Physical properties of breads containing hydrocolloids stored at low temperature: II—Effect of freezing

Bread types such as dough samples (DB), semi-baked (SB) and full-baked (FB) breads were frozen stored for a week and further baked (DB or SB). Structure stabilizers such as xanthan (X), hydroxypropylmethylcellulose (HPMC), guar gum (GG) or locust bean gum (LB) were also added to the dough. Baking stage is important for bread quality after storage; additionally hydrocolloids provide stability in many frozen foods. Fresh bread samples were prepared for comparison. Yield in baked product, dough characteristics, specific volume, porosity, textural properties of both crumb/crust, moisture content of crumb/crust and finally crust thickness and colour were measured. Data grouping was performed using PCA analysis and correlations among the properties measured were found. X and LB addition resulted in the most stable dough, since strength and dough extensibility change during storage was low. Hydrocolloid stabilizers’ (HS) influence on final bread characteristics was more pronounced in DB and SB breads. Crust moisture content was higher in SB breads, and it reached values 11–19% higher in control and galactomannan-containing breads than in DB respective samples. Bread specific volume was highly correlated to the crumb moisture content, to the crumb/crust textural characteristics and to the yield in the baked product. It was not correlated to crust moisture content and thickness. Porosity and bread colour were not correlated to any of the other properties. Bread type and HS selection are important factors for improving stability during storage.     

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 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.     

Influence of Final Baking Technologies in Partially Baked Frozen Gluten‐Free Bread Quality

The effect of final baking in convection oven (FBC), microwave oven (FBM), and microwave oven with susceptor packaging material (FBMS) on partially baked (PB) frozen gluten‐free bread characteristics was investigated. Specific volume and crust color of loaves were measured at day 0. Bread moisture, water activity, and crumb and crust texture (at 15, 45, and 90 min after baking) were analyzed at day 0 and after 28 d of frozen storage (?18 °C). Volatile compounds from breads baked in convection oven or microwave oven with susceptor packaging material were also evaluated. Bread finally baked in convection oven or in microwave oven with susceptor packaging increased crust browning. Crumb and roll hardness increased with time after final baking (measured at 15, 45, 90 min) and after 28 d of frozen storage. Bread finally baked in microwave oven was the hardest, due to high water losses. At day 0, bread finally baked in convection oven had softer crumb than bread finally baked in microwave oven with susceptor packaging but, after 28 d of frozen storage, there were no differences between them. Moreover, FBC and FBMS rendered gluten‐free breads that could not be distinguished in a triangular test and had the same volatile compounds profile. In conclusion, FBMS could be an alternative to FBC.     

Influence of yeast and vegetable shortening on physical and textural parameters of frozen part baked French bread

The objective of this project was to study the influence of yeast and vegetable shortening on physical and textural parameters of frozen part baked French bread stored for 28 days and to produce a frozen part baked bread with physical and textural characteristics similar to those of the fresh one. Four formulations were used with different quantities of yeast and vegetable shortening. Dough was prepared by mixing all ingredients in a dough mixer at two speeds. After resting, the dough was divided into 60 g pieces, molded and proofed. The bread was partially baked for 7 min at 250°C, in a turbo oven. After cooling, it was frozen until the core temperature reached −18°C and stored at the same temperature up to 28 days. Once a week, samples were removed from the freezer to complete the baking process, without previous thawing. Mass, volume, water content, firmness, cohesiveness and springiness were measured 1 h after final baking. Resistance to extension and extensibility of dough were measured after mixing. Specific volume and chewiness were determined. Bread with higher yeast content presented a higher specific volume, whereas vegetable shortening reduced its crumb firmness and chewiness.     

Influence of Amyloglucosidase in Bread Crust Properties

Enzymes are used in baking as a useful tool for improving the processing behavior or properties of baked products. A number of enzymes have been proposed for improving specific volume, imparting softness, or extend the shelf life of breads, but scarce studies have been focused on bread crust. The aim of this study was to determine the use of amyloglucosidase for modulating the properties of the bread crust and increase its crispness. Increasing levels of enzyme were applied onto the surface of two different partially bake breads (thin and thick crust bread). Amyloglucosidase treatment affected significantly (P?<?0.05) the color of the crust and decreased the moisture content and water activity of the crusts. Mechanical properties were modified by amyloglucosidase, namely increasing levels of enzyme promoted a decrease in the force (Fm) required for crust rupture and an increase in the number of fracture events (N _wr) related to crispy products. Crust microstructure analysis confirmed that enzymatic treatment caused changes in the bread crust structure, leading to a disruption of the structure, by removing the starchy layer that covered the granules and increasing the number of voids, which agree with the texture fragility.     

