The effects of different levels of hydrocolloids on external appearance and internal structure of gluten-free control (GFC) breads was presented in Fig. 1a. The effects of the addition of various levels of amaranth flour, quinoa flour, chia flour, and mixture flour with different levels of hydrocolloids on external appearance and internal structure of GF breads was presented in Fig. 1b, 1c, 1d, and 1e, respectively.
Bread moisture
Table 2 presents the moisture content of GF bread formulations. The addition of hydrocolloids increased bread moisture in all formulations of GFC and pseudocereal breads. An increase in the moisture content of breads was observed when the concentration of hydrocolloids was increased. Increasing the ratio of pseudocereal flours, also, led to an increase in the moisture content of breads. All formulations of pseudocereal breads had moisture contents higher than those of GFC breads except in two cases; Q1 had the same moisture content with that of GFC1, also M3 had the same moisture content with that of GFC3 (P<0.05). Hydrocolloids decrease the loss of moisture content during bread storage, and thus reduce the dehydration rate of crumb. The increasing of the crumb moisture content was attributed to constant dough consistency, and to the water binding capacity of the hydrocolloids [25-26]. Hydrocolloids are applied in bakery products to control water absorption and, consequently, improve the shelf life of products by keeping the moisture content constant and, retarding the staling as well [27].
These findings are consistent with the reports of Guarda et al. [25] and Dizlek and Özer [2] who found that the addition of hydrocolloids increased the moisture content of the fresh bread and GF bread, respectively, and that increase was clearer at high levels of hydrocolloids (P<0.05). Mohammadi et al. [28] obtained the same results and found that xanthan gum-CMC significantly augmented the bread moisture (P<0.05). Ozturk and Mert [29] also, reported that the addition of xanthan gum to the formulation of bread prepared from corn starch had higher moisture content than that of the control breads. On the other hand, the inclusion of the pseudocereal flours slightly increased the moisture content of the pseudocereal-containing GF breads. Alvarez-Jubete et al. [16] found that no significant differences were observed in the moisture content of the pseudocereal-containing breads in comparison to the GFC breads. Additionally, Steffolani et al. [30] reported that the addition of chia at a ratio of 15 g per 100 g of rice flour reduced weight loss during baking.
When comparisons were made between amaranth, quinoa, chia and mixture breads, significant differences were found. The highest moisture content was found for the 30% chia flour-containing breads.
Specific volume of breads
The results for the specific volume of the baked breads are presented in Table 2. The specific volume index of all breads significantly improved by increasing the level of hydrocolloids except for some formulations, especially, the formulations of GF breads which were prepared using high ratios of pseudocereal flours (30%). The addition of hydrocolloids significantly increased the specific volume of the GFC breads and the pseudocereal-containing GF breads which prepared with low and medium ratios (10% and 20%) except for A5 and A6, and that raise was significantly evident at high levels (4%) of hydrocolloids (Fig. 1a–1e).
According to Rosell et al.,22 hydrocolloids can improve the dough development and gas retention. An improvement in the specific volume was obtained when adding 0.1-0.5% HPMC and 0.1-0.5% xanthan gum to wheat bread formulations [25]. In a similar way, Sciarini et al. [31] found a positive effect of hydrocolloids especially xanthan, followed by CMC on the specific volume of GF breads made of 40% rice flour, 40% corn flour and 20% soy flour (P<0.05). Dizlek and Özer [2] reported that, volumes and softness of the GF breads have been measured as maximum when HPMC was used alone in increasing order from 1% to 2%. They found that, while HPMC gum improved the volume and softness of bread more than xanthan gum, xanthan gum improved the pore structure of crumb more than HPMC. In general, these hydrocolloids gave good quality bread in terms of moisture content, pore structure and Neumann baking coefficient values, when they were used with combinations rather than being used individually. Ozturk and Mert [29] reported that the specific volume analysis showed that the addition of xanthan gum resulted in bigger breads than control breads.
The replacement of corn starch by each of the pseudocereal flours adversely affected the specific volume of the pseudocereal-containing GF breads in comparison to the GFC breads, with the exception of some formulations which were better than control (P<0.05). This effect was clearer with increasing the ratio of pseudocereal flours.
