5 Vegetables Cooking Increases Their Antioxidants

How do you like your vegan dish, raw or cooked? If you believe that cooked fruits and vegetables have less antioxidant properties, the answer is that it’s not always like this.

Many vegetables are vital sources of natural antioxidants such as vitamins E and C, carotenoids, phenolic compounds, which help to keep healthy and to prevent heart attacks and cancer. Followed by processing and cooking, different agents affect the antioxidant activity influencing eating habits and health.

Cooking, particularly frying, of most fruits and vegetables results in formation of free hydroperoxide radicals, acceleration of breaking of antioxidants like vitamin C, and reduction of phenols by up to 70–80 percent, but boiling, streaming, or using microwave at about 5 minutes leads to inhibit oxidation of antioxidants in some vegetable cultivars due to inactivation of oxidative enzymes and addition of water-soluble antioxidants like phenols. This contradiction is caused by:

• Releasing fairly high values of antioxidants and phenols because of thermal decomposition of the cell wall and intracellular components.

• Breaking complicated phenols, e.g. tannin, into simple substances.

• Releasing phenols from proteinaceous structures during cooking vegetables owning to a structural change of the plant cell, matrix change, or inactivation of polyphenol oxidases—arresting oxidation and polymerization of phenols.

• Producing stronger radical-scavenging antioxidants through thermal chemical reactions.

• Preventing oxidative capacity of antioxidants by thermal inactivation of oxidative enzymes.

• Producing new non-nutrient compounds such as Maillard reaction products with antioxidant activity.

So, should we eat such vegetables in cooked? However, vegetable cultivars and the cooking method should be considered. In this article, you will be familiar with the good behavior of some fruits and vegetables to the heat of the cooking to keep the antioxidants.

1. Artichoke

The edible flower artichoke is a common vegetable in the Mediterranean diet. This vegetable has potentially healthy properties including protection of liver and inhibition of cholesterol formation in liver.

The cooking methods in the recipes with artichoke differ as increased phenolic content by 66, 71, and 94 percent through 5-minute boiling, 5-minute frying—at 170 degrees centigrade, and 20-minute streaming, respectively.

Nevertheless, if you want to receive more antioxidants of artichoke, the steamed food has more antioxidant activity, 15 times, than those of boiled, 8 times, and fried, 7 times. Moreover, carotenoids undeniably contribute to increased antioxidant activity, even though it is negligible. Amounts of carotenoids increase by 7 times in boiled, by 6 times in streamed, and by 4 times in fried artichokes (Ferracane et al., 2008).

2. Eggplant

Eggplant is a native vegetable of subtropics and tropics but owns interesting healthy properties like blood-fat-lowering effects due to various phytochemical compounds such as phenols, flavonoids, and anthocyanins, e.g. nasunin. Boiling eggplant for 30 minutes increases the antioxidant activity by up to 2.5 times; this reaches to 4 times using microwave just in 3 minutes (Jiménez-Monreal et al., 2009). However, this is not only the solution to achieve further antioxidants of eggplant, but pressure-cooking, baking, and even frying can also be used (Yamaguchi et al., 2001).

3. Tomato

Tomato contains significant amounts of vitamins C and E, carotene, lycopene, and folate—about 70 percent of them is found in the pericarp (Gahler et al., 2003). You might expect that the cooking eliminates these compounds, but tomato exposed at about 90 degrees centigrade in 15 minutes has more amount of lycopene over 1.5 times; thus, absorption of lycopene is more in the cooked tomato than in the raw one. The antioxidant activity also increases by 60 percent in 30 minutes likely due to releasing antioxidants from the plant tissue. The largest increase in antioxidant values during cooking is related to tomato seeds (Dewanto et al., 2002).

4. Pumpkin

Although pumpkin is botanically a fruit, it is referred to as vegetable among consumers. Its flesh and seeds have dietary and medicinal uses, enriched from starch, free sugars, and vitamins B1, B2, and C as well as bioactive materials such as beta-carotene.

Generally, streaming pumpkin in 10 minutes increases its phenolic content by about 40 percent and its antioxidant activity over 30 percent (Adefegha et al., 2011). On the other hand, both boiling and frying in 5 minutes increases amounts of beta-carotene approximately 2–4 times and lycopene 17–40 times—the main agents of the orange color of a pumpkin.

In comparison with frying, boiling retains more carotenoids because they are dissolved in oil during frying probably owning to the more solubility in oil, entailing the reduction of them in pumpkin. Furthermore, the boiled pumpkin undergoes less temperature than the fried one with 180 degrees centigrade (Azizah et al., 2009).

5. Sweet Corn

Sweet corn as a type of grains is the main source of carbohydrates in many foods. For choosing an eating method of this foodstuff, you should know that frying at 170 degrees centigrade up to 5 minutes, using a microwave at about 80 degrees centigrade up to 1 minute, and boiling up to 5 minutes increases sweet corn carotenoids by 1.8, 1.6, and 1.3 times, respectively.

Although frying of sweet corn doesn’t affect on the phenolic content, boiling and microwave enhance the phenolic content by 1.2 and 1.9 times in time-independent, respectively. The antioxidant activity change in sweet corn also has a constant rate when cooking and increases up to 15 percent in method- and time-independent. The enhancement in the antioxidant activity is probably due to releasing phytochemical compounds like ferulic acid from cells interacting with water-soluble antioxidants.

Aside from the fire, freezing also improves the antioxidant properties of sweet corn; so, the freezing increases carotenoids of the maize and positively influences the bioavailability and healthy properties since the freezing is believed to exude water from the maize up to 5 percent, resulting in increased carotenoids, phenolic compounds, and antioxidant activity by about 30 percent. The bad news is that cooking frozen corn decreases 47–80 percent of phenolic content and 10–39 percent of carotenoids (Song et al., 2013).

These five cases are to illustrate the positive role of heat on the antioxidant activity of vegetables. Oppositely, there are further vegetables including turmeric, mint, carrot, broccoli, and celery the antioxidant activity of which doesn’t undergo so big change. Now, you can meal hot foods prepared from the vegetables above with peace of mind.