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tea directory


“Genetic Determinants of Liking and Intake of Coffee and Other Bitter Foods and Beverages”, Cornelis & Dam 2021

“Genetic determinants of liking and intake of coffee and other bitter foods and beverages”⁠, Marilyn C. Cornelis, Rob M. van Dam (2021-12-13; ; similar):

Coffee is a widely consumed beverage that is naturally bitter and contains caffeine⁠. Genome-wide association studies (GWAS) of coffee drinking have identified genetic variants involved in caffeine-related pathways but not in taste perception. The taste of coffee can be altered by addition of milk/​sweetener, which has not been accounted for in GWAS.

Using UK and US cohorts, we test the hypotheses that genetic variants related to taste are more strongly associated with consumption of black coffee than with consumption of coffee with milk or sweetener and that genetic variants related to caffeine pathways are not differentially associated with the type of coffee consumed independent of caffeine content.

Contrary to our hypotheses, genetically inferred caffeine sensitivity was more strongly associated with coffee taste preferences than with genetically inferred bitter taste perception. These findings extended to tea and dark chocolate.

Taste preferences and physiological caffeine effects intertwine in a way that is difficult to distinguish for individuals which may represent conditioned taste preferences.

“Black Tea Quality Is Highly Affected during Processing by Its Leaf Surface Microbiome”, Tong et al 2021

2021-tong.pdf: “Black Tea Quality is Highly Affected during Processing by its Leaf Surface Microbiome”⁠, Wei Tong, Jie Yu, Qiong Wu, Lizhen Hu, Dina Tabys, Yijun Wang, Chaoling Wei, Tiejun Ling, Mallano Ali Inayat et al (2021-06-21; ; similar):

Microbiomes can greatly affect the quality of fermented food and beverages, including tea. In this study, microbial populations were characterized during black and green tea manufacturing, revealing that tea processing steps can drive both the bacterial and fungal community structure.

Tea leaves were found to mostly harbor Proteobacteria⁠, Bacteroidetes⁠, Firmicutes⁠, and Actinobacteria among bacteria and Ascomycetes among fungi. During processing, tea microbial populations changed especially between sterilized and unsterilized samples. The surface sterilization of fresh leaves before processing can remove many microbes, especially the bacteria of the genera Sphingomonas and Methylobacteria⁠, indicating that these are mostly phylloplane microbes on tea leaves. The surface sterilization removed most fungi, except the Debaryomyces⁠.

We also observed a fluctuation in the content of several tea-quality-related metabolites during processing. Caffeine and theanine were found in the same quantities in green tea with or without leaf surface sterilization. However, the sterilization process dramatically decreased the content of total catechins and theanine in black tea, indicating that microbes on the surface of tea leaf may be involved in maintaining the formation of these important metabolites during black tea processing.

[Keywords: tea quality, microbial community, tea processing, black tea, surface sterilization]

Figure 3: Black and green tea microbiome compositions described at the level of genus. (A) Bacterial composition of routine and sterilized samples. (B) Relative abundance of bacteria in all the black and green tea samples from the processing steps. (C) Relative abundance of fungi between routine and sterilized groups. (D) Sample-wise relative abundances of fungi from the different processing steps. Fresh, fresh leaves before processing; Green, samples of green tea; Routine, routine processing samples of black tea; Sterilized, samples of black tea after leaf surface sterilization.

“Self-Blinded Mineral Water Taste Test”, Branwen 2017

Water: “Self-Blinded Mineral Water Taste Test”⁠, Gwern Branwen (2017-02-15; ⁠, ⁠, ; backlinks; similar):

Blind randomized taste-test of mineral/​distilled/​tap waters using Bayesian best-arm finding; no large differences in preference.

The kind of water used in tea is claimed to make a difference in the flavor: mineral water being better than tap water or distilled water. However, mineral water is vastly more expensive than tap water.

