Role of fat on the quality and shelf-life of gluten-free bread baked by Ohmic heating and conventional deck oven

Evaluation and analysis of transglutaminase-modified gluten-free soybean bread processed using ohmic heating with varied voltage levels

Due to the absence of gluten, several challenges arise during gluten-free (GF) bread baking, affecting the mid-and-end-product quality. The main approach to overcome this issue is to combine certain functional ingredients and additives, to partially simulate wheat bread properties. In addition, the optimization of the baking process may contribute to improved product quality. A recent and very promising alternative to conventional baking is the use of ohmic heating (OH). Due to its volumetric and uniform heating principle, crumb development during baking and consequently bread volume is improved, which enhances the overall GF bread quality. Depending on the GF formulation, critical factors such as the electrical conductivity and viscosity of the batter may vary, which have a significant effect on the OH process performance. Therefore, this review attempts to provide a deeper understanding of the functionality of GF bread ingredients and how these may affect critical parameters during the OH processing.

Effect of arabinoxylans and laccase on batter rheology and quality of yeast-leavened gluten-free breads

The use of gluten-free products is increasing since an increasing number of people (1–2 %) are suffering from Celiac disease and thereby need a gluten-free diet. Gluten-free bread tends to have shorter shelf life and quality compared with white wheat bread. In this study, 3 % (flour basis) of pre-gelatinized oat and barley flour as well as an emulsifier were added to a gluten-free mix to increase the water content by 1.5–2 %, affect the starch retrogradation and the formation of amylose lipid complex. The staling was followed measuring the firmness (texture analyzer), water content and distribution (nuclear magnetic resonance), amylopectin retrogradation and the formation of amylose–lipid complex (differential scanning calorimetry) in order to see the impact of both macroscopic and molecular changes on firmness. Both gluten-free bread and a white wheat bread were used as control loaves. Largest specific volume was found in the gluten-free control. The firmness varied with both the specific volume and the point of measurement. The amount of retrograded amylopectin increased the firmness, although this effect was dependent on the type of bread, in terms of distribution and availability of the water within the system. The proton relaxation time, which was representing movable water, decreased during storage and revealed that both the amylopectin retrogradation and the lipid complex formation were affecting the rigidity of the amorphous domain and not only the crystalline regions. In contrast to the other recipes, the use of emulsifier caused limited retrogradation and a low correlation between the texture properties and time-dependent events.

The objective is to verify if gluten-free (GF) and gluten-containing (G) breads differ in their sodium content and lipid profile. Samples of GF (n = 20) and G (n = 14) sliced white sandwich bread of commercial brands most frequently consumed in Spain were collected. The fatty acid (FA) composition and the contents of sodium, fat, cholesterol and phytosterols were determined. Sodium, fat and cholesterol contents were significantly higher in GF bread. The FA composition also differed, while G breads declared in most instances the use of sunflower oil as fat ingredient and presented a higher polyunsaturated FA percentage; GF breads declared a wide variety of fats and oils as ingredients (coconut, palm, olive, sunflower, etc.) which was reflected in their FA profile. Cholesterol content was higher in GF bread because five samples declared the use of whole egg, while G samples did not include any egg product in their formulas. Phytosterol content was higher in G bread but its variability was greater in GF bread. In conclusion, nutritional quality of GF bread varied depending on the ingredients used and might be lower than that of G bread. However, these differences in composition could be reduced or eliminated through changes in the formulation of GF bread. Moreover, the comparison of the results obtained in our laboratory for fat and salt content with the declared contents on the labels showed a much higher deviation for GF samples and it can be concluded that the quality of the nutritional information declared was lower in GF samples.

Gluten-free (GF) breads available on the market are still mainly produced from refined flours or starch, thus they lack nutritional quality, like dietary fiber, minerals and vitamins. Incorporation of micronized oat husk (MOH) could improve these properties. MOH is a dietary fiber and a food by-product, rich in polyphenols exhibiting antioxidant properties. This study investigated the addition of 0–20% MOH (in 5% steps) to GF breads baked conventionally (deck oven) and by ohmic heating (OH). Incorporation of ≤20% MOH had only a slight effect on the bread texture properties (specific volume, pore properties, crumb firmness and relative elasticity), and was less pronounced for OH baked breads. Both, the crumb and crust color, darkened proportionally to the added amount of MOH. Total phenolic content (TPC) and antioxidative properties were significantly increased by MOH addition, as well as the ability to protect lipids from oxidation. In vitro starch digestibility was improved with MOH addition for OH-baked breads. GF breads containing ≥15% MOH can be claimed as “source of fiber”, ≥20% MOH as “high in fiber”. Overall, this study demonstrated that micronized oat husks have a good potential to enhance the quality of GF breads.

