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.     

Physico-chemical changes in breads from bake off technologies during storage

Quality of several bread specialties from frozen partially baked breads was assessed to define main quality features. Loss of crust freshness shortly after baking was also determined. Quality parameters that characterize bread crust and crumb were determined by instrumental methods in nine different (regarding to formulation and bake off duration) bread types obtained from frozen partially baked breads. Principal component analysis (PCA) allowed discriminating among bread specialties. Quality parameters that enable the differentiation of wheat bread types were crust mechanical properties together with specific volume, crumb hardness and structure. Crust flaking barely represented a problem in the studied types of bread. Crust mechanical properties were rapidly lost during the first 4 h after baking and the rate of the process was greatly dependent on the bread type. The force to promote crust fracture underwent increase up to 6 h after baking and those changes occurred in the Aw range of 0.50-0.74 or moisture content 9-15 g/100 g.     

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 the soluble fibres inulin and oat β-glucan on quality of dough and bread

Bread represents a suitable food product for the addition of functional ingredients, such as the cholesterol-lowering dietary fibre oat β-glucan and the prebiotic inulin. Therefore, these soluble fibres were incorporated into wheat as well as gluten-free bread, and their effects on rheological properties of the dough, on bread quality and on crumb microstructure were compared. The level of remaining β-glucan as well as its molecular weight was determined using an enzyme kit and size-exclusion chromatography. The addition of oat β-glucan resulted in a higher water addition level, whereas incorporation of inulin had the opposite effect. Rheological testing showed that the incorporation of oat β-glucan results in a more elastic dough. The baking characteristics mainly affected by fibre addition were volume and crust colour, with inulin increasing and oat β-glucan decreasing loaf-specific volume in the gluten-free breads. Inulin led to a darkening of the crust of both bread types, whereas addition of oat β-glucan resulted in a lighter crust of gluten-free bread. Oat β-glucan softened the crumb of gluten-free bread, but had the opposite effect on wheat bread. Inulin resulted in an increased crumb hardness as well as the rate of staling. Beta-glucan breakdown was more pronounced in wheat bread than in gluten-free bread. The results show that the use of β-glucan to increase the nutritional value of wheat bread is limited due to negative influences on technological properties. However, this soluble fibre is highly suitable for incorporation into gluten-free bread.     

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.     

Gas chromatographic–mass spectrometric characterisation of the Italian Protected Designation of Origin “Altamura” bread volatile profile

Dynamic headspace extraction technique coupled to the gas chromatography–mass spectrometry analysis was applied to characterize volatile compounds of both crust and crumb of the Protected Designation of Origin Italian durum wheat sourdough “Altamura” bread. Volatile compounds of crust and crumb were characterized and statistically compared and their relative abundance was also calculated. A total of 89 compounds belonging to different chemical classes were identified in the crust. More abundant compounds detected in the crust were ethanol (20 ± 6%), 2-furfural (14 ± 7%) and 3-methyl-1-butanol (9 ± 5%). A lower number of volatile compounds (74) was identified in crumb, among which ethanol (32 ± 7%), 3-methyl-1-butanol (23 ± 6%) and 3-pentanol (7 ± 3) were the most abundant. The influence of different baking modes (wood- or gas-fired) on volatile compounds, macroscopic appearance and selected physico-chemical parameters (colour and texture) of bread samples were also evaluated.

Samples baked in wood-fired oven showed larger amount of volatile compounds such as furans and aldehydes that could positively influence the flavour of the product.

Crust of wood-fired breads showed higher amounts of compounds from Maillard reaction, resulting in harder and browner breads than gas-fired samples. Macroscopic appearance of crumb of wood-fired breads showed higher percentages of larger pores, being also less hard and cohesive than gas-fired samples.     

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.     

Effect of temperature and time on the formation of acrylamide in starch-based and cereal model systems,flat breads and bread

Dry starch systems, containing varying amounts of asparagine and glucose, freeze-dried rye-based flat bread doughs, flat bread and bread, were baked at varying temperatures and times according to central composite designs. In the starch-based model system the amount of acrylamide went through a maximum when the level of asparagine increased. No such maximum was found for glucose. In the starch system, freeze-dried flat bread doughs and flat breads, the amount of acrylamide formation went through a maximum at approximately 200 °C, depending on the system and the baking time. The amount of acrylamide was reduced at long baking times. However, in bread crust, the amount of acrylamide increased with both baking time and temperature in the interval tested.     

