6 Fermentation and EnzymeTechnologies in Food Processing

Fermentation is a microbial biotechnology whereby natural renewable substrates are converted to value-added products such as enzymes, organic acids, alcohols, polymers, and more. Fermentation end-products such as ethanol and lactic acid are proton sinks, whereby NADH is recycled to NAD, which allows the cell to continue producing energy via glycolysis by substrate-level phosphorylation. Thus, microorganisms generate many endor by-products to maintain energy balance. Today, enhanced production of economically important fermentation products has benefited from targeted genetic engineering techniques to established industrial microbial strains (Campbell-Platt, 1994). The formation of endor by-products is dependent on microbial strain and the environmental conditions employed. For an optimum fermentation process, a microbial strain should be selected and developed based on the desired product. Strain development technologies include mutation and recombinant DNA technology. Growth of microorganisms and product formation are also affected by temperature, pH, dissolved oxygen, and fermentation medium composition. Therefore, the fermentation media and growth conditions need to be optimized. Moreover, the metabolic pathways should be determined. Knowledge of biochemical changes in fermented foods can help producers to manipulate the production by changing strains and/or conditions. In addition to growth conditions, types of strains, and media, fermentation modes affect the productivity. Batch, fed-batch, and continuous fermentation modes can be selected for high productivity. Fed-batch and continuous modes can overcome the substrate limitation during fermentation processes. Higher productivity can also be achieved by cell immobilization, which results in increases in the biomass concentration in the bioreactor, and thus an increased concentration of biocatalysts in the reactor. After the fermentation process, recovery methods of the product from the fermentation medium need to be evaluated and optimized, and are often an economic limitation factor. Indeed, purification of the end-product is often a high-cost step of the process. The microbial end-products can be biomass itself, extracellular products, or intracellular products. Filtration, homogenization, and extraction (liquid and solid) are examples of recovery methods. Enzymes are products of living organisms and have been used in the industry for many years due to their catalytic activities. Enzyme activity depends on temperature, substrate, pH, inhibitors, etc. and should be optimized for each process. Since enzyme recovery is difficult, the application of enzyme immobilization may reduce process cost. Enzymes can be isolated from plants and mammalian tissues, or can be produced by microorganisms. However, microbial enzymes are preferred due to availability and specificity. Enzymes are used in the production of over 500 commercial products (Johannes & Zhao, 2006). They have a broad range of applications from food to detergents. Most enzymes are commercially available and used to enhance the product quality in food, detergents, leather, paper, cosmetics, and pharmaceuticals. Commercial enzymes include lipase, amylases, proteases, pectic enzymes, and milk clotting enzymes (rennet). In this