3.3. The Quality Parameters of Breads and Their Evolution during Storage
-values for all the physical and textural parameters of the bread types with respect to storage time are reported in Table 4
The specific volumes and weights of the loaves were significant for each of the two factors of variability (type (A), storage time (B), and their interaction (A × B), even with different p
≤ 0.001 for storage time, p
≤ 0.01 A × B interaction, and p
≤ 0.05 per type; see Table 4
The results of the physical and textural properties of the industrial breads in the MAP conditions during 90 days of storage are shown in Table 5
and Table 6
No significant differences in specific volumes were shown among the bread samples, regardless of the type and level of sea salt (Table 4
These findings agree with those reported by [23
], but they disagree with those reported by [24
]. Additionally, no significant differences in specific weight were observed among the controls and other bread samples or during storage time. The addition of different types and quantities of sea salt did not decrease bread yield. After 60 days of storage, the specific weight decreased.
The ratio between the height and diameter of the loaves used in the baking industry to parametrize possible dough failure was significant (p
≤ 0.001) for all the factors and their interaction (Table 4
). At time 0, control A was found to have the greatest h/d ratio (approximately 4.5) due to the addition of ordinary sea salt (Table 5
). The other bread samples, as expected, showed a lower ratio during storage, especially the bread samples containing less traditional sea salt and sea salt with reduced Na+
. These findings agree with those reported by [28
Significant differences were found for loaf porosity among the types (p
≤ 0.001) and the A × B interaction (p
≤ 0.05), but not for storage time (B) (Table 4
). After baking (t0), almost all the types, except for 2B, showed proper development of crumb porosity. Starting from 15 days of storage, the performance of 2A also slightly decreased (Table 5
Significant differences were found between the types (p
≤ 0.001) and storage times (p
≤ 0.01 and p
≤ 0.001, respectively) but not for A × B interaction as regards internal structure and top crust thickness (Table 4
). As for internal structure, only control A had an irregular structure over the whole storage time. Similar results were reported by [28
As for top crust thickness, for up to 30 days of storage, no remarkable differences were recorded among the types (mean value of 3.8 mm); after 60 days, the values decreased up to 2.67 mm for control B.
No significant difference was highlighted for basis crust thickness between the types, the different storage times, and their interactions (Table 4
). Almost all the bread samples exhibited a mean value of basis crust thickness of 4 mm. These findings agree with those reported by [28
Three of the five parameters of texture profile analysis (hardness, gumminess, and chewiness) were always significant (p
≤ 0.001), while resilience and springiness were significant per type and storage time (p
≤ 0.001), but not for A × B interaction (Table 4
). The two control breads (1A and 1B), as expected, showed lower values for the first three parameters. Starch retrogradation (i.e., the recrystallization of polysaccharide in gelatinized starch) is believed to be the main cause of crumb firmness change during storage [56
Textural data highlighted high values of hardness, with significant differences among the samples, as reported by [39
], and storage time (Table 6
The hardness values, as expected, increased as the storage period progressed. As regards the bread samples, control A reported the lowest values during the entire storage period. Up to t30, the two controls, albeit with statistically different values, recorded the lowest hardness values. From t60, the control A values remained low, while the control B values increased until reaching about 55 N at the end of storage.
No significant differences in springiness or resilience were shown among the bread samples and during the storage times, whatever the type and level of salt (Table 6
). Up to 30 days of storage, no remarkable differences were recorded among the breads (mean value of 5.7 mm); after 60 days, the values of springiness increased by up to 7.0 mm. These findings do not agree with those reported by [39
As for resilience, the average value was around 0.80. During the entire storage period, the two controls showed higher resilience values. From the end of the baking to the end of storage, resilience values decreased slightly. These findings agree with those reported by [39
With regard to gumminess and chewiness, they increased progressively with increasing storage times and with decreasing salt content, regardless of type, until they reach the maximum at t90 for 2B (58.0 and 426.0). During the entire storage time, the two controls always showed the lowest values, and were similar to each other, except for t90.
