Introduction
Emulsified cooked sausages are the most consumed meat products in industrialized countries (Almeida et al., 2014). These are made from a meat paste based on meat, pork fat and seasonings, and are stuffed into natural or artificial casings. Pork backfat is the main component in most processed meat products, and influences flavor and aroma characteristics (Álvarez et al., 2012). However, some researchers point out that meat products can contribute to the appearance of degenerative and chronic diseases, due to their fat and cholesterol content (Diego-Zarate et al., 2021). Orozco et al. (2019) note that changes in diet can reduce the risk of acquiring cardiovascular disease or modulate physiological functions. Therefore, meat products should be reformulated to reduce their fat content with bioactive components such as walnut to achieve a functional effect.
The cultivation and marketing of walnuts in Nuevo León, Mexico, particularly the Bustamante and Rayones varieties, is important because of their profitable and sustainable agricultural practices and increasing production. Kernels make up 34 to 54 % of these varieties, which have a paste yield of 40 and 55 % oil, respectively, making them a viable option as a functional ingredient in the production of meat products (Reyes-Vázquez et al., 2021).
Walnuts contain 8.04 % crude protein, 17.70 % carbohydrates, 64.11 % lipids (oleic [45 %], linoleic [43 %] and palmitic [7 %] acids), 7.10 % fiber and 677.88 Kcal∙100 g-1 (Flores-Córdova et al., 2016). These components make walnuts a nutritious and healthy food due to their energy contribution, source of antioxidants, natural phenolic compounds and high content of polyunsaturated fats (Flores-Córdova et al., 2017).
The replacement of animal fat with vegetable oils and dietary fiber provides nutritional quality to meat products (Choi et al., 2014). In this sense, the use of walnut paste in meat products could improve their nutritional value and technological quality due to its content of dietary fiber, unsaturated fatty acids and phenolic compounds (Jahanban-Esfahlan et al., 2019). Alvarez et al. (2012) observed that walnut, in combination with vegetable oils and rice bran, improved the textural properties of Frankfurter sausages, as well as their consistency and gelling capacity. In this sense, walnut by-products can be used as substitutes for animal fat in the formulation of meat sausages. The partial replacement of pork fat with walnut paste in the preparation of Frankfurter sausages could improve their physicochemical stability, chemical composition, texture and sensory properties. Considering the above, this study aimed to evaluate the walnut paste of the Bustamante (B) and Rayones (R) varieties as a substitute for pork backfat in Frankfurter sausage formulation by means of emulsion stability, pH, color, water holding capacity (WHC), composition, texture and sensory properties.
Materials and methods
Experimental design
The study was conducted using a completely randomized design with five treatments, which consisted of replacing the backfat in the sausage formulation with the paste of two walnut varieties (Bustamante [B] and Rayones [R]). The percentage of oil in the fruit of these varieties was 73.80 ± 0.03 % in B and 70.80 ± 0.01 % in R, and the walnut paste had an oil content of 61.00 ± 0.24 % in B and 64.30 ± 0.0 % in R. The treatments were: T0 (control: 100 % backfat), T1 (65 % backfat and 35 % B walnut paste), T2 (30 % backfat and 70 % B walnut), T3 (65 % backfat and 35 % R walnut paste) and T4 (30 % backfat and 70 % R walnut paste). Each treatment was formulated for 1.3 kg of product, with two experimental replicates per treatment.
Sausage preparation and sampling for analysis
The Frankfurter sausage was prepared according to the methodology of Alvarez et al. (2012), with slight modifications. The meat paste was placed into Eppendorf™ tubes with lids and cooked in a water bath at 75 °C for 90 min, until the internal temperature of the sausage reached 71 °C. The sausages were then cooled to room temperature (20 °C) for 20 min. The sausage was removed from the tubes, packaged and stored at 4 °C. Measurements were made after 12 h of refrigeration. The composition of each treatment is shown in Table 1.
