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The inherent safety, convenience, availability, nutritional content, aesthetic appeal, and variety that characterize food supplies are a hallmark of modern life. Chemical engineering knowledge can be accredited with improving the conversion of raw foodstuffs into safe consumer products of the highest possible quality. Among those, membrane-based separation and other filtration techniques are most common. Chemical engineers have applied their expertise to chemically synthesize fertilizers, herbicides, and pesticides that promote crop growth and protect crops from weeds, insects, and other pests (AlChe, 2009). It's so easy to feel the contribution of chemical engineering in food sector if we observe the morning tea to late night beverage. All processed food stuffs around us is more or less subject to different types of filtration. One of the fastest growing parts of the whole sector is the mineral water and soft drinks sector, which has a sizeable requirement for fine filtration (Sutherland, 2010).
Modern techniques are used to improve the flavour, texture, nutritional value, safety, appearance and overall aesthetic appeal of various foods. Modern food processing can also improve the quality of life for people with food allergies and for diabetics. Foods processed using aseptic packaging retains their vitamins, minerals, and desired textures, colours, and flavours more effectively than those processed with traditional canning. Nestlé, Wal-Mart, Unilever, PepsiCo etc. are some world famous food companies without whom modern life cannot be imagined.
Filtration in food processing
Filtration is a process where solid particles present in a suspension are separated from liquid or gas employing a porous medium (Srikanth, 2012). Surface, depth and cake filtration are different types based on filtration mechanism. Two types of filtration theory are widely known which are gas filtration theory and liquid filtration theory. These theories have also some limitations. There are some criteria for choice of filter medium such as particle size that has to removed, permeability of clean medium, solid holding capacity of the medium, flow resistance of medium etc. Filter aid is a very important factor which forms a surface deposit to screen out the solids and it also prevents the plugging of the supporting filter medium (Srikanth, 2012).
Chemical engineers have invented a variety of engineered processes that allow food processors to remove impure substances to improve food quality, safety, and aesthetics. Today's membrane-based separation is used widely to remove impurities during food processing by pressure to force unwanted substances in food ingredients to pass through a semi permeable membrane and it is also applied majorly in the dairy industry, mainly as a processing phase in production soft cheeses. Chemical engineers strive to maximize the available surface area in filter, reduce membrane pore size, minimize the pressure drop the fluid will experience when flowing through the unit and maximize cost-effectiveness (AIChe, 2009). For food industries, there are some specific requirements to choose filter media such as dissipation of electrostatic charges, high abrasion resistance, available clean-in-place system etc. In this dissertation, some food processing industries have been presented where different types of filtration are the key factor. Among those cane and beet sugar industry, starch and sugar industry, beverage industries like wine, beer etc. are notable. Filtration should be the most prior subject to enhance food safety management of an industry. It can help to remove physical, chemical and other microbiological contaminants with great efficiency.
This also focuses on advantages of self-cleaning filters over manual and mechanical cleaning. Advances in filtration technology include the development of continuous processes to replace old batch process technology (Patel R. et al, 2010).
FOOD PROCESSING INDUSTRIES
Chemical engineering innovation in food production
"If the grass on the other side of the fence appears greener . . . it must be all the fertilizer they are using." - Kevin Rodowicz.
The food industry is a complex, global collective of diverse businesses that supply much of the food energy consumed by the world population. Before modern engineering advances were widely adopted by the food industry, the variety of foods available at stores were determined by what was produced locally, since transportation limitations predicted the distance that perishable foods could travel (AIChe, 2009).
Chemical engineers routinely develop advanced materials and techniques used for, among other things, chemical and heat sterilization, advanced packaging, and monitoring and control, which are essential to the highly automated facilities for the high-throughput production of safe food products (AIChe, 2009). Chemical engineering unit operations and procedures, established for other industrialized reasons, are used by the food industry like drying, milling, extrusion, refrigeration, heat and mass transfer, membrane-based separation, concentration, centrifugation, fluid flow and blending, powder and bulk -solids mixing, pneumatic conveying, and process mode ling, monitoring, and control. Among these, membrane-based separation and other filtration techniques are mostly common (AIChe, 2009).
