Faizan OP 155.ppt
Download as PPT, PDF0 likes49 views
Microwave heating is used in many food processing applications like reheating, precooking, tempering, baking, drying, pasteurization and sterilization. Microwaves are electromagnetic waves with frequencies between 300 MHz to 300 GHz that travel at the speed of light. Microwave ovens operate at 2.45 GHz. Microwaves penetrate foods and are absorbed, causing molecules to vibrate and generate heat. The dielectric properties of foods like water content, temperature and composition determine how microwaves interact with them. Microwave heating has advantages like short cooking times and lower nutrient loss but also disadvantages like difficulty controlling heat and risk of overheating closed containers. It can both positively and negatively impact the nutrient content of foods.
Faizan OP 155.ppt
- 1. 1 Microwave Heating of Food Faizan Ahmad Assistant Professor Department of Post Harvest Engineering & Technology Faculty of Agricultural Sciences Aligarh Muslim University Aligarh (India) 202 002
- 2. 2 Microwave Heating Microwave and radiofrequency (RF) heating are used in many processes in industry and home Reheating Precooking Tempering Baking Drying Pasteurization Sterilization Microwave heating of food depends on dielectric properties of a material/foods
- 3. 3 What are microwaves? Microwaves are electromagnetic waves like light waves or radio waves. Their frequencies (wavelengths) are in the range from 300 MHz (λ = 1m) up to 300 GHz (λ = 1 mm). Microwaves travel at the speed of light (186,282 miles per second). Microwave ovens operate at frequencies of about 2.45 GHz, i.e. λ = 12.23 cm. All wave energy changes polarity from positive to negative with each cycle of the wave. In microwaves, these polarity changes happen millions of times in every second. Electromagnetic waves are, in themselves, stored energy in motion
- 4. 4 What are microwaves? Cont…. Microwaves penetrate and are absorbed by some substances, primarily food products. As the energy penetrates the food, its power is gradually absorbed, or lost, to each successive layer of molecules. The rate of energy loss and depth of penetration vary with the depth, density, chemical properties and temperature of the food waves of
- 5. 5 Characteristics of Microwaves Just as sunlight shines through a window, microwaves pass right through some materials. Materials such as glass, paper, and plastic are transparent to and generally unaffected by microwaves. Microwaves are reflected by metal surfaces, much as a ball would bounce off a wall. The metal walls of the cooking space in microwave ovens actually form a cavity resonator. The waves of microwave energy are cycling above and below a horizontal baseline. The half cycle below the baseline possesses negative properties, and the half cycle above the line is correspondingly positive. Basically, the effect of this wave, as it alternates between positive and negative, would be like a magnet flipping back and forth.
- 6. 6 Microwave Oven Components of Microwave oven : Magnetron (heart of a microwave oven) wave guide Turntable and base plate Power supply/Capicator stirrer Cooking Cavity
- 7. 7 How does microwave cooks food? Inside the strong metal box, there is a microwave generator called a magnetron. When you start cooking, the magnetron takes electricity from the power outlet and converts it into high-powered, 12cm (4.7 inch) radio waves. The magnetron blasts these waves into the food compartment through a channel called a wave guide. The food sits on a turntable, spinning slowly round so the microwave cooks it evenly.
- 8. 8 How does microwave cooks food? The microwaves bounce back and forth off the reflective metal walls of the food compartment, just like light bounces off a mirror. When the microwaves reach the food itself, it penetrate inside the food. As they travel through it, they make the molecules inside it vibrate more quickly. Vibrating molecules have heat so, the faster the molecules vibrate, the hotter the food becomes. Thus the microwaves pass their energy onto the molecules in the food, rapidly heating it up.
- 9. 9 Dielectric Properties of Food Dielectric constant, ε’ Ability of a material to store microwave energy Dielectric loss factor, ε’’ Ability of a material to dissipate microwave energy into heat Parameter that measures microwave absorptivity Dielectric constant and loss factor – important role in determining interaction of microwaves with food
- 10. 10 Dielectric Properties of Food Cont…. Dielectric properties of water and high-moisture- containing foods such as fruits, vegetables, and meat are high because of dipolar rotation Dielectric Constant Dielectric Loss Factor
- 11. 11 Dielectric Properties of Food Dielectric properties of food depends on: Moisture content Temperature Composition of the material Also a function of frequency of oven
- 12. 12 Advantages and disadvantages of Microwave heating Advantages: Cooking time is short Destruction of nutrients is less No physical change of foods Melting process is easy Sterilization effect exists There is no flame, then treatment is easy Microwaves heat and cook your food from the inside out rather than going through your food, from the outside in Microwave ovens work quickly and save energy as compared to other conventional cooking methods
- 13. 13 Advantages and disadvantages of Microwave heating Disadvantages: Constraint with metal container Heat force control is difficult Water evaporation Closed container is dangerous because it could be burst Surface toasting is impossible
- 14. 14 Positive Effects of Microwave heating on foods Using a microwave oven can prevent the loss of important vitamins and minerals in your food. Vitamin C and potassium are often lost in liquid used to boil food. Cooking broccoli in your microwave oven may prevent the loss of glucosinolate, a compound in broccoli which may be responsible for its cancer- fighting properties, and which is lost in boiling.
- 15. 15 Negative Effects of Microwave heating on foods Microwaves Zap Food Nutrition - diminishes the nutrient content in the food. if food is heated at a high temperature and used for a long time. - The correct combination of time and temperature can help preserve most nutrients while also improving the foods’ taste, texture and colour. Microwaves Destroy Vitamin B-12 (raw beef, pork and milk) - 30 to 40 % loss of the vitamin when the foods received microwave exposure. - health benefits of vitamin B-12 are instantly neglacted once heated in a microwave
- 16. 16 Negative Effects of Microwave heating on foods Contd. Microwaves Create Carcinogens In Food - plastic containers used to heat these microwave meals have been found to release the carcinogens along with other harmful toxins into your food. Microwaves Can Change the Makeup of Your Blood - In a Swiss clinical study, researchers found that blood changes in individuals who consumed microwaved milk and vegetables. - red blood cells decreased while white cell levels increased, along with cholesterol levels.
- 17. 17 THANKS FOR YOUR ATTENTION!