IMMOBILIZATION OF Penicillium purpurogenum GH2 IN SYNTHETIC SUPPORT FOR PIGMENT PRODUCTION
Recent investigations on natural pigments sources had increased due to the toxicity of synthetic colorants used in foods, pharmaceuticals and cosmetic preparations. Fungi provide a readily available alternative source of natural pigments. Submerged fermentation usually results in uncontrolled growth of mycelium and presents high viscosity that could affect oxygen and mass transfer, and in consequence the overall productivity. Therefore, the control of hyphal growing is critical when the fermentation process is carried out at bioreactor scale. Fungi immobilization in a support material may be an alternative to control the growth rate. Furthermore, the biomass of an immobilized fungus is easily removed from the culture media, reducing the downstream processing operations. The aim of the present study is to evaluate the production of pigments by free and immobilized mycelia of Penicillium purpurogenum GH2 using different support materials.The medium Potato Dextrose Broth (ATCC medium: 336) was used for the seed culture preparation. Different commercial synthetic sponges (Scotch brite®) were tested to select the most suitable one to produce pigments: (A) White scouring sponge, (B) Heavy duty black scouring pad, (C) Yellow scouring sponge and (D) Heavy duty green scouring pad. Prior to use in the fermentation experiments, the fiber cubes (1 cm x 1 cm x 1 cm) were pre-treated by boiling during 10 min, and washed thoroughly three times with distilled water. After that, cubes were dried overnight at 60 °C and autoclaved at 121 °C for 20 min. Pigment production was carried out in Erlenmeyer flasks with and without the support for immobilization in Czapeck modified medium. A mycelial suspension was used as inoculum. The inoculated flasks were incubated at 30±2°C on an orbital shaker (Inova 94, New Brunswick Scientific, USA) at 200 rpm for 7 days. For pigment extraction, each sample was pressed and the obtained extract was then subjected to centrifugation at 8000 rpm for 30 min at 4oC. The supernatant was then filtered through a 0.45 μm cellulose filter (Millipore, USA). The concentration of red pigments was quantified indirectly measuring the optical density at 500 nm using a spectrophotometer (Cary 50, UV-Visible Varian, USA). The biomass concentration was determined using the gravimetric method. P. purpurogenum GH2 was able to grow in the different synthetic fibers studied. Among the supports used, the maximum percentage of immobilized mycelium was on sponges A and B (91.874.55 and 96.170.96 %, respectively). The maximum pigment production by immobilized mycelium was achieved by using sponge A (10.080.16 OD500nm), and did not show a significant increase in pigment yield in comparison to free mycelium (10.170.43 OD500nm). However, the immobilization is a culture engineering strategy allowing a downstream-processing intensification and a cost reduction. The use of synthetic fibers for immobilization of Penicillium purpurogenum GH2 did not present a significant increase in pigment production in comparison to free mycelium. However immobilization of Penicillium purpurogenum GH2 represents a highly advantageous strategy to improve the separation of biomass from the reaction mixture, simplifying the downstream processing during the pigment production process.
Keywords: Fungal pigments, immobilization, synthetic support.