Today, biofuels represent a hot topic in the context of petroleum and adjacent products decrease. As biofuels production increase, so does the production of their major byproduct, namely crude glycerol. The efficient usage of raw glycerol will concur to the biodiesel viability. As an inevitable waste of biodiesel manufacturing, glycerol is potentially an attractive substrate for the production of value-added products by fermentation processes, due to its large amounts, low cost and high degree of reduction. One of the most important usages of glycerol is its bioconversion through microbial fermentation to value-added materials like 1,3-propanediol and citric acid. There is a considerable industrial interest in 1,3-propanediol and citric acid production based on microbial fermentations, as it seems to be in competition with traditional technologies utilized for these products. In the present work, yields and concentrations of 1,3-propanediol and citric acid registered for different isolated strains are also described. Microbial bioconversion of glycerol represents a remarkable choice to add value to the biofuel production chain, allowing the biofuel industry to be more competitive. The current review presents certain ways for the bioconversion of crude glycerol into citric acid and 1,3-propanediol with high yields and concentrations achieved by using isolated microorganisms.
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.
The aim of this study was to encapsulate the oleoresins rich in carotenoids extracted from sea buckthorn (Hippophae rhamnoides) fruits into a blend of sodium-alginate and κ-carrageenan microbeads (2% w/v) coated by a sodium-alginate (2% w/v) layer prepared using an ionotropic gelation technique with calcium chloride (2% w/v) by dropping method. The fresh obtained coated microbeads had a “fried eggs” like appearance with a size distribution ranging from 4 to 6 mm. The coated microbeads were analyzed for their SEM and fluorescence. The encapsulation efficiency was 92%. Their stability was investigated by evaluation of the physical integrity performance in aqueous media with different pH to mimic the gastrointestinal tract for 24 h at 37 °C under laboratory conditions. The results demonstrated the limitation of the coated microbeads swelling ability under pH 7. The coated microbeads could be a good tool to guarantee oleoresins rich in carotenoids stability and colon delivery. The present study shows an attractive encapsulation system of oleoresins, in order to obtain stable products for further applications.
During biodiesel production, massive amounts of raw glycerol are created generating an environmental issue and the same time an increase of biodiesel production cost at the same time. This raw glycerol could be converted by specific strains into value-added products, like 1,3-propanediol (1,3-PD), an important monomer used in the synthesis of biodegradable polyesters.The present work is based on recent scientific articles and experimental studies on the targeted topic, namely on the use of bacterial strains for bioconversion of biodiesel-derived glycerol into valuable products, like 1,3-PD. Concentrations, yields and productivity of 1,3-PD are presented for various bacterial strains. Important results as respects the microbial bioconversion of biodiesel-derived glycerol into 1,3-PD were registered for strains like Klebsiella pneumoniae, Citrobacter freundii, Escherichia coli and Lactobacillus diolivorans.From this study can be concluded that waste glycerol may be used as a nutrient source for microbial development and the production of 1,3-propanediol with high concentrations and yields.
The goal of this research is the investigation of a way to maximize the production of docosahexaenoic acid (DHA) and β-carotene by optimizing the culture conditions of their sources, microalgae Schizochytrium limacinum and fungus Blakeslea trispora respectively, in a fermentation medium. The influencing factors in the fermentation process for producing DHA and β-carotene have proven to be: the concentration of carbon source (different glycerol crude and pure concentrations) for both of them, and in particular temperature for DHA and pH for β-carotene. Testing the effect of these parameters was determined: biomass, DHA and β-carotene concentration. The highest production by S. limacinum was obtained at 25 °C, while using a quantity of 90 g/L of glycerol (crude or pure) as a carbon source. Temperature was the main factor that influenced the biosynthesis of DHA. The quantification of DHA was made by GC–MS chromatography, followed by a purification process, with the end result of DHA in pure phase. The maximum quantities for β-carotene production were obtained with pH 7 and 60 g/L of crude glycerol. The results highlight the possibility of using crude glycerol as a low-cost substrates for growth of microalgae S. limacinum and of fungus B. trispora in order to obtain the crucial molecules: docosahexaenoic acid and β-carotene.
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