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ELSEVIER
FoodChemistry, Vol. 63, No. 1, pp. 61-64, 1998
0 1998 Elsevier Science Ltd. All rights reserved
Printed in Great Britain
PII: SO308-8146(97)00219-7 0308-8146/98 $19.00 + 0.00
The impact of mechanization of tea harvesting on
the quality of south Indian CTC teas
Ramaswamy Ravichandran* & Ramaswamy Parthiban
Tea Technology Division, UPASI Tea Research Institute, Valparai 642127, India
(Received 30 May 1997; revised version received and accepted 29 September 1997)
The chemical quality parameters and sensory evaluation of black teas changed
with method of plucking. Hand-plucked teas were very rich in their green-leaf
biochemical precursors and had higher contents of made-tea quality constituents
than shear-plucked teas. The quality deterioration was mainly due to mechanical
injury and non-selective plucking with shear-harvesting. However, tea obtained
by shear-harvesting from a continuously sheared field over a prolonged period
was found to be superior. The use of shears reduced the yield and increased the
plucking average with a net decrease in cost of production compared to hand
plucking. 0 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION
Black tea is the cheapest non-alcoholic stimulant taken
throughout the world and is manufactured from the
young tender shoots of Camellia sinensis (L) 0 Kuntze,
grown in some tropical and temperate countries
(Hampton, 1992). India is the major producer, con-
sumer and exporter of tea. The profitability of the
operation is governed by the quantity and quality of the
plucked shoots (Mamedor and Dzhafarof, 1974; Baruah
et al., 1986; Obanda and Owuor, 1995; Owuor and
Odhiambo, 1993). So far, tea leaves are harvested by
hand-plucking without causing mechanical injury and
manufactured under optimal conditions in order to
maintain quality (Palmer-Jones, 1977; Tanton, 1979;
Mahanta et al., 1993; Owuor et al., 1987). However, due
to the sharp rise in the labour costs and shortage of
manpower, along with the ever-increasing cost of pro-
duction/power, the tea industries in south India have
become non-profitable (Sharma, 1987; Sharma et al.,
1981). Thus, with this changing economic scenario, sci-
entists have been asked to enhance profitability. This
has led to the partial mechanization of shoot-harvesting
by using hand-operated shears (Fay, 1950; Harler, 1949;
Gokhale, 1959; Myers, 1967; Shih et al., 1974; Othieno
and Anyuka, 1982). This process increases the rate of
plucking and reduces the manpower involved. In this
direction, UPASI TRI has offered new recommenda-
tions on harvesting using shears alternately with
hand-plucking, depending on the season (UPASI,
1996a,b). However, in shear-harvesting, the selectivity in
*To whom correspondence should be addressed. 61
plucking is lost and enormous mechanical injury is
caused to the leaf harvested (Dutta, 1956; Mwakha,
1986, 1990; Owuor et al., 1991). This will certainly lead
to deterioration of tea quality and hence price and
profitability (Shkvatsabaya, 1972; Mwakha and Any-
uka, 1984). This study was
changes in biochemical and
vested shoots and black
plucked and shear-plucked
conditions.
undertaken to compare the
quality constituents of har-
tea obtained from hand-
shoots under south Indian
MATERIALS AND METHODS
Tea leaves were collected from UPASI TRI experi-
mental farm (altitude 1050MSL), from UPASI-9 (chin-
ary) clone in triplicate. Hand-plucking was done
without breaking-back by removing all the available
young shoots, irrespective of the number of leaves on
them. Leaves were hand-plucked, as well as sheared
(shear-plucked-A), from the fields which had been under
continuous hand-plucking since being planted
(30 years). Leaves were also shear-plucked from the field
which had been under continuous shearing for the last
5 years (shear-plucked-B).
The leaves were manufactured in triplicate, by the
crush, tear and curl (CTC) method, and subjected to
chemical analysis and sensory evaluation. The profes-
sional tasters, based at different locations in India,
assessed the teas blind and independently.
The biochemical constituents and quality parameters
of both green-leaf and made-tea were analysed by fol-
lowing the methods reported by the AOAC (1996) and
62 R. Ravichandran, R. Parthiban
others (Mahanta et al., 1993; Owuor and Odhiambo,
1993; Obanda and Owuor, 1995). The lipids were
extracted by homogenizing the sample with chloroform:
methanol (2: 1) for 5 min, filtering and concentrating to
dryness. The residue was then hydrolysed with IM
alcoholic KOH (refluxing for 2 h), washed with light
petroleum (b.p. 40-60°C): diethyl ether (1: 1) (to remove
non-saponifiables), acidified and extracted with diethyl
ether. Methylations of fatty acids were carried out by
refluxing in anhydrous methanol with 2 drops of cont.
