CRUDE FIBRE, WATER EXTRACTS, TOTAL ASH, CAFFEINE AND MOISTURE CONTENTS AS DIAGNOSTIC FACTORS IN EVALUATING GREEN TEA QUALITY

Abstract

This experiment was carried out to diagnose the qualities of green tea from Nigeria using some quality markers like crude fibre, water extracts, total ash, caffeine and moisture contents respectively. Green Tea was processed from seven different tea clones from Mambilla Highland located on 1840m above mean sea level. The clonal materials used were processed into green tea using Chinese methods viz: Plucking, Fixing (Pan firing), Rolling and Drying. The green tea produced were analyzed for moisture contents, (MC); Crude Fibre, (CF).; Water Extract, (WE).; Total Ash, (TA).; Water Soluble Ash, (WSA).; Alkaline Insoluble Ash, (ALIA) and Acid Insoluble Ash, (AIA). The quality of the green tea produced was compared to the recommended ISO standard for Tea. Our findings showed that there were significant differences (p<0.05) in the chemical components studied as a result of clonal variations which made the quality characteristics of the green tea to vary accordingly. The WE, of all the green tea examined except sample made from clone 236 were within values recommended for good quality green tea as speculated by ISO 3720, % MC was between 4.11-12.5% with average value being 10.2%. The High MC recorded was due to the high humidity of the processing environment where sunlight was inadequate The percentage CF ranged between 4.37-20.8%, the ALIA, 0.90-1.30, TA, 4.2-6.5%, WSA, 50-67% and WE 21.7-43.6% and the caffeine contents were within 1.29-2.56%. In conclusion, quality of green tea produced in Nigeria has comparable quality characteristics with other tea producing countries of the world and conformed to international standard for green tea. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

This experiment was carried out to diagnose the qualities of green tea from Nigeria using some quality markers like crude fibre, water extracts, total ash, caffeine and moisture contents respectively.

Green Tea was processed from seven different tea clones from Mambilla Highland located on 1840m above mean sea level. The clonal materials used were processed into green tea using Chinese methods viz: Plucking, Fixing (Pan firing), Rolling and Drying. The green tea produced were analyzed for moisture contents, (MC); Crude Fibre, (CF).; Water Extract, (WE).; Total Ash, (TA).; Water Soluble Ash, (WSA).; Alkaline Insoluble Ash, (ALIA) and Acid Insoluble Ash, (AIA). The quality of the green tea produced was compared to the recommended ISO standard for Tea.

Our findings showed that there were significant differences (p<0.05) in the chemical components studied as a result of clonal variations which made the quality characteristics of the green tea to vary accordingly. The WE, of all the green tea examined except sample made from clone 236 were within values recommended for good quality green tea as speculated by ISO 3720, % MC was between 4.11-12.5% with average value being 10.2%. The High MC recorded was due to the high humidity of the processing environment where sunlight was inadequate The percentage CF ranged between 4.37-20.8%, the ALIA, 0.90-1.30, TA, 4.2-6.5%, WSA, 50-67% and WE 21.7-43.6% and the caffeine contents were within 1.29-2.56%.

In conclusion, quality of green tea produced in Nigeria has comparable quality characteristics with other tea producing countries of the world and conformed to international standard for green tea.

- Keywords: tea clones, green, black, crude fibres, water extracts, caffeine -

INTRODUCTION

Crude fibre in plants originates from certain structural units, cellular walls, skelrenchyma, collenchymas and transporting tissues. Young cells have thin cellular walls that becomes hard as the plant grows and provide the plants with protection from excess transpiration and influence of other undesirable factors (STRASBERGER, 1962). Fibre is composed of many different compounds in particular cellulose, hemicelluloses and wood-wool. Most of them are polysaccharides with the exception of wood-wool. The content of crude fibre in young tea leaves is much less than in older ones. The fundamental (and one of the older) definition of crude fibre states that it is the residue after treating with boiling 0.255N sulfuric acid and 0.3 13N sodium hydroxide (BARTMIKOWSKA, 1997). Crude fibre is the main part of the insoluble matter of black tea. The fibre content can vary and ranges between 7 and 20% in tea products. In general, when the fibre content of tea increases, most of the quality characteristics component decreases (FERMUZ et al, 1993). Coarse plucking and aged leaves result in higher levels of Fibre. Coarse leaves and stalks are mixed with the finer parts of the shoots during the different rolling processes and it is very difficult to remove all of them from tea in later processes. Tea is one of the oldest beverages in the world. It is second most popular beverage after water (SMIECHOWSKA and DMOWSKA, 2006). Its quality is determined among other things by aroma and taste properties. Much attention has been drawn to the fact that crude fibre is an important parameter in the quality evaluation of tea and influences its sensory properties. Another very important parameter that determines tea quality according to FERMUZ et al (1993) is water extract (WE). A tea shoot of two leaves and a bud contain about 25% solid matter. About half of the solid matter is soluble in water and this is termed extract. Many components of the liquor influence tea quality. The amount of these components generally increases in proportion to the amount of Tea extract. Thus, the percentage of extract is limited by the International Standard Organization (ISO). The amount of extracts decreases as plucking intervals lengthens and also decreases due to coarse plucking and aging of the leaf (SMIECHOWSKA and DMOWSKA, 2006).

