Isolation of hemicellulose from corn fiber by alkaline hydrogen peroxide extraction

For the first time, alkaline hydrogen peroxide (AHP) extraction conditions were used to isolate hemicellulose (arabinoxylan) from destarched corn fiber. Yields of the water-soluble hemicellulose B ranged from 35% (24 hr extraction at 25 degrees C) to 42% (2 hr extraction at 60 degrees C). The hemicellulose B resulting from the 2 hr extraction (pH 11.5) was off-white in color, and a very low proportion (1.7%) of water-insoluble hemicellulose A was extracted. AHP treatment caused delignification and facilitated the alkaline extraction of hemicellulose from the lignocellulosic fiber matrix. In the absence of H2O2, yields were reduced by more than one-third when using otherwise identical extraction conditions of time, temperature and pH. In the standard protocol, corn fiber, NaOH solution, and H2O2 were mixed in a 1:25:0.25 (w/v/w) ratio. Extractions were conducted at pH 11.5 at 25 degrees C or 60 degrees C. The pH was adjusted to 11.5 by addition of NaOH at ambient and elevated temperatures. The optimum hemicellulose yield (51.3%; dry, starch-free basis) was obtained when the pH was increased to 12.5 for the final one-half of the extraction period. Products obtained after extraction at pH values greater than 11.5 were tan in color, however, and the goal of the research has been to isolate white hemicellulose B and then evaluate its properties. Under most conditions, the yields of hemicellulose B, potentially the most useful form for food and industrial applications, exceeded those of hemicellulose A by more than 10-fold. The hemicellulose B products were lighter in color than those obtained using traditional alkaline extraction conditions of refluxing with calcium or sodium hydroxide. Steps prior to extractions with alkaline H2O2, such as grinding to 20 mesh and extracting with azeotropic toluene-ethanol, were found to be unnecessary.