The effect of milk proteins on the bioaccessibility of green tea flavan-3-ols

- Milk protein-flavan-3-ol interactions in beverages are altered by digestive conditions.
- Protein has minimal impact on flavan-3-ol bioaccessibility from tea beverages.
- Milk mineral-flavan-3-ol interactions appear to effect protein interactions.

While the impact of interactions between flavan-3-ol and protein on food quality has been reported, the ability of these interactions to modify flavan-3-ol bioavailability remains unclear. The objectives of this study were to characterize the influence of milk proteins and mineral components of the milk matrix on in vitro bioaccessibility of green tea flavan-3-ols and to assess the relative impact of protein digestibility in the GI tract on protein-flavan-3-ol binding. Protein solutions containing sodium-caseinate (S-CSN, 35.6 mg/mL), α-lactalbumin (α-LA, 1 mg/mL), β-lactoglobulin (β-LG, 3.5 mg/mL), or non-fat dry milk (NFDM) were prepared in Jenness Koops (JK) buffer containing milk salts and formulated at 10-40% (v/v) into green tea beverages containing 0.6 mg/mL total flavan-3-ols. Samples were subjected to a three-stage in vitro digestion to assess flavan-3-ol digestive release and stability (bioaccessibility). Milk protein, most notably S-CSN, significantly decreased (p < 0.05) bioaccessibility of flavan-3-ols relative to JK buffer controls (10 relative to 32%). Interestingly, the presence of milk minerals significantly increased (p < 0.05) flavan-3-ol bioaccessibility compared to that of controls (32 relative to 18%). These data combined with SDS-PAGE and fluorometric analyses suggest that both milk proteins and minerals may alter flavan-3-ol bioaccessibility, but normal GI digestion appears to minimize the impact of specific protein interactions.