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

Sydney Elizabeth Moser, Purdue University

Abstract

While information regarding the impact of flavan-3-ol-protein interactions on food quality attributes (flavor, texture, and physical stability) exists, insight into the potential consequence of these interactions on bioavailability of health-promoting flavan-3-ols remains unclear. The ability of nonspecific protein interactions in flavan-3-ol rich foods and beverages to alter digestive stability and/or digestive release (bioaccessibility) of flavan-3-ols has been previously proposed but unconfirmed. The primary objective of this study was to characterize effects of individual milk proteins and the milk matrix on in vitro bioaccessibility of green tea flavan-3-ols from model beverage systems. As a secondary objective, the impact of protein gastrointestinal digestion on protein-flavan-3-ol binding was assessed using fluorometry. Protein solutions containing sodium-caseinate (S-CSN), &agr;-lactalbumin (&agr;-LA), β-lactoglobulin (β-LG) (0.356 mg/100 mL, 0.01 mg/100 mL, 0.035 mg/100 mL, respectively), or non-fat dry milk (NFDM, 0.1 mg/mL) were prepared in Jenness Koops buffer containing milk salts or dd water and formulated at dosages of 10, 20, and 40% (v/v) into model green tea beverages containing 60 mg/100 mL total flavan-3-ols. Samples were then subjected to in vitro digestion simulating human gastric and small intestinal conditions. Pre- and post-digestion flavan-3-ol profiles were assessed by HPLC and relative (%) and absolute (&mgr;mol/g) bioaccessibility of individual flavan-3-ols were calculated. With regards to green tea beverages formulated to 40% with milk protein solutions, inclusion of S-CSN significantly decreased (p<0.05) bioaccessibility of all flavan-3-ols, β-LG significantly decreased (p<0.05) bioaccessibility of all flavan-3-ols except EGC, and &agr;-LA significantly decreased (p<0.05) bioaccessibility of only gallated catechins compared to buffer controls. Furthermore, S-CSN effects on flavan-3-ol absolute bioaccessibility were more notable compared to whey proteins, decreasing bioaccessibility of EGC, EC, EGCG, and ECG from 98.29±9.22, 30.88±0.52, 40.52±1.16, and 6.51±0.16 &mgr;mol/g, respectively, from JK buffer control to 17.82±4.68, 21.72±1.23, 11.29±1.18, and 2.86±1.20 &mgr;mol/g, respectively. Interestingly, milk minerals from JK buffer increased flavan-3-ol stability during digestion compared to water control, significantly increasing (p<0.05) absolute and, by extension, relative bioaccessibility from 18 to 32%.While some individual trends were exhibited, no overall significant dose-dependent effects (p>0.05) were observed at protein and JK levels tested. SDS-PAGE results demonstrated only partial digestion of protein after peptic digestion, and degradation of proteins to <10 kDa after only 15 minutes of duodenal digestion. These results compared well with fluorometry results suggesting that maximum binding of S-CSN by>EGCG, the main flavan-3-ol in green tea, occurs when protein is partially digested by pepsin in the gastric phase. Further digestion by pancreatin in the small intestinal phase appeared to reduce capacity for binding. Combined these data suggest that interactions between individual milk proteins and flavan-3-ols may alter bioaccessibility. However, the extent of these effects is subtle and dependent on the ability of individual interactions to survive normal digestive conditions. Interestingly, salts typically found in milk serum may exert protective effects on polyphenols from tea, stabilizing them to digestive reactions that may lead to their degradation.

Degree

M.S.

Advisors

Ferruzzi, Purdue University.

Subject Area

Food Science

COinS