BIOtechMASS Unit, Biotechnology Laboratory, Chemical Engineering Department, National Technical University of Athens, Iroon Polytechniou St, Zografou Campus, 15700, Athens, Greece.
Biotechnol Biofuels. 2009 Feb 10;2(1):4. doi: 10.1186/1754-6834-2-4.
Brewer's spent grain (BG), a by-product of the brewing process, is attracting increasing scientific interest as a low-cost feedstock for many biotechnological applications. BG in the present study is evaluated as a substrate for lignocellulolytic enzyme production and for the production of ethanol by the mesophilic fungus Fusarium oxysporum under submerged conditions, implementing a consolidated bioconversion process. Fermentation experiments were performed with sugar mixtures simulating the carbohydrate content of BG in order to determine the utilization pattern that could be expected during the fermentation of the cellulose and hemicellulose hydrolysate of BG. The sugar mixture fermentation study focused on the effect of the initial total sugar concentration and on the effect of the aeration rate on fermenting performance of F. oxysporum. The alkali pretreatment of BG and different aeration levels during the ethanol production stage were studied for the optimization of the ethanol production by F. oxysporum.
Enzyme yields as high as 550, 22.5, 6.5, 3225, 0.3, 1.25 and 3 U per g of carbon source of endoglucanase, cellobiohydrolase, beta-D-glucosidase, xylanase, feruloyl esterase, beta-D-xylosidase and alpha-L-arabinofuranosidase respectively, were obtained during the growth stage under optimized submerged conditions. An ethanol yield of 109 g ethanol per kg of dry BG was obtained with alkali-pretreated BG under microaerobic conditions (0.01 vvm), corresponding to 60% of the theoretical yield based on total glucose and xylose content of BG.
The enzymatic profile of the extracellular extract from F. oxysporum submerged cultures using BG and corn cob as the carbon source was proved efficient for a successful hydrolysis of BG. The fermentation study carried out using sugar mixtures simulating BG's carbohydrates content and consecutively alkali-pretreated and untreated BG, indicates that BG hydrolysis is the bottleneck of the bioconversion process. However, a considerable bioconversion yield was achieved (60% of the theoretical) making this bioprocess worthy of further investigation for a potential commercial application.
啤酒糟（BG）是酿造过程的副产品，作为许多生物技术应用的低成本原料，正引起越来越多的科学关注。本研究将 BG 评估为木质纤维素酶生产和嗜热真菌粉红镰刀菌在浸没条件下生产乙醇的基质，实施整合生物转化过程。进行了发酵实验，使用模拟 BG 碳水化合物含量的糖混合物，以确定在 BG 的纤维素和半纤维素水解物发酵过程中可能预期的利用模式。糖混合物发酵研究侧重于初始总糖浓度的影响以及通气率对粉红镰刀菌发酵性能的影响。研究了 BG 的碱预处理和乙醇生产阶段的不同通气水平，以优化粉红镰刀菌的乙醇生产。
在优化的浸没条件下的生长阶段，分别获得了高达 550、22.5、6.5、3225、0.3、1.25 和 3 U/g 碳源的内切葡聚糖酶、纤维二糖水解酶、β-D-葡萄糖苷酶、木聚糖酶、阿魏酸酯酶、β-D-木糖苷酶和α-L-阿拉伯呋喃糖苷酶的酶产量。在微需氧条件下（0.01 vvm），用碱预处理 BG 获得了 109 g 乙醇/公斤干 BG 的乙醇产量，对应于 BG 总葡萄糖和木糖含量的理论产率的 60%。
用 BG 和玉米芯作为碳源的粉红镰刀菌浸没培养物的细胞外提取物的酶谱证明对 BG 的成功水解有效。使用模拟 BG 碳水化合物含量的糖混合物进行的发酵研究以及随后的碱预处理和未处理的 BG 表明，BG 水解是生物转化过程的瓶颈。然而，实现了相当大的生物转化产率（60%的理论值），使该生物过程值得进一步研究，以实现潜在的商业应用。