Among the pseudocereal-containing breads, quinoa breads had better specific volume than that of chia, mixture, and amaranth breads as presented in Fig. 1b–1e. It is worthy to note that Q1, Q2, C1, and M1 breads had better specific volume than that of their counterparts of control breads GFC1 and GFC2. The specific volume of Q3, C3, and M3 breads were the closest to that of GFC3 bread. While all the amaranth breads had the lowest specific volume among the pseudocereal-containing breads (P<0.05).
Alvarez-Jubete et al. [16] reported that the replacement of potato starch by quinoa flour resulted in breads with higher volume (P<0.05) in comparison with the control which made from 50% rice flour and 50% potato starch. While no difference in volume was found when potato starch replaced by amaranth flour. Steffolani et al. [30] found that the inclusion of chia flour at a ratio of 15 g per 100 g of rice flour reduced the specific volume of breads. They reported that these differences could be attributed to the lower level of water in the formulation, because larger levels of water produce breads with larger specific volumes [32].
Texture profile analysis of bread crumb
The crumb hardness results of bread samples are shown in Table 2. Increasing hydrocolloid concentration significantly increased the crumb hardness of GFC and pseudocereal-containing GF breads especially the breads which formulated with the highest hydrocolloid concentration (4%) (P<0.05), except in a case in amaranth breads; no significant difference was found between A8 and A9 (P<0.05).
In previous studies, it was found that using several hydrocolloids, such as HPMC and xanthan gum [2], xanthan gum and CMC [28], and xanthan gum, guar gum, locust bean gum, HPMC and pectin [33], causes crumb softening in the GF bread, while some other studies showed that the addition of xanthan gum results in an increase in the hardness of GF bread [21, 34], and wheat bread [25]. Despite there are some hypotheses about the hydrocolloid’s mechanism, it has not been completely understood yet. The effects of hydrocolloids on the starch structure and mechanical properties are results from two opposite phenomena: (1) an increase in the rigidity because of the decrease in the swelling of the starch granules and amylose leaching, (2) a weakening effect on the complex starch network structure due to the prohibition of interparticle contacts among swollen granules. It is perhaps a combination of both factors that determine the overall influence on the mechanical properties of bread structure, however, each effect is dependent on the specific hydrocolloid used for fortification [21, 25, 28].
Lazaridou et al. [21] reported that the crumb firmness was not significantly affected by the addition of CMC when added at 1–2% concentration compared to the GF control formulations prepared from rice flour and corn starch. Xanthan gum at both supplementation levels (1–2%) had an unfavorable influence on crumb firmness (P<0.05). They also pointed out that the crumb firmness values increased by increasing storage time (P<0.05); this is expected because of moisture loss as well as due to starch retrogradation phenomena. Similarly, Schober et al. [34] found an increase in the crumb firmness observed by the addition of xanthan gum in GF breads prepared from sorghum (P<0.01). Also, Guarda et al. [25] reported that the hardness of the wheat bread increased by adding xanthan gum after 24 h of storage.
Contrary to these results, Mohammadi et al. [28] found that xanthan gum and CMC significantly decreased the crumb hardness of both fresh and stored breads (P<0.05) in comparison with control made from corn starch and rice flour. The reason for the softness is that water retention increases moisture content and thus, causes retrogradation of starch and bread firming is retarded [28]. Also, Demirkesen et al. [33] investigated the optimization of GF formulations based on rice flour prepared using different hydrocolloids and emulsifiers, they reported that the hardness of GF bread decreased with the addition of hydrocolloids. Similarly, Dizlek and Özer [2] reported that, GF breads which contains only xanthan and/or HPMC in their composition as an additive (without surfactant), the penetrometer values of bread increased (hardness of GF bread decreased), as the level of hydrocolloid increased. Ozturk and Mert [29] also found that the addition of xanthan gum caused lower hardness for bread based on corn starch. This can be attributed to the water binding ability of hydrocolloids, leading the prevention of water transfer from the bread crumb to the crust and delayed starch retrogradation.
A possible explanation for these contradictory results in these studies is that GF breads were prepared by different methods. In this study, the level of water used in the preparation of GF breads was low and kept constant in all formulations, while Mohammadi et al. [28] considered the level of water needed to maintain consistency. In addition to that, we used corn starch as a flour base to produce GFC breads and other pseudocereal-containing GF breads.
