Thermo-physical assessment of bread during staling

Staling of bread is a highly complex phenomenon that is not yet fully understood. This study examined the effect of staling on thermal (DSC) and thermo-physical (DMA) properties of bread. The staling process increased water migration from the crumb to the crust and increased unfreezable water (UFW) fraction. Amylopectin retrogradation incremented during bread staling, and it was showed that the loss in freezable water (FW) was caused from water incorporation into the starch crystalline structure and water migration from the crumb to the crust. DMA was able to follow the shrinking behavior of bread crumb during freezing. Crumb shrank through the entire cooling and freezing process. The matrix shifts through their freezing process incremented the rate of their contraction, probably due to the matrix dehydration as consequence of ice formation. The ageing process changes the thermo-mechanical profile of the crumb, and it was showed that a greater amount of retrogradated starch, affected significantly the contraction capacity of bread crumb.     

Combined Effects of Baking Conditions and Bacterial α-Amylases on Staling Kinetics of Degassed and Porous Bread Crumb

Enzymes such as ??-amylase are extensively used to retard the staling process. Enzymes are acting both during fermentation and during baking. The objective of this work was to determine the relative action of ??-amylase during fermentation and during baking. The impact of the baking conditions (time, temperature) was also considered. To attain this aim, a degassed bread crumb was baked in a miniaturized system using two programs of baking: heating rates 10.27 and 6.88?°C/min corresponding to 180 and 220?°C baking temperatures, respectively. Mechanical and thermodynamic properties of the degassed crumb were assessed during aging of bread by determining the Young??s modulus E, the amount of freezable water, and the melting enthalpy of retrograded amylopectin. A first-order kinetic model was used to determine the different parameters of staling kinetics. Results showed that the hardening of crumb increased during storage. The kinetics were faster for samples baked with fast heating rate than for those baked with slow heating rates. The use of enzymes decreased the Young??s modulus but did not have any effect on the staling rate. Calorimetric analysis of the starch retrogradation showed a reduction of the amount of freezable water during storage with an increase of retrograded amylopectin. A comparison between mechanical properties of conventional crumb and of the degassed dough confirmed that experimental data fitted correctly the Gibson and Ashby??s model.     

Effect of chitosan and chitooligosaccharide lactate on free lipids and reducing sugars content and on wheat bread firming

The amount of free lipids and reducing sugars as well as crumb color for wheat bread samples containing different amounts of chitosan and chitooligosaccharide lactate have been determined. Firmness of bread containing various contents of low molecular weight chitosan and chitooligosaccharide lactate was studied as a function of storage time. Possible mechanisms of redistribution of free and bound lipids during bread making are discussed. Addition of chitooligosaccharide lactate in wheat bread results in reduction in lipid binding to starch and gluten. Free lipid content increases from 0.11 to 0.35% in the presence of 1% chitooligosaccharide lactate. The total color changes in bread crumb containing chitosan are higher compared with the color changes in bread crumb containing chitooligosaccharide lactate. So it can be supposed that Maillard reactions proceed more intensively in the presence of chitosan than in the presence of chitooligosaccharide lactate.     

Impact of the Baking Duration on Bread Staling Kinetics

This paper presents a study on the impact of the duration of the baking plateau on staling kinetics in the case of bread crumb made of sourdough; it follows Le-Bail et al. Journal of Cereal Science 50:235–240, (2009)a previous study proposed by Le-Bail et al. Journal of Cereal Science 50:235–240, (2009) on the impact of heating rate during baking on staling parameters. Degassed bread dough was baked in a miniaturized baking system with baking plateau of 0, 4, and 8 min at 98 °C corresponding to a total baking time of 10, 14 and 18 min respectively (simulating from underbaked to fully baked bread). Results showed that longer baking time resulted in the higher Young’s modulus of the baked dough at the end of staling was. It was observed as in Le-Bail et al. Journal of Cereal Science 50:235–240, (2009) that the crystallization of amylopectin occurred a few days before the hardening of the baked crumb during staling. The amount of freezable water decreased during staling (over 10 days period), which was in agreement with the increase in amylopectin crystallites during staling which trap water. The amount of soluble amylose increased with increasing duration of the baking plateau at 98 °C, indicating that for prolonged baking, an increasing amount of amylose is leached outside of the starch granules. This was proposed as an explanation for the higher Young’s modulus of the crumb at the end of staling.     

