with low temperatures are ideal conditions for budding
in tea plants. Semchenko,Lepik, Götzenberger, and
Zobel (2012) noted in their study on perennial herbaceous species that moderate shade had a strongly
facilitative effect on plant growth.
3.3 Green leaf yield
Monthly mean seasonal yields ranged between 32
kg.mt/ha for unshaded regime during the HD season
to 339 kg.mt/ha for 30% shaded regime during CW
season (Table 2). Significant difference was observed
within the shading regimes and seasons and between
their interactions. Overall, the lowest yields (201
kg.mt/ha) were recorded in the unshaded regime compared to the significantly higher yields (260 kg.mt/ha)
recorded under 30% shading regime (Table 2), whereas
significantly higher seasonal yields were observed
during the WW season (254 kg.mt/ha) as compared
to the HD season (122 kg.mt/ha) that had the lowest
yields. The significantly low yields recorded in the HD
season for the unshaded regime of 32 kg.mt/ha must
have been caused by low rainfall precipitation and photoinhibition caused by high temperatures coupled with
long sunshine hours. Further, Barua (1969) in a study
conducted in North East India reported that tea yields
in plants grown under 35% light intensity were higher
than in plants grown in full sun. Fu et al. (2015) also
noted prolonged shading might lead to reduced tea leaf
biomass.
3.4 Total catechins
The total catechin (TC) contents in tea products ranged
from 1.21% in BCTC processed from 90% shade
regime during the HD season to 22.24% in GO processed from unshaded regime during CW season
(Table 2). An increase in shading intensity subsequently reduced the accumulation of catechins, with
90% shading regime giving significantly lower TC
(10.81%) levels compared to the unshaded regime
(12.45%) (Table 2). The CW season accumulated maximum catechins (13.01%) compared to HD (10.7%)
season that recorded the lowest level with higher TC
content being recorded in the GO product (19.82%)
compared to BCTC (3.19%) (Table 2). All variables and interactions were significantly (P≤0.05)
different. Song et al. (2019) concluded that the concentration of total catechins was higher in unshaded
than in shaded leaves, and lower in early January
than at other times, indicating that catechin accumulation is proportional and inversely proportional to
humidity and temperature, respectively. Similar observations by Astill, Birch, Dacombe, Humphrey, and
Martin (2001) explained that catechin content of the
CTC-manufactured black teas is lower as a function
of the greater leaf disruption, and enzymatic oxidation
during withering and fermentation in CTC manufacture results in the conversion of catechins to theaflavins
and thearubigins.
3.5 Caffeine content
As depicted in Table 2, caffeine content was significantly (P≤0.05) influenced by all factors and their
interactions. Caffeine content decreased significantly
with an increase in shade intensity to a minimum of
2.59% under 90% shading regime for BCTC product,
with the highest content of caffeine being recorded in
the HD season (3.64%) under unshaded regime in GO
product (Table 2). Caffeine content for GO product
during HD season under 30 and 60% shading regimes
was 2.64% and 2.61%, respectively, which is below
Yatakamidori (Japanese green tea cultivar) with 2.67%
(Kerio, Wachira, Wanyoko, & Rotich, 2013).
Caffeine content was affected positively by high
temperature and dry conditions (Table 1). This is in
order with the findings of Lee et al. (2010) that caffeine content was higher in tea under high temperature
and long-time sun exposure. Kirakosyan et al. (2004)
also explained that tea cultivars had high levels of caffeine during the dry season due to the accumulation of
secondary metabolites such as caffeine by plants as a
form of defense mechanism. In order to respond and
adapt to environmental stresses, caffeine acts through
allelopathy (Kim & Sano, 2008) as repellant (Chou
& Waller, 1980) and signaling molecules to activate
plant defense responses (Nathanson, Owuor, Netondo,
& Bore, 1984).
3.6 Total polyphenols
Total polyphenols content analysis revealed a varied
difference between shading regimes, seasons, and tea
products. The amount of TP ranged from 18.95% for
BCTC product of 30% shaded regime during the HD
season to 24.70% for GO product of 90% shaded
regime. The densest shading regime (90%) had the
highest level of total polyphenols (22.35%) compared
to unshaded regime (21.61%) (Table 2), supporting the
idea of Lee et al. (2013) that individual phenolic compounds resulted in increased levels of total phenolic
compounds in the shaded tea plants. Also, Wang et al.
(2012) noted that there was a marked increase in concentration of phenolic acids in shaded leaves in tea.
The content of total polyphenol was also affected by
seasonal variations, with CW season having the highest level (23.04%) followed by WW and finally HD,
showing that TP content is elevated by high humidity
and low temperatures (Table 2). This finding was also
inferred from the results of Ghabru and Sud (2017),
i.e., that the synthesis of TP was assisted by minimum
temperature and evaporation. Cherotich et al. (2013)
also explained that polyphenols content are lower in
the dry season compared to the wet season in most tea
cultivars, because water is one of the raw materials for
photosynthesis and it has direct impacts on the organic
synthesis of plants of both the primary and the secondary metabolites. Generally, GO product registered
higher content of total polyphenols (23.45%) (Table 2).