On the other hand, the inclusion of the pseudocereal flours with low and medium ratios (10% and 20%) of flours significantly decreased the crumb hardness of the pseudocereal-containing GF breads in comparison with GFC breads, except for some formulations. The inclusion of the pseudocereal flours with high ratios (30%) of flours significantly increased the crumb hardness of the pseudocereal-containing GF breads in comparison with GFC breads, apart from the 30% quinoa flour-containing breads.
Alvarez-Jubete et al. [16] reported that the replacement of potato starch by pseudocereal flour resulted in a softer crumb in comparison with the GFC. Amaranth breads had the softest crumb, and they are followed by the buckwheat and quinoa breads. Moreover, the crumb hardness of GF breads increased with storage time. All the pseudocereal-containing GF breads were characterized by a significantly softer crumb. This is attributed to the presence of natural emulsifiers found in the pseudocereal flours [16]. Steffolani et al. [30] found that the inclusion of chia flour at a ratio of 15 g per 100 g of rice flour resulted in a considerable increase in the crumb hardness of breads. This effect cannot be opposed to our findings for the chia breads and can be explained by the differences in the levels of water used. In our study, the amount of water used was at a fixed level (120%) in each bread formulation, while the amount of water used was 100% in the study of Steffolani et al. [30]. This agrees with McCarthy et al. [32] who found that; the increasing levels of water used significantly increased the specific volume (P<0.01) and decreased the crumb hardness (P<0.01) of breads.
This study reports a negative relation between the specific volume and the crumb hardness of the pseudocereal-containing breads. The increase in the ratio of pseudocereal flours significantly decreased the specific volume and, simultaneously, increased the crumb hardness of the pseudocereal-containing GF breads except for the quinoa breads. Steffolani et al. [30] found that the inclusion of 15 g chia flour resulted in a reduction in the specific volume and a greater increase in the crumb hardness of breads.
Crust and crumb color of the breads
Average values of GF doughs color and crust color of bread samples were given in Online Resource. As shown in Table 3 and Fig. 1a–1e, increasing hydrocolloids concentrations significantly resulted in a lighter color (higher L values) for the crumb in all bread formulations (P<0.05) and this effect was clearly observed at the highest hydrocolloid concentration (4%) but did not significantly affect the values of a and b except in few cases. The lightening effect is attributable to the effect of the addition of hydrocolloid on the water distribution which, thus, influences Maillard browning and caramelization reactions [35].
Mohammadi et al. [28] found that the inclusion of CMC and xanthan gum resulted in a lighter color for the crumb and crust in all formulations, compared to the GFC breads which does not contain gums (P<0.05). The a and b scales of the crumb were not affected by the addition of gums in comparison with the control. The similar results were also found by Lazaridou et al. [21] The inclusion of xanthan gum gave a lighter color for the crumb and crust (P<0.05), compared to the GFC breads which were prepared from rice flour and corn starch, whereas the presence of CMC at 1% or 2% caused no significant increase in the lightness (L value) of the crumb.
As presented in Fig. 1a–1e, the addition of the different pseudocereal flours significantly gave a darker color for the crust (data not shown) and crumb (lower L values) and higher a and b values of the bread crumb, compared to the GFC breads. This effect was clearer in the pseudocereal-containing GF breads which prepared using high ratios of flours (30%) followed by those containing medium ratios of flours (20%) (P<0.05).
Gómez et al. [36] pointed out that the original color of ingredients can slightly affect the crust color of the breads. The main reasons for the crust color are Maillard and caramelization reactions. Crumb color of breads, however, is usually like the color of the ingredients. This is attributed to the fact that the crumb does not reach such high temperatures as the crust. Among the pseudocereal-containing breads (Fig. 1b–1e), quinoa breads which were prepared using high ratios of quinoa flour (30%) had the darkest crumb color. In contrast, chia breads which were made using high ratios of chia flour (30%) had the darkest crust color (data not shown). Amaranth breads which were prepared from the lowest ratio of amaranth flour (10%) had the lightest color for the crumb and crust.
