Gorte Olga, Hollenbach Rebecca, Papachristou Ioannis, Steinweg Christian, Silve Aude, Frey Wolfgang, Syldatk Christoph, Ochsenreither Katrin
Institute of Process Engineering in Life Science 2: Technical Biology, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Institute for Pulsed Power and Microwave Technology, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Front Bioeng Biotechnol. 2020 Apr 24;8:355. doi: 10.3389/fbioe.2020.00355. eCollection 2020.
Single cell oil (SCO) produced by oleaginous yeasts is considered as a sustainable source for biodiesel and oleochemicals since its production does not compete with food or feed and high yields can be obtained from a wide variety of carbon sources, e.g., acetate or lignocellulose. Downstream processing is still costly preventing the broader application of SCO. Direct transesterification of freeze-dried biomass is widely used for analytical purposes and for biodiesel production but it is energy intensive and, therefore, expensive. Additionally, only fatty acid esters are produced limiting the subsequent applications. The harsh conditions applied during direct esterification might also damage high-value polyunsaturated fatty acids. Unfortunately, universal downstream strategies effective for all yeast species do not exist and methods have to be developed for each yeast species due to differences in cell wall composition. Therefore, the aim of this study was to evaluate three industrially relevant cell disruption methods combined with three extraction systems for the SCO extraction of two novel, unconventional oleaginous yeasts, DSM 27192 and DSM 27194, based on cell disruption efficiency, lipid yield, and oil quality. Bead milling (BM) and high pressure homogenization (HPH) were effective cell disruption methods in contrast to sonification. By combining HPH (95% cell disruption efficiency) with ethanol-hexane-extraction 46.9 ± 4.4% lipid/CDW of were obtained which was 2.7 times higher than with the least suitable combination (ultrasound + Folch). was less affected by cell disruption attempts. Here, the highest disruption efficiency was 74% after BM and the most efficient lipid recovery method was direct acidic transesterification (27.2 ± 0.5% fatty acid methyl esters/CDW) after freeze drying. The study clearly indicates cell disruption is the decisive step for SCO extraction. At disruption efficiencies of >90%, lipids can be extracted at high yields, whereas at lower cell disruption efficiencies, considerable amounts of lipids will not be accessible for extraction regardless of the solvents used. Furthermore, it was shown that hexane-ethanol which is commonly used for extraction of algal lipids is also highly efficient for yeasts.
产油酵母生产的单细胞油（SCO）被认为是生物柴油和油脂化学品的可持续来源，因为其生产不与食品或饲料竞争，并且可以从多种碳源（如乙酸盐或木质纤维素）中获得高产率。下游加工成本仍然很高，这阻碍了SCO的更广泛应用。冻干生物质的直接酯交换反应广泛用于分析目的和生物柴油生产，但它能源密集，因此成本高昂。此外，仅生产脂肪酸酯限制了后续应用。直接酯化过程中应用的苛刻条件也可能损害高价值的多不饱和脂肪酸。不幸的是，不存在对所有酵母物种都有效的通用下游策略，由于细胞壁组成的差异，必须为每种酵母物种开发方法。因此，本研究的目的是基于细胞破碎效率、脂质产量和油质量，评估三种工业相关的细胞破碎方法与三种提取系统相结合，用于两种新型非常规产油酵母DSM 27192和DSM 27194的SCO提取。与超声处理相比，珠磨法（BM）和高压均质法（HPH）是有效的细胞破碎方法。通过将HPH（细胞破碎效率为95%）与乙醇-己烷提取相结合，获得了46.9±4.4%的脂质/细胞干重，这比最不合适的组合（超声+ Folch法）高出2.7倍。 受细胞破碎尝试的影响较小。在这里，BM后最高破碎效率为74%，冻干后最有效的脂质回收方法是直接酸性酯交换反应（27.2±0.5%脂肪酸甲酯/细胞干重）。该研究清楚地表明细胞破碎是SCO提取的决定性步骤。在破碎效率>90%时，可以高产率提取脂质，而在较低的细胞破碎效率下，无论使用何种溶剂，大量脂质将无法提取。此外，结果表明，常用于提取藻类脂质的己烷-乙醇对酵母也非常有效。
