Physicochemical characteristics
The addition of pecan nut paste in meat emulsions could not only offer possible health benefits, but also provide important effects on sensory and technological quality. Considering that sausages are a multiple emulsion and according to the nature of the organic, oily, and aqueous phases that comprise it, significant differences are expected in their organoleptic and physicochemical characteristics. Hydrogen potential (pH), WHC, DL, color (L*, a*, b*, C*, and h*), and SF are indicators of the quality of fresh meat and meat products [
15].
In previous work we showed that the partial replacement of fat with pecan nut paste added to oregano oil does not change the proximate composition of frankfurters [
5]. The average values for moisture, protein, fat, and ash content of sausages of all the treatments are 69.39%, 14.89%, 8.17%, and 3.71%, respectively.
The results of the physicochemical analyses are presented in
Table 2. The addition of pecan nut paste to frankfurters increased (p<0.05) the pH, potentially due to the pH of pecan nuts. Several authors have reported increases in pH of meat products due to the addition of peanut paste [
16], while others did not find significant changes in the pH of frankfurters made with walnuts [
17]. A basic parameter of meat quality assessment is pH, since it directly affects the stability and properties of proteins as well as quality attributes such as WHC, DL, and color of meat [
15]. Also, the pH is responsible for the quality of the products, a decrease in pH causes denaturation of muscle proteins and a shrinkage of the polypeptide chain network that leads to a decrease in the ability of meat to retain water. On the other hand, an increase in the pH causes an increase in the WHC of the meat due to the changes in the electrical charges of the muscle proteins [
15]. In the present study the pH of the frankfurtes increased suggesting an improvement in the quality of the product.
No differences (p>0.05) were found in the WHC or DL of the six treatments in this study (
Table 2). Thus, replacing 6.0% fat in the original frankfurter formulation did not affect the water retention of the product. A recent study [
18] shows that sausages containing walnut and olive oil had lower cooking losses and higher emulsion stability than control sausages. These authors prepared chicken sausage with the addition of PUFAs containing 2.5 g/100 g walnut in their formula. WHC is defined as the ability of meat or muscle proteins to firmly retain and/or mobilize meat's own or added water during the application of a known force. Some characteristics of meat that are linked to WHC are color, texture, tenderness, juiciness, and DL [
15]. The increase in pH observed in the frankfurters did not cause a change in the WHC of the product. Probably that differences in pH value was not enough to cause significant changes in the muscle proteins of polypeptide network that retain water.
Colour is crucial in both, quality, and acceptability of meat products. The colour parameters of frankfurters are shown in
Table 2. Analysis of colour parameters displayed that the luminosity (L*) was not significantly affected (p>0.05) by the addition of MO and pecan nut paste. Similarly, other authors reported no changes in L* of sausages with 3% oregano essential oil [
19].
The addition of pecan nut paste decreased (p<0.05) the redness (a*) of the sausages, whereas the MO did not significantly affect this parameter. The dilution of the meat pigments responsible for colour by the outer water of the meat lattices contributes to lower the colour parameters due to a different concentration of myoglobin. This is the case of the frankfurters containing nut and/or MO which lack of the red colour of meat myoglobin. In addition, the pecan paste, and the MO are mixed with muscle proteins and water form an emulsion which in turn causes a light dispersion, that can also cause a change in colour. These findings were consistent with the results of Baek et al [
20], who replaced animal fat with canola and flaxseed oils and observed a decrease in redness of chicken sausages. The results of the present study confirm that the replacement of animal fat with vegetable oils results in a decrease in the redness of the meat products.
The yellowness (b*) of frankfurters was different (p<0.05) between treatments. In general, sausages that contained both, MO, and pecan nut paste, had greater yellowness than the control sausages. This could be due to the presence of red tannins from the nuts [
21]. The effect of vegetable ingredients on the colour of meat products has clearly been presented by Youssef and Barbut [
22] who explained that the during the emulsion making, the distribution of oil into the protein matrix results in colour changes due to differences in particle area (bigger in fat than in oil particles). Furthermore, vegetable oil is homogenous and more easily dispersed in an emulsion than fat of animal origin.
