Effect of storage temperature on starch retrogradation of bread staling

The objective of the present work was to study the effect of bread storage temperature on starch retrogradation, using water activity measurement and X‐ray diffractometry technique to analyse the changes produced in the crumb firmness such as recrystallization. When storing bread with crust, the crust tends to trap moisture from the crumb, resulting in a dehydration of the crumb with faster staling. For storage temperatures of 25 and 4°C, water activity decreases as a function of storage time whereas at −18°C it is maintained at an almost constant level for 23 days. During storage, the starch molecules are reassociated and generate a new crystalline order which has a typical XRD pattern: the B‐type structure. The peak at 17.4° is indicative of this structure and is related to bread aging. As observed with the recrystallization kinetics, at −18°C only crystal growth may occur, whereas at 25 and 4°C there would be not only growth but also formation of new crystals. At 4°C the rate of starch retrogradation is the highest for the studied conditions.     

Effect of frozen storage time on the bread crumb and aging of par-baked bread

The effect of frozen storage time of par-baked bread on the bread crumb and staling of bread obtained after thawing and full baking is described. The moisture content, hardness and retrogradation enthalpy of the amylopectin were determined in the par-baked bread and in the full baked bread after 7, 14, 28 and 42 days of frozen storage at −25 °C. In addition, the effect of frozen storage on the crumb microstructure was analyzed by cryo scanning electron microscopy (Cryo-SEM). The moisture content of both partially and full baked bread decreased with the time of frozen storage. The crumb hardness of the par-baked bread after different periods of frozen storage was kept constant, while that of their full baked counterpart increased with the time of frozen storage. In both types of breads, the enthalpy of amylopectin retrogradation did not vary with the period of frozen storage. The staling, measured as hardness increase and amylopectin retrogradation, increased along the frozen storage. The changes observed on the frozen par-baked bread after thawing were attributed to the damage of bread structures produced by the ice crystallization, and the microstructure study support that conclusion.     

Optimization of ingredients and baking process for improved wholemeal oat bread quality

Baking technology for tasty bread with high wholemeal oat content and good texture was developed. Bread was baked with a straight baking process using whole grain oat (51/100 g flour) and white wheat (49/100 g four). The effects of gluten and water content, dough mixing time, proofing temperature and time, and baking conditions on bread quality were investigated using response surface methodology with a central composite design. Response variables measured were specific volume, instrumental crumb hardness, and sensory texture, mouthfeel, and flavour. The concentration and molecular weight distribution of β-glucan were analysed both from the flours and the bread. Light microscopy was used to locate β-glucan in the bread. Proofing conditions, gluten, and water content had a major effect on specific volume and hardness of the oat bread. The sensory crumb properties were mainly affected by ingredients, whereas processing conditions exhibited their main effects on crust properties and richness of the crumb flavour. β-glucan content of oat bread was 1.3/100 g bread. The proportion of the highest molecular weight fraction of β-glucan was decreased as compared with the original β-glucan content of oat/wheat flour. A great part of β-glucan in bread was located in the large bran pieces.     

The use of normal and heat-treated barley flour and waxy barley starch as anti-staling agents in laboratory and industrial baking processes

Normal and heat-treated barley, both as flour and waxy starch, were added at a concentration of 3% to a white wheat bread. The effect not only of selected additives, but also of laboratory- and industrial baking processes on stalling was evaluated. Laboratory baked breads with heat-treated barley flour differed from control breads with regard to water content, firmness and amylopectin retrogradation. The influence of water content on firmness increased with storage time. All laboratory baked breads with barley additives, except normal barley flour, were less firm after 7 days of storage as compared to the control although amylopectin retrogradation tended to increase. Improved water absorption, and consequently, increased water content and/or different water binding capacities of the flour/starch could explain these results. Industrial baking caused higher water losses, especially in breads containing additives, thus reducing the effects on amylopectin retrogradation and firmness.     

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.     

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.     

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.     

Effect of green plantain flour addition to gluten‐free bread on functional bread properties and resistant starch content

Green plantain flour (GPF) was used as a functional ingredient to produce gluten‐free (GF) bread based on a flour blend of rice flour and GF wheat starch (50:50) to improve their functional properties and to increase their resistant starch (RS) content. In pretrials, an addition of up to 30% GPF provided acceptable bread quality with maximum RS content. Based on these trials, two 2³ factorial screening experimental designs were applied, where water content, baking temperature and baking time of GF bread containing 30% GPF addition were optimised. The best baking conditions to achieve satisfying GF bread quality – higher loaf volume, softer crumb firmness and regular porosity structure at the highest RS content could be defined to a maximum addition of water at 160%, baking temperature of 180 °C and baking time of 90 min. The incorporation of GPF showed good potential to improve the quality of GF bread.     

