freeze drying ppt
TRANSCRIPT
-: Presented by :-Monika K. TambakheDr. P.A. Pawar
FREEZE DRYING
University Department of Chemical Technology, Sant Gadge baba Amravati University ,Amravati. Maaharashtra,INDIA.444602.
INTRODUCTIONFreeze drying is a relatively recent method of preserving food. Although it is not widely used in the food industry due to high operation costs, new improvements such as adsorption, fluidization, and microwave have been researched in order to reduce costs.
It is the most important technique to dry coffee, enzymes, food ingredients, high value foods.
This process could be considered as a valuable alternative to preserve foods.
INTRODUCTION
Stabilization of enzymatic systems, new ingredients in the field of functional foods, and exotic foods are examples of new applications of this technology.In a general way, freeze-drying or lyophilization, is the process of removing water from a product by sublimation and desorption. Sublimation is the transformation of ice directly into a gas without passing through a liquid phase. Sublimation occurs when the vapor pressure and the temperature of the ice surface are below those of the triple point (4.58 mm Hg, 0 ºC), as shown in the pressure-temperature phase diagram of pure water(Figure 1).
INTRODUCTION
Figure No.1 - Pressure-temperature phase diagram of pure water and zones of processes for phase changes
INTRODUCTIONIn short, freeze drying is a multiple operation in which the material to be stabilized is-
1. Frozen hard by low-temperature cooling
2. Dried by direct sublimation of the frozen solvent and by desorption of the sorbed or bound solvent , generally under reduced pressure.
3. Stored in the dry state under controlled conditions.
INTRODUCTION
However, freeze drying is an expensive form of dehydration for foods because of the slow drying rate and the use of vacuum. The cost of processing is offset to some extent by the absence of any need for refrigerated handling and storage. Increasingly, freeze drying is used for dehydrating foods otherwise difficult to dry, such as coffee, onions, soups, and certain sea foods and fruits. Freeze drying is also increasingly employed in the drying of pharmaceutical products.
INTRODUCTIONDifference between Conventional drying and freeze drying
HISTORY-
The history of freeze drying goes back to the ancient Inca’s, who preserved their food stuff by freezing it in the mountains in winter time. At the same time the frozen water is removed through the low vapor pressure of the water in the surrounding air at those high altitudes.
Of course this process was rather slow, but during the drying process the quality of the food was maintained due to its frozen state. Once dried the food materials like potatoes and vegetables showed a remarkably increased quality over time.
HISTORY-
Especially the need for improving shelf life of pharmaceuticals like penicillin and the preservation of blood plasma in war time was a drive for the development of the modern tray-type Lyophilizer as it is still used in many industries today.
Another catalyst for the development of the freeze dry technology was the surplus of coffee in countries like Brazil in the late 30’s of the previous century.
HISTORY-
Also here the tray-type freeze dryer was used for the sublimation of the water from the frozen coffee granules. Brand names like Nescafe were founded at that time. Instant coffee is now the most well-known freeze dried product.
After the war period the technology emerged into its current popularity for the drying of many different temperature sensitive materials like pharmaceuticals and food materials.
There exist already 400 different freeze dried food materials alone.
FREEZE DRYING PROCESS -
Freeze drying is a process by which a solvent (usually water) is removed from a frozen foodstuff or a frozen solution by sublimation of the solvent and by desorption of the sorbed solvent (nonfrozen solvent), generally under reduced pressure. The freeze drying separation method (process) involves the following three stages: (a) the freezing stage, (b) the primary drying stage, and (c) the secondary drying stage.
FREEZE DRYING PROCESS -
Figure No.2 – Diagram of a material on a tray during freeze drying. The variable X denotes the position of the sublimation
FREEZING STAGE-
The freezing stage represents the first separation step in the freeze drying process, and the performance of the overall freeze drying process depends significantly on this stage. The material system to be processed (e.g., gel suspension, liquid solution, or foodstuff) is cooled down to a temperature (this temperature depends on the nature of the product) that is always below the solidification temperature of the material system. The objective of the freezing stage is to freeze most of the water originally present in the product for its posterior sublimation.
PRIMARY DRYING STAGE After the freezing stage, the drying chamber where the product is placed is evacuated and the chamber pressure is reduced to a value that would allow the sublimation of solvent (water) to take place in the primary drying stage. When the water molecules sublime and enter the vapor phase, they also keep with them a significant amount of the latent heat of sublimation (2840 kJ/kg ice) and thus the temperature of the frozen product is again reduced.
