3.1. Mixolab Rheological Profiles
Table 3 shows the average results of farinographic tests conducted on rice flour blends with
Plantago psyllium seeds (PPS),
Plantago ovata seeds (POS) and
Plantago ovata husk (POH) at 0, 3, 6 and 9% levels of substitution. Rice flour dough had a hydration of 61.2%, a dough development time of 2.3 min, a dough stability of 1.45 min, a dough softening of 95 FU and a mixing tolerance index (MTI) of 128.4 FU. Both during the analysis of the farinographic profile and the full Mixolab profile, the resistance of the dough made of rice flour alone decreased in the first minutes of mixing. The resistance then stabilized after the rice proteins were hydrated reaching the target dough torque. This effect was eliminated with the use of
Plantago additives, which allowed the water to be evenly distributed in the dough in the first stage of mixing (
Figure 1). Mixolab water absorption indicates the amount of water needed for obtaining the dough of the consistency of 1.1 ± 0.05 N·m. Each of the additives significantly increased the water absorption of the blend compared to the control, which was rice flour without any addition. Blends with POH incorporation had the highest water absorption, while the lowest were those with PPS. At 9% of the rice flour substitution, the hydration increased by 22.4% (PPS), 23.9% (POS) and 60.3% (POH). According to Santos et al. (2020) [
26], the dough resistance at each stage of the Mixolab assay increases with the addition of psyllium if the dough hydration is not increased sufficiently. Thanks to psyllium’s ability to gel and absorb water an increased farinographic water absorption along with an increased proportion of Psyllium have also been observed in studies conducted by Kamaljit et al. (2011) [
12] and Mariotti et al. (2009) [
17]. Ferrero (2017) [
33] showed that the type of hydrocolloid used had a greater impact on water absorption than its share in the dough. Other farinographic parameters, such as dough development time and dough stability, indicate the flour’s strength. The addition of PPS did not affect dough development time. POS and POH additives extended dough development time along with their increasing share. With 9% POS addition, the dough development time was extended from 2.3 to 5.1 min and with POH to 8.8 min. The increase in dough development time was caused by an increased amount of fiber content, which requires longer water absorption [
21]. The dough stability was extended only in the case of 9% POH rice flour substitution (from 1.45 to 2.50 min); in other blends, the stability of the dough did not change when compared with the control. The increasing share of PPS contributed to the increased dough softening (to 6% addition) and increasing mixing tolerance index (up to 9% addition). Mixing tolerance index (MTI) is the difference in FU between the top of the curve at the peak and the curve position measured 5 min after reaching the peak; therefore, higher MTI values mean lower resistance of the dough towards mechanical damage [
13]. Sim et al. (2015) [
13] observed a significant increase in MTI with the addition of non-starch polysaccharides to the dough. On the other hand, in the present study, the increasing share of POS and POH in flour blends resulted in a decrease in both dough softening and MTI. This means that the gels formed by both the seed and the husk of
Plantago ovata are strong and resistant to mechanical deformation.
The results of the remaining parameters based on the complete Mixolab profile are presented in
Table 4. Graphs made with Mixolab are shown in
Figure 1. Point C2 measures protein weakening due to mechanical work and increasing temperature. In this study, PPS incorporation, regardless its level, resulted in lowering the point C2. This confirms that doughs with this additive was less resistant to mixing and temperature. On the other hand, with the increasing share of POS (up to 6%) and POH (up to 9%), C2 points were higher, confirming the stability of their mucilage. Cappa et al. (2013) [
15] and Mariotti et al. (2009) [
17] observed improved dough workability with psyllium addition to the gluten-free blends as the network structure of the added hydrocolloids affects dough rheological behavior. Mariotti et al. (2009) [
17] observed an improvement in the physical properties of the dough with the addition of psyllium resulting from the formation of a film-like structure and a continuous protein phase, as visualized by scanning electron microscopy and confocal laser scanning microscopy. Current research indicates that the
Plantago ovata seeds strengthened the structure of the dough similar to the husk.
Plantago psyllium seeds, on the other hand, caused the opposite effect. Point C3 measures starch gelatinization, point C4 indicates hot gel stability and point C5 retrogradation of starch in the cooling phase. The dough pasting properties and potential staling trends of bread are shown in
Table 4. Dough pasting properties (especially peak viscosity at C3 and C5–C4 setback) correlate with bread staling kinetics [
34].
