(563b) Water Soluble Pigments From Biomass for Energy Applications

The increasing interest in microalgal-based fuel feedstock such as lipids for biodiesel and starches for alcohols provides an economic opportunity based on the large amounts of biomass needed for these biofuels. Valuable co-products can help make these fuels economically viable. Among these products are some polymers and pigments that can provide added value to the biomass.

Most current microalgal operations use single species cultures of eukaryotic organisms generally from collections, that are difficult to maintain and can be contaminated by competing or predatory species. The use of mixed cultures of microalgae and cyanobacteria can provide some added benefits, including production of vitamins and probiotics that microalgae need and cannot synthesize. Additionally, the use of native species reduces the risk associated with the introduction of non-native species.

In this work, mixed cultures of cyanobacteria and microalgae isolated from natural water bodies in Baton Rouge, Louisiana were used to produce lipids and pigments. The water soluble pigments are of particular interest to this work, as they can be extracted from the microalgal/cyanobacteria biomass with aqueous based solvents. These solvents do not affect the lipids in the biomass.  The target lipids are non-polar fatty acids, as these can be readily converted to biofuels.

The objectives of this work are to identify pigments that can provide an added value to native aquatic microbial biomass used as feedstock for biofuels. Water soluble pigments were the main targets of this research, due to their compatibility with the lipid extraction process and the high value of these pigments in diverse markets that go from feed and cosmetics to analytical and biotechnological products.

To reach the objective, single and mixed species of aquatic photosynthetic organisms were isolated from a Louisiana natural water body. The cultures were isolated based on their resistance to environmental changes and their growth rate. One mixed culture of a microalgae (Chlorella vulgaris) and a cyanobacteria (Leptolyngbya sp.), called in this document LA coculture,  was selected for this work.  

The LA coculture was maintained in Erlenmeyer flasks with a culture volume of 500 ml at temperatures of 25°C±2, under PAR irradiance of 400 µmol cm^-2 s^-1 with aeration of 14 lph (0.5 scfh). The light was supplied with HPS (high pressure sodium) 400 watts lamps. The biomass was collected at the onset of the stationary phase of the cultures, where lipid accumulation occurs. An aliquot of 150 mL of the culture was extracted with water or with phosphate buffer 0.1, 0.5 and 1 M. The extracted pigments were analyzed by spectrophotometry and the absorbance spectra of the pigments solution obtained with the each one of the aqueous solvents was compared. The maximum absorbance of the pigments was at 620 nm, characteristic of the C-phycocyanin.  The ratio A620/A68 (an indicator of the purity of phycocyanin) from each solution was calculated. The pigment was further purified by rinsing it with different solvents. The highest purity was obtained on the pigment extracted by freezing and thawing with phosphate buffer 0.1 M, after rinse with hexane (purity 3.11-3.67). The lowest purity was btained with pigment extracted with phosphate buffer 1.0 M.   Filtration and centrifugation of the pigment after extraction increased its purity in all cases. A second phycobilin in minor quatities was also identified in the extract.

The lipids were extracted with Folch’s method at room temperature, with chloroform:methanol. The lipid content was 33 % with a SD of 5%. No significant differences were observed with the extraction of pigments, compared with the non-extracted biomass.