Abstract
BackgroundOleaginous filamentous fungi can accumulate large amount of cellular lipids and potentially serve as a major source of oleochemicals for food, feed, chemical, pharmaceutical, and transport industries. Transesterification of microbial oils is an essential step in microbial lipid production at both laboratory and industrial scale. Direct transesterification can considerably reduce costs, increase sample throughput and improve lipid yields (in particular fatty acid methyl esters, FAMEs). There is a need for the assessment of the direct transesterification methods on a biomass of filamentous fungi due to their unique properties, specifically resilient cell wall and wide range of lipid content and composition. In this study we have evaluated and optimised three common direct transesterification methods and assessed their suitability for processing of fungal biomass.ResultsThe methods, based on hydrochloric acid (Lewis method), sulphuric acid (Wahlen method), and acetyl chloride (Lepage method), were evaluated on six different strains of Mucoromycota fungi by using different internal standards for gas chromatography measurements. Moreover, Fourier transform infrared (FTIR) spectroscopy was used for the detection of residual lipids in the biomass after the transesterification reaction/extraction, while transesterification efficiency was evaluated by nuclear magnetic resonance spectroscopy. The results show that the majority of lipids, in particular triglycerides, were extracted for all methods, though several methods had substandard transesterification yields. Lewis method, optimised with respect to solvent to co-solvent ratio and reaction time, as well as Lepage method, offer precise estimate of FAME-based lipids in fungal biomass.ConclusionsThe results show that Lepage and Lewis methods are suitable for lipid analysis of oleaginous filamentous fungi. The significant difference in lipid yields results, obtained by optimised and standard Lewis methods, indicates that some of the previously reported lipid yields for oleaginous filamentous fungi must be corrected upwards. The study demonstrates value of biomass monitoring by FTIR, importance of optimal solvent to co-solvent ratio, as well as careful selection and implementation of internal standards for gas chromatography.
Highlights
Microbial oils, produced by a range of oleaginous microorganisms, are being considered as one of the primary sources of oleochemicals for food, feed, chemical, Langseter et al Microb Cell Fact (2021) 20:59 pharmaceutical, and transport industries
Fungal strains The studied species of filamentous fungi, namely Mucor circinelloides, Umbelopsis vinacea, Absidia glauca, Lichtheimia corymbifera, Cunninghamella blakesleeana, and Amylomyces rouxii, are considered as either model organisms (Mucor circinelloides) or oleaginous filamentous fungi of high industrial potential for production of microbial oils [43]
The results show that both Lepage methods were able to convert almost all C13:0 TAG into C13:0 fatty acid methyl esters (FAMEs), as previously indicated by the nuclear magnetic resonance (NMR) analysis (Table 2; Fig. 2)
Summary
Microbial oils, produced by a range of oleaginous microorganisms, are being considered as one of the primary sources of oleochemicals for food, feed, chemical, Langseter et al Microb Cell Fact (2021) 20:59 pharmaceutical, and transport industries Oleaginous microorganisms, such as algae, bacteria and fungi, can accumulate cellular oils in amounts above 20% of dry biomass (%w/w), and often in 50–80%w/w range [1, 2]. Amongst various types of oleaginous microorganisms, Mucoromycota fungi have gained interest due to their versatile metabolism capable to utilize a wide range of feedstock, including waste materials and industrial raw rest materials [3,4,5] These filamentous fungi are powerful cell factories able to valorize various feedstocks into a range of marketable products, such as lipids, biopolymers, pigments, proteins, enzymes, and organic acids [6, 7]. In this study we have evaluated and optimised three common direct transesterification methods and assessed their suitability for processing of fungal biomass
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