Effect of HPMC addition on the microstructure, quality and aging of wheat bread

The effect of hydroxypropylmethylcellulose (HPMC) addition on a basic bread formulation is described. The effect of HPMC as bread improver and antistaling agent was analysed in terms of microstructure. Bread quality was assessed by physical parameters (volume, width/height ratio, moisture content and hardness), crumb grain structure (number of air cells, cells area and the ratio between cells area and total area) and sensory evaluation (appearance, aroma, taste and texture). Bread staling was determined by following both the hardness increase and the starch retrogradation during storage. The microstructure was analyzed by cryo scanning electron microscopy (cryo-SEM). The results confirm the ability of the HPMC for improving fresh bread quality and for delaying staling. The presence of HPMC decreased the hardening rate of the bread crumb and also retarded the amylopectin retrogradation. The microstructure analysis revealed the possible interaction between the HPMC and the bread constituents, which could partially explain the antistaling effect of this hydrocolloid.     

Studies on glass transition and starch re-crystallization in wheat bread during staling using electrical impedance spectroscopy

Bread staling is a very complex phenomenon that is not yet completely understood. The present work explains how the electrical impedance spectroscopy technique can be utilized to investigate the effect of staling on the physicochemical properties of wheat bread during storage. An instrument based on electrical impedance spectroscopy technique is developed to study the electrical properties of wheat bread both at its crumb and crust with the help of designed multi-channel ring electrodes. Electrical impedance behavior, mainly capacitance and resistance, of wheat bread at crust and crumb during storage (up to 120 h) is investigated. The variation in capacitance showed the glass transition phenomenon at room temperature in bread crust after 96 h of storage with 18% of moisture in it. The resistance changes at bread crumb showed the starch recrystallization during staling.Industrial relevanceSimultaneous measurement of moisture content, glass transition and starch recrystallization is possible with the designed instrument without disturbing the experimental set-up. Thus, the present work is going to help manufacturers and researchers to understand the bread staling phenomenon at crust and crumb without opting very complex instrumental procedures.     

Bread staling. IV. Electrical properties of the crumb during staling

A new technique for studying the staling of bread is described based on conductance and capacitance measurements on the isolated centre-crumb. It is proposed that the observed changes (up to 17%) in the electrical properties are due to retrogradation of the starch as well as the changes undergone by the transforming protein. Moisture redistribution is thought not to play a significant role during staling of the crumb at temperatures of less than about 10 °C. At 36 °C the first-order rate-constant for the protein transformation was estimated to be 0.7 day^?1 and 0.3 day^?1 for the rate constant for retrogradation of the starch fraction of the crumb. At 0 °C, the protein transformation was insignificant and the rate constant for the starch change was 1.03 day^?1. The thickness of the gluten membrane surrounding the starch granules in bread was approximated to be less than 1 μm.     

Effects of sourdough and enzymes on staling of high-fibre wheat bread

The effects of sourdough and enzyme mixture (α-amylase, xylanase and lipase) on the specific volume, staling and microstructure of wheat pan bread supplemented with wheat bran were studied. Staling of bread was followed for 6 days by measuring the crumb firmness, changes in crystallization of amylopectin (DSC), increase in signal from the solid phase (NMR) and by light microscopy. The most effective treatment in improvement of quality was the combination of bran sourdough and enzyme mixture. During storage the rate of changes in crumb firmness, amylopectin crystallinity and rigidity of polymers were greatest for the white wheat bread. The most pronounced microstructural changes were swelling of starch granules and separation of amylose and amylopectin in the starch granules. Least changes in crumb firmness, amylopectin crystallinity and rigidity of polymers were observed in bran sourdough bread with enzymes. In contrast to white wheat bread, the starch granules were very much swollen in bran sourdough bread with enzyme mixture. This was hypothesized to be due to the higher water content of bran bread, and degradation of cell wall components leading to altered distribution of water among starch, gluten and bran particles during storage.     

Bread staling: I.—Experimental study

Starting with a typical baker's dough, a model system was constructed in order to examine whether moisture re-distributed itself between the two principal components, gluten and starch, of crumb during ageing. Separation of the components of dough was achieved by ultra-centrifugation. It was estimated that up to 30% of the moisture associated with the gluten fraction, migrated to the starch during 120 h of storage of the baked system at 25°c. The rate of migration decreased approximately exponentially with time. Moisture from the gluten was also found to migrate to the starch during baking, but at an accelerated rate. The rate of moisture migration in the model system, both at 100 and 25°c, was consistent with a diffusion-controlled process involving migration of the gluten-released moisture to the gluten-starch interface. Experimental results show that staling of bread involves (in addition to the generally accepted retrogradation of the starch) an irreversible modification in the water structure of the gluten, leading to the formation of labile water, which becomes available for absorption by the incompletely gelatinised starch. Since the gluten forms the continuous matrix of the crumb, the modification results in a rigidification or firming process.     

