Center for BioProcess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs Lyngby, Denmark.
Novozymes A/S, Krogshøjvej 36, DK-2880 Bagsværd, Denmark.
Biotechnol Biofuels. 2014 Jun 20;7:95. doi: 10.1186/1754-6834-7-95. eCollection 2014.
Ensiling may act as a pretreatment of fresh grass biomass and increase the enzymatic conversion of structural carbohydrates to fermentable sugars. However, ensiling does not provide sufficient severity to be a standalone pretreatment method. Here, ensiling of grass is combined with hydrothermal treatment (HTT) with the aim of improving the enzymatic biomass convertibility and decrease the required temperature of the HTT.
Grass silage (Festulolium Hykor) was hydrothermally treated at temperatures of 170, 180, and 190°C for 10 minutes. Relative to HTT treated dry grass, ensiling increased the solubilization of dry matter (DM) during HTT and gave increased glucan content, but lower lignin in the insoluble fiber fraction. Ensiling improved glucose yields in the enzymatic hydrolysis of the washed solid fiber fraction at the lower HTT temperatures. At 170°C glucose yield improved from 17 to 24 (w/w)% (45 to 57% cellulose convertibility), and at 180°C glucose yield improved from 22 to 29 (w/w)% (54 to 69% cellulose convertibility). Direct HTT of grass at 190°C gave the same high glucose yield as for grass silage (35 (w/w)% (77% cellulose convertibility)) and improved xylan yields (27% xylan convertibility). The effect of ensiling of grass prior to HTT improved the enzymatic conversion of cellulose for HTT at 170 and 180°C, but the increased glucose release did not make up for the loss of water soluble carbohydrates (WSC) during ensiling. Overall, sugar yields (C6 + C5) were similar for HTT of grass and grass silage at both 170 and 180°C, but at 190°C the overall sugar yield was better for HTT of dry grass.
This study unequivocally establishes that ensiling of grass as a biomass pretreatment method comes with a loss of WSC. The loss of WSC by ensiling is not necessarily compensated for by providing a lower temperature requirement for HTT for high enzymatic monosaccharide release. However, ensiling can be an advantageous storage method prior to grass processing.
青贮可以作为新鲜草生物质的预处理方法，并增加结构碳水化合物向可发酵糖的酶转化。然而，青贮本身并不能提供足够的苛刻条件来作为一种独立的预处理方法。在这里，将草青贮与湿热处理（HTT）相结合，旨在提高酶生物质转化率并降低 HTT 的所需温度。
将草青贮（Festulolium Hykor）在 170、180 和 190°C 下分别进行 10 分钟的湿热处理。与 HTT 处理的干草相比，青贮在 HTT 过程中增加了干物质（DM）的溶解，并增加了葡聚糖含量，但不可溶纤维部分的木质素含量降低。青贮提高了经洗涤的固体纤维部分在较低 HTT 温度下的酶水解葡萄糖产量。在 170°C 时，葡萄糖产量从 17 提高到 24（w/w）%（45 至 57%纤维素转化率），在 180°C 时，葡萄糖产量从 22 提高到 29（w/w）%（54 至 69%纤维素转化率）。在 190°C 下直接进行 HTT 处理，得到的葡萄糖产量与草青贮（35（w/w）%（77%纤维素转化率））相同，并提高了木聚糖产量（27%木聚糖转化率）。在 HTT 之前对草进行青贮的效果提高了在 170 和 180°C 下 HTT 对纤维素的酶转化，但在青贮过程中损失的水溶性碳水化合物（WSC）增加了葡萄糖的释放量。总体而言，在 170 和 180°C 下，HTT 处理草和草青贮的糖产量（C6+C5）相似，但在 190°C 下，HTT 处理干草的总糖产量更好。
本研究明确表明，作为生物质预处理方法的草青贮会导致 WSC 的损失。青贮过程中 WSC 的损失不一定会通过为 HTT 提供较低的温度要求来补偿以实现高酶单糖释放。然而，青贮可以作为草加工前的一种有利的储存方法。
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