These findings agree with Alvarez-Jubete et al. [16] who found that the replacement of potato starch by each of quinoa and amaranth significantly exhibited darker color for the crumb and crust (P<0.05) in comparison with the control. No significant differences between quinoa and amaranth breads were determined for the crumb color, whereas quinoa breads had darker crust color. Also, Steffolani et al. [30] reported that GF bread color was affected by the addition of 15 g chia flour and this flour led to a decrease in the L values of the bread crumb and an increase in the values of a and b.
Sensory evaluation of breads
The formulations prepared at the highest hydrocolloid concentration (4%) were selected for sensory evaluation test due to their high values in bread evaluation. Table 4 shows that there are significant differences among the breads in terms of appearance, color, texture, taste, and overall acceptability; M3 gained the highest score (3.97) of appearance, while Q9 gained the lowest score (2.33) (even lower than 2.5 (neither like nor dislike)) in comparison to GFC (3) (P<0.05). Q3 and M6 gained the same score of bread color (4) which was the highest score for color evaluation. GFC gained the lowest score (2.53) (slightly exceed a score of 2.5) (P<0.05). M3 showed the highest score (4.30) of bread texture, while M9 showed the lowest score (2.63) in comparison to GFC (3.67) (P<0.05). Also, M3 showed the highest score (3.62) of bread taste, while GFC showed the lowest score (2.62) (P<0.05). Regarding overall acceptability of breads, M3 gained the highest score (3.84), while Q9 gained the lowest score (2.83) in comparison to GFC (3.03) (P<0.05).
It must be considered that the participants in the sensory evaluation test were not CP and were accustomed to eating wheat bread. Changes both in the flavor and in the texture of the GF breads adversely influenced overall evaluation [30]. In general, as expected, GF breads containing low ratios of pseudocereal flours (10%) gained the highest scores (M3, Q3, A3, and C3) among other breads. Pseudocereal flours may be introduced into a GF bread formulation without negatively affecting the sensory properties of the loaves. Moreover, pseudocereal flours represent feasible ingredients in the production of good-quality, healthy GF breads [16]. Bodroža-Solarov et al. [37] reported that the sensory characteristics of the supplemented breads are acceptable with 10-15% amaranth grain, while supplementation of 20% resulted in loaves with lower specific volumes compared to the control. Sanz-Penella et al. [38] indicated the level of amaranth flour addition in bakery products should not exceed 20 g/100 g to maintain product quality and preserve the principal nutritional benefit of this ingredient. In addition, Steffolani et al. [30] pointed out the addition of 15% chia did not change the overall evaluation of GF breads.
Increasing hydrocolloid concentration and the ratio of pseudocereal flours, generally, produced darker dough (data not shown). Moisture content of bread is associated with the increasing of the levels of gums as well as in the increase of the ratios of pseudocereal flours. The specific volume index of all breads significantly improved by the increasing hydrocolloid concentration except in some formulations of pseudocereal-containing GF breads, especially, in breads formulated with the highest ratio of pseudocereal flours (30%). The addition of the pseudocereal flours adversely affected in the specific volume of the pseudocereal-containing GF breads in comparison with the GFC breads, except for some formulations which were better than control. The use of hydrocolloids significantly showed a lighter crumb color in all bread formulations. The incorporation of pseudocereal flours into a GF formulation produced a darker GF bread crumb than that of control bread (P<0.05). Increasing the addition of the pseudocereal flours produced a darker color for the bread crust in all pseudocereal-containing GF breads. The addition of hydrocolloids increased the crumb hardness of all bread formulations. The inclusion of the pseudocereal flours with low and medium ratios (10% and 20%) significantly decreased the crumb hardness of the pseudocereal-containing GF breads in comparison to GFC breads, apart from some formulations had higher values of crumb hardness than that of their counterparts of the control breads. The inclusion of the pseudocereal flours with high ratios (30%) significantly increased the crumb hardness of the pseudocereal-containing GF breads in comparison to GFC breads, except for the 30% quinoa flour-containing breads.
It is important to develop novel, nutritious and healthy food products and bring them to the food market and gastronomy. CP can find a limited number of products in the market where especially in developing countries. Based on these facts, in this study, which was handled and put into practice, 39 different gluten-free bread were produced particularly for a disadvantaged group, CP. The findings obtained from the study will contribute to the food science and technology.