Welcome to a world where your favourite ready-to-eat meal is cooked in a fraction of the time it takes traditional methods, while preserving more nutrients and flavour. This is made possible through microwave heating. It's not just about reheating last night's leftovers anymore, we're talking about a sophisticated tool that's reshaping food safety protocols, enhancing product quality, and pushing the boundaries of what's possible in food processing
In recent years, microwave oven has become one of the most popular home appliances for food processing applications. The consumers have widely accepted the microwave technology due to its wide range of advantages, which has helped them to overcome the fears and taboos that existed in the beginning.
What is microwave heating?
Microwave heating is a volumetric heating process, where heat is generated evenly throughout the entire volume of the food material. This is due to the complete interaction between microwave, polar water molecules and charged ions in food. Microwave energy is selectively absorbed by areas of greater moisture, with more uniform temperature and moisture profiles.
The microwave technology has emerged as one of the most promising food processing technologies. It has gained popularity due to its considerable advantages over conventional heating methods. It has been applied in various food processing industries such as cooking, pasteurization, sterilization, thawing, baking, blanching and drying of food materials. Some advantages of microwave heating include high heating rates, lower processing time and more uniform heating. Moreover, microwave heating might change flavor and nutritional qualities of food in a lesser extent as opposed to conventional heating during cooking or reheating process. Microwaves are electromagnetic waves whose frequency varies within 300 MHz to 300 GHz. Domestic microwave appliances operate generally at a frequency of 2.45 GHz, while industrial microwave systems operate at frequencies of 915 MHz and 2.45 GHz.
Principles of microwave heating
Microwave heating is caused by the ability of the materials to absorb microwave energy and convert it into heat. Microwave heating of food materials mainly occurs due to dipolar and ionic mechanisms. Presence of moisture or water causes dielectric heating due to dipolar nature of water. When an oscillating electric field is incident on the water molecules, the permanently polarized dipolar molecules try to realign in the direction of the electric field. Due to high frequency electric field, this realignment occurs at million times per second and causes internal friction of molecules resulting in the volumetric heating of the material. Microwave heating might also occur due to the oscillatory migration of ions in the food which generates heat in presence of high frequency oscillating electric field. There are many factors which affect the microwave heating and its heat distribution and the most important of them are the dielectric properties and penetration depth.
Advantages of microwave heating
Rapid heating of food: One of the most significant advantages of microwave heating is its ability to heat food rapidly and volumetrically. Unlike conventional heating methods that rely on conduction and convection, microwaves penetrate the food material, causing water molecules to vibrate and generate heat from within (Chandrasekaran et al., 2013). This results in significantly faster heating times compared to traditional methods.
Improved energy efficiency: Microwave heating offers substantial energy savings compared to conventional heating methods. The direct transfer of energy to the food product, without the need to heat the surrounding air or cooking vessel, results in higher energy efficiency. This energy efficiency not only reduces operational costs for food manufacturers but also aligns with growing global initiatives for sustainable and environmentally friendly food production.
Food safety: Microwave heating can significantly contribute to food safety by effectively inactivating pathogenic microorganisms. The rapid and uniform heating achieved through microwave technology can ensure that safe temperatures are reached throughout the product, reducing the risk of cold spots where harmful bacteria might survive.
Preservation of nutritional quality: The shorter processing times associated with microwave heating can lead to better retention of heat-sensitive nutrients. Vitamins, particularly water-soluble vitamins like vitamin C, are often degraded during prolonged thermal processing. Microwave heating, with its rapid heating profile, can minimize this nutrient loss.
Improved sensory qualities: Microwave heating can help preserve the sensory qualities of food products including color, texture, and flavor. The rapid heating and shorter processing times mean that foods are exposed to high temperatures for shorter periods, reducing the likelihood of overcooking or development of off-flavors.
