title: Potent inhibitory effects of black tea theaflavins on off-odor formation from citral.
abstract: The present study was conducted to investigate the ability of black tea theaflavins to inhibit the off-odor formation from citral under acidic aqueous conditions. Acidic buffer solutions (pH 3.0) containing citral (10 mg/L) and an inhibitor (0-5 mg/L) were stored at 40 degrees C for 2 weeks. The formation of possible off-odorants p-cresol and p-methylacetophenone in the citral solutions was monitored by high-performance liquid chromatography. A mixture of the theaflavins showed inhibitory effects on the formation of both p-cresol and p-methylacetophenone with 50% inhibitory concentrations (IC(50)) of 0.18 and 0.10 mg/L, respectively. Individual theaflavins and a structurally related compound, purpurogallin, also inhibited the formation of both off-odorants, with the lowest IC(50) values for theaflavin 3,3'-digallate (0.17 and 0.06 mg/L for p-cresol and p-methylacetophenone, respectively). On the other hand, a mixture of green tea catechins and its major constituent, (-)-epigallocatechin gallate, showed relatively high IC(50) values for the formation of p-methylacetophenone (1.29 and 1.28 mg/L, respectively) and showed no inhibitory effect on the formation of p-cresol. The results of the sensory evaluation showed that the off-odor intensity of the stored citral solution was significantly decreased by the addition of the theaflavin mixture at concentrations of 0.5 mg/L and above. In addition, the calculation of the odor activity values (OAVs) for the volatile compounds detected by a gas chromatographic analysis indicated that the total OAVs of the major volatile compounds in the citral solution were significantly decreased by the addition of the theaflavins.
authors.affiliation: Ogawa & Company, Ltd., Urayasushi, Chiba 279-0032, Japan. ueno.toshio@ogawa.net
authors.forename: Toshio
authors.initials: T
authors.lastname: Ueno
authors.forename: Susumu
authors.initials: S
authors.lastname: Kiyohara
authors.forename: Chi-Tang
authors.initials: CT
authors.lastname: Ho
authors.forename: Hideki
authors.initials: H
authors.lastname: Masuda
mesh_terms: D000098:Acetophenones / Q000032:analysis / Q000737:chemistry; D000080462:Acyclic Monoterpenes; D044946:Biflavonoids / Q000494:pharmacology*; D002021:Buffers; D002392:Catechin / Q000494:pharmacology*; D003408:Cresols / Q000032:analysis / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D039821:Monoterpenes / Q000737:chemistry*; D009812:Odorants / Q000032:analysis*; D012903:Smell; D012996:Solutions; D013662:Tea / Q000737:chemistry*
chemical_list: D000098:Acetophenones; D000080462:Acyclic Monoterpenes; D044946:Biflavonoids; D002021:Buffers; D003408:Cresols; D039821:Monoterpenes; D012996:Solutions; D013662:Tea; C056068:theaflavin; C032538:4-cresol; D002392:Catechin; C492488:p-methylacetophenone; C007076:citral