Prediction of cell wall polysaccharide and lignin concentrations of alfalfa stems from detergent fiber analysis

Identification of superior biomass feedstocks for conversion to ethanol requires accurate, rapid, and inexpensive measurement of cell wall polysaccharide and lignin concentrations. A study was undertaken to determine if cell wall characteristics measured with the Uppsala dietary fiber method could be accurately predicted from detergent fiber data. Spring and summer growth alfalfa (Medicago sativa L.) stems were harvested from two germplasm sources for 2-years. Samples were analyzed for neutral sugars, uronic acids, and Klason lignin using the Uppsala dietary fiber method, and neutral detergent fiber, acid detergent fiber, and acid detergent lignin by sequential detergent analysis. Cell wall, hemicellulose, cellulose, and lignin concentrations derived from these two methods were positively correlated, but detergent estimates of cell wall and lignin concentration were lower and hemicellulose and cellulose concentrations were higher than for the Uppsala method. These patterns were attributed to solubility of pectin in neutral detergent solution and poor lignin recovery in acid detergent lignin. Regression equations for prediction of cell wall characteristics using detergent results were significant and accounted for 35–92% of the variation in the data. Significant deviations between predicted and observed cell wall results were observed when the equations were tested using an independent sample set, although the deviation was very small for cellulose concentration. It does not appear that most cell wall characteristics of alfalfa stems obtained using the Uppsala dietary fiber method can be accurately predicted using detergent fiber results; however, cellulose concentration might be predicted with acceptable accuracy.