Each of the additives used contributed to the reduction in the dough resistance at point C3, at its greatest extent after the addition of PPS. A decrease in the value of the C4 point was also observed along with an increasing share of all additives, the strongest in the case of PPS and POH. The value of C3 depends on the starch characteristics and amylase activity of the sample; decreased resistance of the dough at the C3 and C4 point means the increase in the activity of amylolytic enzymes. A significant reduction in the point C5 level was also shown along with an increase in the share of each of the additives. The highest decrease was recorded for POH (from 2.008 to 1.277 N·m), PPS to 1.376 N·m, and the lowest for POS to 1.568 N·m. The use of materials from the
Plantago genus contributed to reducing the tendency of the dough to retrograde (C5–C4). The reduced rate of starch retrogradation was particularly evident with the increasing proportion of POH in the blends. The staling tendency of bread during storage is strongly correlated with starch gelatinization properties, especially with peak viscosity and setback [
34]. Cappa et al. (2013) [
15] and Mancebo et al. (2015) [
16] showed that, if the dough is well hydrated, the soluble fiber from psyllium can soften the crumb, while insufficient hydration results in crumb hardening. The results of Aprodu and Banu (2015) [
14] showed that, when the amount of water was insufficient, the addition of psyllium increased the C4 and C5 parameters, while with the increased amount of water, they were lower. They explain this by the competition for water by starch and fiber. The addition of psyllium to the gluten-free dough results in the formation of a thin protein–hydrocolloid network, which contributes to the reduction in starch swelling and gelatinization. High water-binding capacity, the improvement of its distribution and retention contribute to the delay of starch retrogradation, improving the shelf-life of bread [
13,
15,
17].
3.2. Uniaxial Deformation
The addition of all
Plantago materials affected the behavior of rice flour dough during uniaxial deformation (
Table 5). The rice flour dough, which was the control sample, had a resistance to extension of 0.123 N, dough energy of 0.863 N·mm and extensibility of 10.806 mm. These values are very low compared to those of the wheat flour for which this determination is usually performed, proving the low elasticity of the dough from rice flour alone. A dough suitable for bread making must have a sufficient strength to be able to stretch during expansion due to fermentation gases. The peak force, i.e., resistance to extension, increased under the influence of increasing proportions of
Plantago additives. Their 9% shares improved dough resistance to extension at 87% (PPS), 158% (POS) and 290% (POH). The energy of the dough also increased under the influence of the increasing addition of products derived from
Plantago ovata. The 9% of seeds (POS) incorporation increased the energy of the dough by 128% and the husks (POH) by 237%. The addition of
Plantago psyllium seeds (PPS) had no effect on the dough energy. None of the
Plantago additives used had a significant effect on the dough extensibility. The rice flour dough was unable to stretch sufficiently, which is needed for leavened baked products. A strong network of the dough components is required for the gas retention. The increase in the resistance to extension and dough energy indicate an improvement in dough behavior, especially under the influence of
Plantago ovata products incorporation and the effect was dependent on the additive concentration. Improving the elastic properties of the dough allows the volume of the dough to increase during fermentation due to gas entrapment [
35].
3.3. Bread Quality
The quality parameters of gluten-free bread formulations containing different PPS, POS and POH levels are shown in
Figure 2.
Plantago incorporation had a strong influence on bread quality. The volume of bread obtained from 100 g of flour or a flour blend determines its technological efficiency. This volume was increased by all the applied
Plantago additives. The POH addition affected the bread quality to the greatest extent. The use of both
Plantago psyllium and
Plantago ovata seeds (PPS and POS) resulted in an increase in the volume of bread obtained from 100 g of flour to a small extent and regardless of their share in the blends. On the other hand, the increasing addition of
Plantago ovata husk (POH) resulted in a gradual increase in this parameter up to 27% with a 9% share of POH. The bread volume indicates how thin the dough structure may be stretched [
13,
16]. Aprodu and Banu (2015) [
14] also observed an increase in the loaf volume as a result of adding psyllium. The gelling ability of psyllium hydrocolloids allows the structure of the dough with its addition to strengthen the gas cells and support their expansion, leading to an increase in the bread volume [
33]. Loaf specific volume (ml/g) indicate the ratio of the bread’s volume to its weight. Due to the use of bread recipes that take into account the water absorption of the blends, higher water retention of blends made the breads heavier. Therefore, the use of
Plantago products contributed to a reduction in the bread’s loaf specific volume. As in the case of blends’ water absorption, the greatest effect was observed for POH and the lowest for PPS. In the results of Fratelli et al. (2018) [
10], it was possible to improve the loaf specific volume of gluten-free bread with psyllium addition using optimized dough hydration. Kamaljit et al. (2011) [
12], Mancebo et al. (2015) [
16] and Sim et al. (2015) [
13] also described the decrease in the specific volume of bread when POH was added to the dough. Water loss during baking (%) decreased with the use of
Plantago additives, proving their strong water-holding capacity. The increasing PPS and POS additives resulted in a gradual decrease in water loss, while the addition of POH significantly reduced water loss, regardless of the amount used.