Table 1.
| Ingredients (g∙100 g-1) | Treatments | ||||
|---|---|---|---|---|---|
| T0 | T1 | T2 | T3 | T4 | |
| Meat | 62.50 | 62.50 | 62.50 | 62.50 | 62.50 |
| Fat | 20.00 | 13.00 | 6.00 | 13.00 | 6.00 |
| BWP | 0.00 | 7.00 | 14.00 | 0.00 | 0.00 |
| RWP | 0.00 | 0.00 | 0.00 | 7.00 | 14.00 |
| Salt | 1.50 | 1.50 | 1.50 | 1.50 | 1.50 |
| Sausage seasoning | 0.60 | 0.60 | 0.60 | 0.60 | 0.60 |
| Sodium erythorbate | 0.05 | 0.05 | 0.05 | 0.05 | 0.05 |
| Sodium tripolyphosphate | 0.30 | 0.30 | 0.30 | 0.30 | 0.30 |
| Sodium nitrite | 0.015 | 0.015 | 0.015 | 0.015 | 0.015 |
| Ice | 15.00 | 15.00 | 15.00 | 15.00 | 15.00 |
Seventeen Eppendorf™ tubes were randomly selected per treatment per replicate. Five tubes were used to determine emulsion stability (n = 10; five per treatment per replicate), six tubes for texture analysis (n = 12), three tubes for physicochemical tests measured in duplicate (n = 12; three tubes × two measurements × two replicates) and three tubes for sensory evaluation (n = 6).
Emulsion stability in meat paste
This variable was determined according to the methodology of Silva-Vazquez et al. (2018), with slight modifications. First, the weights of the 50 mL Eppendorf™ tubes (capped and without sample) were recorded, filled with 45 g of meat paste and cooked (75 °C for 90 min). The exudate (supernatant) was removed and the tubes were weighed again. The supernatant was placed in previously weighed aluminum trays (without sample), and the weights of the tray with wet supernatant and dry supernatant were recorded. Total expressible fluid (TEF) and total fat exudated (TFE) were expressed in %.
pH, water holding capacity and color
The pH was measured with a potentiometer (HI99163, HANNA, USA) by inserting the electrode directly into the sausage. WHC was determined using the methodology of Méndez-Zamora et al. (2015). Color was analyzed with a colorimeter (Colorimeter-SC20, SADT®, Chin Spec®, China) on the inside of the sausages, and the L* (lightness), a* (redness), b* (yellowness), C* (saturation index) and Hue angle were recorded.
Bromatological analysis
According to the Association of Official Analytical Chemists (AOAC, 2016), moisture (method 934.01), fat (method 920.30), protein (Kjeldahl method 954.01) and ash (method 942.05) content were determined. Carbohydrate content was obtained by difference of the other components: Carbohydrate = 100 - (% fat + % protein + % ash). These analyses were determined in duplicate in each experimental replicate.
Texture analysis
Shear force was applied to 3.0 cm long × 2.6 cm diameter segments using a texturometer (TA.XT.Plus, Stable Micro Systems, England). A Warner-Bratzler knife was used to make the cut in the center of each sausage segment. The pre-test speed was 2 mm∙s-1 and the post-test speed was 10 mm∙s-1. The maximum point displayed in each graph was considered as the shear force value (N; newton) for each sample. Texture profiling was performed using the same texturometer and the variables hardness (N), adhesiveness (N∙s), springiness (mm), cohesiveness (dimensionless), gumminess (N), chewiness (N∙mm) and fracturability (dimensionless) were obtained (Méndez-Zamora et al., 2015). Measurement speeds were set at 1.0 mm∙s-1 in pre-test, 2 mm∙s-1 in test and 5 mm∙s-1 in posttest, with a double compression cycle of 60 % of the original height of the sample and time between compression of 5 s. For these analyses, the sample was standardized into 2.6 cm diameter × 2.0 cm high segments.
Sensory evaluation
Sensory evaluation was carried out using a consumer test by attributes according to the method established by Méndez-Zamora et al. (2015). To do this, 24 consumers evaluated appearance, pinkness, smell, taste and overall acceptability using a five-point hedonic scale (1 = I dislike it very much and 5 = I like it very much). Each evaluator carried out the test in individual booths, equipped with a sink, white light, a chair and direct access to the samples for evaluation.
Statistical analysis
The data arrangement for the statistical analysis was a completely randomized design. The H 0 (equality of treatments) was rejected when the probability value was less than 0.05 (P ≤ 0.05) for each variable studied. In cases where H 0 was rejected, a comparison of means was performed with Tukey’s range test (P ≤ 0.05). The analysis was carried out in the Minitab® statistical program (2014), with the GLM (general linear model) function. The results of the sensory evaluation were analyzed with the Friedman test, considering the evaluator as a block effect (Minitab®, 2014), and when the H 0 was rejected (P ≤ 0.05), the comparison of means was performed with the Nemenyi test (Núñez-Colín, 2018).
