Quality changes during frozen storage and thawing of mixed bread

In the present work investigations of the dependence between frozen storage time, the method of thawing (air blast at 50 degrees C and microwave), organoleptic and physico-chemical changes in bread are reported. The quality of the thawed product was analysed directly after thawing and after two days of storage at room temperature. It was found that changes in quality of bread are more affected by frozen storage than by the employed thawing method. The thawing methods had a significant (p < or = 0.01) effect on the investigated physico-chemical parameters of the product, however, their statistically significant (p < or = 0.01) effect on the sensory quality could only be revealed after two days of storage of the previously thawed bread at room temperature rather than directly after thawing. The results obtained in the present study suggest that bread which underwent microwave thawing had generally better quality in comparison with air blast thawing.     

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.     

Quality and storage life of par-baked frozen breads

During storage of frozen par-baked breads for a prolonged period of time, bread quality may undergo changes such as increased firmness, moisture and flavour losses resulting in product deterioration. Four categories of par-baked breads namely—variety, white, multi-grain and rye were stored at −18°C for 9 months to evaluate the effects of storage period on product quality, and to develop prediction models that describe kinetics of deterioration of selected quality parameters. The quality was evaluated based on sensory, chemical and physical attributes and properties. Storage life was determined based on the changes in bread quality below certain level. The principal component analysis indicated that approximately 90% of the total variability of 19 quality parameters can be explained with only two principal components. The zero-order kinetic reaction showed good agreement (R²>80%) with quality changes observed by the sensory panel over the storage period. A prediction model, based on the bread quality at zero time and the quality at the time when the bread was rejected by the sensory panel, was developed. The proposed prediction model would provide a useful means of estimating storage life of par-baked breads made with similar formulations.     

面包新鲜度量化指标的测定及研究

利用先进的物性测试仪对面包储存期间的物性参数进行了测定,得出了面包老化的物性参数变化规律,探讨了面包老化的机理,分析了面包老化过程中硬度与弹性的相关性,确定了面包老化的定量物性参数范围,为面包老化定性分析向定量参数分析转变作了有益的探索。     

Charakteristik der Stärke ausgewählter Kartoffelsorten Teil 1. Änderung des Stärkegehalts und der Stärkekorngröße während der Lagerung

Characteristics of Starch of Selected Potato Varieties. Part 1. Change of Starch Content and Starch Granule Size During Storage . Selected varieties of potatoes of the Czechoslovakian assortment were tested as to their contents of dry matter and starch, as well as to quality of their starch in three-years storage tests. Potatoes were stored in airconditioned boxes at temperatures of + 2 and + 10 °C. Analyses were carried out after harvesting and after storage. It was found that the content of dry matter was higher near the end of storage time. This increase was depending on temperature. Yet, related to dry matter the starch content had not diminished near the end of storage time. During storage of potatoes changes in the share of individual starch granule sizes do also occur. Larger granules were degraded to smaller ones, thereby increasing the latter's share. Higher temperature would also lead to an increase in these changes. The tests were supposed to show, wether during potato storage a change in size of starch granules takes place, and wether storage temperature may influence this change. Work on this problem will be continued.     

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.     

Methodological developments in bread staling assessment: application to enzyme-supplemented brown pan bread

In this study, texture profile analysis (TPA) at 40 and 80% compression and a newly proposed penetration test were used to evaluate the effects of amylolytic and non-amylolytic enzymes on the textural properties of fresh and stored brown pan breads. The correlations between instrumental parameters and sensory attribute results obtained by a trained panel of assessors were also investigated. Comparison of the results obtained through TPA at the two compression rates was very useful, as the 40% compression TPA hardly reflected the changes that took place in the enzyme-supplemented bread samples over a storage time of 20 days. The penetration curve profiles provided very valuable information, which complemented the TPA for the purposes of assessing bread ageing and the effect of adding enzymes.     

Effect of storage conditions on the solubility and viscosity of β-glucan extracted from bread under in vitro conditions

