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.     

Oscillatory water sorption dynamics of bread crust

Step-wise and oscillatory gravimetric sorption experiments were used to study the equilibrium and dynamic water sorption behavior of bread crust. Water uptake kinetics is strongly related to crispness retention of composite products consisting of a dry crispy part and a more humid and soft part. We show that oscillatory sorption experiments of bread crusts could be very well described by a Fickian diffusion model. Many essential features, such as the shape of the oscillatory sorption curves, and the dependency of water sorption rates on time, time-interval between successive step-wise changes in relative humidity, and particle size are understood now to a great detail.     

Influence of the amount of steaming during baking on the kinetic of heating and on selected quality attributes of bread

The effect of the amount of steam injection on selected bread characteristics were investigated using a deck oven (1 m² internal surface). Baking was done at 200 °C for 20 min with steaming of 100, 200, 300, 400 and 500 ml. The temperature at center of the bread and the CO₂ concentration in the oven have been measured during baking. Specific volume, moisture loss and crust crumb ratio were measured after baking.The heating rate between 35 and 55 °C was considered to compare the steaming conditions. For low steaming (100 and 200 ml), the heating rate was significantly higher (p < 0.05) than those at higher steaming (400-500 ml). The heating rate at 300 ml was between the 100-200 and 400-500 ml groups. This difference was attributed to the condensation of steam on the loaf for higher steaming, which in turns slows down the heating rate. The largest bread volume was obtained either for low or high steaming. However, tearing of the crust was observed for low steaming. The crust-crumb ratio was increasing with decreasing amount of steaming. The amount of CO₂ released during baking was higher for the highest amount of steaming; however, this result was not statistically different except between 100 and 500 ml. This could be attributed to a slower heating rate which in turns favors the secondary production of CO₂ during baking until thermal inactivation of CO₂.     

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.     

Effects of crust constraints on bread expansion and CO2 release

Artificial covers were designed and used to study the effects of crust constraints on bread expansion and gas release during baking. The results were interpreted by comparison with the results of simulations using a mathematical model of baking. The cover levels were set at 45 mm, 50 mm and 55 mm, as the maximum height reached by the dough without cover under the conditions studied was 60 mm. MRI images were used to evaluate the local porosity of the crumb. Porosity kinetics showed that different cover levels resulted in densification within the crumb structure: the later the dough encountered the cover, the deeper the dense crumb formed in the loaf. The kinetics of CO₂ release were monitored with an infrared detector and the results showed that the lower the cover level the shorter the induction time. The predominant role of crust setting in the CO₂ release response was demonstrated.     

Effect of chitosan on physical and chemical processes during bread baking and staling

The objective of this research was to investigate the effect of chitosan on the interaction of water with bread ingredients and on the rate of staling. The changes in freezable bound water and total water contents in bread crumb were assessed by differential scanning calorimetry from water melting and evaporation endothermic peak areas. It was found that freezable water content and total water content in bread crumb decrease during staling more rapidly in the presence of chitosan. The weak interaction of freezable water with protein and starch polymeric chains in bread crumb becomes stronger, but the interaction of nonfreezable bound water with protein and starch molecules in bread crumb becomes weaker in the course of staling during bread storage. Two stages of bread crumb staling were indicated. Chitosan increases the rate of bread staling during both stages. It was suggested that during bread staling chitosan increases water migration rate from crumb to crust, prevents amylose-lipid complexation, and increases dehydration rate both for starch and gluten.     

Influence of inulin on physical characteristics and staling rate of gluten-free bread

Inulin preparations with different degree of polymerization (HSI with a DP < 10, GR − DP ? 10 and HPX − DP > 23) were used for the production of gluten-free bread. It was found that an addition of investigated compounds resulted in an increase of loaf volume and reduction of crumb hardness. However, internal structure of the obtained loaves was less uniform and more open than in control bread. Generally, inulin preparations with lower degree of polymerization had stronger effect on all analyzed parameters than that with higher DP. A decrease in staling was observed (measured as the rate of crumb hardening), which was caused by the presence of inulin. The highest content of retrograded amylopectin was found for crumb with HSI, and the lowest for samples with HPX.     

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 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.     

