1.FREEZE DRYING

Submitted by:-

Aarti Nimesh(FPEM/213001)

2.INTRODUCTION

• Food freeze drying is a dehydration process in which the water in food is frozen, and then sublimated directly from the solid phase to vapor by heating under vacuum.

• Freeze Drying preserves the integrity of the product’s biological and chemical structure and activity.

• Chemical decomposition is minimized since drying takes place at low temperature.

3.Theoretical Basis of Freeze Drying

• At the triple point (0.0098°C and 4.58 mm Hg), ice , water and water vapor coexist in equilibrium..

Normal (right) and freeze-dried (left) spaghetti

Completely remove water from some material, such as food, while leaving the basic structure and composition of the material intact

Two reasons

Keeps food from spoiling for a long period of time Significantly reduces the total weight of the food

How? Freeze the material Lower the pressure (<0.006 atm) Increase the temperature slightly

Freeze drying4.

5.Heat transfer during freeze drying

• Heat transfer through the frozen layer

• Heat transfer through the dried layer

• Heating by microwave

6.Mass transfer during freeze drying

• When heat reaches the sublimation front, it raises the temperature and the water vapor pressure of the ice. Vapor then move through the dried food to a region of low vapor pressure in the drying chamber.

• 1 g of ice forms 2 m3 of vapor at 67 Pa.

7.

8.Freeze drying process

3- stages:- freezing/Solidification:- Cooling the material

until completely frozen.

Sublimation drying:- Sublimation of ice from product reducing pressure in the chamber and providing heat to the product.

Desorption drying:- Desorption of residual moisture from the product

9.Freeze drying process

10.Process overview

• Vials are aseptically filled with the solution or suspension to be freeze dried and partially stoppered with a special rubber closure that allows to escape the water vapor.

11.Schematic diagram of freeze drier

12.Glass transition temperature (Tg)

o Tg may be used to judge the stability of freeze dried products.

o Higher the value of Tg , the more stable the product is.

o The value of Tg can be measured by DSC.o the storage temperature should be at least 20K

lower than its glass transition temperature.

13.Types of freeze dryers

Conduction type:- Contact freeze dryers Accelerated freeze dryers

Radiation type:- Radiation freeze dryers Microwave and dielectric freeze dryers

14.Vacuum pump for freeze dryingTasks and characteristics of vacuum pumps in freeze-

drying:- Removing air and other non-condensable gases leaking into

the drying chamber from atmospheric environment. Removing air and other non-condensable gases released from

the materials in the drying chamber. In a freeze-drying system, the commonly used vacuum range

is from 1 Pa to 10 Pa.

15.Advantages of freeze dried food

(1) Very high retention of sensory characteristics and nutritional qualities and a shelf-life longer than 12 months when correctly packaged.

(2) Freeze-dried food is porous and easy to be rehydrated and instantly dissolved. It can be consumed directly or after rehydration.

(3) Aroma retention up to 80 – 100 %

(4) No additives are added into the food during the freeze drying process.

(5)The texture of freeze-dried foods is well maintained; little shrinkage and no case hardening.

(6)Only minor changes to proteins, starches or other carbohydrates.

16.Disadvantages of freeze dried food

Freeze-drying is a time-consuming and energy-consuming process, which lead to higher product costs of freeze-dried food.

Freeze drying system includes vacuum and refrigeration equipments. The initial costs are relatively high.

The open porous structure of the food may allow oxygen to enter and cause oxidative degradation of lipids (packaging in inert gas necessary)..

17.Examples of freeze dried foods

18.

19.Recent advancements in freeze drying

Atmospheric freeze drying:

Dr Harold Meryman is considered the inventor of the science

of atmospheric freeze drying.Compared to vacuum freeze drying- reduce the energy consumption compared to vacuum freeze

drying while maintaining a high product quality. the temperature is higher, typically in the range of -3 to -10C. improved heat and mass transfer between circulating drying

medium and the frozen sample. high quality and homogeneous quality properties of the dry

product with an increased retention of volatile aromatic compounds.

20.CONT…. uses heat pump systems in combination with a fluid bed dryer.The heat pump dehumidifies the air, condenses the water vapor and conserves the heat. There is a very high mass-and-heat transfer.

21.Advantages of atmospheric freeze drying process

Low initial investment cost since expensive vacuum auxiliary equipment could be eliminated.

The process could be designed as a continuous system with higher productivity and lower operating cost.

The application of a heat pump system and different

process temperature elevating modes in AFD would

decrease energy consumption and drying time.Inert gas drying environment such as nitrogen or

helium can be applied to minimize the product degradation caused by oxidation.

22.Suppliers of freeze driers

Address: UG- 37, Vishal Tower, District Center, Janak Puri, New Delhi - 110058, Delhi, IndiaPhone:  08586979463 Website: http://www.accumax-india.com/

1.Accumax India, New Delhi

features-Coming fitted with 100 liters/ min double stage rotary vane type vacuum pump with air ballast providing for vacuum of 1x10-3 torr on pump head.High accuracy maintained in temperature control through use of microprocessor based digital temperature indicator cum controller.Temperatures range up to (-)40° C at ambient temperature of 20° C.

2. Sub Zero Lab Instruments, Chennai

Features-Well-arranged ports for convenient placement of flask.Efficient dual stage rotary vane vacuum pumpCastor wheels for easy movementAvailable in two models -55°C and -85°CSafety cut-off for vacuum pumpEasy cleanable trap and drying chamber

 

Address: 67, Thiruvalluvar Street, Jagahambikai Nagar, Ptadi , Chennai - 600050, Tamil Nadu, IndiaPhone:  08377801581Website: http://www.indiamart.com/subzeroindia/

3. SGM Lab Solutions, New Delhi

• Address: BA- 15, Mangolpuri Industrial Area, Phase- 2 , New Delhi - 110034, Delhi, IndiaPhone:  08376808239Website: http://www.laboratory-equipments.in/

Features:Light weight.Energy Efficient.Low maintenance.

25.Conclusion

A freeze dried product with the best attributes and quality.

In freeze drying, minimal structural changes or shrinkage.

In freeze drying process, nutrients are largely retained.

Freeze drying system includes vacuum and refrigeration equipments. The initial costs are relatively high upto 4 times than conventional drying.

Reference

Atmospheric Freeze Drying—A Review

I. C. Claussen a , T. S. Ustad a , I. Str mmen a & P. M. Walde ⊘ a )Department of Engineering Science and Technology,

Norwegian University of Science and Technology, Trondheim, Norway

b )SINTEF Energy Research, Kolbj rn Hejes vei 1D, ⊘Trondheim, Norway Published online: 16 Jun 2010.

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