The best way to get the most out of spinach is to consume it in the form of a juice or smoothie, say researchers. That is, if you want to get as much lutein as possible, says a team from Linköping University in Sweden.
Lutein, an antioxidant, is a xanthophyll and one of six-hundred naturally-occurring carotenoids. Only plants synthesize lutein, especially green leafy vegetables. Spinach, kale, and yellow carrots are good sources of the antioxidant. Lutein and other carotenoids are also the basis for red feathers in birds.
Rosanna W. S. Chung, Per Leanderson, Nelly Gustafsson, and Lena Jonasson wrote about their study and findings in the journal Food Chemistry (citation below). They are all from Linköping University.
The researchers compared different ways of preparing fresh spinach. They focused on maximizing lutein levels in the finished food.
Lutein and patients with atherosclerosis
Atherosclerosis patients suffer from the narrowing of the arteries. Blood tests show that they have low-grade inflammation.
This inflammation is associated with an elevated risk of myocardial infarction. ‘Myocardial infarction‘ is the medical term for ‘heart attack.’
In a previous study, Linköping University scientists studied the role of lutein. They showed that the antioxidant can reduce inflammation in the immune cells of individuals with coronary artery disease.
The researchers also found that immune cells can store lutein. In other words, we can build up a reserve of the antioxidant in our bodies.
This finding made scientists wonder whether we could influence levels of lutein in the blood. In other words, would changes in dietary intake influence levels of lutein?
How to best obtain lutein
In this latest study, the research team focused on finding the best way to obtain lutein. They experimented with spinach because of its relatively high levels of lutein. Also, many people eat spinach.
As is the case with many nutrients, heat degrades the antioxidant.
Comparing preparation methods, temperatures, and heating times
Co-author, Lena Jonasson, a Professor in the Department of Medical and Health Sciences, and a Consultant in cardiology, said:
“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.”
The researchers wanted to simulate the most common preparation methods. So, they bought baby spinach at the local supermarket.
They fried, steamed, and boiled the spinach for up to ninety minutes. They also measured lutein levels at different times during cooking.
Spinach in a soup or stew, for example, is not heated for as long or to as high a temperature as spinach in a lasagne. That is why the research team compared several different heating times.
Boiling or frying
When we boil spinach, heating time matters, the authors said. Lutein levels decline over time when we boil spinach.
How we cook the spinach also matters. When we fry it, for example, most of the lutein degrades after just two minutes.
Reheating lunch boxes
In modern life, reheating lunch boxes in a microwave oven is extremely common. Microwaving the food to some extent compensated for the loss of lutein in cooked food, the researchers found. In the microwave oven, the spinach released more lutein as its structure broke down further.
Principal author, Rosanna Chung, a Postdoc Researcher at Linköping University, said:
“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 yogurt.”
“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.”
The Swedish Research Council and the Swedish Heart-Lung Foundation funded the study.
“Liberation of lutein from spinach: Effects of heating time, microwave-reheating and liquefaction,” Rosanna W. S. Chung, Per Leanderson, Nelly Gustafsson, and Lena Jonasson. Food Chemistry, Volume 277, 30 March 2019, Pages 573-578. DOI: https://doi.org/10.1016/j.foodchem.2018.11.023.