# Enhancing the Integration of Protein-Rich Oat Waste Material into Meat Formulations
## 4 Discussion
### Assessing the Possibility of Using OPH as a Meat Additive
As plants naturally contain nitrates, which could contribute to meat colour formation, the nitrite and nitrate content was analysed in both the OPH and in the meat samples. Additionally, we tested the samples for the presence of the nitroso pigment. We suspected that even low nitrite/nitrate concentrations could have reacted with myoglobin, forming nitroso hemochromogen during heating. In this case, nitrites/nitrates would not be present, as opposed to the stable nitroso pigment. All the results were negative, which indicates that the nitrogen-involving reactions did not occur. Although the pink colour of meat is usually discussed in the context of myoglobin and its forms [47], some other factors, such as polyphenols or amino acid content, may play role in colour formation [48; 49]. Furthermore, zinc protoporphyrin IX could play a role, as was suggested by [PERSON] et al. [50]. Nonetheless, this pink effect is worth further investigation. The samples were comparable on the first day of storage, and all of them were oxidised during the storage process, which is typical for meat products [19; 40]. Thus, various strategies are applied to inhibit the process to the highest extent. Recent trends indicate that natural additives, preferably of plant origin, are accepted by consumers [51]. The results of our study show that OPH not only inhibited meat oxidation, but even increased the process. Analysing the trends of TBARS increase in all the samples, it may be concluded that the higher addition of OPH promotes oxidation in meat samples. However, due to strong batch-to-batch variations, those differences were not statistically significant. Similar results were obtained in our previous study, in which soy husk protein was used [19]. Interestingly, the positive oxidation inhibiting effects of oat protein hydrolyses on meat samples have been presented by other researchers [25; 52]. Yet, this study is the second hydrolysate we used in meat preparation, each showing oxidation enhancing properties, which is in contrast with the literature data. On the other hand, in another research, in which plasma hydrolysate was added to sausage, peroxide values increased significantly, and TBARS values increased slightly. The highest TBARS levels were noted in the sample with a 2.5% concentration of the hydrolysate, but the differences were not statistically significant [42]. As was previously mentioned, hydrolysis may lead to different results, depending on the extension and general condition of the process. Oxidation control can be achieved through the utilization of antioxidant additives, which can be either natural or synthetic. A diverse range of compounds, including phenols, flavonoids, tannins, lignans, tocopherols, and carotenoids, offer different modes of action in this regard. Ascorbic acid and rosmarinic acid are among the commonly used additives in the meat industry [16; 51; 53]. Nevertheless, these interactions might lead to unforeseen outcomes, underscoring the importance of conducting thorough investigations. It is possible that sodium chloride present in the OPH, due to HCl and NaOH used during hydrolysis, may be an important factor for increasing oxidation in the samples [54]. It is difficult to verify whether the hydrolyses used in other studies were obtained with considerable amounts of sodium chloride, as it is usually not mentioned in the description of the methods. Moreover, some polyphenols present in the OPH may also be significant. The pro-oxidant activity of flavonoids is believed to be proportional to the number of hydroxyl groups, especially in the B ring [55]. According to [PERSON] et al. [56], the presence of ortho- or para-substituted polyphenol structures was observed to promote the oxidation of oxymyoglobin. Additionally, certain polyphenols containing transition metals can cause prooxidant properties, as these have the ability to reduce metal ions involved in redox-cycling, thereby facilitating the production of hydroxyl radicals through Fenton and Fenton-like reactions [57].