Laccase/TEMPO oxidation in the production of mechanically strong arabinoxylan and glucomannan aerogels.

New wheat arabinoxylan and konjac glucomannan hydrogels and aerogels were prepared by hemiacetal crosslinking induced by laccase/TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) -catalysed oxidation, which selectively converts the primary hydroxyl groups to aldehydes. The degree of oxidation of the product aldehydes was ca. 10% of the total carbohydrates of the polysaccharides, and the determination of storage and viscous moduli of the oxidised samples showed that they had formed true hydrogels. Two freezing methods for the hydrogels, conventional freezing and ice crystal templating, were investigated for aerogel production, the ice crystal templated products especially were mechanically strong in compression test against the ice crystals' growth direction. The compressive moduli were ca. 1200kPa for wheat arabinoxylan aerogels and ca. 650kPa for konjac glucomannan aerogels. A morphological study with a scanning electron microscope revealed the inner structure of the aerogels. Ice crystal templated konjac glucomannan aerogel formed round pores with a diameter of ca. 50-100μm. The arabinoxylan aerogel consisted of long and narrow pores with a length of a few hundred μm and width of 50-100μm, which had formed in the direction of the ice crystals' formation. Konjac glucomannan and wheat arabinoxylan are approved food-grade materials, and wheat arabinoxylan is particularly interesting because it can be obtained from cereal processing side streams - thus, these novel products have potential in various applications, including the food, food packaging, and pharmacological fields.