Combined processes enzyme treatment

Another approach is the combination of an enzyme treatment with hydrogen peroxide [26]. By combining enzyme treatment (a simultaneous treatment of pectinase and cellulase), or alkaline boil-off, with an alkaline peroxide bleaching, the total degree of whiteness is reported to be higher in combination with enzyme treatment. The combined process, including an enzyme treatment, deliver results comparable with those of alkali treatment [27]. 

Nature, however, has performed more than simple stepwise transformations using a combination of enzymes in so-called multienzyme complexes, it performs multistep synthetic processes. A well-known example in this context is the biosynthesis of fatty acids. Thus, Nature can be quoted as the inventor of domino reactions. Usually, as has been described earlier in this book, domino processes are initiated by the application of an organic or inorganic reagent, or by thermal or photochemical treatment. The use of enzymes in a flask for initiating a domino reaction is a rather new development. One of the first examples for this type of reaction dates back to 1981 [3], although it should be noted that in 1976 a bio-triggered domino reaction was observed as an undesired side reaction by serendipity [4]. 

Xylanase + Mannanase. The combined action of xylanase and mannanase leads to a degradation of wall material, which resembles the mode of attack met with in the individual enzyme treatments only the degree of dissolution is rather more intense in the combined treatment. Of special interest is the decrustation of the cell corners, which appear to be attacked on a large scale (Figure 11). The Sx and tertiary wall zones also undergo a decomposition process (Figure 11). 

Physical, as well as chemical, pretreatment processes have been combined with the enzyme treatment of wool. A low-temperature plasma is applied to the fibres prior to treatment with polymeric shrinkproofing agent [122]. Combined protease and heat treatment with a saturated steam [123] and the use of high frequency radiation on enzyme treated materials are reported. 

Biocatalytic membrane reactors combine selective mass transport with chemical reactions and the selective removal of products from the reaction site increases the conversion of product-inhibited or thermodynamically unfavorable reactions. Membrane reactors using biological catalysts can be used in production, processing and treatment operations. Recent advances towards environmentally friendly technologies make these membrane reactors pai ticulaiiy attractive because they do not require additives, are able to function at moderate temperatures and pressrue, and reduce the formation of by-products. The catalytic action of enzymes is extremely efficient and selective compared with chemical catalysts. Uiese enzymes demonstrate higher reaction rates, milder reaction conditions and greater stereospecificity. 

Harrison et extracted polymer from R. eutropha upon treatment with lytic enzymes of Cytophaga sp. without any mechanical processing and 90% purity was achieved by this method. Lu et al., 2006 developed a combined method involving enzyme and sodium hypochlorite for extraction of polymer from Burkholderia sp. PTU9. A recovery of 89% was achieved by this process. De Koning and Witholt reported a combined process involving sequential treatment with heat, alcalase, and SDS assisted by Ethylene Diamine Tetraacetic Acid (EDTA) treatment for the recovery of the polymer from Pseudomonas. A recovery rate of 95% was achieved by this process. 

In the combined processes, the cuticle surface is modified by the respective pretreatment removing lipids and cleaving disulfide bridges and, by the proteolytic post-treatment, enhancing the number of hydrophilic binding sites in the fibres. Both pre- and post-treatment lead to electrostatic repulsion of the fibres, to an enhanced degree of fibre swelling and to an improved dye uptake. If the fibre modification is successfully performed by the use of enzymes alone. 

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