遠紅外線烘焙溫度與時間對包種茶品質之影響

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1 農業機械學刊第 17 卷第 2 期 2008 年 6 月 15 遠紅外線烘焙溫度與時間對包種茶品質之影響 張連發 1, 盛中德 2, 黃裕益 3 1. 行政院農業委員會茶業改良場助理研究員 ˉˉˉˉˉˉˉ 2. 國立中興大學生物產業機電工程學系教授, 本文通訊作者 3. 國立中興大學生物產業機電工程學系教授 ˉˉˉˉˉˉˉ 摘 要 本研究以半球型包種茶為材料, 並以電熱焙茶法為對照組, 探討不同溫度與時間的遠紅外線烘焙對茶葉品質之影響 結果顯示, 電熱焙茶法製淂的成茶含水率及 ph 值較低, 茶湯之色澤呈黃 亮趨勢 遠紅外線烘焙樣品之 folin 含量較高,EGC ((-)Epigallocatechin) 含量則較低 其他多元酚成分在兩處理間差異並不明顯 另隨烘焙溫度之提高, 遠紅外線烘焙樣品之含水率 phenol folin EC ( (- )Epicatechin ) ECG ( (-)Epicatechin gallate ) 與 EGCG ( (-)Epigallocatechin gallate) 等含量及 ph 值呈下降趨勢, 而咖啡因含量以及茶湯 Hunter b( 黃色度 ) 增加, 但 Hunter L ( 亮度 ) 及 Hunter a ( 紅色度 ) 則無顯著變化 另隨烘焙時間延長, 成茶之含水率 phenol 總游離氨基酸 folin EGCG ECG 等含量及 ph 值與 Hunter a 值均呈下降趨勢, 而其他成分和茶湯色澤則無顯著差異 關鍵詞 : 包種茶 遠紅外線 烘焙 EFFECTS OF FAR INFRARED ROASTING TEMPERATURE AND TIME ON THE QUALITY OF POACHUNG TEA Lien-Fa Chang 1, Chung-Teh Sheng 2,Yu-I Huang 2 1. Assistant Researcher, Taiwan Tea Experiment Station, Council of Agriculture, Executive Yuan. 2. Professor,Department of Bio-Industrial Mechatronics Engineering, National Chung Hsing University, Corresponding Author. 3. Professor, Department of Bio-Industrial Mechatronics Engineering, National Chung Hsing University.

2 16 農業機械學刊第 17 卷第 2 期 2008 年 6 月 ABSTRACT Using semi-spherical-type Poachung tea as experimental material, the effects of far infrared radiation (FIR) roasting with different temperature and time on the quality of Poachung tea were studied and the made tea from using electric (EL) roasting was used as the control. The moisture and ph of the made tea from EL roasting were lower than those from FIR, and the infusion of EL roasting was more yellowish and brighter than that of FIR roasting. The folin and EGC ( (- )Epigallocatechin) contents in tea sample of FIR were higher and lower than those of EL, respectively while the other phenolic constituents were not significantly different between these two samples. As the roasting temperature increased, the moisture, phenol, folin, EC((-)Epicatechin), ECG((-)Epicatechin gallate) and EGCG((-)Epigallocatechin gallate) contents and ph of FIR samples decreased while the caffeine content and yellowish (Hunter b value) color of tea infusion increased with no significant changes for the Hunter L value (brightness) and Hunter A value (redness). As the roasting time increased, the moisture, phenol, total free amino acids, folin, EGCG and ECG contents and ph and Hunter A values decreased. The other constituents and color did not show significantly different. Keywords: Poachung tea, Far infrared radiation, Roasting Introduction Poachung tea, one of partially fermented teas, is famous and popular in the Chinese society worldwide. Its manufacturing process includes withering, fermentation, blanching, rolling and drying. Due to its light fermentation, Poachung tea often presents a green grass odor. In order to get ride of this bad odor and enhance the color and aroma, the roasting process is usually carried out after drying and before selling. It may not only lower down the moisture content, but also increase the storage period (Ou, et al., 1988). The types for roasting include charcoalroasting, electric-heat roasting and far infrared roasting. The tea roasted by traditional charcoalroasting usually has its unique aroma, but it does need more operating time and more manpower. On the other hand, the electric-heat roasting method is widely adopted in the tea industry because of its efficiency and convenience on operation. Both methods do have a very similar heat transfer phenomenon between the heater and tea. The main heat transfer mechanism is the convection between the electric heater and tea. The transferred energy is absorbed by the surface tea, later the energy is transferred into the interior tea and bottom tea via the heat conduction. This heat transfer phenomenon does create a big thermal gradient, and the surface tea does suffer over-heated. Far infrared is a kind of infrared, which can be used to heat the interior of an object. The range of wavelength is um ( 橋口, 1986). The heat of a far infrared heater can be directed added on the be-heated object via radiation. The heating time can be shortened and