Water dynamics in white bread and starch gels as affected by water and gluten content

Three levels of water (180, 220 and 260 g/345 g flour) and three levels of gluten (giving 11.2, 13.0 and 14.2 g protein/100 g flour) were used to study the effects of water and gluten on water mobility in white bread using ¹H nuclear magnetic resonance (NMR) relaxometry. Changes in the transverse relaxation time (T₂) were related to water mobility. The three water levels resulted in three different moisture contents in the finished bread (0.55-0.77 g H₂O/g solids). Distributed exponential analysis showed two distinct regions of T₂ (30-600 μs and 1-60 ms), associated with multiple domains of water in the bread crumb. There was no significant difference in peak T₂ values with different gluten content, but significant differences were observed with different moisture content. The results suggested that the mobility of water associated with starch decreased dramatically because of gelatinization. To further investigate the effect of gluten on starch gelatinization, NMR measurements were made directly on model systems containing starch and various gluten amounts. The starch-gluten gels had higher T₂ values than pure starch gels, indicating less swelling of starch granules and absorption of water. This was attributed to less water available to starch in the presence of gluten.     

Glucose oxidase effect on dough rheology and bread quality: A study from macroscopic to molecular level

Enzymes are used in baking to improve dough handling properties and the quality of baked products. Glucose oxidase (GO) is an enzyme with oxidizing effect due to the hydrogen peroxide released from its catalytic reaction. In this study, the macroscopic effect of increasing glucose oxidase concentrations on wheat dough rheology, fresh bread characteristics and its shelf life during storage was determined. A reinforcement or strengthening of wheat dough and an improvement of bread quality can be obtained with the addition of GO, although inverse effects were obtained when excessive enzyme levels were added. The analysis of the gluten proteins at molecular level by high performance capillary electrophoresis and at supramolecular level by cryo-scanning electron microscopy revealed that the GO treatment modified gluten proteins (gliadins and glutenins) through the formation of disulfide and non-disulfide crosslinks. The high molecular weight glutenin subunits showed to be the most susceptible glutenin fraction to the oxidation action of GO. Excessive addition of GO produced an excessive crosslinking in the gluten network, responsible of the negative effect on the breadmaking properties.     

The effect of direct acidification on the microbiological,physicochemical and sensory properties of probiotic Minas Frescal cheese

Minas Frescal cheeses produced with the addition of the probiotic culture Bifidobacterium Bb‐12 and without (C1) or with (C2) lactic acid were evaluated in relation to the microbiological, physicochemical and sensory properties. After 28 days of storage, the cheeses without lactic acid showed lower moisture and pH, in addition to higher acidity and syneresis. This behaviour influenced the texture profile of the cheeses, making them harder and chewier. The colour attributes L* and b* diminished during the storage. The majority of the consumers classified the cheeses as having good acceptability and they would buy this type of functional food.     

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.     

Optimization of the rheological properties of probiotic yoghurts supplemented with milk proteins

This study aimed to optimize the rheological properties of probiotic yoghurts supplemented with skimmed milk powder (SMP), whey protein concentrate (WPC) and sodium caseinate (Na-Cn) by using an experimental design type simplex-centroid for mixture modeling. It included seven batches/trials: three were supplemented with each type of the dairy protein used, three corresponding to the binary mixtures and one to the ternary one in order to increase protein concentration in 1 g 100 g⁻¹ of final product. A control experiment was prepared without supplementing the milk base. Processed milk bases were fermented at 42 °C until pH 4.5 by using a starter culture blend that consisted of Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, and Bifidobacterium animalis subsp. lactis. The kinetics of acidification was followed during the fermentation period as well the physico-chemical analyses, enumeration of viable bacteria and rheological characteristics of the yoghurts. Models were adjusted to the results (kinetic responses, counts of viable bacteria and rheological parameters) through three regression models (linear, quadratic and cubic special) applied to mixtures. The results showed that the addition of milk proteins affected slightly acidification profile and counts of S. thermophilus and B. animalis subsp. lactis, but it was significant for L. delbrueckii subsp. bulgaricus. Partially-replacing SMP (45 g/100 g) with WPC or Na-Cn simultaneously enhanced the rheological properties of probiotic yoghurts taking into account the kinetics of acidification and enumeration of viable bacteria.     

