This doctoral thesis aimed to understand the effects of formulation and alternative (PEF, HPP) compared to traditional thermal processing on complex food systems, focusing on the stability and bioaccessibility of anthocyanins and proteins. It was hypothesized that targeted formulation of food systems consisting of an anthocyanin-rich matrix (strawberry), and a relatively protein-rich matrix (kale), treated with selected processing technologies (thermal, PEF, HPP) resulting in a minimum 5-log microbial reduction can lead to a different extent of interactions between the polyphenols and proteins and can affect the stability and bioaccessibility of anthocyanins and proteins after the treatment and during refrigerated storage. For an enhanced mechanistic understanding of the results in the complex system, a concise study on a model system containing anthocyanins and a purified protein treated with the processing technologies was conducted. Different formulations of strawberries and kale exhibited a significant effect on the stability of anthocyanins and proteins. This was reflected in reduced amounts of free anthocyanins in the mixed strawberry-kale system, compared to the single strawberry system, suggesting interactions with compounds of the kale matrix, in particular with the present protein. As a result of these interactions, the antioxidant capacity of the formulations also decreased. Thus, the combination of anthocyanins, but possibly also other polyphenols, and proteins in the investigated systems resulted in the formation of insoluble complexes and increased particle size. During refrigerated storage, accelerated degradation was observed in the complex strawberry-kale system. This could be partially explained by an increased activity of oxidative enzymes, such as polyphenoloxidase and peroxidase, originating from the kale matrix. The processing technologies, or rather their processing effect, can be classified based on their thermal load: thermal, having the highest thermal load, followed by PEF having a medium thermal load, and finally, HPP where the thermal load is considered marginal. After thermal and PEF treatments, anthocyanins and antioxidant contents showed an apparent increase, while the content of soluble protein decreased at the selected processing intensities. The temperature increase during these two treatments, as well as the electroporation effect, might have had an impact on the matrix and present cells, resulting in an improved extraction of such compounds from the food matrix, and their apparent increase in analytical assessment. Similarly, the thermal load might have led to partial or complete denaturation of proteins. The HPP treatment, however, resulted in no major changes of anthocyanins and protein in the complex systems compared to the untreated samples. Furthermore, the thermal treatment resulted in stronger interactions between anthocyanins and protein-rich matrix in the complex systems. In the model systems, the increased interactions between anthocyanins and proteins were observed after thermal and PEF treatment probably due to a modified protein conformation and the exposure of reactive groups. Increased degradation during storage in the strawberry-kale system was observed after thermal treatment compared to PEF and HPP processing. The thermal load plays a significant role in the interactions of anthocyanins and their stability during processing, as well as during storage. Within the bioaccessibility assessment, a release of antioxidants during the in-vitro digestion was suggested for any of the systems independent of the processing technologies. Anthocyanins were stable during the gastric phase but significantly decreased during the intestinal phase. This was associated with their pH value dependent structure and stability. In addition, the gastric bioaccessibility of anthocyanins was significantly higher after thermal and PEF treatment, compared to HPP treatment and untreated sample, while the formulation had no impact on gastric bioaccessibility of anthocyanins. The intestinal bioaccessibility was low for any of the investigated formulations or processing technologies. However, it further decreased during storage, probably due to the polymerization of anthocyanins.


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    Title :

    Impact of formulation, processing technology and storage on anthocyanins, proteins and their interactions in complex systems


    Additional title:

    Einfluss von Formulierung, Prozesstechnologie und Lagerung auf Anthocyane, Proteine und deren Interaktionen in komplexen Systemen


    Contributors:

    Publication date :

    2022



    Type of media :

    Miscellaneous


    Type of material :

    Electronic Resource


    Language :

    English



    Classification :

    DDC:    629



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