INTRODUCTIONCellodextrins are linear polymers of two to seven p-1-4 linked glucose molecules.Properties of these oligosaccharides include a decreasing water solubility with increasing molecular weight, limited solubility in nonaqueous or partially aqueous solvents, and a melting point which increases with increasing weight. These and other properties are summarized in Table I.Cellodextrins are reaction intermediates for the formation of glucose from cellulose, which is one of the United States most abundant renewable resources. One billion tons of cellulose-containing residues are generated annually. These residues have a potential for yielding over 6 x 10" pounds of a valuable chemical feedstock, glucose, from which fuel alcohol and other fermentation derived chemicals can be made. At present the hydrolysis of cellulose to glucose is being intensely studied with the objective of obtaining quantitative data on this process for the engineering design of cellulose saccharification plants. For this research, relatively large quantities of individual pure-component cellodextrins are required. Unfortunately, except for cellobiose, cellodextrins are not commercially available.Cellodextrin mixtures are readily prepared by the classic method of Miller et al.8 In their approach, cellulose was carefuUy hydrolyzed with fuming HCI to give a distribution of oligosaccharides from celloheptaose to cellobiose, as well as glucose. The separation of the mixture was accomplished by chromatography on a charcoalcelite column (90 cm long x 5 cm i.d.) using gradient elution with ethanol-water as the eluent. Separation of 2 g of a mixture of cellobiose through cellohexaose required two to three days of continuous elution. Once used the column-packing material had diminished separation capability. Hence, new adsorbent had to be prepared and the column repacked before each run. This method is quite satisfactory for preparing cellodextrins in small quantities and is much cited in the literature. However, owing to the heavy demand for cellodextrins in our laboratory for use in enzyme kinetics studies on cellulose hydrolysis, a less time-consuming separation of cellodextrins was needed. Developmental work was, therefore, carried out which resulted in several schemes for increasing productivity.
MATERIALS AND METHODS
Cellulose Hydrolysis to Form CellodextrinsHydrolysis of cellulose was carried out by a modified method of Miller et aL8 The procedure consisted of dissolving 10 g Whatman CF-I I cellulose in ice-cold fuming HCI. The clear viscous solution which formed was warmed to 25°C and kept at this temperature for 2 hr. During this time the cellulose was hydrolyzed to cellodextrins. Next, the HCI was partially stripped from the hydrolyzate under 20 mm Hg vacuum with an aspirator for 15 min. The mixture was then added to 500 ml ice-cold distilled water. This caused the unhydrolyzed portion of the cellulose to precipitate. The precipitate was then filtered off and the filtrate, containing the cellodextrins, was subjected to a neutralization a...