To test the claim, I run a preliminary test of pure water to see if any water differences are detectable at all. Compared my tap water, 3 distilled water brands (Great Value, Nestle Pure Life, & Poland Spring), 1 osmosis-purified brand (Aquafina), and 3 non-carbonated mineral water brands (Evian, Voss, & Fiji) in a series of n = 67 blinded randomized comparisons of water flavor. The comparisons are modeled using a Bradley-Terry competitive model implemented in Stan; comparisons were chosen using an adaptive Bayesian best-arm sequential trial (racing) method designed to locate the best-tasting water in the minimum number of samples by preferentially comparing the best-known arm to potentially superior arms. Blinding & randomization are achieved by using a Lazy Susan to physically randomize two identical (but marked in a hidden spot) cups of water.

The final posterior distribution indicates that some differences between waters are likely to exist but are small & imprecisely estimated and of little practical concern.

“A Pilot Study to Assess Lead Exposure from Routine Consumption of Coffee and Tea from Ceramic Mugs: Comparison to California Safe Harbor Levels”, Anderson et al 2017

“A pilot study to assess lead exposure from routine consumption of coffee and tea from ceramic mugs: comparison to California Safe Harbor Levels”⁠, Grace L. Anderson, Lindsey Garnick, Mai S. Fung, Shannon H. Gaffney (2017-02-06; similar):

Background: Lead (Pb) is a pervasive metal that can be found in, and potentially leached from, ceramics, particularly into acidic foods and beverages. The purpose of this study was to investigate potential lead exposure from coffee and tea consumption, given that both are acidic and routinely consumed from ceramic mugs. We measured the concentration of lead in coffee and tea at 2 different time points brewed in 5 readily available mugs known to contain lead. Results were compared to EPA’s action level for drinking water and FDA’s allowable level for bottled water. The measured concentrations, along with consumption patterns, were also used to calculate potential daily lead doses, which were compared to California’s Safe Harbor Levels under Proposition 65⁠. Additionally, we estimated changes in adult and fetal blood lead levels using EPA’s Adult Lead Methodology model.

Findings: The results of this pilot study suggest that lead in ceramic mugs can leach into coffee and tea. The measured lead concentrations ranged from 0.2 to 8.6 μg/​L in coffee, and from <0.2 to 1.6 μg/​L in tea. No statistical differences were found between the measured concentrations in coffee, tea, or water within each cup, or in the measured concentrations between retention times within each cup. However, a statistically-significant difference was observed in the lead concentrations measured between cups, indicating that the lead concentrations were dependent on the cup used, rather than on the beverage or retention time. The estimated daily dose of lead exceeded the California Maximum Allowable Dose Level of 0.5 μg per day for one of the 5 mugs tested. Blood lead levels did not increase above regulatory or guidance values.

Conclusions: This preliminary investigation provides data on potential lead exposures from daily beverage consumption among typical consumers, relevant to a substantial portion of the population, with particular implications for pregnant women.

Materials and methods: The 5 mugs chosen for this study were selected because they were found to contain lead in a screening-level assessment. Specifically, 24 mugs from the authors’ office were tested using an Olympus Innov-X Delta handheld X-Ray fluorescent (XRF) analyzer. Each mug was measured once with the XRF gun at its highest sensitivity setting, which required the tester to hold the analyzer over the mug for 45s. The 3 mugs with the highest resulting lead concentrations (1,223 to 7,034 mg/​kg) were selected for the present study. These mugs each had decorative elements and will be referred to by their predominant colors: Green Decorative, Yellow Decorative, and Red Decorative. In addition, 2 representative mugs were selected from the batch of office mugs baring the authors’ company’s logo. These will be referred to as Black Logo1 and Black Logo2. All 5 mugs selected were in active use in the authors’ San Francisco, California, office environment, and were typically washed daily in an automatic dish washer. 4 of the 5 mugs were purchased in the U.S., and one was purchased in Europe (Red Decorative). The mugs all appeared to be in good condition, with no obvious signs of damage or wear.