3 遠紅外線烘焙溫度與時間對包種茶品質之影響 17 the heat can penetrate to the inside of object due to its effective heat transfer mechanism of radiation. However, the heat transfer is also heavily affected by the relevant characters of the object; e.g. size and shape, density, specific heat, thermal conductivity, and optic properties. (Shimizu, 1986). Ceramics and metal oxides are generally used to make far infrared generators which include impedance object (electric heating wire), radiation material and isolation object to dry food ( 西呎, 1986; 依籐, 1986). In the literature, it is pointed out that when the far infrared is applied for withering tea leaves, the temperature controlled in the range of may enhance the mellow flavor and create better aroma and quality of tea than that by sunwithering. In addition, when the far infrared is applied for drying the tea, the time needed is shortened, but the quality did not have significant changes (Ou, et al. 1988). Therefore, the aim of this study was to investigate the effect of far infrared roasting on the quality of semi-spherical type Poachung tea. After the fresh tea leaves going through the semi-spherical Poachung tea manufacturing process of sun withering, indoor withering, fermentation, blanching, rolling and drying, The roasting temperatures selected were 80, 100, 120 and 140 and the time for roasting selected was 2, 4, and 6 hrs. The objective of this paper was to use the electric-heat roaster at 100 for 4 hrs as the control, the differences in ph, infusion color and contents of moisture, reducing sugar, and caffeine between far infrared roasted tea and the control samples were compared. Materials Materials and Methods Tea samples: the fresh tea leaves of Chinshin Oolong variety bought from tea farmers in Jen-ai Village, Nan-tao County and picked up in the summer of 2001 were used. Roasting machine 1. Electric-heat roasting machine (EHR): It is made by Taihao Company, Taiwan and composites a stainless steel tank with a twolayer jacket and heating wire at both sides (Fig 1). A temperature sensor at the outlet is used to measure the temperature and a timer is used to control the heating time. Inside the tank, ten stainless steel perforated trays are used to hold the experimental tea and a fan is used to force hot air circulating evenly for avoiding the tea to get burnt. Figure 1 A schematic diagram of an electricheat roasting 2. Far infrared roasting machine (Fig 2): It is developed by the authors. The size is 74cm long, and 67cm in diameter. The stainless steel plate for far infrared radiation emission

4 18 農業機械學刊第 17 卷第 2 期 2008 年 6 月 with wavelength range of um and the average emission rate of 0.82 at 370 was designed and manufactured by Industrial Technology Research Institute. Figure 2 A schematic diagram of far infrared roastor Reagents Theanine, Rochelle salt, iron sulfate heptahydrate, 3,5-dinitrosalicylic acid, sodium acetate, ninhydrin, sodium carbonate, Polyvinyl Polypyrolidone and Standards of GC((+)Gallocatechin), EGC((-)Epigallocatechin), C((+)Catechin), EC((-)Epicatechin), EGCG((- )Epigallocatechin gallate) and ECG((-)Epicatechin gallate) and caffeine were purchased from Sigma Co. Methods 1. Determination of moisture content: Moisture Analyzer (HR73, METTLER TOLEDO, Switzerland) was used. Three grams of tea sample were placed in a sample tray and heated at 105 until the weight was remained unchanged. Each sample was done triplicates. 2. Determination of Infusion color: The method of Ou, et al. (1988) were followed. 3. ph value 4. Determination of phenolic compounds contents: The methods of Ou, et al. (1988) were followed. a. Rochella salt method. b. Folin-Ciocalteu method. 5. Determination of reducing sugar content: The method of Ou, et al. (1988) were followed. 6. Analysis of total free amino acids: The method of Ou, et al. (1988) were followed. 7. Determination of total nitrogen content: The method of AACC (1995) was followed. 8. Determination of caffeine and catechins: The method of Ou, et al. (1988) were followed. 9. Statistics analysis: Analysis of Variance (ANOVA) in Statistic Analysis System (SAS) was used and significance difference was done by using Duncan s multiple range test (DMRT). Results and Discussion The total 40 tea samples are prepared for tested. The un-roasted made tea samples are used to test the effects of 4 different roasting temperatures (80, 100, 120, and 140 ) and 3 various roasting time periods (2, 4, and 6 hours). The fresh sample is used to analyze the raw material quality. And the control sample (100 and 4 hours) are prepared and tested to compare with the FIR samples. Every experiment is done triplicate in order to get the enough data for analysis. 1. The effects of roasting by different roasting machines on the quality of tea Table 1 shows the preparation of samples.

