# Microencapsulation of Polyphenols and Their Application in Food Technology
## 3 Polyphenols: Properties and Significance in Food
### Biological and Functional Properties of Polyphenols  
Polyphenols are a diverse group of phytochemicals known for their potent antioxidant properties. They combat oxidative stress by neutralizing reactive oxygen species (ROS), such as hydroxyl radicals and superoxide anions, which can damage cellular components like DNA, proteins, and lipids. By scavenging ROS, polyphenols protect cells from the oxidative damage that can lead to aging and various diseases. In addition to direct ROS scavenging, polyphenols chelate transition metals such as iron and copper, which are involved in free radical generation through Fenton and Haber-Weiss reactions. This further reduces oxidative damage and enhances their protective properties [16,17]. Flavonoids, a major subclass of polyphenols found in foods like citrus fruits and green tea, are particularly effective in reducing oxidative stress. They do so by modulating the expression of antioxidant enzymes such as superoxide dismutase (SOD) and catalase, which play key roles in the cellular defence against ROS. For instance, flavonoids in green tea have been shown to increase the activity of these enzymes, thereby strengthening cellular antioxidant defences and promoting health [18, 19, 20, 21]. Besides their antioxidant activity, polyphenols are also known for their anti-inflammatory effects. These compounds inhibit pro-inflammatory signalling pathways, such as NF-kB and COX-2. NF-kB is a transcription factor that regulates the production of pro-inflammatory cytokines, while COX-2 is an enzyme involved in the synthesis of pro-inflammatory prostaglandamins. By suppressing these pathways, polyphenols reduce the levels of inflammatory markers, such as TNF-\(\alpha\) and IL-6, which are implicated in chronic diseases like atherosclerosis and neurodegeneration [22]. For example, studies have demonstrated that regular consumption of green tea, which contains flavonoids like epigallocatechin gallate (EGCG), can lead to a decrease in the expression of these inflammatory markers. Polyphenols also have significant anticancer properties. Resveratrol, a polyphenol found in red wine and grapes, is particularly well studied for its anticancer effects. It exerts its anticancer action by modulating the key molecular path  
Figure 1: Key polyphenic compounds and food sources thereof (created in BioRender. [PERSON] (2025) [[https://BioRender.com/o801442](https://BioRender.com/o801442)]([https://BioRender.com/o801442](https://BioRender.com/o801442)); accessed on 13 December 2024). ways involved in cell cycle regulation and apoptosis. Resveratrol inhibits the activity of cyclin-dependent kinases, which control cell cycle progression, and promotes apoptosis by activating caspases. Additionally, it inhibits the expression of anti-apoptotic proteins, such as Bcl-2, enhancing the susceptibility of cancer cells to programmed cell death [23]. This mechanism helps in the elimination of cancerous cells and reduces the risk of tumorigenesis, especially in colon, breast, prostate, and melanoma cancers. Furthermore, polyphenols have beneficial effects on vascular health. They enhance endothelial function by promoting the production of nitric oxide (NO), a molecule that induces vasodilation and lowers blood pressure. NO is produced by endothelial cells in response to polyphenol consumption, leading to relaxation of smooth muscle cells in blood vessels and improved blood flow. This mechanism is particularly beneficial for preventing cardiovascular diseases, as polyphenols have been shown to reduce LDL cholesterol oxidation and improve vascular elasticity. Dark chocolate, rich in polyphenols, has been linked to improved blood pressure and vascular health, demonstrating its cardioprotective effects [24; 25]. In metabolic health, polyphenols improve insulin sensitivity and regulate lipid metabolism. Green tea catechins, such as EGCG, enhance insulin signalling and promote glucose uptake in muscle cells, reducing blood sugar levels, especially after meals.