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

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INTERNATIONAL JOURNAL FOR THE ADVANCEMENT OF SCIENCE AND ARTS, VOL. 2, NO. 2, 2011 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 17
INTERNATIONAL JOURNAL FOR THE ADVANCEMENT OF SCIENCE AND ARTS, VOL. 2, NO. 2, 2011 (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. 18
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