Impact of thermostable amylases during bread making on wheat bread crumb structure and texture

Thermostable amylases [Bacillus subtilis α-amylase (BSuA) and B. stearothermophilus maltogenic amylase (BStA)] with different modes of action and impacts on firming properties were added during straight-dough bread making. BSuA continuously degraded the starch fraction during bread making. Its action resulted in larger gas cells than in control bread, but did not change initial firmness. In contrast to BSuA, BStA mainly degraded starch at the end of the baking phase and during bread cooling, which caused little if any impact on bread crumb texture. However, it led to higher initial firmness readings than for the control breads. Neither BSuA nor BStA were inactivated during bread making. The results evidence that starch properties have a large impact on bread crumb structure and initial firmness and are highly influenced by the mode of action of the enzyme.     

Effect of the amount of steam during baking on bread crust features and water diffusion

Surface mechanical properties in fresh bread and during storage are greatly affected by the water plasticizing effect. However, the incidence of steaming during baking on the crust mechanical properties remains still unclear. The impact of the amount of steam (100, 200 and 400 ml) during baking on the crust features and water diffusivity was investigated. The amount of steam significantly (p < 0.05) affected the crust colour, glossiness and mechanical properties. An increase in the amount of steam led to reduced colour, failure force and failure firmness, whereas increased glossiness. Water vapour transfer rate and water vapour permeability of the bread crust significantly decreased when increasing the amount of steam applied during baking. Crust microstructure studies carried out by scanning electron microscopy and X-ray microtomography confirmed that the amount of steam greatly affected the surface starch gelatinization and also the protein-starch network.     

Bread Staling: Changes During Storage Caused by the Addition of Calcium Salts and Inulin to Wheat Flour

The objective of this work was to study changes in staling parameters of wheat bread formulated with different calcium salts (carbonate, citrate, or lactate) and inulin. The moisture content and texture of crumbs were studied. Moreover, the effect of calcium and inulin levels on crumb firmness during storage was estimated by fitting the Avrami equation. Starch retrogradation and the amylose-lipid complex were evaluated by differential scanning calorimetry (DSC) and X-ray diffraction. Crumbs with high inulin content retained water during storage, regardless of the nature of the calcium salt used. In addition, they presented lower loss of elasticity and cohesiveness than the control crumb. Crumbs with calcium citrate and low inulin content produced the lowest increase in crumb firmness. In addition, elasticity and cohesiveness of crumbs containing low amount of inulin and organic salts were almost maintained. The salt that favored the retrogradation process was calcium lactate with high inulin content, evidenced by the shorter half-time obtained with the kinetic studies. Also, the increase in crystallinity of B-type starch in crumbs with organic calcium salts and high inulin content, correlates with the highest values of retrogradation enthalpy obtained by DSC.     

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.     

Effects of purified monoglycerides on Canadian short process and sponge and dough mixing properties,bread quality and crumb firmness during storage

The effects of increasing levels of a wide range of purified saturated (C12:0–C22:0) and unsaturated (C18:1 cis, C18:1 trans, C18:2, C18:3) monoglycerides on Canadian short process (CSP) and sponge and dough (SDP) mixing properties, bread quality and crumb firmness during storage have been studied. For both processes, higher levels (0.5–1.0%) of polyunsaturated monoglycerides (C18:2, C18:3) caused the largest significant (p < 0.05) increases in mixing time and mixing energy requirements while shorter chain saturated monoglycerides (C12:0, C14:0) significantly increased mixing time and energy requirements for the CSP. Most monoglycerides had positive effects on CSP loaf volume and bread score while no improvement was evident for the SDP. For both processes, crumb firmness during storage was significantly reduced by addition of C16:0 and C18:0 saturated and cis- and trans- monounsaturated monoglycerides and was significantly increased by addition of C12:0 and the polyunsaturated monoglycerides. Changes in crumb firmness during storage were attributed to the effects of monoglycerides on both initial crumb firmness and the rate of crumb firming. The baking process appeared to have a strong influence on the relative impact of monoglycerides on overall crumb firmness and, in particular, initial firmness.     