The viscosity and solubility of β-glucan in muffins have been shown to be reduced by certain storage conditions, though the effect of storage on bread fortified with barley β-glucan concentrate has not been investigated. Therefore, this study investigated the effect of storage temperature and time (23 °C for 1, 4, and 7 d, 4 °C for 4, 7, and 14 d, and -20 °C for 1, 2, 4, and 8 wk) on the solubility and viscosity of β-glucan upon incorporation into bread at levels corresponding to 0 or 1.5 g β-glucan/serving, with or without vital gluten addition. The firmness and moisture content of bread following each storage treatment were also evaluated. The highest moisture and lowest firmness values were found in fresh bread, though these parameters were still maintained at appreciable levels upon room temperature storage of the 1.5 g β-glucan/serving bread with added gluten and at either room temperature or frozen storage for the 1.5 g β-glucan/serving bread for 4 d. If it is desirable to store bread for 7 d or more, frozen storage should be utilized in order to best maintain bread moisture and firmness levels. It is recommended that β-glucan-fortified bread be consumed fresh for greatest β-glucan solubility and viscosity, though β-glucan solubility of approximately 40% is still achievable upon frozen storage of the bread for up to 2 wk. It is still unclear, however, as to what extent of reductions in the solubility and viscosity of β-glucan would lower its physiological effectiveness. PRACTICAL APPLICATION: Previous research has demonstrated that solubility and thus viscosity of β-glucan, which is an important property associated with its health benefits can be impacted by different storage conditions applied to some bakery products, like muffins. This study demonstrates the extent of changes in the solubility and viscosity of β-glucan incorporated into bread. Therefore, storage time and temperature should be optimized to minimize changes in β-glucan for maintaining its efficacy for its health benefits.     

Non-destructive Evaluation of Bread Staling Using Gray Level Co-occurrence Matrices

The potential application of image texture processing for non-destructive evaluation of bread staling was investigated by monitoring the changes in gray level co-occurrence matrix (GLCM) features (energy, contrast, homogeneity, correlation, and entropy) of baguette bread over a 5-day storage period. Energy experienced a significant reduction after 2 days of storage and increased significantly afterwards. However, contrast tended to increase dramatically over the entire storage time. While homogeneity and correlation showed a decreasing trend during the storage period, no meaningful trend was observed for changes of entropy. The GLCM texture features contrast, homogeneity, and correlation showed high correlations with the instrumental texture parameters and physicochemical properties of the bread during storage; in fact, the breads with firmer and less springy crumbs and higher crust moisture contents (the stale breads) had noticeably higher contrast and lower homogeneity and correlation values compared to the freshly baked samples. The results suggested that the GLCM texture features are promising indices for non-destructively assessing bread staling progress.     

Quality and sensory characteristics of hard red wheat after residential storage for up to 32 y

Samples of hard red wheat packaged for long-term storage, ranging in age from 0 to 32 y, were obtained from donors in residential households. All samples had been stored under nonabusive conditions (7% to 10% moisture, 13 to 27 °C). Selected quality parameters of the wheat (moisture, thiamin, free fatty acids, flour extraction rate, bread loaf volume, and bread firmness) and sensory properties of bread made from the stored wheat (aroma, appearance, texture, flavor, overall liking, acceptance for use as part of the regular diet, and acceptance for use in emergency situations) were evaluated. Free fatty acids increased significantly from 0.897 to 11.8 μmol/g, and flour extraction rate decreased significantly from 76.5% to 69.9% over time. None of the other quality parameters measured (moisture, thiamin, bread loaf volume, and bread firmness) were significantly correlated with wheat storage time. Panelists who frequently or occasionally consume whole wheat bread rated all breads made from the stored wheat with hedonic scores (9-point scale) of at least 6.4 (like slightly to moderately). Consumer ratings of bread texture, flavor, and overall acceptability were negatively correlated with storage time (P < 0.001); however, at least 70% of panelists indicated that they would consume the bread as part of their regular diet even after 32 y of wheat storage, while over 97% would do so in an emergency. These data indicate that wheat maintains nutritional quality and makes acceptable bread when stored up to 32 y at 13 to 27 °C and 7% to 10% moisture. Practical Application: Wheat stored for the purposes of disaster relief has the potential of being stored for extremely long periods of time, which may result in undesirable changes in milling and baking quality. Therefore, we tested wheat that had been stored under residential conditions for up to 32 y to determine its functional quality and consumer acceptability. Our results indicate that wheat of low moisture (7% to 10%) packaged in sealed cans and stored for up to 32 y at or below typical room temperature retains quality and can be made into bread that is well accepted by consumers. Thus, whole wheat has good long-term storage stability and can be recommended for emergency food supplies.     

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 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     

Studies on electrical properties of wheat bread as a function of moisture content during storage

Bread undergoes several physicochemical changes during storage that results in a rapid loss of freshness. These changes depend on the moisture content present in the bread product and collectively termed as staling. The present work explains how the electrical properties of bread vary with time and moisture content at its crust and crumb. An instrument based on electrical impedance spectroscopy with multichannel electrodes is developed for the present investigations. Detailed studies have been carried out to understand the influence of changes in moisture profile at bread crust and crumb in terms of electrical properties during the storage of 120 h. A linear relationship is observed between the measured impedance and capacitance and residual moisture content in bread at crust during storage. It is observed that the measured Resistance at bread crumb has a nonlinear mathematical relationship with moisture content present at crumb.     

