Water-soluble hemicellulose was extracted from corn fiber with
microwave-assisted heat treatment. The effects of treatment temperature and initial
pH of the aqueous extraction media were investigated regarding hemicellulose recovery
and molecular mass of the isolated polysaccharides. In treatments carried out at neutral
pH (simple water extraction), it has been demonstrated that hemicellulose recovery
could be increased by applying higher treatment temperatures. However, the molecular
weight of isolated hemicellulose gets significantly lower.
For example, 10% of the raw materials' xylan was extracted at 160 degrees C and about
30% recovery was reached at 210 degrees C. However, the molecular mass of the isolated
polysaccharide at 210 degrees C (5.82 x 10(4)) was about half of that measured at
160 degrees C (1.37 x 10(5)). Reducing the pH with sulfuric acid resulted in shorter
polymer chains (1.7 x 10(4)) and lower hemicellulose yields (2.2%). Application of
sodium hydroxide in the treatment showed that, compared with acid, considerably higher
yields (11%) with longer polysaccharide chains (1.3 x 10(5)) could be obtained.