Analysis and Evaluation of Sensory Properties and ... - UCSI University

INTERNATIONAL JOURNAL FOR THE ADVANCEMENT OF SCIENCE AND ARTS, VOL. 2, NO. 2, 2011 

Analysis and Evaluation of Sensory 

Properties and Consumer Acceptability 

of Thunbergia laurifolia Teas 

Eric Chan Wei Chiang, Eng Suit Ying, Tan Yuen Ping, Wong Zhiew Cheng 

Faculty of Applied Sciences, UCSI University, 56000 Cheras, Kuala Lumpur, Malaysia 

chanwc@ucsi.edu.my 

___________________________________________________________________________ 

Abstract 

Sensory properties and consumer acceptability of herbal teas of Thunbergia laurifolia produced from 

four different drying methods were evaluated using quantitative descriptive analysis (QDA) and 

hedonic survey, respectively. Comparisons were made with the commercial T. laurifolia or Rang 

Chuet (RC) tea from Thailand. Teas from microwave-dried (MD), freeze-dried (FD), oven-dried (OD) 

and freeze-withered (FW) leaves of T. laurifolia were extracted with boiling water and infusions were 

allowed to steep to mimic tea brewing. The QDA evaluated sensory attributes of fermented flavour, 

unfermented flavour, bitterness, astringency, grassiness and sourness. The MD and FD teas can be 

categorised as green tea while the FW, RC and OD teas are characteristic of black teas. Results of the 

hedonic survey, which scored attributes of appearance, aroma, flavour, overall acceptability and 

preference ranking, showed that the MD tea was the most preferred, being the least bitter and has a 

sweet after-taste. The OD tea had the lowest scores for aroma, flavour and overall acceptability. 

Preference ranking of the T. laurifolia teas was MD > FD ~ FW > RC > OD. In terms of purchase 

intent, 34% of the respondents would definitely or probably buy the tea products. Bitterness of T. 

laurifolia teas was a crucial factor in determining consumer acceptance or rejection. 

Keywords: Thunbergia laurifolia, quantitative descriptive analysis, hedonic survey, sensory 

characteristics, consumer acceptability, herbal teas 

______________________________________________________________________________ 

1. INTRODUCTION 

In recent years, herbal teas (infusions of dried leaves, flowers, seeds, roots and barks steeped 

in boiling water) are gaining popularity and a great variety is sold in health food stores. They 

are popular because of their fragrance, antioxidant properties and therapeutic applications 

[1,2]. Consumers believe that herbal teas are natural and safe as herbs can promote health and 

assuage illness [3]. They are considered an important alternative source of antioxidants and 

are often classified based on their therapeutic actions. However, modern medicine does not 

advocate the use of herbal teas as their mechanisms of action and effectiveness of active 

ingredients are not evidence-based or scientifically-proven. The chemistry and pharmacology 

of many herbal tea plants are still poorly studied, with the exception of herbs of the family 

Labiatae [4-6]. 

In Thailand, several herbal companies are producing and marketing herbal teas from 

medicinal plants. Herbal teas are sold as ground herbs packed in tea bags, which can be 

consumed by steeping in hot water. Most are made of only one kind of herb although some 

may be blended. Among the herbal teas sold is Thunbergia laurifolia. The species is a fast- 

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growing ornamental vine with heart-shaped leaves and pale purplish-blue flowers (Figure 1). 

Leaves of T. laurifolia are used as an antidote for poisons including drugs and cigarettes 

[7,8]. The plant has also been reported to have anti-inflammatory, anti-diabetic and 

antipyretic properties [9,10]. The antioxidant properties of T. laurifolia are well studied 

[11,12]. In Malaysia, T. laurifolia has been planted as an ornamental climber and is not 

recognised to have any medicinal properties. The phytochemistry and pharmacological 

properties of T. laurifolia have recently been reviewed [13]. 