The rheological properties of Gluten-Free (GF) batter are an important factor to consider for designing GF bread recipes, which is critical when they are baked by ohmic heating. This research demonstrated that batter properties are not only significantly modified by the starch:water ratio, but also greatly by the starch source and structure, which influenced its physical properties (e.g., water holding capacity, swelling power, solubility, starch damage, and pasting properties). This study aimed to investigate the role of GF starches (corn, wheat, potato, cassava) and flours (rice and buckwheat), as well as the rheological behavior of GF batter and the final bread quality after baking with ohmic heating. The starch (or flour) to water ratios were 1:0.9, 1:1.3, and 1:1.7, while buckwheat needed higher water ratios of 1:1, 1:1.5, and 1:2. The attempt was to thoroughly understand the interaction between the rheological properties and ohmic baking and to define a suitable viscosity range for this processing approach. All batters consistently exhibited shear-thinning and dominant viscous behavior. Between viscosity and ohmic-heated bread properties, a non-linear relationship was observed. These breads were generally higher in volume and softer in texture as opposed to conventional baked bread. Two categories of required water content or viscosity ranges were defined for estimating final ohmic-heated GF bread properties: low water content with a viscosity range of 47.12–56.20 Pa·s for B-type starches (tuber starches) and medium water content with a low to medium viscosity range of 2.29–15.86 Pa·s for A-type starches (cereal starches). This fact showed that viscosity played a critical role in determining GF bread structure and crumb properties. This finding could be useful for further research to design GF batter viscosities for tailored bread quality.

Recently there has been increasing interest in the production of gluten-free (GF) foods and studies on minor cereals and pseudocereals without celiac activity in order to fulfill the specific needs of people affected by celiac disease. GF bread, pasta, biscuits are usually manufactured using different combinations of thickenings and particular food processing procedures that could affect starch digestibility. Carbohydrates, mainly starch from cereals, play an important part in a balanced diet, and dietary guidelines suggest a diet with low glycemic index foods, that is to say rich in slowly digested carbohydrates. The present study was aimed at evaluating: 1) the importance of some GF food characteristics in relation to their effects on in vitro starch accessibility to digestion, in comparison with traditional gluten products; 2) the in vivo metabolic responses to GF foods. Firstly, starch digestibility of several products was evaluated in vitro. Then, an in vivo study was performed on a group of healthy volunteers. Postprandial glucose and insulin responses were evaluated after administration of three GF foods and traditional bread. Triglycerides and free fatty acids (FFA) were also evaluated. Attempts were also made to explore differences in metabolic responses to GF foods in healthy subjects with respect to celiac subjects. The area under the curve (AUC) of digested starch of GF bread was slightly higher than that of the traditional counterpart. No significant difference was observed in AUCs of digested starch between GF pasta and the traditional pasta. The AUCs of digested starch of quinoa and the two samples of pasta were not statistically different. Significant differences were observed between GF bread and bread-like products. Statistic differences in glucose responses to GF pasta were observed between healthy and celiac subjects. In healthy subjects, the AUCs of glucose response after GF bread were higher than those after bread with gluten. No significant differences were observed between the AUCs of insulin responses to all products tested. Glycemic index (GI) for GF pasta was similar to GI for GF bread while GI for quinoa was slightly lower than that of GF pasta and bread. Two-way ANOVA revealed that quinoa induced lower FFA levels with respect to GF pasta. In addition, triglyceride concentrations were significantly reduced for quinoa with respect to GF bread and bread. Our results indicate that the different formulations and the food processing procedures used in the manufacturing of GF products may affect the rate of starch digestion both in vitro and in vivo. It may be worthwhile improving the formulation of these products. Furthermore, quinoa seems to represent a potential alternative to traditional foods, even if further and larger studies are required to demonstrate its hypoglycemic effects.