H2S04 for 2 h. Fatty acid methyl esters were determined
by gas chromatography with FID, using a 10% DEGS
column, programmed from 120 to 190°C at @C/min.
Volatiles were extracted in a simultaneous distillation
and extraction apparatus, using dichloromethane. They
were analysed by GLC using a DB-Wax fused-silica
capillary column, programmed from 50 to 230°C at
2”C/min. Identification was done by comparision with
authentic chemical standards obtained from Sigma.
RESULTS AND DISCUSSION
The changes in black tea quality parameters due to
shear-plucking are summarized in Table 1. Most of the
quality parameters show a decrease on using shears for
harvesting. Theaflavins (TF), an important quality
parameter, which are directly correlated with quality,
show a decline with shearing. At the same time, the
contents of thearubigins (TR) and highly polymerized
substances (HPS), which are undesirable beyond a cer-
tain value, are seen to increase with shearing. Total
liquor colour (TLC) showed a minor decline with
shearing which was significantly observed by the tasters.
The water extract value, which determines the cuppage
Table 1. Changes in black tea chemical quality parameters due
to mechanization of harvestinga
Parameters Hand- Shear- Shear-
plucked plucked-A plucked-B
Theaflavins (%)
Thearubigins (%)
High polymerised
substances (%)
Total liquor colour
Water extract (%)
Crude fibre (%)
Caffeine (%)
Lipid (%)
Protein (%)
Taster’s score:
A
B
Yield (kg/ha/year)
Leaf distribution
Plucking average
(kg/worker)
Cost of production
@s/kg)
0.78 0.71 0.76
7.60 8.10 7.90
7.10 7.70 7.30
2.60 2.50 2.60
41.90 40.70 41.60
15.40 14.90 15.20
3.30 3.00 3.10
3.00 3.30 3.10
16.0 16.6 16.2
33.00 30.00 32.00
36.00 32.00 33.00
11250 11064
good poor good
24.00 30.00 -
34.30 31.00 -
aAverage of three trials with standard deviation less than 1%.
value, also declined with shearing. The crude fibre con-
tent, an undesirable parameter whose limit has been
fixed around 16%, decreased with shearing. A slight
decrease in the caffeine content along with a slight
increase in lipid content occurred with shearing com-
pared to hand-plucking. The analytical data observed
were complemented by organoleptic evaluation. The
professional tasters rated the tea made from hand-
plucked leaves much higher than that obtained from
shear-plucked leaves. More specifically, they com-
mented that both flavour and colour of tea infusion
obtained from hand-plucked leaves were distinctly
higher than those obtained by shear-harvesting. The
quantity of green leaf harvested by use of shears was
much higher than that by hand-plucking. Shear-har-
vesting leads to a reduction in plucker requirement. The
cost of production, worked out taking all aspects into
consideration, was found to be quite cheap by shear-
harvesting. The use of shears increased the plucking
interval and decreased the net yield/productivity. How-
ever, the decrease in productivity was not significant.
The field observation showed poor leaf distribution in
shear-operated fields. Also, hand-plucking produced
more fine leaf than shearing. Indeed, shear-harvesting
collected more coarse, mechanically injured leaves than
intact standard leaf, while the hand-plucked harvest
contained only ‘three leaf and a bud’. Shear-plucking is
non-selective and removes all available shoots, even
immature ones, which could grow into the next generation
of shoots within a short interval.
Table 2 shows the variation in green-leaf quality pre-
cursors upon mechanization of plucking. A significant
decline in the content of total catechins and total poly-
phenols was registered due to shear-harvesting. This
very much reflects the decline in made-tea quality para-
meters. In the case of pigments, while the carotenoids
showed a reduction, the chlorophylls increased with
mechanization. The lipoxygenase activity increased
with shearing, but the opposite was observed with
polyphenol oxidase. Both the total lipid and total
protein increased with mechanical harvesting.
The data on changes in fatty acid composition with
shearing are given in Table 3. While the content of
Table 2. Changes in green leaf biochemical constituents due to
machine plucking”
Parameters Hand- Shear- Shear-
plucked plucked-A plucked-B
Total catechins (%) 18.4 17.8 18.2
Total polyphenols (%) 27.7 26.6 27.5
Carotenoids (mg/ 100 g) 71.0 66.0 69.1
Chlorophyll a (mg/lOOg) 1091 1201 1137
Chlorophyll b (mg/lOO g) 448 493 482
Lox activity (U/mg protein) 11.5 14.0 12.9
PPO activity (U/mg protein) 24.4 23.1 23.0
Total lipid (%) 6.3 7.7 7.3
Total protein (%) 14.1 15.3 15.1
=Average of three trials with standard deviation less than 1%.
