Microbial production of potent antioxidants from fungal fermentation of tannin-rich plants

Tannins are high molecular weight plant polyphenols divided into two chemically and biologically distinct groups: condensed tannins or proanthocyanidins (e.g. from tea, grapes, cranberries etc.) and hydrolysable tannins or ellagitannins (ETs) (e.g. from raspberries, strawberries, pomegranates etc.) and gallotannins (GTs). Tannins gained original popularity in the commercial 'tanning' industry where animal hides were converted into leather by using plant extracts but have attracted much recent attention due to their numerous biological activities and implications in potential benefits to human health. In this work, creosote bush (Larrea tridentata) and pomegranate peels (Punica granatum) were characterized for their use as support of solid state cultures and source of antioxidants. This work was focused in the kinetic evaluation of physicochemical changes during the fungal fermentation of two tannin-rich plant materials, mainly in the polyphenolic content. Aspergillus niger GH1 was used in the fermentation processes, the cultures were monitored during 96h. Protein, crude fiber, lipid, reducing and total sugars contents were evaluated following the AOAC methods. Tannins were analyzed using Folin-Ciocalteu method. Nordihydroguaiaretic acid (NDGA), gallic and ellagic acids accumulation was determined by HPLC. Results demonstrated that pomegranate peels is an excellent source of ellagic acid while creosote bush leaves for NDGA, when they are used as support of fungal solid state fermentation.