If there is no heat supplied to the product by a heat source, then the vapor pressure of the water at the temperature of the product reaches the same value as that of the partial pressure of the water vapor in the drying chamber; therefore, the system reaches equilibrium and no additional water sublimation from the product would occur.
PRIMARY DRYING STAGE
The water vapor produced by the sublimation of the frozen water in the frozen layer and by the desorption of sorbed (non frozen) water in the dried layer during the primary drying stage travels by diffusion and convective flow through the porous structure of the dried layer and enters the drying chamber of the freeze dryer. (It should be noted that most of the water removed during the primary drying stage is produced by sublimation of the frozen water in the frozen layer.) The time at which there is no more frozen layer is taken to represent the end of the primary drying stage.
SECONDARY DRYING STAGE
The secondary drying stage involves the removal of water that did not freeze (sorbed or bound water). In an ideal freeze drying process, the secondary drying stage starts at the end of the primary drying stage.
In the secondary drying stage, the bound water is removed by heating the product under vacuum; the heat is supplied to the product usually by conduction, convection, or radiation. The following product temperatures are usually employed: (a) between 10° and 35°C for heat sensitive products and (b) 50°C or more for less-heat-sensitive products.
The residual moisture content in the dried material at the end of the secondary drying stage, as well as the temperature at which the dried material is kept in storage, are critical factors in determining product stability during its storage life.
HEAT AND MASS TRANSFER IN FREEZE-DRYING -
Rate of heat transfer-There are three methods of transferring heat to the sublimation front. 1. Heat transfer through the frozen layer2. Heat transfer through the dried layer 3. Heating by microwaves
Heat SourceCondenserMass Transfer
Heat Transfer
Frozen Portion part
Dry Portion part
Rate of mass transfer-When heat reaches the sublimation front, it raises the temperature and the water vapour pressure of the ice. Vapour then moves through the dried food to a region of low vapour pressure in the drying chamber. The factors that control the water vapour pressure gradient are:the pressure in the drying chamberthe temperature of the vapour condenser, both of which should be as low as economically possible.the temperature of ice at the sublimation front, which should be as high as possible, without melting.
(a)Heat transfer through frozen layer(b)Heat transfer from hot surfaces through dry layer(c)Heat generated in ice by microwaves
COMPONENTS OF A FREEZE-DRYER -
Figure: Components of freeze dryer
COMPONENTS OF A FREEZE-DRYER -
The drying chamber, in which the sample is placed and heating/cooling takes place, must be vacuum tight and with temperature controlled shelves. The condenser must have sufficient condensing surface and cooling capacity to collect water vapor released by the product. As vapors contact the condensing surface, they give up their heat energy and turn into ice crystals that will be removed from the system. A condenser temperature of -65 ºC is typical for most commercial freeze dryers. The vacuum pump removes non-condensable gases to achieve high vacuum levels (below 4 mm Hg) in the chamber and condenser. The heat source provides the latent heat of sublimation, and its temperature may vary from –30° to 150 ºC .
In the freeze drying plant, three process sections are especially energy consuming. Process section 1 involves the freezing of the wet product. As this is normally considered one of the preparatory steps before the freeze drying proper, we will concentrate on the other two that take place in the freeze drying cabinet .Process section 2 involves the controlled supply of heat to the product to cover requirements for the sublimation and desorption processes.Process section 3 involves the removal from the freeze drying chamber of the vast volumes of water vapor released drying the sublimation and desorption processes. Of these three process sections, removal of the water vapour always consumes the largest amount of energy. The efficiency of water vapor removal, the vapor trap system, therefore has a decisive effect on the total energy consumption of the freeze drying plant.
FREEZE DRYING PLANTS AND EQUIPMENT -
1. Pilot freeze drying 2. Industrial freeze drying a. Tray and Pharmaceutical Freeze Dryersb. Multibatch Freeze Dryersc. Continuous Freeze Dryersd. Tunnel Freeze Dryers e. Vacuum-Spray Freeze Dryers
FREEZE DRYING PLANTS AND EQUIPMENT -
1. PILOT FREEZE DRYING
Freeze drying pilot units appropriate for use in the pharmaceutical and food industries, as well as in the laboratory, are in high demand because they are used to explore possibilities for the preservation of labile products, especially with those of biological origin. They can freeze-dry batches consisting of from 2 to 20 kg of frozen product.The unit consists of (a) a freezing fluid system that can be sent to the heat exchanger in
the section of the condenser or into the refrigeration coils for product freezing,
(b)a heating circuit (silicon oil is the heating fluid) for plate heating and defrosting of the condenser, and
(c) a vacuum system for evacuating air from the apparatus before and during drying.