Besides the effect of pecan nut paste, the impact of MO on frankfurter colour should also be considered. Thus, the increase in b* value of sausages containing MO could also be due to the brownish-yellow colour of the oregano oil as reported by Cao et al [
23]. These authors prepared inulin/chitosan blend films containing oregano and thyme essential oils and found important changes in the film colour with a decrease in L* and increased in a* and b* values. Al-Hijazeen et al [
24] and Al-Hijazeen et al [
25] have reported that oregano essential oil improved the stability of the raw and cooked chicken meat colour with better colour values (L* and a*) than untreated meat. The increase in b* agrees with previous studies for meat products manufactured with linseed oil [
7]. Da Costa et al [
19] reported the effect of oregano and Rosemary essential oils on the quality of chicken sausages. They evaluated the colour of sausages both, externally and internally. The results showed a significant increase (p<0.05), during storage, for L*, a*, and b* values. This possibly occurred because of the presence of the essential oil that contributed to their antioxidant properties. Moreover, they reported no differences in colour between treatments with essential oil and control during storage of sausages. Similar results were reported in cooked ham prepared with pecan and peanut paste [
26].
Frankfurters made with MOP (Oregano [
P. longiflora Gray] essential oil) were tougher (p<0.05) than the control with lower SF values. However, no difference was observed in the rest of the treatments, which showed similar (p>0.05) SF values to the control and to the MOP treatment. In general, the SF tended to increase slightly when animal fat was replaced with MO and pecan nut paste (
Table 1). It has been reported that some vegetable oils help to restore textural parameters that are modified when animal fat is reduced in comminuted meat products. That is the case of the study of Youssef and Barbut [
22] who substituted beef fat with canola oil in comminuted meat products. They observed that reducing fat from 25% to 10% decreased hardness, but textural parameters of the products were restored by the addition of canola oil. Similar results were reported by Baek et al [
20] who observed that the texture profile of sausages manufactured with canola oil showed the highest profile values for texture among the treatments studied. The results published are very variable and it may be due to the properties of the oil and the product formulation itself. In a recent work, pork fat in frankfurters was replaced by soybean oil oleogels structured with rice bran wax and no effects (p>0.05) were found on the texture profile of sausages [
27]. In general, texture of frankfurters made with vegetable oil is softer than those products made with animal fat since oil emulsify better than solid fats commonly used in the manufacture of meat products, therefore, the end product could have better texture.
Acceptability
Colour, texture, flavour, and aroma of frankfurters are crucial attributes in purchase decision and they are critical factors influencing consumer satisfaction. Consumers were presented with traditional frankfurters (control), frankfurters prepared with two species of MO, and frankfurters prepared with MO and pecan nut paste, and they then scored different characteristics of each product. The consumer acceptability of frankfurters is presented in
Table 3. The partial substitution of pork fat with pecan nut paste and MO decreased the acceptance of colour, texture, and flavour of the frankfurters (p<0.05). Panellists scored the treated samples (with MO and/or N) lower than the control for colour, texture, and flavour, however, scores were not dramatically lower than the control (
Table 3). Frankfurters containing pecan nut paste and MO did not change the aroma scores given by the panellists as no significant difference (p>0.05) was observed in that attribute. The concentration of oregano essential oil (0.01%) used in this study was not high enough to negatively affect the odour of frankfurters. While low (0.01%) concentration of oregano oil influenced the acceptability of frankfurter flavour, higher concentration would be needed to influence the acceptability of frankfurter odour.
When MO was added to the frankfurters, the overall acceptability decreased (
Figure 1). The control sausage showed the highest acceptability (37%), followed by the sausage containing 6% pecan nut paste without oregano oil (C-N) (25%), while the sausages prepared with MOP [oregano (
P. longiflora Gray) essential oil] showed the lowest consumer acceptability (5%). However, when pecan nut paste was added together with MOL, the acceptability increased. This might indicate that oregano oil flavour and odour compounds negatively affect the acceptability of frankfurters. (
Figure 1). The higher acceptability of the control frankfurter could be attributed to its conventional characteristics of a commercial sausage. It is important to take into account that the development of new meat products containing new ingredients should consider evaluating sensory traits and consumer acceptability.
It has been reported that when peanut paste, pecan nuts, and walnuts were added to ham, the acceptability decreased [
26]. Also, the low acceptability could rely on the oregano oil compounds. The highest amount of volatiles components present in oregano are carvacrol and thymol [
5]. However, Al-Hijazeen et al [
25] observed that a 200 ppm oregano oil combined with 10 ppm of tannic acid presented high score on the overall acceptability of the cooked chicken meats.
