Enzymes production costs

The advantages of such biotransformation processes are (1) the relatively high yields which can be achieved with specific enzymes, (2) the formation of chiral compounds suitable for biopharmaceuticals, and (3) the relatively mild reaction conditions. Key issues in industrial-scale process development are achieving high product concentrations, yields and productivities by maintaining enzyme activity and stability under reaction conditions while reducing enzyme production costs. 

One of the bottlenecks of enzyme technology is enzyme availability. When the biocatalyst is commercial, the price may be too high, but in most cases there is no commercial source available so that the enzyme must be produced by means of an overproducing strain and finally the enzyme should be purified. Enzyme purification (discussed in section 6.3.1) is a time consuming process and may represent up to 80% of the enzyme production cost. The usual procedures for lipase purification are sometimes troublesome, time consuming and result in low final yields (Gupta et al. 2004). Enzyme immobilization overcomes this handicap because it allows its reuse and can also enhance enzyme stability and activity (Sharma et al. 2001) furthermore, enzyme immobilization facilitates bioreactor design and final product downstream from reaction medium (see section 4.1). 

In general, enzymatic degumming minimizes oil retained in the gum, resulting in improved oil yields. The enzymatic hydrolysis reaction typically requires 5-6 hours and utilizes less water than water and acid degumming processes. Reductions in enzyme production costs and enhanced enzyme activity and stability could make enzymatic degumming process very attractive for oil refining industry in the near fumre. 

SoKd substrate fermentation using agricultural wastes was considered to be used for the production of both enzymes in order to reduce the production costs. Production of glucoamylase from Aspergillus niger J8 was reported (1,3). This report concerned on the production of pectinases from Rhizopus sp. 26R in solid substrates composting of agricultural wastes, optimization of the conditions for pectinases production in solid substrates and the estimation of the production cost. 

Using agricultural wastes as solid substrates for the production of pectinase from Rhizopus sp. 26R gave benefit, not only to the utilization of the wastes but also to the reduction of the cost of the enzyme production. 

Cost of the enzyme production in solid substrate was estimated to be US 180 for 10 million units of crude pectinase. This price included the production of fungal spore inoculum. This production of pectinases from Rhizopus sp. 26R using agricultural wastes as solid substrates was one of the way to utilize agricultural wastes to value-added products and the cost of the enzyme production was very reductive. 

While many virtues of enzyme catalysis need to be recognized, it should be realized that industrial enzymes can cost from US 10,000 to 11,000 per kg. Therefore, the enzyme catalysed production of chemicals that sell at US 1 to 5 per kg may not be economical even if the yield is 100 % and downstream cost is not excessive. Enzymes are easier to justify for pharmaceutical that sell at US 30 to 50,000 per kg. Even noble metal catalysts like 5% Pd on carbon cost about US 720 per kg. 

Some of the industrial biocatalysts are nitrile hydralase (Nitto Chemicals), which has a productivity of 50 g acrylamide per litre per hour penicillin G amidase (Smith Kline Beechem and others), which has a productivity of 1 - 2 tonnes 6-APA per kg of the immobilized enzyme glucose isomerase (Novo Nordisk, etc.), which has a productivity of 20 tonnes of high fmctose syrup per kg of immobilized enzyme (Cheetham, 1998). Wandrey et al. (2000) have given an account of industrial biocatalysis past, present, and future. It appears that more than 100 different biotransformations are carried out in industry. In the case of isolated enzymes the cost of enzyme is expected to drop due to an efficient production with genetically engineered microorganisms or higher cells. Rozzell (1999) has discussed myths and realities... 

In general, microsomes/S9 and cofactor (NADPH or UDPG A) are the most costly components of an incubation, but substrate, especially for early discovery compounds, is sometimes scarce. Higher enzyme concentration will lead to higher volume productivity and less amount of the cofactor to maintain the same cofactor concentration. However, the relationship of reaction rate and enzyme concentration may not be linear, so a higher enzyme concentration may yield lower enzyme productivity (amount of product per milligram enzyme used). Therefore, different protein concentration levels should be screened to obtain a good balance between volume and enzyme productivities. 

If a high turnover (>50%) is observed in the initial screening incubation at 10-50 iM, then a higher substrate concentration should be tested to obtain a good balance between the enzyme productivity and the conversion yield. The substrate concentration should be mainly selected based on the activity of enzymes, and may be increased until the benefit of enzyme productivity increase is offset by cost and availability of the substrate. The solubility of substrate in buffer may limit the use of high concentrations, but a low aqueous solubility compound is readily absorbed by microsomes/S9, which will help to keep the substrate in the incubation mixture even at a much higher concentration than its buffer solubility. Substrate concentration up to sub-millimole level can be used as long as no inhibitory effect is shown and a reasonable turnover is achieved. 

New biocatalysts (genetically modified bacteria) could break up cellulose/ hemicellulose, but it is necessary, on one hand, to decrease the cost of enzyme production and, on the other hand, to improve reactor and process technology,... 

Cost sensitivity studies have shown that the successful commercialization of cellulase-based processes, such as the conversion of cellulose to fermentable sugars, is highly dependent on the cost of enzyme production (i). Because fungal -D-glucosidase (EC 3.2.1.21) is the most labile enzyme in this system under process conditions (2), and k to efficient saccharification of cellulose, this enzyme was targeted for application of stabilization technology, both through chemical modification and immobilization to solid supports. 

One of the major expenses incurred in the application of enzymes for bioconversion processes is the cost of enzyme production (1). The total cost of production includes the cost of fermentative production as well as downstream processing requirements. Both of these factors must be optimized and integrated for maximum cost-effectiveness. 

The application of pentosanase-based enzyme products to wheat-based piglet diets is also cost-effective, with improvements in live-weight gain and feed conversion of about 5% commonly reported. Further, lower incidences of digestive disorders... 

The fermentation step to produce penicillin GA is the major cost element in the overall process to produce 6-APA. This is substantially due to the high cost of sterile engineering (Table 4.6 and 4.7). Clarification, extraction and solvent recovery steps are also significant, a reflection of the dilute and impure composition of fermentation broths. The concentration of 6-APA in the final broth has a big effect on total process costs. Thus increasing final 6-APA concentrations from 1.2-6.0% have been calculated to reduce production costs by over 50% (Table 4.8). By contrast the 6-APA production step cost is quite small, and is less that half the cost of the solvent recovery process (Table 4.6). The costs of the immobilized enzyme is not insignificant in a recent calculation it was estimated at 2.5 /kg 6-APA (Rasor and Tischer, 1998). 

Very many technical and commercial factors are important such as the utility of the product (cost-benefit relationships), ease of scale-up, the productivity of the process etc. Process design, for instance, involves a series of choices, such as the use of isolated enzyme or intact microorganism, use of free or immobilised cell or enzyme, use of mutant or genetically modified cell, or batch or continuous processing etc. Such choices depend on other factors such as the availability and cost of precursors, product purity required, intended scale of operation and existing skills and equipment available within the Organisation. 

For more expensive enzymes the continuous use of enzymes made possible by their iimnobihsation can result in considerable savings. By comparison typical chemical catalysts represent a smaller proportion of the total manufacturing costs. Thus the catalysts used in ammonia, cyclohexane and styrene manufacture have been estimated to cost approximately only 0.7, 0.6 and 0.6% of the total production costs respectively. Thus biocatalysts are still in general comparatively expensive compared with chemical catalysts. 

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