Catechin Photolysis Suppression by Aluminum Chloride under Alkaline Conditions and Assessment with Liquid Chromatography-Mass Spectrometry.

Tea is rich in catechins and aluminum. In this study, the process of catechin photolysis was applied as a model for examining the effects of aluminum chloride (AlCl3) on the structural changes of catechin and the alteration of aluminum complexes under blue light irradiation (BLI) at pH 8 using liquid chromatography and mass spectrometry techniques. Additionally, the effects of anions on catechin upon the addition of AlCl3 and treatment with BLI were also studied. In this study, when 1 mM catechin was treated with BLI, a superoxide anion radical (O2•-) was generated in an air-saturated aqueous solution, in addition to forming a dimeric catechin (proanthocyanidin) via a photon-induced redox reaction. The relative percentage of catechin was found to be 59.0 and 95.7 for catechin treated with BLI and catechin upon the addition of 1 mM AlCl3 treated with BLI, respectively. It suggested that catechin treated with BLI could be suppressed by AlCl3, while AlCl3 did not form a complex with catechin in the photolytic system. However, under the same conditions, it was also found that the addition of AlCl3 inhibited the photolytic formation of O2•-, and reduced the generation of proanthocyanidin, suggesting that the disconnection of proanthocyanidin was achieved by AlCl3 acting as a catalyst under treatment with BLI. The influence of 1 mM fluoride (F-) and 1 mM oxalate (C2O42-) ions on the photolysis of 1 mM catechin upon the addition of 1 mM AlCl3 and treatment with BLI was found to be insignificant, implying that, during the photolysis of catechin, the Al species were either neutral or negatively charged and the aluminum species did not form a complex with anions in the photolytic system. Therefore, aluminum, which is an amphoteric species, has an inherent potential to stabilize the photolysis of catechin in an alkaline conditions, while suppressing the O2•- and proanthocyanidin generation via aluminum ion catalysis in the catechin/Al system under treatment with BLI.

Effects of Epigallocatechin Gallate on the Stability of Epicatechin in a Photolytic Process.

Catechins belonging to polyhydroxylated polyphenols are the primary compounds found in green tea. They are associated with many physiological properties. Epicatechin (EC) is a non-gallate-type catechin with four phenolic hydroxyl groups attached. The changes in EC treated with color light illumination in an alkaline condition were investigated by chromatographic and mass analyses in this study. In particular, the superoxide anion radical (O2•-) was investigated during the EC photolytic process. EC is unstable under blue light illumination in an alkaline solution. When EC was treated with blue light illumination in an alkaline solution, O2•- was found to occur via a photosensitive redox reaction. In addition, the generation of monomeric, dimeric, and trimeric compounds is investigated. On the other hand, epigallocatechin gallate (EGCG), which is a gallate-type catechin, is stable under blue light illumination in an alkaline solution. Adding EGCG, during the blue light illumination treatment of EC decreased photolytic formation, suggesting that gallate-type catechins can suppress the photosensitive oxidation of EC. Gallate-type catechins are formed via the esterification of non-gallate-type catechins and gallic acid (GA). The carbonyl group on the gallate moiety of gallate-type catechins appears to exhibit its effect on the stability against the photosensitive oxidation caused by blue light illumination.

Effects of Blue-Light-Induced Free Radical Formation from Catechin Hydrate on the Inactivation of Acinetobacter baumannii, Including a Carbapenem-Resistant Strain.

