Álvarez-Cao María-Efigenia, Cerdán María-Esperanza, González-Siso María-Isabel, Becerra Manuel
Grupo EXPRELA, Centro de Investigacións Científicas Avanzadas (CICA), Facultade de Ciencias, Universidade da Coruña, A Coruña, Spain.
Front Microbiol. 2019 Mar 7;10:405. doi: 10.3389/fmicb.2019.00405. eCollection 2019.
Molasses are sub-products of the sugar industry, rich in sucrose and containing other sugars like raffinose, glucose, and fructose. Alpha-galactosidases (EC. 3.2.1.22) catalyze the hydrolysis of alpha-(1,6) bonds of galactose residues in galacto-oligosaccharides (melibiose, raffinose, and stachyose) and complex galactomannans. Alpha-galactosidases have important applications, mainly in the food industry but also in the pharmaceutical and bioenergy sectors. However, the cost of the enzyme limits the profitability of most of these applications. The use of cheap sub-products, such as molasses, as substrates for production of alpha-galactosidases, reduces the cost of the enzymes and contributes to the circular economy. Alpha-galactosidase is a specially indicated bioproduct since, at the same time, it allows to use the raffinose present in molasses. This work describes the development of a two-step system for the valuation of beet molasses, based on their use as substrate for alpha-galactosidase and bioethanol production by . Since this yeast secretes high amounts of invertase, to avoid congest the secretory route and to facilitate alpha-galactosidase purification from the culture medium, a mutant in the gene (encoding invertase) was constructed. After a statistical optimization of culture conditions, this mutant yielded a very high rate of molasses bioconversion to alpha-galactosidase. In the second step, the wild type yeast strain fermented the remaining sucrose to ethanol. A procedure to recycle the yeast biomass, by using it as nitrogen source to supplement molasses, was also developed.
糖蜜是制糖工业的副产品，富含蔗糖，并含有棉子糖、葡萄糖和果糖等其他糖类。α-半乳糖苷酶（EC. 3.2.1.22）催化水解低聚半乳糖（蜜二糖、棉子糖和水苏糖）和复杂的半乳甘露聚糖中半乳糖残基的α-(1,6)键。α-半乳糖苷酶有重要应用，主要在食品工业，但也在制药和生物能源领域。然而，该酶的成本限制了这些应用中大多数的盈利能力。使用廉价的副产品，如糖蜜，作为生产α-半乳糖苷酶的底物，可降低酶的成本并有助于循环经济。α-半乳糖苷酶是一种特别合适的生物产品，因为它同时能利用糖蜜中存在的棉子糖。这项工作描述了一种两步系统的开发，用于甜菜糖蜜的增值，该系统基于将糖蜜用作α-半乳糖苷酶的底物以及通过[具体微生物]生产生物乙醇。由于这种酵母分泌大量转化酶，为避免堵塞分泌途径并便于从培养基中纯化α-半乳糖苷酶，构建了[具体基因]（编码转化酶）的突变体。在对培养条件进行统计优化后，该突变体使糖蜜生物转化为α-半乳糖苷酶的速率非常高。在第二步中，[具体野生型酵母菌株]将剩余的蔗糖发酵成乙醇。还开发了一种回收酵母生物质的程序，即将其用作氮源来补充糖蜜。