Results and discussion
Physicochemical stability
The stability of the Frankfurter sausage meat pastes was different (P ≤ 0.05) among treatments for TFE (Table 2), while TEF did not vary significantly among treatments. These results may be due to the fiber content of the walnut paste, since it allowed the meat emulsion matrix to retain more water and be stable (Alvarez et al., 2012). TFE increased significantly in T2 and T3, compared to T0 and T1, which was attributed to the type of fat (Baer & Dilger, 2014), as well as to the amount and way of adding the walnut, and to the mobility of the vegetable oil during heat treatment (Salejda et al., 2016). The results obtained indicate that the use of 35 % B walnut paste kept the TFE percentage statistically equal to that of the control, with which the stability of the product was preserved. In contrast, 35 % R walnut paste significantly increased TFE, resulting in greater fat loss (poor stability).
Table 2.
| Treatments | Stability parameters | pH | ||
|---|---|---|---|---|
| TEF | TFE | WHC | ||
| T0 | 1.36 ± 0.70 a | 4.19 ± 1.85 b | 60.50 ± 4.47 b | 6.19 ± 0.10 c |
| T1 | 1.12 ± 0.33 a | 4.54 ± 2.80 b | 65.08 ± 3.48 a | 6.23 ± 0.05 c |
| T2 | 0.71 ± 0.23 a | 7.76 ± 5.29 a | 65.94 ± 2.40 a | 6.25 ± 0.05 bc |
| T3 | 0.90 ± 0.67 a | 7.90 ± 4.64 a | 66.32 ± 4.47 a | 6.31 ± 0.07 ab |
| T4 | 1.02 ± 0.87 a | 6.94 ± 2.64 ab | 65.46 ± 2.39 a | 6.33 ± 0.07 a |
| P-value | 0.176 | 0.025 | 0.004 | 0.000 |
WHC and pH in Frankfurter sausage were influenced by the replacement of fat with walnut paste (Table 2). Treatments formulated with walnut paste (T1, T2, T3, and T4) had a higher WHC than T0 by 4.5 to 5.0 %. The pH increased in sausages from T4 compared to T0, which had the lowest pH, but without significant difference with T1 and T2. This proved that sausages made with Bustamante walnut paste maintain the pH of the product, while those made with Rayones walnut paste increase their pH by 2 % (T3 and T4).
Jahanban-Esfahlan et al. (2019) point out that walnut is a source of unsaturated fatty acids, phenolic compounds, dietary fiber and digestible proteins. Therefore, walnut paste can improve the WHC in a meat emulsion, which was observed in sausages with walnut paste, since WHC increased in these treatments (T1-T4) by at least 4 % compared to the control. The pH values obtained in sausages with walnut paste are consistent with those reported by Salejda et al. (2016), who found that replacing pork backfat with walnut modified pH. These findings indicate that stability and the water-protein-fat ratio improve in sausages with B and R walnut paste, since increasing pH and WHC results in greater stability in the physicochemical properties of the meat product.
Sausage color
The treatments affected the color parameters (Table 3). Relative to T0, L* decreased (P ≤ 0.05) from 6.96 to 8.18 units in the treatments with 70 % walnut paste (T2 and T4, respectively). The a* increased from 1.64 to 1.72 units in the sausages with 35 and 70 % B walnut paste (T1 and T2). On the other hand, sausages with 70 % R walnut paste (T4) increased 42.35 % in b*, 30.62 % in C* and 10.56 % in Hue, compared to the control. Therefore, the carotenoids of the treatments with 70 % walnut paste increased the saturation (C*) and Hue of the sausages.
Table 3.
