Spinach is a superfood, known to contain loads of nutrients in a low-calorie package. These dark, leafy greens are important for skin, hair and bone health, while also providing essentials like protein, iron, vitamins and minerals. However, taking advantage of all these nutrients is not possible, as much of these get lost in the cooking process. Recently, researchers from the Linköping University (Sweden) undertook the challenge of finding the best way to harness the antioxidant lutein from spinach and found that a smoothie or a juice is the best way to do so.
Lutein is a natural fat-soluble pigment found in plants, particularly in dark green vegetables. In an earlier study, these researchers had studied the role of lutein and discovered that it dampens inflammation in immune cells from patients with coronary artery disease (CAD). They also showed that lutein can be stored in immune cells; this means that it is possible to build up a reserve of lutein within your body. This led the researchers to wonder whether it is possible to influence the level of lutein in the blood by increasing its dietary intake.
In the latest study, the researchers have investigated which method of ingestion is the best way of obtaining lutein. Spinach was chosen for the fact that it contains comparatively high levels of lutein and is commonly eaten by many people. In the process of cooking, nutrients are lost; also, lutein degrades with the application of heat. “What is unique about this study is that we have used preparation methods that are often used when cooking food at home, and we have compared several temperatures and heating times. We have also investigated methods of preparation in which the spinach is eaten cold, such as in salads and smoothies.” says Prof Lena Jonasson, from the department of medical and health sciences at Linköping University who is also a consultant in cardiology.
The research team purchased baby spinach at a supermarket, to simulate methods of preparation that are often used in everyday life. They then subjected this spinach to methods such as frying, steaming or boiling for up to 90 minutes and measured the lutein content at different times. The team decided to compare different heating times in the lab as the spinach may be heated to varying temperatures depending on the type of meal being prepared.
The results indicated that heating time is critical when spinach is boiled; the longer it is boiled, the lesser lutein it retains. Similarly, the cooking method is also important - spinach fried at high temperatures loses a large fraction of the lutein after only two minutes. A very common practice in modern life is to reheat lunch boxes in a microwave oven. Researchers found that this reheating in a microwave explains, to some extent, the loss of lutein in cooked food. They explain that more lutein is released from the spinach as the plant structure is broken down further by the microwave.
“Best is not to heat the spinach at all. And even better is to make a smoothie and add fat from dairy products, such as cream, milk or yoghurt. When the spinach is chopped into small pieces, more lutein is released from the leaves, and the fat increases the solubility of the lutein in the fluid,” says Dr Rosanna Chung the lead author of the study.