Different approaches for increasing the shelf life of partially baked bread: Low temperatures and hydrocolloid addition

Partially baked bread is a product with short shelf life that requires sub-zero temperatures for extending it. The storage of par-baked bread at low temperatures and the addition of bread improvers with antistaling effects, such as hydroxypropylmethylcellulose (HPMC), are very attractive alternatives for extending the shelf life of these products. In this study, staling during storage of partially baked bread (in the presence and absence of HPMC) at low temperatures (2 °C) is studied in terms of hardness increase and amylopectin retrogradation. Simultaneously, the staling of the derived full baked breads when stored at 25 °C is assessed. During the storage of par-baked bread at low temperatures, progressive crumb hardening and rapid crystallization of the amylopectin chains were produced. However, heat applied during full baking reversed those processes, and the extent of that improvement was dependent on the time of par-baked bread storage. Concerning the staling of the derived full baked bread, the time of par-baked bread storage did not significantly (P < 0.05) affect the staling process of the resulting full baked breads. The addition of HPMC decreased the crumb hardness in both par-baked and full baked breads, and also promoted a reduction of the amylopectin retrogradation. Overall results indicate that HPMC addition significantly retards the staling of par-baked bread during its storage at low temperatures and, moreover, the same effect is observed in the full baked bread.     

Effect of freezing and frozen storage on the staling of part-baked bread

The effect of part-baking, freezing, frozen storage, thawing, rebaking on the aging behaviour of bread was evaluated. The amylopectin modification during the process was assessed by differential scanning calorimetry (DSC), while changes in bread quality were followed by crumb hardness measurements. During frozen storage no retrogradation of amylopectin was detected in the part-baked dough. When analysing the aging of the rebaked samples, it was observed that the time of frozen storage produced a progressive increase of the retrogradation temperature range of the amylopectin, and also great energy was required for amylopectin melting at longer storage period, indicating that structural changes of amylopectin were produced during frozen storage. Regarding the quality of the fresh bread resulted after rebaking, crumb hardness increase with the time of frozen storage, and also the hardening rate during aging was dependent on that time. Crumb hardness results of the fresh bread and also DSC studies indicate that some changes are produced during the frozen storage.     

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.     

Investigation of physicochemical properties of breads baked in microwave and infrared-microwave combination ovens during storage

Staling of breads baked in different ovens (microwave, infrared-microwave combination and conventional) was investigated with the help of mechanical (compression measurements), physicochemical (DSC, X-ray, FTIR) and rheological (RVA) methods. The effect of xanthan-guar gum blend addition on bread staling was also studied. Xanthan-guar gum blend at 0.5% concentration was used in bread formulation. The gums were mixed at equal concentrations to obtain the blend. After baking, the staling parameters of breads were monitored over 5 days storage. During storage, it was seen that hardness, retrogradation enthalpies, setback viscosity, crystallinity values, and FTIR outputs related to starch retrogradation of bread samples increased, whereas FTIR outputs related to moisture content of samples decreased significantly with time. The hardness, retrogradation enthalpy, setback viscosity, and crystallinity values of microwave-baked samples were found to be highest among other heating modes. Using IR-microwave combination heating made it possible to produce breads with similar staling degrees as conventionally baked ones in terms of retrogradation enthalpy and FTIR outputs related to starch retrogradation. Addition of xanthan-guar gum blend decreased hardness, retrogradation enthalpy and total mass crystallinity values of bread samples showing that staling was delayed.     

