3.1. CIELab Colour
Table 3 provides the lightness (L*), redness (a*) and yellowness (b*) values of Spanish and Frankfurt reduced-fat sausages. There were statistical differences for all parameters, with the exception of the angle hue. There was a reduction in lightness in both products and in response to both strategies (
p < 0.001). This was expected, as the increase in the fat proportion contributed to an increase in L* value [
22] that was likely due to a major light reflection. Šojić et al. [
22] also observed this phenomenon in cooked sausages made with 5% inulin, where these sausages exhibited significantly lower L* values than did the controls. The authors of that study showed that colour is a very interesting parameter for cooked meat products, as consumers associate this type of meat product with a bright and characteristic pink colour. Similar results were found by Ryu, Shim, & Shin [
23] in a study in which grape skins and seed pomace were added to cooked pork sausages. It was observed that the L* value was lower when doses were higher, although they did not reduce the fat content.
Riazi et al. [
24] evaluated the colour of cooked beef sausages that were treated with a lower concentration of nitrites from red grape pomace (2%). This treatment resulted in a product with L*, a*, and b* values that were significantly decreased in comparison to those of the control. In agreement with previous studies, they suggested that browning of sugars and the oxidative browning of the tannins that are present in grape pomace could be responsible for the product darkening. Browning reactions are typically accelerated at high temperatures, and this can result in an increase in the extent of the Maillard reaction that occurs in the sausages containing grape pomace powder. A similar trend was observed in regard to a* by Ryu, Shim and Shin [
23] when grape skins and seed pomace were added to cooked pork sausages. Sausages supplemented with 0.5% and 1% grape products exhibited reduced CIELab a* values, and these could be related to the anthocyanins present in grape skin. Similar results were observed by Choi et al. [
25] when pork fat was reduced and partially substituted for using a mix of grape seed oil (0%, 5%, 10%, and 15%) and 2% rice bran fibre.
Contrasting results were found by Šojić et al. [
22], who observed that cooked sausages made with 5% inulin exhibited a significantly higher a* value compared to that of the control. This was expected, as the increase in the fat proportion contributed to a decrease in a* value. Additionally, these results were not unique, as they are also observed in this study.
Other authors also observed a reduction in b* after the addition of vegetable fibres [
21,
24]. Mainente et al. [
26] revealed that flavonoids are the molecules that are primarily involved in the colour of grape pomace, and it must be considered that the colour of anthocyanins could vary from red to blue depending on the pH value. However, phenols can influence the colour of meat based on their antioxidant activity, there they primarily act on myoglobin [
27] but can also influence lipid oxidation. The variation of a* value appears to be related to lipid oxidation, while changes in the b* value could be correlated to the oxidation of heme [
26].
3.2. Texture Profile Analysis
Frankfurt sausages exhibited no differences (
Table 4) between the control and fibre-replaced groups (
p > 0.05). Šojić et al. [
22] observed similar results in cooked sausages made with 5% inulin, and Han and Bertram [
28] observed similar results using 2% inulin. The authors remarked that the results could be explained by the protein content of both groups of sausages, as these contents were highly similar and appeared to play a major role in the tenderness of the cooked sausages. Ryu et al. [
23] also did not observe differences in a study where grape skins and seed pomace (0.5% and 1%) were added to Chinese-style cooked pork sausages, and Huang et al. [
29] also did not observe any differences.
Other studies have found that hardness is higher in fibre sausages than it is in controls; however, inulin was combined with other fibres such as oat and wheat fibre [
30]. It has been reported that insoluble fibre can increase the cohesiviness of meat products by forming an insoluble three-dimensional network that is capable of modifying the rheological property of the continuous emulsion stage [
31]. The same results were observed by Selgas et al. [
32] when they studied inulin (in powder form and as gel) that was incorporated into the elaboration of reduced-fat (30% less than normal content) cooked meat sausages. In this research, the authors speculate that the greater hardness is due to the lower amount of fat. Despite this, the addition of inulin caused a significant softening of the sausages when it was added in gel form.
