Tea: cultivation, processing and preparation

Tea: form bush to cup for your health

Tea is an aromatic infusion extracted from the dried leaves of Camellia sinensis, a member of the Theaceae family.
Tea is a beverage with very ancient origins, dating back to almost 4000 years ago, and it is one of the most consumed beverage worldwide, particularly in Asia, with an estimated per capita consumption of approximately 0.12 L/d.
Owing to its high consumption, even small effects on person’s health could have large effects on public health.

Cultivation of Camellia sinensis

Tea Fields
Fig. 1 – Tea Fields

Camellia sinensis is an evergreen plant, native to South, East, and Southeast Asia, which is currently cultivated in at least 30 countries, mainly in tropical or sub-tropical climates, even if some varieties grow in Cornwall, in Europe, and Washington State, in the USA.
In nature, if left undisturbed, Camellia sinensis can grow up to 15-20 meters (49-65 ft), while in plantations it is generally pruned to height less than a meter and a half, that is, like a small tree or bush, to facilitate cultivation and harvesting of the leaves.
It can also be cultivated in mountain, up to 1500-2000 meters (4900-6550 ft) above sea level. Many of the high-quality teas are produced from mountain crops, as the plant grows more slowly acquiring a better flavor.
Currently, the two most used varieties, of the four ones recognized, are:

  • Camellia sinensis var. sinensis, native to China;
  • Camellia sinensis var. assamica, native to India.

Processing of leaves

All the types of teas commercially available are produced from fresh leaves of the plant. During harvesting, young leaves are generally picked, as the older ones are considered to be inferior in quality.
The differences between the types of teas, e.g. green tea, oolong tea and black tea, depend on how Camellia sinensis leaves are processed after harvesting, since processing may cause a different degrees of oxidation of the substances present, in particular of catechins, a flavonoid subgroup, and the main responsibles of the benefits of green tea.
The organoleptic characteristics of the different types of tea are influenced, in addition to the processing of the leaves, even from the cultivar, the characteristics of the soil where the plant grown up, the methods of cultivation, the altitude, the climate, and the time of year in which the harvest of the leaves occurs.

How to prepare a perfect cup of tea

  • Due to the sensitiveness of dried leaves, it is good to store the packaging in cool dry place, free of fragrances that may alter its aroma.
  • Use fresh water and warm it to a temperature of 95-100°C for black tea, and about 90°C for green tea.
  • In order not to alter flavor, it is advisable to use a ceramic or porcelain teapot, avoiding those of steel. For teapot washing, avoid detergents, preferring water plus baking soda.
  • To prevent sudden changes in water temperature during the infusion, it is advisable to preheat the teapot pouring a bit of boiling water. Then, emptied the pot, add hot water (about 200-250 mL/filter).
  • How many filters/g of leaves to use? Typically, a filter (about 1.5-2 g) per person, or a teaspoon of loose tea leaves per person.
    If you prepare the beverage for some people, you add a filter/teaspoon more than the number of persons.
  • The infusion time should not exceed 10 minutes in order to avoid the development of bitter flavors; it should be 3-4 minutes for black tea, and 2-3 minutes for green tea.
    If you are using filters, you should remove them at the end of the infusion time.
    Approximately 30% of the material present in the leaves is extracted in the water.

Now, it’s time to enjoy your tea.

References

Asil M.H., Rabiei B., Ansari R.H. Optimal fermentation time and temperature to improve biochemical composition and sensory characteristics of black tea. Aust J Crop Sci 2012;6(3):550-8.

Huang W-Y., Lin Y-R., Ho R-F., Liu H-Y., and Lin Y-S. Effects of water solutions on extracting green tea leaves. ScientificWorldJournal 2013;Article ID 368350 doi:10.1155/2013/368350

Kuhnert N. Unraveling the structure of the black tea thearubigins. Arch Biochem Biophys 2010;501(1):37-51 doi:10.1016/j.abb.2010.04.013

Li S., Lo C-Y., Pan M-H., Lai C-S. and Ho C-T. Black tea: chemical analysis and stability. Food Funct 2013;4:10-18 doi:10.1039/C2FO30093A

Menet M-C., Sang S., Yang C.S., Ho C-T., and Rosen R.T. Analysis of theaflavins and thearubigins from black tea extract by MALDI-TOF mass spectrometry. J Agric Food Chem 2004;52:2455-61 doi:10.1021/jf035427e

Proanthocyanidins and procyanidins in foods

CONTENTS

Proanthocyanidins in foods

The interest on proanthocyanidins, and their content in foods, has increased as a result of the discovery, due to clinical and laboratory studies, of their anti-infectious, anti-inflammatory, cardioprotective and anticarcinogenic properties. These protective effects have been attributed to their ability to:

  • act as free radical scavenger;
  • inhibit lipid peroxidation;
  • act on various protein targets within the cell, modulating their activity.

Proanthocyanidins in different foods vary greatly in terms of:

  • total content;
  • distribution of oligomers and polymers;
  • constituent catechin units and bonds between units.

In some foods, such as black beans and cashew nuts, only dimers are present, whereas in most of the foods proanthocyanidins are found in a wide range of polymerizations, from 2 to 10 units or more.

