Michael H. Penner, Stefanie K. Nguyen, and Eugene Kim. Food Science & Technology, Oregon State University, 100 Wiegand Hall, Corvallis, OR 97331
Cereal and commercial grass-seed straws are promising feedstocks for biochemical and cellulosic fuel-ethanol production. A low, but significant, fraction of the carbohydrate portion of these feedstocks is often composed of fructose/fructosyl-containing components (“fructose equivalents”); such carbohydrates include sucrose, fructo-oligosaccharides, and fructans. Standard methods used for the quantification of neutral monosaccharide equivalents are not particularly well suited for the quantification of fructose equivalents due to the inherent instability of fructose (> 50% degradation) under the prescribed hydrolysis conditions (oligo/polysaccharide hydrolysis conditions of 4% sulfuric acid, 121oC, 1 hr). The objective of the presented study was thus to determine conditions better suited for fructose-equivalent quantification, focusing on fructan/fructo-oligosaccharide hydrolysis. Time, temperature and acid concentrations were considered, using wheat and tall fescue straws as representative feedstocks. Included in the study were model fructose-containing oligosaccharides/polysaccharides. The instability of fructose, relative to glucose and xylose, at higher acid/temperature combinations was demonstrated, all rates being acid and temperature dependent. Fructans are shown to be effectively hydrolyzed at acid concentrations as low as 0.1%, when at 121oC for 1 hr. Lower temperatures can also be effective, with corresponding adjustments in acid concentration and time. The data indicates that the buffer capacity of the feedstock should be taken into account when using the lower acid concentrations, this being relevant to the appropriate conditions for the determination of degradation “correction factors”. The presented hydrolysis data, which focuses on acid-catalysis, is discussed with reference to the application of appropriate hydrolytic enzymes.