Spanish sausages supplemented with grape pomace (SR2) exhibited reduced hardness, gumminess, and chewiness (
p < 0.05) compared to these values in the controls. Frankfurts were prepared in a smaller minced meat batter than were Spanish sausages, and this resulted in more homogeneous products and could explain the differences between the products. Elleuch et al. [
33] (2011) proposed that the effectiveness of various fibres in ground meat mixtures and emulsions is usually affected by particle size and the type of ions present in the system [
28]. The different characteristics of dietary fibres, such as molecular weight and hydrophobicity, cause differences in their physicochemical properties, including water solubility, viscosity enhancement, opacity, surface activity, and binding capacity [
34]. However, this characteristic could be interesting, as products elaborated with meat from non-castrated male pigs are hardener than those made from castrated pigs, likely due to the lower fat content (and possibly also lower WHC) of the raw material. Based on this, higher processing losses may occur, and this can result in drier and harder final products [
4].
These results are similar to those of Wan Rosli et al. [
35] who examined chicken meat frankfurter sausages that had their fat replaced by oyster mushroom powder (rich in β-glucan; up to 6%). They observed that the hardness attribute was significantly lower than that of the control. It is possible that the results from the present study are related to the presence of higher levels of β-glucan and grape pomace fibres. Gumminess and chewiness are secondary parameters that depend on the hardness, and based on this, they behave similarly [
32]. Selgas et al., [
32] observed that a reduction in fat caused a decrease both in the force and in the work of cutting. This decrease in hardness could be related to the presence of fibre incorporated in the form of an aqueous solution. The author observed that the composition of the fibre sausages contained more water (10%) than did sausages manufactured by other authors, who found an increase in these texture parameters. Differences in composition result in a different protein:fat:water ratio. If the ratio is a determining factor in the consistency of the resulting meat gel, it is possible that the higher fat content in Spanish sausages formulation influenced the texture differences that were observed. Additionally, SR2 possessed half the concentration of inulin. This is consistent with the findings of Selgas et al. [
32], who reported that there was a tendency to decrease hardness and shear force as the concentration of inulin increased. Additionally, the literature described an inverse correlation between the shear strength of the samples and the amount of white grape pomace powders that were added [
26].
Both products exhibited no differences in adhesiveness and resilience (
p < 0.05). Other studies observed similar results in fat-reduced Frankfurt sausages [
31,
34].
Cohesiveness and elasticity were not affected by fibre replacement in Frankfurter sausages, while there was reduction in cohesiveness in the Spanish sausages SR1 and SR2 (
p < 0.05) and in elasticity in SR1. Similar to results observed for Frankfurter sausages, Selgas et al. [
32] found that the springiness and cohesion in cooked meat sausages were very similar across all batches. In accordance with this, Wan Rosli et al. [
35] found that the addition of up to 6% concentration of oyster mushroom powder led to results that were similar to these of the control or of Barretto et al. [
30] when only 0.58% wheat fibre was added.
The cohesiveness of the control samples was generally higher than that of the fibre groups in regard to Spanish sausages. Similar results were found when meat and fish products were enriched with grape pomace [
26]. According to Han and Bertram [
28], the majority of previous studies have shown that a reduction of fat in emulsified meat products leads to a firmer texture due to the presence of more tight connections among the meat particles and a more dense structure caused by the reduction in fat. This flavours increased hardness, cohesiveness, and chewiness; however, the doses used in this study did not result in any texture (Frankfurt sausages) or a reduction (Spanish sausages) in texture.
3.3. Sensory
Figure 2 shows the results delivered by the principal components analysis. Principal component 1 (PC1) was the most relevant accounting for 44.6% of the total variability. The PC1 was positively related with overall rating and colour intensity and negatively related with boar taint odour and boar taint flavour. The results for both R2 formula products placed then on the right side of the chart, SC and SR1 products on the left side, and FC and FR1 products on the right side, but in an intermediate position. SR2 and FR2 took the best position in relation with a low boar taint odour and flavor perception; conversely, Spanish C and R1 score the worst position. Principal component 2 (PC2) explained 24.1% of the total variability. The PC2 was positively related with colour intensity and brightness, and negatively related with cohesiviness, homogeneus colour, sausage odour and flavour. Spanish sausages occupied a less negative area, while Frankfurt sausages (FC, FR1 and FR2) occupied the negative extreme. Frankfurt sausages are related with homogeneous colour and cohesiviness. The R2 sample was closely related to colour intensity, probably due to its grape pomace content.
The sensory evaluation results are presented in
Table 5 and
Table 6. Reduction of brightness was only perceived by a trained panel in FR2 (
p < 0.05). SR2 presented higher values than SR1 (
p < 0.05). Colour changes were only detected on R2 for both products, and these values were higher than those of the control and R1 (
p < 0.001). As observed from CIElab results, the presence of anthocyanins and tannins from grape pomace could be related to these results.