Caffeine is an alkaloid that can constitute approximately 5% of the Dry Matter in fine tea shoots. Tea is widely consumed all over the world and caffeine plays a very important role in explaining why Tea is used as a beverage because it has a stimulating effect on the human body. A high content of caffeine contributes to briskness, which is one of the factors indicating Quality Tea. The Caffeine content of green tea increases after harvesting particularly during the withering process. Some authors have reported that different rolling process do not affect the caffeine content of processed black tea Green tea (unfermented tea) is a major beverage in Asian Countries such as China and Japan whereas, black tea (fermented tea) is more popular in other parts of the world. Although green tea and black tea are made from the leaves of the same plant, Camellia sinensis, differences in the processing of the leaves result in differing chemical components. Since this study is the first report on green tea production in Nigeria, with no previous reports in the literature. This work was, however, designed with the objective of diagnosing the quality of green tea processed from Nigerian tea clonal materials using quality markers like crude fibre, Caffeine, Moisture contents, water extracts and total Ash according to the International quality standards for tea.

MATERIALS AND METHODS

Green tea samples used in this study were processed on the Mambilla Highland from seven different tea clones 35, 68, 228, 318, 363, 61 and 236, respectively The fresh tea leaves used in the green tea production were plucked from vegetatively propagated (VP) tea fields at the Cocoa Research Institute of Nigeria (CRIN) substation, Kusuku, Mambilla located around 1,840 m above mean sea level, latitude 6° 24' ? and longitude 10° 35?. The plants were grown under recommended agronomic conditions. The tea clones were plucked at the tea plantation and processed by the miniature green tea processing facilities. The plucked tea leaves were withered shortly followed by fixing to inactivate the activities of the polyphenol oxidase enzyme using the Chinese methods of Pan fixing. The pan-fixed leaves were later rolled and dried using oven. The green tea produced were later packaged in paper board boxes and reserved for Analysis.

Preparation of the tea solution

The tea preparations consisted of addition of boiling water (200 mL) to leaf tea (2 g), then the tea solution was filtered through cotton wool and the residue was washed with distilled water (30x10 mL). The tea solution was cooled to room temperature and washings were diluted 250 mL with distilled water. The samples were analyzed in triplicate.

Caffeine and water extracts

The methods used for the analyses of caffeine and water extracts of the tea solution were based on international standards (ISO 1839), 1980; (ISO 9768, 1994); YAO et al. (1992) as stated below.

Caffeine

Lead Acetate solution (CH3COO)2Pb.

100 g was dissolved and diluted to 200 mL with distilled water.

Hydrochloric acid solution, HCl.

36%, specific gravity, 1.18, 0.9 mL was diluted to 100 mL with distilled water.

Sulphuric acid solution

Sulphuric acid (98%) H2S04, specific gravity, 1.84, 16.7 mL) was diluted to 100 mL with distilled water.

Measurements: Tea solution (10 mL), HCl (5 mL) and Lead acetate solution (1 mL) were mixed in a 1 00 mL volumetric flask and diluted with distilled water. The solution was then filtered through Whatman No. 1 quantitative filter paper. The filtrate (25 mL) and sulphuric acid solution (0.3 mL) were placed in a volumetric flask and diluted to 50 mL with distilled water. The solution was filtered using the same type of filter paper. The absorbance of the filtrate was measured using Ultraspec III UV /visible spectrophotometer at 274 nm. The measurement was performed in triplicates.

Standard curve

Caffeine stock solution (10 mL), 1 mg/mL, w/v in distilled water was diluted to 200 mL with distilled water. Next, 0, 10, 20, 30, 40, or 50 mL of the diluted caffeine solution were separately mixed, each with Hydrochloric acid solution (4 mL) in a volumetric flask are diluted to 100 mL with distilled water. Thereafter, the remaining steps were repeated as described earlier. The readings of the standard solution against the concentrations were used to prepare the standard curve.