Over the years, engineered solutions have increased the production of processed fruits and vegetables, dairy, meat and poultry, and seafood products, and have allowed more widespread distribution of such foods. The following are some of the most revolutionary improvements in food processing noted in the "Milestones of the Twentieth Century" by the Institute of Food Technologists (AIChe, 2009).
1900s: Vacuum packaging, which removes the oxygen from inside the food package, was invented to prolong the shelf life of foods, and the widespread practice of freezing foods began with fruit and fish. The first ready-to -eat cereals using many chemical engineering unit operations appeared as well (AIChe, 2009).
1920s: Fast-freezing practices for foods were first commercialized by Clarence Birdseye, whose name has become practically known with frozen foods. Birdseye found that by blanching vegetables (cooking them for a short time in boiling water) just before freezing, the process could deactivate certain enzymes that cause off-colours and off-flavours, thereby enhancing the quality of the thawed vegetables. The first commercial use of "puffing" to produce such cereals as Cheerios and puffed rice also began (AIChe, 2009).
1930s: Freeze-drying processes were pioneered in this decade, and frozen foods are dried after deep freezing, in which the entrained water is removed by a process known as sublimation by heating the frozen product in a vacuum chamber. Freeze-dried foods in turn become shelf-stored foods that quickly regain their original flavour, aroma, size, shape, and texture after rehydration. The removal of water slows spoilage, thus providing longer shelf life, and reducing the weight of the food, which makes it cheaper and easier to transport (AIChe, 2009).
1940s: The advent of automated processes to concentrate, freeze, and dehydrate foods enabled a greater variety of foods to be mass-produced and packaged for shipment overseas to military personnel during World War II. Disease-free packaging extremely improved food quality, safety, and nutrient retention (AIChe, 2009).
1950s: During this era, monitored-atmosphere packaging using plastic increased the shelf life of fresh foods. The process controls oxygen and carbon dioxide levels inside the packaging environment to reduce respiration by fruits and vegetables (similar to human breathing) and reduces the amount of off-gas ethylene produced, which delays maturing and damage (AIChe, 2009).
1960s: The first commercial-scale producing machine began producing cold-dried foods and coffee. Advances in aseptic processing allowed shorter heating times for sealed food containers (AIChe, 2009).
1970s: The period of the 1970s saw growing usage in the chemical process industries (paint, textile, oil recovery, pulp and paper). In this decade, the major effects of this technology is in the food and biotechnology processing industries, where ultrafiltration and cross-flow microfiltration are finding increasing uses as a gentle and efficient way of fractionating, concentrating and clarifying a variety of food from milk products, fruit juices and alcoholic beverages to fermentation broths, protein fractions and wastewaters (Cheryan M, 1986).
1980s: Advanced-atmosphere packaging began to be used widely during this era and It is a more progressive difference of controlled-atmosphere packing, in which the "head space" atmosphere within a food package or the transportation/ storage vessel is modified by flushing it with a blend of inert (nonreactive) gases (AIChe, 2009).
1990s: High-pressure processing was commercially applied first to fresh packaged foods to kill microorganisms that cause spoilage without altering flavours, texture, or appearance (AIChe, 2009).
After 2000: Recent food trends are actually based on fat calculation but tasty, healthy and doctor-designed. Different types of cupcakes, cheese, pizza, fast foods etc. are people's first choice. Also various types of grain made foods are getting popularity day by day (AIChe, 2009).
Advances in chemical fertilizers, herbicides, and pesticides
Early mankind experimented with human and animal wastes, seaweed, ashes and other substances to fertilize crops and increase productivity. Chemical engineers have applied their expertise to chemically synthesize fertilizers, herbicides, and pesticides that promote crop growth and protect crops from weeds, insects, and other pests. Today, the use of these products is more important than ever to meet the needs of an ever-expanding population (AIChe, 2009).
