Different Types of Food Product Drying (Foam mat, heat pump and osmotic drying: principles, methods, heat utilization factor and thermal efficiency))
- 1. Different Types of Drying FOAM MAT, HEAT PUMP AND OSMOTIC DRYING: PRINCIPLES, METHODS, HEAT UTILIZATION FACTOR AND THERMAL EFFICIENCY Presentaion by: Maneesh Sonkar
- 2. What is Drying? Drying is the process for food preservation, is one of the most used processes to improve food stability owing to reduce the water activity of the food material which in turn inhibits microorganisms and decreases undesirable enzymatic reactions and minimizes physical and chemical alterations during storage (Mayor and Sereno, 2004).
- 3. Foam mat drying (FMD) ❑FMD is the process in which liquids or semi-liquid/solid food products such as fruit juices, vegetables puree or cereal pastes are transformed into stable foam to subsequently be dried under thin-layer conditions. ❑This starts by whipping the raw material under controlled conditions using various means such a blender or specially designed devices in the presence of edible foam agent and/or foam stabilizer. ❑The stable form foamed product is consequently spread as a thin sheet or mat to be exposed to stream of relatively hot air until it is dried to desired moisture.
- 4. Contd. ❑The drying process can systematically be performed under soft conditions with relatively low airflow temperature. It results in a thin porous honeycomb sheet or mat. ❑The dried sheet product is then converted into fine powder by simple and easy grinding resulting in fine powder. ❑Drying can be carried out either by hot air drying, freeze drying and or spray drying. The difference between foam mat drying and the other drying methods is that in foam mat drying, the physical structure of raw food material is changed by breakdown of the cell walls and gas (air) incorporation.
- 5. Foam mat drying process Drying of Papaya fruit
- 6. Foaming agents ❑A foaming agent is a surfactant material that reduces the surface tension between two liquids or between a liquid and a solid and facilitates the foam formation. ❑A good foaming agent can be adsorbed immediately at the air-water interface, reduce interfacial tension, mutually interact among the proteins that unfold at the interface, and form a strong cohesive, visco-elastic film which can resist the mechanical agitations. ❑Soy protein, egg albumin, monoglycerides and Fatty esters are the most commonly used foaming agent.
- 7. Proteins (Foaming agent) ❑Proteins give a good foaming ability and high foam stability through their hydrophobicity and possible conformational rearrangements, which allow rapid adsorption at the air-water interface leading to the formation of a coherent elastic adsorbed layer (Dickinson, 1998). The most widely used protein foaming agents are egg white, gelatin, milk proteins like whey protein, casein and soy protein. i. stabilize foams effectively and rapidly at low concentrations. ii. perform effectively in wide range of foods. iii. perform efficiently in the medium with foam inhibitors such as fat, alcohol or flavor substances (Zayas, 1997).
- 8. Types of protein foaming agents 1. Egg albumin (EA)- Egg albumen or egg white is the main protein found in eggs. When it is whipped, proteins denature at the interface and interact with one another to form stable, viscoelastic interfacial film thereby resulting in foam formation. 2. Whey protein - Whey protein is a by-product of the cheese-making process. Whey protein concentrate (WPC) with more than 25% protein needs about 50 min of whipping time to produce stable foam, while EA foam is usually obtained in 20 min. 3. Soy protein - Soy protein isolate (SPI) is a highly refined or purified form of soy protein with a minimum protein content of 90%. The functional characteristics of SPI are gelation, emulsification, viscosity, water binding, dispersibility and foaming. 4. Guar foaming albumin (GFA)-GFA is an albumin fraction extracted from guar meal, with high foaming and stabilizing ability. The foaming activity of GFA is 10 folds higher than egg white at low protein concentrations. GFA can produce smaller and more uniform bubbles than EA
- 9. Structure of egg albumen foams after one, three and five minutes whipping and after 10 minutes standing Albumen foams immediately after formation Albumen foams after 10 min rest (Kapf et al., 2003)
- 10. Drying of foam 1. Vacuum foam drying 2. Foam spray drying 3. Tray Foam dryer 4. Belt type foam mat dryer Belt type foam dryer Tray foam dryer
- 11. Drying of foam ❑Continuous foam mat dryer: used for drying of milk foam was designed (Aceto et al., 1972), where the foamed milk of 45% w/w solids was deposited on the Steel belt, tensed over heating and cooling drums. then the dried product was scraped from the belt which rolled over cooling drum. ❑Microwave foam mat drying- foams are dried in a thin layer which resulted in limited throughput even in optimized drying conditions, is a main drawback of the foam mat drying this could be overcome by the use of microwaves. ❑Foam mat freeze drying- manufacture dehydrated food products with excellent final quality because of the low temperature during the process and the direct sublimation of water from solid to vapour states.
- 12. Characteristics and Quality of Foam ❑Foam density: Foam Density is calculated as the ratio of mass of foam to the volume of foam. Numerous studies indicated that higher foam density in the range of 0.2 to 0.6 g cm-3 is suitable for foam mat drying. ❑Foam expansion: Where, Mf is the mass of foam, g Vf is the final valume of formed material, cm3. Where, V0 = Initial volume of material, cm3 Vf = Initial volume of material, cm3.