Figure 1: Leaf (left) and plant (right) of Thunbergia laurifolia 

Much research has been conducted on the sensory properties of green, oolong and black teas 

of Camellia sinensis [14-18]. With the exception of teas of rooibos [19] and ginseng [20], 

hardly any work has been done for most of the herbal teas. In this study, the sensory 

properties and consumer acceptability of T. laurifolia teas produced from four different 

drying methods were assessed in comparison with the commercial T. laurifolia (Rang Chuet) 

tea from Thailand. Sensory characteristics were determined using quantitative descriptive 

analysis (QDA) by trained panellists. A hedonic survey was conducted to evaluate consumer 

acceptability of the five teas. This study represented the first evaluation of the sensory 

properties and consumer acceptability of T. laurifolia teas. 

2. MATERIALS AND METHODS 

2.1 Plant Materials 

The commercial T. laurifolia (Rang Chuet) tea was purchased from Bangkok, Thailand. Sold 

under the brand name of TriSiam New Life Tea, it consisted of 10 sachets per packet with 

each sachet containing 2 g of tea. Fresh leaves of T. laurifolia (Figure 1) were collected from 

Bandar Sri Menjalara, Kepong, Kuala Lumpur. Collected leaves (500 g) were cleaned, 

shredded into 0.2 cm strips with a pasta maker (GCH Retail, Malaysia) and dried. 

2.2 Drying Methods 

The drying methods used were microwave drying, oven drying, freeze drying and freeze 

withering. For each treatment, 600 g of leaves were dried in batches. The microwave-dried 

(MD) tea was produced by drying 12 g leaves in a microwave oven (Sharp, Malaysia, Model 

R-397JS, 230–240 V, 50 Hz) for 1.5 min. The oven-dried (OD) tea was produced by drying 

15 g leaves in a fan oven (Memmert UFB500, Germany) for 3 h at 50 o C. The freeze-dried 

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(FD) tea was produced by drying 30 g of leaves in a freeze dryer (Martin Christ-Alpha 1-4 

LD plus, Germany) for 5 h at less than 1.0 mbar and ice condenser at –40 o C. For the 

production of the freeze-withered (FW) tea, 15 g of leaves were vacuum-packed and stored in 

the freezer (Copens Scientific, Malaysia) at –20 o C for 1 day. After thawing for 3 min, the 

leaves were dried in an oven for 1 h at 30 o C. 

2.3 Extraction 

For tea extraction, 1 g of tea in bags was extracted with 50 ml boiling water. To mimic tea 

brewing, infusions were allowed to steep for 1 h with continuous swirling and allowed to cool 

throughout the period. Extracts were filtered and stored at 4 o C for further analysis. Analyses 

of aqueous tea extracts were done in triplicate. 

2.4 Quantitative Descriptive Analysis 

Twelve Food Science and Nutrition students of UCSI University participated in pre-screening 

tests. Candidates first filled a questionnaire on their personal background, time available, 

health conditions and food habits, answered a simple flavour quiz, and undertook a scaling 

test. Those who answered 80% of the questions correctly would undertake the acuity tests for 

detection and description. In the detection test, six sets of three samples were provided and 

candidates were required to identify the odd sample in each set. In the description test, 

candidates were required to describe the sensory characteristics of six sets of samples using 

their own descriptors. Candidates who scored 80% in the acuity tests would progress with the 

ranking test. In the ranking test, candidates were provided with six sets of samples, each 

containing four samples with same attribute but of different intensity. Candidates were 

required to rank the samples of each set in ascending order of intensity. 

Nine of the candidates qualified and were subsequently trained as panellists for the 

quantitative descriptive analysis (QDA). Panellists attended a series of training sessions, 

which included initial practice, rating practice, small product difference test and final practice. 

An array of commercially available products, that represented as many as possible attributes 

of T. laurifolia teas under investigation, was prepared as references. Panellists were required 

to describe these products based on their appearance, flavour, aroma, colour and clarity. 

Subsequently, a discussion was held to develop the terminologies and definitions for the 

products as standard references (Table 1). The panellists were then introduced to descriptive 

scaling. Three sessions of rating tests using a 15-cm line scale [21] were conducted. They 

were required to rate the different intensities of several attributes based on a set of references. 

The continued use of the intensity reference scale enabled the panellists to produce consistent 

and reproducible results. The training sessions ended with the small product difference test 

and final practice. The small product difference test involved four sets of two similar samples 

and panellists were required to identify the minor differences between samples. For the final 

practice, a sample similar to actual tea sample was tested. This was to ensure that the 

panellists were fully ready for the actual evaluation. The training sessions were for one hour, 

and after each training session, a discussion was held on results, problems, controversies and 

improvements of the sensory evaluation procedures. 

