Abstract
The effect of binding between the lignin isolates from an alkali (NaOH)– and an acid (H2SO4)– pretreated Miscanthus and cellulolytic enzymes in Cellic® CTec2 was investigated. Additonally, cellobiose and Avicel were enzymatically hydrolyzed with and without lignin isolates to study how enzyme binding onto lignin affects its conversion to glucose. Three carbohydrate–lignin loadings (0.5:0.25, 0.5:0.5, and 0.5:1.0% (w/v)) were employed. The results indicated that β-glucosidase (BG) had a strong tendency to bind to all lignin isolates. The overall tendency of enzyme binding onto lignin isolate was similar regardless of pretreatment chemical concentration. Though enzyme binding onto lignin isolates was observed, hydrolysis in the presence of these isolates did not have a significant (p > 0.05) impact on glucose production from cellobiose and Avicel. Cellobiose to glucose conversion of 99% was achieved via hydrolysis at both 5 and 10 FPU/g carbohydrate. Hydrolysis of Avicel with 5 and 10 FPU/g CTec2 resulted in 29.3 and 47.7% conversion to glucose, respectively.
Highlights
There is a significant interest in renewable energy production from lignocellulosic biomasses such as Miscanthus sp., due to their fast growth rates and high productivity, even with minimal agronomic input [1,2,3,4]
In one of their studies, Pareek et al [17] systematically investigated six lignins derived from various biomasses and observed that the source of lignin played a significant role in the enzyme adsorption
The pretreatment temperature was set at 121 ◦ C for both chemicals, but alkali pretreatment was conducted with NaOH concentrations of 0.5, 1.0, and 1.5% (w/v) for 30 min, while H2 SO4 concentration was performed using 1, 2, and 3%
Summary
There is a significant interest in renewable energy production from lignocellulosic biomasses such as Miscanthus sp., due to their fast growth rates and high productivity, even with minimal agronomic input [1,2,3,4]. Miscanthus is made of cellulose, hemicellulose, and lignin chemically bonded together [5,6]. The remaining component, lignin, as a non-carbohydrate aromatic polymer, mainly consists of three phenolic compounds: guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) propanol [8]. It forms a complex with cellulose and hemicellulose, and this conformational feature in lignocellulosic feedstocks confers their structural stability [9]. This very structural rigidity makes lignin a key obstacle to fermentable sugar productions from cellulose and hemicellulose by physically, chemically, and structurally protecting them from hydrolytic enzyme access [10,11]. During the Processes 2019, 7, 755; doi:10.3390/pr7100755 www.mdpi.com/journal/processes
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