In this brief guide, we are going to answer the question “how to preserve nutrients while cooking” and discuss the different methods of preserving nutrients while cooking.
How to preserve nutrients while cooking
Nutrients can be preserved by using cooking techniques such as steaming, microwaving and baking. Blanching food before storage will also preserve its nutrient content. All these techniques use either minimum heat or minimum amount of water.
In 2019, approximately 10.5% (or 13.7 million) US households experienced food insecurity; however, in the early months of the coronavirus disease (COVID-19) pandemic approximately one-quarter to one-third of all Americans, and 44% of low-income Americans, were estimated to experience food insecurity (1).
What are the nutrients destroyed while cooking
Nutrients that are most affected by cooking include minerals, water-soluble vitamins and fat-soluble vitamins. Cooking is responsible for losses of vitamins and minerals in foods. However, the bioavailability of some minerals, for example iron, may be increased by cooking. Thiamin and Vitamin C are heat sensitive. Loss of vitamins and minerals from vegetables is mainly because of extraction into the cooking liquid rather than their destruction (2). Fat-soluble vitamins and essential polyunsaturated fatty acids (PUFA) are nutrients that are sensitive to heat treatment and oxidation and therefore can be partly lost during cooking. It is well-documented that a long-term deep-frying process leads to a substantial degradation of PUFA and vitamins in a frying medium (5).
- Minerals: Minerals include sodium, calcium, potassium and magnesium (3).
- Water-soluble vitamins: Vitamins B and C are water-soluble. Cooking techniques that use a lot of water such as boiling causes a loss of these vitamins (4).
- Fat-soluble vitamins: Vitamins A, D, E and K are fat-soluble. Cooking techniques that use a lot of fat such as deep-frying causes a loss of these vitamins.
How to preserve the nutrients while cooking
- Steaming: Steaming is generally the best cooking technique to preserve nutrients.
During steaming, food is kept separate from water so that nutrients remain in the food without leaching into the water. Slicing the vegetables before steaming will reduce the cooking time and retain more nutrients. Care must be taken not to slice into very small pieces as this exposes more surface area, causing more nutrients to be lost. Using minimal cooking water and cooking for shorter time periods should result in higher vitamin C retention (6).
A drawback of steaming is that it doesn’t add much flavour to food and the food may taste bland. This can be remedied by adding extra seasonings such as salt, pepper and spices.
- Microwaving: Microwaving is a convenient and safe method to cook food while preserving nutrients. Microwaving is also suitable for preserving the nutrients as it uses a minimal amount of water and has a short cooking time and lower temperature. Microwaving also preserves the antioxidants in food such as mushrooms and garlic. In a study, microwaving could retain more vitamin C than steaming and boiling or blanching of vegetables (6).
- Roasting and baking: Both roasting and baking involve the use of dry heat to cook. This could negatively affect thermal stable vitamins, such as vitamin C and Thiamin (2).
The term roasting usually refers to meat while baking refers to vegetables, bread and baked desserts.
Since these techniques do not use water, the loss of most nutrients is reduced. However, high temperatures and long cooking times may break down some nutrients. The content of vitamin C in meat products will reduce during baking and roasting due to the high temperature.
- Blanching: Blanching is the process of immersing food in boiling water and then transferring it into an ice water bath. Blanching reduces the enzyme activity in food that cause changes in flavour, colour and texture. Blanching also reduces the loss of nutrients during storage, thus it is a.thermal treatment designed to inactivate a target enzyme to a given extent, preventing the formation of negative compounds during storage (8). Blanching of broccoli, spinach and beetroot has been reported to cause substantial losses of folate and the extent seems to depend on the time and amount of water used (7).
What destroys the nutrients
- Incorrect storage conditions: Storing both raw and cooked food under the proper recommended storage conditions will minimise the loss of nutrients. Storing raw fruits and vegetables exposed to sunlight or in a warm environment may destroy the nutrients (9).
- Incorrect cleaning method: Fruits and vegetables must not be soaked in water (10). Loss of water-soluble nutrients can be minimized by scrubbing off the loose soil and dirt under cool, running water and using a paper towel to pat dry.