During the actual QDA, T. laurifolia teas from four different drying methods were freshly 

prepared by infusing 2 g of leaves and one sachet of commercial Rang Chuet (RC) tea in 200 

ml of hot water. The infusing conditions were set at 2 min and 80 o C for all five teas. 

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Fermented, unfermented, bitterness, astringency, grassiness and sourness were six sensory 

attributes evaluated by the panellists using the 15-cm line scale. 

Table 1: Definitions and standard references for quantitative descriptive analysis of Thunbergia 

laurifolia teas produced from different drying methods 

Sensory attribute Definition Standard reference * 

Fermented Aromatics association with 

fermented teas such as oolong 

tea or black tea 

Unfermented Aromatics associated with green 

tea 

Bitterness Fundamental taste sensation 

associated with caffeine and quinine 

Astringency Feeling which shrivels the tongue 

and associated with tannins 

Grassiness Aromatics associated with cut grass Cut grass 

Citric acid Aromatics associated with citrus 

fruits 

Roasted grain Aromatics associated with roasted 

grain 

Floral Aromatics associated with flowers 

such as jasmine 

* Intensity scale of 2 

Oolong tea (5 g) from Xiamen Tea 

Co. Ltd., China, infused with 200 

ml boiling water for 2 min 

Green tea (1 g) from Xiamen Tea 

Co. Ltd., China, infused with 200 

ml boiling water for 2 min 

Caffeine solution (0.05 %) from 

Merck, Germany 

Tannic acid solution (0.08 %) from 

Acros Organics, USA 

Citric acid solution (0.05 %) from 

Fisher Scientific, UK 

Roasted barley tea (3 g) from Dong 

Suh Food Co. Ltd., Korea infused 

with 250 ml boiling water for 2 min 

Jasmine tea (1 g) from Xiamen Tea 

Co. Ltd., China infused with 200 ml 

boiling water for 2 min 

Two standard references per attributes were provided to the panellists, one had a low 

intensity while another had a high intensity (Table 2). These standard references provided 

them with an idea of the range of samples intensities. Panellists were instructed to evaluate 

the given samples, one at a time for all six attributes, in separate booths to reduce distraction 

and interaction. They were not allowed to discuss their results after each session. 

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Table 2: Low and high intensities of standard references per attribute 

Sensory attribute Intensity Standard reference 

Fermented 

Unfermented 

Bitterness 

Astringency 

Grassiness 

Sourness 

2.5 Hedonic Survey 

Low – 1 

High – 2 

Low – 1 

High – 2 

Low – 1 

High – 2 

Low – 1 

High – 2 

Low – 1 

High – 2 

Low – 1 

High – 2 

Oolong tea (16 g/L) 

Oolong tea (25 g/L) 

Green tea (3.3 g/L) 

Green tea (5.0 g/L) 

Caffeine (0.03%) 

Caffeine (0.05%) 

Tannic acid (0.05%) 

Tannic acid (0.08%) 

Cut grass (50%) 

Cut grass (100%) 

Citric acid (0.03%) 

Citric acid (0.05%) 

A hedonic survey of consumer acceptability of the five T. laurifolia teas was conducted in the 

Food Science Laboratory of UCSI University. A total of 129 respondents, including students, 

lecturers and other staff members of UCSI University, as well as family members, 

participated in the survey. 

Respondents were invited to evaluate the tea samples, one at a time, in separate booths. The 

samples were coded with three-digit random numbers and were served warm in transparent 

testing cups in randomised presentation order to minimise bias. The evaluation was done 

under normal white fluorescent light, as appearance was an evaluated attribute of the survey. 

The respondents were then asked about their degree of liking of the teas in terms of 

appearance, aroma, flavour and overall acceptability, based on a 9-point hedonic scale, 

ranging from dislike extremely (1) to like extremely (9) [22]. A questionnaire was also 

provided to obtain their opinions on the tea samples, tea preferences and purchase intent. 

