Unlocking the potential of Psidium guajava leaves: From traditional uses to functional foods

• Guava leaves are rich in phenolics, flavonoids, tannins, and minerals. • Green extraction (UAE, MAE) improves yield and stability of bioactives. • Extracts show antioxidant, antidiabetic, and antimicrobial activities. • Guava leaf phytochemicals suit nutraceuticals and antimicrobial biopolymer films. • Gaps include non-standardized extraction and limited clinical validation. This review critically discusses the multiple-use potential of Psidium guajava , commonly known as guava, especially how traditionally used leaves can be applied to functional food systems and sustainable packaging technology. Three important dimensions are argued: i) the nutritional and phytochemical profile of guava leaves, since it characterizes sufficient levels of polyphenol, flavonoid, tannin, and terpenoid species; ii) excellent techniques of extraction and characterization that include the development of emerging green technologies such as ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE), among others, that enhance bioactivity recovery and stability; iii) the biological activities of the guava leaf constituents-antioxidant, antidiabetic. The research gap identified in this review is the lack of a uniform method for extracting and assessing the clinical efficacy of phytochemicals in plants, as well as the variability in phytochemical content across plant species. Future research prospects have been proposed, including data-driven optimization and multidisciplinary research. The combination of these elements makes guava leaf a contender as a natural product in the pursuit of traditional knowledge, modern food innovation, and sustainable development.