Rawv materials_Food Fermentation Tech.pptx

Rawv materials_Food Fermentation Tech

1. Raw materials for fermentation process

2. Substrate Choice The chemical nature of the carbohydrate substrate, whether and which mono-, di- or polysaccharide can be used for a particular fermentation process, depends on the genetic constitution of the microbe. Most organisms grow on glucose; many strains can also hydrolyze sucrose. Lactose utilization depends on the induction of a β -galactosidase and a transport system for lactose through the cell membrane. Similarly, many important fermentation organisms cannot grow on starch, which is the least-expensive defined carbohydrate substrate available, because it lacks amylases for starch liquefaction and saccharification. Enzymatically liquefied starch is a preferred substrate for those strains that have sufficient own β -amylase or glucoamylase activity for converting dextrins into maltose and glucose, respectively.

3. Gluconic acid production from glucose, where the straightforward formation of the metabolite depends on a particular carbohydrate substrate. In all other cases the genetic characteristics of the production strain determine the substrate choice rather than the biochemical pathway leading to the relevant end product. Simplified, any carbohydrate is finally directed into the central metabolism via fructose as the central entry door. It is an empirical observation that the sugar or carbohydrate with the best growth characteristics is not necessarily the substrate for the best product formation. Growth-limiting carbohydrates often provide higher substrate yields and improved volume productivity. Similarly, carbohydrates that are metabolized via different catabolic shunts can strongly influence the over-all product yield. This may further narrow the range of substrates available for the particular production process and may often give preference to comparatively expensive carbohydrates.

4. Within the range of carbohydrates that is accepted by the microbial strain depending on its genetic constitution, the final substrate choice for commercial production is directed by an interactive ranking of quality, price, and technological and processing features. The special properties of major carbohydrates as fermentation substrates are listed in Table 1. Pure glucose, sucrose or lactose of food- or even pharma-grade is used in expensive cell culture media for monoclonal antibody production, or in bacterial fermentations for recombinant human proteins that depend on excessive downstream processing and purification. For all other fermentation systems, regardless of the relative impact of raw material costs, sooner or later the price of the carbohydrate becomes an important issue in the development process and is under continuous surveillance in current production. Sucrose, the most expensive food-grade sugar, is therefore a rare fermentation substrate in contrast to the inexpensive byproducts of sugar refining, cane and beet sugar molasses. Cane sugar molasses is an important substrate for ethanol fermentation in Brazil; beet sugar molasses for yeast fermentation, and both types of molasses are still in use for citric acid fermentation.

5. Yield on substrate and volume productivity In a typical fermentation process, the carbohydrate serves as the main carbon and energy source of the organism, while nitrogen is derived from ammonia, nitrate, amino acids or proteins. A certain amount of carbohydrate substrate is therefore inevitably converted into energy and CO 2 ,which necessarily results in a molar product yield per substrate below 1.0. In anaerobic fermentations, the carbohydrate substrate is predominantly used as energy source. In the absence of oxygen, the carbohydrate is incompletely oxidized and fermentation end products such as ethanol and lactic acid are massively secreted into the fermentation medium as a kind of metabolic waste.

6. However, in aerobic microorganisms the carbohydrate consumption is strictly regulated in order to obtain maximum resource management. The carbohydrate demand for growth and energy metabolism strongly competes with product synthesis and accumulation. As a condition for metabolite and end product oversupply, the genetic and biochemical control of the particular synthetic pathway must be overcome. The product yield on carbohydrate feedstock is further reduced by the number of enzymatic steps that are necessary for its synthesis, and by the number of alternative metabolic outlets, which compete for carbon precursors provided by the central metabolism. The most important task in the development of industrial fermentation processes is therefore increasing the product yield per substrate and the over-all or volume productivity of the process. This must be achieved in a coordinated approach by improving the microbial production strain and by over-all process engineering.

7. Carbohydrate uptake as well as the regulatory pattern and the absolute activity/ concentration of all necessary enzymes of the respective synthetic route can be optimized by strain selection, conventional mutagenesis and genetic engineering (Fig. 2). Moreover, the synthesis of undesired by-products can be diminished through strain selection and mutation. Similarly, the over-all fermentation conditions - substrate choice, substrate concentration and substrate feeding, pH and temperature profile, agitation and aeration - strongly influence the yield of product on carbohydrate substrate and the ratio of product to by-products, and also the over-all productivity of the system. Contrary to organic chemistry, biotechnology generally depends on water as the reaction medium. Volume productivity, commonly referred to as fermentor yield, is therefore the major parameter for process feasibility in order to cope with product separation from biomass and water-soluble by-products as well as product recovery from aqueous solution.

8. Figure 2. Fermentation products - strain and process optimization

9. At least in theory any microbial synthesis can now be shifted to industrial yields by strain improvement through genetic engineering. Evidently this is most straightforward for pharmaceutical proteins and industrial enzymes, and also very efficient for amino acid fermentations and for many secondary metabolites. Genetic engineering, however, cannot overcome physicochemical limitations of fermentation processes, for example product inhibition or cell membrane damage caused by high concentrations of alcohols or acetic acid as fermentation products. Process engineering and the development of new or improved recovery technologies is therefore the other condition for an extended application of fermentation and biotechnology.

10. Scale up Microbial fermentation processes play a critical role in many important industrial applications. In various applications, fermentation processes are utilized to produce a final product, convert substrates, catalyze reactions, remediate environmentally toxic materials, or simply make mass biological materials. Process scale-up, in a broad sense, is a critical activity that enables a fermentation process achieved in research and development to operate at a commercially viable scale for manufacturing. A successful scale-up involves many aspects of successful preparation and planning beyond pure process scale-up technology. These include setting up clear goals and expectations, timelines and milestones, resources and organization, facility fit considerations, and quality and specifications.

11. The first step is to define the project goals, targets, facility, and timeline for completion. Common project goals and targets include the following parameters. Annual output of products (in grams or kilograms), based on an analysis of market demand and manufacturing capacity Productivity targets (such as grams/day, grams/liter/day, or lot/number of days, etc.), based on process capability and facility capability Yield per lot (grams or kilograms/lot), based on process capability, facility scale, and operational capability Process cycle time (days/lot), based on throughput, process, and operational constraints Cost targets (cost/gram, cost/lot, etc.), based on process capability, product price, market demand, and facility operating cost.

12. There may be other special targets as well. Ideally, one may have a strong desire to optimize all the targets for maximum benefit of a process. In reality, facility utilization and availability sometimes place a critical constraint on process scale-up planning. A firm may have to use an existing facility that confines how a new process may be scaled up to fit into the facility. In this case, it may not be possible to optimize all of the above targets, and they have to be balanced and prioritized. Setup of the right objectives and targets is a cross-functional activity with business input and technology input. With clear targets, the next step is to organize a team with all the necessary expertise. A detailed analysis of technical risks and challenges may lead to the appropriate level of resources and a realistic timeline. A project timeline with verifiable milestones is essential at the beginning of a project.