## 3 Results and Discussion
### Sensory Characteristics
The Control group reached the highest values and the NITRASC the lowest, whereas the pomace groups had intermediate values statistically similar to them (Table 7). The effect of the grape pomace was not statistically different from the effect of the synthetic antioxidants, but it was not sufficient to decrease the off-odor developed in the Control samples (Table 7). The results followed a roughly similar trend to pH and \(b^{\star}\) (Table 3). In fact, Figure 1b shows that both traits were closely related to pH, \(b^{\star}\), and protein oxidation. In fact, there were significant correlations between the off-odor and pH (0.545, \(p\) = 0.013), and between off-odor and off-flavor, and \(b^{\star}\) (0.533 and 0.506, \(p\) = 0.016 and 0.023, respectively) and also between off-odor and off-flavor, and protein oxidation (0.603 and 0.591, \(p\) = 0.005 and 0.006, respectively). Both characteristics were scarcely correlated with the volatile compounds; they were only correlated with 2-phenylacetaldehyde (R: 0.463 and 0.530, \(p\) = 0.040 and 0.016, respectively), and the off-odor also correlated with disulfide, methyl 2-propenyl (R: \(-\)0.499, \(p\) = 0.025). This suggests that the off-odor and off-flavor (both with low values) were not caused by any compounds from the grape pomace. Juiciness reached the highest values in the NITRASC group and the lowest in the 3%Pomace group, which also had the highest value for the defective texture (Table 7). Conversely, when the pomace was added at 0.5%, no detrimental effect appeared in the texture traits. This reveals that the pomace added at 3% may be an issue for consumers since both traits are key parameters for the quality of meat products, whereas at 0.5%, it might not be an issue. A previous study reported an abnormal appearance and flavor in dry-cured sausages produced with grape-seed-based commercial extracts at 0.5%, either a dry one or a leucocyanidin one [3], which led to ruling out both extracts. In our study, the grape pomace at 0.5% did not show such an effect, probably because it was not as concentrated as those extracts. To sum up, the pomace was not as effective as the synthetic additives at improving lean and fat color and at preventing off-odor and off-flavor development, and the only  
Figure 1: Projection of the samples (**a**) and variables (**b**) onto the space defined by the first two principal components (PC1/PC2) extracted from the variables in Tables 1–5. \(\blacklozenge\): Control; \(\blacktriangle\): NITRASC; \(\blacklozenge\): 0.5%Pomace; \(\blacklozenge\): 3%Pomace. difference caused by the pomace addition with respect to the Control samples was an increase in the defective texture when added at 3%, without sensory differences when added at 0.5%. The lack of a detrimental effect of the lower pomace dosage on the sensory characteristics (and therefore on what consumers are expected to perceive) and its benefits to prevent lipid oxidation suggest that it could be a feasible option to improve the sausage quality by adding a grape by-product processed without chemicals. Conversely, the higher pomace dosage, with a detrimental effect on some key sensory characteristics and a lack of benefits, would not be advisable.