A hydrodynamic cavitation-assisted system for optimization of biodiesel production from green microalgae oil using a genetic algorithm and response surface methodology approach.

In the present research work, the effect of operating parameters such as molar ratio (3:1-7:1), catalyst concentration (0.5-1.5%), reaction time (5-25 min), and operating pressure (0-4 bar) on the rate of biodiesel conversion percentage for the transesterification reaction using hydrodynamic cavitation (HC) has been studied. Response surface methodology (RSM) and genetic algorithms (GA) were used to find the best condition. The best conditions for biodiesel generation were a molar ratio of 6.5:1, a catalyst concentration of 1.301 wt.%, a reaction period of 11.5 min, and operating pressure of 3.6 bar. The maximum yield of biodiesel obtained under optimal conditions was 97.3%. The reaction time for biodiesel produced by HC under similar conditions as the conventional technique was reduced by 85%. The HC approach is preferable to the conventional method due to its shorter processing time.

Pressurized liquid extraction of Neochloris oleoabundans for the recovery of bioactive carotenoids with anti-proliferative activity against human colon cancer cells.

In recent years, the green microalgae Neochloris oleoabundans have demonstrated to be an interesting natural source of carotenoids that could be used as potential food additive. In this work, different N. oleoabundans extracts obtained by pressurized liquid extraction (PLE) have been analyzed in depth to evaluate the influence of different culture conditions (effect of nitrogen, light intensity or carbon supplied) not only on the total carotenoid content but also on the carotenoid composition produced by these microalgae. Regardless of the cultivation conditions, lutein and carotenoid monoesters were the most abundant carotenoids representing more than 60% of the total content in all extracts. Afterwards, the effect of the different N. oleoabundans extracts and the dose-effect of the most potent algae extracts (namely, N9, PS and CO2 (-)) on the proliferation of human colon cancer cells lines (HT-29 and SW480) and a cell line established from a primary colon cancer cell culture (HGUE-C-1) were evaluated by an MTT assay whereas a stepwise multiple regression analysis was performed to get additional evidences on the relationship between carotenoid content and the antiproliferative activity. Results revealed that, as a general trend, those extracts with high total carotenoid content showed comparably antiproliferative activity being possible to establish a high correlation between the cell proliferation values and the carotenoid constituents. Monoesters showed the highest contribution to cell proliferation inhibition whereas lutein and violaxanthin showed negative correlation and diesters and zeaxanthin showed a positive significant contribution to cell proliferation.

Heterotrophic growth of Neochloris oleoabundans using glucose as a carbon source.

BACKGROUND: In comparison with phototrophic growth, heterotrophic conditions can significantly increase growth rates, final cell number and cell mass in microalgae cultures. Neochloris oleoabundans is a microalga of biotechnological interest that accumulates lipids under phototrophic and nitrogen-limited conditions. Heterotrophic flask culture experiments were conducted to identify carbon sources that can be metabolized by N. oleoabundans, and bioreactor batch and fed-batch (nitrate pulse additions) cultures supplemented with glucose were performed to study the cellular composition of the microalgae under balanced and high C/N ratios (glucose/nitrate). RESULTS: N. oleoabundans was able to grow using glucose and cellobiose as sole carbon sources under strict heterotrophic conditions. Under a balanced C/N ratio of 17 and using bioreactor batch cultures containing 3 g/L glucose, a maximal cell mass of 1.72 g/L was found, with protein being the major cell component (44% w/w). A maximal cell mass of 9.2 g/L was obtained using batch cultures at a C/N ratio of 278. Under these conditions, lipid accumulation was promoted (up to 52% w/w) through N-limitation, resulting in high lipid productivity (528.5 mg/L/day). Fed-batch cultures were performed at a C/N ratio of 278 and with nitrate pulse additions. This condition allowed a maximal cell mass of 14.2 g/L to be achieved and switched the metabolism to carbohydrate synthesis (up to 54% of dry weight), mainly in the form of starch. It was found that transmembrane transport under these conditions was dependent on a proton-motive force, indicating that glucose is transported by a symporter. CONCLUSIONS: N. oleoabundans was able to grow under strict heterotrophic culture conditions with glucose or cellobiose as the only carbon source. The glucose used is transported by a symporter system. Batch cultures with a balanced C/N ratio accumulate proteins as the major cellular component; a high C/N ratio significantly increased the dry cell mass and resulted in a high lipid content, and a high cell density was achieved using fed-batch cultures promoting carbohydrate accumulation. These results suggest heterotrophic batch cultures of N. oleoabundans as an alternative for the production of proteins or lipids with simple culture strategies and minimal-mineral media supplemented with glucose.