Postharvest quality and processing of sugarcane and sweet sorghum for sugar and ethanol production
Location: Commodity Utilization Research
Title: Sugarcane internode composition during crop development
Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 7, 2011
Publication Date: March 31, 2012
Citation: Lingle, S.E., Thomson, J.L. 2012. Sugarcane internode composition during crop development. BioEnergy Research. 5:168-178.
Interpretive Summary: Sugarcane is used to make sugar, but the plant material left over from the sugar making process could be used to make ethanol for fuel. Use of the plant material in this way requires a better understanding of its composition. In this study, two experiments were done to examine how composition of sugarcane stalk sections, called internodes, change with age of the section, and as the crop matures from a rapid growth phase (grand growth) to a slower growth phase (ripening). Composition of the plant material was determined using a method that sequentially extracts different types of compounds from it using successively stronger chemicals. The weakest extraction removes soluble compounds such as sugars, leaving what is called neutral detergent fiber (NDF). The next extraction uses a mild acid solution and removes a portion of the NDF, leaving acid detergent fiber (ADF). A final extraction using a stronger acid solution removes even more of the material, leaving acid detergent lignin (ADL). The remaining material is burned to leave only minerals, called ash. NDF and ADF are important because much of them is carbohydrate that microorganisms can use to make ethanol. ADL is important because it acts like glue in the plant, preventing microorganisms from getting to the carbohydrates. This study showed that in early growth, the sugarcane internodes build structure, so NDF, ADF, and ADL increase. Then, sugar accumulates so that NDF and ADF decrease. However, ADL continues to increase; the older an internode is, the more ADL it has. Growth stage (grand growth vs ripening) had no influence on NDF and ADF, but ADL was slightly higher at ripening than at grand growth. Ripening is important for sugar production, but would not have much effect on the use of the remaining plant material for making ethanol.
The utilization of sugarcane (Saccharum spp. hybrids) as a feedstock for cellulosic ethanol or other biofuel requires a better understanding of its composition. Two experiments were designed to better understand how cell wall composition changes over with development over time and with season in sugarcane internodes. In experiment 1, an internode from 5 modern cultivars were marked just as elongation was starting, and then sampled every 1 to 2 weeks from July until October. A sequential detergent method was used to determine neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL) and ash content of the material. In experiment 2, internodes 1, 3, 5, 7, 9 and 11 down the stalk were sampled in late July (grand growth) and late September (ripening). In this experiment, internode length, fresh weight, dry weight, water content, and sugar contents were determined as well as NDF, ADF, ADL and ash contents. Both experiments were repeated in two years. NDF and ADF initially increased until the internodes were completely elongated then fell as sugar accumulated, before reaching plateaus of 370 and 250 g kg-1 DW for NDF and ADF, respectively in Experiment 1, and 340 and 220 g kg-1 DW for NDF and ADF in Experiment 2. ADL increased with development in both experiments, consistent with anatomical and histochemical studies of developing sugarcane internodes. In Experiment 2, ADL was slightly higher on average at ripening (31.6 g kg-1 DW) than at grand growth (27.7 g kg-1 DW). Ash content was also higher on average at ripening (3.9 g kg-1 DW) than at grand growth (2.8 g kg-1 DW). Growth stage was not a significant effect for NDF or ADF.