Quercetin in food: structure, biosynthesis, toxicity, analytical method, occurrence and risk assessments

Quercetin is a prominent member of the flavonol subclass within the flavonoid family and is a biologically active compound widely distributed in various foods, such as onions, kale, broccoli, red wine, green tea, and black tea. It is well known for its diverse physiological activities, including antioxidant, anti-inflammatory, anticancer, antiviral, and antimicrobial effects, which contribute to its recognized health benefits. Owing to these properties, quercetin has been extensively utilized in medical and pharmaceutical applications. While quercetin is generally considered safe when consumed through the diet, concerns have been raised regarding its potential toxicity at high doses. Given its widespread occurrence in foods and its potential for clinical and nutritional use, a comprehensive safety assessment is essential. This includes evaluations through genotoxicity assays and acute, subacute, chronic, and reproductive toxicity studies. Furthermore, accurate quantification of quercetin in various sample matrices is critical for monitoring its levels and assessing associated risks. Therefore, the development of reliable and sensitive analytical methods is of significant importance. This review provides a comprehensive summary of current research on quercetin, as found in food, covering its chemical structure and biosynthesis, toxicity, analytical methodologies, occurrence, and risk assessment.