Tea and coffee are widely consumed beverages across the world and they are rich sources of various polyphenols. Polyphenols are responsible for the bitterness and astringency of beverages and are also well known to impart antioxidant properties which is beneficial against several oxidative stress related diseases like cancer, cardiovascular diseases, and aging. On the other hand, proteins are also known to display many important roles in several physiological activities. Polyphenols can interact with proteins through hydrophobic or hydrophilic interactions, leading to the formation of soluble or insoluble complexes. According to recent studies, this complex formation can affect the bioavailability and beneficiary properties of both the individual components, in either way. For example, polyphenol-protein complex formation can reduce or enhance the antioxidant activity of polyphenols; similarly it can also affect the digestion ability of several digestive enzymes present in our body. Surprisingly, no review article has been published recently which has focused on the progress in this area, despite numerous articles having appeared in this field. This review summarizes the recent trends and patterns (2005 onwards) in polyphenol-protein interaction studies focusing on the characterization of the complex, the effect of this complex formation on tea and coffee taste, antioxidant properties and the digestive system.

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A series of ion conductors have been synthesized in which the degree of facial hydrophilicity has been systematically varied. Specifically, conjugates have been prepared from cholic acid and spermine in which the hydrophilic face of each sterol bears methoxy (1), hydroxy (2), carbamate (3), or sulfate groups (4). The ability of these conjugates to promote the transport of Na(+) across phosphatidylcholine membranes of varying thickness has been investigated by (23)Na NMR spectroscopy. Examination of observed activities in three different phosphatidylcholine membranes has provided evidence for membrane-spanning dimers as the transport-active species. In the thinnest membranes investigated, made from 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (C14), Na(+)-transport activity was found to increase, substantially, with increasing facial hydrophilicity. In thicker membranes, made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (C18), observed activities were found to decrease with increasing facial hydrophilicity; with a membrane of intermediate thickness, prepared from 1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine (C16), ion-conducting activity increased and then decreased, with continuous increases in facial hydrophilicity. The possible origins for these variations in activity are briefly discussed.

We report a special, hitherto-unexplored property of (-)-epigallocatechin gallate (EGCG) as a chiral solvating agent for enantiodiscrimination of α-amino acids in the polar solvent DMSO. This phenomenon has been investigated by (1)H NMR spectroscopy. The mechanism of the interaction property of EGCG with α-amino acids has been understood as arising out of hydrogen-bonded noncovalent interactions, where the -OH groups of two phenyl rings of EGCG play dominant roles. The conversion of the enantiomeric mixture into diastereomers yielded well-resolved peaks for D and L amino acids permitting the precise measurement of enantiomeric composition. Often one encounters complex situations when the spectra are severely overlapped or partially resolved hampering the testing of enantiopurity and the precise measurement of enantiomeric excess (ee). Though higher concentration of EGCG yielded better discrimination, the use of lower concentration being economical, we have exploited an appropriate 2D NMR experiment in overcoming such problems. Thus, in the present study we have successfully demonstrated the utility of the bioflavonoid (-)-EGCG, a natural product as a chiral solvating agent for the discrimination of large number of α-amino acids in a polar solvent DMSO. Another significant advantage of this new chiral sensing agent is that it is a natural product and does not require tedious multistep synthesis unlike many other chiral auxiliaries.

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Polysaccharide-induced protein fluorescence 'turn-on' responses have been studied in the presence of similarly charged micelle at pH ∼3. Quenched protein fluorescence is selectively recovered ('on' state) for bovine serum albumin (BSA) with sodium carboxy methyl cellulose (SCMC) and for pepsin (PS) with chitosan (CS) with starting ultra low concentrations of 0.04 μM and 0.008 μM respectively.

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