Isolation of Hemicellulose from Corn Fiber by Alkaline Hydrogen Peroxide Extraction

Abstract

Cereal Chem. 74(2):176-181For 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 25ºC) to 42% (2 hr extraction at 60ºC). 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 H 2 O 2 , 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 H 2 O 2 were mixed in a 1:25:0.25 (w/v/w) ratio. Extractions were conducted at pH 11.5 at 25ºC or 60ºC. 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 H 2 O 2 , such as grinding to 20 mesh and extracting with azeotropic toluene-ethanol, were found to be unnecessary.

Combination of Low-pressure Steam Explosion and Alkaline Peroxide Pretreatment for Separation of Hemicellulose

“…The amount of arabinose in the hemicellulose fraction H 0 (2.8%) was higher than that in the other fractions (1.6%) ( Table 2). Apart from the above reasons, pigmentation possibly resulted from chromophores that were generated by alkalicatalyzed modification of reducing end groups on the polysaccharides at the elevated pH, especially at 60 °C (Doner and Hicks 1997). The color (data are not shown) of the H 2 and H 3 fractions was darker than that of H 1 .…”

“…There is a possibility that more severe conditions result in an increase in the hydrolysis of hemicelluloses and the cleavage of bonds between hemicelluloses and lignin. Ester-bound p-coumaric and ferulic acids are liberated under milder alkaline conditions as compared to those commonly used to extract hemicelluloses (Doner and Hicks 1997). Peroxide serves to oxidize lignin to low molecular weight (LMW) organic acids, thereby facilitating alkaline extraction of hemicellulose from the lignocellulosic fiber matrix (Doner and Hicks 1997).…”

“…Ester-bound p-coumaric and ferulic acids are liberated under milder alkaline conditions as compared to those commonly used to extract hemicelluloses (Doner and Hicks 1997). Peroxide serves to oxidize lignin to low molecular weight (LMW) organic acids, thereby facilitating alkaline extraction of hemicellulose from the lignocellulosic fiber matrix (Doner and Hicks 1997). The hemicellulose yield after alkaline peroxide post-treatment ranged between 11.2 and 12.2% (based on the initial Lespedeza stalks), which means about 76.7 to 78.9% of the total released hemicelluloses.…”

“…Hemicelluloses have a backbone of β-1,4-D-pyranosyl residues in which O-4 is in the equatorial orientation (e.g., glucose, mannose, and xylose) (Shallom and Shoham 2003). Because of their various functional properties, the potential applications of hemicelluloses are immense and span diverse fields (Chimphango and Görgens 2012;Doner and Hicks 1997). However, the natural structures of lignocellulosic materials make it hard for extraction of hemicelluloses.…”

Graded Ethanol Fractionation and Structural Characterization of Alkali-Extractable Hemicelluloses from Olea europaea L.

“…The hemicellulose fractions with narrow molecular weight distribution in the present study would be commercially utilized in many fields, such as conversion to xylose, xylitol, and furfural in an industrial scale, modification through esterification, etherification, and graft polymerization for adhesives, thickeners, stabilizers, film formers, etc. (Doner and Hicks 1997;Ebringerová and Heinze 2000). …”