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 prebaking and frozen storage on the sensory quality and instrumental texture of bread

The effect of part‐baking, freezing, frozen storage, thawing and rebaking on the quality of bread has been investigated. Quality evaluation of the stored bread was done using sensory analysis, instrumental texture profile analysis (TPA) and cutting tests of the crumb and crust. It was found that frozen bread with 71% fraction of baking time showed high stability of sensory features and rheological parameters during the entire storage period (11 weeks) and, after thawing and rebaking, had superior quality in comparison with its frozen and thawed full‐baked (100%) counterpart. Second‐order regression showed that the optimal time for the initial prebaking lies within the wide range from 74 to 86% of the time needed for the full‐baking of unfrozen bread. It is therefore a good method for preventing the staling process and obtaining a product of a quality close to that of fresh, not frozen bread. It has also been shown that a fraction of baking time equal to 43% was too small to ensure desirable sensory and textural features of bread after its frozen storage and rebaking. © 2002 Society of Chemical Industry     

The impact of baking time and bread storage temperature on bread crumb properties

Two baking times (9 and 24 min) and storage temperatures (4 and 25 °C) were used to explore the impact of heat exposure during bread baking and subsequent storage on amylopectin retrogradation, water mobility, and bread crumb firming. Shorter baking resulted in less retrogradation, a less extended starch network and smaller changes in crumb firmness and elasticity. A lower storage temperature resulted in faster retrogradation, a more rigid starch network with more water inclusion and larger changes in crumb firmness and elasticity. Crumb to crust moisture migration was lower for breads baked shorter and stored at lower temperature, resulting in better plasticized biopolymer networks in crumb. Network stiffening, therefore, contributed less to crumb firmness. A negative relation was found between proton mobilities of water and biopolymers in the crumb gel network and crumb firmness. The slope of this linear function was indicative for the strength of the starch network.     

Staling of cereal bran enriched cakes and the effect of an endoxylanase enzyme on the physicochemical and sensorial characteristics

Abstract: The staling of cakes enriched with untreated brans and endoxylanase‐treated brans was evaluated by monitoring the changes in physicochemical, thermal, and sensorial properties of cakes during 7‐d storage. Oat and rice bran were treated with different levels (0, 70, and 700 ppm) of an endoxylanase enzyme and added to cakes on 30% flour weight basis. Moisture losses, water activity, crumb firmness, starch retrogradation, and sensorial characteristics were used as staling indicators. Avrami‐type equations were efficiently used for modeling the starch retrogradation kinetics, while linear models most adequately described crumb firming kinetics. Cake staling induced an increase in crumb firmness and enthalpy of amylopectin retrogradation, and a decrease in crumb moisture and sensory quality and acceptability scores of cakes. Oat bran‐containing cakes better maintained their characteristics compared to the ones containing rice bran along the 7‐d storage. Endoxylanase treatment of brans delayed the changes naturally induced during staling in crumb moisture content, amylopectin retrogradation enthalpy, and crumb firmness in the respective cakes. Deterioration of the sensorial characteristics was slower for the cakes containing endoxylanase‐treated brans, as well. The level of endoxylanase treatment did not differentiate significantly (P < 0.05) any of the staling indicators. Overall, this study demonstrated that addition of endoxylanase‐treated brans can result in cakes with improved nutritional characteristics and increased shelf life. Practical Application: The results of the study show the potential of using enzymes to modify underutilized food sources that can be properly incorporated in baked goods, improving their nutritional value, their quality characteristics, and providing longer shelf life. The developed procedure and results can be utilized by the bakery industry to make high fiber and low cost bakery products with improved sensorial characteristics that are appealing to the consumers.     

The staling of bread: an X-ray diffraction study

Bread crumb X-ray patterns were analysed by different methods, the objective being to provide more in-depth knowledge of the relationships among starch crystallinity, amylopectin retrogradation and bread firming. Both crumb-firming and amylopectin retrogradation increased with storage time. However, total mass crystallinity grade and relative crystallinity increased only in the first 24 h. The determination of starch crystallinity requires the separation of the crystalline and amorphous intensities, which is sometimes arbitrary, so it would be useful to improve this methodology. Different methods used to determine total crystallinity grade only show the differences existing between fresh and stored bread. B-type crystal structure—corresponding to the amylopectin retrogradation—increased during bread storage, showing a high correlation with bread-firming and storage time. This fact emphasized the above results and suggested that amylopectin retrogradation is an important component to the elucidation of bread staling.     