Water activity (aw
) and moisture content were significant compared to all the factors of variability (Table 7
). As for pH and HMF, they were significant compared to all the factors of variability (p
≤ 0.001; Table 7
Crumb lightness and redness were significant compared to all the factors of variability. Crumb yellowness was significant for bread (A) and storage time (B) (p
≤ 0.001) but not for their interaction (A × B) (Table 7
). The effect of the addition of sea salt with reduced Na+
on the L
* parameter of crumb during the entire time storage was not significant (Table 7
Chemical properties of the breads during the storage time are reported in Table 8
Crumb aw is an important parameter of food processing and conservation technologies that comes into play for food stability and safety. It indicates the amount of free water not linked by bonds with the soluble constituents of the food, i.e., the water that can participate in chemical, physical, biological, and enzymatic reactions.
In general, water activity is a relatively easy parameter to measure, which can be an advantage, especially in the food industry [57
value ranged from about 0.88 for Control A at t90, to 0.93 for 2A at t0 (Table 7
). Similar values have been reported by [55
After baking, and up to t15, there is no difference among the breads. From t30, water activity decreases for both controls. From t60 to the end of storage, aw
decreases slightly for all the types. At t90, only the aw
value of Control A is lower than the other types. Moisture content ranged from about 35.5–38.4% at the beginning (Table 8
). Bread samples containing natural low Na+
sea salt show the highest moisture content, and significant differences were found between all the breads. During storage, the breads with NaCl generally show the highest levels of moisture, and at 90 days of storage, the moisture content decreased, ranging from 35.3–32.4%. No significant differences were found between control B and samples 1B (1.22% and 0.25% Saltwell®
) and the bread samples with the lowest levels of salt (2A and 2B).
The pH ranges from 5.36 to 5.93 at the beginning; at 90 days of storage, it ranges from 5.73 to 5.82 (Table 8
). The variability seems to be more related to the storage time rather than to the different levels and salts used in the recipe. Similar trends were reported both for durum wheat bread with yeast extract and fortified with fiber [28
HMF is a widely used compound as heat induces the chemical index generally used for monitoring thermal abuse [58
]. In bread and in other baking products, HMF is used to monitor the heating process, and several factors influence its formation, such as manufacturing conditions and recipe [57
]. Even if the toxicity risk of HMF is still debated, nowadays, HMF is under evaluation as an emerging ubiquitous processing contaminant since there is evidence to suggest that HMF and its metabolites may have harmful effects on human health [60
Among foods, coffee and bread contribute the most HMF exposure, about 85% of total intake [64
The HMF parameter was significant compared to all the factors of variability (p
≤ 0.001; Table 7
). HMF levels at the beginning ranged from about 23 to 39 mg/kg of dry matter (Table 8
), and significant differences were found between all samples. These levels were lower than those reported for durum wheat bread with KCl and taste enhancer [28
], and it is known that differences in water content in the leavening and/or baking time and the ratio between crumb and crust of the loaf could influence HMF content [58
]. Bread samples with the lowest levels of natural low Na+
sea salt (2 B) had the lowest HMF content. During storage, a decrease in HMF amount was highlighted, though the trend in decrease was not regular. Generally, the bread samples with the lowest levels of salt had the lowest HMF content due to the effects of a high level of NaCl on starch degradation and yeast growth, resulting, in both cases, in higher levels of Maillard indicators [65
]. At 90 days of storage, this parameter ranged from about 20.6 to 25.5 mg/kg of dry matter. The HMF trend during storage was similar to those reported by [28
], suggesting that HMF decrease is more related to storage time rather than recipe.
During storage, crumb redness in the traditional sea salt (control A) test slowly decreased. After t15, the a
* value begins to decrease for all breads (Table S1
3.4. Sensory Evaluation
The addition of different types and quantities of sea salt had little effect on the sensory characteristics of the bread sample. Table 9
reports the ANOVA results of sensory data and the bread attributes, which significantly differentiated at different p
≤ 0.05; p
≤ 0.01; p
≤ 0.001), at each sampling. Mean values were reported only for significantly different attributes.