Psyllium as an improver in gluten-free breads: Effect on volume, crumb texture, moisture binding and staling kinetics

Modified Sweet Potato Flour has been done by oxidation using H2O2 and irradiation. This flour was used to develop gluten free bread with addition Nuts (soy, mung bean, and red bean kidney) flour. The aim of this research was to determine the physicochemical, baking quality, and sensory evaluation of gluten free bread. Gluten Free Bread sample was compare with wheat flour and native sweet potato flour for the physicochemical (texture, color properties, proximate, and dietary fiber) and baking quality. The sensory evaluation was obtained only for the gluten free bread from modified sweet potato flour. Result showed that chemical properties bread made from modified sweet potato has higher moisture content, dietary fiber, moderate ash, and lower protein than wheat and native flour bread. The physic properties showed that the free gluten bread has higher hardness, springiness than wheat flour bread. The L color score of bread based modified sweet potato was not significantly different compare with wheat flour. Baking quality of the gluten free bread was lower than wheat flour. Sensory evaluation for the bread based on modified sweet potato with addition soybean flour showed the highest score for taste, aroma, color, and overall acceptance.

Celiac disease (CD) is an immune-mediated disease, triggered in genetically susceptible individuals by ingesting gluten from wheat, rye, barley, and other closely related cereal grains. Currently, the estimated prevalence of CD is around 1 % of the population in the western world and medical nutritional therapy (MNT) is the only accepted treatment for celiac disease. To date, the replacement of gluten in bread presents a significant technological challenge for the cereal scientist due to the low baking performance of gluten free products (GF). The increasing demand by the consumer for high quality gluten-free (GF) bread, clean labels and natural products is rising. Sourdough has been used since ancient times for the production of rye and wheat bread, its universal usage can be attributed to the improved quality, nutritional properties and shelf life of sourdough based breads. Consequently, the exploitation of sourdough for the production of GF breads appears tempting. This review will highlight how sourdough LAB can be an efficient cell factory for delivering functional biomolecules and food ingredients to enhance the quality of gluten free bread.

The objective of this study was to determine the impact of adding xanthan and guar gums at different levels 2, 3 and 4% on the rheological behavior of rice flour, corn and potato starches batter, as well as, gluten-free bread quality. It could be found that consistency coefficient and apparent viscosities were gradually increased with increased the level of xanthan and guar gums from up to 4%. Addition of xanthan gum at level 3 and 4% to prepared gluten-free formula resulted in significant improvement in bread specific volume (2.94 and 2.79 cm3/g, respectively) compared with other investigated treatments. Also, the prepared gluten-free bread containing 4% of guar gum showed significant higher of lightness value 74.9 followed by 66.5 and 66.5 which given by prepared gluten-free bread with added 2 and 3% of guar gum, respectively. Gluten-free bread sample with adding 3% of xanthan and guar gums mixture was the more acceptable in sensory attributes followed by gluten-free bread by 3% of xanthan gum compared with other studied treatments. Gluten-free bread with adding 3% of xanthan and guar gums mixture was more freshness and keeping high moisture content from zero time until 72 hours of storage period followed by gluten-free bread containing 3% and 4% of xanthan gum. It could be concluded that glutenfree pan bread can be prepared with acceptable quality using rice flour, corn and potato starches by adding 3% mixture of xanthan and guar gums at 1:1 ratio.