Inulin and oligofructose as fat and sugar substitutes in quick breads (scones): a mixture design approach

Mixture (D-optimal) design was used to investigate the effects of prebiotics such as inulin and oligofructose as fat and sugar replacers on quality parameters of quick breads (scones). Crust and crumb colour increased with the inclusion of prebiotics. Higher concentration of inulin and oligofructose in quick breads also showed a slight increase in crust and crumb hardness. Loaf volume significantly increased with the inclusion of prebiotics. The optimization tool indicated that by using a mixture of margarine (3.53%), oligofructose Orafti^? L95 (10%), caster sugar (0.55%) and inulin Orafti^? GR (5.92%), a quick bread with similar baking properties and textural attributes to the control can be achieved. The mixture design was successfully used to reduce the original levels of 10% fat and 10% sugar (percentages are based on flour weight). The calculated model performance indices accuracy factor and bias factor of the predicted quick-bread formulations showed a high applicability of the model. The variations between the predicted and experimental values obtained were within the acceptable error range, as depicted by the average mean deviation. Therefore, the predictive performance of the established model may be considered acceptable.     

Effect of crust temperature and water content on acrylamide formation during baking of white bread: Steam and falling temperature baking

The effect of crust temperature and water content on acrylamide formation was studied during the baking of white bread. To assess the effect of over-baking, we used a full factorial experimental design in which the baking time was increased by 5 and 10 min at each baking temperature. Additional experiments were performed with steam baking and falling temperature baking. Immediately after baking, the crust was divided into the outer and inner crust fractions, and the water content and acrylamide concentration of each fraction was measured. The outer crust had a significantly lower water content and higher acrylamide concentration than the inner crust did. Crust temperature in combination with water content had a significant effect on acrylamide formation, higher temperatures resulting in higher acrylamide concentrations. However, at very high temperatures and lower water contents, acrylamide concentration was observed to decrease, though the bread colour was then unacceptable for consumption. Steam and falling temperature baking, on the other hand, decreased the acrylamide content while producing bread crust with an acceptable colour. The lowest acrylamide values and an acceptable crust colour were produced by steam baking.     

Release of free ferulic acid and changes in antioxidant properties during the wheat and rye bread making process

Changes in the free ferulic acid (FFA) contents and antioxidant properties during bread making processes were determined. Experimental breads were produced from whole meal and white wheat and rye flours, and fermented using either baker’s yeast or sourdough starter. Sourdough fermented bread contained the highest content of FFA. Release of occurred mainly during dough fermentation. A further increase in the ferulic acid content in the bread crumb and a decrease in the crust was observed. Total antioxidant properties of sourdough bread, defined as the sum of lipophilic and hydrophilic compound activities, were significantly (p<0.05) higher than for yeast bread. Sourdough bread contained more methanol soluble phenolic compounds, proteins, tocochromanols, and oxidized products of fatty acids than yeast bread. The equilibrium between the anti- and pro-oxidative compound contents resulted in similar antioxidant properties for bread using both types of fermentation, and to results observed for the flour used for baking.     

Viability of some probiotic coatings in bread and its effect on the crust mechanical properties

The objective of this study was to obtain functional bread combining the microencapsulation of Lactobacillus acidophilus and starch based coatings. Different probiotic coatings (dispersed or multilayer) were applied onto the surface of partially baked breads. In all treatments, microencapsulated L. acidophilus survived after baking and storage time, although reduction was higher in the sandwich treatment (starch solution/sprayed microcapsules/starch solution). Despite coatings significantly affected the physicochemical properties of the crust, increasing water activity and reducing the failure force, the sensory evaluation revealed a good acceptability of the functional breads. Scanning electron microscopy revealed the presence of scattered microcapsules onto the bread crust, being highly covered in the sandwich coating. Therefore, L. acidophilus included in microcapsules can be incorporated to bread surface through edible coatings, leading functional bread with similar characteristics to common bread, but with additional healthy benefits.     

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.     

Furan quantification in bread crust: development of a simple and sensitive method using headspace-trap GC-MS

To study reactivity in bread crust during the baking process in the pan, we followed furan mainly resulting from Maillard and caramelisation reactions in cereal products. Furan quantification is commonly performed with automatic HS-static GC-MS. However, we showed that the automatic HS-trap GC-MS method can improve the sensitivity of the furan quantification. Indeed, this method allowed the LOD to be decreased from 0.3 ng g^–1 with HS-static mode to 0.03 ng g^–1 with HS-trap mode under these conditions. After validation of this method for furan quantification in bread crust, a difference between the crust extracted from the bottom and from the sides of the bread was evident. The quantity of furan in the bottom crust was five times lower than in the side crust, revealing less reactivity on the bottom than on the sides of the bread during the baking process in the pan. Differences in water content may explain these variations in reactivity.     

