|TEUTSCH, CRAIG - Virginia Polytechnic Institution & State University|
|PLEASANT, R. SCOTT|
Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2013
Publication Date: 1/27/2014
Citation: Kagan, I., Kirch, B.H., Thatcher, C.D., Teutsch, C.D., Pleasant, R. 2014. Chromatographic profiles of nonstructural carbohydrates contributing to the colorimetrically determined fructan, ethanol-soluble, and water-soluble carbohydrate contents of five grasses. Animal Feed Science And Technology. 188:53-63.
Interpretive Summary: Four forage species were extracted according to standard procedures for colorimetric water-soluble carbohydrate (WSC) and ethanol-soluble carbohydrate (ESC) analysis. Extracts were prepared for HPLC by pH adjustment to <8 if necessary, followed by passage through a C18 solid-phase extraction column and dilution to a concentration permitting peak resolution. Peaks were quantified in terms of the sugars used to analyze WSC and ESC colorimetrically, and the results of HPLC and colorimetric assays were compared. ESC extracts consisted of glucose, fructose, and sucrose. WSC extracts before hydrolysis contained high-M.W. fructans in tall fescue, bluegrass, and orchardgrass (C3 grasses), but not in bermudagrass (C4). After hydrolysis, those fructans disappeared, and glucose and fructose peak areas increased. The percentage of ESC and WSC determined by HPLC and colorimetric assay differed, but trends were similar, demonstrating that HPLC could provide information in the terms traditionally used for carbohydrate profiling of forages.
Technical Abstract: Nonstructural carbohydrates in forages are often analyzed by colorimetric assays of water and ethanol extracts. Water-soluble carbohydrates (WSC) include polysaccharides (starch and fructan) and mono- and disaccharides. Ethanol-soluble carbohydrates (ESC) consist only of mono-, di- and oligosaccharides. Colorimetric assays can quantify total WSC or ESC but cannot identify different sugars in an extract. High-performance liquid chromatography (HPLC) can identify different sugars in extracts, but because grasses are often extracted and treated differently for HPLC than for the colorimetric assays, comparing data can be difficult. In this study, vegetative tissue from 5 forage grasses (bermudagrass, orchardgrass, Kentucky bluegrass, and endophyte-infected and endophyte-free tall fescue) was extracted and analyzed according to standard protocols for WSC and ESC extraction and colorimetric analysis. The same extracts were analyzed by HPLC after minimal sample preparation. Comparison of hydrolyzed and unhydrolyzed WSC extracts demonstrated that the unhydrolyzed C3 grasses contained long-chain fructans, while bermudagrass (C4) did not. Amounts of ESC and WSC differed in the HPLC and colorimetric analysis, but trends were similar, demonstrating that HPLC could provide information in the terms traditionally used for carbohydrate profiling of forages.