Mirta Daz

Antibacterial activity of naringin derivatives against pathogenic strains

Aims:  To study the antimicrobial activity of naringin (NAR), a flavonoid extracted from citrus industry waste, and NAR derivatives [naringenin (NGE), prunin and alkyl prunin esters] against pathogenic bacteria such as L. monocytogenes, E. coli O157:H7 and S. aureus. The relationship between the structure of the chemical compounds and their antagonistic effect was also analysed.

Antimicrobial properties of prunin, a citric flavanone glucoside, and its prunin 6″-O-lauroyl ester

Aims:  To determine the antimicrobial potential of prunin (P), a flavanone glucoside resulting from the hydrolysis of naringin present in grapefruit, and of its prunin 6″‐O‐lauroyl ester (PL), synthesized by enzymatic catalysis.

Synthesis of rutinosides and rutinose by reverse hydrolysis catalyzed by fungal α-l-rhamnosidases

The synthesis of α-l-rhamnosyl(1→6)-β-d-glucosides (rutinosides) and α-l-rhamnosyl(1→6)-β-d-glucose (rutinose) catalyzed by several fungal α-l-rhamnosidases was studied by the reverse hydrolysis reaction between rhamnose plus naringenin 7-β-d-glucoside (prunin) and rhamnose plus glucose, respectively. The products of the reaction were determined by HPLC with some available standards. As expected, the major product of prunin rhamnosylation was always narirutin (naringenin-7-β-d-rutinoside), which originated from the glycosylation of the primary alcoholic group of the glucoside. Whereas, Aspergillus terreus, Penicillium decumbens and P. ulaiense α-l-rhamnosidases gave other minor derivatives besides narirutin, two commercial A. niger enzymes synthesized it as the unique reaction product. Initial rate kinetics of narirutin synthesis catalyzed by the purified A. niger α-l-rhamnosidase did not permit distinction between sequential and ping pong mechanisms, but showed strong inhibition by the substrate l-rhamnose. Equations derived for competitive inhibition together with non-exclusive inhibition by this substrate, gave the best fit to the kinetic experimental data. When glucose was rhamnosylated by the A. niger enzyme, two other minor products appeared together with the disaccharide rutinose. Conditions for obtaining maximum rutinose yield were determined.

Prunin- and hesperetin glucoside-alkyl (C4-C18) esters interaction with Jurkat cells plasma membrane: consequences on membrane physical properties and antioxidant capacity.

Prunin (P)- and hesperetin glucoside (HG)-alkyl esters are lipid-soluble compounds with antimicrobial and antioxidant capacities in vitro. The effects of P- and HG-alkyl (C4-C18) esters (0.1-100μM) on human leukemia T (Jurkat) cells viability and plasma membrane fluidity were evaluated. After 1h of exposure, cell viability was not affected in the range 0.1-10μM. The decrease of cell viability found at 100μM concentration depended on the length of the alkyl chain and reached a maximum with C6-C12 derivatives. At this concentration, cell hyperpolarization and shrinkage were also observed. Cell plasma membrane fluidity was not affected, regardless the depths of the membrane level evaluated, but mild changes in plasma membrane hydration were found. Esterification did not affect the antioxidant capacity of P and HG (0.1-10μM) against 1mM H2O2. When exposed to 1mM AAPH, P-alkyl esters retained P antioxidant capacity, but HG-derivatives acted as pro-oxidants. Together, present experimental evidences suggest that short term exposures to 0.1-10μM concentrations of P- and HG-alkyl (C4-C18) esters can be considered safe for cultured human cells, and further studies are required to investigate their long term effects, as well their safety for human consumption.