How to prepare meals to preserve nutritional value?
Vitamins and minerals can be obtained from food and supplements. How do you prepare a meal without losing its nutritional value? Find out!
Vitamins and minerals are essential for the proper functioning of the body. They can be obtained from food and supplements. Food preparation can be divided into two stages: preliminary processing and main processing. What do these stages involve and how do they affect the food? How do you prepare a meal without losing its nutritional value? How do you choose kitchen equipment and cooking methods that are beneficial for health, well-being, and taste? Find out!
Every product we consume contains specific substances needed for the proper functioning of the body – nutrients. In addition to essential nutrients, a product may also contain substances that limit or even prevent the body’s use of nutrients from consumed products or have a harmful effect on the body.
What is the nutritional value of a product?
Nutritional value is the measure of how well a given food meets the body’s needs for metabolic processes. We distinguish:
- Products with high nutritional value, which provide many nutrients (e.g., vegetables, eggs, nuts, fruits, whole grain carbohydrates, etc.)
- Products with low nutritional value, which are poor in essential nutrients (e.g., sugar, alcohol, etc.)
Preliminary processing
This is the first fundamental stage of meal preparation. Preliminary processing aims to remove all impurities and shape the products appropriately. This phase prepares the product for final processing. The most common types of preliminary processing include:
- Thawing
- Cleaning
- Washing
- Rinsing
- Portioning
- Sorting
- Peeling
- Cutting
- Chopping
Thermal processing
This is the second essential part of the meal preparation process, involving the heat treatment of food. It can change the consistency, appearance, color, chemical composition, and taste of the food. The most common types of thermal processing include:
- Stewing
- Blanching
- Steaming
- Boiling
- Microwave cooking
- Baking
- Grilling
- Frying
- Roasting
What can be achieved through thermal processing?
- Deactivation of microbial contaminants: Pathogenic bacteria (e.g., Salmonella, Shigella, Escherichia) in food are often killed during proper thermal processing.
- Deactivation of enzymes in food: Enzymes, which are proteins or glycoproteins produced by organisms, exhibit catalytic properties. They are used as food additives. Deactivation occurs when the enzyme is exposed to conditions it does not normally function in, such as temperature changes, high or low salt levels, or pH changes.
- Increased shelf life: Pasteurization is the best-known home method for preserving food. The shelf life of food products varies, with some being very perishable (e.g., vegetables, fruits, meat, milk). Proper pasteurization allows these products to be enjoyed for many months.
- Increased nutrient absorption: Thermal processing can make nutrients more absorbable, and sometimes increase their content. Examples include carotenoids (found in carrots) and lycopene (found in tomatoes), whose availability increases with heat treatment.
- Improved digestibility: Foods containing starch (e.g., potatoes) become digestible through thermal processing due to gelatinization. Heat treatment of proteins in meat also enhances digestibility, making cooked meat easier to digest than raw meat.
- Removal of anti-nutritional substances: Thermal processing often removes anti-nutritional substances. Examples include starch in potatoes or protease inhibitors in many legumes. Raw foods containing these substances are inedible, but they can be safely consumed after heat treatment.
- Achieving variety: Using different thermal processing methods allows the same product to be served in various ways, altering its effect on the body. For instance, chicken meat can be boiled, baked, or fried, each resulting in different flavors and nutrient content.
Stewing
A thermal processing method combining searing (brief frying to brown the surface, create aromatic, flavorful, and colorful substances, and retain more water inside the product) and cooking in a small amount of water or a prolonged cooking process in a small amount of water and fat (without searing). Stewing uses pots with fitted lids to prevent steam from escaping, which penetrates the food tissues, accelerating the softening process. Stewing can achieve enzyme deactivation, reduction of microbial contamination, and improved digestibility.
Blanching
A thermal processing method involving immersing the product in boiling water for several seconds to a few minutes, then cooling it quickly in cold water or ice water. Blanching is mainly performed on delicate vegetables and fruits to preserve their vitamin content and intense color. This method is often used in Asian cuisine and before freezing. Blanching can achieve enzyme deactivation, reduced microbial contamination, and improved food texture. Blanching can be done by:
- Immersing in hot water with a salt or sugar solution.