The consumer acceptance of fresh bread and after storage expressed on a 9-point hedonic scale is presented in
Figure 3. Despite the lack of statistically significant differences between the scores of fresh bread, it can be noticed that all of the used
Plantago additives resulted in deterioration of product acceptance compared to the control rice bread. Among the
Plantago-enriched bread, the highest rating was given to bread with 3% PPS and the lowest with 9% POH. Gupta et al. (2014) [
3] also reported a decrease in overall quality score with addition of 5 g/100 g of POH. Using the
Plantago ovata husk incorporation to gluten-free bread of a level up to 3 g/100 g by Zandonadi et al. (2009) [
18] resulted in a good acceptance by individuals with and without celiac disease, and Kamaljit et al. (2011) [
12] observed a better overall acceptability of breads with 3% POH incorporation than control. After 24 h of storage the breads with 3 and 6% of PPS incorporation received a higher score than the control bread, while lower scores were given to samples with POH and 9% POS. Comparing the ratings of fresh and stored bread, it was observed that the addition of seeds (PPS and POS) did not contribute to the deterioration of the acceptance of the bread after storage, which occurred in the case of the control rice bread and with the addition of husk (POH).
3.4. Texture Profile Analysis
The textural properties of fresh and stored breads are shown in
Table 6. The hardness of the fresh bread with all the used
Plantago additives was lower than that of the bread without their incorporation. The elastic properties of
Plantago-enriched dough allow the dough to entrap gases, decreasing the breads’ hardness. The increasing share of PPS successively decreased the hardness of the fresh bread. After storage, the breads with the addition of PPS had a lower hardness than the control bread, but it increased with the increasing share of PPS. Bread made from rice flour alone and with a 3% PPS content decreased its hardness after storage and with 6 and 9% PPS increased its hardness within 24 h of storage. The POS incorporation to bread caused a decrease in fresh and stored breads’ hardness compared to control; however it was increasing together with the increasing share of POS. The addition 6 and 9% of POH significantly decreased the hardness of fresh and stored breads. According to research by Cappa et al. (2013) [
15], Mariotti et al. (2009) [
17] and Santos et al. (2020) [
26], a higher water content in the dough, such as in the case of dough with 6 and 9% POH, may help to keep the bread crumb soft during storage. The lower hardness of bread crumb may be also related to lower setback values [
16]. Breads’ cohesiveness is the ability to withstand compressive or tensile stress. It was not strongly affected by
Plantago seeds (PPS an POS) incorporation, a significant increase in breads’ cohesiveness was observed only with the 9% addition of POH. A slight reduction in cohesiveness after storage was observed for control bread, and with 9% of PPS and 3% of POH incorporation. Springiness is the ability of the crumb of the bread to spring back after deformation during the first compression. Fresh breads’ springiness increased slightly with the use of
Plantago additives (with the exception of 3% POS); after storage, breads with 6 and 9% POH addition were characterized by higher springiness than the others. Breads’ chewiness was decreased by
Plantago products incorporation, mostly with the use of 3% of POS and 9% of POH. In the case of the control bread and the those with the addition of 3 and 6% of PPS and 3% of POH, a reduction in the chewiness of the breads after storage was observed. In the remaining samples (9% PPS, each with POS addition and 6 and 9% POH), the chewiness after storage increased. The results of Filipčev et al. (2021) [
25] indicate that the addition of psyllium caused a reduction in the crumb hardening rate of buckwheat–carob bread and Santos et al. (2021) [
27] observed that psyllium addition to gluten-free bread delayed the loss of its cohesiveness and springiness. The
Plantago additives used did not significantly affect the resilience of breads’ crumb.
Significant Pearson’s correlation coefficients between the variables are shown in
Table S1 of the supplementary data. A significant, positive correlation was found between farinographic parameters, water absorption, dough development time and dough stability, as well as between dough softening and MTI. Dough hydration was positively correlated with the C3–C4 setback, dough resistance to extension, dough energy and bread volume per 100 g of flour and negatively with Mixolab torque at C4, C5, C5–C4 setback, water loss during baking and hardness of fresh bread. This confirms the positive effect of using highly water-absorbing additives for gluten-free bread on the improvement of dough elasticity and reduction in bread’s hardness. Dough resistance to extension was positively correlated with the C3–C4 setback denoting the rate of amylolysis. There was also a positive correlation between the value of the dough resistance at point C2 (protein weakening during mixing and heating) and the dough energy. Bread hardness was related to the value of the dough resistance at the C5 point, which was responsible for the retrogradation of starch during cooling.