Some researchers observed that sensory parameters could not be substantially improved when pork back fat was replaced with a linseed oleogel [
7]. In another study, Yildiz-Turp and Serdaroglu [
28] reported the effect of replacing beef fat with hazelnut oil in the production of emulsified meat and observed a reduction in quality due to lipid instability and a risk of oxidation of the product containing hazelnut oil. Also, the development of healthier lipid pâtés with beeswax oleogels as fat replacer showed no significant effects on sensory quality, whereas substitution by ethyl cellulose had an undesirable effect and the authors assumed that it was due to the substitution level [
11]. It is, however, important to mention that some reports found no changes in the acceptability of fat-replaced meat products [
6,
29]. Da Silva et al [
9] demonstrated that replacing of up to 50% of pork back fat by oleogel prepared with pork skin and sunflower oil did not affect the sensory quality of bologna-type sausages.
Furthermore, there are reports showing that burger acceptability increased with the addition of healthy fat replacers. Martins et al [
8] showed that hamburgers enriched with omega-3 and PUFAs oleogels were high scored during sensory evaluation, but the panellists preferred the control samples. Contrarily to this study, Oh et al [
10] found that the replacement of beef tallow with hydroxypropyl methylcellulose containing canola oil oleogels for meat patties showed a good overall consumer acceptability at the 50% replacement level, and finally, a recent study of low fat PUFAs-enriched pork burgers made with oleogels and curcumin as an antioxidant showed that Beeswax oleogel presented good overall sensory acceptability [
11]. These reports provide evidence that research on fat replacement with oleogels enriched with PUFAs or other natural antioxidants requires further work regarding sensorial acceptability.
Correspondence analysis is an exploratory data analysis tool that not only helps to identify the existence of relationship between variables but also shows how variables are related. The correspondence analysis plot based on the treatments and the attribute acceptability measured in the consumer test is shown in
Figure 2. The two axes accounted for 100% of the inertia or total variance for texture (dimension 1, 77.52% and dimension 2, 22.48%), 99.9% of the total variance for odour (dimension 1, 94.0% and dimension 2, 5.9%), and 100% of the total variance for flavour (dimension 1, 93.28% and dimension 2, 6.72%) and colour (dimension 1, 81.74% and dimension 2, 18.26%). Practically, the total variance could be explained in the first dimension. Therefore, the association between MO levels and/or pecan nut paste and the sensory attributes in sausages is one-dimensional, indicating that it contributed to a greater extent to the discrimination of the treatments, grouping them according to the degree of acceptability by the consumer. Moreover, significant differences in the acceptability of the attributes existed between treatments.
Texture was directly correlated with MOL, which was the most acceptable treatment, but was negatively correlated with MOP and CN (control + 6% pecan nut paste), which were the less acceptable treatments. In contrast, odour and flavour were majorly explained by MOP-N (mexican oregano Poliomintha oil + pecan nut), whereas colour was majorly explained by MOL-N (mexican oregano Lippia oil + pecan nut), which had the highest acceptability. This result suggested that sausages manufactured with oregano oil, with or without pecan nut, contributed the most to the acceptability attribute. As it is known, fat plays an important role in the sensory characteristics of meat products, thus, any change in the quantity or type of fat in formulation may give place to changes in quality properties [
30].
The results of the overall liking test showed that MO-containing frankfurters were less acceptable than control sausages which could be attributed to differences between individual attributes and the acceptability of the whole product. These findings also indicate that acceptability is a complex attribute, and that analysis of individual attributes does not necessarily correlate with overall liking. In general, the attributes of colour, texture, and odour were all well accepted, whereas acceptability of flavour was low.
Sensory quality depends on the interaction between the ingredients of the formulation for the development of texture and mouth feel of a food. In addition, the quality of technology also is the result of these interactions in the emulsion that can affect changes in its stability. A reduced stability of the emulsion would mean eventually a phase separation, which in practice, supposes the breakage of the emulsion and, therefore, a final product of low performance and quality, economic losses, and consumer rejection.
The fiber (6.7 g/100 g) and protein content (16.7 g/100 g) of walnut paste used in the formulation of Frankfurt sausages produces interactions between fiber binders and fat-protein during the emulsification process that allows low values of total expressible fluids and fat exudates. This means a high capacity to retain water and fatty exudates, indicates better emulsion stability and rheological properties [
17].