- Using steam.
- Microwave heating.
Steaming
A thermal processing method that involves placing the product on a sieve, perforated insert, or basket over boiling water and covering it for a short time. Steaming is mainly used for preparing delicate vegetables, certain types of dumplings (e.g., yeast dumplings, baozi, idli), or reheating previously prepared meals (e.g., dumplings, rice). This method prevents the loss of minerals and some vitamins while preserving the intense color of vegetables. Steaming is similar to classic boiling, but since the product is not submerged in water, vitamin and mineral losses are significantly lower.
Boiling
The most popular thermal processing technique involves bringing water to a boil (100°C) and maintaining it at this temperature for the desired time. During this process, proteins in the food coagulate, and starch gelatinizes, making the ingredients digestible. The proper boiling temperature ensures that no harmful decomposition products form in the dish. Boiling can achieve:
- The transfer of food components from the cooked product to the broth, desired in soup preparation. To achieve this, boil for a long time in a large amount of water, starting at a low temperature.
- Retaining nutrients in the cooked product by boiling in a small amount of boiling water for no longer than indicated.
Microwave Cooking
A thermal processing method involving heating food in a microwave oven by exposing it to microwaves. Microwaves cause water molecules in the food to rotate, dissipating energy and increasing the food’s thermal energy, raising its temperature. Food must contain water, a property shared by almost all kitchen-prepared dishes. Metal objects (including aluminum foil) should not be placed in a microwave oven as they can cause arcing, leading to potential fire hazards. Closed containers (e.g., bottles, jars) and eggs in shells should not be microwaved as steam and boiling increase pressure, causing explosions and significant contamination or even damage to the microwave. Nutritional losses in microwave-cooked meals are comparable to standard thermal processing methods. For the best taste and texture, use the microwave at the lowest possible power and the longest heating time, though this compromises the microwave’s speed advantage.
Baking
Alongside boiling, baking is one of the most popular thermal processing techniques. It involves heating food in an oven or furnace with hot air at temperatures usually between 160 to 250°C. Depending on the type and size of the dish, baking can last from a few minutes to several hours. During baking, proteins coagulate, and starch gelatinizes, making the ingredients digestible. Water loss also occurs. In the outer parts of the dish subjected to high temperatures, Maillard reactions occur, forming compounds from fats, proteins, and sugars. These compounds give the dish a specific taste and appearance but are not digested by the human body. Excessive consumption can be unhealthy. Baking in „closed” environments (e.g., in a baking dish, foil) can help, similar to steaming.
Grilling
A thermal processing method that involves placing food on a grill directly above a heat source. Types of grills include charcoal, gas, and electric. Grilling is mainly used for preparing meats, fish, and vegetables. Depending on the grill type, different flavor profiles can be achieved. Gas and electric grills have features that prevent fat combustion from prepared products, avoiding the emission of harmful substances, making them healthier than charcoal grills.
Frying
A prevalent thermal processing method involves heating food directly on a pan, usually with added fat. Some foods can be fried without added fat. Frying temperatures range from 150 to 200°C. Maillard reactions occur, forming a crust that prevents excessive water loss from the food. Frying introduces breakdown products of fats (mainly acroleins), which are considered harmful. Frying involves both positive and negative processes, such as protein coagulation and starch gelatinization, making ingredients digestible. However, higher temperatures, longer frying times, and more fat usage can produce more harmful compounds.
Roasting
A thermal processing method that aims to bring out new flavors and aromas, typically used for seeds, grains, and leaves. Roasting can be:
- Gentle at 140-160°C.
- Proper at over 160°C.
Every thermal processing method has benefits and potential risks. Higher heating temperatures cause more vitamin losses, but processing time can compensate for high temperatures. The time and temperature should be ideally matched to heat the product or coagulate enzymes (e.g., proteins) throughout without adverse combustion processes. The minimum internal temperature is crucial for preparing meats and starchy products, especially during frying. Food thermometers can be helpful. For meats and fish, the internal temperature should be around 70-100°C (depending on the type) to deactivate enzymes or microbial contaminants. The chosen method should be ideal for the specific product.
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