Nitrogen is the most plentiful part of the air we breathe, present at 79% by volume and a prime nutrient (most often in the form of ammonia). Modern fertilizers stem from a chemical engineering breakthrough pioneered by Fritz Haber in 1908 that developed a process to synthesize ammonia by reacting hydrogen with nitrogen and in 1918, he was awarded the Nobel Prize in Chemistry for this discovery (AIChe, 2009).
Working with industrialist Carl Bosch, Haber scaled up the successful Haber-Bosch process that allows ammonia to be produced cost-effectively in commercial quantities for use in nitrogen fertilizers. Haber's original reaction was carried out under high pressures. The improved ammonia synthesis process carries out the reaction at lower pressures and temperatures, which helps save money by reducing the amount of energy required by the process (AIChe, 2009).
Pesticides and herbicides
Chemists and chemical engineers have also been helpful in the discovery, synthesis and commercial-scale manufacture of various chemical compounds that are used as pesticides (to kill insects) and herbicides (to kill weeds). For example, chemical engineers discovered that when glyphosate (the primary ingredient in Monsanto's widely used herbicide Roundup) is applied to a crop, it inhibits a specific growth enzyme called the EPSP synthase. Glyphosate is rapidly metabolized by weeds, and unlike many other earlier herbicides, it binds tightly to soil so that it does not accumulate in runoff to contaminate surface waters or underground aquifers. According to its manufacturer, it eliminates more than 125 kinds of weeds, but does not affect mammals, birds, fish, or insects (AIChe, 2009).
Advanced food processing techniques
Today, imaginative and effective engineered approaches many drawn directly from the chemical engineers' toolbox routinely add nutrients, improve aesthetic appeal (in terms of a food's flavours, texture, and appearance), enable longer distance transport (leading to multi-seasonal availability), extend shelf life, and remove microorganisms that contribute to spoilage and are responsible for food-borne illnesses. Modern food processing can also improve the quality of life for people with food allergies (by removing or neutralizing the proteins and other substances that create allergic reactions in certain people) and for diabetics (by reducing sugar content and providing sugar-free alternatives).
The roasting of coffee beans requires exceptionally precise control of the chemical and physical reactions over time. Depending on the progressive bean temperature experienced during roasting, final flavours characteristics can vary widely. Chemical engineers have devised ways to make timely adjustments to the roaster to moderate airflow rates and manipulate bean temperatures without changing the flavours (AIChe, 2009).
Sterilizing and packaging perishable foods
Sterilization is a key aspect of any food -packaging operation. The ability to sterilize foods to protect them against spoilage by oxidation, bacteria, and moulds has always presented an important engineering challenge. Throughout history, people have experimented with the use of dehydration, smoking, salting, pickling, candying and the use of certain spices. They include high-temperature pasteurization and canning, refrigeration and freezing, chemical preservatives (using such compounds as sulphite, sodium nitrite, ethyl formate, propionic acid, sorbic acid, and benzoic acid), and irradiation (AIChe, 2009).
In the early years, no one knew how Nicolas Appert's process preserved foods successfully, but the ability to can foods meant that Napoleon's army fighting a long way from home could be fed properly and safely and that British sailors could maintain a healthier diet by feasting on fruits, vegetables, and meats while on long voyages overseas.
More than 50 years later, Louis Pasteur (1822-1895) explained the mystery by proving that the growth of microorganisms is the primary cause of food spoilage and food -borne illnesses and that a high percentage of them could be killed by heating liquids to about 130°F (55°C) or higher, for relatively short periods, without altering the chemical makeup of the food. This simple process became known as pasteurization and was quickly and widely adopted (AIChe, 2009).