The diet based on gluten free products is characterised by a low content of some nutritional components such as proteins and mineral components, as well as non-nutritional but physiologically important components like dietary fibre. Buckwheat grains are a rich source of proteins, which have a high biological value due to the well-balanced amino-acids composition, although its digestibility is relatively low. The aim of the present research was to investigate the influence of buckwheat flour addition on gluten free bread quality and their antioxidant capacity. In this study, own gluten free bread formula, composed of corn starch, potato starch, salt, yeast, pectin, sugar and sunflower oil was investigated. The buckwheat flour substituted corn starch at final amount of 10, 20, 30, 40% w/w of total ingredients in gluten free bread formula. The breads were baked in electric oven at 200°C for 25 min. The bread samples were freeze-dried, ground and sieved. The sensory quality of buckwheat enhanced gluten free breads was analysed using sensory profiling (QDA) and hedonic tests. The measurement of macroelements content in the crumb was carried out using the atomic absorption spectroscopy (AAS) method (SORAL-SMIETANA et al. 2001). The antioxidant capacity (AC) of the breads was evaluated by cyclic voltammetry (CV) method and free radical scavenging activities of 67% methanol extracts against 2,2-diphenyl-1-picryhydrazyl radical (DPPH.) as DPPH Radical Scavenging Activity (DPPH RSA). All breads were analysed for their total phenolics content. The buckwheat enhancing gluten free breads were in accordance to the requirements of Polish Standards (PN-A-74123) for gluten-free bread. The sensory profiles of gluten-free breads were dependant on the amount of buckwheat flour added. The overall quality of breads was the highest for bread with 40% buckwheat flour addition. The positive correlation between macroelements content and increasing amount of buckwheat flour was observed in breads. The antioxidant capacity of buckwheat enhanced gluten free breads determined by CV and DPPH RSA was related to the amount of added buckwheat flour. The total phenolics content was positively correlated with antioxidant capacity of the breads. In summary, buckwheat flour as a natural source of minerals and antioxidant activity, and also as a structure-forming factor improving the sensory quality, can be used for preparation of new buckwheat enhanced gluten free breads.

Gluten-free (GF) batters usually present several technological challenges that limit the performance during conventional baking and the resulting product quality. Due to the volumetric heating principle and faster heating rates, ohmic heating (OH) may be advantageous compared with conventional baking. Therefore, the potential of using ohmic heating as a novel approach for gluten-free bread baking was explored. In detail, the effect of different OH process parameters (power input, holding time) on the chemical and functional properties (specific volume, crumb firmness and relative elasticity, pore properties, color, starch gelatinization) and digestibility of breads was investigated. Results showed that GF breads could benefit from the uniform rapid heating during processing, as these breads showed superior functional properties (specific volume, 2.86–3.44 cm3/g; relative elasticity, 45.05–56.83%; porosity, 35.17–40.92%) compared with conventional oven-baked GF bread (specific volume, 2.60 cm3/g; relative elasticity, 44.23%; porosity, 37.63%). In order to maximize bread expansion and the OH performance, it was found that the OH process could be improved by applying the electrical energy in three descending power steps: first step with high power input (in this study, 2–6 kW for 15 s), followed by 1 kW for 10 s, and 0.3 kW for 1–30 min. In total, ohmic baking only needed a few minutes to obtain a fully expanded GF bread. The determination of pasting properties and starch digestibility demonstrated that these breads were comparable or even superior to GF breads baked in a conventional baking oven.

Ingredients used to enhance sensory quality of gluten-free (GF) bread often lack in nutrients. This presents nutritional challenges for celiac-positive individuals and fails to meet expectations of healthfulness for non-celiac GF consumers. Sorghum (Sorghum bicolor L. Moench) flour can provide acceptable GF bread properties, and tannin-containing varieties contain antioxidants concentrated in the bran along with dietary fiber. Using a central composite design, tannin-containing sumac sorghum bran, gum (xanthan+guar), and water levels were optimized in a GF sorghum-based bread formulation. Loaf specific volume and gas cells/cm2 were maximized while minimizing hardness and cell wall thickness. The optimum formulation containing 14.2% sorghum bran, 1% gum, and 145% water (flour basis) effectively increased dietary fiber in bread to 13.4% (considered "high fiber") and showed oxygen radical absorbance capacity of 61.6µmolTE/g. This optimum formulation did not differ from a sorghum flour-based control bread in consumers' (N=100) liking of color, texture, flavor, overall acceptability, nor willingness to buy (WTB). All mean hedonic scores (numbered 9-point scale) were above 5, whereas average WTB was 4.7 for the optimum formulation and 4.6 for the control (9-point Likert scale) among consumers varying in GF bread consumption habits. Perceived bread bitterness was low (averaging 2.85 on 9-point intensity scale), did not vary between samples despite marked differences in antioxidant capacity, and was not correlated with WTB. When utilizing effective optimization models with key functional ingredients, sumac sorghum bran addition can enhance dietary fiber and antioxidant potential in sorghum-based GF breads without compromising quality attributes.