Hollenbach Rebecca, Bindereif Benjamin, van der Schaaf Ulrike S, Ochsenreither Katrin, Syldatk Christoph
Institute of Process Engineering in Life Sciences II: Chair of Technical Biology, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Institute of Process Engineering in Life Sciences I: Chair of Food Process Engineering, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Front Bioeng Biotechnol. 2020 May 5;8:382. doi: 10.3389/fbioe.2020.00382. eCollection 2020.
Glycolipids are considered an alternative to petrochemically based surfactants because they are non-toxic, biodegradable, and less harmful to the environment while having comparable surface-active properties. They can be produced chemically or enzymatically in organic solvents or in deep eutectic solvents (DES) from renewable resources. DES are non-flammable, non-volatile, biodegradable, and almost non-toxic. Unlike organic solvents, sugars are easily soluble in hydrophilic DES. However, DES are highly viscous systems and restricted mass transfer is likely to be a major limiting factor for their application. Limiting factors for glycolipid synthesis in DES are not generally well understood. Therefore, the influence of external mass transfer, fatty acid concentration, and distribution on initial reaction velocity in two hydrophilic DES (choline:urea and choline:glucose) was investigated. At agitation speeds of and higher than 60 rpm, the viscosity of both DES did not limit external mass transfer. Fatty acid concentration of 0.5 M resulted in highest initial reaction velocity while higher concentrations had negative effects. Fatty acid accessibility was identified as a limiting factor for glycolipid synthesis in hydrophilic DES. Mean droplet sizes of fatty acid-DES emulsions can be significantly decreased by ultrasonic pretreatment resulting in significantly increased initial reaction velocity and yield (from 0.15 ± 0.03 μmol glucose monodecanoate/g DES to 0.57 ± 0.03 μmol/g) in the choline: urea DES. The study clearly indicates that fatty acid accessibility is a limiting factor in enzymatic glycolipid synthesis in DES. Furthermore, it was shown that physical pretreatment of fatty acid-DES emulsions is mandatory to improve the availability of fatty acids.
糖脂被认为是石化基表面活性剂的替代品，因为它们无毒、可生物降解，对环境危害较小，同时具有相当的表面活性。它们可以通过化学方法或酶法在有机溶剂或由可再生资源制成的深共熔溶剂（DES）中生产。DES不易燃、不挥发、可生物降解且几乎无毒。与有机溶剂不同，糖易溶于亲水性DES。然而，DES是高粘性体系，传质受限可能是其应用的主要限制因素。DES中糖脂合成的限制因素通常尚未得到很好的理解。因此，研究了两种亲水性DES（胆碱：尿素和胆碱：葡萄糖）中外部传质、脂肪酸浓度和分布对初始反应速度的影响。在60 rpm及以上的搅拌速度下，两种DES的粘度均不限制外部传质。0.5 M的脂肪酸浓度导致最高的初始反应速度，而更高的浓度则有负面影响。脂肪酸可及性被确定为亲水性DES中糖脂合成的限制因素。通过超声预处理可显著降低脂肪酸-DES乳液的平均液滴尺寸，从而使胆碱：尿素DES中的初始反应速度和产率显著提高（从0.15±0.03 μmol单癸酸葡萄糖酯/g DES提高到0.57±0.03 μmol/g）。该研究清楚地表明，脂肪酸可及性是DES中酶促糖脂合成的限制因素。此外，研究表明对脂肪酸-DES乳液进行物理预处理对于提高脂肪酸的可用性是必不可少的。
