DOI: 10.47743/achi-2024-2-0012 ACTA CHEMICA IASI, 32_2, 207-236 (2024) BIOACTIVITY OF ETHANOL EXTRACTS AND LIPOSOMAL FORMULATIONS FROM PSIDIUM GUAJAVA LEAVES: ANTIOXIDANT, ANTIBACTERIAL, AND α-GLUCOSIDASE INHIBITION EFFECTS Cong Phuc Huynh a , Thanh Phong Pham a , Minh Khoi Nguyen a , Quang Hieu Tran b a Tran Khai Nguyen High School, 225 Nguyen Tri Phuong, District 5, Ho Chi Minh City 700000 b Basic Sciences Department, Saigon Technology University, 180 Cao Lo, District 8, Ho Chi Minh City 700000, Vietnam Abstract: This study investigated polyphenol extraction from guava (Psidium guajava) leaves using ethanol and various organic solvents. The resulting extracts exhibited significant antioxidant, antibacterial, and α-glucosidase inhibitory activities. The EtOAc fraction demonstrated the strongest antioxidant activity (IC50 55.61 µg/mL), comparable to vitamin C (IC50 65.09 µg/mL). The hexane fraction exhibited the most potent antibacterial activity (MIC 1000 µg/mL against P. aeruginosa and 1400 µg/mL against S. aureus). The EtOAc fraction extract showed potent α-glucosidase inhibition (IC50 2.98 µg/mL), 28.16 times lower than acarbose (IC50 83.91 µg/mL). Notably, nanoliposome system encapsulating the ethanol extract was successfully prepared (average particle size 159 nm, PDI 0.384, zeta potential -11.5 mV), displaying significantly enhanced antioxidant activity compared to the unencapsulated extract. These findings suggest considerable promising food and pharmaceutical applications of guava leaf extract, particularly the EtOAc fraction and its nanoliposomal formulation. Keywords: guava leaves, polyphenols, α-glucosidase, flavonoids, quercetin, nano liposome  Tran Quang Hieu, e-mail: hieu.tranquang@stu.edu.vn