Preparation of the product

This study was carried out between January and June 2010, in the facilities of the Agriculture and Livestock Science Institute of the Autonomous University of the State of Hidalgo. To prepare the product 45 kg of eviscerated carp were used (450 g carp^-1), which were transported at a temperature of 4 °C from a commercial farm in Tezontepec de Aldama, Hidalgo, to the meat products workshop of the Agriculture and Livestock Science Institute (ICAp) located in Tulancingo, Hidalgo. The meat was ground, homogenized, and split into two batches: the first was kept for 24 h at 4 °C in a Torrey brand refrigerator (Model R36, Monterrey, Nuevo León, Mexico), and the second was frozen at -18 °C for 15 d in a Torrey brand freezer (Model CHC25, Monterrey, Nuevo León, Mexico). The meat from the first batch underwent 12 sausage emulsion treatments (Guerrero et al., 2000) (Table 1), to evaluate texture (greater, intermediate, and lower), color and firmness, according to the level of inclusion of fat and water. The meat from the second batch also underwent 12 sausage emulsion treatments (Guerrero et al., 2000), but was added phosphates (Emulfos 2000^®, Fabpsa, Mexico) and carrageenan (Fabpsagel^®, Fabpsa, Mexico) in its formulation (Table 2).

Table 1 Treatments with different amounts of fat and water in a product emulsified with carp meat (g). 

Table 2 Treatments with different inclusion of phosphates and carrageenan in a product emulsified with carp meat (g). 

Chemical analyses

The proximal chemical analysis was carried out according to the ^{AOAC (1999)}: moisture (method 934.01), fat (method 948.15) and raw protein (method 981.10).

Quality analyses

Determining color

Color was determined with parameters L*, a* and b* (^{AMSA, 2012}), using a Minolta 508d spectrophotometer (Minolta Inc., Tokyo, Japan), with a D65 light and an angle of the observer of 10°, and three color measurements were taken on the surface of each portion of the mass. The values were registered according to recommendations by the Comission Internationale de l'Éclairage (CIE).

Texture profile analysis

For the texture profile analysis, cubed pieces measuring 2.5 cm on each side were cut, enough to cover the surface of the texture analyzer P25/L (cylindrical perspex, 25 mm diameter, Stable MicroSystems, Surrey, UK), which was placed on the base of the texture analyzer (TA-HDi Instruments, Stable MicroSystems, Surrey, UK) and compressed using a 5 kg load cell at 50 %, with a speed of 1 mm s^-1. The texture profile analysis (TPA) gave the following parameters: firmness, elasticity, resilience, and cohesiveness. Analyses were carried out in triple.

Resistance to cutting with a Warner-Bratzler blade

A Warner-Bratzler blade (HDP/BSW, Stable MicroSystems, Surrey, UK) was used for this test, adapted to the texture analyzer. Samples were analyzed according to indications by ^{Ruiz de Huidobro et al. (2005)}, with the following modifications: the 9 cm long sample was placed horizontally between the base of the cell and the blade that made the cut by descending vertically until it cut the sample in two pieces. Resistance to the cut was evaluated using a test speed of 1 mm s^-1 and a return speed of 2 mm s^-1 with a 5 kg load cell; each sausage was cut in three places, and the maximum firmness and effort for cutting were reported during the test.

Maximum firmness detected with a Kramer shear cell

This test was performed according to ^{Cavestany et al. (1994)} with the following modifications: we used a 10 - blade Kramer shear cell (TA-91, Stable MicroSystems, Surrey, UK) adapted to the texture analyzer, with a load cell of 50 kg at a speed of 1 mm s^-1. The sample was cut in a piece 8 cm long and was placed horizontally between the mass of the cell where it was cut, and the cell fell vertically until the complete penetration of the blade along the structure of the product. The maximum strength found during the compression-extrusion g^-1 of the sample was reported.