“Human Disposition of L-theanine in Tea or Aqueous Solution”, Pijl et al 2010

2010-vanderpijl.pdf: “Human disposition of L-theanine in tea or aqueous solution”⁠, P. C. van der Pijl, L. Chen, T. P. J. Mulder (2010-10-01; ; backlinks; similar):

After consumption of tea, L-theanine enters systemic circulation and is assumed to enter the brain. Several human studies indicate that L-theanine influences brain functioning. Knowledge about the pharmacokinetics of L-theanine facilitates further study of this health effect.

Volunteers received 25–100 mg of L-theanine as tea, as L-theanine-enriched tea, and as biosynthetic L-theanine in aqueous solutions. Plasma was analysed for L-theanine content after which data were fitted with a 1-compartment model. For all interventions, the lag time was ~10 min and half-lives of absorption and elimination were approximately 15 and 65 min respectively. After ~50 min, maximum plasma concentrations of between 1.0 and 4.4 mg⁄L were achieved. Maximum plasma concentration and area under the plasma-concentration/​time curve were dose-proportional.

This knowledge allows prediction of plasma concentrations for various dose regimens supporting further study of a health benefit of L-theanine.

“Ginseng for Cognition”, J et al 2010

2010-geng.pdf: “Ginseng for cognition”⁠, Geng J, Dong J, Ni H, Lee, Wu T, Jiang K, Wang G, Zhou AL, Malouf R (2010-01-01; ; backlinks)

“Earl Grey Tea Intoxication”, Finsterer 2002

2002-finsterer.pdf: “Earl Grey tea intoxication”⁠, Josef Finsterer (2002-04-27; similar):

A 44-year-old man presented in May, 2001, with muscle cramps. He had no medical history of note, but volunteered the fact that he had been drinking up to 4 L of black tea per day over the past 25 years. His preferred brand was GoldTeefix (Tekanne, Salzburg, Austria). Since this type of tea had given him occasional gastric pain, he changed to Earl Grey tea (Twinings & Company, London, UK), which he thought would be less harmful to his stomach.

1 week after the change, he noticed repeated muscle cramps for some seconds in his right foot. The longer he drank Earl Grey tea, the more intense the muscle cramps became. After 3 weeks, they also occurred in the left foot. After 5 weeks, muscle cramps had spread towards the hands and the right calf. Occasionally, he observed fasciculations of the right adductor pollicis and gastrocnemius. Additionally, he noted distal paraesthesias in all limbs, and a feeling of pressure in his eyes, associated with blurred vision, particularly in darkness.

On neurologic examination he had reduced visual acuity and fasciculations in the right tibialis anterior and adductor pollicis. Motor and sensory nerve conduction studies of the right median, peroneal and sural nerves were normal. Needle electromyography of the right tibialis anterior showed fasciculations at 6 of 20 sites, but motor unit architecture was preserved. Ophthalmological tonometry and fundoscopy, and cerebral magnetic resonance imaging were normal. Tests of thyroid, hepatic, adrenal, and kidney functions showed no abnormalities. Serum and urine potassium, chloride, calcium, magnesium, and phosphate were all within the normal range. He did not have polydipsia, and was quite capable of reducing his fluid intake to 1–2 L per day. I excluded motor neurone disease, polyneuropathy, myopathy, neuromyotonia, stiff-man syndrome, and Machado-Joseph disease by appropriate tests.

The patient assumed that there was a relation between his symptoms and his tea consumption, and stopped drinking Earl Grey after 5 months, reverting to pure black tea again. Within 1 week, his symptoms had completely disappeared. Symptoms also remained absent if he completely withdrew from tea, which he did in the nature of experiment, for about a week. He found that his symptoms did not recur as long as he consumed no more than 1 L of Earl Grey daily.

When last seen in November 2001, neurological examination, nerve conduction studies, and electromyography were normal. He was still drinking 2 L of plain black tea daily (his entire fluid intake), and had no complaints.