Fermentation cellulase production

A literature survey indicated that very little work has been done to produce an optimal cellulase system as described above. Here, we used solid-state fermentation (SSF) to achieve this objective. SSF processes, such as the "koji" process, have been used extensively for amylase production on wheat bran in Japan its application was extended to cellulase production on wheat bran and Ugnocellulosic materials by Toyama (13), Since then, wheat bran has become an important substrate for producing various products by SSF (14-20), In this study, we tested various lignocellulosic substrates for the production of cellulase and )3-glucosidase from T, reesei QMY-1 by SSF. 

When wheat straw was fermented in LSF, the FP cellulase level reached 6 lU/ml (300 lU/g cellulose or 120 lU/g substrate) (Table I) by day 11, decreasing thereafter. This showed that SSF was better than LSF for cellulase production when using wheat straw. 

A maximum FP cellulase of 6.3 lU/ml (191 lU/g cellulose or 126 lU/g substrate) was obtained on NaOH-treated CTMP after 20 days in SSF. On untreated CTMP, the FP cellulase remained about 5 lU/ml from 20 to 26 days of fermentation and then increased to 7.2 at 30 days of fermentation (Table III). This indicated that CTMP was a good substrate for cellulase production in SSF even without the mild NaOH treatment. 

RunUnococcus albus and Ruminococcus flavefadens. These bacteria are important cellulose-degraders found in the rumen of cattle and sheep (2). Most isolated strains ferment cellulose and xylan and all ferment cellobiose. Fermentation of glucose and some other carbohydrates depends on the particular strain. R flavefadens and B. succinogenes can ferment the highly ordered crystalline cellulosic su trates but R albus cannot. No evidence has been found for extracellular cellulase production by R albus, but Ohmiya et al. purified cellobiosidase from this culture 17). Laboratory growth of R albus has been conducted at pH 7.0 and 37 C. 

Much effort has been expended over the years on increasing enzyme production of T. reesei by isolation of high yielding mutants and optimizing media and fermentation conditions. Strains have been isolated that produce 2-6 times the cellulase productivity of the parent wild strain (QM 6a) in batch culture. The mutants produce higher levels of cellulase protein but the specie activity of the enzymes and the proportions of the individual components (ca. 30% endo- -glucanase, 70% o- -glucanase, and less 1% cellobiase) are similar to those of the parent. 

Cellulases endo-1,4 p-glucanase, cellobiohydrolase, p-glucosidase Brewing, cereal processing, fruit and juice processing, food fermentation, wine production, alcohol fermentation, vegetable processing. 

This commentary is based on cellulase production by Trichoderma and is consistent with the general fermentation technology of Wang et al. [40]. 

An interesting alternative, however, is batch culture using cellulose as the feedstock. Because cellulose will only be consumed gradually, the effective value of S is much lower than the actual cellulose concentration, which decreases the rate of cell growth u and, according to Fig. 4, increases. In this system, the substrate uptake rate will depend on the amount of cellulase present. Because of its complexity, the kinetics of fermentation of cellulose will not be developed further here. However, batch culture has been used for cellulase production and is an option to consider in a fermentation design, as the feedstock is inexpensive. Handling and sterilization of the insoluble solid is a concern. 

Keywords. Cellulase production. Solid-state fermentation. Operating conditions, Bioreactor, Mathematical model... 

Process Description of Solid-State Fermentation for Cellulase Production. 72... 

In solid-state fermentation, the productivity per unit reactor volume is high and the solid cellulase koji can be directly applied to hydrolyze cellulosic materials. 

The equipment in the solid-state fermentation process is relatively simple and the capital investment is low. However, new types of fermentor for large-scale cellulase production need to be developed. 

The most attractive features of solid-state fermentation include low capital investment and low operational costs. These features are favorable in the hydrolysis of cellulosic materials because the cost of cellulase is a key factor for commercial production. Currently, cellulase production by submerged culture has made great progress and been commercialized, while solid-state fermentation is only operated on a small scale in a few countries, such as China, and further efforts in research and development are still needed in order to improve the process and the equipment. 

It is a commonly held view that cellulase is an inducible enzyme, and that cellulose is the best inducer. In solid-state fermentation for cellulase production, cellulosic materials act as either the carbon source or the inducer. Some of the raw materials for solid-state fermentation and their composition are listed in Table 1. From Table 1 it is very clear that the raw materials for cellulase production using solid-state fermentation are abundant and cheap. Proper pretreatment of raw materials is generally required. The nitrogen source for solid-state fermentation includes inorganic compounds, such as urea and (NH4)2SO4, or natural products, such as bran. 

