Food is an essential life requirement related to every function our body performs. It is a source of nutritional components like vitamins, minerals, essential oils, and antioxidants which benefit our health in every possible aspect.
But every food has its specific shelf-life and gets spoiled after harvesting or slaughtering. Based on spoilage, foods are categorized as perishable: foods that deteriorate within 1- 5 days and need immediate freezing; semi-perishable: foods that don’t need immediate freezing and can be stored for 3 to 5 months; and non-perishable: foods stored for a much more extended period.
Foods need to be processed further to increase their shelf-life, prevent the growth of microorganisms, and preserve the food’s nutritional value, known as food preservation. The procedure includes altering atmospheric conditions, enzymatic reactions, chemical treatment, and food moisture.
Methods of Food Preservation
Food preservation is the natural or mechanical action performed on food to elongate its shelf life after harvesting or slaughtering. These procedures can reduce food deterioration by inhibiting microorganisms’ growth, enzymatic reactions, and auto-oxidation.
Food preservation by drying, dehydration, and fermentation is the oldest method, and cold treatment, heat treatment, blanching, irradiation, and canning are the modern methods.
Food preservation by the drying method has been followed for centuries. Drying refers to removing water from a solid compound (meat, fruits, vegetables, and nuts). Sun drying, solar drying, and air drying are the most performed drying methods. In industry, drum drying, spray drying, vacuum drying, freeze drying, bed drying, and convection air drying are also performed. Drying removes food’s moisture and prevents the growth of yeast, bacteria, and mold, which are responsible for damaging food quality.
Dehydration removes moisture (water content) from solid or liquid. It differs from drying because the application of artificial heat under a controlled atmosphere is performed. It is also an old method of food preservation. Dehydration makes food lighter and smaller. Dehydrated foods are preferred during trekking and traveling. Example: Mango, Broccoli, Beets, Grapes, Chicken Fish, etc.,
Food Preservation by Fermentation
Fermentation refers to the metabolic phenomenon of food preservation that occurs in the absence of oxygen. Bacteria and yeast are active microorganisms for the breakdown of components. Fermentation promotes the production of organic acids, alcohol, and carbon dioxide, preventing pathogens’ growth and preserving food. Fermented foods are rich in health-benefiting probiotics. Example: Tempeh, wine, tongba, cheese, kimchi, nato, yogurt, etc.,
Preservation by Cold Treatment
Food preservation by cold treatment includes chilling, freezing, and refrigeration.
Chilling is the food preservation method where food temperature is lower, above its freezing point but below atmospheric temperature. The chilling temperature is −1℃ to +8℃, depending upon the variety of food. Salads, pizza, seafood, and dairy products are preserved by chilling.
In freezing, the food is preserved by lowering its temperature below its freezing point. Butter, ice cream, milk, nuts, and grains are preserved by freezing.
Food preservation by refrigeration is when the food temperature is maintained between 0℃ and 8℃. Jam, jelly, pickle, and sauce are preserved by refrigeration.
Food Preservation by Heat Treatment
Food preservation by heat treatment includes sterilization and pasteurization.
Sterilization is a food preservation process where all the microorganisms and spores with minimal chances of causing spoilage are destroyed. Two methods do sterilization: i) Physical sterilization (cold sterilization, heat sterilization), ii) Chemical sterilization (gas sterilization, cold chemical sterilization). Meat, fish, cream, soup, and sauce are usually sterilized.
Pasteurization is a method where pathogenic bacteria and certain microorganisms are destroyed, and enzymes are inactivated by heating up to a specific temperature. There are two methods for pasteurization i)Batch pasteurization and ii)Continuous pasteurization. Milk, juice, almonds, and acidic canned foods are preserved by pasteurization.
Preservation by Blanching
Blanching is a type of mild-heat treatment (performed on fresh harvest) where the foods are exposed to hot water or steam to maintain their physical and physiological properties and extend the shelf-life. Blanching is usually performed before freezing, canning, or drying. Hot steam is preferred over hot water or high temperature to avoid the side effects of blanching (protein denaturation, damage to tissue cells). High-temperature treatment can make fruits and vegetables lose their color. So, to avoid that, sodium carbonate or calcium oxide is added to blancher water. Broccoli, fennel, green beans, and asparagus spears are preserved by blanching.
Preservation by Irradiation
Food irradiation is a treatment method that exposes the food to ionizing radicals (x-ray, gamma ray, and electron beam). It helps to reduce the harmful bacteria and parasites which can cause spoilage. Beef, pork, poultry, lettuce, eggs, coffee, fresh fruits and vegetables, and spices are approved for irradiation by FDA.
Food Preservation by Canning
Storing food in containers or jars by hermetically sealing (tightly closed to prevent air from entering) and sterilizing it with heat is canning. Canning prevents the growth of microorganisms and the activity of food enzymes that can spoil food. The containers are first sterilized, and the food is sealed by vacuum packaging. After that, the container is exposed to heat and cooled. Pressure canning, water bath canning, and steam canning are the methods of canning. Meat, dairy products, and sea foods are preserved by canning.
Importance of Food Preservation
Food preservation has much importance, mainly in preventing the spoilage of food. Spoilage reduces the quality of food. Some of the importance of food preservation are as follows:
- Preventing microbial growth: Stored foods become a great nutritional medium for the growth and colonization of microorganisms. Preservation methods remove some growth-promoting components, like moisture, warmth, etc., from the food, making the storage longer.
- Preserving nutritional components: Spoilage of foods degrades the quality of food. Applying preservative methods helps to maintain the dietary details of the food. Although some changes occur during preservation, the stored food is still nutritionally dense.
- Preventing physical and chemical damage in food: Preservation methods help avoid auto-oxidation and enzymatic reactions that occur in the foods. Heat and moisture can also cause food spoilage, and applying preservation methods can protect from such damage.
- Elongating shelf-life: Since food preservation methods help avoid spoilage of foods, they automatically elongate the shelf-life of perishable and semi-perishable foods.
- Save money: Time and again, buying food is the most significant area to spend money. Storage of nutrition for a more extended period means having consumable foods for longer. It means less expense in food which can help save cash.
Drawbacks of Food Preservation
Although food preservation is highly advantageous for long-term savings, it also has different drawbacks. Some of the disadvantages of methods of food preservation are as follows:
- Adding sugars and salts to preserve food can make the food unsuitable for consumption by people with different health conditions.
- Sometimes food preservation can lead to loss of nutrients as chemical and physical states may change after treatment with different preservation methods.
- Long-term use of preserved foods can lead to gastrointestinal disorders like gastritis and indigestion.
- Handbook of Food Preservation – Cold [Internet]. [cited 2023Jan18]. Available from: http://www.cold.org.gr/library/downloads/Docs/Handbook%20of%20Food%20Preservation.PDF
- Prokopov, Tsvetko & Tanchev, Stoyan. (2007). Methods of Food Preservation. 10.1007/978-0-387-33957-3_1.
- UGA [Internet]. [cited 2023Feb5]. Available from: https://nchfp.uga.edu/publications/usda/GUIDE01_HomeCan_rev0715.pdf