Green Tea Polyphenols Are Bioactive When Consumed in Milk

Green tea polyphenols are often studied for their cancer-fighting effects; unfortunately, these polyphenols also tend to be poorly bioavailable and taste bad, researchers say. In a new Journal of Dairy Science study, these researchers suggest milk as an effective delivery system for tea polyphenols, keeping the polyphenols bioactive and enabling them to continue reducing cancer cell proliferation-specifically, colon cancer cells.

Catechins are the main polyphenols in green tea (comprising up to 85%). Epigallocatechin gallate (EGCG) is considered the most biologically active of the green tea catechins. But the researchers say there are various reasons why polyphenols, including EGCG and green tea catechins, may still be poorly bioavailable. Reasons can include molecular structure and intestinal absorption.

Additionally, the type of food delivery system can impact polyphenol bioavailability. “[T]he interactions between the bioactive molecules and the food matrix are considered critical factors limiting or enhancing bioavailability,” the researchers wrote.

In the study, EGCG was nanoencapsulated and dispersed in milk samples. In one experiment, human colorectal cancer cells were grown for 24 hours in the presence of the EGCG in milk. Researchers then tallied the number of living cancer cells. When in milk, EGCG continued to reduce the viability of cancer cells. This decrease happened in a dose-dependent manner, meaning the higher the EGCG concentration (higher than 0.03 mg of EGCG/ml of milk), the higher the decrease in cancer cell proliferation. (This effect plateaued at very high concentrations, however.)

The researchers also tested EGCG’s effect on cancer cell proliferation in different types of milk samples-skim milk, milk whey, and milk serum-and again found that EGCG reduced cancer cell proliferation.

How does milk help keep EGCG bioactive? It may have to do with the way polyphenols bind to milk proteins (casein micelles), researchers said. “Polyphenols are known to have strong affinities to proteins rich in proline and proteins with an open and flexible structure, such as caseins….Protein and polyphenol interactions are driven by hydrogen bridging between the phenolic hydroxyl and peptide carbonyl, as well as interactions between hydrophobic amino acid residues and the phenolic rings.”

“These results support a new role for milk as an ideal platform for delivery of bioactive compounds and opens the door to a new generation of dairy products providing additional benefits to human health,” said the study authors Sanaz Haratifar and Milena Corredig from the University of Guelph in Ontario, Canada.       

It’s important to ensure that polyphenols can still deliver their benefits in functional foods. “In order to exert their biological health benefits in vivo, polyphenols must be available and still active, even when present in a food matrix,” said Haratifar and Corredig.

Encapsulating EGCG in the milk did not lower EGCG’s bioaccessibility either. “As casein micelles may act as protective carriers for EGCG in foods, it was concluded that nanoencapsulation of tea catechins in casein micelles may not diminish their antiproliferative activity on colon cancer cells compared with free tea catechins,” they wrote.

Nanoencapsulation may also combat some of the “off taste” issues associated with polyphenols when used in food products. “Sensory studies have shown that caseins…due to their strong binding ability to tea catechins, decrease the sensation of astringency caused by the tea polyphenols,” the researchers wrote.

The Ontario Dairy Council and the Natural Sciences and Engineering Council of Canada funded the study.