This thesis work focused on a specialized plant metabolite group called hydrolysable tannins with the aim of expanding the knowledge on their hydrophobicity, interactions with lipid membranes and antibacterial capacity. Hydrolysable tannins are known to possess many nutritionally and pharmacologically beneficial properties, which is why it is important to find the effective structures and unravel the mechanisms behind these activities.

Initially, the hydrophobicities of 47 chromatographically purified and spectrometrically characterized hydrolysable tannins were determined with octanol/water partitioning measurements. These results revealed that increased flexibility of the structure and larger molecular weight increased the hydrophobicity of the compounds while rigid substituent groups and macrocyclicity decreased it.

In the second and third study, the lipid interactions of hydrolysable tannins were studied with nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry (ITC) using a phospholipid extract of Escherichia coli. The NMR results revealed how some hydrolysable tannins were able to penetrate to lipid moieties that reside inside the lipid bilayer structures thus verifying that hydrolysable tannins are able to perturb surface structures of lipid bilayers. Again, the more flexible structures proved to be more effective but the larger tannins were not able to perturb deep into the lipid bilayers most probably due to their bulkier structures. The thermodynamic results obtained with ITC corroborated the NMR results by showing increased interaction from the same compounds.

In the final part of this work, the antibacterial capacity of selected hydrolysable tannins was evaluated against Escherichia coli and Staphylococcus aureus cultures using an untargeted NMR metabolomics approach and plated inhibition results. All the tested hydrolysable tannins showed antibacterial activity and were able to influence the bacterial metabolome of the bacterial cultures. The altered bacterial metabolome results correleted with the plated inhibition results confirming that the NMR based method was able to reveal inhibition results directly from the culture medium.