Heat penetration

The reading of the internal temperature of the meat was taken every minute for 20 min with a digital Hanna Instruments HI98609 thermometer which was introduced in the center at the middle of the sausage, which rose up to, and remained at, 85 °C.

To determine thermal diffiusivity of the meat, the equation (1) proposed by ^{Markowski et al. (2004)} was used.

(1)

where α: thermal diffusivity of the meat (m² s^-1), B: gradient of each treatment, R: radius of the sausage (m), L: length of the sausage (m).

To evaluate the changes between the temperature in the center and the surface of the sample against time, equation 2 was used, proposed by ^{Markowski et al. (2004)}. To calculate the gradient of each treatment it was necessary to graph the values for ln [ Ts-Tc ] min^{- 1} for which the temperature was monitored.

(2)

where Ts: temperature on the surface of the sample (°C); Tc: temperature in the center of the meat (°C); A: intersection; B: gradient of each treatment; t: min time.

The calculation of the theoretical temperatures was obtained with a quadratic function, using the time taken for cooking, in order to obtain the description of the penetration of heat.

(3)

where Y: temperature in the center of the product and x: time for cooking.

Experimental design and statistical analysis

The experimental design was completely randomized and treatments are described in Tables 1 and 2. To determine the statistical differences in color and texture of the emulsified carp meat products, an ANDEVA was applied, and the measurements of the treatments were compared with Tukey's test (p≤0.05), for which we used the GLM procedure (^{SAS, 2002}).

Chemical composition of carp meat

The variation in the chemical composition of carp meat is due to age, sex, environment, season of the year, and feeding (^{Guler et al. 2007}). The carps used in our study were taken from tanks in a farm, under the same feeding and age conditions. The amount of fat in the carp meat in this study was 0.1 % (Table 3), which is lower than that reported by ^{Guler et al. (2007)}, who found that lipids in fresh muscle are low (0.91 %) during the warm season, and high (1.73 %) in the cold season; ^{Mahmoud et al. (2006)} reported 3.90 % fat, and ^{Ganesh et al. (2005)} 2.8 %. Regarding moisture, values were similar (Table 3) to those reported by ^{Mahmoud et al. (2006)}, 76 % for carp fillets, and by ^{Ganesh et al. (2005)}, 78.3 %. Protein and ash (Table 3) were higher than those found by ^{Ganesh et al. (2005)}, 17.8 % and 0.95 %, respectively.

Table 3 Chemical composition of the fish (Cyprinus cardio) from a farm, in Tezontepec de Aldama, Hidalgo. 

% Carbohydrates= 100 % - % Moisture + % Ashes + % Fat + % Protein (^{FAO, 1999}).

Effect of added fat and water on the texture

The loss in texture during the storage of fish products is related to a low pH in muscles, a hard texture, high loss of water due to dripping and enzyme activity. Fish muscles can be more complex when it constantly loses fluids; water retention capacity is reduced, which is a good quality indicator for fish and this is shown with a loss in texture (^{Ocaña-Higareda et al. 2009}). In our4hy the meat recovers more water in its structure and improves its texture. As more fat and water are used, the product becomes less sensitive to breakages, the product can be more homogenous, elastic, cohesive, and with a firmness that allows a greater use of water in its structure, which improves the performance and economic benefit. These observations are similar to those by ^{Ayadi et al. (2009a)}, who consider that the differences between the amount of fat/moisture and protein/moisture are factors that influence the elasticity of products made with turkey meat. ^{Huda et al. (2012)} point out that there is a relationship between the moisture and firmness of fish sausages, as well as ^{Intrapichet et al. (1995)}, who show that reducing the fat in sausages with a mixture of goat meat and pig fat increases elasticity.

There was no effect of the amount of fat, meat or water on firmness. In the values obtained for the effort for cutting with both analyzers, the increase in the amount of water and fat reduced it, except for the first treatment using the Warner-Bratzler, in which it increases (Table 5).

