Foam mat drying

Details description fmd

1. PRESENTED BY Ankan Kheto Foam Mat Drying

2. Why Foam mat Drying Dehydration of heat-sensitive, high sugar content and viscous foods, which are difficult-to-dry and sticky under relatively mild conditions. Liquid food should be capable of forming stable foam.

3. I ntroduction Foam mat drying is special form of conveyor driers in which liquid foods (usually fruit juices) converted to stable foam and placed on a perforated conveyor. The foam is usually 2-3 mm thick and dried rapidly in two stages by parallel and then counter current air flows. Vegetable (i.e. solubilized soya protein) protein, gum and various emulsifiers (e.g. glycerol, monosterate and propylene glycol) are used as foaming agents.

4. Process diagram for Foam Mat Drying Cooler Heater Screens Flaker Dryer Gas Warm air Moist air Concentrate Dense Powder Dense Solid Foam Porous Solid Containers Foaming agent Hot liquid

5. Key parameters Stable gas-liquid foam is the primary condition for successful foam drying. Surface area exposed is directly proportional to moisture removal rate. Capillary diffusion is also the main reason for the moisture movement within the product.

6. Foa m Structure Colloidal dispersion in which gas is dispersed in a continuous liquid phase Dispersed phase (internal phase) is larger than the continuous phase (external phase ) Polyhedric foam Ratio of dispersed phase to continuous phase is larger Large number of bubbles and form a honeycomb structure Examples: Egg white foam and beer foam Dilute bubbly foam Ratio of dispersed phase to continuous phase is small Individual bubbles retain their spherical shape Examples: Choco mousse

7. Foam formation methods Sparging or bubbling: A known amount of air is bubbled through an orifice into a known quantity of liquid Liquid may be completely converted to foam if a large amount of gas is introduced Stability of the bubble formed highly depends on the viscosity of the liquid This method manages the desired bubble size by adjusting the diameter of the orifice This method is not used in food processing industries ; however, it is commonly used for basic foam studies

8. Contd.. Whipping or beating: Incorporation of unlimited amount of air into known quantity of liquid. The size of the air bubble will increase and subsequently break into small bubbles because of the mechanical agitation. The final size of the bubble depends on the speed of the agitator , the geometry of the apparatus and the rheological properties of the liquid. Widely used in the food processing industries Electric hand blender takes about 3–5 min to obtain consistent foam.

9. Contd.. Shaking Foam is obtained by agitating the liquid forcefully. The volume of the foam formed by shaking depends on the factors like the amplitude and frequency of shaking, shape of the container, the volume, protein content and temperature of the liquid taken. This method tends to be slower than by bubbling or whipping under same conditions; hence, it is not commonly practiced on large-scale foam production.

10. Foam Characteristics Foam Expansion (FE) = {( Vol u of Foam - Initial vol u of Pulp) / (Initial vol u of Pulp)} * 100 Foam Stability = (Initial foam vol u * time interval) / change in foam vol u Foam Density (g/cm 3 ) = mass of foam / vol u of foam Mechanical or thermal stability: Foam not collapsing for at least 1 hr.

11. Foaming Agents A surfactant that reduces the surface tension between two liquids or between a liquid and a solid and facilitates the foam formation. It should be able to adsorb readily at the air-water interface, reduce interfacial tension, withstand thermal and mechanical agitation F oaming agents should posses the following properties Stabilize foams effectively and rapidly at low concentrations Perform effectively over the pH range Perform efficiently in the medium with foam inhibitors such as fat, alcohol or flavor substances

12. Foam Stabilizers Decrease the instability of foams, polysaccharides are employed as stabilizers. Being hydrophilic, they do not adsorb at the interface. Enhance the stability of foam proteins by a thickening or a gelling effect. Act by either increasing the viscosity of the continuous phase or by forming a 3D network that retards the movement of components within the foam. Example: C ellulose gum, Xanthan gum, Arabic gum, Starches , Pectins and Gelatin etc.

13. T ypes Continuous Foam Mat Dryer Continuous belt vacuum dryer for drying of milk foam, where the foamed milk of 45% w/w solids was deposited on the stainless steel belt, tensed over heating and cooling drums. Various combinations of radiant heaters were placed above and below the belt to precondition the feed, and to dry the product. Then, the dried product was scrapped from the belt, which rolled over the cooling drum . Microwave Foam mat Drying (MFD) 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. Foam Mat Freeze-Drying D ehydrated products with excellent final quality because of the low temperatures during the process and the direct sublimation of water from solid to vapor states.

14. Advantages Rapid drying and low temperature of products results in high quality product. Foam drying is three times faster than drying a similar type of liquid. Considerably cheaper than vacuum, freeze and spray drying method. Uniform heating, Storage reliability and Simplicity.

15. Disadvantages High capital cost (but lower than vacuum drying). Large surface area is required for high production rate.

16. References: Kudra , T. and Ratti , C. (2006) Foam-mat drying: Energy and cost analyses. Can. Biosyst . Eng. 48, 3.27–3.32 Mehran Azizpour , Mohebbat Mohebbi , Mohammad Hosein Haddad Khodaparast .(2016) Effects of foam-mat drying temperature on physico -chemical and microstructural properties of shrimp powder, Innovative Food Science and Emerging Technologies , 34, 122–126 Sangamithra a, Sivakumar Venkatachalam, Swamy Gabriela John and Kannan Kuppuswamy . (2015), Foam mat drying of food materials: A review , Journal of Food Processing and Preservation , 39, 3165–3174 Z. Hardy & V. A. Jideani .(2017) Foam-mat drying technology: A review, Critical Reviews in Food Science and Nutrition , 57:12, 2560-2572 Ana María Chaux-Gutiérrez, Adriana Barbosa Santos, Diana Maria Granda- Restrepo & Maria Aparecida Mauro. (2017) Foam mat drying of mango: Effect of processing parameters on the drying kinetic and product quality, Drying Technology , 35:5, 631-641

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