- High temperature: High temperatures are responsible for destroying most of the nutrients while cooking. Opt for cooking methods that use low heat. Nutrients may be destroyed or lost when foods are processed because of their sensitivity to heat, light, oxygen, pH of the solvent or a combinations of these (2).
- Too much water: Water-soluble nutrients such as Vitamins B and C are unstable and will leach out of food and degrade easily. To minimise the loss of water-soluble nutrients, use cooking methods that need less water such as microwaves (6).
Cooking vegetables without peeling will also reduce the quantity of vitamins lost by leaching to water.
If you are using a cooking technique that used a lot of water such as boiling, try to use the left-over water as a stock for a soup.
- Incorrect cooking method: Methods such as grilling and broiling are commonly used to cook meat products due to the unique flavour they produce. However, both grilling and broiling reduce the content of minerals and vitamin B in meat by about 40% (2).
Frying is another technique that significantly reduces the nutrients of the food (5). For example, deep-frying fish such as tuna reduces the content of omega-3 fatty acids by 70 – 85%.
- Freezing and defrosting: Freezing fruits, vegetables and meat for long periods and then defrosting them will cause a loss of nutrients. This applies to both raw and cooked food. The losses occur by the leaching of vitamins and minerals due to cell disruption rather than the freezing itself. Because of this, fast freezing is less negative (8).Especially with cooked vegetables, try to consume them within 2 days after cooking to get the maximum nutrient content .
- Using baking soda: Certain recipes recommend the use of baking soda when cooking vegetables as it retains the colour of the vegetables. However, baking soda also creates an alkaline environment that causes the loss of vitamin C (11).
In this brief guide, we answered the question “how to preserve nutrients while cooking” and discussed the different methods used to preserve nutrients while cooking.
If you have any questions or comments, please let us know.
- Wolfson, Julia A., et al. Food Insecurity and Less Frequent Cooking Dinner at Home Are Associated with Lower Diet Quality in a National Sample of Low-Income Adults in the United States during the Initial Months of the Coronavirus Disease 2019 Pandemic. J Acad Nutr Diet, 2022.
- Severi, S., et al. Effects of cooking and storage methods on the micronutrient content of foods. Eur J Cancer Prev, 1997, 6, S21-S24.
- Kimura, Mieko, and Yoshinori ITOKAWA. Cooking losses of minerals in foods and its nutritional significance. J Nutr Sci Vitaminol, 1990, 36, S25-S33.
- Rumm-Kreuter, D., and I. Demmel. Comparison of vitamin losses in vegetables due to various cooking methods. J nutr sci vitaminol, 1990, 36, S7-S15.
- Hrncirik, Karel. Stability of fat‐soluble vitamins and PUFA in simulated shallow‐frying. Lipid Technol, 2010, 22, 107-109.
- Lee S, Choi Y, Jeong HS, Lee J, Sung J. Effect of different cooking methods on the content of vitamins and true retention in selected vegetables. Food Sci Biotechnol. 2017, 27, 333-342.
- Stea, Tonje Holte, et al. Retention of folates in cooked, stored and reheated peas, broccoli and potatoes for use in modern large-scale service systems. Food Chem, 2007, 101, 1095-1107.
- Evans, Judith A., ed. Frozen food science and technology. John Wiley & Sons, 2009.
- Nhlapo, Nthabiseng. Hygiene and nutritional content of the national school nutrition programme in Bloemfontein, South Africa. Diss. Central University of Technology, Free State, 2013.
- Afify, Abd El-Moneim MR, et al. Biochemical changes in phenols, flavonoids, tannins, vitamin E, β–carotene and antioxidant activity during soaking of three white sorghum varieties. Asian Paci J fTrop Biomed, 2012, 2, 203-209.
- El-Ishaq, Abubakar, and Simon Obirinakem. Effect of temperature and storage on vitamin C content in fruits juice. Int j Chem Biomol sci, 2015, 1, 17-21.