## 3 Results and Discussion
The addition of turmeric powder can be considered a good natural agent to inhibit the growth of aerobic bacteria and extend the shelf life of ground beef stored in refrigeration [19], of beef chorizo sausages [17], and meatballs [37]. Texture is considered an important qualitative feature of meat and its products as it influences consumers' product acceptability [18]. Hence, the maximum shear force value, a key parameter of meat tenderness, was evaluated in the study. Our research showed that the toughness of burgers with turmeric added during refrigerated storage changed in relation to burgers without the additive (Table 2). On the first day of the evaluation, no differences in the toughness of the tested products were found, while from the sixth day of storage, the burgers with turmeric in all the forms used were characterised by lower toughness, which was maintained until the end of the storage time. The increase in toughness of the product from the control group (group I) during refrigerated storage may be related to the lower water absorption of the product. Similar results were obtained by [PERSON] et al. [38] in the storage of beef cutlets. In the studies of [PERSON] et al. [18], the applied curcumin in the form of microcrystals did not affect the toughness of the stored mortadella sausage. Curcumin, the key colouring matter in turmeric, is extractable and useful as a natural food colourant [15]. The characteristic yellow colour of turmeric is the result of its three major pigments: curcumin (50-60%), demethylox curcumin (20-30%), and bis demethylox curcumin (7-20%) [39]. All these curcuminoids have been shown to have antioxidant activities [15]. The colouring effect of curcumin was confirmed in our own studies (Table 3). On the first day of evaluation, the duck burgers with the addition of powder and paste were brighter, characterised by a significantly higher L* brightness index and a* red parameter, and a much higher colour saturation parameter towards yellow b*. On the other hand, burgers with the addition of turmeric extract had a higher value of the red a* parameter compared to the control group and other study groups. The remaining colour parameters were similar to the colour parameters of burgers without additives. Similar results were obtained by [PERSON] et al. [18] using the addition of curcumin microcrystals to a mortadella sausage. Additionally, studies by [PERSON] et al. [40] showed that the addition of turmeric in the form of powder increased the brightness of chorizo sausage. The authors' research showed that the storage time had an effect (\(p\leq 0.001\)) on the brightening of the colour of all tested burgers (Table 3). On the sixth day of the evaluation, the control group and the group of burgers using turmeric extract showed a decrease in colour saturation towards red (a*), while the group of burgers with the addition of turmeric powder and paste showed a decrease in yellow tone (b*). The decrease in yellow colour saturation during storage was most likely due to changes in turmeric's natural pigments associated with enzymatic oxidation of phenolic compounds [16; 41]. On subsequent dates of the evaluation, this tendency was maintained only in the group of burgers with the addition of paste. The effect of the addition of natural extracts as an antioxidant substance on the colour of beef balls was also demonstrated by [PERSON] et al. [42], who stated that with the increase in the amount of the additive, the colour of the products lightened. The cited authors explained this by the presence of antioxidant compounds that delay the formation of metmyoglobin responsible for the darker colour of meat products. Lipid oxidation in meat products during refrigerated storage is one of the factors determining the consumption quality and nutritional value of the product [5,17]. The thiobarbituric acid value is a measure of secondary lipid oxidation products in meat [23].