Foods with the highest proanthocyanidin content are cinnamon and sorghum, which contain respectively about 8,000 and up to 4,000 mg/100 g of fresh weight (FW); grape seeds (Vitis vinifera) are another rich source, with a content of about 3,500 mg/100 g dry weight.
Other important sources are fruits and berries, some legumes (peas and beans), red wine and to a less extent beer, hazelnuts, pistachios, almonds, walnuts and cocoa.
The coffee is not a good source.
Proanthocyanidins are not detectable in the majority of vegetables; they have been found in small concentrations in Indian pumpkin. They are not detectable also in maize, rice and wheat, while there are present in barley.

A-type procyanidins in foods

Although many food plants contain high amounts of proanthocyanidins, only a few, such as plums, avocados, peanuts or cinnamon, contain A-type procyanidins, and none in amounts equal to cranberries (Vacciniun macrocarpon).

Procyanidins
Fig. 1 – Procyanidin A2

Note: A-type procyanidins exhibit, in vitro, a capacity of inhibition of P-fimbriated Escherichia coli adhesion to uroepithelial cells greater than B-type procyanidins (adhesion represents the initial step of urogenital infections).

B-type procyanidins in foods

B-type procyanidins, consisting of catechin and/or epicatechin as constituent units, are the exclusive proanthocyanidins in at least 20 kinds of foods including blueberries (Vaccinium myrtillus), blackberries, marion berries, choke berries, grape seeds, apples, peaches, pears, nectarines, kiwi, mango, dates, bananas, Indian pumpkin, sorghum, barley, black eye peas, beans blacks, walnuts and cashews.

Procyanidins
Fig. 2 – Procyanidins B1-B4

Proanthocyanidins in fruits

In the Western diet, fruit is the most important source of proanthocyanidins.

  • The major sources are some berries (blueberries, cranberries, and black currant) and plums (prunes), with a content of about 200 mg/100 g FW.
  • Intermediate sources are apples, chokeberries, strawberries, and green and red grapes (60-90 mg/100 g FW).
  • In other fruits the content is less than 40 mg/100 g FW.

In fruit, the most common proanthocyanidins are tetramers, hexamers, and polymers.
Good sources of proanthocyanidins are also some fruit juices.

Proanthocyanidins in grape seeds

A particularly rich source of proanthocyanidins is the seeds of grape.
Proanthocyanidins in grape seeds are only B-type procyanidins, for the most part present in the form of dimers, trimers and highly polymerized oligomers.
Grape seed proanthocyanidins are potent antioxidants and free radical scavenger, being the more effective either than vitamin E and vitamin C (ascorbic acid).
In vivo and in vitro experiments support the idea that proanthocyanidins, and in particular those from grape seeds, can act as anti-carcinogenic agents; it seems that they are involved, in cancer cells, in:

  • reduction of cell proliferation;
  • increase of apoptosis;
  • cell cycle arrest;
  • modulation of the expression and activity of NF-kB and NF-kB target genes.

References

de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar G.A. Fruit and vegetable phytochemicals: chemistry, nutritional value, and stability. 1th Edition. Wiley J. & Sons, Inc., Publication, 2010

Gu L., Kelm M.A., Hammerstone J.F., Beecher G., Holden J., Haytowitz D., Gebhardt S., and Prior R.L. Concentrations of proanthocyanidins in common foods and estimations of normal consumption. J Nutr 2004;134(3):613-617. doi:10.1093/jn/134.3.613

Han X., Shen T. and Lou H. Dietary polyphenols and their biological significance. Int J Mol Sci 2007;9:950-988. doi:10.3390/i8090950

Manach C., Scalbert A., Morand C., Rémésy C., and Jime´nez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr 2004;79(5):727-47 doi:10.1093/ajcn/79.5.727

Nandakumar V., Singh T., and Katiyar S.K. Multi-targeted prevention and therapy of cancer by proanthocyanidins. Cancer Lett 2008;269(2):378-387. doi:10.1016/j.canlet.2008.03.049

Ottaviani J.I., Kwik-Uribe C., Keen C.L., and Schroeter H. Intake of dietary procyanidins does not contribute to the pool of circulating flavanols in humans. Am J Clin Nutr 2012;95:851-8. doi:10.3945/ajcn.111.028340

Santos-Buelga C. and Scalbert A. Proanthocyanidins and tannin-like compounds: nature, occurrence, dietary intake and effects on nutrition and health. J Sci Food Agr 2000;80(7):1094-1117. doi:10.1002/(SICI)1097-0010(20000515)80:7<1094::AID-JSFA569>3.0.CO;2-1

Tsao R. Chemistry and biochemistry of dietary polyphenols. Nutrients 2010;2:1231-46. doi:10.3390/nu2121231

Wang Y.,Chung S., Song W.O., and Chun O.K. Estimation of daily proanthocyanidin intake and major food sources in the U.S. diet. J Nutr 2011;141(3):447-452. doi:10.3945/jn.110.133900


Flavonols: definition, structure, food sources

CONTENTS

What are flavonols?