2.6 Statistical Analysis 

Analysis of QDA and consumer acceptability of the T. laurifolia teas were performed in 

triplicate, and results were presented as means ± standard deviations (SD). Analysis of 

variance (ANOVA) was calculated using the Tukey’s HSD test at P < 0.05. Correlation 

analysis was also performed to determine the relationship between the QDA data and hedonic 

survey data. 

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3. RESULTS AND DISCUSSION 

3.1 Sensory Characteristics 

Values of sensory attributes of the T. laurifolia teas are shown in Table 3. It was noted that 

the SD of some attributes were large because their intensities were approaching the lower 

limit of detection. The precision of the analysis can be improved by better training and 

providing lower concentrations of standards for comparison. 

Table 3: Values of sensory attributes of Thunbergia laurifolia teas produced from four different 

drying methods with comparisons to the commercial Rang Chuet tea 

Sensory 

Intensity of sensory attribute of T. laurifolia tea* 

attribute MD FW FD OD RC 

Fermented 0.34 ± 0.26 c 

Unfermented 1.76 ± 0.51 a 

Bitterness 0.18 ± 0.16 c 

Astringency 0.77 ± 0.18 c 

Grassiness 1.27 ± 0.16 a 

Sourness 0.09 ± 0.12 b 

2.05 ± 0.18 a 

0.14 ± 0.15 c 

0.19 ± 0.15 c 

1.58 ± 0.14 a 

0.46 ± 0.14 b 

1.18 ± 0.19 a 

0.40 ± 0.17 c 

1.61 ± 0.22 a 

0.42 ± 0.23 b 

0.83 ± 0.37 c 

1.40 ± 0.26 a 

0.14 ± 0.19 b 

1.53 ± 0.16 b 

0.37 ± 0.17 b 

1.21 ± 0.19 a 

1.24 ± 0.14 b 

0.64 ± 0.26 b 

0.95 ± 0.34 b 

1.33 ± 0.16 b 

0.66 ± 0.15 b 

0.35 ± 0.18 b 

1.02 ± 0.17 b 

0.22 ± 0.21 c 

0.01 ± 0.02 b 

* Data from panellists represent the mean ± SD (n = 9), and are based on a 15-cm line scale with 0 cm as 

the zero intensity and 15 cm as the highest intensity. Within the same row, different superscripts (a–c) are 

significantly different at P < 0.05, as measured by the Tukey’s HSD test. Analysis of variance does not 

apply between attributes. Abbreviations: MD = microwave-dried, FW = freeze-withered, FD = freeze-dried, 

OD = oven-dried, RC = Rang Chuet, HSD = honestly significant difference and SD = standard deviation. 

Sensory attributes of the T. laurifolia teas were generally very low, ranging from 0.01 for 

sourness in the RC tea to 2.05 for fermented taste in the FW tea. The mild taste perceived in 

the teas could be due to the use of C. sinensis teas as standard references. From the results, 

MD and FD teas can be categorised as green teas in view of their strong unfermented and 

grassiness attributes [17]. The strong fermented and astringency attributes of FW, RC and 

OD teas are characteristic of black teas. 

Rating of fermented flavour was highest in the FD tea, followed by the OD and RC teas. The 

fermented flavour of the RC tea was 3.9 and 3.3 times higher those of MD and FD teas, 

respectively. 

The MD and FD teas had significantly stronger unfermented flavour than the RC tea. In green 

tea, the unfermented flavour is mainly contributed by catechins [16, 23]. Associated with this 

attribute is the sweet after-taste due to the production of pyrazine compounds from sugars and 

amino acids [17,23]. 

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Rating of bitterness was highest for the OD tea, and lowest for the MD and FW teas. The 

stronger bitterness perceived in the OD tea contradicts reports that phenolic compounds 

notably catechins in teas are responsible for their bitter taste [24]. Simple phenolics are more 

bitter than polymerised phenolics such as tannins i.e. bitterness decreases as the degree of 

polymerisation of tannin increases [25]. Freeze withering of tea resulted in an increase in 

caffeine content [26] and therefore the FW tea should be more bitter. However, this study 

showed otherwise. Disparity in the rating of bitterness of T. laurifolia teas is probably due to 

the sweet after-taste of the MD and FW teas. Panellists might have been affected by the sweet 

after-taste, which reduced their bitterness perception of the tea. 

