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. 2019 Aug 16;7(8):265.
doi: 10.3390/microorganisms7080265.

Biodiesel-Derived Glycerol Obtained from Renewable Biomass-A Suitable Substrate for the Growth of Candida zeylanoides Yeast Strain ATCC 20367

Laura Mitrea  1 , Floricuța Ranga  1 , Florinela Fetea  1 , Francisc Vasile Dulf  2 , Alexandru Rusu  3 , Monica Trif  4 , Dan Cristian Vodnar  5
Affiliations

Biodiesel-Derived Glycerol Obtained from Renewable Biomass-A Suitable Substrate for the Growth of Candida zeylanoides Yeast Strain ATCC 20367

Laura Mitrea et al. Microorganisms. .

Abstract

Used kitchen oil represents a feasible and renewable biomass to produce green biofuels such as biodiesel. Biodiesel production generates large amounts of by-products such as the crude glycerol fraction, which can be further used biotechnologically as a valuable nutrient for many microorganisms. In this study, we transesterified used kitchen oil with methanol and sodium hydroxide in order to obtain biodiesel and crude glycerol fractions. The crude glycerol fraction consisting of 30% glycerol was integrated into a bioreactor cultivation process as a nutrient source for the growth of Candida zeylanoides ATCC 20367. Cell viability and biomass production were similar to those obtained with batch cultivations on pure glycerol or glucose as the main nutrient substrates. However, the biosynthesis of organic acids (e.g., citric and succinic) was significantly different compared to pure glycerol and glucose used as main carbon sources.

Keywords: Candida zeylanoides; crude glycerol; fermentations; organic acids; renewable biomass; used kitchen oil.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Samples derivatization flowchart adapted after Imbert et al. [53]. Glucose consumption was measured with an enzymatic test kit from Boehringer Mannheim-R-Biopharm. Biomass and metabolites production yields (Y) were calculated by using the formula [38]. Y (g/g) = Product concentration (g/L)/Initial substrate concentration (g/L).
Figure 2
Figure 2
The fatty acids profile in vegetable oil before and after processing. UVO, unprocessed vegetable oil; RVO, recycled vegetable oil.
Figure 3
Figure 3
The crude glycerol obtaining process through transesterification.
Figure 4
Figure 4
FTIR spectra of crude glycerol obtained from recycled kitchen oils through alkali transesterification. The blue bonds are linked with polyalcohols (glycerol) and the orange ones are associated with the impurities existing in the crude glycerol phase.
Figure 5
Figure 5
C. zeylanoides ATCC 20367 after 48 h in inoculum fermentation medium that contained crude glycerol under microscopic light. The blue stained dots represent viable cells, while the transparent shapes are the dead cells. The big yellow circles represent lipid droplets from the crude glycerol fraction.
Figure 6
Figure 6
Yeast cell viability, biomass, pH, organic acids (citric, succinic), and substrate consumption on different carbon sources. (A) crude glycerol; (B) pure glycerol; (C) glucose.
Figure 7
Figure 7
Comparison between the yeast cell growth (viability, biomass) on crude glycerol, pure glycerol, and glucose during 163 h of batch cultivation.
See this image and copyright information in PMC

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