| Treatments | Color variables | ||||
|---|---|---|---|---|---|
| L* | a* | b* | C* | Hue | |
| T0 | 77.76 ± 0.97 a | 7.86 ± 1.35 b | 8.17 ± 0.64 b | 11.43 ± 0.87 c | 46.32 ± 5.99 abc |
| T1 | 72.25 ± 1.14 b | 9.58 ± 0.97 a | 8.82 ± 0.96 b | 13.03 ± 0.96 b | 42.42 ± 4.39 c |
| T2 | 70.80 ± 1.58 c | 9.50 ± 0.54 a | 10.74 ± 1.06 a | 14.38 ± 0.84 a | 48.30 ± 3.25 ab |
| T3 | 72.79 ± 1.56 b | 9.14 ± 0.96 a | 8.92 ± 1.05 b | 12.83 ± 1.10 b | 44.22 ± 3.96 bc |
| T4 | 69.58 ± 1.30 c | 9.26 ± 0.78 a | 11.63 ± 1.36 a | 14.93 ± 0.79 a | 51.21 ± 5.10 a |
| P-value | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
There are few studies reporting the color of sausages made with walnut paste as a fat substitute. However, Salejda et al. (2016) found differences in L*, a* and b* when using 1, 2 and 3 g∙100 g-1 of walnut green husk; they also observed that walnut paste enhanced pinkness (a*). Likewise, Sousa et al. (2017) reported that L* decreased and b* increased in sausages prepared with hydrolyzed collagen compared to the control.
Bromatological analysis
The replacement of fat with walnut paste in the sausage formulation had a significant effect on moisture, fat, protein and carbohydrates (Table 4). Moisture decreased and carbohydrates increased when 70 % R walnut paste (T4) was used in the sausages, and protein decreased with 35 % B walnut paste (T1). T0 had the highest percentage of moisture and protein, and the lowest carbohydrate content. Orozco et al. (2019) observed no significant differences in the composition of Frankfurter sausages with 6 % pecan nut paste. The protein content found was similar to that reported by Salejda et al. (2016), when using 3 g of walnut in sausages. In the present study, sausages formulated with 35 and 70 % B and R walnut paste had lower moisture and protein content, but higher carbohydrate content. This could be due to the carbohydrates that form a structural part of the fiber (Flores-Córdova et al., 2016), which increase the carbohydrates and moisture of the sausages. What is remarkable about these results is that the fat content in the sausages was not statistically different among treatments; that is, the oil content of B walnut paste (61.0 ± 0.24 %) and R walnut paste (64.3 ± 0.0 %) balanced the fat content of the sausages when the amount of fat in the formulation decreased.
Table 4.
| Treatments | Component (%) | ||||
|---|---|---|---|---|---|
| Moisture | Fat | Protein | Carbohydrates | Ash | |
| T0 | 64.89 ± 2.10 a | 15.54 ± 0.89 a | 12.69 ± 0.51 a | 2.98 ± 1.38 b | 3.90 ± 0.27 a |
| T1 | 64.32 ± 0.09 ab | 16.57 ± 0.30 a | 11.46 ± 0.71 b | 3.86 ± 0.51 ab | 3.79 ± 0.11 a |
| T2 | 62.82 ± 0.64 ab | 16.75 ± 1.29 a | 11.99 ± 0.27 ab | 4.58 ± 0.67 ab | 3.87 ± 0.20 a |
| T3 | 63.94 ± 1.63 ab | 16.60 ± 1.66 a | 11.65 ± 0.36 ab | 3.99 ± 0.76 ab | 3.82 ± 0.07 a |
| T4 | 62.23 ± 0.35 b | 16.02 ± 1.37 a | 11.91 ± 0.54 ab | 5.82 ± 1.99 a | 4.02 ± 0.14 a |
| P-value | 0.018 | 0.611 | 0.042 | 0.013 | 0.216 |
Texture analysis
Shear force, hardness and springiness were different among treatments (Table 5). Shear force increased significantly in sausages with walnut paste with respect to the control (T0). Hardness was higher in sausages with 35 % B walnut paste (T1) than in sausages with 35 and 70 % R walnut paste (T3 and T4). Springiness decreased by 0.19 mm in T4 compared to T0 (> springiness).
Table 5.
| Treatments | Shear force (N) | Hardness (N) | Adhesiveness (g∙s) | Springiness (mm) |
|---|---|---|---|---|
| T0 | 4.98 ± 0.77 b | 51.61 ± 5.68 abc | -51.47 ± 30.82 a | 0.83 ± 0.02 a |
| T1 | 6.47 ± 1.04 a | 59.46 ± 5.23 a | -58.30 ± 38.90 a | 0.77 ± 0.10 ab |
| T2 | 7.34 ± 0.78 a | 55.37 ± 6.12 ab | -66.10 ± 42.10 a | 0.75 ± 0.04 b |
| T3 | 7.00 ± 1.73 a | 47.20 ± 7.86 bc | -48.00 ± 42.60 a | 0.72 ± 0.08 b |
| T4 | 7.13 ± 1.74 a | 42.17 ± 16.17 c | -61.70 ± 52.30 a | 0.64 ± 0.11 c |
| P-value | 0.000 | 0.000 | 0.806 | 0.000 |
The results obtained in this research coincide with those reported by Méndez-Zamora et al. (2015), who used inulin and pectin as fat substitutes in the preparation of Frankfurter sausages. Several authors indicate that treatments with higher fat content have lower shear force and hardness (Álvarez et al., 212; Méndez-Zamora et al., 2015; Tahmasebi et al., 2016).
