## 3 Results and Discussion
### Colour Analysis during Exposure to Light  
During exposure to white fluorescent light and after production and eight weeks of storage, the model products showed a lower redness (a*). Together with lower redness in the product colour tone during light exposure the yellow (b*) colour share increased and sample lightness increased (L*) (Tables 2 and 3). Light has a negative influence on the colour of meat products surfaces due to oxidation processes [48; 49]. Iron oxide formed during heme pigments light exposure is responsible for a greenish or grey-brown colour due to different forms of myoglobin, and mainly metmyoglobin [50; 51].  
The effect of light on the products surface caused lower colour saturation (C*) and colour tone change (higher h\({}^{*}\) value) of the model products. The hue angle value change (h\({}^{*}\)) was caused by the higher yellow colour share (b*) and lower red colour share (a*) in the tones of the tested samples (Tables 2 and 3).  
The differences were proved (\(p<0.05\)) in the total colour change (\(\Delta\)E*) of products being the subject of light exposure after production. The highest \(\Delta\)E* value was observed in all experimental treatments after 2 h of light exposure, which indicates the biggest dynamics of colour change in this period. In the further hours of light exposure, colour change of the model products was less intense (Tables 2 and 3). A similar dependence was reported in previous research [15].  
After production and 5 h after light exposure the highest \(\Delta\)E* value was reported in the SL treatment (\(p<0.05\)). It indicates that this treatment was of lower colour stability after 5 h of light exposure than in the C and M treatments. Such dependence was not observed in the remaining light exposure periods of the tested samples both after production and after storage (Tables 2 and 3). Lower SL treatment stability after 5 h of light exposure was most likely the result of lower residual nitrite content in the product. Nitrites and their derivates may react with free iron and other metals present in meat, blocking their prooxidative functions [1,3]. The products of nitrogenous compounds transformations may react with muscle tissue elements forming nitrosyl compounds with antioxidative activities [3] that could slower the nitromiochromogen oxidation process.  
All treatments (C, M, SL) after production exposed to light were of a similar value of yellowness (b*). After eight weeks of storage, the b* parameter value after exposure to light was the highest in the SL treatment (\(p<0.05\)). After production and eight weeks after storage, the highest L* parameter after light exposure was reported in the C treatment. The L* parameter value in the M and SL treatments were similar (Tables 2 and 3).  
Changes in colour parameters (a* and b*) during light exposure influenced the saturation and hue angle values of the model products. The SL treatment was of the highest colour saturation (C*) after light exposure. No statistically significant differences between the C and M treatments were found (\(p<0.05\)). The highest red colour share in the product (the lowest h\({}^{*}\) value) after light exposure was found in the SL treatment. Nevertheless, statistically significant differences (\(p<0.05\)) between variants were not confirmed in all periods of light exposure. A similar relation was reported after production and storage (Tables 2 and 3).