5 遠紅外線烘焙溫度與時間對包種茶品質之影響 19 Fresh indicates the raw material, which is used to analyze the quality of fresh tea leaves, which will be used to produce the experimental samples. Control indicates the samples are roasted with EHR with the conditions of 100 C and 4 hours. The labels of rest samples are used to describe the roasting temperature and time period. R1, R2 and R3 are used to point the repeats. The results of comparing the quality of tea samples roasted at 100 C for 4 hrs by EHR and FIRR were shown in Table 2. The moisture content of these two roasting machine were found 1.96% (EHR) and 2.98% (FIRR). Although there is a difference in moisture content between these two machine, they were all below the standard for moisture content of normal tea (3-5 %). For storage, it should be no problem. Table 1: Reference of table of tea sample NO. *1. Roasting treatment : electric roaster *2. R1, R2, and R3: triple samples For infusion color, the Hunter L value of tea infusion by EHR were significantly higher than those by FIRR while the values of Hunter a and b were no significant difference between these two samples. Shyu et al (1998) have pointed out that the color of Poachung tea towards the dark green with oily bright to mean the higher quality. This study does show the similar results. In addition, roasting condition also affects the infusion color of Oolong tea. The experimental results show that the Hunter a and b values increase with the roasting time increased. It resulted in the infusion color become brown red. The major reason for that is tea leaves may undertake the Maillard reaction vigorously (Chen et al., 1986). In this study, for roasting at 100 C for 4 hrs, the Hunter L values of for FIRR and for EHR. The L value of EHR is higher than the L value of FIRR, which indicates les Maillard reaction for the method FIRR. Both methods show the positive Hunter a value of tea infusion color indicates the appearance and color of teas are good. Inducing sugars of roasted tea are the main source for the sweet taste of tea infusion. Among them, glucose, fructose and the non-reducing sugar, sucrose are the major sugars in tea. During roasting process, the reducing sugar together with sucrose may undertake the Maillard reaction and caramel reaction. It causes the tea produced a special roasting aroma and the tea infusion become brown red Ou, et al. (1988). The content of reducing sugar in tea of EHR was significantly higher than that of FIRR (12.82 g/100g vs 9.96g/100g). It indicates that at the same condition of roasting, the FIRR could reach the roasting requirement easier than EHR. During roasting process, the amino acids in tea decreased with higher roasting temperature and longer roasting time. Roasting with longer high temperature caused the dramatic decrease of amino acids, but roasting aroma produced with decrease of amino acids. From Table 2, the total free amino acids in tea of EHR (34.91%) is significantly higher than that of FIRR (31.52%). Polyphenols and caffeine are the major and

