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Course:FNH200/Projects/2025/Frozen Meals

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1. Introduction

Frozen foods have become the cornerstone of contemporary living, providing convenience, variety, and accessibility to busy families in Canada and worldwide. Additionally, whether it's a fast dinner after work, a ready-to-use meal in the fridge, or a standby for people with little cooking time, frozen ready-to-eat meals are now a standard in the food sector. However, beneath the seeming simplicity of heating and consumption is a rich dynamic of food science, engineering, and consumer aspirations.

From manufacturing to plate, a frozen meal requires meticulous freezing technique selection, rigorous temperature and packaging control, and a thorough comprehension of how these elements affect the food's texture, flavour, and nutritional content. Furthermore, techniques like liquid nitrogen cryogenic freezing are intended to maintain freshness and reduce quality loss, but even the quickest technology eventually has to deal with organic chemical reactions like protein denaturation and lipid oxidation. Furthermore, preserving the safety and visual appeal of frozen foods depends heavily on how they are transported, stored, thawed, and reheated.

2. Processing

2.1 Freezing methods

Simple illustration of a typical immersion freezer

Currently, there are three methods through which freezing occurs: cold air blasts, direct liquid immersion, and indirect contact with refrigerated surfaces. The cold blast (Cryogenic freezing) is the most commonly used method for frozen meals, utilizing liquid nitrogen. The food is placed on conveyor belts and then sprayed with liquid nitrogen that boils as soon as it comes into contact with the food.[5] The boiling occurs since liquid nitrogen has a boiling point of around -196 degrees. When the food is cooled down using this freezing method, small ice crystals form on the food. If the freezing is not rapid enough, large ice crystals form throughout the food, causing a breakdown in its structure. When thawed, this results in an undesirable taste and appearance. [5] As mentioned in lesson 7, Cryogenic freezing is commonly used as this method requires “Almost no dehydration,” and removing the oxygen removes oxidative spoilage. [6]

2.2 Impact on texture, nutrient retention, and microbial safety

Improper freezing and storing of frozen foods causes the quality to diminish significantly.  “When foods with high amounts of water are frozen slowly, they may experience a loss of fluid, called drip, upon thawing”. This leads to water loss, and consequently, dehydration and loss of nutrition occur. Furthermore, “Improperly packaged frozen foods lose small amounts of moisture during storage,” which leads to a phenomenon called freezer burn,  which comes from surface dehydration of the food. “Frozen meats with freezer burn have the appearance of brown paper and quickly become rancid.” Using the title route packages illuminates the fluctuation in the temperature during storage and reduces the risk of freezer burn. [4] Maintaining consistent low temperatures is just as important as the initial freezing method. Even small temperature changes can accelerate quality loss, so proper packaging and stable storage help preserve the texture, flavour, and nutrition closer to their fresh state.

3. Chemical Reactions

3.1 Lipid oxidation

One key issue with frozen meals is lipid oxidation where it changes the taste/flavour and smell of foods, making it unpleasant to eat [2]. This occurs by the oxidation of unsaturated fat where primary and secondary oxidation products form[2]. Lipid oxidation is a chain of free-radical reactions where oxygen interacts with fatty acids, breaking fats down and producing rancid flavors[3]. The free radicals and by-products like aldehydes can react with the different food components like proteins, sugars, pigments, and vitamins therefore affecting the chemistry of these components[3]. Ultimately this will contribute to the unpleasant taste and smell of the food as well as the appearance and the overall quality of the food. Lipid oxidation is very problematic for the human body, especially for the older population as there are associations with many diseases like Alzheimer's, Parkinson's, cancer, and more[3].

Factors like temperature, how much oxygen is around, and if there pro-oxidants or antioxidants that are present will determine how quickly fat oxidation will occur[2]. Therefore it is important to use antioxidants like vitamin C and E which function as preservatives in food when added to control the free radicals and the rancidity and were also mentioned in lessons 2.2.2.4[2]. Controlling the availability of oxygen through different types of packaging and controlling the freezer temperature by keeping it below -18°C will help control the risk of lipid oxidization[2]. According to lesson 7.3 the freezing helps prevent or slow down microbial growth but does not destroy all of the microorganism epically when you thaw the frozen meal. Lastly, freezing helps lower the water activity or freeze the free water in the food into crystal forms because microorganisms will grow in line with the amount of free water that is available.