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.     

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     

Energy demand for selected bread making processes: Conventional versus part baked frozen technologies

This article presents some results on the energy demand in conventional bread baking and in the processing of frozen part baked breads, resulting from the “EU-FRESHBAKE” European project (FP6). Bread baking is one of the most energy demanding processes (around 4 MJ/kg), compared with other thermal processes such as canning. However, there is a large variability of data in the literature. For partial baking, bread has to be baked twice. It may also be frozen after part baking, which will increase the total energy demand. Results obtained with equipment used by craft bakeries are presented. Conventional and frozen part baked processes are compared. The effect of occupation ratio on the overall energy demand is also assessed. It was observed that 15–20% of the total energy is used for heating up the dough and 10–20% for crust drying. Pre-heating of the oven represents another significant energy demand. The energy demand for freezing is comparable to that for baking. An Energy Efficiency Index is used to assess the ratio of energy effectively transferred to the dough during baking. Part baked frozen technology demands about 2.2 times as much energy as conventional bread making process.     

EFFECT OF SODIUM METABISULFITE ADDITION AND BAKING TEMPERATURE ON MAILLARD REACTION IN BREAD

ABSTRACT

In this study, the effect of sodium metabisulfite (SMBS) doses (0, 25, 50, 100 mg/kg dough) and baking temperatures (200, 230 and 250C) on the physical, chemical and sensory properties of bread were researched to reduce 5‐hydroxymethyl‐2‐furfural (HMF) and acrylamide contents. HMF and acrylamide contents of bread crust were decreased significantly by increasing SMBS dose and decreasing baking temperature. The HMF (137.29 mg/kg) and acrylamide (671.44 µg/kg) contents of bread crust were decreased by 33 and 67%, respectively by addition of 100 mg/kg SMBS. The maltol content of bread crusts were significantly affected by baking temperature, and were 7.19, 10.23 and 22.69 mg/kg in breads baked at 200, 230 and 250C, respectively. No HMF, acrylamide and maltol were detected in the bread crumb. The sulfur dioxide content of the crust and crumb of control bread was 6.99 and 10.69 mg/kg, and increased by 49 and 59%, respectively at 100 mg/kg SMBS dose. All breads were evaluated as acceptable by a sensory panel.

PRACTICAL APPLICATIONS

Since Maillard reaction products such as acrylamide and 5‐hydroxymethyl‐2‐furfural (HMF) are known as toxic compounds, mitigation of these compounds is important subject for health and nutrition. There is not an efficient method to prevent the formation of acrylamide and HMF in bread crusts comparison with potato crisps. The purpose of this research is to slow down Maillard reaction by addition of sodium metabisulfite in bread‐making process. As a result of this research, acrylamide and HMF content of bread crusts decreased by 33 and 67%, respectively with acceptable sensory evaluation.     

Shelf-life stability of artisanally and industrially produced durum wheat sourdough bread (“Altamura bread”)

Physico-chemical properties and volatile compounds of three commercial Altamura breads were evaluated during storage at 25 °C. Two protected denomination of origin (PDO) artisanally produced Altamura breads (Bari, Italy), characterized either by high (High A) or low (LowA) loaf, and an industrial product, commercialized as “Altamura like” (IndA), were studied.HighA and LowA breads had a tick crust that was also detached from the crumb creating an air cushion between crust and crumb. IndA products had a thinner crust, a more homogeneous crumb structure as well as a more homogeneous water distribution among the different portion of the bread loaf than HighA and LowA. A more pronounced water gradient characterized the artisanal breads. Crust and under crust portion of all breads, and crumb for IndA product, underwent a significant reduction of moisture content and a_w during storage. Both artisanal breads were subjected to a more significant crumb hardening than IndA sample. Fresh crusts of artisanally produced breads were also significantly harder than IndA. Fresh IndA samples were significantly less cohesive and less springy than artisanal products; cohesiveness significantly decreased in all samples during storage. A more complex gas chromatographic profile was found in the artisanal bread as a larger amount of volatile compounds was present as compared to the IndA bread. Volatile compounds originated both from microbial activity and non-enzymatic browning. Larger amount of volatile compounds characteristics of yeast fermentation was found in IndA. Volatiles decreased over storage in both samples, more significant in the IndA product.     

