There is an interest in the use of compounds able to prevent organism damages. Antioxidants are such compounds that can protect from cells damages caused by free radicals and may be used in the treatment and prevention on many diseases, such as cancer, cardiovascular disease, diabetes, brain stroke, skin diseases as well as they delay the aging process. There are many sources of antioxidants. They can be synthetic or natural and especially those derived from natural sources, demand special attention. Phenolic compounds are substances which mainly possess such activity, but also vitamins and minerals. There are a lot of antioxidants, but in that review, the chosen compounds with outstanding antioxidant activity, mainly used in pharmaceuticals and cosmetics were described. The review shows the activity of phenolic acids (ferulic acid and caffeic acid) and polyphenols (ellagic acid, curcumin, genistein, hydroxytyrosol, resveratrol) and vitamins (C and E).

The aim of this research was to conduct biotransformation of phenolic compounds, prochiral ketone acetophenone into optically pure (R)-and (S)-1-phenylethanol and 2-phenylethanol into tyrosol and hydroxytyrosol. For acetophenone reduction reaction, the biocatalysts of choice were cyanobacteria, phototrophic microorganisms with biocatalytic potential that have not yet been fully discovered. For the hydroxylation reaction of 2-phenylethanol, instead of using vital Aspergillus niger cells, the reaction was carried out using the spores. As a result, high conversion rates were obtained (79.6%) for the reduction reaction performed by photobiocatalyst Nodularia sphaerocarpa, although the enantioselectivity was moderate (enantiomeric excess, ee 48%). The reaction carried out by cyanobacterium Leptolyngbya foveolarum yielded 25.7%, but with high enantioselectivity of (S)-1-phenylethanol 95% ee was received. It has also been proven that the acetophenone reduction did not depend on the light regime. For aromatic ring hydroxylation, several modifications of the conditions of biooxidation were introduced to maximize the effectiveness; the addition of glucose into the reaction medium gave the best results. As a result, new methods of bioconversion of phenylethyl alcohol have been developed, leading to the formation of desired products: 1-phenylethanol, tyrosol, and hydroxytyrosol antioxidants, compounds of utilitarian meaning.

Aspergillus niger (IAFB 2301) was employed for bioconversions of 2-phenylethanol as an immobilized or free mycelium and also as a spore suspension. Experiments were conducted on laboratory and half-preparative scale (bioreactor New Brunswick Scientific, BioFlo Model C32). Thus, A. niger applied as free mycelium, depending on the outcome, supported formation of the mixture of 4-hydroxyphenylacetic acid and hydroxytyrosol (final concentration of 13.8 mg/L and 3.7% efficiency) or 4-hydroxyphenylacetic acid, as single product (final concentration of 140 mg/L and 18% efficiency). In case of scaling experiments conducted with flow and batch reactors, accordingly, the following results were achieved: 1. mixture of antioxidants 4-hydroxyphenylacetic acid and hydroxytyrosol formed with final concentration of 76 mg/L and 10% efficiency (simplified flow system and immobilized mycelium); 2. (S)-1-phenylethane-1,2-diol synthesized with a final concentration of 447 mg/L and 65% (1.3 L batch reactor).

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