DiSC (direct saccharification of culms) process for bioethanol production from rice straw

The RURAL (reciprocal upgrading for recycling of ash and lignocellulosics) process: A simple conversion of agricultural resources to strategic primary products for the rural bioeconomy

Rice straw (RS), an agricultural resource for lignocellulosic biorefineries, can deteriorate when sun-drying is ineffective. Poultry litter ash (PLA) has been considered as a renewable phosphorus source for crops but is highly alkaline. Here, a simple process was developed for their reciprocal upgrading. RS, PLA, and water were mixed for wet storage and alkali pretreatment of the RS at 25 °C for 14 d, and solid-solid separation was performed to obtain PLA-treated RS (PT-RS) and RS-treated PLA (RT-PLA). PT-RS was susceptible to enzymatic saccharification, and 65.5-68.6% of total sugar residues in PT-RS was converted to lactic acid by its nonsterile application for simultaneous saccharification and fermentation using Bacillus coagulans. RT-PLA exhibited 1.8-points lower pH and a more sensitive response of phosphorus solubilization to acid than those of PLA. This process could thus provide a breakthrough for the rural bioeconomy by manufacturing two strategic primary products for various commercial bioproducts.

Increased lodging resistance in long-culm, low-lignin gh2 rice for improved feed and bioenergy production

Lignin modification has been a breeding target for the improvements of forage digestibility and energy yields in forage and bioenergy crops, but decreased lignin levels are often accompanied by reduced lodging resistance. The rice mutant gold hull and internode2 (gh2) has been identified to be lignin deficient. GH2 has been mapped to the short arm of chromosome 2 and encodes cinnamyl-alcohol dehydrogenase (CAD). We developed a long-culm variety, 'Leaf Star', with superior lodging resistance and a gh phenotype similar to one of its parents, 'Chugoku 117'. The gh loci in Leaf Star and Chugoku 117 were localized to the same region of chromosome 2 as the gh2 mutant. Leaf Star had culms with low lignin concentrations due to a natural mutation in OsCAD2 that was not present in Chugoku 117. However, this variety had high culm strength due to its strong, thick culms. Additionally, this variety had a thick layer of cortical fiber tissue with well-developed secondary cell walls. Our results suggest that rice can be improved for forage and bioenergy production by combining superior lodging resistance, which can be obtained by introducing thick and stiff culm traits, with low lignin concentrations, which can be obtained using the gh2 variety.

Glucose content in the liquid hydrolysate after dilute acid pretreatment is affected by the starch content in rice straw

Lignocellulosic biomass, such as rice straw, is often utilized as a bioresource after being hydrolyzed using dilute acid and separated into liquid hydrolysate and acid-insoluble residue. However, the biomass component that determines the distribution between liquid hydrolysate and acid-insoluble residue has not yet been clarified. In this study, the glucose content in the liquid hydrolysate and weight of acid-insoluble residue of 13 rice cultivars were analyzed. Starch content was positively correlated with glucose content in the liquid hydrolysate, and negatively correlated with acid-insoluble residue weight. These results indicate that the glucose in the liquid hydrolysate is mainly liberated from starch rather than cellulose in the rice straw. These observations suggest that starch content is a good indicator of the glucose distribution between the liquid hydrolysate and insoluble residue.

Readily-milled fraction of wet sugarcane bagasse as an advanced feedstock for monosaccharide production via the RT-CaCCO process

The RT-CaCCO process for enzymatic saccharification was applied to readily-milled fractions of wet sugarcane bagasse. Wet bagasse immediately after juice extraction was crushed with shark-mill blades to prepare two fractions referred to as readily-milled (RF) and hardly-milled fraction (HF). Monosaccharide recoveries from RFs via the RT-CaCCO process were 1.03-1.21 times higher than those from HFs. Moreover, when the wet weight ratio of RF/HF was adjusted to 2/8, the hexose recovery from RF was 90.9%, which was 1.3 times higher than that of the wet bagasse before fractionation. The results show that this process can be used for efficient monosaccharide recovery from RF of wet bagasse. In addition, the process can be adapted to more fibrous HF for multiple uses such as fuel for boilers and fibers for particleboards.