- 13. Contd. ❑Foam stability (FS): Mechanical and thermal stability of foam is necessary for successful foam mat drying. The stable foams are made using appropriate foaming agents and stabilizers. The foam should be rigid enough to not flow through the openings of the supporting grid. The mechanical strength of lamella determines the stability of the foam along with their air/ water interface properties. Where, ∆V = change in volume of foam occurring during the time interval ∆ t, V0 = Initial volume of foam directly after whipping (cm3).
- 14. Heat utilization factor Heat Utilization Factor (HUF): The heat utilization factor (HUF) in foam mat drying represents the proportion of the total heat supplied that is effectively utilized in moisture evaporation. A higher HUF indicates better energy efficiency in the drying process, ensuring minimal heat loss to the environment. It is calculated using: Thermal Efficiency: Thermal efficiency in foam mat drying assesses how effectively the input thermal energy is converted into useful drying energy. It is calculated as:
- 15. Factors Affecting HUF and Thermal Efficiency in Foam Mat Drying: ❑Foam thickness: Thinner foams improve heat transfer but may lead to excessive drying. ❑Air velocity and temperature: Higher air velocity enhances drying efficiency but may reduce heat utilization if not optimized. ❑Initial moisture content: Higher moisture content requires more energy for evaporation. ❑Drying chamber design: Proper insulation minimizes heat loss, improving HUF.
- 16. Selection criteria Foam mat drying is ideal for products that: ❑Have high moisture content and are difficult to dry in their natural form. ❑Require rapid drying at lower temperatures to retain nutrients and sensory properties. ❑Need to maintain good solubility and rehydration characteristics. Examples of Suitable Products: Fruits and Vegetables: Mango, banana, papaya, tomato, pineapple, citrus fruits. Dairy Products: Milk, yogurt, and whey proteins. Egg Products: Whole egg, egg white, and egg yolk powders. Beverages and Instant Mixes: Coffee, tea extracts, fruit juices. Nutraceuticals & Pharmaceuticals: Herbal extracts, probiotics, and medicinal formulations.
- 17. Advantages ❑Enhanced Drying Efficiency: The foam structure increases the surface area for moisture removal, leading to faster drying compared to traditional drying methods. ❑Lower Drying Temperature: Suitable for heat-sensitive products where high temperatures can degrade nutrients and bioactive compounds. ❑Improved Product Quality: Produces powders with better solubility, rehydration, and texture compared to spray or drum drying. ❑Energy Efficiency: Requires less energy than freeze drying while maintaining similar product quality. ❑Minimal Structural Damage: Prevents crystallization or textural damage, ensuring product integrity.
- 18. Heat pump drying ❑Same thermodynamic cycle as refrigerator. ❑The heat pump originates from the operation of standard heat pump, where the low temperature heat from the heat sources is upgraded by bringing it to the higher temperature in a heat sink. ❑This drying technology is designed to operate at atmospheric pressure, in single or multiple stages, in batch or continuous modes, with a moving or fluidized bed for further enhancement of energy use and water removal rate. It can also operate in a stationary bed with lower rates.
- 19. Contd. ❑The heat pump dryer recovers heat from the drying exhaust vapour that is lost in open conventional dryers. ❑A properly designed heat pump dryer has a closed loop and fully recovers energy that is distributed for both the heating and cooling required in a drying process. ❑The refrigerant flows through the evaporator where it absorbs latent heat from the exhaust vapour and recycles it through the condenser (Lock 1996). ❑Valuable volatiles can be recovered and harmful condensable vapors can be separated and discarded. ❑The magnitude of heat recovery in a heat pump dryer depends on the area available for heat transfer and on the properties of the refrigerant and moist air. ❑It also depends on the moist air and evaporating refrigerant temperatures as well as on the difference between evaporating and condensing temperature.
- 20. Single-Stage vapour compression ❑The single-stage vapour compression is a commonly applied heat pump cycle. In this case, only one evaporator cools the moist air, condenses the water vapour fraction and absorbs (for boiling the refrigerant) the corresponding latent heat of vapour condensation. ▪CON- condenser ▪EVA-evaporator ▪COM- compressor ▪THR –expansion valve
- 22. Working Principle ❑The main components are the expansion valve, evaporator, internal and external condensers and the compressor. ❑After flowing through the heat pump evaporator and the condenser, the dry and warm air is ready to flow into the drying chamber. ❑The simplified heat pump dryer has two separated loops with common heat exchangers. The drying air loop (abca) contains the air cooler (EVA), heater (CON), blower and the drying chamber. ❑The main components of the refrigerant loop (12341) are the expansion valve (THR), evaporator (EVA), condenser (CON) and compressor (COM).The heat pump fluid and drying air loops are coupled through the common evaporator and condenser to recover the exhaust energy.