Analysis of volatile compounds in polished-graded wheat flour bread using headspace sorptive extraction

Flavor compounds are one of the very important factors for the taste of commercial breads, and then the volatile flavor compounds in the present novel polished-wheat-flour breads were determined by headspace sorptive extraction method to develop the baking properties, comparing two baking procedures of straight-common- and sourdough-methods. The polished flours of outermost, middle and innermost fractions, and common flour, CW were used. There were some differences on the compounds and proportions of volatile flavors in all flours between the both methods. The sourdough-method increased the proportions of acids and aldehydes in crust, but decreased those of alcohols and methoxybenzenes identified in the outermost fraction, rather than the straight-common-method. In addition, the sourdough-method lowered the amounts of some compounds related to oxidation products from unsaturated fatty acids and metabolites of species with moldy grains, as compared with the straight-common-method. Furthermore, the amounts of 2-methylpropanol (iso-butanol) and 2-phenylethanol (β-phenyl-ethyl-alcohol) that have been known as favorable flavor compounds on breadmaking distinctly increased in polished flour breads than CW bread, regardless of baking methods. Therefore, the sourdough-method with lactic acid fermentation would be suitable baking procedure for polished flours from the viewpoints of flavor properties. Furthermore, the utilization of sourdough-method for polished flours from middle and innermost fractions might be appropriate to taste and texture of consumers’ request for bread qualities.     

Immobilization of kefir and Lactobacillus casei on brewery spent grains for use in sourdough wheat bread making

New types of bread were produced employing baker’s yeast, kefir or Lactobacillus casei immobilized on brewer’s spent grains. Bread was produced either by the straight-dough or the sourdough method. All the studied biocatalysts and their corresponding sourdoughs were found efficient for breadmaking. Good rising was achieved and the produced breads had good overall quality and remained fresher for longer, compared to commercial type baker’s yeast bread. The best results were obtained for sourdough breads, with higher moisture retention during baking, lower rates of water evaporation and staling, and maintenance of freshness for longer (4–5 days). Consumer evaluation showed bigger preference for the sourdough breads as far as aroma, taste and overall quality were concerned, justified by the GC-MS analysis of volatiles that revealed a different aroma profile, with more compounds identified than in breads produced by the straight-dough method, obviously due to variations in microbial populations.     

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.     

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.     

Protein profile and sensorial properties of rye breads

The protein profile of four types of traditional rye breads formed on rye flours with the extraction rate of 100, 95, 85 and 70% and baked at 260 °C for 40 min was investigated as a nutritional quality indicator. A fractionation process was applied to discriminate high-molecular- (HMW >3 kDa) and low-molecular weight compounds (LMW <3 kDa) present in extracts of rye bread and its crumb and crust. The content of soluble proteins, available lysine, carbohydrates and total phenolic compounds was analysed before and after ultrafiltration in both retentates (HMW >3 kDa) and filtrates (LMW <3 kDa). The dependence between sensory quality of rye breads and composition on soluble proteins, available lysine, carbohydrates and total phenolic compounds was provided. Baking caused a decrease in rye bread protein content. The content of available lysine was the lowest in crusts and it was dependent on the rye flour extraction rate taken for rye bread making. The SDS-PAGE analysis showed that the primary structure of the rye bread proteins was modified in the highest extent in the crust’s bread of all types. The analyses of both retentates and filtrates after ultrafiltration demonstrated that the most of carbohydrates and phenolic compounds were incorporated into the HMW fraction suggesting their conjugation with proteins due to the Maillard reaction. Compounds able to react with Folin Ciocalteu reagent were also detected in filtrates of crust’s extracts (MW ≤3 kDa) from all breads indicating their distribution between LMW and HMW fractions. About 22.5, 27, 11.2 and 46.8% of the phenol compounds forming crusts of breads based on the flours with extraction rates of 100, 95, 85 and 70% were recovered in the corresponding LMW fractions.The sensory analysis of the four types of rye breads indicated for a high correlation between overall quality of breads and their content of carbohydrates. The highest correlation was noted for a rye bread formed on flour with extraction rate of 95%. This finding suggested that the content of carbohydrates as a substrate for Maillard reaction has had an influence on palatability by consumers of rye bread formed on flour with the extraction rate of 95% which had also the highest overall quality.     

Wheat bran particle size effects on bread baking performance and quality

Commercial hard red spring, hard red winter, soft white and durum wheat brans were used to evaluate the particle size effect of wheat bran on bread baking performance and bread sensory quality. Three different particle size bran samples were obtained from each bran by grinding, not by sifting, the bran samples. The bran samples were similar in chemical composition, but different in particle sizes. Results of baking experiments showed that breads containing fine bran had lower specific loaf volume and darker crumb colour than breads containing coarse or medium size bran. Sensory test panellists found that fine bran contributed smoother crust appearance and less gritty mouthfeel than the coarse bran. The sensory panel also indicated that breads containing soft white wheat bran had significantly better flavour and mouthfeel than breads containing hard red spring wheat bran. © 1999 Society of Chemical Industry