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

More documents

Recommendations

Info

INTERNATIONAL JOURNAL FOR THE ADVANCEMENT OF SCIENCE AND ARTS, VOL. 2, NO. 2, 2011 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]. 21
INTERNATIONAL JOURNAL FOR THE ADVANCEMENT OF SCIENCE AND ARTS, VOL. 2, NO. 2, 2011 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. 22
Page 1 and 2: INTERNATIONAL JOURNAL FOR THE ADVAN
Page 5: INTERNATIONAL JOURNAL FOR THE ADVAN
Page 11: INTERNATIONAL JOURNAL FOR THE ADVAN

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

Create successful ePaper yourself

Delete template?

Save as template?