Islam S M Mahfuzul, Ju Lu-Kwang
Department of Chemical, Biomolecular, and Corrosion Engineering, The University of Akron, Akron, OH, United States.
Front Bioeng Biotechnol. 2023 Jan 9;10:1042001. doi: 10.3389/fbioe.2022.1042001. eCollection 2022.
Enzyme production is critical and often costly for biorefinery. It is challenging to produce enzymes with not only high titers but also proper combinations of all required activities in a single fermentation. This work aimed at improving productivity and composition of the multiple enzyme activities required for hydrolysis of complex soybean carbohydrate in a single fermentation. A previously selected strain was used for its high carbohydrases and low protease production. Strategies of fed-batch substrate addition and programmed pH-decrease rates were evaluated. Cheap soybean hull (SH) was confirmed to induce production of all necessary carbohydrases. Surprisingly, fed-batch SH addition, originally thought to sustain substrate-inducer availability and reduce feedback repression by sugars, did not increase pectinase and cellulase production significantly and even lowered the α-galactosidase production, when compared with batch fermentation having the same total SH amount (all added initially). On the other hand, the pH-decrease rate could be effectively optimized for production of complex enzyme mixtures. The best fermentation was programmed to lower pH from 7 to 4 in 84 h, at a drop rate of .0357 per h. It produced the highest pectinase (19.1 ± .04 U/mL), α-galactosidase (15.7 ± .4 U/mL), and cellulase (.88 ± .06 FPU/mL). Producing these high enzyme activities in a single fermentation significantly improves the effectiveness and economics of enzymatic soy processing, which, e.g., can hydrolyze the 30%-35% carbohydrate in soybean meal to sugars, with minimal protein degradation, to generate high-value protein-rich products and a hydrolysate as fermentation feedstock.
酶的生产对于生物炼制至关重要且成本高昂。在单一发酵过程中，要生产出不仅滴度高而且具备所有所需活性适当组合的酶具有挑战性。这项工作旨在提高单一发酵中水解复杂大豆碳水化合物所需的多种酶活性的生产率和组成。先前筛选出的一株菌株因其高碳水化合物酶产量和低蛋白酶产量而被使用。评估了分批补料添加底物和设定pH降低速率的策略。廉价的大豆皮（SH）被证实可诱导产生所有必需的碳水化合物酶。令人惊讶的是，与具有相同总SH量（全部最初添加）的分批发酵相比，最初认为可维持底物诱导剂可用性并减少糖的反馈抑制的分批补料添加SH并未显著提高果胶酶和纤维素酶的产量，甚至降低了α-半乳糖苷酶的产量。另一方面，对于复合酶混合物的生产，可以有效地优化pH降低速率。最佳发酵方案是在84小时内将pH从7降至4，下降速率为每小时0.0357。它产生了最高的果胶酶（19.1±0.04 U/mL）、α-半乳糖苷酶（15.7±0.4 U/mL）和纤维素酶（0.88±0.06 FPU/mL）。在单一发酵中产生这些高酶活性显著提高了大豆酶解加工的效率和经济性，例如，可以将豆粕中30%-35%的碳水化合物水解为糖，同时蛋白质降解最少，从而生产出高价值的富含蛋白质的产品和一种水解产物作为发酵原料。