Table 4 Profile analysis for texture by the effect of added water, fat and carp meat in an emulsified sausage product. 

Means with different letters in a column indicate statistical difference (p≤0.05).

Table 5 Averages of the least squares of the maximum strength detected with the Kramer shear cell (K) and strength in the cut using a Warner- Bratzler blade (W) by effect of the added water, fat, and carp meat in an emulsified sausage. 

Means with different letters in a column indicate statistical difference (p≤0.05).

Effect of fat and added water on the color

The highest value in L* was with treatments with a greater amount of far and less meat, whereas in parameters a* and b* there was no difference between treatments (Table 6). This is different to ^{Ocaña-Higareda et al. (2009)} who mention that parameters a and b are low in the product when low amounts of fat are added.

Table 6 Color in mixed fish meats, L*, a*, and b* obtained by the effect of added water, fat and carp meat in a sausage-type emulsified product. 

Means with different letters in a column indicate statistical difference (p≤0.05).

Effect of added fat and water on heat penetration

^{Markowski et al. (2004)} determined the effective thermal diffusivity for Lyoner sausages cooked by immersion in hot water with a diameter of 96 mm, and thermocouples were used to measure the increase in temperature during cooking, one thermocouples submerged in hot water, a second one placed in the center of the meat product and a third one on the surface of the product, with a water bath at a constant temperature of 95 °C; once the samples reached 75 °C in the center, the samples were removed from the water and cooled using cold water. ^{Ayadi et al. (2009)} determined the thermal diffusivity in formulations for salami and ham made with turkey meat, cooked by immersion in hot water, used a system of thermocouples and took the temperature in the center and surface of the product, as well as the temperature of the constant water bath at 90 °C; once the internal temperature of the sample reached 74 °C, they were removed from the hot water. Like these authors, a scheme was carried out in which the experimental data were taken during the cooking of the meat. The temperatures obtained from the monitoring for 20 min showed that the heat penetration of the sausages are similar in the different treatments and indicate that there is no difference in the time of cooking (Figure 1).

Figure 1 Temperatures monitored in the meat during cooking in treatments with different amounts of fat and water in a sausagetype emulsified product with carp meat. 

Effect of the addition of phosphates and carrageenan on texture

The use of table salt and phosphates increases the capacity of emulsification of carp meat (^{Yapar et al. 2006}), and improves its texture. The firmness increases with the amount of carrageenan, which correlated positively with the amount of fat, and negatively with the amount of water (Table 7). ^{Ayadi et al. (2009)} studied the influence of adding carrageenan on the properties of sausages produced with turkey meat, and mention that the carrageenan reduces the stability of the emulsion and increases the water capacity, it produces more firm and cohesive, and less elastic sausages. Hsu and Chung (2001) also observed an increase in the performance of low-fat meatballs with 2 % de carrageenan. According to ^{Totosaus and Pérez-Chabela (2009)}, the mix of gellan gum and MgCl₂ in low-fat meats improves the texture, producing firmness values of 3365 to 3773 g due to the capacity of carrageenan to catch water in the three-dimensional mesh it forms; water is not released as cooking juice, but it remains inside the product. This is an advantage in the use of carrageenan, which also controls the leakage during storage. Another advantage is that it improves the slicing and performance in emulsified products (^{Abdolghafour and Saghir, 2014}).

Table 7 Texture profile in treatments with different inclusions of phosphate and carrageenan in a sausage-type emulsified product with carp meat. 

Means with different letters in a column indicate statistical difference (p≤0.05). F: phosphates, C: carrageenan.

Elasticity increased in the treatments with a greater inclusion of phosphate and a lower amount of water (Table 7), since phosphate helps proteins retain water, and therefore added water (^{Lin and Lin, 2002}; ^{Son Long et al. 2011}). This indicates that the product recovers part of its initial form after the first compression, since the added water was not released as cooking juice, but remained in the product, (^{Abdolghafour and Saghir, 2014}).

