The absorption of manganese from polyphenol-containing beverages in suckling rats

Abstract

Polyphenol-containing beverages, such as tea and wines, have a high content of manganese, but the nutritional bioavailability of manganese in these beverages is unknown. Manganese content of tea infusion, coffee and white and red wines were determined as (mg/1) 2.16, 0.15, 0.96 and 0.56, while tannins contents (mg/1) were 745, 1440, 300 and 1980, respectively. Of the total manganese in tea leaves (495 mg/kg), 21% was extracted in tea infusion. Dialysability of manganese in tea infusion through a 10 000-12 000 mw cut-off membrane was 92.5%, similar to that for Ma added to the infusion. Absorption of manganese from beverages and control MnS04 solutions was determined in 16-day-old suckling rats. Rat pups (4-6/group), fasted overnight, were fed by gavage with 0.2-0.4 ml of beverages or MnS04 solutions, which were extrinsically labelled with ⁵⁴Mn. After 6 h the rats were sacrificed and absorbed isotope was determined as the difference between the dose administered and that recovered in the stomach, the washings of the small intestine and the caecum-colon. Manganese absorption was estimated as (%): tea, 90.9 (s.e. 2.5); tea with milk, 91.1 (1.9); coffee, 91.7 (0.6); white wine, 87.7 (1.2) and red wine, 87.7 (0.8). Absorption of manganese from beverages was not significantly different from that from MnSO₄ solutions in water (88.6-93.1%). Tannic acid (1360mg/l) slightly reduced the absorption of manganese from a MnSO₄ solution from 91.0 (1.1) to 77 (3.2)%. These findings suggest that polyphenols have little effect on manganese absorption and that the bioavailability of manganese from polyphenol-containing beverages is high.