Calculation

Caffeine (%)= E/ 1,000 xV0 x (100/V1)x x (50/25)/W = O.2EV0/V1/W

Where E is 'mg' of caffeine from the standard curve against the reading of the spectrophotometer and E/ 1,000 is to convert 'mg' into 'g'. V0 is the total volume of the tea solution (250 mL); V1 is the volume used for the measurements (10 mL), and 100/V1 indicates 10 mL tea solutions that were diluted to 100 mL, while 50/25 shows that another dilution from 25 mL tea filtrate made to 50 mL in the measurement. W is the dry weight of the tea sample.

Water extracts

Measurements

Tea solution (50 mL) was placed in a weighed evaporating dish and was then evaporated to dryness over a water bath. The residue (tea extracts) in the dish was fully dried in a vacuum oven at 75°C with a negative pressure of 65kPa for 4h until the weight of the dish with extract was constant.

Calculation

Water extract (%) = (D1-D0) x V0 x 100/V1W

Where D1 is the weight of the dry tea extracts with the dish; D0 is the weight of the dish, V0 is the total volume of the tea solution (250 mL), V1 is the volume used for the analysis (50 mL); W is the dry weight of the tea sample Moisture Content.

The tea moisture was measured using a vacuum oven based on an international standard method ISO 1573, BS 6049-2, 1981.

Statistical analysis

One way Analysis of Variance (ANOVA) was performed to show the general trend of the experimental data. SPSS version 10.0 (SPSS Inc. Chicago, IL, USA) statistical Package was used. The mean and standard errors of means (SEM) in terms of the chemical compositions of the tea clones were expressed by Box plot using SPSS 10.0. version.

RESULTS AND DISCUSSION

Some samples of the results are shown in Table 1 while the summary has been displayed in the box plots (Fig. 1). To avoid error of interpretation, it should be noted that certain variables, such as water soluble ash (WSA), water extracts and crude fibre (CF) of the tea samples, have higher numerical values compared to other chemical components like the ash content, alkaline insoluble ash and moisture contents respectively (Fig. 1).

One of the parameters described in quality norms is crude fibre content. According to Table 1, the averages of the crude fibre contents ranged between 4.30-20.80% dry matter for the tea clones from Nigeria. The crude fibre contents were generally similar in values to the values determined in Turkish black tea samples as reported by FERMUZ et al. (1993). Crude fibre of tea has been linked to shooting period. Black tea from the first shooting period has been reported to have the lowest amount of fibres whereas the fibre contents were found to be higher in the tea of the third shooting period. This result indicated that the seven tea clones used in this study differed significantly in crude fibres, suggesting large generic variations (MAGOMA et ed., 2000). Indeed, the significant differences (p<0.05) in the levels of the crude fibres suggested that the quality potential of these clones could be different. It is noteworthy that the quality requirements for black tea states that crude fibre contents should not exceed 16.5% (ISO 3720, 1986). From the data collected in our own studies, it appears that on average, the least crude fibre was found in clone 236, whereas the highest crude fibre was recorded only for both clones 61 and 363. In all the seven tea clones analyzed, only these two clones deviated from the ISO standard 37201986 for crude fibre. From our data, it was obvious that minimum crude fibre from clone 236 was lower than the minimum from China and the maximum was recorded for samples from, Malawi. (Table 2). Moreover, the extent of crude fibre in tea from Malawi ranged very drastically from 5.83 to 43.27%. SMIECHOWSKA and DMOWSKA (2006) reported that the crude fibre can be accurate parameters to describe tea age. The younger the tea leaves used to process the green tea, the lower is the fibre content. In the so called leafy teas, a significant content of fibre in the products may show that lower quality material has been used in the production (5th to 6th leaf) due to high contents of careless mechanical harvest of tea when the yield contained not only leaves but also stems. This factor may not be significant in this study as leaves plucked were strictly 1 leaf + a bud for green tea. It could be suspected that the maturity of the tea used in the experiment might not have been the same. The genetic nature of the tea clones might also be responsible. The knowledge of water extracts, caffeine, moisture contents, crude fibre are very important physical and chemical parameters' as well as economic in screening tea clones for green tea and black tea processing. The water extracts found in this study ranged between 21.7-43.4% giving a mean of 39.3%. This is in agreement with previous studies (FERMUZ et al., 1993). According to the international standard, water extracts of a tea is the soluble matter extracted from a test portion by boiling water, under the condition specified in this international standard expressed by mass on a dry basis (ISO 9768, 1994). In this study, the water extracts of all the tea clones examined except clone 236 conformed to the ISO 9768, 1994 standard which stipulated that the water extract in tea should be more than or equal to 32% of the dry mass. Compared to the water extracts of green tea produced from other Countries like Chinese green tea, 36.79%; India, 36.89-41.95%, but lower than water extracts of tea from Sri- Lanka, 36.72-46.9% and Kenya, 44.12%. It is however established that the mean contents of water extracts in green tea from Nigerian tea clones as evidenced in this study is relatively high and compared favourably well with the water extracts from leading tea producing Countries of the world. The mean content of water extracts in all the tea clones were within those reported by LIU et al, 2006, who reported 39. 18% in six green tea bags from Australian supermarkets. The similarity in the values obtained in our experiment is not unexpected as water extracts from black and green tea cannot be the same, green being reportedly higher than black tea due to differences in manufacturing conditions leading to decomposition of tea components to different degrees (HARA et al, 1995; HARBOWY and BALENTINE, 1997).

