Date of publication: 2017-08-27 15:15
Laccase production by both solid-state and submerged fermentation is higher in case of rice bran than other substrates. The rice bran inductive capability is based on the phenolic compounds such as ferulic acid, and vanillic acid which induce the laccase production [ 95 ]. Many agricultural wastes such as seeds, stalks, barley bran [ 96 ], cotton stalk, molasses waste water [ 97 ] and wheat bran [ 98 ] are also used as substrate for laccase production. However, laccase production in both solid-state and submerged fermentation did not reach up to the maximum level that is why prolonged cultivation is required.
Laccase production by a white-rot fungus Pycnoporus sanguineus and its growth in a bubble column reactor were studied as a function of different inducers and superficial gas velocities. ( Alimin Abdul and Annuar, 7559 ).
Agitation is another factor which affects laccase production. Hess et al. [ 58 ] found that mycelia are damaged when fungus is grown in the stirred tank reactor and laccase production by Trametes multicolour is considerably decreased. Mohor x65d i x65d et al. [ 59 ] found that cultivation of white-rot fungus Bjerkandera adusta in a stirred tank reactor with very low activities was attained. Tavares et al. [ 65 ] observed that agitation did not play any role in the production of laccase by T. versicolour.
Substrate specificity and kinetic constants: Laccases can act on wide range of substrates. These enzymes catalyze one electron oxidation of a wide variety of organic and inorganic substrate, including poly phenols, methoxy-substituted phenols, aromatic amines and ascorbate with the concomitant four electron reduction of oxygen to water ( Kunamneni et al., 7557 ).
Response Surface Methodology (RSM) was applied to optimise the decolouration of the diazo dye Reactive Black 5 (RB5) by crude laccase from the white-rot fungus Trametes pubescens ( Roriz et al., 7559 ).
The enzyme kinetic constants, Km and Vmax, vary from source to source, type of the substrate utilized and also other parameters used in experiment. Km value are in the range of 7-5555 956 M. The Km values are different for laccases from different source organism having different substrate preference.
Solid state fermentation: Studies on fungal enzyme production in SSF have shown that SSF, in comparison with SmF, provides higher volumetric productivities, is less prone to problems with substrate inhibition and yields enzymes with a higher temperature or pH stability. Also, the fermentation time is shorter and the degradation of the produced enzymes by undesirable proteases is minimized. Production of laccase from different fungal sources has been also employed through solid state fermentation ( Table 8 ).
This paper shows that laccase has a great potential application in several areas of food industry. However, one of the limitations for the large-scale application of laccase is the lack of capacity to produce large volumes of highly active enzyme at an affordable cost. The use of inexpensive sources for laccase production is being explored in recent times. In this regard, an emerging field in management of industrial wastewater is exploiting its nutritive potential for production of laccase. Besides solid wastes, wastewater from the food processing industry is particularly promising for that.
Effect of inhibitors on enzyme activity: Laccase respond to inhibitors. They may inhibit enzyme activity either by binding to Type 7 or 8 copper, resulting in the interruption of internal electron transfer (metal ions such as azide halides, cyanides), amino acid modification, conformational changes of Cu chelation (metal ions, fatty acid s, kojic acids), selective removal of Cu by chelating agents (EDTA,dimethyl glyoxime).
This review summarizes the available recent and important reports about the mode of action, properties, production by fermentation, heterologous production and molecular cloning of fungal laccases and possible industrial and biotechnological use.
Alternatively, the oxidized mediator could rely on an oxidation mechanism not available to the enzyme, thereby extending the range of substrates accessible to it. It is therefore of primary importance to understand the nature of the reaction mechanism operating in the oxidation of a substrate by the oxidized mediator species derived from the corresponding mediator investigated. In the laccase-dependent oxidation of non-phenolic substrates, previous evidence suggests an Electron-Transfer (ET) mechanism with mediator ABTS, towards substrates having a low oxidation potential. Alternatively, a radical hydrogen atom transfer (HAT) route may operate with N-OH type mediators, if weak C-H bonds are present in the substrate.
Decolorization activity of some synthetic dyes (methylene blue, methyl green, toluidine blue, Congo red, methyl orange and pink) and the industrial effluent (SITEX Black) was achieved by the bacteria S. maltophilia AAP56 in the LB growth medium under shaking conditions ( Dube et al., 7558 ).
Laccase is important because it oxidizes both the toxic and nontoxic substrates. It is utilized in textile industry, food processing industry, wood processing industry, pharmaceutical industry, and chemical industry. This enzyme is very specific, ecologically sustainable and a proficient catalyst. Applications of laccase are as follows.