Cohesiveness, gumminess, chewiness and fracturability were significantly different (P ≤ 0.05) among treatments (Table 6), where the values decreased significantly in T4 compared to T0. Henning et al. (2016) showed that reduced-fat sausages have lower gumminess and chewiness. Tahmasebi et al. (2016) obtained similar results when using 3 % walnut paste to replace fat in sausages. These effects can be attributed to the walnut paste and the proteins enveloping the fat globules, which causes stable interactions among fat, protein and water molecules in the food matrix and results in high compressive strength (Tahmasebi et al., 2016). Therefore, T3 and T4 sausages maintained low texture values compared to the control. The decrease in fracturability of the walnut paste treatments may be due to the higher water and unsaturated fat content of the walnut.
Table 6.
| Treatments | Cohesiveness | Gumminess (g) | Chewiness (N∙mm) | Fracturability |
|---|---|---|---|---|
| T0 | 0.41 ± 0.07 a | 20.99 ± 3.13 a | 17.42 ± 2.73 a | 0.20 ± 0.05 a |
| T1 | 0.35 ± 0.11 ab | 20.68 ± 4.6 a | 15.52 ± 2.24 a | 0.13 ± 0.07 b |
| T2 | 0.29 ± 0.01 b | 16.07 ± 2.12 b | 12.04 ± 1.99 b | 0.09 ± 0.01 bc |
| T3 | 0.32 ± 0.08 b | 15.43 ± 4.95 b | 11.33 ± 4.07 b | 0.11 ± 0.04 c |
| T4 | 0.29 ± 0.07 b | 12.87 ± 6.7 b | 8.61 ± 4.94 c | 0.09 ± 0.03 c |
| P-value | 0.000 | 0.000 | 0.000 | 0.000 |
Sensory evaluation
The treatments were different in appearance, pinkness and overall acceptability (Table 7). T0 sausages had the best acceptance of the attributes, with no significant differences with the other treatments in smell and taste. Regarding overall acceptability, T1, T2 and T3 were statistically equal to T0. In addition, it can be observed that the acceptance of pinkness in sausages is better with 35 % walnut paste (T1 and T3) than with 70 % walnut paste (T2 and T4). Salejda et al. (2016) obtained lower preference in terms of juiciness, color, taste and overall acceptability when using 1, 2 and 3 % walnut green husk. Overall, the use of 70 % walnut paste had the lowest sensory acceptance, which can be attributed to the high use of this substitute (Salejda et al., 2016). Choi et al. (2014) replaced pork backfat with fiber extracted from makgeolli and obtained the highest color score in the control, as in the present study.
Table 7.
| Treatments | Appearance | Pink color | Smell | Taste | Overall acceptability |
|---|---|---|---|---|---|
| T0 | 4.35 a | 4.03 a | 4.28 a | 4.38 a | 4.33 a |
| T1 | 3.50 ab | 3.53 ab | 4.03 a | 4.33 a | 4.13 ab |
| T2 | 3.50 ab | 3.13 b | 3.73 a | 3.83 a | 3.88 ab |
| T3 | 3.55 ab | 3.48 ab | 3.88 a | 4.13 a | 3.68 ab |
| T4 | 3.10 b | 3.23 b | 3.98 a | 4.08 a | 3.63 b |
| P-value | 0.000 | 0.008 | 0.096 | 0.079 | 0.026 |
Conclusions
Bustamante walnut paste can replace 35 and 70 % of backfat in the formulation of Frankfurter sausage because it improves their physicochemical, bromatological, textural and sensory characteristics. The Bustamante and Rayones walnut paste increased the pinkness of the sausages, but decreased their lightness.
The use of walnut paste in emulsified meat products can be a viable alternative for obtaining low-fat products with greater nutritional value and benefits for consumers requiring special diets. It is advisable to evaluate the shelf life and fatty acid content of the sausage when natural by-products such as walnut paste are incorporated.