MECHANISM AND THEORY OF STALING OF BREAD AND BAKED GOODS, AND ASSOCIATED CHANGES IN TEXTURAL PROPERTIES

Abstract. A critical review of the literature on the staling of bread has been presented with particular emphasis on developments during the last decade. The staling of bread has been discussed from a structural point of view with separate contributions due to starch retrogradation, a modification in the gluten structure and a partial re-distribution of moisture from the gluten to the starch fraction of the crumb. Both model systems and studies on the natural crumb are considered including the contribution to staling of macroscopic moisture re-distribution and deterioration in flavour volatiles. The staling of baked goods has also been reviewed and it is proposed that certain analogies from the bread situation might provide a suitable basis for an overall theory of cake staling. It seems possible that a considerable contribution to the staling of cake sponge may be due to changes undergone by the various proteins; the free moisture produced from the transforming proteins may be absorbed by the sugars and gelatinised starch. Retrogradation of starch appears to be less important than changes in the proteins during the staling of cake. Dehydration of the cake crumb is perceived to play an important role in the sensory evaluation of cake staleness.     

馒头老化指标的初步研究

研究了馒头在储存过程中物理化学特性的变化并进行了相关性分析，初步确定馒头芯的硬度与弹性、馒头瓤上清液中干物质和蛋白质含量以及上清液与碘试剂络合吸光度为馒头老化的代表指标。     

Starch affecting anti-staling agents and their function in freestanding and pan-baked bread

Anti-staling agents with different mechanisms were added to a normal white wheat bread to investigate the relation between bread staling, amylopectin retrogradation and water-related properties (i.e. water content and distribution between crumb and crust). Bread was baked both as pan-baked and freestanding loaves. The anti-staling agents maltogenic α-amylase, distilled monoglyceride and lipase had a direct influence on starch retrogradation, whereas gluten and waxy wheat flour diluted the amylopectin content or changed the ratio between amylose and amylopectin. The degree of staling was measured as the firmness and springiness, together with two new methods, crumbliness and cutability. In addition, the degrees of amylopectin retrogradation and amylose–lipid complex formation were analyzed by differential scanning calorimetry, and the water content, water loss and water migration were measured. The addition of α-amylase improved most staling parameters, although the changes were not as large as expected. Furthermore, monoglyceride and lipase increased the formation of amylose–lipid complexes, but only lipase gave better results regarding the specific volume and firmness. Increased amylose–lipid complex formation was seen to increase water migration from crumb to crust. Adding 10% waxy wheat flour appeared to lead to a slight overall improvement i.e. lower water migration and better cutability. Adding gluten or 3% waxy wheat flour only improved the specific volume. The method of baking the loaves, i.e. freestanding or pan-baked, had a greater influence than the anti-staling agents, which shows that bread quality is not always improved by starch affecting anti-staling agents without process changes.     

Wheat starch structure–function relationship in breadmaking: A review

Bread dough and bread are dispersed systems consisting of starch polymers that interact with other flour components and added ingredients during processing. In addition to gluten proteins, starch impacts the quality characteristics of the final baked product. Wheat starch consists of amylose and amylopectin organized into alternating semicrystalline and amorphous layers in granules that vary in size and are embedded in the endosperm protein matrix. Investigation of the molecular movement of protons in the dough system provides a comprehensive insight into granular swelling and amylose leaching. Starch interacts with water, proteins, amylase, lipids, yeast, and salt during various stages of breadmaking. As a result, the starch polymers within the produced crumb and crust, together with the rate of retrogradation and staling due to structural reorganization, moisture migration, storage temperature, and relative humidity determines the final product's textural perception. This review aims to provide insight into wheat starch composition and functionality and critically review recently published research results with reference to starch structure–function relationship and factors affecting it during dough formation, fermentation, baking, cooling, and storage of bread.     

Effect of baking conditions and storage with crust on the moisture profile,local textural properties and staling kinetics of pan bread

To investigate the impact of baking conditions on staling kinetics and mechanical properties, pan breads were baked at 180 °C/34 min and 220 °C/28.6 min using a ventilated oven and metallic moulds. After baking, bread slices were stored with and without crust at 15 °C in hermetic boxes for 9 days. This investigation provides a textural and physical analysis by examining the Young's modulus, crumb density and crust/crumb ratio during storage. In order to understand the relationship between firmness and moisture content, a moisture profile and a Young's modulus profile were determined during the storage of bread. To fit the staling, a first order model was used. It was found that the kinetics were faster for samples baked with a fast heating rate than for those baked with a slow heating rate. Moreover, the staling rate of bread stored with crust was faster than for bread without crust and the outer crust area staled more rapidly than the centre of the bread slice. These results suggest that the firming of the crumb is related to moisture distribution between the crumb and crust and to the impact of local baking conditions on local firmness.     

