Proximate composition
The results of the proximate composition of black tea powder are presented in Table 1. It is recommended that the moisture content of the tea should be less than 6.5% for marketing purposes
(Robinson and Owuor., 1993) and results in the present study shows value of 3.3% moisture content which are in line with these.
In black tea, 15-23% of proteins have been determined
(Stagg and Millin 1975). Present investigation obtained 21.15% of protein in black tea powder and is in accordance with the same. Lipids constitute about 2-3% by weight of unprocessed and black tea
(Stagg and Millin 1975). In the present study we obtained 1.3% of lipids which is slightly lower for black tea powder.
Indian standards for black tea (IS 3633: 2003) for total ash are 4-8%. In the present study the total ash obtained was 9.91% which is slightly higher than Indian standards. The total ash content in tea correlates with the mineral content of the tea sample and also measures the physiological ash, which is derived from the plant tissue itself and hence it does not necessarily indicate high quality except when there is a favourable balance of the essential minerals
(Jayawardhane, 2016).
As per Indian standards the crude fibre maximum should be 16.5%. But the crude fibre content in black tea (g/100 g) ranges from 5.83 to 43.27 g/100 g, in teas from China, India and Malawi and that for Indian black tea ranges 9.56-27.89
(Smiechowska and Dmowski, 2006). We obtained 18.35% of crude fibre in the present study and the results are in agreement with these. The differences in the proximate composition of tea powders might be associated with the different species of tea plants, climatic conditions, geographical features, cultivation, harvesting and processing conditions
(Cheruiyot et al., 2008).
Quantitative and qualitative analysis
Total phenolic content (TPC) depends on many factors such as tea types, commercial brands of tea, origin, tea plantation area and infusion conditions, different parts used including antioxidant activity and found to be optimum in young leaves and decreases with ageing of leaves
(Suteerapataron et al., 2008). Highest levels are present in the bud and first leaf and lowest levels in the internodes
(Khanum et al., 2017). The results of TPC in the present study are 220.02 mg GAE /gm dry tea powder.
Khokar and Magnusdottir, (2002) using ethanol as a solvent estimated TPC from four brands of black tea in supermarkets of United Kingdom and results derived for black tea ranged between 80.5 mg GAE/g to 134.9 mg GAE/g of dry matter. In present study we obtained higher results as compared to above which may be attributed to the modified method using ethanol as a solvent for preparation of crude black tea extract.
Total 12 bioactive compounds were extracted from the black tea powder by using ethanol as solvents were
viz. catechin derivatives (Epicatechin Monogallate, 2’,2’- Bisepigallo catechin digallate and Hydroxyhydroquinone), Flavonoid derivatives (Apiin, Hieracin and Cosmosiin), Flavanol (Rutin and Kaempherol), theaflavin (Theaflavin monogallates and Theaflavin digallate), coumarins and derivative / oxyaromatic acids (Aesculin), derivatives of glucuronic acid (Mebeverine metabolite a veratric acid glucuronide).
Above compounds have already been identified in black tea;
Apiin by Wang, (2019). Rutin,
(Chaturvedula and Prakash, 2011), Theaflavin monogallates and Theaflavin digallate
(Okada, 1978; Chaturvedula and Prakash, 2011), Aesculin and 2’,2’- Bisepigallo catechin digallate
(Weerawatanakorn et. al., 2015), Epicatechin Monogallate
(Kim et al., 2011; Pubchem), Hydroxyhydroquinone
(Lee, Liang and Lin, 1995), Kaempferol
(Finger and Engelhardt, 1991;
Jeganathan et. al., 2016), Hieracin
(Su et al., 2018), Cosmosiin also known as Apigenin
(Harbowy and Balentine, 1997).
Considering black tea attributes, theaflavins (TF) are formed by the polymerization of polyphenols during fermentation, catalysed by the enzyme polyphenoloxidase and considered unique in predicting the quality of tea
(Kumar et al., 2013) on a dry weight basis. Thearubigins are again an important group of pigments formed from catechins and by oxidative degradation of theaflavins. Kaempferol is a polyphenol antioxidant and known in reducing the risk of chronic diseases, especially cancer
(Chen and Chen, 2013). Both catechins and theaflavins have been shown to have various health benefits, which include antiviral, antioxidative, antimutagenic, anticarcinogenic and antiobesity activities
(Kobayashi and Ikeda 2014). Aesculin shows anti-inflammatory, anti-oxidant, anti-tumour, anti-viral properties
(Wang et al., 2018).
In the present study we found that ethanol based extraction gave higher amount of TPC content as well as higher number of polyphenolic compounds which comprises Epicatechin Monogallate, Cosmosiin, Theaflavin monogallates, Theaflavin digallate, Kaempherol and Aesculin which can act as low cost polyphenol source.
Antioxidant properties
The antioxidant properties of ethanol based was determined for DDPH, FRAP, ABTS and Metal chelating activity of black tea powder was studied. The results for antioxidant properties are DPPH (88.84%), ABTS (74.94%), FRAP (1398.24 µ mol Trolox/gram dry tea powder) and metal chelating activity (25.13%).
Al-Obaidi and Sahib 2015 reported DDPH activity of black tea to be 63%.
Turkmen et al., 2006 reported the DPPH activity of black tea extract prepared using 50% ethanol as 68.7%.
Nadiah and Uthumporn (2015) reported 81.88% DDPH in normal black tea and 50.14 % DDPH by Ethanol based extraction thus higher DPPH inhibition indicates higher antioxidant activity in tea. The FRAP values of different 30 tea infusions are reported to vary from 504.80±17.44 to 4647.47 ± 57.87 µmol Fe2+/g DW
(Zhao et al, 2019). The metal chelating activity of black tea extract prepared with ethanol based extraction is reported to be 31.89% and ranged from 22.45% to 33.50% for 11 different tea types. Our results for DDPH, FRAP and ABTS are in agreement with these studies except showing a slight lower value of metal chelating activity.