Catechin is a flavan-3-ol, a derivative of flavans, with four phenolic hydroxyl groups, which exhibits a wide range of physiological properties. Chromatographic analyses were employed to examine the effects of blue light irradiation on the changes of catechin hydrate in an alkaline condition. In particular, the detection of a superoxide anion radical (O2•−), a reactive oxygen species (ROS), and the inactivation of Acinetobacter baumannii (A. baumannii)­including a carbapenem-resistant A. baumannii (CRAB)­was investigated during the photoreaction of catechin hydrate. Following basification with blue light irradiation, the transparent solution of catechin hydrate turned yellowish, and a chromogenic catechin dimer was separated and identified as a proanthocyanidin. Adding ascorbic acid during the photolytic treatment of catechin hydrate decreased the dimer formation, suggesting that ascorbic acid can suppress the photosensitive oxidation of catechin. When catechin hydrate was irradiated by blue light in an alkaline solution, O2•− was produced via photosensitized oxidation, enhancing the inactivation of A. baumannii and CRAB. The present findings on the photon-induced oxidation of catechin hydrate provides a safe practice for the inactivation of environmental microorganisms.

Analysis of aroma compounds and nutrient contents of mabolo (Diospyros blancoi A. DC.), an ethnobotanical fruit of Austronesian Taiwan.

Diospyros blancoi A. DC. is an evergreen tree species of high-quality wood. Mabolo, the fruit of this plant, is popular among the natives in Taiwan, but its potential in economic use has not been fully explored. Mabolo has a rich aroma. Of the 39 different volatile compounds isolated, its intact fruit and peel were found to both contain 24 compounds, whereas the pulp contained 28 compounds. The most important aroma compounds were esters and α-farnesene. Our data show that mabolo is rich in dietary fiber (3.2%), and the contents of other nutrients such as malic acid, vitamin B2, vitamin B3, folic acid, pantothenic acid, and choline chloride were 227.1 mg/100 g, 0.075 mg/100 g, 0.157 mg/100 g, 0.623 mg/100 g, 0.19 mg/100 g, and 62.52 mg/100 g, respectively. Moreover, it is rich in calcium and zinc; the contents of which were found to be 42.8 mg/100 g and 3.6 mg/100 g, respectively. Our results show that D. blancoi has the potential to be bred for a novel fruit.

Effect of shaking process on correlations between catechins and volatiles in oolong tea.

Shaking the tea leaves is the key manipulation to making oolong tea. It contributes to the formation of flavor and fragrance in oolong tea. The dynamic variations of catechins and volatile organic compounds (VOCs) during the shaking process were investigated. The results showed that the contents of epicatechin, epigallocatechin, epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) first decreased after the shaking and then increased to the initial value before the next shaking. Geraniol, linalool and its oxides, and phenylethyl alcohol showed similar variations. The contents of trans-ß-ocimene, 1H-indole, and 3-hexenyl hexanoate increased after the second or third shaking (the late fermentation stage). However, the contents of aldehydes showed an opposite trend to other VOCs. The abundance of phenylethyl alcohol was positively related to the content of ECG and EGCG ​during fermentation, whereas the abundance of cis-3-hexenal was negatively related to the content of ECG. The correlations between catechin and VOCs indicated that shaking affected the chemical transformation of the compounds in oolong tea.

Volatile organic components of fresh leaves as indicators of indigenous and cultivated citrus species in Taiwan.

The volatile components of fresh leaves from 15 citrus species were investigated by headspace SPME with a GC-MS analysis. Three indigenous Taiwan citrus species, Citrus taiwanica, C. tachibana and C. depressa, were the major subjects. Eighty volatile organic compounds were detected as indicators of the genetic relationship. Linalool was the most abundant compound, and citronellal, geranial, neral, limonene and trans-beta-ocimene were the major volatile compounds in fresh leaves. Linalool (56.37%) and myrcene (7.21%) were predominant in C. tawanica. An aldehyde-rich profile with citronellal (24.54%) contributed most to the aroma of leaves in C. tachibana, while Citrus depressa exhibited a high linalool/citronellal composition (23.56%/12.51%). The qualitative and quantitative patterns of the volatiles revealed that C. taiwanica was linked with sour orange, and either C. tachibana or C. depressa belonged to the mandarin group with C. tankan. Dendrograms also showed that the volatile patterns were related to the genetic classification.