1. PILOT FREEZE DRYING
Figure : Pilot Freeze dryer
2. INDUSTRIAL FREEZE DRYING -
(a)Tray and Pharmaceutical Freeze Dryers: By far the largest number of the industrial freeze dryers in operation is of the vacuum batch type with freeze drying of the product in trays. There are two main types, depending on the type of condenser used. In the first type, the condenser plates are alongside the tray heater assembly and in the same chamber; in the second type the condenser is in a separate chamber joined to the first by a wide, in general, butterfly valve. This latter type of plant is always used in pharmaceutical industries, but it can also be used for the freeze drying of foods.
(b)Multibatch Freeze Dryers :The freeze drying process in a batch plant is normally program controlled to minimize the drying time and to maximize the production of the plant. With a single-batch plant the load on the various systems will be very variable throughout the drying cycle. The optimal utilization of resources will not be possible in a single-cabinet batch plant. The extent of this disadvantage can be eliminated when an industrial freeze drying plant is built with a number of batch cabinets. This makes possible the simultaneous production of different products, which increases the operation flexibility of the plant .A large number of industrial freeze drying plants operate today in this way as multi-cabinet batch plants .
Batch freeze dryer
(c)Continuous Freeze Dryers : Recent years have shown a growing interest in freeze drying plants operating with a continuous flow of material through the process. Particularly in industries working with a single standardized product and the preparation of the product is by a continuous process, such plants are really profitable. They give continuity in processing throughout and constant operating conditions that are easily controlled, and they require less manual operation and supervision.Continuous freeze dryers are used for freeze drying of product in trays and for freeze drying of agitated bulk materials.
Continuous freeze dryer
(d)Tunnel Freeze Dryers :
Large commercial plants for processing cottage cheese and coffee have been built up in this way. The tunnel freeze dryers have the same advantages of plant capacity utilization that can be achieved as in multi-batch plants, but the flexibility for simultaneous production of different products or in switching from one product to another is lacking.
In the tunnel type of freeze dryer, the process takes place in a large vacuum cabinet into which the tray-carrying trolleys are loaded at intervals through a large vacuum lock at one end of the tunnel and discharged similarly at the other end.
(d)Tunnel Freeze Dryers :
(e)Vacuum-Spray Freeze Dryers: This dryer has been developed for coffee extract, tea infusion, or milk. The product is sprayed from a single jet upward or downward in a cylindrical tower of 3.7m diameter by 5.5m high. The liquids solidify into small particles by evaporative freezing The whole plant operates under a vacuum of about 67 Pa. Frozen particles obtained by spraying into a vacuum are about 150 mm in diameter and lose about 15% moisture in the initial evaporation. There is no sticking of these particles.
Vacuum spray freeze dryer
THE MANUFACTURING PROCES -
THE MANUFACTURING PROCES - Raw Materials :• Some foods are extremely well-suited to the freeze-
drying process; others do not fare so well. Liquids, thin portions of meat, and small fruits and vegetables can be freeze-dried easily. Coffee is the most common freeze-dried liquid.
• Thick portions of meat and larger, whole vegetables and fruits cannot be freeze dried with any success
Testing and preparation:• The food is first checked for contamination and purity. • Some kinds of food, like seafood and meats, must be
cooked before freeze drying.
THE MANUFACTURING PROCES - Freezing : Temperature is as low as -40°F (-40°C). In this extremely cold temperature, the food is quickly frozen. Drying : The carts are wheeled out of the cold room and into a vacuum drying chamber. In a large plant, there may be 20 to 30 drying chambers in operation at any time. The drying procedure involves a sublimation process.Sizing and blending :Some food pieces may be ground to a smaller size or may be reduced to a powder. Others may be screened to separate them by size. Two or more different products may also be blended together to meet a customer's specific specifications.Packing :Freeze-dried foods must be sealed in airtight containers to prevent them from absorbing moisture from the air. Several types of containers may be used: plastic laminated foil pouches, metal and plastic cans, or metal and fiber drums for bulk packaging. Some freeze-dried food is vacuum packed, in which the air is evacuated from the container before sealing.
