The Effect of Steaming and Fermentation on Nutritive Values, Antioxidant Activities, and Inhibitory Properties of Tea Leaves

Abstract

Fermented tea (Cha-miang in Thai) is a local product made by traditional food preservation processes in Northern Thailand that involve steaming fresh tea leaves followed by fermenting in the dark. Information on changes in nutritive values, bioactive compounds, antioxidant activities, and health properties that occur during the steaming and fermenting processes of tea leaves is, however, limited. Changes in nutritive values, phenolics, antioxidant activities, and in vitro health properties through inhibition of key enzymes that control obesity (lipase), diabetes (α-amylase and α-glucosidase), hypertension (angiotensin-converting enzyme (ACE)), and Alzheimer’s disease (cholinesterases (ChEs) and β-secretase (BACE-1)) of fermented tea were compared to the corresponding fresh and steamed tea leaves. Results showed that energy, carbohydrate, and vitamin B1 increased after steaming, while most nutrients including protein, dietary fiber, vitamins (B2, B3, and C), and minerals (Na, K, Ca, Mg, Fe, and Zn) decreased after the steaming process. After fermentation, energy, fat, sodium, potassium, and iron contents increased, while calcium and vitamins (B1, B2, B3, and C) decreased compared to steamed tea leaves. However, the contents of vitamin B1 and iron were insignificantly different between fresh and fermented tea leaves. Five flavonoids (quercetin, kaempferol, cyanidin, myricetin, and apigenin) and three phenolic acids (gallic acid, caffeic acid, and p-coumaric acid) were identified in the tea samples. Total phenolic content (TPC) and antioxidant activities increased significantly after steaming and fermentation, suggesting structural changes in bioactive compounds during these processes. Steamed tea exhibited high inhibition against lipase, α-amylase, and α-glucosidase, while fermented tea possessed high anti-ChE and anti-ACE activities. Fresh tea exhibited high BACE-1 inhibitory activity. Results suggest that tea preparations (steaming and fermentation) play a significant role in the amounts of nutrients and bioactive compounds, which, in turn, affect the in vitro health properties. Knowledge gained from this research will support future investigations on in vivo health properties of fermented tea, as well as promote future food development of fermented tea as a healthy food.

Tea as a Source of Biologically Active Compounds in the Human Diet

“…They demonstrated that quercetin (which is an important phenolic component of tea) can react with a magnesium cation (Mg +2 ) through the chelation site in the quercetin molecule, which increases its antioxidant activity. Many authors proved that polyphenols are the most important antioxidant components found in tea leaves [3,5,6,10,19]. Samadi & Fard [29] indicated that a particular antioxidant effect in tea infusions was exhibited by tannins and flavonoids, for which the correlation coefficient values specifying their relationships with antioxidant activity were statistically significant and amounted to r = 0.721 and r = 0.740, respectively.…”

“…The most common classification of teas involves their division according to the leaf fermenting method. A distinction is made here between the almost unfermented white, yellow, and green teas, partially fermented oolong and pu-erh, and the fully fermented black tea [5]. Due to the sensory characteristics, the most popular is black tea, although interest in green tea has also been on the increase for many years [6].…”

In Vitro Phytotherapeutic Properties of Aqueous Extracted Adenia viridiflora Craib. towards Civilization Diseases

“…The lipase inhibitory activity was determined using Candida rugosa lipase (tуре VII, 700 unit/mg, 100 μL of 0.01 mg/mL) as an enzyme, 5-5ʹ-dithiobis(2-nitrobenzoic-Nphenacyl-4,5-dimethyуhiаzolium bromide) (50 μL of 0.2 mM) as a substrate, 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB, 10 μL of 16 mM) as an indicator, and a plant extract (40 μL) as an inhibitor as previously described [56]. The inhibitory activity was monitored at 412 nm using the microplate reader, and the results were expressed as the inhibition percentage using the following equation…”

“…where A is the initial velocity of the control reaction with an enzyme (control), a is the initial velocity of the control reaction without enzyme (control blank), B is the initial velocity of the enzyme reaction with extract (sample), and b is the initial velocity of the reaction with extract but without enzyme (sample blank). The α-glucosidase inhibitory activity was determined using Saccharomyces cerevisiae α-glucosidase (type 1, ≥10 U/mg protein, 100 μL of 0.1 U/mL) as an enzyme, p-nitrophenylα-D-glucopyranoside (50 μL of 2 mM) as a substrate and an indicator, and a plant extract (50 μL) as an inhibitor as previously described [56]. The inhibitory activity was monitored at 405 nm using the microplate reader, and the results were expressed as the inhibition percentage as above.…”

“…The acetylcholinesterases (AChE) inhibitory activity was determined using Electrophorus electricus AChE (1,000 units/mg, 100 μL of 20 ng) as an enzyme, acetylthiocholine (40 μL of 0.8 mM) as a substrate, DTNB (10 μL of 16 mM) as an indicator, and a plant extract (40 μL) as an inhibitor as previously described [56]. The inhibitory activity was monitored at 412 nm using the microplate reader, and the results were expressed as the inhibition percentage as above.…”