At t0, the bread samples were evaluated similarly by panellists, with the exception of the “salty” attribute. Obviously, the control breads (Control A and Control B) had the highest value of saltiness.
At 15 and 30 days of storage, the samples were significantly different for the attributes sweet, salty, bread flavor, and overall evaluation. The 0.15 NaCl sample showed the highest intensity of sweet taste, while the control samples, as expected, had the highest score of salt, bread flavor, and overall evaluation.
At 60 and 90 days of storage, the attributes of sweet, salty, and overall significantly differentiated the bread samples. The 0.15 NaCl and 0.15 Saltwell® bread samples had the highest intensity of sweet and the lowest of the attributes salt and overall. The control samples showed the highest intensity of the attribute overall.
The different levels of sea salt did not influence the attributes of texture (i.e., softness), as reported by [28
reports the sensory attributes which significantly differentiated (p
≤ 0.05) during the 90 days of storage.
Control A showed a significant decrease during storage but only for the attributes of humidity and softness. At 0 and 15 days of storage, Control A had the highest intensity of these two sensory attributes.
Control B showed a significant decrease during storage for the attributes of elasticity, humidity, and softness. These attributes began to decrease after 30 days of storage.
Sample 2A showed a significant decrease only for the attribute humidity, while bread samples 1A, 1B, and 2B did not show any significant differences during the 90 days of storage.
During storage, the bread samples did not develop off-odors or off-flavors in agreement with those reported by [28
3.5. Multivariate Statistical Analysis
Principal component analysis (PCA) is a multivariate analysis that allows the reduction and interpretation of large multivariate datasets with some underlying linear structure. In this trial, it was carried out to determine if and which salt (type and concentration) had an influence on the qualitative and sensory traits of the breads. The PCA included the following 24 dependent variables: specific volume, specific weight, h/d ratio, crumb porosity, hardness, gumminess, chewiness, springiness, resilience, water activity, moisture, pH, HMF, acidity, and crust and crumb color parameters (as L*, a*, b*, h, C).
The two main factors accounting for 56.92% of the total variance were PC1 and PC2 at 37.08% and 19.84% (Figure 1
There are two types of trends on the first axis: (1) based on salt content, the groups shift from the negative to the positive section, from the breads with minimum salt concentrations (2A and 2B), to those with more (Control A and Control B) (Figure 1
); (2) based on days of storage, from the longest (t90) to the shortest (t0) (Figure 1
). Convex hulls were used to highlight these trends. They can be defined as the intersection of all convex sets containing a given subset of a Euclidean space. The convex hull of a set of data is the smallest convex set that contains it.
The variables that determined these trends were resilience, crust color (as a*, C), h/d ratio, crumb color (h), and moisture, which showed the highest positive loading values (0.272, 0.230, 0.227, 0.228, 0.218, and 0.209 respectively), chewiness, hardness, gumminess, and springiness, with the highest negative loadings (−0.314, −0.311, −0.309, −0.263, respectively).
The groups also showed a gradient with respect to the days of storage, if PC2 is observed: from the positive scores of the longer storage time to the gradually lower scores of the shorter ones (Figure 1
The variables that positively correlated with PC2 were crust color parameters (L*, h, b*) and moisture (loading values, 0.367, 0.334, 0.271, 0.292, respectively). Moreover, PC2 negatively correlated with aw, specific volume, and crust hardness (−0.294, −0.266, −0.248, respectively).
In summary, sorting the data according to the first two axes distributes the groups in relation to the lowest salt concentration with the maximum storage time, and so on, up to the breads with the highest salt concentrations with the shortest storage times.
PCA loadings did not have the necessary strength to affect the net separation of groups, but this seems to support the hypothesis that the different breads and salt concentrations do not lead to substantial differences in the overall qualitative characteristics and acceptability of the product.