The FW tea had the highest astringency rating, followed by the OD and RC teas. In black tea, 

polymeric tannins such as theaflavins and thearubigins are produced during the fermentation 

process [27]. Phenolic compounds with higher molecular weights are more astringent than 

those with lower molecular weights [24,25]. 

The FD and MD teas had significant higher rating for grassiness than the OD and FW teas. 

The RC tea was rated the lowest. Green tea has stronger fresh green characteristic than 

oolong and black teas [23]. The grassiness attribute of C. sinensis tea decreases with 

fermentation. 

Sourness was rated the highest in the FW tea. The sour taste in teas is attributed to amino 

acids and is stronger in fermented teas [23]. The slightly sour taste in oolong tea is due to the 

presence of gallic acid, myricetin, quercetin and kaempferol [16]. 

3.2 Consumer Acceptability 

Consumer acceptability of the T. laurifolia teas produced from the different drying methods 

was assessed through a hedonic survey that involved 129 respondents. The degree of liking 

was based on a 9-point hedonic scale. Mean hedonic scores of sensory attributes of 

appearance, aroma, flavour and overall acceptability are tabulated in Table 4. 

In terms of appearance, all the T. laurifolia teas scored between 5 (neither like nor dislike) 

and 6 (like slightly). The FD, OD, FW and MD teas had comparable values ranging from 5.6 

to 5.8. The slightly turbid, walnut-brown colour of the RC tea with a score of 5.3 was the 

least favoured in terms of appearance (Figure 2). The respective golden and yellowish-green 

MD and FD teas, and the light brown and dark brown OD and FW teas were more desirable 

in appearance. In black tea, the higher contents of theaflavins and thearubigins contribute to 

the brownish colour. 

Rating for aroma of the T. laurifolia teas was between 5 and 6, with the exception of the OD 

tea with a score of 4.8. The RC and MD teas had the highest scores of 5.5 and 5.4, 

respectively. Most of the respondents did not like the flavour of T. laurifolia teas except for 

the MD tea, which scored 5.1. Most of the respondents opined that they liked the sweet aftertaste 

of the MD tea, but not the strong astringent and bitter taste of the OD tea. Some 

respondents expressed their dislike for the grassy and sour flavours of the teas. 

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Table 4: Hedonic score of sensory attributes and preference ranking of Thunbergia laurifolia teas 

produced from four different drying methods with comparisons to the commercial Rang Chuet tea 

Sensory 

Hedonic score for T. laurifolia tea* 

attribute MD FW FD RC OD 

Appearance 5.8 ± 1.3 a 

Aroma 5.4 ± 1.2 a 

Flavour 5.1 ± 1.5 a 

Acceptability 5.3 ± 1.5 a 

5.7 ± 1.2 ab 

5.2 ± 1.5 ab 

4.9 ± 1.6 a 

4.9 ± 1.6 a 

5.6 ± 1.5 ab 

5.1 ± 1.4 ab 

4.9 ± 1.6 a 

5.0 ± 1.6 a 

5.3 ± 1.3 b 

5.5 ± 1.4 a 

4.9 ± 1.7 a 

5.1 ± 1.6 a 

5.6 ± 1.3 ab 

4.8 ± 1.6 b 

4.1 ± 1.7 b 

4.2 ± 1.7 b 

Preference+ 338 369 370 408 447 

* Data from respondents represent the mean ± SD (n = 129), and are based on a 9-point hedonic scale with 

1 = dislike extremely; 5 = neither like nor dislike and 9 = like extremely. Within the same row, the same 

superscript (a–b) is not significantly different at P < 0.05, as measured by the Tukey’s HSD test. Analysis 

of variance does not apply between attributes. + Lower ranking denotes greater preference by respondents. 

Abbreviations: MD = microwave-dried, FW = freeze-withered, FD = freeze-dried, RC = Rang Chuet, OD 

= oven-dried, HSD = honestly significant difference and SD = standard deviation. 

Freeze-dried Microwave-dried Oven-dried Rang Chuet Freeze-withered 

Figure 2: Infusions of Thunbergia laurifolia herbal teas produced from four different 

drying methods with comparisons to the commercial Rang Chuet tea 

In terms of overall acceptability, the MD, FW and FD teas were comparable to the RC tea. 

