Jiang Ting-Ting, Liang Yan, Zhou Xiang, Shi Zi-Wei, Xin Zhi-Jun
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, Gansu, P.R. China.
University of Chinese Academy, Beijing, P.R. China.
PeerJ. 2019 Jan 10;6:e6186. doi: 10.7717/peerj.6186. eCollection 2019.
Sweet sorghum bagasse (SSB), comprising both a dermal layer and pith, is a solid waste generated by agricultural activities. Open burning was previously used to treat agricultural solid waste but is harmful to the environment and human health. Recent reports showed that certain techniques can convert this agricultural waste into valuable products. While SSB has been considered an attractive raw material for sugar extraction and the production of value-added products, the pith root in the SSB can be difficult to process. Therefore, it is necessary to pretreat bagasse before conventional hydrolysis.
A thorough analysis and comparison of various pretreatment methods were conducted based on physicochemical and microscopic approaches. The responses of agricultural SSB stem pith with different particle sizes to pretreatment temperature, acid and alkali concentration and enzyme dosage were investigated to determine the optimal pretreatment. The integrated methods are beneficial to the utilization of carbohydrate-based and unknown compounds in agricultural solid waste.
Acid (1.5-4.5%, v/v) and alkali (5-8%, w/v) reagents were used to collect cellulose from different meshes of pith at 25-100 °C. The results showed that the use of 100 mesh pith soaked in 8% (w/v) NaOH solution at 100 °C resulted in 32.47% ± 0.01% solid recovery. Follow-up fermentation with 3% (v/v) acid and 6.5% (w/v) alkali at 50 °C for enzymolysis was performed with the optimal enzyme ratio. An analysis of the surface topography and porosity before and after pretreatment showed that both the pore size of the pith and the amount of exposed cellulose increased as the mesh size increased. Interestingly, various compounds, including 42 compounds previously known to be present and 13 compounds not previously known to be present, were detected in the pretreatment liquid, while 10 types of monosaccharides, including D-glucose, D-xylose and D-arabinose, were found in the enzymatic solution. The total monosaccharide content of the pith was 149.48 ± 0.3 mg/g dry matter.
An integrated technique for obtaining value-added products from sweet sorghum pith is presented in this work. Based on this technique, lignin and hemicellulose were effectively broken down, amorphous cellulose was obtained and all sugars in the sweet sorghum pith were hydrolysed into monosaccharides. A total of 42 compounds previously found in these materials, including alcohol, ester, acid, alkene, aldehyde ketone, alkene, phenolic and benzene ring compounds, were detected in the pretreatment pith. In addition, several compounds that had not been previously observed in these materials were found in the pretreatment solution. These findings will improve the transformation of lignocellulosic biomass into sugar to create a high-value-added coproduct during the integrated process and to maximize the potential utilization of agricultural waste in current biorefinery processing.
甜高粱渣（SSB）由皮层和髓部组成，是农业活动产生的固体废弃物。以前采用露天焚烧处理农业固体废弃物，但这对环境和人类健康有害。最近的报告表明，某些技术可将这种农业废弃物转化为有价值的产品。虽然甜高粱渣被认为是用于糖提取和生产增值产品的有吸引力的原料，但其髓部难以加工。因此，在常规水解之前对蔗渣进行预处理很有必要。
基于物理化学和微观方法对各种预处理方法进行了全面分析和比较。研究了不同粒径的农业甜高粱渣茎髓对预处理温度、酸碱浓度和酶用量的响应，以确定最佳预处理方法。这些综合方法有利于农业固体废弃物中碳水化合物类和未知化合物的利用。
使用酸（1.5 - 4.5%，v/v）和碱（5 - 8%，w/v）试剂在25 - 100℃下从不同目数的髓部收集纤维素。结果表明，使用100目髓部在100℃下浸泡于8%（w/v）NaOH溶液中，固体回收率为32.47%±0.01%。后续在50℃下使用3%（v/v）酸和6.5%（w/v）碱进行酶解发酵，并采用最佳酶比例。预处理前后表面形貌和孔隙率分析表明，随着目数增加，髓部孔径和暴露的纤维素量均增加。有趣的是，在预处理液中检测到多种化合物，包括42种先前已知存在的化合物和13种先前未知存在的化合物，而在酶解液中发现了10种单糖，包括D - 葡萄糖、D - 木糖和D - 阿拉伯糖。髓部的总单糖含量为149.48±0.3mg/g干物质。
本文提出了一种从甜高粱髓部获得增值产品的综合技术。基于该技术，木质素和半纤维素被有效分解，获得了无定形纤维素，甜高粱髓部中的所有糖类都水解为单糖。在预处理的髓部中总共检测到42种先前在这些材料中发现的化合物，包括醇、酯、酸、烯烃、醛酮、烯烃、酚类和苯环化合物。此外，在预处理溶液中还发现了几种先前在这些材料中未观察到的化合物。这些发现将改善木质纤维素生物质向糖的转化，在综合过程中创造高附加值的副产品，并最大限度地提高当前生物炼制过程中农业废弃物的潜在利用率。
