Abstract
BackgroundThe sustainability of microbial lipids production from traditional carbon sources, such as glucose or glycerol, is problematic given the high price of raw materials. Considerable efforts have been directed to minimize the cost and find new alternative carbon sources. Volatile fatty acids (VFAs) are especially attractive raw materials, because they can be produced from a variety of organic wastes fermentation. Therefore, the use of volatile fatty acids as carbon sources seems to be a feasible strategy for cost-effective microbial lipid production.ResultsLipid accumulation in Y. lipolytica using synthetic and food waste-derived VFAs as substrates was systematically compared and evaluated in batch cultures. The highest lipid content obtained with acetic, butyric, and propionic acids reached 31.62 ± 0.91, 28.36 ± 0.74, and 28.91 ± 0.66%, respectively. High concentrations of VFA inhibited cell growth in the following order: butyric acid > propionic acid > acetic acid. Within a 30-day experimental period, Y. lipolytica could adapt up to 20 g/L acetic acid, whereas the corresponding concentration of propionic acid and butyric acid were 10 and 5 g/L, respectively. Cultures on a VFA mixture showed that the utilization of different types of VFA by Y. lipolytica was not synchronized but rather performed in a step-wise manner. Although yeast fermentation is an exothermic process, and the addition of VFA will directly affect the pH of the system by increasing environmental acidity, cultures at a cultivation temperature of 38 °C and uncontrolled pH demonstrated that Y. lipolytica had high tolerance in the high temperature and acidic environment when a low concentration (2.5 g/L) of either synthetic or food waste-derived VFA was used. However, batch cultures fed with food fermentate yielded lower lipid content (18.23 ± 1.12%) and lipid productivity (0.12 ± 0.02 g/L/day). The lipid composition obtained with synthetic and food waste-derived VFA was similar to commercial biodiesel feedstock.ConclusionsThis work demonstrated the feasibility of utilizing synthetic and food waste-derived VFA for lipid production by Y. lipolytica. The good adaptability of Y. lipolytica to the high temperature and acidic environment further illustrated its considerable potential for practical application.
Highlights
The sustainability of microbial lipids production from traditional carbon sources, such as glucose or glycerol, is problematic given the high price of raw materials
Effect of VFA types and initial concentrations on cell growth and lipid production The effects of different VFA types and initial concentrations on the microbial conversion of volatile fatty acids to lipid by the oleaginous yeast Y. lipolytica were evaluated in flask batch cultures under optimal culture conditions (28 °C, initial pH 6.0) based on previous studies [1, 14, 17]
It was found that biomass and lipid productivities obtained with low concentration (2.5 g/L) of VFAs, especially with acetic acid, were close to those achieved with glucose
Summary
The sustainability of microbial lipids production from traditional carbon sources, such as glucose or glycerol, is problematic given the high price of raw materials. Considerable efforts have been directed to minimize the cost and find new alternative carbon sources. The use of volatile fatty acids as carbon sources seems to be a feasible strategy for cost-effective microbial lipid production. Among the potential lipid sources of biodiesel, microbial lipid, which is known as single-cell oil and produced by oleaginous microorganisms, is the most promising [7, 8]. Volatile fatty acids (VFAs) are especially attractive raw materials because they can be produced from the fermentation of a variety of organic wastes [14]. Microbial lipid production from VFAs seems to be a feasible strategy for cost-effective biodiesel production and could contribute to waste utilization and remediation
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