Most effective liquids to increase antioxidant content of spinach smoothies

LINKOPING (SWEDEN): When it comes to releasing the antioxidant lutein from spinach in smoothies, different market goods have extremely variable results. Only four of the 14 common dairy and plant-based products studied by researchers at Linkoping University in Sweden increased lutein liberation. Some drinks had a negative effect on the lutein content of spinach smoothies when compared to water.

Most individuals are aware that spinach is beneficial to one's health. Lutein, for example, is a chemical present in spinach and kale. Several experimental studies have shown that lutein can suppress inflammation-related processes, and there is now abundant evidence that chronic low-grade inflammation is an important risk factor in cardiovascular disease.

"Lutein is a bioactive substance. We investigated lutein in the same way that we would investigate a pharmaceutical medication. "We looked at lutein liberation from fresh spinach in this study," explains Rosanna Chung, assistant professor at Linkoping University's Department of Health, Medicine, and Caring Sciences, who led the study published in Nutrients.

As our bodies cannot produce lutein, the researchers behind the study were interested to find out how to optimise lutein intake from foods. The research group previously showed that preparation methods where the spinach is heated break down some of the lutein, whereas mixing it into a smoothie makes more lutein available for absorption.

The type of liquid used in the smoothie can also affect lutein content. As lutein dissolves in fat but not in water, it needs gastric juice and/or other food components to be liberated from the plant material and absorbed by our intestines.

The researchers suspected that some components in our food, such as fat, carbohydrates, proteins and fibres, can affect the amount of lutein available for absorption.

The effect of products such as yoghurt may also differ due to fermentation. However, products widely available on the market are rarely examined in scientific studies.

The researchers have examined the effects of various products available from food shops on the amount of lutein liberated in smoothies. Both dairy and plant-based liquids were tested. The researchers blended spinach with various products.

They then used a method simulating human digestion in the gastrointestinal tract, by adding digestive enzymes. Finally, the amount of lutein available for the body to absorb in smoothies made with various products was compared to that in smoothies made with just water.

"We could see that only 4 of the 14 examined products increased the liberation of lutein from spinach compared to water. Cow's milk with a high-fat content as well as coconut milk improved lutein liberation. Yoghurt, however, which is regarded as comparable to cow's milk and is often used in cafes and similar, did not show particularly good results," says Rosanna Chung.

The fact that yoghurt is not that good at liberating lutein may have to do with the fermentation process. It also turned out that plant-based drinks, often made from nuts, legumes or oats, showed significantly different results.

"Plant-based liquids have become increasingly common in smoothies. We saw that soymilk was actually less effective than water when it comes to liberating lutein in spinach smoothies. In other words, soymilk had a negative effect on lutein liberation in our study," says Jan Neelissen, a doctorate student and one of the researchers behind the study.

The other plant-based products in the study did not affect lutein liberation compared to water. As a general piece of information, smoothies should be consumed as soon as possible, because lutein breaks down quickly.

It is important to note that whereas the results from this study indicate how much lutein is available for the body to absorb, no conclusions can be drawn as to how much lutein is actually absorbed. Therefore, the researchers will be conducting a human study in which they will measure the amount of lutein absorbed from smoothies made with different products.