Abstract
The emergence of bacterial strains resistant to different antibiotics has prompted the search for new sources of antimicrobial compounds. Studies have shown that jambolan [Syzygium cumini (L.) Skeels], a tropical fruit from the Mirtaceae family, contains a great variety of phytochemical compounds with high antioxidant and antimicrobial activity. This study aimed to determine the centesimal composition and physicochemical characteristics of the pulp and seed of S. cumini (L.) Skeels, as well as the content of total phenolic compounds and the antioxidant, antibacterial, antibiofilm and anti-quorum sensing (QS) activities of the phenolic extracts obtained from the pulp and the seeds of this fruit. The in vitro antibacterial and anti-QS activities of active films incorporating phenolic extracts were also evaluated. Additionally, we performed molecular docking of phenolic compounds present in jambolan with the CviR QS regulator of Chromobacterium violaceum. The composition and physicochemical characteristics of the samples presented similar values to those found for the species. However, the seed phenolic extract had a higher content of phenolic compounds and antioxidant activity than the pulp. Both phenolic extracts presented antibacterial activity against Aeromonas hydrophila, C. violaceum, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica serovar Typhimurium, Serratia marcescens, Listeria monocytogenes, and Staphylococcus aureus. The seed phenolic extract was particularly inhibitory against S. aureus. The pulp phenolic extract inhibited swarming motility and biofilm formation of A. hydrophila, E. coli, and S. marcescens in sub-MIC concentrations. The pulp and seed phenolic extracts inhibited violacein production in C. violaceum. Films incorporating both phenolic extracts inhibited the growth of bacteria, particularly Pseudomonas fluorescens, L. monocytogenes, and S. aureus, as well as QS in C. violaceum. Molecular docking showed that a variety of compounds found in pulp and seed extracts of jambolan, particularly chlorogenic acid and dihydroquercetin, potentially bind CviR protein and may interfere with QS. Our results indicate that pulp and seed of jambolan are good sources of antibacterial, antibiofilm, and anti-QS compounds that can be used in the development of natural preservatives and for application in antibacterial active films.
Highlights
Syzygium cumini (L.) Skeels, known as jambolan or by its several popular names in Brazil, black plum, northeastern olive, nun berry, and earth olive, belongs to the Myrtaceae family
Seed phenolic extract showed greater anti-quorum sensing (QS) activity against C. violaceum compared to the pulp phenolic extract
The films incorporating both phenolic extracts were inhibitory to most evaluated bacteria, especially P. fluorescens, L. monocytogenes and S. aureus
Summary
Syzygium cumini (L.) Skeels, known as jambolan or by its several popular names in Brazil, black plum, northeastern olive, nun berry, and earth olive, belongs to the Myrtaceae family. Syzygium cumini (L.) Skeels presents a high antioxidant activity and high levels of phenolic compounds, which have a protective effect on food, mainly because of its antioxidant properties (Tavares et al, 2017). The antioxidants may present antimicrobial activity (Loguercio et al, 2005). Several studies using leaves, bark, essential oils, fruits, and seeds have demonstrated the beneficial effects of jambolan, such as antioxidant (Vizzotto and Pereira, 2008; Singh et al, 2016) and antimicrobial activities (Singh et al, 2016). Nothing is known about the inhibition of bacterial quorum sensing (QS) by S. cumini (L.) Skeels
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