First introduced in the U.S. in the early 1960s, it provides major advantages over traditional canning. It allows many products once considered perishables such as milk and juice to be packaged, distributed, and stored for months or longer without the need for refrigeration, irradiation, or chemical preservatives. In general, during aseptic packaging, both the food and packaging are sterilized at high temperatures for very short periods (AIChe, 2009).
The original technology superheated steam to sterilize cans. Pressurized heat exchangers and holding tubes allows the foods and beverages to be sterilized at around 300°F. Foods processed using aseptic packaging retains their vitamins, minerals, and desired textures, colours, and flavours more effectively than those processed with traditional canning. In 1989, aseptic-packaging technology was voted the food industry's top innovation of the last 50 years by the Institute of Food Technologists (AIChe, 2009).
Some world famous food companies
In terms of corporate size, food manufacture has no companies to match the giants of other sectors (Sutherland, 2010). Although still by far the largest of the food producers, Nestlé, with annual sales in 2009 of about $95 billion (well down on 2008), is only a quarter of the size of the largest petroleum companies such as Exxon or Shell (Sutherland, 2010). (There are, of course, food retailers much larger than Nestlé, especially Wal-Mart whose 2009 sales of $400 billion made it the third largest company in the world in terms of turnover, with Carrefour a long way behind at second in the list of retailers, at $130 billion (Sutherland, 2010).
The next largest company classified as a food producer is Unilever, with total 2009 sales of $53 billion (although the Unilever picture is complicated by its extensive range of non-food household goods businesses) (Sutherland, 2010). Unilever is closely followed by Cargill, the largest private company in the USA, and by Archer-Daniels-Midland, although both of these are large natural product commodity dealers as well. Then come ConAgra, Kraft Foods, Danone, Kellogg, General Mills, and H J Heinz (Sutherland, 2010).
For some time, the leading beverage companies have been the soft drink makers Pepsico (2009 sales of $43 billion) and Coca Cola ($32 billion), some distance ahead of the brewers (Sutherland, 2010). This picture changed in 2008 with the purchase of Anheuser-Busch by InBev (itself the fairly recent merger of Interbrew and AmBev) to create a company larger than Coca Cola (although still behind Pepsi) and second in size of the brewers is now SABMiller (a 2002 creation), followed by Heineken and then Carlsberg (Sutherland, 2010). Further consolidation in the beverage sector is being driven by a search for markets, because beer drinking can be very regional. Thus, Heineken has acquired the beer business of Femsa in Mexico - which holds 40% of its domestic market and nearly 10% of that in Brazil and one of the fastest growing parts of the whole sector is the mineral water and soft drinks sector, which has a sizeable requirement for fine filtration (Sutherland, 2010).
Filtration is a process whereby solid particles present in a suspension are separated from the liquid or gas using a porous medium, which retains the solid but, allows the fluid to pass through. It is a common operation used widely in sterile products, bulk drugs and in liquid oral formulation. The suspension to be filtered is called slurry. The porous medium used to retain the solids is known as filter medium and the accumulated solids on the filter are referred as filter cake and the clear liquid passing through the filter is filtrate (Srikanth, 2012). The pores of the filter medium are smaller than the size of particles to be separated. When feed is passed over the filter medium, the fluid flows through it by virtue of a pressure differential across the filter. Gravity is acting on the liquid column; the solids are trapped on the surface of the filter medium. After a particular point of time, the resistance offered by the filter cake is high that stops the filtration (Sambhamurthy, 2005).
Types of filtration
Based on the mechanism, there are 3 types of filtration which are surface filtration, depth filtration and cake filtration.
It is a screening action by which pores or holes of the medium prevent the passage of solids. For this purpose, plates with holes or woven sieves are used (Matteson, 1987). An example is a cellulose membrane filter.
This filtration mechanism retains particulate matter not only on the surface but also at the inside of the filter. It is extensively used for clarification. Ceramic filters and sintered filters are examples of depth filtration (Stephan, 2003).
