It is possible to produce biodiesel from oil extracted from a microorganism that uses industrial waste – glycerol – in its development. This was found in a doctoral study defended by food engineer Susan Hartwig Duarte, supervised by collaborating professor at the Faculty of Food Engineering (FEA) Francisco Maugeri Filho.

To reach this conclusion, Susan explored wild yeasts (a class of microorganisms) isolated from Brazilian ecosystems, such as the Atlantic Forest, the Cerrado, the Pantanal and the Amazon Forest. In the end, she studied a set of 129 yeasts and selected those with the greatest potential for lipid accumulation, as they provide a greater volume of oil. 

The yeast that showed the greatest potential in this aspect was LEB-M3, an acronym named at the FEA Bioprocess Engineering Laboratory. For this reason, it became the focus of analyzes by Susan and the Bioprocess Engineering Research Group, led by Maugeri. 

The author of the thesis managed to produce lipids (biomolecules) from this microorganism present in nature, generating significant amounts of oil inside the yeast cell. 

The researcher used glycerol as an energy source for the growth of the microorganism and, based on the characteristics of the oil produced, suggested that it could be used for the production of biodiesel.

Susan's investigation, Maugeri points out, aimed to use a low-cost raw material that is currently a major problem for the biofuel industry. “The production of biodiesel generates a large percentage of the volume of oil used in crude glycerol, which unfortunately does not yet have a very specific purpose, and its purification would represent a high cost”, she informs. 

For the thesis advisor, the intention was to achieve a product with greater added value for the application of this raw glycerol, in order to obtain fuel from the oil produced or use it for more noble applications, such as in the food industry. “This is because the oil resulting from this microorganism has a quality very close to that of a vegetable oil, especially because it contains fatty acids such as omega 3 and omega 6, considered good fats”, he highlights. 

The professor believes that this oil probably has very interesting characteristics for use in the petrochemical, pharmaceutical and cosmetic industries. 

SELECTION

According to Susan, all yeasts that have more than 20% of their dry mass in lipids can be classified as oleaginous yeasts. 

The researcher highlights that she carried out a genotypic identification of the oleaginous yeast selected in the project as a Candida sp. Furthermore, cultivation media, media optimization and cultivation parameters such as agitation/aeration were studied in a benchtop bioreactor. 

She also analyzed the fatty acid profile of the material produced, which is of great relevance for identifying possible uses for the oil. She then verified that this profile was similar to that of vegetable oils, especially those used in the production of biodiesel.  

These lipids, according to the author, are formed intracellularly and are not easy to extract because the microorganism cell is quite rigid. Therefore, the doctoral student resorted to a cell rupture study, in search of an efficient and alternative method to recover the oil. At this stage, she evaluated different physical and chemical techniques to rupture the cell and facilitate subsequent extraction. 

The researcher also chose to carry out some oil extraction experiments with supercritical carbon dioxide (which has a density close to that of a liquid and has low viscosity and diffuses like a gas). This is a new technology suitable for extracting compounds from microorganisms, in addition to being less aggressive. “The results were very promising”, he guarantees.

There's more: as biodiesel processing requires a catalyst (normally the most adopted industrially are chemical catalysts), Susan chose an enzyme to catalyze the reaction, which in this case was lipase. 

Enzymes, among many advantages of application in this process, can be reused when immobilized on a suitable support. “When biodiesel production reached a certain yield, the enzyme was able to be reused. This is because, when immobilized, it shows greater stability, ensuring that no changes occur in the characteristics that are desirable in the process.” 

The researcher believes that the production of biodiesel using microbial lipids in which enzymes are used as catalysts does not yet exist in the industrial sector. “So, our process is something very innovative.”

EXPERIENCE

During her doctorate, Susan visited the Autonomous University of Barcelona, ​​Spain, where she stayed for six months for a well-defined mission: to apply the oil obtained for the production of biodiesel. This part of the work was carried out under the guidance of Spanish professor Francisco Valero at the Applied Biocatalysis Laboratory. 

The group from this University, reveals, already had experience in the production of biodiesel with enzymes, but with oils from other sources. “We took the yeast oil there and it was very well received”, he highlights. 

According to Susan, this research allowed us to see an alternative source of oil for the production of biodiesel, because the sources of oil most used at the moment are soybeans, peanuts, castor beans and sunflower, among others, which require their planting. in large areas of cultivable land, which would end up competing with the food sector – a dispute for land space.

The researcher reports that the biggest bottleneck in her study was in the cell rupture and lipid extraction stage. In her opinion, less aggressive methodologies for oil recovery should also be studied and put into practice. 

In the laboratory, as a rule, chloroform and methanol are used for extraction, and in the industrial sector, hexane. It turns out that these solvents are potentially toxic. Therefore, there is a need to look for new alternatives to avoid damage, including the inhalation of these solvents. 

Nowadays, reveals the doctoral student, all diesel used in Brazilian public transport must contain 7% biodiesel in its composition. This is a requirement of the law and therefore it is important to unveil other innovations in biodiesel production to comply with the legislation. 

The increase in the percentage of biodiesel added to diesel has been increasingly encouraged in the country, as this biofuel does not originate from petroleum, because above all it is a renewable source of energy, notes the food engineer.

Publications

- DUARTE, SH, DEL PESO, G., CANET, A., BENAIGES, MD, MAUGERI, F., VALERO, FB Enzymatic biodiesel synthesis from yeast oil using immobilized recombinant Rhizopus oryzae lipase. Bioresource Technology, v. 183, p. 175-80, 2015.

- DUARTE, SH, ANSOLIN, M., MAUGERI, F. Cultivation of Candida sp. LEB-M3 in glycerol: Lipid accumulation and prediction of biodiesel quality parameters. Bioresource Technology, vol. 161, p. 416-22, 2014.

Tese: “Production and extraction of microbial lipids for enzymatic synthesis of biodiesel”

Author: Susan Hartwig Duarte

Advisor: Francisco Maugeri Filho

Each: Faculty of Food Engineering (FEA)

Financing: CNPq and Capes