Phenoloxidase-bonded

Kharazipour etal. (1998) used a peroxidase enzyme in combination with H2O2 to activate the surface of TMP fibres for self-bonding. Fibres were activated in a wet system, then dewatered and fluffed out before pressing at 190 °C for 5 minutes. The best IBS recorded for boards of 5 mm thickness made from the activated fibres was 0.55 MPa. The IBS was found to be dependent upon the pH of the treatment solution, the time of treatment and the board density. The authors noted that phenoloxidase gave comparable results to laccase, which was unexpected, since it was thought that the phenoloxidase would lead only to depolymerization of the lignin. 

Milled wood lignin was mixed with the crude enzyme solution of Tram-ties versicolor extracellular phenoloxidases produced on spent sulfite liquor in a ratio of approximately 2 1. This comprised the main part of the two-component bio-adhesive. Industrial particles were bonded with 15% bioadhesive under conventional pressing conditions to have 19 mm particle boards (40 x 50 cm) of the properties described in Table IV. The bonding reaction (crosslinking) took place in aqueous solution at room temperature. If conventional pressing technology is applied, the temperature should be elevated in order to maintain water evaporation within a reasonable press time. 

In order to eluddate the mechanism of the further transformations of the primary lignin decomposition products including the cleavage reactions, we synthesized some of the important primary products labelled with Cu and introduced these into the cultures of fungi or enzymes. Thus, it could be shown, for example, that the breakdown of the side chain of ferulic acid occurs at the double bond vanillic acid is found. During polymerization in the presence of phenoloxidases, in the case of carboxyl-labelled ferulic acid, about 60% of the activity is split off as Cli02. The polymers labelled in the 2 and 3 position in the side chain or in the methoxyl group contain the whole applied activity. 

Another approach to curing SSL by oxidative polymerization employs the use of enzymes (54 ) In that study, SSL was treated with the white-rot fungus Fomes annosus and a laccase-inducing phenoloxidase until the solution reached a honeylike consistency. This viscous liquid was then subsequently used to bond wood particles together at a pressure of 0.03 kg cm-2. It now needs to be established whether the mechanical properties of these boards survive accelerated aging tests. 

The phenoloxidase-lignin-bonded particleboards are free of any emission. 

The flavonols and their glycosides contribute to specific taste characteristics such as bitterness and astringency in berry fruits and their products (Shahidi and Naczk, 1995). The molecular structure of flavonols lacks the conjugated double bonds of the anthocyanins, and they are thereby colorless. They may, however, contribute to discoloration of berry fruits, as they are readily oxidized by O-phenoloxidase in the presence of catechin and chlorogenic acid. Discoloration may also occur as a consequence of complex formation with metallic ions. On the other hand, the flavonol glycoside rutin is known to form complexes with anthocyanins, thus stabilizing the color of these compounds. 

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