An approach to studying the effect of different bread improvers on the staling of pre-baked frozen bread

The usefulness of different bread improvers (-amylase, sourdough, -carrageenan, hydroxypropylmethylcellulose) in an interrupted baking process was evaluated by using a differential scanning calorimeter as an oven. The thermal transitions of the wheat starch produced during the part-baking process, frozen storage at –18 °C, finish baking and aging of the baked dough at 4 °C were registered. The thermal properties of wheat starch during gelatinisation measured by differential scanning calorimetry were slightly affected by the dough formulation: only the peak temperature and the onset temperature underwent an increase, whereas the gelatinisation enthalpy decreased. The presence of the bread improvers minimised the negative effect of the frozen storage observed in the control sample, which showed an increase in the retrogradation temperature range. Concerning the aging of the baked dough after freezing and re-baking, all the improvers decreased the retrogradation enthalpy of the amylopectin, retarding the staling. Bread improvers can act effectively in the interrupted baking processes with frozen storage of the part-baked breads.     

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.     

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.     

Fibre-rich additives--the effect on staling and their function in free-standing and pan-baked bread

BACKGROUND: The use of dietary fibre in bread products is increasing because of consumer demand for healthier products. However, an increase in dietary fibre level changes the rheological properties of the dough and also the quality properties of the final bread product. In this study, effects on dough and bread staling were followed after replacing 3% of wheat flour by fibre‐rich additives (fine durum, oat bran, rye bran and wheat bran). Free‐standing and pan‐baked loaves were baked to compare the influence of baking method and loaf shape. RESULTS: All additives increased dough stability, with oat bran giving the greatest stability and longest development time. Parameters measured during storage were distribution, migration and loss of water, cutability, crumbliness, firmness and springiness. Furthermore, amylopectin retrogradation and amylase‐lipid complex formation were assessed. Oat bran provided similar or better results than the control for all staling parameters, while other additives gave no general improvements. Cutability reached a plateau when crumb firmness was ≥ 4 N. CONCLUSION: Small amounts of fibre‐rich additives had a significant influence on staling. However, the baking method (free‐standing or pan‐baked bread) had a greater impact on staling than the additives, thus displaying the importance of the baking method. Cutability was found to be related to firmness. Copyright © 2011 Society of Chemical Industry     

A Study on Staling Characteristics of Gluten-Free Breads Prepared with Chestnut and Rice Flours

The effects of chestnut flour and a xanthan–guar gum blend–DATEM mixture on staling of gluten-free rice breads baked in conventional and infrared–microwave combination ovens were studied. Staling properties of the bread were assessed using mechanical compression (TA), differential scanning calorimetry, X-ray diffraction, and fourier transform infrared spectroscopy (FT-IR). Hardness, moisture loss, and retrogradation enthalpy values for all bread samples increased significantly during storage. FT-IR spectra showed that the integrated area of peaks around 1,041 and 1,150 cm^?1 wave lengths, which are related to the structure of starch retrogradation, increased with storage time. The X-ray diffractograms of aged breads indicated a B-type structure with the appearance of peaks at around 17°, 19.5°, and 22°. An additional peak at 24° was observed in breads stored for longer periods. Higher values of hardness and lower moisture contents were obtained for breads baked in an infrared–microwave combination oven, but the use of infrared–microwave combination oven did not result in excessive hardness after storage. Retrogradation enthalpies and total crystallinity values of breads did not show significant differences with baking type.The replacement of rice flour with chestnut flour and addition of xanthan–guar gum blend–DATEM mixture in formulations significantly delayed staling of gluten-free breads by decreasing moisture loss, hardness, retrogradation enthalpy, and total mass crystallinity.     

