Comparing the Effect of Whey and Soy Protein on the Absorption of Pomegranate Polyphenols in the Human Body

Pomegranate (Punica granatum L.) fruits are widely consumed as pomegranate juice (PJ), and their health benefits have been studied extensively in animals and humans (1-6). The pomegranate fruit is a rich source of polyphenols, most of which are ellagitannins (ETs). Pomegranate extracts,which incorporate these major polyphenols from the pomegranate fruit, have been developed in dry and liquid forms to provide alternative convenient sources for obtaining the bioactive polyphenols found in PJ. We have previously reported on the pharmacokinetics and metabolism of pomegranate polyphenols, after the consumption of PJ in normal healthy human volunteers (7). In humans, ETs are converted to ellagic acid (EA) in the small intestines and absorbed with a maximum plasma concentration observed at approximately 1 hour. EA disappears from plasma 6 hours after administration of PJ. Ellagitannins and ellagic acid remaining in the intestine and are then further converted by gut microflora to urolithin-A, absorbed and derivatives, which are metabolized by phase II enzymes and excreted in human urine for up to 48 hours after consumption of PJ(7). Polyphenols are dietary constituents of plants associated with health-promoting effects. In the human diet, polyphenols are generally consumed in foods along with macronutrients. Because the health benefits of polyphenols are critically determined by their bioavailability, the effect of interactions between plant phenols and food macronutrients is a very important topic. The protein-polyphenol complexes can significantly change the plasma kinetics profile. (8) Protein-polyphenol binding is mediated by a combination of hydrogen and hydrophobic bonding depending on chemical (polarity) and structural (size/shape) properties of interacting molecules. Covalent interactions between purified glycinin, a soybean storage protein, and selected flavonoids and phenolic acids have also been reported. Recently it is reported that protein-rich defatted soybean flour protects anthocyanins during transit through upper digestive tract for subsequent colonic delivery/metabolism (9).