Does Microwaving Milk Destroy Nutrients

In this brief article, we will be discussing “does microwaving milk destroy nutrients”. We will be addressing certain misconceptions about heating milk in a microwave and will also tell you the safe way of warming up your beverage in the appliance. 

Does Microwaving Milk Destroy Nutrients?

No, microwaving milk does not destroy nutrients.

In fact, microwave cooking is actually among the safest forms of cooking. This is because the more time it takes to cook foods, the more nutrients break down. Since microwave cooking takes less time, it helps preserve some of the nutrients that would otherwise be broken down and lost as a result of boiling. 

Hence, microwaving milk is not only quick but may also be nutritionally advantageous.

What Happens When Milk is Heated In A Microwave?

When milk is heated in a microwave, the milk molecules vibrate in response to the energy emitted by the microwave core; the magnetron, which actually produces the electromagnetic waves. The heat is the result of this vibration.

Microwave radiation uses electromagnetic energy in the microwave region (300 MHz–300 GHz). The basic principle of the process by using a microwave is the baking by molecular vibration that penetrates superficially in the foods, and the depth of penetration ranges from 2 to 4 cm. The process makes the food vibrate and consequently heating the water, fat, and sugar molecules. However, microwave heating leads to uneven distribution of the temperature in the product. 

When food is irradiated, its components may be subject to significant changes. Milk contains carbohydrates, protein and fat. Among these existing macronutrients, the carbohydrates are less sensitive to radiation. Some of the glycosidic bonds linking the monosaccharides break when exposed to radiation, reducing the degree of polymerization and subsequently increasing the viscosity of polysaccharide solutions. Regarding proteins, the amino acid chains can be altered in the presence of water, due to electron transfer, and might accelerate the denaturation protein process by altering the secondary and tertiary structures before destroying the amino acid chains. 

Nevertheless, the denaturation is less intense than in thermal processing. In the case of lipids, in the presence of oxygen, radiation processes can accelerate oxidation, and other reactions such as the production of free radicals, the formation of hydrogen peroxides, and the destruction of compounds as carboxylic acids and antioxidants. Thus, radiation processes are not recommended for products with a high fat content (1).

Which Heat Treatments Destroy Milk Nutrients?

All heat treatments destroy the nutrients in milk. Raw milk is an unsafe food and must be thermally treated prior to its consumption or commercialization. Not only heat treatments, which are necessary to reduce the microbial load of the milk, but also many other processes, such as homogenization, standardization and packaging, are applied to milk and also change the physicochemical characteristics of the milk as well as its nutritional properties.

However, heat treatments that are more aggressive destroy the milk nutrients more intensively. Pasteurization, for example, 72°C for at least 15 seconds causes no change in the vitamin A, vitamin E and carotene content of milk. By evaporation as in the manufacture of condensed milk, there are losses of 20% of the vitamin A, and 9% of the vitamin E although carotene is not affected. 

Vitamin D also appears to suffer no changes during heat treatments. There are losses of B1 (thiamin), B12 and C increase from 10-20% in pasteurization and UHT treatment, to 90 % loss of B12 in bottle sterilization and evaporation. While pasteurization causes no damage to the milk proteins, sterilization procedures of UHT milk (a high temperature of 135 °C for 1-2 seconds) cause losses in true digestibility and a fall in biological value of the milk proteins (5).

When milk is heated at home, you may use the microwave or conventional cooking. As mentioned above, microwave heating is more effective and needs a shorter time than conventional boiling of milk and therefore destroys its nutrients to a lesser extent. 

In a study, it was reported that microwave heating of milk did not lead to a significant reduction in soluble protein content compared to raw milk, while boiling promoted significant reduction. The results suggest that boiling causes severe thermal damage to the nutritional quality of raw milk and microwave heating may be an alternative to preserve its nutritional characteristics (6).

Does Microwaving Milk Destroy Vitamins and Proteins?

No, microwaving does not destroy vitamins and proteins. However, vitamins are unstable in food and dependent on specific parameters such as the cooking time. Vitamin B1 and B2, vitamin A and B-carotene are stable up to 90 °C, but vitamin C is easily destroyed by any heat treatment (2). 

Proteins lose their chemical structure and are destroyed when milk is boiled at temperatures above 100 degrees Celsius for more than 15 minutes. Microwaving milk is nowhere near that temperature.

Does Microwaving Breast Milk or Formula Destroy Nutrients?

Microwaving does not destroy the nutritional value of breast milk and formula milk. However, it is not recommended to heat breast milk in the microwave. 

This is because breast milk contains antibodies as well as living cells (stem cells), hence microwaving breast milk on high heat for long periods can be highly damaging to these components. The same is true for formula milk – it also contains essential fatty acids and growth hormones that might be damaged from extensive heat. 

In a study, Lysozyme activity, total IgA and specific secretory IgA were determined before and after exposure of fresh frozen milk samples to heat by microwave for 30 seconds at low or at high power settings. All components were decreased, especially at high power. Total IgA was unchanged at low power. IgA was decreased by 98% and lysozyme activity by 96% (3).

Also, a microwave heats breastmilk and formula unevenly. This causes ‘hot spots’ (uneven hot and cold patches) in the milk which could scald your baby’s throat and mouth.

Why Does Milk Sometimes Curdle When Microwaved?

The milk can sometimes curdle when microwaved. This is a sign that the milk has an increased acidity. Acidified milk curdles faster under heat. If the milk curdles, it means that naturally occurring bacteria that were not eliminated during pasteurization produced acids by fermentation of lactose during long storage times. By lowering the pH value of the milk, protein becomes unstable and may curdle when heated (milk curdles at a pH value of 4.5). If not heated, it will naturally curdle in the refrigerator, but it will take longer (4).

Is Microwaving Food Advantageous for heating milk?

Yes. There are some advantages of using a microwave oven instead of conventional heating to heat milk. Examples are:

• Shorter processing time: Uses about a quarter of the time used in conventional heating; 
• Better quality retention of the milk: because of the high heating rate the target temperature is reached quickly, thus reducing the thermal impact on the milk and minimizing the destructive effects on its sensory and nutritional properties.

Conclusion

In this brief article, we discussed “does microwaving milk destroy nutrients”. We also discussed certain misconceptions about heating milk in a microwave and told you the safe way of warming up your beverage in the appliance. 

If you have any questions or comments please let us know.

References

1. Lima, Fabiana, et al. Effects of radiation technologies on food nutritional quality. Descriptive food science 1, 2018, 17.
2. Dumuta, Anca, et al. Physical and chemical charateristics of milk. Variation due to microwave radiation. Croat Chem Acta, 2011, 84, 429-433.
3. Woodward, Bill, and Harold H. Draper, eds. Immunological properties of milk. Kluwer Academic/Plenum Press, 2001.
4. Erkmen, Osman, and T. Faruk Bozoglu. Spoilage of Milk and Milk Products. Food Microbiology, 2 Volume Set: Principles into Practice. John Wiley & Sons, 2016, 307-336.
5. Bezie, Assefa. The effect of different heat treatment on the nutritional value of milk and milk products and shelf-life of milk products. A review. J. Dairy Vet. Sci, 2019, 11, 555822.
6. Martins, Carolina PC, et al. Microwave processing: current background and effects on the physicochemical and microbiological aspects of dairy products. Comprehen Rev Food Sci Food Safe, 2019, 18, 67-83.