Staling of potato and wheat steamed breads: physicochemical characterisation and molecular mobility

To clarify the physicochemical characterisation and water status of potato steamed bread (PSB) and wheat steamed bread (WSB) during the staling process, texture, amylopectin retrogradation, crystalline structure, water migration and microstructure were evaluated by texture analysis, differential scanning calorimetry, X-ray diffraction, nuclear magnetic resonance (¹H NMR) and scanning electron microscopy (SEM). Results showed that starch molecules in PSB and WSB were recrystallised and formed B-type starch, which had a positive correlation with hardness and thermal enthalpy. Compared to WSB, PSB had a relatively low B-type crystallinity; moreover, a smaller decrease of free water in PSB was also detected in the NMR test, which indicated that more moisture can be used to plasticise crumb, thus contributing to a softer texture of PSB. SEM revealed that the amount and size of the cracks on the interface of starch and gluten matrix in WSB increased with the prolongation of storage time.     

Effect of damaged starch levels on flour-thermal behaviour and bread staling

The effect of the amount of damaged starch in two different flours (wheat and triticale) on the bread quality and its behaviour during storage has been analysed. Two wheat and one triticale flour cultivars were milled in a disc mill to obtain different levels of damaged starch. Differential Scanning Calorimetry (DSC) and Rapid Visco Analyser (RVA) were used to characterize the flour properties and TA-XT2 textural analyses were made on breadcrumb. The effect of the damaged starch content on the bread firming, the amylopectin retrogradation and starch-pasting properties were studied in order to establish any relationship between damaged starch and bread staling. DSC analysis showed that the damaged starch content changed the thermal behaviour of flour–water mixtures: the higher the levels of damaged starch the lower the starch-gelatinization enthalpy and the higher the melting enthalpy of amylose–lipid complexes. The amount of amylopectin retrogradation and breadcrumb firming increased with the damaged starch content at the beginning of storage time; however, differences were decreasing at final storage time. The flour viscosity during pasting decreased as their damaged starch content increased.     

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.     

Effect of different carbohydrases on fresh bread texture and bread staling

The effect of cellulase, xylanase and #-glucanase on the properties of wheat bread and its staling during storage was studied. The presence of the carbohydrases tested led to breads with high specific volume compared to the control. The texture profile analysis was greatly modified in that the firmness of bread crumb was reduced by all the carbohydrases. A kinetic study of the firmness along with the storage by the Avrami equation showed that the presence of carbohydrases produced softer crumbs and also reduced the rate of bread firming, although no great differences were found between enzymes. Since retrogradation of starch is one of most important factors related to bread staling, the modification of the amylopectin retrogradation was measured by scanning calorimetry. Those studies showed that all the carbohydrases decrease the starch retrogradation, and that the xylanases had the greatest effect. The simultaneous analysis of the firming and starch retrogradation results revealed that the anti-staling effect of xylanase might be due to the retardation in the starch retrogradation, while in the case of cellulase and #-glucanase some other mechanism should be implied in their anti-staling action.     

脱毒亚麻籽粕在面包中的应用研究

由于亚麻籽富含各种营养成分,目前正作为一种功能食品来源。本文将亚麻籽粕脱除毒性物质生氰糖苷后,将其添加到面粉中,以研究其对面团特性、面包烘焙品质以及面包贮存过程中老化程度的影响。结果表明,水煮法处理对除去生氰糖苷有较好的效果,通过正交实验确定以2%的比例添加可改善面团特性及面包烘焙品质,并增加面包的抗老化作用,延长了货架期。     

Effect of soy milk powder addition on staling of soy bread

Effect of soy milk components (soluble fibre (SF), insoluble fibre (ISF), soy protein) on physicochemical properties (crust and crumb colour, water activity, total moisture content, “freezable” water (FW), “unfreezable” water (UFW), amylopectin recrystallisation (ARC), stiffness and firmness) of soy breads stored for 7 days was studied. By the end of storage ISF additions significantly increased ARC (from 0.01 to 0.57 W/g), whereas SF additions (0.30 W/g) retarded staling with respect to soy flour bread (0.39 W/g). Principal Component Analysis (PCA) of all the different treatments and formulations indicated that SMP addition resulted in the lowest firmness and least amylopectin retrogradation at the end of storage, likely due to the synergistic effect of soluble fibre, partly denatured soy proteins and lipid content of this ingredient.