- 23. Drying air cycle ❑c–a: Adiabatic drying process where the drying air at the set temperature flows through the drying chamber and removes moisture from the bed of wet material. ❑a–b: Cooling the moist air and water vapour condensation with liquid drainage. As the moist air flows through the evaporator, the vapour condenses to liquid and is drained out of the drying loop. To perform this step, the evaporator surface is kept at state point L with a temperature below the dew-point temperature in the air at the inlet drying chamber (point c). ❑b–c: Heating of the moist air by the condenser using the energy recovered by the evaporator. The low-temperature energy absorbed in the evaporator promotes boiling of the refrigerant, and then it is compressed to high-temperature energy and reused by the condenser to heat the drying air. This completes the cycle of energy recovery in the heat pump dryer.
- 24. Two stage heat pump dryer ❑the two-stage heat pump dryer that operates with a large evaporating and condensing temperature difference and provides two airstreams with different conditions. ❑The refrigerant liquid from the condenser D is collected in the receiver E, flows into the expansion valve F and is collected in the intermediate pressure tank G. ❑Simultaneously, this tank receives intermediate pressurized superheated vapour from the first stage compressor A1. ❑In the tank G, the refrigerant is separated into two phases. One phase is saturated liquid that enters the expansion valve H connected to the evaporator 1 and the low-stage compressor A1. ❑The other phase is saturated vapour that flows to the suction line of the high- stage compressor A2.
- 25. Contd. ❑This compressor discharges superheated vapour to the three-way valve B, which directs the vapour to the external and internal condensers C and D, respectively. ❑Vapour to the three-way valve B, which directs the vapour to the external and internal condensers C and D, respectively. ❑The second stage drying involves moisture removal by evaporation at higher rates. The two- stage heat pump dryer operates with energy recovery for high efficiency (superior-quality dried product), resulting in reduced energy use and costs.
- 26. Selection criteria •Moisture Content: Suitable for products with moderate to high initial moisture content (e.g., fruits, vegetables, herbs, meat, fish). •Heat Sensitivity: Ideal for nutrient-rich and heat-sensitive materials like pharmaceuticals, herbs, and bioactive compounds. •Physical Form: Works well for sliced, whole, or granulated products but may not be ideal for liquid- based materials. •Final Product Quality: Ensures color, texture, flavor, and bioactive retention for premium-quality products.
- 27. Drying Efficiency & Performance Energy Efficiency: HPD should provide at least 30–50% energy savings compared to conventional drying. Temperature Range: Typically 30–60°C, but should match the product's drying requirements. Relative Humidity Control: Ability to adjust humidity levels for uniform drying and to prevent case hardening. Drying Time: While HPD operates at lower temperatures, optimized airflow and heat recovery should ensure reasonable drying durations. Moisture Removal Rate: Should be suitable for the desired drying speed and final moisture content.
- 28. Osmotic drying Osmotic drying, also known as osmotic dehydration, is a food preservation technique that utilizes the principles of osmosis to remove water from food products. This method involves immersing the food in a hypertonic solution, typically composed of sugar or salt, which has a higher osmotic pressure than the food itself.
- 29. Mechanism of Osmosis The fundamental principle behind osmotic drying is osmosis, which is the movement of water across a semi-permeable membrane from an area of lower solute concentration (inside the food) to an area of higher solute concentration (the osmotic solution). 1.Water Movement: When food is placed in the osmotic solution, water from the food diffuses into the solution due to the osmotic pressure difference. This results in a reduction of moisture content in the food. 2.Solute Penetration: Simultaneously, some solutes from the osmotic solution penetrate into the food. This dual movement helps enhance flavor and sweetness while reducing moisture content.
- 31. Osmotic Agent Osmotic Agent Effects Malto Dextrin It can be used as an osmosis solute at higher total solids concentration in mixed systems high solid gain. Sodium Chloride Mostly used for vegetables as it retards oxidative and non enzymatic browning. Sucrose/Sugar High water loss and low solid gain, it reduces browning by preventing the entry of oxygen. Starch/Corn syrup Flavours similar final water content with minimal solid gain. Calcium Chloride Increases the firmness of fruits and preserves texture during storage. Ethanol Decreases viscosity and freezing point of the osmotic solution in cooling and freezing processes. Fructose Leads to high water loss and low solid gain. Increases dry matter content, and the final product has lower water activity. Lactose Has much lower sweetness than sucrose. Low solubility in aqueous solution makes it less suitable for some applications. Source: International journal of prevention of fruits and vegetables
- 32. Factors Influencing Osmotic Drying •Concentration of the Osmotic Solution: Higher concentrations lead to increased water removal rates. •Temperature: Elevated temperatures can enhance diffusion rates, facilitating faster dehydration. •Duration: The length of time the food is immersed in the osmotic solution influences water loss and solute absorption. •Geometry of Food: The size and shape of the food pieces impact how quickly water can be removed. •Solution to sample ratio: a higher ratio ensures a constant osmotic gradient, leading to faster water removal. •Agitation: stirring improves mass transfer, increasing efficiency.
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