3.2 Nutrient Retention of Microwaving

When considering microwaving food, one may expect that microwaving the food may negatively affect how well the nutrients are retained in the food. Contrary to this belief several sources have shown otherwise. The act of microwaving food may actually be a better alternative for nutrient retention when compared to certain cooking methods like boiling, poaching or blanching for example, which hurt vitamin C and B retention[7]. These vitamins, C and B, especially vitamin C, are water soluble which make them much more susceptible to being lost during the cooking process[7]. Steaming was shown to hurt vitamin C retention whereas microwaving, although it did impact vitamin C retention, it did to a lesser extent[7]. Although this is particularly when being compared to cooking methods using water, when compared to a conventional oven it was shown most nutrients were unchanged like potassium, sodium, fat, carbohydrate, protein, thiamine, and riboflavin in both[9]. For both vitamin A and folic acid decreased to a similar amount but vitamin E increased after heating[9]. Although, there is no statistically meaningful difference between the convectional oven and microwave; the convectional oven does have slightly worse nutrient retention likely due to being heated for longer than in the microwave[9]. As the microwave retains vitamin C when compared to the convectional oven[9]. the microwave has also been shown to increase levels of polyphenols when compared to other cooking methods[9]. For ideal nutrient retention we want a method “that cooks quickly, heats food for the shortest amount of time, and uses as little liquid as possible”, microwaving fulfills these criteria quite well[8]. Surprisingly microwaving, in terms of nutrient retention is one of the best ways to heat food, especially since the microwave is often one of the fastest, easiest and most convenient ways to heat food.

3.3 Preservation of Nutrients

In terms of preserving the nutritional value of frozen meals, blanching/heating the frozen meal will contribute to inactivating the enzymes, helping preserve the nutrients[2]. It is noted that the way frozen meals are transported and handled with care will influence the overall quality of the meal. This includes maintaining the freezer's temperature constant while being transported, using special vehicles that have insulated containers and refrigerated trucks, handling frozen food with minimum stress being placed, and tightly sealed packaging[2]. Freezing has minimal impact on the nutrition, flavour, or colour but texture of food will be affected the most while improper long storage in a freezer and inadequate thawing will noticeably reduce the food’s quality[1]. Freezing will not stop the deterioration process of food, the chemical changes will happen, but over a longer period of time due to the frozen state[1]. The most common deterioration occurring in frozen meals is protein denaturation where proteins will lose their structure and function making the protein source tough 1 While the interaction of proteins with fat and oxidation damage will results in decreasing vitamins and pigments[1]. A steady storage temperature is crucial to note, where the refreezing of unfrozen water on top of smaller ice crystals will create larger ice crystals when temperatures increase and decrease, which affects the food’s quality. Alongside this, consider the rate of freezing, storage temperature, and rate of thawing according to lessons 7.3 in determining the overall quality of frozen foods/meals as well.

4. Packaging

4.1. Visual design

Packaging plays a crucial role in protecting the food during storage and transport, as well as when it's on display to consumers. Research shows that consumers in Canada are demanding more transparency in their food products and labelling.[13] This has led to many changes in food packaging, including clear windows or plastic film on frozen meals, nutrition facts, or QR codes that provide easy and accessible access to ingredient information.[13] Many frozen ready-made meals are appealing to consumers due to their convenient nature, and the packaging reinforces this with easy to store and use packaging.

4.2. Types of materials

The safety of all packaging materials for food in Canada is controlled under Division 23 of the Food and Drugs Act.[11] Some packaging requires specific information be provided to Health Canada, and packaging materials may be submitted voluntarily to the Food Directorate (FD) for a premarket assessment.[11] Many polymers are traditionally used in the packaging of frozen dinners in Canada, in which the Health Canada website includes a list of approved polymers for use in packaging applications.[11]

Many frozen food products including TV Dinners must require packaging that can withstand the cold temperatures of the freezing process as well as the (re)heating process. TV Dinners are usually manufactured using blast freezing and sometimes cryogenic freezing which retains quality due to the rapid rate of freezing and small ice crystal formation.[12]

Common container materials include polymers such as polyethylene (PE), aluminum, or paperboard.[12] Polyethylene is commonly favored for its durability and microwave/oven save properties. Plastic trays contribute to watertight properties and preventing dehydration during shipping that is required for frozen ready-made meals.[12]

Popular frozen meal brands such as Lean Cusuine use plastic trays with outer sleeves of paperboard or cardboard, whereas brand Hungry Man primarily uses paper for the tray and a plastic film to seal the package.[12] This plastic film creates a barrier that keeps the food fresh and helps to prevent freezer burn.

4.3. Green Alternatives

In recent years there has been a significant push by consumers for green alternatives of packaging materials for food products. Considering the significant amount of plastic commonly used for frozen ready-made meals, many brands have switched to incorporating recycled plastic and paperboard materials.[13]

5. Conclusion

With elements like freezing speed, temperature control, and packaging playing crucial roles in maintaining texture, flavour, nutrients, and safety, frozen ready-made meals combine the knowledge of food scientists, engineers, and manufacturers. While creative packaging increases shelf life and satisfies sustainability objectives, quick techniques like cryogenic freezing preserve freshness. Nonetheless, consumers must store, transport, and reheat food properly because improper handling can degrade nutrients and cause quality loss.

