A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

(1997). The chemistry of tea flavonoids. Critical Reviews in Food Science and Nutrition: Vol. 37, Tea and Health, pp. 693-704.

The chemistry of tea flavonoids

Tea polyphenols: prevention of cancer and optimizing health. Discussion 4.

Effects of extraction solvents on concentration and antioxidant activity of black and black mate tea polyphenols determined by ferrous tartrate and Folin–Ciocalteu methods

The flavonoids are plant polyphenols found frequently in fruits, vegetables, and grains. Divided into several subclasses, they include the anthocyanidins, pigments chiefly responsible for the red and blue colors in fruits, fruit juices, wines, and flowers; the catechins, concentrated in tea; the flavanones and flavanone glycosides, found in citrus and honey; and the flavones, flavonols, and flavonol glycosides, found in tea, fruits, vegetables, and honey. Known for their hydrogen-donating antioxidant activity as well as their ability to complex divalent transition metal cations, flavonoids are propitious to human health. Computer-controlled high-performance liquid chromatography (HPLC) has become the analytical method of choice. Many systems have been developed for the detection and quantification of flavonoids across one, two, or three subclasses. A summary of the various HPLC and sample preparation methods that have been employed to quantify individual flavonoids within a subclass or across several subclasses are tabulated in this review.

Measurement of food flavonoids by high-performance liquid chromatography: A review.

Estimation of black tea quality by analysis of chemical composition and colour difference of tea infusions

Processing and chemical constituents of Pu-erh tea: A review

Many in vitro studies have shown that tea catechins had vevarious health beneficial effects However, inconsistent results between in vitro and in vivo studies or between laboratory tests and epidemical studies are observed Low bioavailability of tea catechins was an important factor leading to these inconsistencies Research advances in bioavailability studies involving absorption and metabolic biotransformation of tea catechins were reviewed in the present paper Related techniques for improving their bioavailability such as nanostructure-based drug delivery system, molecular modification, and co-administration of catechins with other bioactives were also discussed

https://www.mdpi.com/1420-3049/23/9/2346/pdf

Bioavailability of Tea Catechins and Its Improvement.

Volatile compounds are important components of tea aroma, a key attribute of sensory quality. The present review examines the formation of aromatic volatiles of various kinds of teas and factors influencing the formation of tea volatiles, including tea cultivar, growing environment and agronomic practices, processing method and storage of tea. The determination of tea volatiles and the relationship of active-aroma volatiles with the sensory qualities of tea are also discussed in the present paper.

https://www.mdpi.com/1420-3049/21/3/338/pdf

Recent Advances in Volatiles of Teas

Chemical compositions and infusion colour differences of seven pu-erh tea samples and their correlation to sensory quality were investigated. The results showed that the pu-erh tea contained 37.1 mg g−1 caffeine, 15.7 mg g−1 amino acids, 67.0 mg g−1 polyphenols and 8.41 mg g−1 total catechins, on average. Among the 17 tested volatile compounds, n-valeraldehyde was not detected. The most abundant volatile was β-ionone and the next was linalool oxide II. Infusion colour analysis showed that the pu-erh tea had deep hue with ΔE ranging from 66.8 to 79.2. Spearman's linear correlation analysis showed that total quality score (TQS) of the pu-erh tea was significantly correlated to concentration of amino acids, linalool oxide II and infusion colour indicator ΔE. Five components were extracted from the 34 tested indicators by principal component analysis and were regressed on the TQS to produce six Pearson's linear regression equations for estimating sensory quality of pu-erh tea, among which two were statistically significant, ie TQS = 57.47 − 0.18geraniol + 0.33polyphenols − 1.14n-caproaldehyde − 1.38linalool oxide I + 0.21caffeine (p < 0.01) and TQS = 57.42-0.03Citral + 0.33polyphenols − 1.14n − caproaldehyde − 1.40linalool oxide I + 0.20caffeine (p < 0.01). Copyright © 2004 Society of Chemical Industry

Yue-Rong Liang

Papers

Estimation of black tea quality by analysis of chemical composition and colour difference of tea infusions

Processing and chemical constituents of Pu-erh tea: A review

Bioavailability of Tea Catechins and Its Improvement.

Recent Advances in Volatiles of Teas

A study on chemical estimation of pu-erh tea quality