Production of L-carnitine-enriched edible filamentous fungal biomass through submerged cultivation

The edible filamentous fungi are hot candidate for future supply of functional food and feed with e.g. protein, essential amino acids, and compounds with immunostimulant activity. L-carnitine that plays a crucial role in energy metabolism represents a functional compound normally produced by Zygomycetes filamentous fungus Rhizopus oligosporus in solid-state fermentation. The present study provides the first insights on production of L-carnitine-enriched edible fungal biomass through submerged cultivation of several Ascomycetes and Zygomycetes including Aspergillus oryzae, Neurospora intermedia, Rhizopus oryzae, and Rhizopus oligosporus. A. oryzae with 3 mg L-carnitine yield per gram of fungal biomass, indicates great potential on production of this bioactive compound which is remarkably higher than the other tested fungi in this work and also previous studies. In addition to fungal strain, other factors such as cultivation time and presence of yeast extract were found to play a role. Further studies on submerged growth optimization of A. oryzae in both high-quality recipes and in medium based on low-value substrates are proposed in order to clarify its potential for production of L-carnitine-enriched fungal biomass.

可食用丝状真菌是未来功能性食品与饲料供给的热门备选资源，其可提供蛋白质、必需氨基酸及具有免疫刺激活性的化合物等多种营养与活性组分。在能量代谢中发挥关键作用的L-肉碱（L-carnitine）是一类功能性活性物质，通常由接合菌门（Zygomycetes）丝状真菌少孢根霉（Rhizopus oligosporus）通过固态发酵制备。本研究首次针对富含L-肉碱的可食用真菌菌体生产开展探索，采用液体深层发酵（submerged cultivation）培养了多个子囊菌门（Ascomycetes）与接合菌门菌株，受试菌株包括米曲霉（Aspergillus oryzae）、中间脉孢霉（Neurospora intermedia）、米根霉（Rhizopus oryzae）以及少孢根霉。实验结果显示，每克真菌菌体可产出3毫克L-肉碱的米曲霉，在该活性物质的生产中展现出极大应用潜力，其L-肉碱产量显著高于本研究中的其他受试菌株，同时也优于既往相关研究的报道结果。除真菌菌株本身的特性外，培养时长、酵母提取物添加与否等其他因素同样对产量存在显著影响。为进一步明确米曲霉生产富含L-肉碱真菌菌体的应用潜力，本研究提出后续需开展两方面优化研究：一是基于高品质培养基的米曲霉液体生长条件优化，二是以低值底物为原料的低成本培养基体系优化。