Table 3.

Summary of recent publications on fungal pretreatment.

3. Parameters affecting pretreatment process

Fungal Pretreatment of Lignocellulosic Materials DOI: http://dx.doi.org/10.5772/intechopen.84239

of laccase by T. versicolor.

lignocellulosic biomass pretreatment.

3.2 Inoculum concentration

3.3 Moisture content

49

3.1 Fungal strain

High lignin degradation can be achieved by having high activities of white-rot

In order for the white-rot fungi to be used in the pretreatment process, screening of a large number of fungal isolates is important in order to have the right isolates for the process. Screening step allows the selection of isolates with the highest ligninolytic enzymes production and activity as well as high lignin degradation on the specific substrates. In order to limit matter losses, selective delignification is crucial and high fermentable sugar losses must be avoided. White-rot fungi strains should therefore be carefully selected based on these important parameters. Table 4 summarizes some of white-rot fungi species that have been studied for several

Inoculum concentration is an important factor in biological pretreatment. Suffi-

Moisture content of the solid state fermentation is a critical aspect for fungal growth and activities. Lignin degradation is significantly influenced by this factor as it affects the growth and activities of the fungal. Increasing the moisture content enhances the nutrient transfer but reduces the porosity of the substrate and limits oxygen transfer [28]. However, insufficient water content in the substrates may cause deactivation of the fungi. Optimum moisture content depends upon the organism and the substrate used for SSF [30]. The range of moisture content of substrate for SSF using white-rot fungi is usually between 45 and 85% [29]. A study on the effect of moisture content for delignification of cotton stalks by Daedalea flavida MTCC 145 (DF-2) in SSF found that the highest ligninolytic enzyme

cient amounts of inoculum must be defined to ensure good fungal growth and substrate colonization. The time required for the colonization of the substrate is affected by the type and amount of inoculums [31]. Higher concentration of inocu-

lum will lead to shorter time of colonization of the substrate [49].

fungi and production of ligninolytic enzymes. This is influenced by several pretreatment parameters such as fungal strain, inoculum concentration, moisture content, aeration, pH, temperature, supplements and incubation time [28–30]. Moreno et al. [29] reviewed that for solid state fermentations (SSF), depending on the strain used, the usual conditions that have been used are at moisture content 45–85%, pH 4–5, with an inoculum level of 1–10mg/g substrate (dry weight), at temperatures ranging from 15 to 40°C and over 1–12 weeks. The optimization of these parameters is important to increase the efficiency of the pretreatment by reducing the carbohydrate loss and pretreatment time [31]. However, for most of these factors, the optimal conditions are depended on the substrate and fungal strain [28]. Temperature and pH are reported to affect fungal metabolism, spore germination and growth. Low moisture content can reduce nutrients availability and growth, while higher moisture content can boost contamination, reduce heat and oxygen transmission, and affect enzyme production [32]. Adekunle et al. [33] reported that the pH and temperature of the SSF play a vital role in the production