The impact of mechanization of tea harvesting 63
Table 3. Changes in fatty acid composition due to shearing (%)a
Fatty acid Hand- Shear- Shear-
plucked plucked-A plucked-B
Palmitic ( 16:O) 15.3 14.6 14.9
Stearic (l&O) 8.0 7.7 8.0
Oleic (18:l) 7.4 8.8 8.1
Linoleic (18:2) 20.7 22.5 21.3
Linolenic (183) 37.2 37.0 36.8
Others 11.4 9.4 10.9
aAverage of three trials with standard deviation less than 1%.
saturated fatty acids showed a decline, that of unsatu-
rated fatty acids showed a marked enhancement except
for linolenic acid, which remained almost constant. The
changes in volatile flavour compounds (VFC) are given
in Table 4. In general, all VFC Group I showed an
increase and VFC Group II a decline with machine
plucking. Accordingly, the Flavour Index value declined
with shear-harvesting.
Harvesting is the most expensive of all the agri-
cultural operations in tea production. It presents a very
delicate balance. It should aim at maximum production
of shoots, without impairing the bush health and the
end-product quality. The method of harvesting should
represent the optimal compromise between yield, qual-
ity and cost. Hand-plucking is accompanied by short
plucking intervals (32 rounds per year), but shears can
only be used with long plucking intervals (24 rounds
per year) (UPASI, 19966). The highest yields were
Table 4. Effect of mechanization of harvesting on black tea
VFC composition”
VFC Hand Shear Shear
plucked plucked-A plucked-B
Group I
I-Penten-3-01
n-Hexanal
n-Hexanol
cis-3-Hexenal
truns-2-Hexenal
cis-3-Hexenol
truns-2-Hexenol
Pentanol
0.05 0.09 0.09
0.24 0.30 0.28
0.04 0.09 0.08
0.33 0.42 0.39
3.11 3.14 3.13
0.07 0.12 0.11
0.11 0.16 0.14
0.05 0.08 0.08
Group II
Linalool
Linalool oxides
Methyl salicylate
Phenyl acetaldehyde
Geraniol
Benzyl alcohol
2-Phenyl ethanol
Benzaldehyde
ar-Ionone
/?-Ionone
0.92 0.87 0.91
0.13 0.11 0.13
0.49 0.40 0.47
1.31 1.21 1.30
1.07 1.01 1.05
0.15 0.11 0.14
0.43 0.39 0.41
0.07 0.06 0.06
0.36 0.36 0.35
0.27 0.28 0.28
Sum of VFC Group I 4.00 4.40 4.30
Sum of VFC Group II 5.20 4.80 5.10
Flavour Index (II/I) 1.30 1.10 1.20
“As ratio of peak area to that of internal standard. Average of
three trials with standard deviation less than 1%.
obtained only by short plucking intervals and so
favour hand-plucking. However, the cost is much lower
with shear-harvesting.
It needs to be noted that each clone will respond dif-
ferently to shearing and efforts are being made to
identify the elite clones that can respond well to shearing.
The present study shows that quality decreases by the
use of shears. However, south India produces mainly
RC CTC teas, which lack quality/aroma and are mar-
keted mainly for plain black-liquor-producing teas.
Hence, quality reduction due to shearing is not likely to
have a significant impact as far as the market is con-
cerned. Taking all these factors into consideration,
UPASI TRI has recommended an integrated harvesting
system, consisting of mother-leaf addition by hand-
plucking from January to March, followed by shear-
harvesting in April to June, hand-level plucking from
July to September and shearing from October to
December (UPASI, 1996a). It is not advisable to use
shears in freshly pruned fields, at least for 18 months.
This kind of mixed use of hand- and shear-plucking
helps to achieve optimal yield, quality and profitability
in south Indian tea industries. It could also be argued
that mechanical tea harvesters, capable of harvesting
only tender shoots, could produce good tea. Harvesting
tender shoots only could be achieved by raising the
plucking height at definite intervals. On the other hand,
use of a mechanical harvester over several years might
change the plucking table, allowing only the tender
shoots to emerge out of the plucking table and keeping
the mother leaf uniformly in a plain, horizontal level,
thereby allowing the harvest of tender shoots alone.
Preliminary data obtained on the changes in quality
parameters of both green leaf and made tea, obtained
by shear harvesting from fields under continual shearing
over several years, are presented here in the various
tables (shear-plucked-B). As anticipated, all the quality
parameters were found to improve and to be very close
to those of hand-plucking. The data obtained very
clearly indicate that the quality deterioration on shear-
ing decreases with time and normalises after several
years of continuous shearing.
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