Case study of depth filtration (Carey, 2008):
Several forces have driven changes in filtration technology during the last few decades, including environmental concerns, the health and safety of winery employees and wine quality. The major active component in traditional depth filtration is diatomaceous earth, which has several major problems. First, it is difficult to dispose because it does not decompose. Second, it can cause symptoms similar to coalminers 'black lung' disease when inhaled over long periods of time. To overcome these drawbacks, cross flow filtration and ultra-filtration are being practiced in recent years.
Cross flow filtration:
It ranges between ultra-filtration and reverse osmosis and the nominal pore size of the membrane is typically below 1 nanometer (Wikipedia, 2012). Nano filtration membranes are still subject to scaling and fouling and often modifiers such as anti-scalants are required for use (Hillie, 2007).
It is a pressure driven membrane transport process that has been applied on both the laboratory and industrial scale. It is becoming a powerful separation tool for the rapidly growing biotechnology industry (Goldsmith et al., 1974).
By this mechanism, the cake accumulated on the surface of the filter is itself used as a filter. A filter consists of a coarse woven cloth through which a concentrated suspension of rigid particles is passed so that they bridge the holes and forma bed.
Theory of filtration
Depending on dispersing medium filtration theory is divided in two parts;
Gas filtration theory
It mainly includes filtration of aerosols and lyosols. There are several mechanisms for this theory. They are as follows (Wilson & Cavanagh, 1969).
The trajectories of individual small particles do not coincide with the streamlines of the fluid because of Brownian motion. With decreasing particle size the intensity of Brownian motion increases and, as a consequence, so does the intensity of diffusion deposition.
This mechanism involves the finite size of particles. A particle is intercepted as it approaches the collection surface to a distance equal to its radius.
The presence of a body in the flowing fluid results in a curvature of the streamlines in the neighbourhood of the body. Because of their inertia, the individual particles do not follow the curved streamlines but are projected against the body and may deposit there. It is obvious that the intensity of this mechanism increases with increasing particle size and velocity of flow.
Every particle has a definite sedimentation speed due to gravity. As a consequence, the particles deviate from the streamlines of the fluid and owing to this deviation; the particles may touch a fibre.
Both the particles and the fibres in the filter may carry electric charges. Deposition of particles on the fibres may take place because of forces acting between charges or induced forces.
Liquid filtration theory
The term solid-liquid filtration covers all processes in which a liquid containing suspended solid is freed of some or the entire solid when the suspension is drawn through a porous medium (Melia & Weber, 1972).
Kozeny - Carman equation
= â€¦â€¦â€¦â€¦. (1)
A = filter area
V = total volume of filtrate delivered
t = filtration time
âˆ†P = pressure drop across cake and medium
r = specific cake resistance
µ = filtrate viscosity
l = cake thickness
L = thickness of cake equivalent to medium resistance (Skilling, 2001).
This equation does not take into account of the fact that depth of the granular bed is lesser than the actual path traversed by the fluid. The actual path is not straight throughout the bed, but it is sinuous (Chowdiah et al., 1981).
This Law considered that filtration is similar to the streamline flow of a liquid under pressure through capillaries.
= â€¦â€¦â€¦â€¦. (2)
Cake resistance, RM = â€¦â€¦â€¦â€¦â€¦â€¦â€¦â€¦. (3)
Specific cake resistance, Î± = Î±×³âˆ†Pâ€¦â€¦â€¦...................... (4)
The filter resistance is much less than the cake resistance (RC << RM).
The filter medium acts as a mechanical support for the filter cake and it is responsible for the collection of solids (Srikanth, 2012). Minimum cake thickness of discharge for different types of filter is presented in Table 1 (Subramanyam et al., 2005).
Table 1: Minimum cake thickness for discharge (Andrew et al., 2002)
Minimum design thickness
Materials used as filter media (Rushton, 2008)
Different types of materials used as filter media for various applications industrially and domestically are presented in Table 2.
Table 2: Type of filter media, features and their application (Patel R. et al, 2010).
Type of filter media