Effect of Black Tea adulteration on quality parameters of Black Tea
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Date
2015
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Uva Wellassa University of Sri Lanka
Abstract
Black tea is produced by withering, rolling, fermentation and drying from the tender shoots of
varieties of the species Camellia sinensis (L.) (ISO 3720, 2011). Black tea adulteration is a
particularly massive problem because of the universality of its consumption (Kariyawasam, 2014).
Since black tea is a pure beverage material, it should be free from extraneous matter, added colouring
matter and harmful substances (FSSAI, 2011). But sugar, ferrous sulphate and sodium bicarbonate
are added majorly to black tea during manufacturing to improve colour of tea particles and weight of
tea (Deshappriya, 2013; Kariyawasam 2014). The current study was carried out at Sri Lanka Tea
Board to investigate the effect of major adulterants on quality parameters of black tea.
Materials and Methods
Black tea manufacturing was carried out in Uva medium black tea manufacturing factory following
general requirements and steps (withering, rolling, fermentation and drying). 50% sugar, 10% sodium
bicarbonate and 10% ferrous sulphate solutions in mass fraction were treated separately to first dhools
as adulterants after rolling and kept it for fermentation. Those adulterated black tea samples and pure
black tea samples were analysed for quality parameters such as, total polyphenol content, moisture
content, total ash, water soluble ash, alkalinity of water soluble ash, water extract, total plate count,
total liquor colour and brightness.
These quality parameters were analysed in accredited analytical laboratory at Sri Lanka Tea Board
according to the ISO 14502-1: 2005 for total polyphenol content of black tea, ISO 1573: 1980 for
loss in mass at 103 C (moisture content), ISO 1575: 1987 for total ash, ISO 1576: 1988 for water
soluble ash and water insoluble ash, ISO 1578: 1975 for alkalinity of water soluble ash, ISO 1574:
1980 for water extract, SLS 516-1: 1991/ ISO 4833: 2003 for total plate count, spectrophotometric
method described by Roberts, and Smith (1963) for determination of total colour and brightness of
black tea. The data were statistically analyzed with ANOVA using Minitab statistical package. Mean
comparisons with control level (pure black tea) and multiple mean comparison were performed by
Dunnett simultaneous test and Tukey simultaneous test using General Linear model at 5 %
significance level.
Results and Discussion
Externally added sugar, sodium bicarbonate and ferrous sulphate significantly (p<0.05) affected on
total polyphenol content, total ash, water soluble ash, alkalinity of water soluble ash, water extract,
total colour, brightness and total plate count except on moisture content.
According to the Figure 1, the highest total polyphenol content (14.38 %) was recorded by pure black
tea while the lowest (8.81 %) was given by ferrous sulphate adulterated black tea. It was lower than
the ISO 3720 limit (9 %) which may be due to formation of Fe-Polyphenol complex during
fermentation stage. High concentration of ferrous result in localized formation of iron polyphenols
complex in made tea (Venkatesan et al., 2006). The total polyphenol content in sodium bicarbonate
and ferrous sulphate adulterated black tea samples were significantly lower (p<0.05) compared to
pure black tea sample whereas mean difference of sugar adulterated black tea sample was not
significant (p>0.05). Total ash, water soluble ash, water extract values recorded by all three
adulterated black teas were within the ISO 3720 limits while alkalinity (3.26 %) of sodium
bicarbonate adulterated black tea was beyond the ISO 3720 limit (1-3 %). The alkalinity of sodium
bicarbonate adulterated black tea sample was significantly higher (p<0.05) than pure black tea. The
alkalinity of sugar and ferrous sulphate adulterated black tea samples were significantly lower
(p<0.05) than pure black tea.
The highest total colour (6.07 %) was observed in ferrous sulphate adulterated black tea while giving
the lowest brightness (13.54 %) due to the lowest polyphenol content. Total polyphenol content is
positively correlated with brightness which is responsible for tea liquor quality (Kottawa-Arachchi
et al., 2011). Total colour for sugar and ferrous sulphate adulterated black tea samples were
significantly higher (p<0.05) compared to pure black tea while the total colour for sodium bicarbonate
adulterated black tea sample was significantly lower (p<0.05) than pure black tea. Brightness values
for all adulterated black tea samples were significantly lower (p<0.05) than pure black tea. TPP - total
polyphenol content, MO - moisture content, TA - total ash, WSA - water soluble ash, ALK -
alkalinity, WE - water extract, TC - total colour, BRI - brightness.
Description
Keywords
Agriculture, Export Agriculture, Black Tea, Tea Industrials, Tea Technology