## 3 Results and Discussion
### Colour Parameters  
The results corresponding to the colour parameters of pig _Biceps femoris_ slices cooked using different methods are reported in Table 2. The outcomes obtained for the values of L* (34.89-52.32), a* (5.89-10.32) and b* (15.81-19.63) were similar to those found by other studies. In this way, several authors reported data between 48 and 81 for L*, between 0.3 and 11 for a*, and among 10 and 24 for b* for cooked pork muscle and derived products [13; 26; 27; 28; 29]. As we can observe, all the colour parameters of our work are in the range of these authors, except for the L* value, which was a little lower in the case of frying for both diets (34.89 for CH and 40.69 for CF diet). In the present study, the diet has not significantly affected the colour parameters, except in the fried samples, where the value of b* was altered, being higher in slices of CF pigs (19.63) than in CH samples (15.81). These results agree with those reported by [PERSON] et al. [7], who also did not find significant differences in the meat colour of Celta pigs fed with commercial feed or with two levels of chestnut. Then again, the different cooking methods did significantly (\(P<0.01\)) affect all the parameters in both diets, with the exception of yellowish of CH pigs. The significant differences derived from the distinct heat treatments could be due to the interconversion of myoglobin in deoxymyoglobin, metmyoglobin and oxymyoglobin. This interconversion takes place through different reactions of oxygenation, oxidation and reduction, which influences the external appearance of meat colour [30]. Aforementioned interconversions and degradations can occur in different ways, depending on the cooking time and temperature used. Thus, different degrees of denaturation of the red heme proteins are generated according to the culinary method used [31]. For instance, [PERSON] et al. [32] observed that the temperature caused a denaturation of myoglobin and haemoglobin which generated brown precipitates in the meat. Comparing our results with a previous study carried out on raw _Biceps femoris_ from Celta pig [33] (L* 48.9; a* 18.1; b* 13.1), a decrease in luminosity (L*) was observed in the case of fried samples (34.89 for CH and 40.96 for CF slices), while, for the rest of the cooking treatments, there seemed to be an increase in this parameter with respect to raw _Biceps femoris_ muscle (L* among 49.25-52.32). In particular, the highest value of L* was obtained for microwaved (51.22 and 51.33 for CH and CF slices, respectively) and for grilled (51.13 for CH and 52.32 for CF slices). In relation to the value of redness (a*), there was a decrease in this parameter in all culinary treatments with respect to uncooked _Biceps femoris_ muscle, where an a* value of 18.1 was found [33]. More specifically, frying was the method that provided the highest value for both diets (9.34 for CH and 10.32 for CF slices) followed by roasted (7.15 and 7.52 for CH and CF slices, respectively), grilled (6.31 for CH and 6.39 for CF samples) and microwaved (5.89 and 6.34 for CH and CF samples, respectively). In general terms, these facts agree with those obtained by others who observed that cooking increased the L* value while generating a loss of redness (a*) in foal [34] and beef meat [35]. More concretely, [PERSON] et al. [34] observed a similar trend to our study, since they reported a lower L* value for fried foal meat with respect to roasted, grilled or microwaved samples. Simultaneously, [PERSON] et al. [34] obtained the highest a* values for fried foal meat, while the lowest were for microwaved meat, as in our work. Finally, the value of yellowness (b*) increased with the cooking treatments (15.8-19.6), in comparison with the raw _Biceps femoris_ muscle (13.1) [33]. In this case, only the CH pigs showed significant differences among cooking treatments. The highest values were obtained for roasted (18.95) and grilled (17.54), being the lowest for frying (15.81).