Morin et al. [
36] found that consumers prefer low brightness. Apparently, this was due to consumers associating lighter colour with a higher fat content, or it may simply be that they did not like lighter sausages as much.
Šojić et al. [
22] cooked sausages made with 5% of inulin, and they found that the appearance did not differ significantly between groups and also that the colour was significantly darker in the reduced sausages compared to that of the controls. The homogeneity was not affected by these treatments (
p < 0.05).
Sausage odour and flavour were reduced in both products for R2 treatment, and they were reduced only in odour for FR1 (
p < 0.05). This parameter measures the intensity of typical sausage odour and flavour in a commercial product with no boar taint. This reduction is related to grape pomace presence in the formulation (R2). In addition, there was an increment in SR1, due to the masking effect of the reduction fat strategy. Similarly, Šojić et al. [
22] cooked sausages made with 5% of inulin, and these sausages exhibited a significantly higher score for “odour and taste” attributes than the scores of the controls.
Off odour and flavour were present only in the SR2 group. Mainente et al. [
26] remarked that phenols and organic acids typically give rise to sensory properties such as bitterness, astringency, and acidity, and studies have described an ‘intense, typical fermented odour’ of grape skin powder. However, punctuation was low (0.4 and 0.3 in 10 scales), and bitterness was not detected. This could be due to the high protein content in meat-based preparations that could prevent the interaction of phenols with salivary proteins, ultimately reducing astringency [
24]. In regard to the principal components of the additives, Selgas et al. [
32] concluded that inulin could be incorporated into cooked meat products as powder or preferably as a gel at concentrations of at least 2.5% and 5% without important sensory modifications, and this was in agreement with results presented in our study.
None of the analysed texture parameters exhibited any differences compared to those of the control group, with the exception of FR2, which yielded high hardness and chewiness values. Similar results were observed by Šojić et al. [
22] for cooked sausages made with 5% inulin, where they found that the scores for sensory evaluated textural properties for sausages supplemented with vegetal fibre were not significantly different (
p > 0.05). Inulin exhibits a high capacity to bind water and forms gels that are firm, soft, and stable. Based on this, it is likely that inulin addition contributed to the formation of optimal sensory–evaluated textural characteristics of sausages even when the fat content was reduced, and this was also observed in our assay. In contrast, Selgas et al. [
32] found that the presence of inulin in powder caused an increase in hardness.
Boar taint odour and flavour were reduced in FR2 (66.7% and 70.8%, respectively), SR1 (35.7% and 49.1%, respectively), and SR2 (85.7% and 87.3%, respectively;
p < 0.05). Frankfurt sausages exhibited lower boar taint scores (3.0 and 2.4) than did Spanish sausages (5.6 and 5.5). This is likely due to the Spanish sausages possessing a higher fat content. Additionally, Frankfurt is minced and heated for a longer period of time during the cooking process. Processing and commercial additive mixes can provide a “smoke” aroma. Previous studies have also demonstrated that cooking could reduce boar taint perception [
37]. The reduction of boar taint is expected due to reduced formulations had 52% and 34% less of fat (Frankfurt and Spanish sausages respectively), and androstenone and skatole are lipophilic components [
3]. Previous studies had demonstrated that using 10% concentrations of tainted meat in products results in high levels of consumer acceptance [
38]. In this sense, Mörlein et al. [
39] found that up to 33% of meat and fat from carcasses possessing skatole concentrations of up to 0.3 μg/g and androstenone concentrations of up to 3.8 μg/g in melted back fat may be used for the production of Frankfurter-type sausages. This is in accordance with the results of Hemeryck et al. [
40], who confirmed that mixing patties with Gilt raw materials processing these into Frankfurter sausages or into restructured ham can potentially reduce rejection by consumers.
The masking sensory capacity was higher for FR2 and SR2. Although some organoleptic characteristics of this strategy are slightly different from those of control products, other studies have observed that the global acceptability (including colour, flavour, tenderness, and odour) of raw and cooked chicken hamburgers was increased by the addition of red grape pomace powders at up to 2% concentration [
41]. In support of this, Riazi et al. [
24] also indicated that pomace from red grapes at concentrations of 1% and 2%
w/w improved the sensory properties and particularly the taste of the meat. Therefore, both strategies, and particularly that of R2, appear to provide good options for supplementing meat products from non-castrated male pigs.