Optimization of baking parameters of part-baked and rebaked Irish brown soda bread by evaluation of some quality characteristics

Summary  Part-baked Irish brown soda bread loaves with bicarbonate levels from 0 to 2.8 % were baked, packed and stored for up to 11 days at 5 C then second-baked at 180 or 200 C for various times to give an oven-fresh end product. The quality of the rebaked bread was dependent on characteristics of the part-baked bread, its storage conditions and the processing parameters of the second baking phase. Quality parameters evaluated were bread volume yield, crumb and crust firmness, moisture content and colour. Staling of the part-baked bread during storage at 5 C and the reversion of this process at 59 C was investigated with regard to rebaking time and temperature. Rebaking conditions were optimized by evaluating the core temperature increase in the centre of the bread. Immediately after the second baking phase a post-baking temperature increase was measured which allowed reduction of the in-oven rebaking time. The data were modelled mathematically using least squares analyses.     

酵子面包在贮藏过程中理化及微生物指标的变化

测定在25 ℃条件下贮藏期间酵子面包和酵母面包的理化指标及微生物指标的变化,得出面包老化的物性参数变化规律,揭示其抗老化机理。对感官指标、硬度、水分活度、热特性、自由水含量、电镜扫描、破碎率、膨润度、质构分析特性等理化指标及微生物指标进行测定。结果表明：随贮藏时间延长,面包水分含量显著下降,硬度明显上升。与酵母面包相比,酵子面包具有水分含量较高,硬度较小,淀粉颗粒更容易发生团聚等特性,物性学研究结果显示,将传统发酵剂酵子应用于面包生产,具有较好地延缓淀粉回生和老化的效果。确定面包老化的定量物性参数范围,为由定性分析向定量参数分析转变作了有益探索。     

Effect of fermentation conditions on bread staling kinetics

The effects of yeast dose, temperature and fermentation time on bread volume, bread density, bread texture (firmness, cohesiveness, resilience, springiness and gumminess) and their change during staling were analysed. Thus, changes in the texture profile (TP) parameters as bread aged were modelled and their initial values and their variation rate were obtained. In white and whole breads, the longer the fermentation time and the higher the yeast dose, the lower the firmness and the firming rate. The fermentation temperature only affected the initial firmness in whole breads. Significant linear correlations were found between bread density and volume (r ² = 0.94 in white bread; r ² = 0.96 in whole bread), between density and the initial firmness (r ² = 0.88 in white bread; r ² = 0.61 in whole bread), and between the first two parameters and the firming rate. Between density and firming rate r ² obtained was 0.72 in white bread and 0.32 in whole bread and between volume and firming rate r ² obtained was 0.58 in white bread and 0.29 in whole bread.     

Sunflower protein concentrate: A possible and beneficial ingredient for gluten-free bread

The global demand for gluten-free products increased and resulted in a significant technological challenge for the bakery industries: producing gluten-free bread with similar quality to wheat bread. This study aimed to analyze the effects of different concentrations of sunflower protein concentrate (SPC) addition on the gluten-free bread quality parameters compared to the use of pea flour. The SPC flour was inserted at 5%, 10%, and 20% on a flour basis mixture (70% rice flour and 30% cornstarch). Some parameters as specific volume, color, and texture profile were evaluated during 21 days of storage. The obtained results showed that SPC has a significant potential to be used in gluten-free bread with high quality and sensory acceptability. The addition of this beneficial ingredient, in all concentrations, resulted in gluten-free bread with lower hardness after 21 days of storage and with a 100% increment in the protein content when compared to pea flour bread.     

Effect of Initial Baking and Storage Time on Pasting Properties and Aging of Par-Baked and Rebaked Rye Bread

Part-baked rye bread with and without Ca-propionate (0.2 g/100 flour) were baked for 10, 15, 20 minutes at 230°C and stored at refrigerator temperature (4°C) for 10, 20, 30 days then second-baked for 5, 10, 15 minutes at the same temperature to give an oven-fresh end product. The effect of antimicrobial additive (Ca-propionate), part-baking, storage in refrigerator and rebaking on quality parameters such as yield of volume and crumb softness, water activity and pasting properties of rye bread crumb was evaluated. Addition of Ca-propionate increased bump area, while yield of volume and softness values of rye bread crumb decreased. The increase in initial baking time caused a decrease in the pasting temperature, water activity, and softness value and an increase in the bump area and viscosity of the rebaked bread crumb. Bump area and pasting temperature of rebaked rye bread crumb increased with longer (intermediate storage) time, while viscosity, yield of volume, water activity, and softness values decreased. A strong negative correlation was observed between pasting temperature and other parameters, which are bump area, peak viscosity, holding end viscosity, cooling end viscosity, and softness value for rye bread that was rebaked after part-baked and storing at refrigerator temperature. The re-baking rye bread after part-baking for 10 and 15 minutes and storage for 7, 14, and 21 days at refrigerator temperature gave softer crumb than the control group.     

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