QUALITY CONTROL -
Each food has different processing, storage, and rehydration requirements. At large freeze-drying facilities, electronic microprocessors regulate the times, temperatures, and pressures throughout each step of the process. A central computer collects this data, analyzes it using statistical quality control methods, and stores it for later reference. This assures that the food sent out to the public for consumption has been through a strictly controlled process that meets government guidelines and varies only slightly from batch to batch
Figure :Effect of freezing-rate and heating temperature on freeze-drying rate of “guacamole”
INFLUENCE OF PARAMETERS -
INFLUENCE OF PARAMETERS -
1. Freezing rate : Influence on the ice configuration and thus on the final structure of the freeze-dried product
2. Heat flux : to reduce drying rate. However, if the drying proceeds too rapidly (high heat flux), the product may melt, collapse or can be blown out of the container Excessive heat may cause the dry cake to char or shrink.
3. Chamber pressure: Chamber pressure affects the transport properties, thermal conductivity and water vapor diffusivity.
4. Temperature: affecting the quality of freeze-dried products .Maintaining low temperatures during primary drying will reduce aroma losses. If the temperature of ice in the condenser is higher than product’s temperature, water vapor will tend to move toward the product, and drying will stop.
Freeze drying is costly because of the long drying times involved; this factor has hindered the application of the technique to drying of materials in bulk. Fixed cost -The average fixed cost is given by the ratio of the annual fixed cost to the annual capacity. Running cost - The running cost consists of labor and utilities costs. The utilities cost can be estimated from a heat and energy balance for 1-kg water undergoing freezing, sublimation, condensation, and melting.
FREEZE DRYING COSTS -
MOST FREEZE DRIED FOODS -
Freeze dried coffee-Types of freeze dried coffee:• 100% Pure Coffee• Decaffeinated•Flavoured
• Organic• Fairtrade Coffee• Rainforest Coffee• Dual Certified Coffee• Triple Certified Coffee
Freeze Dried Strawberries-
Freeze dried papaya- Freeze dried Banana-
Freeze dried black currants-
Freeze Dried Apples-
Freeze Dried Blueberries- Freeze Dried Raspberries-
Freeze Dried Carrots- Freeze Dried Cabbage-
Freeze dried Garlic- Freeze Dried Turmeric-
Freeze Dried Red Chilly and Green Chilly-
APPLICATIONS OF FREEZE DRYING-
Biggest market for freeze-drying is the food industry. Freeze-dried food is used by hikers, hunters, astronauts, the military, as well as being used in the food industry for dehydrated soups and meals for consumers in the supermarket. The largest application is freeze-dried coffee.freeze-dried microorganisms- frequently used for fermentation reactions , used in bioconversion reactions and stored for research.
In the pharmaceutical industry – For savingmany medicines lives and for life saving substance that is blood.
Freeze dried fruit powders/ slices dices are often used: for making many delicious food products like Fruit drinks, ice creams, thick shakes, yogurt and other desserts when fresh fruits are not available. used to make soft candy, toffee and hard candy. making instant juice mixes, flavoring baby / infant foods, preparing food premixes, and range of bakery products.use in rich cream fillings, chocolate products and baked goods as well as in cereals and fruit bars.
FREEZE DRIED FOOD PRODUCT APPLICATIONS -
FREEZE DRIED FOOD PRODUCT APPLICATIONS
Fruit granules are used in products where the fruit content desired also texture and crunchiness is required.Freeze dried spices and vegetable used in manufacturing of instant vegetable noodles, soups, snacks and different kinds of fast food.Freeze dried food is use for making pet foods.
freeze dried soup
ADVANTAGES OF FREEZE DRYING-
1. Retain taste, smell and texture –2. Fewer loss of Nutrient –3. Reduce weight –4. Fewer Preservatives –5. Extended Shelf Life-6. The Safety Advantage-7. Rapid Rehydration Advantage-
Rehydration
DISADVANTAGES OF FREEZE DRYING -
1. Expense-
2. Storing-
3. Select Foods-
convenient method for drying those decomposable products (mostly pharmaceuticals, e.g., plasma, vaccines, antibiotics, sera, and growth hormones) that cannot be stabilized in any other way or that show markedly improved quality for a rather high average cost (coffee, mushroom s, diced chicken, and others ) suitable for high-value products with specific biological or phytochemical properties.
CONCLUSION-