Measurement of Starch Properties During Staling of Arabic Bread

The DSC and X-ray diffraction data showed that the starch crystallinity increased in Arabic bread (khaboos) samples during the storage period. The appearance of crystalline regions during ageing as shown by X-ray diffraction data could serve as an indication of the extent of staling that was observed in these khaboos samples. The information obtained from scanning electron microscopy could not be used for assessing the extent of staling of Arabic bread, but showed interesting differences in the gelatinization behaviour of starch granules in the crumb and crust areas. The crust areas, when viewed under the scanning electron microscope, show intact small as well as large starch granules. The limited amount of water available in the crust area of khaboos may be responsible for the incomplete gelatinization of starch granules.     

Structural changes in the wheat dough and bread with the addition of alpha-amylases

The influence of fungal and bacterial -amylases on the texture and microstructure of dough and bread was investigated. Loaf specific volume, crumb porosity and texture properties were accepted as bread structure and texture characteristics. The microstructure analysis of dough and bread using light and scanning microscopy methods was performed.The changes in loaf specific volume, crumb porosity and texture properties showed different anti-staling activity of the enzymes used. The simultaneous action of enzyme addition and the fermentation process evoked significant changes in the microstructure of dough. The character of these changes depended on the kind of enzyme used. A substantial effect of both amylases on starch behaviour during bread baking and staling was also observed.     

Impact of fibers on physical characteristics of fresh and staled bake off bread

The technological functionality of different fibers (high methylated ester pectin, resistant starch, insoluble-soluble fiber blend) was tested in partially baked breads stored either under sub-zero or low temperatures, in order to assess their possible role as breadmaking ingredients in bake off technologies (BOT). Fiber-containing formulations affected bread specific volume and crumb hardness, and those characteristics were also dependent on both the breadmaking process (conventional or BOT) and the storage conditions of the par-baked bread (low or sub-zero temperatures). The inclusion of resistant starch (RS) and fiber blend in the bread formulation induced a reduction in the specific volume of the bread and an increase of hardness. Crumb image analysis indicated that breadmaking process affected significantly the number of alveoli. The storage of par-baked breads at low temperatures accelerates crumb hardening during staling, and that effect was greatly dependent on the duration of the storage, being that effect magnified in the case of breads containing fiber blend. Therefore, formulations should be carefully checked with the specific breadmaking process to be followed. Special attention should be paid to the storage conditions of the partially baked bread, since they significantly affect the technological quality of fresh breads and their behaviour during staling.     

Effect of zein protein and hydroxypropyl methylcellulose on the texture of model gluten‐free bread

The influence of zein protein and hydroxypropyl methylcellulose (HPMC) on the texture and volume of gluten‐free bread was investigated. The addition of HPMC to starch affected the dough viscoelasticity and it improved the bread volume during baking since it acts as an emulsifier. The addition of zein protein to gluten‐free bread increased the crumb firmness and reduced the crust hardness within the range of concentrations investigated. No zein protein network could be observed in the bread crumb. The zein protein, cold mixed at low concentration, did not enhance the dough elasticity. Due to the lack of a protein network noncovalent interactions may stabilize the bubble structure stabilization within the crumb, rather than covalent links of the protein chain. With an optimized amount of zein protein and HPMC hydrocolloid, the gluten‐free bread showed similar texture and staling behavior to that of model wheat bread. The optimized recipe, compiled into a spreadsheet, is available in the supporting information. The microstructural observations suggest that zein could be replaced with another protein for this recipe resulting in a similar bread texture.     

Application of Glazing for Bread Quality Improvement

Glazing is a surface coating method for enhancement of the quality factors of bakery products. This study was intended to investigate the effect of different bakery glazing groups such as natural, polyols, sugars, and hydrocolloids on Barbari flat bread. Some quality attributes of bread such as moisture content, water activity, specific volume and width/height ratio (0 day) and hardness, crumb, and crust moisture (0–12 days) were evaluated. Results showed that vegetable oil treated samples had the lowest water activity and moisture content. Also, xanthan treatment provided the greatest effect on the specific volume of fresh bread, which enhanced it from 3.94 to 5 cm³/g. Vegetable oil, glycerol, dextrose, liquid glucose, and guar treatments had more significant effect on width/height ratio in comparison to nontreated (unglazed) bread. Evaluation of crumb hardness and moisture during 12 days storage implicated water, egg yolk, starch, and propylene glycol treatments were able to diminish the bread staling and these treated samples had the lowest crumb hardness. Crumb moisture of Barbari bread was affected mostly by water and starch treatments at day 12. Finally, our finding approved that using of glazing as a novel method is an effective technique for improvement of overall quality of flat bread and its application is suggested for large-scale production of other bakery products.