, amylopectin retrogradation, amount of unfreezable water and firmness (measured by compression test) increased during storage at positive temperatures but hardness (determined by Kramer shear test) decreased significantly during first day of storage. The recrystallized amylopectin traps the free water resulting in crumb hardening. Water is also absorbed by the dry crust resulting in changes of rheological properties in the crust and crumb, and finally in staling. Storage at 4 °C resulted in increasing melting enthalpy of amylopectin crystallite in comparison with storage at 20 °C. Also it was found that firmness of PB breads due to rebaking was significantly lower than FB breads. There were no significant changes in staling parameters of FB and PB stored at −18 °C.     

Impact of the baking kinetics on staling rate and mechanical properties of bread crumb and degassed bread crumb

This paper presents a study on the impact of baking conditions on crumb staling. Breads were baked at 220 °C, 200 °C and 180 °C corresponding to 6, 8 and 10 min to rise the temperature to 98 °C in the crumb (heating rates 13, 9.8 and 7.8 °C/min respectively with an initial temperature of 20 °C). A new protocol has been developed, consisting in baking a slab of degassed dough in a miniaturized oven to mimic the baking conditions of conventional bread making. Texture tests were done during staling on degassed crumb and on conventional crumb. Calorimetry tests showed that during storage, amylopectin recrystallisation occurred before crumb stiffening. A first order kinetics model was used to fit the evolution of the crumb texture (Young's modulus) and of the recrystallisation of amylopectin. The results showed that the hardening of the crumb during staling occurred after retrogradation of amylopectin. In addition, the staling rate was faster for faster baking kinetics. A mechanical model showed that the relative Young modulus is proportional to the square of the relative density of the crumb.     

Quality characteristics of northern-style Chinese steamed bread prepared from soft red winter wheat flours with waxy wheat flour substitution

Quality characteristics of northern-style Chinese steamed bread (CSB) prepared from two soft red winter (SRW) wheat flours blended with 0–30% waxy wheat flour (WWF) were analyzed to estimate the influence of starch amylose content. The increased proportion of WWF in blends raised mixograph absorption with insignificant changes in protein content and dough strength-related parameters. WWF incorporation generally increased specific volume and crumb softness of CSB. The analysis of covariance revealed that CSB quality attributes were little affected by protein content and dough strength-related parameters, indicating that starch amylose content was largely responsible for the changes in CSB quality. Flour blends with 5–10% WWF, of which starch amylose content was 22.4–24.7%, produced CSB with superior crumb structure compared to other blends, but insignificant changes in surface smoothness, stress relaxation and total score compared to the respective control wheat flours. Flour blends with 15% WWF to produce a starch amylose content of 21.4–22.7% exhibited reduced staling of CSB with total scores comparable to the respective control wheat flours. CSB prepared from blends with more than 10% WWF exhibited a higher soluble starch content, indicative of reduced starch retrogradation, than that prepared from wheat flours without WWF during storage for 3 days.     

不同添加量产胞外多糖荞麦酸面团对面包烘焙和老化特性的影响

[目的]研究不同添加量的产EPS荞麦酸面团对面包烘焙和老化特性的影响。[方法]应用分离自酒曲中的产胞外多糖食窦魏斯氏菌T5发酵荞麦粉制成产胞外多糖荞麦酸面团和不产胞外多糖荞麦酸面团,比较2种酸面团的添加量对面包烘焙和老化特性的影响。[结果]食窦魏斯氏菌T5在添加蔗糖的条件下,发酵荞麦酸面团产生EPS的含量为9.36 g/kg;含有酸面团(20%和30%)的面包比容、硬度和感官评分都优于空白不含酸面团面包,且含有产EPS酸面团的面包品质更佳;随着酸面团添加量的增加,添加30%不产EPS酸面团对面包比容和硬度产生消极作用,而添加30%产EPS酸面团能改善新鲜面包品质;在相同贮藏期,含有不产EPS酸面团的荞麦面包随着酸面团添加量的增加,面包芯硬度和支链淀粉老化焓值显著增加,而添加30%产EPS酸面团对面包老化具有改善作用。[结论]该研究为开发营养、健康的高品质绿色烘焙发酵食品提供理论依据。