Crust and crumb characteristics of gluten free breads

Gluten free breads often have poor crust and crumb characteristics and the current study was conducted to help alleviate this problem. A commercial wheat starch (Codex Alimentarius) gluten free flour was supplemented with seven dairy powders (0%, 3%, 6%, 9% inclusion rates based on flour weight). Initially a fixed water level was used (trial 1) and the resulting batters were proofed and baked. The breads were tested 24 h after baking. Powder addition reduced loaf volume by circa 6% (P<0.001). Increasing the inclusion levels of the powders decreased loaf volume (P<0.001) with a decrease of 8% for the highest level. Powder addition generally decreased the crumb L^*/b^* (white/yellow) ratio. Crust L^* values were significantly reduced. All of the powders increased crumb hardness (P<0.001) with the exception of demineralised whey powder. Ten and 20% additional water (trial 2) was added to the formulation and the resulting breads had higher volume, and a much softer crust and crumb texture. Sensory analysis revealed a preference for breads containing skim milk replacer, sodium caseinate and milk protein isolate.     

Combined effects of inulin,pectin and guar gum on the quality and stability of partially baked frozen bread

Many attempts have been made to increase the nutritional value of bread by adding dietary fibre. However, fibre enrichment is usually associated with various technological problems. The aim of this study was to optimise the composition of a blend of inulin, pectin and guar gum to enrich the fibre content of partially baked frozen bread without impairing its technological quality. We prepared 20 formulations following a central composite design, together with 4 control breads. Bread enriched with inulin had higher crumb hardness, lower specific volume, shape, moisture content, and crumb cohesiveness than control bread, but improved flavour. Pectin and guar improved moisture content and crumb cohesiveness. There was no interaction between inulin and pectin for any of the bread attributes investigated, while interactions between inulin and guar were small. In contrast, guar and pectin significantly interacted to decrease volume and increase crumb hardness and chewiness. A desirability function method identified the optimised blend as containing 3% inulin, 0.9–1% pectin and 0.3–0.4% guar. Bread enriched with such blend had the following characteristics: specific volume, 4.06 cm³/g; shape, 0.63; crumb hardness, 189 g; resilience, 0.36; cohesiveness, 0.84; chewiness, 169 g; and flavour score, 4.6. Experimental values were close to the predicted ones, with prediction errors below 10% for all attributes tested. The specific volume, crumb hardness and chewiness of the enriched bread were superior to those of unenriched bread. However, undesirable textural changes occurred in the enriched bread during 12 weeks of frozen storage, and these changes strongly depended on the fibre blend composition.     

Physical properties of breads containing hydrocolloids stored at low temperature. I. Effect of chilling

Different bread types, some of them containing also hydrocolloid stabilizers, were cold stored for evaluating the final quality of breads after storage. Dough (DB), semi-baked products (SB) and full-baked (FB) breads were used. After storage their physical characteristics were measured, data grouping was performed using PCA analysis and correlations among the properties measured were found. Fresh samples presented some similarities to DB or SB breads, but FB breads had a completely different behaviour. Crust characteristics were found to be important for the quality characterization of breads, as crust textural characteristics; its colour and moisture content were correlated to other properties. Furthermore, crust viscoelastic characteristics gave an indication of bread staling. Porosity was the only physical property not correlated to other bread characteristics. Differences were noticed according to the bread type before storage and the hydrocolloid used, but the main differences were determined by the baking stage before storage. Furthermore, hydrocolloids addition could result in different final bread properties according to the baking stage before storage. The crumb of FB breads was relatively viscous despite of hydrocolloid addition. Hydrocolloids seem to be more effective as stabilizers in DB and SB breads.     

Influence of inulin on bread: Kinetics and physico-chemical indicators of the formation of volatile compounds during baking

The influence of inulin on the formation and release of white bread volatiles was studied during baking, using an innovative on-line baking extraction device. Kinetic studies were performed to follow the development of crust physical properties and the formation of volatiles responsible for the flavour of breads having different amounts of inulin. It was demonstrated that inulin accelerated the formation of the bread crust and the Maillard reaction. It led to breads with an overall quality similar to that of non-enriched breads, but baked for a shorter time. Correlations between some crust properties and the amount of Maillard volatiles were determined. They showed that crust water activity, moisture and clearness could be good indicators of the Maillard reaction during the baking of bread.     

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.     

