# Physicochemical, Functional, and Antioxidative Characteristics of Oyster Mushrooms
## 1 Introduction  
Oyster mushrooms (_Pleurotus__o_ \(w\) _et_ _atus_) are known for their impressive physicochemical properties, functional traits, and various health benefits. They are rich in essential nutrients, including carbohydrates, proteins, vitamins, and minerals. They also contain abundant polysaccharides, such as chitin and glucan, which play a critical role in the structure and function of the mushroom. The carbohydrate content usually counts around 50-60% dry matter, contributing to the high dietary fibre content [1]. Although lower than animal sources, _P. ostreatus_ proteins include essential amino acids such as lysine and leucine, making them a valuable alternative to animal proteins [2]. Products combining mushroom-derived proteins and potatoes showed potential as meat alternatives, characterized by structural stability and a visually appealing brown appearance due to the inclusion of mushrooms. However, further research is needed to optimize their sensory and nutritional profiles for broader use in plant-based diets [3]. Oyster mushrooms are recognized as functional foods due to their diverse bioactive compounds, including antioxidants, \(\beta\)-glucans, prebiotics, and immune-modulating substances. The \(\beta\)-glucans in mushrooms enhance immune function, reduce inflammation, and exhibit prebiotic effects, promoting a healthy gut microbiome [2,4]. Furthermore, their low-fat and high-fibre content supports digestive health, weight management, and cholesterol reduction [5]. Additionally, ergothioneine, a potent antioxidant in oyster mushrooms, helps combat oxidative stress. Processing methods significantly impact the nutritional composition and functional properties of oyster mushrooms. Among the commonly used methods, drying techniques have been extensively studied for their effects on nutrient retention, structural integrity, and bioactivity [6]. The choice of drying method profoundly impacts oyster mushrooms' nutritional and functional properties [2]. While freeze-drying excels in preserving bioactive compounds and structural integrity [7], vacuum-pulse and microwave drying offer advantages in enhanced nutrient content and reduced processing time [4,8]. Dry-air drying, although less effective in retaining bioactivity, can improve digestibility through increased free amino acid and glucose contents. Also, the health benefits of oyster mushrooms are extensive, as they have been linked to a reduced risk of heart disease, improved immune responses, and even potential anti-cancer properties. Antioxidants like ergothione, phenolic compounds, and flavonoids help protect the body from oxidative stress associated with ageing and chronic disease [1,2]. Research also suggests that oyster mushrooms may help control blood sugar levels, making them useful for diabetes management [9]. This aligns with earlier studies highlighting their potential role in metabolic health [10]. Additionally, they have been shown to have anti-inflammatory, antimicrobial, and hepatotoxicity properties [3]. Oyster mushrooms' physicochemical and functional properties contribute significantly to their high nutritional value and medicinal potential. Rich in essential nutrients and bioactive compounds and low in fat, they have numerous health benefits, making them an essential component of functional foods to improve human health. However, in commercial settings, not all oyster mushrooms maintain their market value, as physical imperfections can reduce their consumer appeal, creating an opportunity to explore alternative applications for these nutritionally valuable but commercially downgraded mushrooms. Low-grade oyster mushrooms in Poland can be classified as mushrooms that do not have significant market value due to certain physical defects that reduce their attractiveness to consumers. Such defects include the following:  
* Small cap size: usually, the diameter of such mushrooms is significantly smaller than that of higher-grade oyster mushrooms, which does not meet standard quality requirements.