The use of the Kramer shear cell gave a greater firmness and effort (Table 8) in the treatments that contained more carrageenan and water, with less meat and fat since carrageenan is more free, therefore it forms a more firm gel and, with that, the effort. This coincides with ^{Totosaus and Pérez-Chabela (2009)}, who point out that the use of the Kramer shear cell causes the gellan gum in combination with MgCl₂ to produce stronger structures, which is why the maximum firmness values are higher. But with the use of the Warner-Bratzler blade (Table 8), no differences were found between treatments: 144.91-316.89 g for firmness and 3012-5406 g*s for effort when cutting. This is explained according to ^{Totosaus and Pérez-Chabela (2009)}, since in meats with added gellan gum a solid structure is obtained, which results in larger values of the area under the curve when using the test with a Warner-Bratzler blade.

Table 8 Maximum strength detected with the Kramer shear cell (K) and strength when cutting with the Warner-Bratzler blade (W) in treatments with different inclusions of phosphates and carrageenan in a sausage-type emulsified product with carp meat. 

Means with different letters in a column indicate statistical difference (p≤0.05). F: phosphates, C: carrageenan.

Effect of the addition of phosphates and carrageenan on color

L* increased when including a greater amount of phosphates in the treatments with less fat, meat, and water (Table 9). This coincides with ^{Hsu and Chung (2000)}, who studied the effect of the k-carrageenan, salt, phosphates and fat on the quality of low-fat meatballs, and found that the poliphosphates affected the values of a* and b significantly. Likewise, ^{Pietrasik and Duda (2000)} reported no effect in the addition of carrageenan and soy protein concentrate on the values of L* and a* in sausages produced with beef and pork.

Table 9 Color in mixed fish meats, L*, a* and b* in treataments with different inclusions of phosphates and carrageenan in an emulsified sausage with carp meat. 

Means with different letters in a column indicate statistical difference (p≤0.05). F: phosphates, C: carrageenan.

Effect of the addition of phosphates and carrageenan on thermal diffusivity

Thermal diffusivity depends on the thermodynamic properties of the raw material, structure, heat transfer mechanisms and mass (^{Markowski et al. 2004}; ^{Marcotte et al. 2008}). That property is closely related to the three thermophysical properties: thermal conductivity, specific heat, and density (^{Marcotte et al. 2008}).

^{Marcotte et al. (2008)} studied the thermophysical properties of process products made with poultry, and point out that thermal diffusivity is a property that changes in regard to temperature; as moisture increases, conductivity and diffusivity increase. This is due to the 2 % of salt added in the emulsion. The proportion of proteins does not have a significant influence on these properties; the results of the calculation of the thermal diffusivity were between 8.30X10^-8 m² s^-1 and 1.36X10^-7 m² s^-1. ^{Ayadi et al. (2009b)} used the same equation to calculate diffusivity in salami and turkey ham, and obtained values between 5.11 X10^-6 m² s^-1 and 7.02X10^-6 m² s^-1 for salami, and for ham, 1.98x10^-8 m² s^-1. ^{Markowski et al. (2004)} determined the thermal diffusivity in Lyoner sausages during cooking and cooling in a water bath, and obtained results between 3.5X10-⁷ m² s^-1 and 4.5X10-⁷ m² s^-1, respectively; besides they point out that the variations in thermal diffusivity are due to the fat and water contents in the product. Both authors determined the thermal diffusivity with the data on the temperature of the center and surface of the sample. The treatment with the highest amount of fat, phosphates and carrageenan with the least amount of meat obtained the highest thermal diffusivity of 9.61X10^-4 m² s^-1, since phosphates capture water and carrageenan makes a gel, that in combination with fat causes this thermal incrementdfd. On the other hand, the treatment with the lowest amount of phosphates, water and meat had a lower value of 7.10 X 10^-4 m²s^-1 (Figure 2).

Figure 2 Thermal diffusivity on carp sausages by the effect of carrageenan and phosphates.