A model approach to starch and protein functionality in a pound cake system

Different modified wheat starches were used in a model pound cake recipe. The properties of the starches were linked to differences in batter viscosity, cake height and protein extractability during baking, collapse during cooling and final cake quality. The impact of incorporation of 30% cross-linked (CL) starches on batter properties during baking was much smaller than that of incorporation of the same level of hydroxypropylated (HP) starches. Incorporation of HP starches with various degrees of modification in the recipe caused batter viscosity during baking to start rising from 92 or 88 °C rather than at 96 °C and diminished oven rise significantly. Furthermore, the extractability of the protein in cakes containing HP starch was significantly higher. During cooling, control cake collapsed less than did CL starch-containing cake, which itself collapsed significantly less than did HP starch-containing cake. Presumably, most of the cake collapse takes place before the starch gel is formed during cooling. Protein and starch apparently function in determining cake quality, by providing the cell walls with structural material and high resistance to collapse. Starch does not prevent cake collapse, but still co-determines crumb structure, whereas a strong correlation was found between the gel-forming capacity of starch blends and intrinsic crumb firmness (r = 0.99). Furthermore, a strong negative correlation was found between springiness and percentage of extractable protein in final cakes (r = −0.95). We conclude that the combination of a protein network, formed during baking, with a starch gel, formed during cooling, makes up the crumb cell walls and determines cake quality.     

Relative importance of moisture migration and amylopectin retrogradation for pound cake crumb firming

Moisture migration largely impacts cake crumb firmness during storage at ambient temperature. To study the importance of phenomena other than crumb to crust moisture migration and to exclude moisture and temperature gradients during baking, crustless cakes were baked using an electrical resistance oven (ERO). Cake crumb firming was evaluated by texture analysis. First, ERO cakes with properties similar to those baked conventionally were produced. Cake batter moisture content (MC) was adjusted to ensure complete starch gelatinisation in the baking process. In cakes baked conventionally, most of the increase in crumb firmness during storage was caused by moisture migration. Proton nuclear magnetic resonance (¹H NMR) showed that the population containing protons of crystalline starch grew during cake storage. These and differential scanning calorimetry (DSC) data pointed to only limited amylopectin retrogradation. The limited increase in amylopectin retrogradation during cake storage cannot solely account for the significant firming of ERO cakes and, hence, other phenomena are involved in cake firming.     

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     

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.     

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.     

Modification of gluten-free sorghum batter and bread using maize, potato, cassava or rice starch

Gluten-free sorghum bread was made from cassava, maize, potato or rice starch and sorghum in the ratios 10:90, 20:80, 30:70, 40:60 and 50:50. The other baking ingredients, on flour-weight-basis, were water (100%), sugar (6.7%), egg white powder (6%), fat (2%), salt (1.7%) and yeast (1.5%). Increasing starch content changed the batters’ consistencies from soft doughs to thin pourable batters. Increasing starch content decreased crumb firmness and chewiness, and increased cohesiveness, springiness and resilience of all breads. Cassava-sorghum and rice-sorghum breads had better crumb properties than maize-sorghum or potato-sorghum breads. Although the crumb properties of all breads declined (i.e. firmness and chewiness increased; cohesiveness, resilience and springiness decreased) on storage, the formulation containing 50% cassava starch retained the best overall texture.     

Impact of sodium chloride on wheat flour dough for yeast-leavened products. II. Baking quality parameters and their relationship

BACKGROUND: The traditional use of sodium chloride (NaCl) fulfills various important rheological, technological and sensory properties in the manufacturing of yeast‐leavened products. However, the use of NaCl in food production has been discussed controversially since a high intake of sodium seems to be associated with hypertension. This study investigates the baking quality parameters of wheat breads containing various levels of NaCl (0–40 g NaCl kg^?1flour). RESULTS: Crumb firmness and rate of bread staling decreased with decreasing NaCl levels. A slight increase in loaf volume was observed based on the increased yeast leavening ability resulting from additional NaCl. Higher crumb retrogradation (measured by differential scanning calorimetry) was observed with low NaCl levels. CONCLUSION: The retrogradation effect is based on the theory that NaCl probably leads to Na⁺ inclusion in starch molecules during storage and thus reduces retrogradation. Further, significant (P?0.05) linear relationships (r ≥ 0.829) between Rheofermentometer results, bread volume and crumb firmness were found, suggesting a predictability of bread quality by measurement of gas release. Copyright © 2011 Society of Chemical Industry