The researchers from the Justus-Liebig-University and the Geisenheim Research Centre in Germany compared the bioavailability of polyphenols such as anthocyanins (ACN) and their metabolites in anthocyanin-rich grape and blueberry juice (841 mg ACN/litre) and smoothie (983 mg ACN/litre) in the body as well as the uptake from grape and blueberry extracts in lab conditions.
Using plasma and urine samples of ten volunteers aged between 23 and 27 years, they found that plasma pharmacokinetics and recoveries of urinary metabolites of ACN did not differ between juice or smoothie. However, the bioavailability of phenolic acid 3,4-DHB was significantly better for juice compared to smoothie.
Lab tests with the extracts and absorptive intestinal cells suggested that "despite their weak chemical stability", ACN and 3,4-DHB could be detected in their native forms.
"High amounts of polyphenols are found in red and purple fruits and account for 50 – 80% of the total polyphenol content in berries. Grapes, blueberries, blackberries, cherries or cranberries can reach concentrations of up to 3000 mg/kg fresh weight. It is estimated that the average total intake of ACN may be approximately 200mg/d, which is four times higher than that of other polyphenols," the researchers wrote.
Writing in the British Journal of Nutrition, they said past research suggested that despite high per mg polyphenol content in berries, bioavailability of these potential antioxidants was low once they had passed through the colon.
But researchers were yet to look at the impact a food matrix had on this rate of metabolism. Data on this was "scarce," they said.
Five a day failing
Polyphenols are present in fruit and vegetables - something which the general population was still failing to reach national intake recommendations for. Juices and smoothies were an increasingly popular way of improving these intakes, particularly for children, the researchers said.
However, they cautioned: "Whether smoothies as well as juices should be recommended to increase the intake of potentially health-promoting ACN and other polyphenols requires the consideration of other ingredients such as their relatively high sugar content."
Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114515000161
"Uptake and bioavailability of anthocyanins and phenolic acids from grape/blueberry juice and smoothie in vitro and in vivo"
Authors: S. Kuntz, S. Rudloff, H. Asseburg, C. Borsch, B. Frohling, F. Unger, S. Dold, B. Spengler, A. Rompp, C. Kunz