5.1 Future trends and emerging technologies

Ultra-rapid freezing techniques, intelligent packaging with temperature and oxygen indicators, and more environmentally friendly materials like plant-based bioplastics and compostable trays are all becoming popular in the frozen food sector. Together, these developments seek to improve freshness, nutrient retention, and consumer trust. For example, blockchain tracking may soon enable consumers to confirm a product's origin, freezing date, and handling conditions.

5.2 Implications for consumer health and industry practice

New packaging and freezing technologies offer consumers increased taste, safety, and nutrient preservation. As they adjust to sustainability requirements, they draw attention to the industry's need for stringent temperature control, reliable quality assurance, and more lucid labelling. Businesses that make these investments will be in the best position to satisfy changing consumer demands, environmental objectives, and health standards.

Final Exam Question

What is the effective strategy or strategies to decrease/minimize the lipid oxidation in frozen foods?

A)   Using Pro-oxidants

B)   Freezer temperature at 18°C

C)   Minimizing oxygen availability

D)   Two of the above

E)    All of the above

Answer:

C. Lipid oxidation occurs when the available oxygen can interact with fat which increases the lipid oxidation instead of slowing it down, therefore it is important to decrease/minimize the oxygen availability. This will not change the overall taste, smell, texture, and not produce this unpleasant rancid flavour. Using pro-oxidants will also increase the lipid oxidation process where antioxidants will slow this process down. Being able to maintain a constant freezer temperature at -18°C and not positive +18°C will help decrease the lipid oxidation.

Reason: This question should be on the final exam because it ties back to some of the content in the lessons (2.2.2.4, 5.5, 7.3) we learned about and there are some tricky answers that requires you to thoroughly read the question and most importantly the answers.

References

  1. Frozen Storage - an overview | ScienceDirect Topics. (n.d.). Sciencedirect.com. https://www.sciencedirect.com/topics/engineering/frozen-storage
  2. Lee, S. (n.d.). The chemistry of frozen foods. https://www.numberanalytics.com/blog/chemistry-frozen-foods-freezing-storage
  3. Lipid Oxidation - an overview | ScienceDirect Topics. (2010). Sciencedirect.com. https://www.sciencedirect.com/topics/medicine-and-dentistry/lipid-oxidation    
  4. Encyclopaedia Britannica. (2025, July 28). Food preservation. In Encyclopaedia Britannica. https://www.britannica.com/topic/food-preservation
  5. Romanowski, P. (2006). TV Dinner. In How Products Are Made (Vol. 5). The Gale Group Inc. Retrieved August 11, 2025, from https://www.madehow.com/Volume-5/TV-Dinner.html
  6. Course:FNH200/Lessons/Lesson 07
  7. Manaker, L. (2024, May 4). Does microwaving your food destroy its nutrients? Here's what dietitians say. EatingWell. Retrieved August 11, 2025, from https://www.eatingwell.com/microwaves-and-nutrients-loss-8643592
  8. Harvard Health Publishing. (2021, August 17). Microwave cooking and nutrition. Harvard Health. Retrieved August 11, 2025, from https://www.health.harvard.edu/staying-healthy/microwave-cooking-and-nutrition
  9. Brown, E. F., Gonzalez, R. R., Burkman, T., Perez, T., Singh, I., Reimers, K. J., & Birla, S. L. (2020, April 23). Comparing nutritional levels in a commercially‑available single‑serve meal using microwave versus conventional oven heating. Journal of Microwave Power and Electromagnetic Energy, 54(2), 99-109. https://doi.org/10.1080/08327823.2020.1755483
  10. Kumar, Y., Tiwari, S., & Kumar, Y. (2018). Cryogenic Freezing Technology. Int. J. Pure App. Biosci., 6(2), 1343-1346. http://dx.doi.org/10.18782/2320-7051.6458
  11. Government of Canada. (2023). Food Packaging Regulations. https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/packaging-materials.html
  12. Global Data Route Analytics. (2025). Canada Frozen Food Packaging Trends Size and Share Analysis 2021 to 2038. https://www.openpr.com/news/4123670/canada-frozen-food-packaging-trends-size-and-share-analysis-2021
  13. Gerke, G. (2024). "Changing Consumer Attitudes on Sustainability Means More Solutions for Plastics" in Food Engineering. https://www.foodengineeringmag.com/articles/102653-changing-consumer-attitudes-on-sustainability-means-more-solutions-for-plastics
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