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Fermentation, and its Control

BY: Akash Mukherjee | Category: Applications | Submitted: 2011-01-22 21:31:29
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Article Summary: "Information about fermentation and its control. A sequel to this article deals with the advanced fermentation control strategies..."


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Fermentation: A Discussion

In a general sense, fermentation is the conversion of a carbohydrate such as sugar into an acid or an alcohol. More specifically, fermentation can refer to the use of yeast to change sugar into alcohol or the use of bacteria to create lactic acid in certain foods. Fermentation occurs naturally in many different foods given the right conditions, and humans have intentionally made use of it for many thousands of years. The earliest uses of fermentation were most likely to create alcoholic beverages such as mead, wine, and beer. These beverages may have been created as far back as 7,000 BCE in parts of the Middle East. The fermentation of foods such as milk and various vegetables probably happened sometime a few thousand years later, in both the Middle East and China.

While the general principle of fermentation is the same across all of these drinks and foods, the precise methods of achieving it, and the end results, differ. Beer is made by taking a grain, such as barley, wheat, or rye, germinating and drying it, and pulping it into a mash. This mash is then mixed with hot water, and some fermentation begins. After being further treated, the liquid is transferred to a fermentation vessel, where yeast is added to the mixture. This yeast "eats" the sugar present in the mash and converts it into carbon dioxide and alcohol. After a few weeks of fermentation and a further period of conditioning, the beer is ready to be filtered and consumed.

Wine is created using a similar method that also involves fermentation. Grapes are crushed to release the sugar-rich juices, which are then either transferred quickly away from the skins or left to rest for a time to absorb some of the flavour, tannins, and colour of the skins. Yeast is then added, and the grape juice is allowed to ferment for a number of weeks, at which point it is moved to different containers and fermented at a slower rate, and eventually aged or bottled.

Pickling foods, such as cucumbers, may be accomplished by submerging the vegetable one wants to pickle in a salty water solution with vinegar added. Over time, bacteria create the lactic acid that gives the food its distinctive flavour and helps to preserve it. Other foods can be pickled simply by packing them in dry salt and allowing a natural fermentation process to occur.
Milk can also be cultured, and people have been using fermentation with dairy products for nearly 5,000 years. It is speculated that early fermented dairy, such as yogurt, was the result of a natural process of fermentation that occurred when the milk was cultured by bacteria that dwelt in skin sacks used to store dairy. Yogurt these days is made by adding a number of special bacteria, such as L. acidophilus and L. bulgaricus to milk and keeping it at the proper temperature. The bacteria begin converting the sugar in the dairy to lactic acid, eventually creating what we know as yogurt.

The two main types of fermentation are alcoholic fermentation and lactic acid fermentation.

Fermentation is widely used within the Pharmaceutical as in the Food industries. It requires the cultivation in submerged culture of an identified micro-organism (mainly bacterial) as a monoculture under defined environmental conditions. The incubation regime imposed is designed to maximize the productivity of the organism of interest by providing optimal conditions for population growth (biomass). The product of interest might be a bioactive metabolite or recombinant protein.

A complete fermentation cycle can typically include the following steps (depending on vessel design):

• Empty (Blank) Sterilization of vessel & pipe work using direct Steam

• Injection

• Charging with base medium

• Indirect Sterilization via Steam Injected into the vessel jacket

• Cooling & Jacket Drain

• Pre-Inoculation - Vessel environment under control

• Inoculation - Injection of a small sample of the monoculture

• Incubation - The Fermentation process itself

• Harvesting - Product removed ready for extraction processes


Fermentation Control

Since prehistoric times humans have been taking control of the fermentation process. From Pasteur to Buchner to the Carlsberg scientists, the conversion of juice into wine, grains into beer, milk to yogurt, carbohydrates into carbon dioxide to raise bread, and sugars in vegetables into preservative organic acids.

A process of culturing a microorganism in a culture medium in which process the addition of feed medium is controlled by using the production of a by-product as a measure of the culture conditions, characterized in that the by-product is an electrically charged metabolite produced by the microorganism, and in that the production of the metabolite is monitored by measuring the conductance of the culture medium. The metabolite may be acetate and the microorganism may be yeast which is genetically engineered to produce a desired polypeptide.

The mode of bio-fermentation control selected has a direct impact on fermentation trajectory accuracy, production quality, and yield. A high performance bio-fermentation control system design that combines a set of sensors and actuators is presented. The bio-fermentation control system uses an embedded microprocessor controller, the SAMSUNG's S3C44BOX microprocessor system. The main fermentation process parameters and the control system hardware construction are discussed in detail. When compared with the single chip microcomputer and personal computer controller, the fermentation control system employing embedded microprocessors promises the advantages of better holistic performance, and higher yield efficiency.

The actual fermentation process is known as the Incubation Phase and is just part of the batch cycle. Incubation control necessitates the precise control of a number of parameters. Of primary importance are: Temperature, pH, DO2 or Redox, agitation, pressure, foam control, auxiliary feed or a combination of these controllers.

The control of these and any other parameters is most usually carried out in fermenter vessels specifically designed for the purpose and accommodating various working volumes depending on the yield and production requirements. Laboratory scale vessels could have a capacity of just 10 liters or less whereas production vessels may be as large as several thousand liters. A control system must therefore provide flexibility in the way in which accurate and repeatable control of the fermentation environment is achieved and will include the following features:

• Precise loop control with Setpoint profile programming

• Recipe Management System for easy parameterization

• Sequential control for vessel sterilisation and more complex control strategies

• Secure collection of on-line data from the fermenter system for analysis and evidence

• Local operator display with clear graphics and controlled access to parameters


pH CONTROL

pH is one of the most important chemical environmental measurements used to indicate the course of the fermentation process. It detects the presence of specific chemical factors that influence growth, metabolism, and final product Dissolved oxygen control in fermentation.

Oxygen control represents an important operational challenge due to the varying biomass concentration. In this study, oxygen control is implemented by manipulating the substrate feed rate, i.e. the rate of oxygen consumption. It turns out that the setpoint for dissolved oxygen represents a tradeoff since a low dissolved oxygen value favors productivity but can also induce oxygen limitation. Regulation of dissolved oxygen using a cascade control scheme that incorporates auxiliary measurements to improve the control performance. The computation of an appropriate setpoint profile for dissolved oxygen is solved via process optimization. For that purpose, an existing morphologically structured model is extended to include the effects of both low levels of oxygen on growth and medium rheological properties on oxygen transfer. Experimental results obtained at the industrial pilot-scale level confirm the efficiency of the control strategy.


List of few advanced control strategies:-

A) Optimal genetic manipulations in batch bioreactor control

B) Control strategies for intermittently mixed, forcefully aerated solid-state fermentation bioreactors based on the analysis of a distributed parameter model

C) Advanced controlling of anaerobic digestion by means of hierarchical neural networks

D) A self-tuning adaptive control applied to an industrial large scale ethanol production

E) Control of fed-batch fermentations

F) Fermentation control with personal computers

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PART 2: http://www.biotecharticles.com/Applications-Article/Advanced-Fermentation-Control-Strategies-580.html

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Comments on this article: (1 comments so far)

Comment By Comment
padmapriya
2012-12-26 06:05:43 371
nice......

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