By Pooja Sainarayan

Local Journalism Initiative

Food preservation has been a practice since ancient times, and basically refers to the process of safely lengthening the lifespan of food while maintaining as much of the nutrient quality as possible. There exists various methods – drying, smoking, salting, freezing, canning, pickling and more. With the increasing demand for fresh food and reducing overall food waste to promote a healthier environment, preservation has become increasingly important in food independence and culture.

One of the oldest methods of food preservation is dehydration. By removing moisture from food, the bacterial growth is inhibited. Depending on the humidity of your location, this method may prove to be a challenge. However, if humidity is an issue, dehydration followed by freezing the food may be the best technique to prevent bacterial growth. Storing dehydrated food in airtight containers is important in maintaining the dehydration levels. Modern-day methods such as water-bath canning which uses heat to kill any bacteria or enzymes in the food products is commonly used for high-acid foods such as tomatoes and fruit jams/jellies. Similarly, pressure canning used for low acid-foods such as vegetables and meats is another method of processing product in a jar. Pickling uses high acid concentration through the pH preservation of food, which needs to be followed by water-bath canning to kill off any potential bacterial growth that remains in the jar. Finally, freezing food is also commonly used and is one of the most affordable methods of food preservation. Freezing slows down the growth of bacteria and enzymes but does not completely eliminate them. For this reason, thawing food in a refrigerator helps keep them safe. So how are the nutrient contents affected by various preservation techniques?

Some vitamins are less impacted by processing than others. Fat-soluble vitamins such as vitamin K, A, D and E are more stable during processing and storage than water-soluble vitamins (vitamin B and C). The most stable vitamins include vitamins B3 (niacin), K, D, B7 (biotin) and B5 (pantothenic acid). The most unstable vitamins are folate, thiamine (B-complex vitamin) and vitamin C. Food processing methods that expose food to high levels of heat, light or oxygen may cause the greatest loss in water-soluble vitamins such as vitamins B and C. However, the fat-soluble vitamins, minerals, protein, fat and carbohydrates would be less affected by processing methods using high heat, such as canning.

Pressure canning may preserve more vitamin content compared to water bath canning, as the food is subject to high pressures rather than heat. Dehydrating food can also reduce the amount of vitamin C, but it can result in higher nutrient contents such as fibre in plant-based foods. As the food becomes more energy-dense when it dries out, over-consuming dehydrated products may result in weight gain. If the dehydrated food is cooked with water, this results in more nutrient loss as they are leached out of the food and into the water. Freeze-drying is also commonly used to preserve food and conserves more nutrients than simple dehydration. In contrast to dehydrated food where roughly 75 per cent of the original nutrients are retained, freeze-dried foods retained approximately 95 per cent of its nutrient value. On the other hand, cooking food has lots of benefits such as breaking down parts of vegetables that are harder to digest, destroying harmful bacteria and releasing phytochemicals (chemicals produced by plants). For instance, phytochemicals are greater in cooked tomatoes than when consumed raw. Freezing food is a great way to preserve the nutrients. The nutrient losses are often due to the processing prior to freezing, such as blanching where the food is heated very quickly with steam or water. Onions, leeks, rutabaga and peppers do not need to be blanched prior to freezing and therefore results in high nutrient yield post freezing. The nutrient loss (mainly vitamins B and C) from blanching is generally only 10 to 20 per cent. Although canning may result in some nutrient loss, other nutrient content may actually increase. Therefore, canned foods and frozen foods are both a comparable means of preservation in terms of retaining the foods nutrient contents.

In summary, there is some vitamin and mineral loss with all preservation methods, but this is relatively minimal. The global impact of food preservation helps the environment by significantly reducing food waste. In addition, there is continual demand for fresh and sustainable food to meet the needs of producers and consumers. Food preservation also faces challenges, in ensuring safety, quality and effectiveness which requires continuous research and education to promote a healthy and durable food system.