In an ideal world, every broccoli floret, every bite of an apple or every bowl of spinach should fill us with vitamins, minerals and antioxidants, and provide us with healthy iron. However, the journey that food follows from the garden to our plate is full of obstacles that can affect its nutritional value and leave it tasteless. On many occasions, this loss begins when it reaches our kitchen.
Plant foods are a very important source of micronutrients (vitamins and minerals) in our diet. These are the compounds that we need to eat because our body cannot manufacture them itself, and they are involved in many chemical reactions that occur in the body constantly.
The vitamins in fruits and vegetables perform important functions such as stimulating the immune system, strengthening bones and teeth, helping the skin stay healthy and allowing the body to metabolize proteins to build tissue and carbohydrates for energy. We are well aware of water-soluble vitamins, such as vitamin C and vitamin B (eg folic acid).
On the other hand, minerals such as potassium, magnesium, iron or calcium are elements that our body uses to maintain the balance of body fluids, strengthen bones, blood clotting, transport oxygen, and basic functioning of the nervous system. Besides vitamins and minerals, vegetables provide other compounds such as antioxidants and fibre, which help us prevent diseases and maintain our gut microbiota. That’s why we shouldn’t lose them.
How to cook without destroying nutrients?
In the kitchen, we use heat to make food more digestible, kill harmful bacteria, and improve its flavor. But this shift comes at a price. Cooking fundamentally changes the chemistry of food: sometimes it improves nutritional values, sometimes it makes them worse, and sometimes it improves some and worsens others.
“The ideal situation is that vegetables, like fruit, can be eaten raw to get that contribution of vitamins, minerals and fiber as well,” says nutritionist Isabelle Soria. “Obviously there are many foods that we have to cook. Steaming, grilling and baking are cooking methods that help preserve vitamins better. But when we boil something at a fairly high temperature, we lose those nutrients because they dissolve in the water, even though we can often drink that broth which also provides us with nutrients,” he adds.
Wet cooking, such as boiling vegetables, is likely to have the greatest negative impact on vitamins and minerals. When we cook broccoli in water for a long time, until it turns brown, vitamin C and B come out of the broccoli and remain dissolved in the cooking water.
If we use dry heat, as we do with baked or grilled vegetables, for example, the problem does not lie in the dissolution of the vitamins, but in the heat. Vitamin C decomposes at a temperature between 70 and 90 degrees Celsius, and the longer we heat food, the less amount remains. Folic acid loss begins at a temperature of 65°C, and at this temperature, it practically disappears within an hour.
The secret to cooking vegetables is to heat them for the shortest possible time and avoid direct contact with water. This is why steam cooking is one of the most respected techniques. Since the food does not come into contact with water, a much higher percentage of vitamins and minerals are preserved, in addition to maintaining the texture and bright color of the vegetables.
And the microwave? Contrary to what some people think, microwave cooking helps preserve more nutrients. Because microwaves penetrate the food, they heat it more efficiently and quickly, so there is less time for vitamins to break down and they don’t form a crust on the outside that is hotter on the inside. According to this study, microwaved foods contain the same levels of nutrients as steamed foods.
Foodstuffs don’t last forever
Just as important as cooking well is preserving food well. Over time, food decomposes, mainly due to the action of oxygen, enzymes, temperature, and bacteria. Various preservation methods seek to stop or slow this process, but also affect nutrients and flavour.
Cold is our preferred preservation method. Low temperatures in the refrigerator (about 4°C) slow down, but do not stop, the action of bacteria and enzymes that break down food. Freezing at around -18°C is most effective, because it turns the water in the food into ice, preventing microorganisms from multiplying.
However, cold has another danger: it affects the sensory properties, that is, the flavour, aroma and texture of the food, and can make it less appetizing. For example, refrigerated broccoli, although safe to consume, becomes more bitter and less appetizing as the days go by. Cold-preserved tomatoes become tasteless because the molecules responsible for their smell decompose. Storing chocolate in the refrigerator does not destroy the nutrients, but moisture and cold can cause the sugar to “bloom” (a white coating) and cause the chocolate to absorb odors from other foods, changing its aroma and flavour.
Freezing also has effects on flavor and texture. If freezing is not fast enough, the ice crystals that form are large and break down the cell walls in vegetables and meat. Broken cell walls allow water to escape as they dissolve, making food softer and harder to chew.
The solution is to freeze as quickly as possible, at the lowest temperature possible. Additionally, for vegetables that will be frozen, pre-blanching (immersing them briefly in boiling water and quickly in ice water) helps inactivate enzymes that, even in the refrigerator, can eventually deteriorate their color, texture, and flavor over time.
How to save nutrients and flavor from your leftovers
Let’s say we cook on the weekend all week using fresh or well-preserved produce. Unfortunately, we’re pretty sure Monday’s food will taste better than Friday’s. How can we better preserve the properties of already cooked foods?
The golden rule is to reheat only the part that we will consume and thus avoid reheating several times. Each heat cycle places new stress on unstable nutrients and greater loss of flavour.
“There are a lot of people who freeze pureed foods, for example,” Soria says. “But if you make zucchini cream, and keep it in a container that’s in a water bath and vacuum-sealed, it will preserve much better than if we do it in the refrigerator.” Nutritionists also recommend this method to preserve the flavor of dishes better.
In fact, to reheat refrigerated foods, if we put them in the microwave at maximum power, we may lose more of the flavor and nutrients. It is preferable to use milder options such as a bain-marie or steam, or alternatively, heat it in the microwave on medium heat and stir it several times, thus avoiding prolonged overheating.
“Not everyone knows how to thaw food well,” says Surya. He adds: “Putting the jar in the refrigerator without freezing it, and gently heating it in a bowl preserves the flavor and texture better than thawing.”
For Syria, “If you put a dish in front of you that has lost colour, flavor and smell, in the end, you will not feel like eating it.” Oddly enough, preserving the nutritional values of our food goes hand in hand with preserving food enjoyment, flavors and textures. You just have to know this technique well.