Relatively lower levels of polyphenols in black tea can
be attributed to the conversion of tea polyphenols into
179
in tea plants. Semchenko,Lepik, Götzenberger, and
Zobel (2012) noted in their study on perennial herbaceous species that moderate shade had a strongly
facilitative effect on plant growth.
3.3 Green leaf yield
Monthly mean seasonal yields ranged between 32
kg.mt/ha for unshaded regime during the HD season
to 339 kg.mt/ha for 30% shaded regime during CW
season (Table 2). Significant difference was observed
within the shading regimes and seasons and between
their interactions. Overall, the lowest yields (201
kg.mt/ha) were recorded in the unshaded regime compared to the significantly higher yields (260 kg.mt/ha)
recorded under 30% shading regime (Table 2), whereas
significantly higher seasonal yields were observed
during the WW season (254 kg.mt/ha) as compared
to the HD season (122 kg.mt/ha) that had the lowest
yields. The significantly low yields recorded in the HD
season for the unshaded regime of 32 kg.mt/ha must
have been caused by low rainfall precipitation and photoinhibition caused by high temperatures coupled with
long sunshine hours. Further, Barua (1969) in a study
conducted in North East India reported that tea yields
in plants grown under 35% light intensity were higher
than in plants grown in full sun. Fu et al. (2015) also
noted prolonged shading might lead to reduced tea leaf
biomass.
3.4 Total catechins
The total catechin (TC) contents in tea products ranged
from 1.21% in BCTC processed from 90% shade
regime during the HD season to 22.24% in GO processed from unshaded regime during CW season
(Table 2). An increase in shading intensity subsequently reduced the accumulation of catechins, with
90% shading regime giving significantly lower TC
(10.81%) levels compared to the unshaded regime
(12.45%) (Table 2). The CW season accumulated maximum catechins (13.01%) compared to HD (10.7%)
season that recorded the lowest level with higher TC
content being recorded in the GO product (19.82%)
compared to BCTC (3.19%) (Table 2). All variables and interactions were significantly (P≤0.05)
different. Song et al. (2019) concluded that the concentration of total catechins was higher in unshaded
than in shaded leaves, and lower in early January
than at other times, indicating that catechin accumulation is proportional and inversely proportional to
humidity and temperature, respectively. Similar observations by Astill, Birch, Dacombe, Humphrey, and
Martin (2001) explained that catechin content of the
CTC-manufactured black teas is lower as a function
of the greater leaf disruption, and enzymatic oxidation
during withering and fermentation in CTC manufacture results in the conversion of catechins to theaflavins
and thearubigins.
3.5 Caffeine content
As depicted in Table 2, caffeine content was significantly (P≤0.05) influenced by all factors and their
interactions. Caffeine content decreased significantly
with an increase in shade intensity to a minimum of
2.59% under 90% shading regime for BCTC product,
with the highest content of caffeine being recorded in
the HD season (3.64%) under unshaded regime in GO
product (Table 2). Caffeine content for GO product
during HD season under 30 and 60% shading regimes
was 2.64% and 2.61%, respectively, which is below
Yatakamidori (Japanese green tea cultivar) with 2.67%
(Kerio, Wachira, Wanyoko, & Rotich, 2013).
Caffeine content was affected positively by high
temperature and dry conditions (Table 1). This is in
order with the findings of Lee et al. (2010) that caffeine content was higher in tea under high temperature
and long-time sun exposure. Kirakosyan et al. (2004)
also explained that tea cultivars had high levels of caffeine during the dry season due to the accumulation of
secondary metabolites such as caffeine by plants as a
form of defense mechanism. In order to respond and
adapt to environmental stresses, caffeine acts through
allelopathy (Kim & Sano, 2008) as repellant (Chou
& Waller, 1980) and signaling molecules to activate
plant defense responses (Nathanson, Owuor, Netondo,
& Bore, 1984).
3.6 Total polyphenols
Total polyphenols content analysis revealed a varied
difference between shading regimes, seasons, and tea
products. The amount of TP ranged from 18.95% for
BCTC product of 30% shaded regime during the HD
season to 24.70% for GO product of 90% shaded
regime. The densest shading regime (90%) had the
highest level of total polyphenols (22.35%) compared
to unshaded regime (21.61%) (Table 2), supporting the
idea of Lee et al. (2013) that individual phenolic compounds resulted in increased levels of total phenolic
compounds in the shaded tea plants. Also, Wang et al.
(2012) noted that there was a marked increase in concentration of phenolic acids in shaded leaves in tea.
The content of total polyphenol was also affected by
seasonal variations, with CW season having the highest level (23.04%) followed by WW and finally HD,
showing that TP content is elevated by high humidity
and low temperatures (Table 2). This finding was also
inferred from the results of Ghabru and Sud (2017),
i.e., that the synthesis of TP was assisted by minimum
temperature and evaporation. Cherotich et al. (2013)
also explained that polyphenols content are lower in
the dry season compared to the wet season in most tea
cultivars, because water is one of the raw materials for
photosynthesis and it has direct impacts on the organic
synthesis of plants of both the primary and the secondary metabolites. Generally, GO product registered
higher content of total polyphenols (23.45%) (Table 2).
Relatively lower levels of polyphenols in black tea can
be attributed to the conversion of tea polyphenols into
179