Impact of emulsifiers on the quality and rheological properties of gluten-free breads and batters

The effects of the emulsifiers lecithin (LC), di-acetyl tartaric ester of monoglycerides (DATEM), distilled monoglycerides (DM) or sodium stearoyl lactylate (SSL) were studied in a gluten-free (GF) batter and bread formulation. Three different levels, i.e. low, medium, and high, were evaluated and compared to a control bread with no emulsifier. The rheological properties of the emulsifiers at their optimum level as well as their effect on starch retrogradation were investigated. Standard baking tests were carried out and the breads were tested over 5 days of storage. Rheological tests suggested that LC reduced the elasticity of the batter and increased the batter consistency during gelatinisation (P < 0.05). A significant increase in the specific volume was found with the addition of the various emulsifiers (P < 0.05). Higher volumes were found for breads with DM whereas lower specific volumes were obtained for the breads with DATEM. With regards to cell size and distribution, significant differences were found across the emulsifiers and the levels used (P < 0.05). Crumb staling revealed significant time effects as well as an increase in the shelf-life by the addition of high levels of DM and SSL. The retrogradation of starch over 5-days did not seem to be affected by the addition of emulsifiers. Overall this study demonstrated that the addition of emulsifiers at their respective optimum level enhanced the quality of the GF breads.     

The effects of chickpea on the functional properties of white and whole wheat bread

The effects of the addition of chickpea (Cicer arietinum), emulsifier and altered amount of water on the functional properties (bread volume, colour of crust, crumb texture and crumb porosity) of white and whole wheat bread were investigated applying a screening three factorial design. Addition of chickpea increased crumb firmness and slightly decreased bread volume in both bread types. Addition of emulsifier increased bread volume and decreased bread firmness. Altering the amount of water addition had no significant effects on white bread, but decreased crumb firmness and increased bread volume in whole wheat bread. None of the investigated parameter had an effect of whole wheat bread colour, while in white bread chickpea addition increased darkness and yellowness of the bread. Optimum addition for breads of highest quality would be 56.9–58% water, 1.0% emulsifier and 10.0–16.0% chickpea in white bread and 58% water, 1.0% emulsifier and 11.8% chickpea in whole wheat bread.     

Effect of oligofructose incorporation on the properties of fermented probiotic lactic beverages

All lactic beverages were considered probiotics. The addition of prebiotic resulted in beverages with higher total solids and total carbohydrates contents, without changing the other physicochemical parameters, including the attributes of colour. All beverages showed non-Newtonian behaviour, with shear thinning characteristics and presence of thixotropy, which is less accentuated in beverages with oligofructose. In these beverages, there was a decrease in apparent viscosity, consistency index and activation energy, and an increase in flow index and frequency factor. The beverages with oligofructose were sensory preferred in relation to the control, also showing good overall acceptability and most judges indicated that they would buy such a product.     

Comparative effect of probiotic and paraprobiotic addition on rheological and sensory properties of yoghurt

Yoghurt was produced using killed cells of Lactobacillus acidophilus ATCCSD 5221 and Bifidobacterium animalis subsp. lactis BB‐12. The rheological and sensory properties of the yoghurt were investigated at the end of the fermentation. The results revealed that the samples made with killed cells gave the lowest storage modulus, loss modulus, stress crossover point and loss tangent. The frequency‐sweep of yoghurt samples containing paraprobiotics added before fermentation showed the highest correlation coefficient. In the case of sensory assessment, significant differences were indicated among treatments. Adding killed cells of B. animalis subsp. lactis BB‐12 before fermentation produced yoghurt with the highest total score, whereas samples containing killed cells of L. acidophilus ATCCSD 5221 and B. animalis subsp. lactis BB‐12 added before fermentation exhibited the lowest total score.     

添加魔芋粉对面包品质的影响及其减肥功效研究

通过测定面包品质参数和魔芋精粉的功能性因子,研究魔芋精粉对面包品质和减肥功能性的影响。结果表明：魔芋精粉能增大面包的比容，改善面包品质、增加面包的营养价值和提高它的减肥功效，其添加量为0．4％。