Impacts of green tea formulation on measures of tea catechin bioavailability.

摘要

Consumption of tea is associated with numerous health benefits and epidemiological evidence suggests a specific role for tea in reduction of chronic disease risk and outcomes. These studies were conducted on the major tea polyphenols epicatechin (EC), epigallocatechin (EGC), epigallocatechin gallate (EGCG), and epicatechin gallate (ECG) as the potential physiologically active agents. Limited data suggest that the stability of tea catechins to digestive conditions is likely poor impacting bioaccessible profiles. Therefore, the overall objective for this thesis was to determine how common formulation factors influence analytical recovery, intestinal profile and accumulation into the intestine of green tea (GT) catechins by human intestinal cells. An enzyme assisted extraction procedure was developed to enhance analytical recovery of catechins from protein-rich tea beverages and biological fluids. A two-stage in vitro digestion model was then used to determine the impact of the gastric and small intestinal conditions on catechin profiles form green tea beverages formulated with different creamers, juices and food grade antioxidants. Finally, catechin uptake/accumulation from digested tea beverages by differentiated Caco-2 human intestinal cells was measured to investigate the extent to which food formulation impacts these initial stages of catechin intestinal uptake.Analytical recovery of catechins from 20% milk-tea beverages was improved by addition of pepsin treatment with individual recovery of gallated catechins (EGCG and ECG) most improved. Digestive stability of catechins in plain GT beverages was poor with 20% catechins remaining post-digestion (EGC and EGCG most sensitive with &le10%). Formulation of GT with 30 mg ascorbic acid (AA) per 250 mL significantly (p0.05) increased catechin digestive recovery to 60%, and addition of citrus juices (lemon (LM), orange, lime, and grapefruit (GF)) at 50% (v/v) resulted in the highest recovery for EGC (81-98%), EGCG (56-76%), EC (86-95%) and ECG (30-55%). Accumulation of catechins from digested GT beverages by Caco-2 human intestinal cells was significantly improved by formulation with LM (330 pmol/mg cell protein) and GF (315 pmol/mg) compared to plain digested GT (176 pmol/mg). Additional experiments demonstrated a dose-dependent effect of digested LM on catechin accumulation of undigested GT (256 to 925 pmol/mg for 0-50% juice in test media). Increase in catechin accumulation was not due to specific LM components such as glucose, citric acid, or AA. However, initial investigations with hesperidin suggest a role for this LM flavonone glycoside in improvement of catechin accumulation by Caco-2.Overall these data suggest that formulation factors may impact the initial stages of catechin absorption in humans including digestive stability and accumulation intestinal tissues. These data will aid in identifying critical formulation factors that may impact catechin physiological profiles and therefore influence clinical outcomes.