Antioxidant, antimicrobial, and α-glucosidase inhibitory activities of saponin extracts from walnut (Juglans regia L.) leaves

Abstract

Objective: To investigate the relationship between triterpenoid saponin content and antioxidant, antimicrobial, and α-glucosidase inhibitory activities of 70% ethanolic, butanolic, aqueous, supernate and precipitate extracts of Juglans regia leaves. Methods: Triterpenoid saponins of different Juglans regia leaf extracts were measured by the vanillin method. Antioxidant activity was evaluated against DPPH and ABTS free radicals. We also assessed α-glucosidase inhibitory and antimicrobial activities of the leaf extracts. Pearson's correlation coefficient was evaluated to determine the correlation between the saponin content and biological activities. Results: The butanolic extract was most effective against DPPH with an IC50 of 6.63 μg/mL, while the aqueous extract showed the highest scavenging activity against ABTS free radical with an IC50 of 42.27 μg/mL. Pearson's correlation analysis indicated a strong negative correlation (r = -0.956) between DPPH radical scavenging activity (IC50) and the saponin content in the samples examined. In addition, the aqueous extract showed the best α-glucosidase inhibitory activity compared with other extracts. All the extracts had fair antibacterial activity against Bacillus subtilis, Escherichia coli, and Klebsiella pneumoniae except for the aqueous extract. Conclusions: Juglans regia extracts show potent antioxidant, antimicrobial, and α-glucosidase inhibitory activities. There is a correlation between saponin levels in Juglans regia leaf extracts and the studied activities. However, additional research is required to establish these relationships by identifying the specific saponin molecules responsible for these activities and elucidating their mechanisms of action.

Exploring the phenolic profile, antibacterial, and antioxidant properties of walnut leaves (Juglans regia L.)

“…This method has been frequently considered to evaluate the antioxidant activities of food materials (Koocheki et al, 2022). Some researchers have reported the antioxidant activity of walnut leaves (Fernández-Agulló et al, 2019;Pereira et al, 2008). In our research, all fractions showed relatively high antioxidant activity.…”

“…The inhibition zone diameters were measured using a ruler with 0.5 mm accuracy, and the average radius of the inhibition zone in mm was calculated from three measurements on three different plates. Control plates inoculated with each sensitive indicator microorganism were also prepared (Fernández-Agulló et al, 2013).…”

“…Therefore, incorporating walnut leaf preparations (food and supplements) into our diet can act as a preventive medicine, providing numerous health benefits (Pires et al, 2018 ). Juglans regia also displays antimicrobial properties that enable it to prevent the growth or destroy microorganisms that can lead to infections (Elouafy et al, 2023 ). Research has demonstrated that several parts of the plant, including the leaves, bark, and nut, contain compounds that possess antimicrobial attributes and can effectively target a broad range of pathogens (Acquaviva et al, 2021 ; Barekat et al, 2022 ; Mateș et al, 2023 ; Żurek et al, 2022 ).…”

A Review on Extracts, Chemical Composition and Product Development of Walnut Diaphragma Juglandis Fructus

“…Numerous studies have shown that compounds extracted from plants, animals, and microorganisms have antibacterial activity and are expected to be novel antibacterial agents. Extensive experiments have demonstrated the antibacterial effects of walnut extract [ 69 , 70 , 71 , 72 , 73 ]. In fact, EeDJF has promising antibacterial activity.…”

Influence of Cold Stress on Physiological and Phytochemical Characteristics and Secondary Metabolite Accumulation in Microclones of Juglans regia L.

“…The walnut (Juglans regia L.) is among the medicinal plants of interest [31][32][33] due to its rich content of antioxidants such as flavonoids, phenolic acids (notably ellagic acid), melatonin, folate, gamma-tocopherol (vitamin E), selenium, juglone, and proanthocyanidins [34][35][36][37] in various organs (kernels, shells, roots, and leaves). Several studies have shown that J. regia, along with its extracts and essential oils, exhibits a range of biological and pharmacological properties, including antibacterial, antifungal, antioxidant, and anti-inflammatory activities, demonstrating effectiveness against a broad spectrum of pathogens [38][39][40][41][42]. Innovative modern biotechnologies are increasingly focused on developing medicinal crops that are rich in biologically active compounds via manipulating growth conditions to enhance the production of these valuable compounds.…”