The work herewith investigated the production of yeast biomass as a source of protein, using Yarrowia lipolytica NRRL YB-423 and raw glycerol from biodiesel synthesis as the main carbon source. A significant influence of glycerol concentration, initial pH and yeast extract concentration on biomass and protein content was observed according to the 2v5-1 fractional design. These factors were further evaluated using a central composite design and response surface methodology, and an empirical model for protein content was established and validated. The biomass of Yarrowia lipolytica NRRL YB-423 reached 19.5 ± 1.0 g/L in shaken flasks cultivation, with a protein content of 20.1 ± 0.6% (w/w).
This article proposes an easy, quick, and efficient microwave method for the routine laboratory extraction of lipids from wet microalgae paste. A microwave synthesis instrument is used, and time and temperature are optimized using a central composite design. A chloroform/methanol mixture (2:1 v/v) is used as extractor solvent and the ideal condition is 1 min of microwave irradiation at 80 °C using power mode at 300 W. The scanning electron microscopy (SEM) analysis shows extensive cell damage leading to cracking, fragmentation, and large debris in a shorter treatment time. In addition, the fatty acids profile shows that microwave irradiation method has no degrading effect on the extracted fatty acids. The extraction by microwave achieves a significantly higher yield (33.6 ± 2.6%) with only 1 min of extraction time than conventional ultrasonic extraction (20 min, 25 °C, 28.51 ± 0.8% yield) from wet Nannochloropsis oculata biomass. Next, the efficiency of the extraction method in is evaluated in terms of species variation by applying it to the algal paste of Amphora coffeaeformis, Chaetoceros gracilis, and Isochrysis galbana. The lipid content obtained from A. coffeaeformis, C. gracilis, and I. galbana is 16.27 ± 1.5, 22.31 ± 2.5, and 19.87 ± 2.4%, respectively. Thus, the microwave method is successfully applied to algal paste.
Practical Applications: The microalgal cell wall disruption is an important and complex stage and effective methods of disruption are fundamental to extracting lipids. This study shows an easy, quick, and efficient microwave method for application in routine laboratory extraction of lipids from wet microalgae pastes. A microwave compact instrument is used and the ideal condition is 1 min of microwave irradiation. The method proves to be robust against variation in mass achieved and significantly higher yield in a shorter time than ultrasonic extraction (conventional method).
The microalgal cell disruption is an important and complex stage. The use of microwaves to induce cell disruption in wet biomass proves to be efficient for lipid extraction with only 1 min of extraction time. The method is applied successfully to wet microalgae pastes with different cell walls and the microwave radiation does not degrade the extracted fatty acids.
The possibility of using raw glycerol as a substrate for yeast biomass production as a source of proteins was investigated. Biomass concentration, protein content and total protein content of four yeasts (Yarrowia lipolytica NRRL YB-423, Candida lipolytica NRRL Y-1095, Candida utilis NRRL Y-900 and Candida rugosa NRRL Y-95) were determinate, comparing analytical grade glycerol and raw glycerol. Y. lipolytica NRRL YB-423 has been selected as promising for cultivation in a raw glycerol-based medium, mainly due to the higher biomass concentration in relation to the other strains. For this strain, four different culture media were tested. The best results were obtained with 50 g/L glycerol, 5.5 g/L ammonium phosphate, 5.5 potassium dihydrogen phosphate, 1 g/L ammonium sulphate, 0.25 g/L magnesium sulphate, 0.021 g/L calcium chloride dehydrate, 1 g/L yeast extract, 1 g/L peptone, pH adjusted to 5.5. In these conditions, it was possible to obtain 17.8 ± 0.6 g/L maximum biomass concentration, 18.2 ± 1.0% protein content and 3.1 ± 0.1 g/L total protein production. These results represent a 1.2-fold increase in biomass concentration, a 1.5-fold increase in protein content and a 1.9-fold increase in total protein production in relation to the results obtained with the previously medium composition.
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