Moisture content of green tea

Moisture content is an important quality parameter of tea (ROBERTS and SMITH, 1963) and is usually neglected by researchers but not by the industries or tea traders. Tea Researchers (OTHIENO and OWUOR, 1984; ROBINSON and OWUOR, 1993) suggested that the moisture content of the teas should be controlled to lie below 6.5% for marketing teas, whereas Millin, 1987 noted that teas had a moisture content of 7.08.5 during retailing. In this study, the mean moisture content obtained was 10.17% which was above 6.5% and deviated from the recommended standard for good quality green tea. The high level of moisture in our study samples was due to the high humidity of the processing environment as dried tea picked up moisture during the holding time between production and Analysis In this study, the variation in tea clones did not have any significant effects on the moisture contents. The main important factor for the moisture recorded was due to the high humidity of the processing environments. The main implications of this finding is that high moisture content will produce negative effects on shelf life of the green tea produced. There is however, a need for an improved quality control for the drying and Packaging of green tea produced in Nigeria. The dried tea leaves must be packaged in a moisture barrier material to prevent moisture pick up after drying. As for Water extracts (WE), ISO 9768 standard, min = 32. All the tea clones have more than this level except clone 363 having only 21.7% WE. The Total Ash of the clones varied according to variations in clones and ranged between 4.2-6.65 and fell within the recommended ISO 1575 standard for total ash of good quality green tea (min, 4, maximum, 8) .The water soluble ash (WSA) of the clones were all within the recommended ISO 1576 standard, minimum = 45%. Acid insoluble Ash (AIA) of all the tea clones were also appropriate when compared to ISO 5998, apart from clone 6 1 and clone 363 with high values of 20.8% each than the recommended.

Caffeine

The caffeine contents varied significantly according to the tea clones. The green tea caffeine for clone 228, 318 and 236 were within the standard level of 2-5%. Other clonal varieties like clone 61, 35, 68 and 363 were relatively low in caffeine. Caffeine is an important component of tea. Green tea contains abundant caffeine, which is an alkaloid that can have negative effects on human body depending on the level of intake. Less than 300 mg intake per day is not harmful for adults, but an intake of more than 500 mg has been shown to cause excessive excitation in the central nervous system and cause arrhythmia and vertigo (PASPA and VASSAILA, 1984; SEALE et al., 1984). Since not all the body can withstand the strong caffeine in the system, green tea from clones 61, 35, 68 and 363 can be good material for producing green tea, with clone 6 1 being the best. It is noteworthy therefore that close attention should be paid to caffeine intake by children and pregnant women because it is slowly metabolized and can remain in the body for a prolonged period (GIANNELLI et al. 2003; RASCH, 2003). Accordingly the removal or marked reduction of the caffeine content of green tea has been actively attempted by establishing a new technique called decaffeination in the manufacturing process. Methods using organic solvents, supercritical carbon IV oxide and hot water have been reported for the decaffeination of green tea (LEE et al., 2007; LIANG et al, 2007; PARK et al, 2008; PARK et al, 2007).

In conclusion, the combination of good yields coupled with processing potential of the clone should be used as a base for plant breeders to develop a clone that can be recommended for use in the processing of green tea with the minimum caffeine contents.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the Executive Director, Cocoa Research Institute of Nigeria, Ibadan for permission to publish this paper. The provision of laboratory facilities to analyze the green tea samples by Nigeria Beverage Production Company, Mambilla, is also appreciated. Miss RE. Magaji is also acknowledged for assisting in data computation.

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Paper received March 21, 2012 Accepted August 18, 2012