The study, published in the Journal of Dairy Science, noted that while polyphenolic compounds found in tea may have potential anti-cancer effects, their use is limited by poor bioavailability and disagreeable taste.
However, when diluted in skimmed milk or other milk complexes EGCG - the major extractable polyphenol in green tea - remains bioactive and continues to reduce colon cancer cell growth in cell cultures.
"In order to exert their biological health benefits in vivo, polyphenols must be available and still active, even when present in a food matrix," commented Dr Sanaz Haratifar from the University of Guelph, Canada. "This study showed that the binding of EGCG to the casein micelles did not affect the bio-efficacy of EGCG and cell uptake at concentrations higher than 0.03 mg of EGCG/mL of skim milk."
"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," added Haratifar.
In one experiment, human colorectal cancer cells (HT-29) were grown for 24 hours in the presence of EGCG in water or dispersed in milk. The number of living cancer cells (cell viability) was then measured - with Haratifar and team finding that EGCG reduced cell viability in a dose-dependent fashion. However the team noted that at higher concentrations (0.15 mg/mL and above), the anti-proliferative effect of EGCG in water was greater than in milk.
A second experiment evaluated cancer cell growth after EGCG was added to different milk products, including skimmed milk, milk whey, and milk serum.
While some differences were noted in cell proliferation at lower concentrations between EGCG in control medium and EGCG diluted in the milk components, at higher EGCG concentrations of 0.8 mg/mL and above the compound was found to reduce cancer cell growth by 80% or more, whether diluted in milk or not.
"This study showed that the binding of EGCG to the casein micelles did not affect the bioefficacy of EGCG and cell uptake at concentrations higher than 0.03 mg of EGCG/mL of skim milk," said the team. "Cell proliferation results showed that the EGCG-milk complexes were still able to significantly decrease the proliferation of HT-29 cancer cells, similarly to free EGCG."
"It is important to note, though, that the present studies were carried out on fresh EGCG. Mixed systems may ensure better stability to tea catechins with storage and during digestion, ultimately improving their bioefficacy," they concluded.
Source: Journal of Dairy Science
Published online ahead of print, doi: 10.3168/jds.2013-7263
"Antiproliferative activity of tea catechins associated with casein micelles, using HT29 colon cancer cells"
Authors: S. Haratifar, K.A. Meckling, M. Corredig