Sugar yield and composition of tubers from Jerusalem Artichoke (Helianthus tuberosus) irrigated with saline waters

Authors: BHAGIA, SAMARTHYA - University Of California; Ferreira, Jorge; KOTHARI, NINAD - University Of California; NUNEZ, ANGELICA - University Of California; Liu, Xuan; DIAS, NILDO - Federal Rural University Of The Semi-Arid; Suarez, Donald; KUMAR, RAJEEV - University Of California; WYMAN, CHARLES - University Of California

Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2018
Publication Date: 2/24/2018
Citation: Bhagia, S., Ferreira, J.F., Kothari, N., Nunez, A., Liu, X., Dias, N.D., Suarez, D.L., Kumar, R., Wyman, C. 2018. Sugar yield and composition of tubers from Jerusalem Artichoke (Helianthus tuberosus) irrigated with saline waters. Biotechnology and Bioengineering. 115:1475-1484. https://doi.org/10.1002/bit.26582.
DOI: https://doi.org/10.1002/bit.26582

Interpretive Summary: Currently, major biofuel crops are also food crops that demand fertile soils and good-quality water for biomass production. Jerusalem artichoke (in the sunflower family) produces high tonnage of tubers that are rich in inulin sugars. In this study, plants grown under five salinity levels were evaluated for their tuber yield. This plant can be classified as moderately salt tolerant if the classification is based on tuber production. Hydraulic pressings of tubers were carried out to quantify mass of juice, bagasse and water, and free sugar (non-structural sugar) yield in juice and bagasse. Overall, tubers contained 15% (fresh weight) or 55% (dry weight) as sugars. 70% of these sugars were in the form of inulin and the rest as fructose, sucrose, and glucose. Hydraulic pressing resulted in juice with high sugar concentrations. In addition, neither total sugar nor inulin content of tubers were affected by salinity. Even after juice extraction by hydraulic pressing, the bagasse retained high quantities of free sugars that needed a washing step for complete sugar recovery from tubers. Tuber bagasse had low lignin content (11-13 wt%) and its structural sugar composition was similar to that of chicory root bagasse. Enzymatic hydrolysis was carried out to breakdown structural sugars for monomeric sugar recovery. Cellulase enzymes could solubilize only around 40% of the cellulose in bagasse, despite the excess addition of the enzyme. However, when pectinase and xylanase were added to cellulase glucose yields from enzymatic hydrolysis of tuber bagasse increased significantly. Our results indicate that Jerusalem artichoke is a biofuel crop that yields more sugars than corn and sugar cane, and that can be cultivated in marginal lands and with saline recycled waters, thus not competing with food crops. Jerusalem artichoke cultivation under moderately saline conditions can result in low-cost production of sugars that can be easily converted to ethanol for transportation fuels. This research is of interest to researchers working on renewable fuels and chemicals, food, bioproducts industry, land managers, and organizations evaluating feasibility of biofuel production on marginal lands or with recycled waters.

Technical Abstract: Currently, major biofuel crops are also food crops that demand fertile soils and good-quality water. Jerusalem artichoke (Helianthus tuberosus, Asteraceae) produces high tonnage of tubers that are rich in sugars, mainly in the form of inulin. In this study, plants of the cultivar “White Fuseau” grown under five salinity levels were evaluated for tuber yield. Results indicated that this cultivar is moderately salt-tolerant if the goal is tuber production. Hydraulic pressings of the tubers produced juice that contained 15% (wet weight) or 55% (dry weight) free sugars, with 70% of these in the form of inulin and the rest as fructose, sucrose, and glucose. Importantly, salinity did not affect the total free sugar or inulin content of the tubers. Tubers were composed of about 12% dry washed bagasse (wet weight) or 44% (dry matter basis) and bagasse retained such high quantities of free sugars after pressing that washing was required for complete sugar recovery. Chemical composition analysis of tuber bagasse suggested that it had low lignin content (11–13 wt%), and its structural sugar composition was similar to chicory root bagasse. Because of the high hemicellulose and pectin content of the bagasse, adding xylanase and pectinase to cellulase substantially improved sugar yields from enzymatic hydrolysis compared to at the same protein loading as cellulase alone. In addition to the high total sugar yield of tuber, these first findings on the sugar and lignin content and enzymatic hydrolysis of tuber bagasse can lead to low-cost production of ethanol for transportation fuels.