## 1 Introduction  
The spoilage of protein-rich foods poses significant challenges, primarily affecting shelf life, color, flavor, and overall nutritional value [1, 2]. By understanding the mechanisms behind these changes, it is possible to predict, control, and regulate reactions during food production, thus reducing or eliminating spoilage's adverse effects on human health. Protein oxidation is a major spoilage in protein-based foods like milk and cheese. Addressing protein oxidation involves understanding the oxidative pathways within food proteins and their impact on food quality. This knowledge can then be applied to enhance antioxidant defenses, thereby improving protein functionality [3, 4]. Riboflavin (Rib) is also known as vitamin B\({}_{2}\), which is essential for energy metabolism, immune system support, skin and eye health, and maintaining nervous system function in the human body [5]. As a vital nutrient in the food system, Rib is abundantly present in dairy products, meats, leafy vegetables, and other foods, helping to fulfill daily nutritional requirements. However, Rib can also act as an efficient photosensitizer. Upon absorbing visible light, it reaches a singlet excited state and undergoes intersystem crossing to a highly reactive triplet state [6; 7], as shown in Equation (1). In dairy products, Rib can oxidize proteins, forming low-molecular-weight sulfur compounds, such as dimethyl disulfide, which imparts an undesirable burnt feather aroma [8; 9]. The above oxidative processes are key factors in protein spoilage. While Rib is commonly present in food systems and is essential for providing nutritional value, it also poses a risk of oxidizing amino acids in biological activities. Photooxidation is an important pathway for protein oxidation. Amino acids, such as tryptophan, tyrosine, phenylalanine, and cystine, are primary targets of photodegradation. Under light exposure, electrons are transferred from amino acids to oxygen molecules, initiating an oxidation reaction. Common photooxidative products of amino acids include dehydrogenation products, phenolic compounds, free radicals, and peroxides, among others [10]. These oxidative products can affect the original physicochemical properties and may even impact the intrinsic value of proteins. Within proteins, tyrosine and phenylalanine can transfer their excited-state energy to tryptophan (Trp), which, despite its relatively low abundance, has the highest molar absorptivity with an indole ring. Consequently, Trp becomes the primary participant in the photodegradation pathway [10]. Trp is highly oxidized and degrades into a variety of products during manufacturing, storage, and processing. As described in detail in the literature [11], many physical and chemical processes cause tryptophan degradation, primarily through oxidation or cleavage of highly active indole rings. The cation radical of Trp (Trp\({}^{\bullet+}\)), with an extinct excited state absorption feature (\(\lambda_{\text{max}}\)) at 550-560 nm, is the major oxidation product of Trp. It has a lifetime of approximately microseconds and reduces the original nutritional value [12], as shown in Equation (2). Therefore, preventing the oxidation of Trp is essential for maintaining the nutritional value of proteins in food. \[\text{Rib}\overset{\text{Inc}}{\rightarrow}\left[{}^{1}\text{Rib}^{\bullet} \right]\overset{\text{ISC}}{\rightarrow}{}^{3}\text{Rib}^{\bullet} \tag{1}\]  
\[{}^{3}\text{Rib}^{\bullet}+\text{Trp}\rightarrow\text{Trp}^{\bullet+}+ \text{Rib}/\text{Rib}^{\bullet-}/\text{Rib}\text{H}^{\bullet} \tag{2}\]  
\[\text{Trp}^{\bullet+}+\varphi-\text{O}^{-}\rightarrow\varphi-\text{O}^{ \bullet}+\text{Trp} \tag{3}\]  
Plant phenols play a crucial biological role, including acting as free radical scavengers to protect organisms from oxidative stress. Plant phenols exert antioxidant effects through a reduction-regeneration mechanism [13].