Applications of microwave heating in the food industry:
Blanching: Blanching serves a variety of functions, one of the main being to destroy enzymatic activity in vegetables and some fruits, prior to further processing. Blanching is not solely a preservation method but acts as a pre-treatment which is normally carried out between the preparation of the raw material and later operations particularly heat sterilization, dehydration and freezing. However, the conventional blanching method is closely associated with the serious issues like loss of weight, leaching and degradation of nutritive components such as sugar, vitamins and minerals. Microwave blanching requires little or no water for efficient heat transfer in food, and hence reduces the leaching of nutrients compared with hot water immersion (Puligundla et al., 2013). The advantage of microwave blanching over conventional method includes speed of operation, no additional water required, energy savings, precise process controls and faster start up and shut down times.
Pasteurization and sterilization: One of the most widespread applications of microwave heating is in the area of food preservation. Microwave pasteurization and sterilization have gained popularity as alternatives to conventional thermal processing methods (Ahmed & Ramaswamy, 2007). These techniques can effectively inactivate harmful microorganisms while better preserving the nutritional content and sensory qualities of foods. For instance, microwave pasteurization of packaged meals can extend shelf life without compromising taste or texture, a crucial factor in the ready-to-eat meal sector.
Baking and cooking: Microwave technology has revolutionized both industrial and domestic food preparation. Industrial-scale microwave ovens are used for partial baking of bread and pastries, allowing for fresh-baked products to be finished at the point of sale (Puligundla et al., 2013). This approach not only ensures fresher products for consumers but also optimizes logistics and reduces waste.
Drying: Microwave drying represents another significant application in food processing. This technique offers faster drying times and lower energy consumption compared to conventional methods. It's particularly effective for drying fruits, vegetables, and herbs as well as helping to preserve colour, flavour, and nutritional value better than traditional hot air drying (Zhang et al., 2006). For example, microwave-dried herbs often retain more of their essential oils, resulting in superior aroma and flavour.
Thawing: The defrosting of frozen foods is another area where microwave technology shines. Rapid and uniform defrosting is crucial in many food processing operations, and microwave systems can accomplish this task more quickly and evenly than conventional methods. This is particularly valuable in the meat processing industry, where uniform defrosting is essential for further processing steps (Farag et al., 2011).
Dairy industry: In the dairy industry, microwave heating has found applications in cheese manufacturing. It can be used for curd cooking and ripening acceleration, potentially reducing production times and improving consistency (Chandrasekaran et al., 2013).
Pest control: Microwave technology has also proven useful in pest control for stored grains and other dry foods. Microwave disinfestation can effectively eliminate insect pests without leaving chemical residues, addressing growing consumer concerns about pesticide use (Yadav et al., 2014).
Conclusion:
From extending shelf life without compromising taste, to extracting valuable compounds with efficiency, microwave heating is proving to be a versatile tool in the food industry. This technology, once confined to the realm of quick home cooking, has evolved into a powerhouse of innovation in industrial food processing. Microwave heating technology will continue to be a driving force in shaping a more efficient, sustainable, and delicious future for the food industry. So, the next time you enjoy a perfectly prepared meal or snack, remember, there might be a bit of microwave magic behind its journey from production to your plate.
References:
Ahmed, J., & Ramaswamy, H. S. (2007). Microwave pasteurization and sterilization of foods. In M. S. Rahman (Ed.), Handbook of Food Preservation (2nd ed., pp. 691-711). CRC Press.
Chandrasekaran, S., Ramanathan, S., & Basak, T. (2013). Microwave food processing—A review. Food Research International, 52(1), 243-261.
Farag, K. W., Lyng, J. G., Morgan, D. J., & Cronin, D. A. (2011). A comparison of conventional and radio frequency thawing of beef meats: Effects on product temperature distribution. Food and Bioprocess Technology, 4(7), 1128-1136.
Puligundla, P., Abdullah, S. A., Choi, W., Jun, S., Oh, S. E., & Ko, S. (2013). Potentials of microwave heating technology for select food processing applications: A brief overview and update. Journal of Food Processing & Technology, 4(11), 1-9.
Yadav, D. N., Anand, T., Sharma, M., & Gupta, R. K. (2014). Microwave technology for disinfestation of cereals and pulses: An overview. Journal of Food Science and Technology, 51(12), 3568-3576.
Zhang, M., Tang, J., Mujumdar, A. S., & Wang, S. (2006). Trends in microwave-related drying of fruits and vegetables. Trends in Food Science & Technology, 17(10), 524-534.
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