Flavonols are polyphenols belonging to the class of flavonoids.
They are colorless molecules that accumulate mainly in the outer and aerial tissues, therefore skin and leaves, of fruit and vegetables, since their biosynthesis is stimulated by light. They are virtually absent in the flesh.

They are the most common flavonoids in fruit and vegetables, where they are generally present in relatively low concentrations.
Due to their widespread in nature and human diet, they should be taken into consideration when the positive effect on health associated with fruit and vegetable consumption is examined. Their effect is probably related to their ability to:

  • act as antioxidants;
  • act as anti-inflammatory agents;
  • act as anticancer factors;
  • regulate different cellular signaling pathways; an example is the action of quercetin, the most widespread flavonols, on the oxidative stress-induced MAPK activities.

Chemical structure of flavonols

Chemically, these molecules differ from many other flavonoids since they have a double bond between positions 2 and 3 and an oxygen (a ketone group) in position 4 of the C ring, like flavones from which, however, they differ in the presence of a hydroxyl group at the position 3. Therefore, flavonol skeleton is a 3-hydroxyflavone.

Basic Skeleton of Flavanols
Fig. 1 – 3-Hydroxyflavone

The 3-hydroxyl group can link a sugar, that is, it can be glycosylated.
Like many other flavonoids, most of them is found in fruit and vegetables, and in plant-derived foods, in glycosylated form. The sugar associated with flavonols is often glucose or rhamnose, but other sugars may also be involved, such as:

  • galactose;
  • arabinose;
  • xylose;
  • glucuronic acid.

Flavonol are mainly represented by glycosides of:

  • quercetin;
  • kaempferol;
  • myricetin;
  • isorhamnetin.
Flavonols
Fig. 2 – Flavonols

The most ubiquitous compounds are glycosylated derivatives of quercetin and kaempferol; in nature, these two molecules have respectively about 280 and 350 different glycosidic combinations.
Finally, it should be underlined that sugar moiety influences flavonol bioavailability.

Foods rich in flavonols

The major sources in human diet are:

  • fruit;
  • vegetables;
  • beverages such as red wine and tea.

In human diet, the richest source are capers, which contain up to 490 mg/100 g fresh weight (FW), but they are also abundant in onions, leeks, broccoli, curly kale, berries (e.g. blueberries), grapes and some herbs and spices, for example dill weed (Anethum graveolens). In these sources, their content ranges between 10 and 100 mg/100 g FW.
Even cocoa, tea, both green and black ones, and red wine are good sources of flavonols. In wine, together with other polyphenols such as catechins, proanthocyanidins and low molecular weight polyphenols, they contribute to the astringency of the beverage.

The main flavonols in foods

The main flavonols in foods, listed in decreasing order of abundance, are quercetin, kaempferol, myricetin and ishoramnetin.

Quercetin

The richest sources of quercetin are capers, followed by onions, asparagus, lettuce and berries; in many other fruit and vegetables, it is present in smaller amounts, between 0.1 and 5 mg/100 g FW.
This flavonol is also present in cocoa and it could be one of its main protective agents against LDL oxidation.
Together with isoflavones, quercetin glycosides are the most well-absorbed polyphenols, followed by flavanones and catechins (on the contrary, gallic acid derivatives of catechins are among the least well absorbed polyphenols, together with anthocyanins and proanthocyanidins).

Kaempferol

Typical dietary sources of kaempferol include vegetables, such as spinach, kale and endive, with concentrations between 0.1 and 27 mg/100 g FW, and some spices such as chives, fennel and tarragon, with concentrations between 6.5 and 19 mg/100 g FW.
Fruit is a poor source of the molecule, with content down to 0.1 mg/100 g FW.

Myricetin

Myricetin is the third most abundant flavonol. It is found in some spices, such as oregano, parsley, and fennel, with concentrations between 2 and 20 mg/100 g FW, but also in tea, 0.5-1.6 mg/100 ml, and red wine, 0-9.7 mg/100 ml.
In fruit, it is only found in high concentrations in berries, while in most other fruit and vegetables it is present in a content of less than 0.2 mg/100 g FW.

Isorhamnetin

A fourth flavonol, less abundant than the previous ones, is isorhamnetin. It is only present in some foods such as some spices: chives, 5.0-8.5 mg/100 g FW, fennel, 9.3 mg/100 g FW, tarragon, 5 mg/100 g FW.
In fruit and vegetables it is only present in almonds, with a concentration between 1.2 and 10.3 mg/100 g FW, pears and onions.

References

de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar G.A. Fruit and vegetable phytochemicals: chemistry, nutritional value, and stability. 1th Edition. Wiley J. & Sons, Inc., Publication, 2010

Han X., Shen T. and Lou H. Dietary polyphenols and their biological significance. Int J Mol Sci 2007;9:950-988. doi:10.3390/i8090950

Manach C., Scalbert A., Morand C., Rémésy C., and Jime´nez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr 2004;79(5):727-47 doi:10.1093/ajcn/79.5.727

Tsao R. Chemistry and biochemistry of dietary polyphenols. Nutrients 2010;2:1231-46. doi:10.3390/nu2121231