**4. Discussion**

Among batches, variations in moisture content were slightly lower than some described by other authors on frankfurters [10,33,34]. Differences in protein content between control sausages and the other batches (SF-25 and SF-50) could be explained by the presence of small lean portions in pork backfat. Other authors have reported frankfurter sausages with protein content between 12.5–15% [10,33,34]. The range of ashes content was higher than those shown by other authors [10,33,34], who indicated values in the range 2.58 to 3.39%. These differences could be explained by variations in the amount of sodium caseinate, salt, and commercial mix among recipes of the studies.

Previous studies have noted the importance of animal fat in this type of meat products, because it plays a significant role in flavor intensity, juiciness, and tenderness. In comminuted meat products and frankfurters, values of around 26% have been found [13,35], but other lower values have been reported as 20.8% in breakfast sausage [16], 14.41% in sausages elaborated with microencapsulated fish oil [34], or even 10.3% for low-fat sausages elaborated with Konjac gel [10]. Regarding cholesterol content, it is remarkable that frankfurters formulated with linseed had the lowest cholesterol content with respect to the control sausages (25.08 vs. 17.23; *p* < 0.05), despite the fact that this result was expectable, because cholesterol is inherent to animal tissues, hence it should not be found in linseed. This is an important improvement from a nutritional point of view.

Overall, the individual FA in the following order (oleic > palmitic > linoleic > stearic) match those reported in earlier studies of frankfurters [33,34,36]. It should be noted that a noticeable SFA reduction (in the range 3.4–7.99%) was achieved as a result of the replacement of pork backfat by linseed oleogel. A similar reduction range (3–8%) was obtained with sausages containing fish oil [37]. Other authors have reported higher reductions in SFA content when replacing pork backfat with fish and/or vegetable oils, e.g., 4.5–11.8% [34] and 3–25% [38] in frankfurter sausages.

Reductions in the main SFA (palmitic and stearic acids) have important and beneficial effects on human health in accordance with the recommendations of WHO [3]. Recommendations include reducing SFA intake, due to the raise of low-density lipoprotein (LDL)-cholesterol producing atherogenic and hypercholesterolemic effects [39]. This result may be explained by the fact that linseed has a lower SFA percentage than pork backfat. These findings match those mentioned in previous reports, in regard to the fat substitution in frankfurters with vegetable oils [10,33,34].

On the other hand, lipid oxidation affects color, texture, nutritional value, taste, and aroma leading to rancidity, which is responsible for off-flavors and unacceptable taste, which are important reasons for consumer rejection [40,41]. Lipid oxidation is a rather complex process, in which unsaturated fatty acids react with molecular oxygen via free radical chain-forming peroxides [42]. The first auto-oxidation is followed by a series of secondary reactions, which lead to lipid degradation and the development of oxidative rancidity products. However, lipid oxidation (Thiobarbituric acid reactive substances values) were not determined in our sausage samples.

Variations in PUFA content, as well as PUFA/SFA and *n*-6/*n*-3 ratios, have important implications for the development of healthy meat products, as it is well known that balanced ratios of *n*-6/*n*-3 and PUFA/SFA have positive e ffects on human health. E ffectively, excessive *n*-6 PUFA content and therefore greater *n*-6/*n*-3 ratios can result in diseases, such as cardiovascular pathology and prostate cancer, whereas an excessive increase of *n*-3 PUFA exerts suppressive e ffects [43]. However, western diets are increasing the amount of *n*-6 PUFA. Higher proportions of *n*-3 PUFA have been recommended by European Food Safety Authority (EFSA) [39] and Food and Agriculture Organization (FAO) [44] in order to decrease the *n*-6/*n*-3 ratio for the prevention of above-mentioned diseases. The present results agree with the findings of other studies in which the inclusion of olive and fish oils, mixture or alone, diminished the *n*-6/*n*-3 ratio in frankfurters [34] and beef burgers [45].

The color parameters of batches formulated with linseed oleogel are strongly related to color characteristics of raw ingredients used in the formulation. The increase in luminosity and yellowness may be explained by the yellow color of linseed oleogel and is associated with the amount used in the elaboration. Other authors have reported similar results in di fferent meat products, replacing pork backfat with vegetable oils (olive, canola), such as frankfurters [34], breakfast sausages [16], pate [46], or pork patties [47]. On the contrary, Barbut et al. [16] indicated a significant decrease in the luminosity of breakfast sausages elaborated with canola oleogel. The significant (*p* < 0.001) reduction of redness values in SF-50 (9.06) and SF-25 (10.15), with respect to the control samples (12.50), seems to be consistent with the study of Lopez-Lopez et al. [9], which found that the substitution of pork backfat by olive oil decreased the redness value in frankfurters.

One of the main issues in the reformulation of meat products, such as frankfurters or sausages, is regarding textural properties, because some of these properties were quite di fferent in new products than original products. For instance, Barbut et al. [16] indicated that the replacement of beef fat by canola oil in comminuted products led to a firmer and higher rubbery product, which is unsatisfactory. However, in our study, changes in the sausage textural profile were not remarkable, in agreemen<sup>t</sup> with [33], who observed no influence on the hardness or chewiness of frankfurters with olive oil replacing pork backfat. However, this issue is controversial, as the increase of hardness and firmness in frankfurters with olive oil instead of pork backfat [48,49], as well as no influence [50], has also been reported. In addition, in the present study, a negative correlation between hardness and fat content was found (*r* = −0.560; *p* < 0.01). A similar behavior was noticed for gumminess and chewiness (*r* = −0.444 and −0.428, *p* < 0.05, respectively) while adhesiveness was positive, correlated with total fat content (*r* = 0.414, *p* < 0.05).

Modifications in the formulation resulted in global perception being significantly di fferent among samples. Thus, samples with linseed oleogel were assessed with a lower preference. The overall acceptability for sausages depends on many attributes and their interactions. Panelists showed significant di fferences regarding the sausages with substitution of pork backfat, with overall acceptability scores of 2.06 ± 0.17, 2.69 ± 0.19 and 3.19 ± 0.17 for CO, SF-25, and SF-50. Although the sausage control showed more acceptability than the modified sausages, the three formulations scored in the positive part of the hedonic scale used in this study, obtaining a positive acceptance. Barbut et al. [13] noticed that there may be a hardness and juiciness tipping-point based on the ethylcellulose (EC) concentration in the organogel, where frankfurters containing organogels of lower EC content resembled those prepared with beef fat (control group). In addition, they reported that organogels with higher EC concentration-yielded frankfurters that resembled the control group, potentially allowing for the custom formulation of hardness and other sensory characteristics. Organogel samples formulated with sorbitan monostearate can further help tailor textural and sensory characteristics of emulsion type meat products by adding plasticity to the organogel structure [13].