Increasing the health benefits of bread: Assessment of the physical and sensory qualities of bread formulated using a renin inhibitory Palmaria palmata protein hydrolysate

This study examined the textural and sensory effects of bread formulated using a Palmaria palmata protein hydrolysate with in vitro renin inhibitory properties. Four formulations were examined; a wheat flour control bread, a control bread containing 4% P. palmata protein hydrolysate, a buckwheat bread consisting of a blend of 70% wheat: 30% buckwheat, and a fourth formulation of the buckwheat bread containing 4% P. palmata hydrolysate. The volume, colour, texture profile, moisture, crumb structure, sensory attributes and renin inhibitory activity of all four baked breads are presented. Bright field light microscopy and confocal scanning laser microscopy images using a new triple labelling protocol were also obtained to visualise the main ingredients of the breads. It was observed that the addition of 4% P. palmata protein hydrolysate to the wheat bread control did not affect the texture or sensory properties of the bread to a large degree. Furthermore, when compared to the control, the bread containing the hydrolysate retained renin inhibitory bioactivity after the baking process. This study highlights that baked products may be a suitable delivery vehicle for bioactive compounds. The study demonstrates that the health value of bread was increased through the addition of a seaweed protein hydrolysate.     

Partial-Baking Process on Gluten-Free Bread: Impact of Hydrocolloid Addition

The objectives of this work were to assess the impact of partial-baking process on gluten-free bread, and to study how carboxymethylcellulose (CMC) and xanthan gum addition affected this process. As different from the conventional baking which involves only one baking step (40 min), the part-baking process consisted in an initial-baking step (25 min), storage (7 days, 4°C), and final-baking step (15 min). Bread-specific volume (SV), crumb hardness, and image analysis were assessed on final products of both processes and intermediate products of part-baking process. Breads were stored at room temperature for 72 h and crumb firming and amylopectin retrogradation were monitored. Freezable water (FW) fraction was determined on fresh and stored samples by using differential scanning calorimetry. Part-baked breads showed lower SV and higher crumb hardness. No SV diminution was observed during cold storage. Hydrocolloids, especially CMC, had a positive effect on these parameters, and during bread storage at room temperature, the increase in crumb hardness was mitigated by hydrocolloid addition. Part-baked breads showed smaller cell area than full-baked ones. Overall, crumb structure was more homogeneous for CMC breads. FW showed no significant differences among processes, formulations, or storage time. Amylopectin recrystallization was higher for part-baked breads. Interrupted-baking process affected the final bread quality, but negative effects could be diminished by hydrocolloid addition. Part-baking process is suitable for obtaining gluten-free breads, stored for a week at 4°C, turning them appropriated for home consumption.     

Quality of wheat bread enriched with onion extract and polyphenols content and antioxidant activity changes during bread storage

We determined the effect of onion skin extract (OE) on the quality of wheat bread: contents of total polyphenols and flavonols, antioxidative activity and their changes during storage. With increasing doses of OE to bread, contents of total polyphenols and flavonols and the antioxidative activity were observed to increase. A higher total flavonol content was found in bread with 1% OE stored at 24 °C than in bread stored at 4 °C. There was no such relationship in the bread with 0.5% OE. Changes in flavonols content during storage for 72 h were insignificant. No clear trends of change in the antioxidant activity could be found at storage of breads. The addition of OE caused no changes in the yield and volume of bread and contributed to a decreasing value of L* parameter and to increasing values of ΔE, a* and b* parameters of bread crumb colour. Consumers accepted the smell and taste of bread with the addition of OE to a lesser extent than the control bread. Bread with 1% OE the taste was rated very low. Consumers rated the taste of bread with 1% OE low because it was bitter. Breads enriched with OE had a proper external appearance as well as crumb and crust features. Roasted onion aroma and taste were perceptible in the obtained breads. A bitterness was perceptible in breads baked with the addition of 1% of OE.     

Effect of Process Modifications in Two Cycles of Dough Mixing on Physical Properties of Wheat Bread Baked from Weak Flour

Common availability of dough improvers permits the production of bread of good quality, but only modifications of the process may be used for the production of natural products. Dough from weak flour, after application of certain treatments, displays poorer baking properties; therefore, in our study, it is proposed to apply slow-speed mixing in two cycles. In the literature, there is a lack of comparisons of results of baking with the straight dough method (one-cycle mixing) with modified methods including the application of two equal cycles of dough mixing and two “incomplete” cycles, the first of which lasts twice as long as the second one [partial two-cycle mixing (PTCM)]. This study involved the determination of the quality properties of bread (loaf volume, specific weight, crust thickness, crumb whiteness, crumb hardness index, and crumb heterogeneity index) under the effect of process modifications, analyzing the effect of dough mixing time and resting time between the mixing cycles. The study included also regression equations describing the physical properties of bread. Based on the tests performed, it was noted that in the case of flour characterized by poor baking quality, the process effectiveness can be enhanced through the application of two incomplete mixing cycles (PTCM), with dough resting time in the range of 10–20 min. This treatment resulted breads with significantly greater loaf volume, lower specific weight, lower whiteness index, and hardness compared to breads baked using the straight dough method. It is not recommended to use two equal duration cycles of dough mixing.