The operating conditions for solid-state fermentation for cellulase production are dependent on the strain to be used, the reactor type and the medium composition, but the basic operating procedure remains the same as shown in Fig. 2. The final product can be obtained as crude solid cellulase, liquid cellulase or powder cellulase according to the application. Figure 3 shows a process flowsheet for cellulase production [25]. In the process, wheat bran is used as substrate. Seeds are prepared in a stirred-tank fermentor and then sprayed into the medium by a spray distributor. The fermentation is performed in a shallow-tray fermentor. The temperature and humidity in the fermentor are automatically regulated. After fermentation, cellulase is recovered by water extraction and purified by salt precipitation and ion exchange. The final product is concentrat-... 

Fig. 2. General flowsheet for cellulase production via solid-state fermentation...

The operating conditions are very important for efficient cellulase production via solid-state fermentation. The effects of operating conditions, such as temperature, water content and water activity, pH, aeration and substrate composition, on the cellulase production by solid-state fermentation will be discussed in this section. 

The most commonly used strain in cellulase production is the mutant from T. reesei, whose optimal temperature for growth is in the range 30-32 °C, and the optimal temperature for cellulase accumulation is 26-28 °C [2, 26]. During solid-state fermentation, a heat of metabolism will be released because of the... 

Kim et al. studied the solid-state fermentation processes of T. reesei and Sporotrichum cellulophilum. The optimal water content for growth phase of T. reesei and S. cellulophilum is 57 and 70%, respectively, but is the same as the cellulase production phase (50%) [31]. 

The sohd-state fermentation for cellulase production is an aerobic process therefore, aeration is necessary for cell growth and cellulase formation. In addition, aeration is important in order to maintain humidity, to remove gaseous metabolites, such as COj, as well as to remove the heat of metabolism [42,43]. In a large-scale solid-state fermentor, aeration is so important that it must be controlled carefully. The aeration method and the flow rate as well as the temperature and humidity of the air supply must be regulated to avoid sudden changes in temperature and water activity of the solid medium [29,31]. 

In the submerged fermentation process for cellulase production, crystal cellulose and paper pulp are commonly used substrates which are expensive. The solid-state fermentation for cellulase production should use a cheap medium. Because cellulase is an inducible enzyme, the inducer must be included in the medium. Cellulose is the best inducer [45,46] and its hydrolysate (glucose) is the carbon source for microbes to grow therefore, cellulosic material is the basic component in the medium. Complex nitrogen sources are used to supply nitrogen and to regulate the pH value. Other nutrient salts, such as Mn + and Zn etc., should also be involved in the medium. 

Wheat bran, which contains cellulose, protein and other nutrients, is an excellent medium for solid-state fermentation [25,47]. Wheat bran is also widely used in other fermentation industries but is still too expensive for economic cellulase production. Agricultural residue is cheaper. For example [30,48], after pretreatment by 4 % NaOH at 121 °C for 0.5 -1.0 h, wheat straw was used as raw material. After mixing with nutrient salts, adding water to a water content of 80%, then adjusting the pH to 5.8, the medium was used for solid-state fermentation. The final cellulase activity was reported to be as high as 200-430 FPIU per gram of cellulose. Deschamps et al. [49] used a mixture of wheat straw and bran (80 20) as raw materials for solid-state fermentation the... 

From the above discussion it is obvious that agricultural residue can be used as substrate and inducer in soUd-state fermentation for economic cellulase production. This is a distinguished advantage of sohd-state fermentation and makes the process more competitive than the submerged culture technique. 

Parameters to describe a solid-state fermentation process for cellulase production include physical properties such as temperature, pH, humidity and water activity, particle size, pile and real densities, pore size and porosity, etc. chemical components such as medium composition, gas-phase composition, amount and properties of microorganisms, activities of cellulases, etc. and kinetic para-... 

A complete mathematical model to describe a batch sohd-state fermentation for cellulase production in a fixed bed should include the following ... 

Growth Characteristics of Microorganisms in Solid State Fermentation for Upgrading of Protein Values of Lignocelluloses and Cellulase Production... 

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