Rating of the OD tea was significantly lower than the other teas. The MD tea was the most 

acceptable, followed by the RC tea, while the OD tea was the least acceptable. 

Preference of respondents towards the T. laurifolia teas was ranked by number with 1 

denoting the most preferred, while 5 being the least preferred. Ranking sums of the teas are 

tabulated in Table 4 with lower values indicating greater preference. The MD tea was the 

favourite while the OD tea was the least preferred. Preference ranking of the teas was MD > 

FD ~ FW > RC > OD. The OD tea had the lowest scores for aroma, flavour and overall 

acceptability. The MD tea was the most preferred as it was the least bitter and had a sweet 

after-taste. 

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Purchase intent of respondents of the various T. laurifolia teas was also considered. Data 

indicated that 11% of the respondents would definitely buy and 23% would probably buy the 

tea products. Conversely, only 10% and 16% of the respondents stated that they definitely 

would not buy and probably would not buy the tea, respectively. Based on the questionnaire, 

most of the respondents who definitely would not buy were those who did not consume tea or 

did not like drinking tea. Most of the respondents were unsure as 40% of the respondents 

opted for maybe or maybe not. This group would be interested and can become potential 

consumers with efforts made on improving and optimising the desired sensory attributes of 

the T. laurifolia teas. 

Data on sensory characteristic and hedonic preferences of T. laurifolia teas were correlated. 

Analysis showed that bitterness of the teas influenced consumer acceptance of flavour and 

overall acceptability. Correlations between bitterness and consumer acceptance of flavour 

(linear equation of –0.899x + 5.203 and R 2 = 0.950), and between bitterness and overall 

acceptability (linear equation of –0.921x + 5.320 and R 2 = 0.888) were strongly negative. 

Bitterness of T. laurifolia teas was therefore a crucial factor in determining consumer 

acceptance or rejection. Results were consistent with the report that food rejection is closely 

associated with heightened perception of bitterness [24]. Low acceptance has also been 

correlated with bitterness of cruciferous vegetables [28] and citrus juice [29]. 

4. CONCLUSION 

QDA of sensory characteristics showed that the MD and FD teas of T. laurifolia can be 

categorised as green teas. The FW, RC and OD teas are characteristic of black teas. The MD 

and FD teas had the highest rating for unfermented flavour and grassiness. The FW tea scored 

the highest for fermented flavour, astringency and sourness. The OD tea was the most bitter. 

Results of the hedonic survey showed that the OD tea had the lowest scores for aroma, 

flavour and overall acceptability. The MD tea was the most preferred as it is the least bitter 

and has a sweet after-taste. In terms of purchase intent, 34% of the respondents would 

definitely or probably buy the tea products. Bitterness of T. laurifolia teas was a crucial factor 

in determining consumer acceptance or rejection. 

5. ACKNOWLEDGEMENTS 

This study formed part of the research project on the effects of different drying methods and 

sensory evaluation of herbal teas, conducted by three final year students of the Faculty of 

Applied Sciences, UCSI University. The support of the faculty and university is gratefully 

acknowledged. 

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[29] Hasegawa, S. and Miyake M., 1996. Biochemistry and biological functions of citrus 

limonoids. Food Reviews International, 12, 413-435. 

Eric Chan Wei Chiang joined UCSI University in December 2009 as a 

lecturer at the Faculty of Applied Sciences. Dr. Eric Chan obtained his B.Sc. 

and Ph.D. from Monash University Sunway Campus. He has published 23 

papers in international refereed journals of which five were with final year 

students of UCSI University. He is a Life Member of Pharmacognosy 

Network Worldwide since 2011; Life Member for Academic Excellence, 

Monash University Chapter of the Golden Key International Honour Society 

since 2002; and Member of International Society of Mangrove Ecosystems 

(ISME), Okinawa, Japan since 2008. He was conferred Prestige Top 40 Under 40 Award 

2010; Consolation Prize of Merck Young Scientist Award 2009, Chromatography Category; 

and Monash University Malaysia Best Honours Student Award 2005. His current research 

interest is on the bioactivities of herbs and spices, and the effects of drying, pickling, brining 

and blanching. 

26

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