Deacidification of grass silage press juice by continuous production of acetoin from its lactate via an immobilized enzymatic reaction cascade

Abstract

An immobilized enzymatic reaction cascade was designed and optimized for the deacidification of grass silage press juice (SPJ), thus facilitating the production of bio-based chemicals. The cascade involves a three-step process using four enzymes immobilized in a Ca-alginate gel and uses lactic acid to form acetoin, a value-added product. The reaction is performed with a continuous, pH-dependent substrate feed under oxygenation. With titrated lactic acid yields of up to 91% and reaction times of ca. 6h was achieved. Using SPJ as titrant yields of 49% were obtained within 6h. In this deacidification process, with acetoin one value-added bio-based chemical is produced while simultaneously the remaining press juice can be used in applications that require a higher pH. Such, this system can be applied in a multi-product biorefinery concept to take full advantage of nutrient-rich SPJ, which is a widely available and easily storable renewable resource.

In vitro biosynthesis of optically pure d‐(−)‐acetoin from meso‐2,3‐butanediol using 2,3‐butanediol dehydrogenase and NADH oxidase

“…However, the cost of enzyme preparation is still a bottleneck in the scale-up process. Screening thermostable enzymes 37 or immobilizing enzymes 39 would be effective strategies to reduce the enzyme costs. To further improve the product yield and productivity, more efforts are also needed to develop a coupling-system to separate AC in time.…”

“…In vivo , AC is synthesized naturally from pyruvate catalyzed by two continuous decarboxylation reactions with high TRY (titer, rate and yield) . Serial efforts were therefore made to realize the in vitro AC synthesis from pyruvate or cheaper precursors such as glycerol, xylose or lactate . However, the low TRY and the inevitable carbon loss impeded industrial application.…”

“…[33][34][35][36] Serial efforts were therefore made to realize the in vitro AC synthesis from pyruvate 37 or cheaper precursors such as glycerol, 38 xylose 31 or lactate. 32,39 However, the low TRY and the inevitable carbon loss impeded industrial application. Optically pure L-(+)-AC was efficiently produced from diacetyl with a high productivity of 9.76 g L −1 h −1 .…”

Extending Designed Linear Biocatalytic Cascades for Organic Synthesis

“…Many other biotransformations have also been reported for the production of acetoin from lactate . For example, enzymes immobilized in a Ca‐alginate gel were designed for the removal of lactic acid from grass silage press juice.…”

“…With 50 mM lactic acid solution, a yield of 91 % was obtained over 6 h reaction time. By using grass silage press juice as the titrant, which was diluted to achieve an equivalent amount of lactic acid, yields of 49 % were obtained within the same reaction time …”