6 20 農業機械學刊第 17 卷第 2 期 2008 年 6 月 Table 2 Tea quality change by different roasting treatments a: RS: Reducing suger ; TN : Total nitrogen ; Phenol : Total phenol using ; Folin : Total phenol using Folin-ciocalteu; TFA: Total free b: Unit, RS, TN, phenol, TFA, folin, GC, EGC, C, Caffeine, EC, EGCG, ECG : % important constituents of tea. Their contents and ratio may affect the appearance, color, aroma and taste of tea infusion. The polyphenols in tea are mainly EGC, EGCG, EC, C, ECG and GC together with others such as gallic acid, coumaric acid, etc. They all change according to the condition of roasting. (Ruan, et. al., 1989). As shown in Table 2, the polyphenol content detected by Folin method in the tea of FIRR was significantly higher than that of EHR while the trend for EGC content was opposite. For other polyphenols, there were found no significant difference between these roasting machines. From Table 2, the differences in tea quality between these two roasting machines were shown in ph, Hunter L value and contents of moisture, reducing sugar, total free amino acid and EGC. The difference in moisture content of tea should be caused by EHR having fan to shorten the water evaporation rate. At the same roasting temperature and time, the ph value of FIRR tea was higher than that of EHR tea and brighter too. The two important constituents, reducing sugar and free amino acids were found higher in EHR than in FIRR. It indicates that the Maillard reaction is less rapid in EHR than FIRR. It is corresponding to the results of sensory test which pointed out that the roasting or firing flavor was less strong in EHR tea than in FIRR. Therefore, in order to reach the same tea quality using EHR, the roasting time for FIRR could be shorten and it results in saving roasting time and men-power need by FIRR method. 2. The effects of roasting temperature and time on the quality of tea Due to lack of the reference for FIRR effects on the tea quality, the different roasting temperature and time of FIRR were studied. The results were shown in Table 3 and 4 for roasting temperature effect and time effect, respectively. As shown in Table 3, the moisture content and ph value of tea samples decreased as the roasting temperature increased. In term of tea infusion color, the brightness (Hunter L value) and redness (Hunter a value) of tea infusion were

7 遠紅外線烘焙溫度與時間對包種茶品質之影響 21 Table 3: Tea quality at different Infrared ray roasting temperatures RS: Reducing sugar, TN: Total nitrogen ; Phenol: Total phenol using; Folin: Total phenol using Folinciocalteu ; TFA: Total free amino acid. Unit : Moisture, RS, TN, Phenol, Folin, GC, EGC, C, Caffeine, EC, EGCG, ECG : % Table 4 Tea quality at different Infrared ray roasting times RS: Reducing sugar, TN: Total nitrogen; Phenol: Total phenol using; Folin: Total phenol using Folinciocalteu; TFA: Total free amino acid. Unit : Moisture, RS, TN, Phenol, Folin, GC, EGC, C, Caffeine, EC, EGCG, ECG : %

8 22 農業機械學刊第 17 卷第 2 期 2008 年 6 月 not significantly different among the samples with different roasting temperatures while the yellowness increased significantly as the roasting temperature increased. It indicated that after roasting by FIRR, the infusion of Poachung tea was towards the reddish yellow color. The result was corresponding to that of Chen et al. s study (1986) on the canning of Poachung tea showing the color towards dark and red at the temperature of UHT (Ultra-high temperature) sterilization. For the comparison of reducing sugar and total free amino acids, their contents all decreased as the roasting temperature increase. The main reason should be due to the Maillard reaction occurred to cause the contents of these two constituents decreased and the color towards darkened. In Table 3, phenols (both measured by iron tartarate and Folin methods) decreased and caffeine increased as the roasting temperature increased. Phenols and caffeine are the important constituents in tea. The reason for caffeine increase may be due to that roasting treatment caused the caffeine from texture-bounded or complex of caffeine-tannate leached out during or after FIRR roasting. The contents of phenols together with many catechins, such as C, EC, ECG and EGCG all decreased as the roasting temperature increased. It may be due to the polymerization or epimerization of catechins occurred through non- enzymatic reactions taken place during roasting. From the results of Table 4, the contents of moisture, total free amino acids, phenols, EC, EGCG and ECG, ph value and Hunter a value of the tea all decreased as the roasting time increased while the Hunter b value increased. But others were all remaining unchanged. If the effects of roasting temperature and time on the all constituents were compared, it is known that the effect of roasting temperature is stronger than that of roasting time. 3. The correlation between the physicochemical constituents of the roasted tea samples by FIRR As shown in Table 5, there were all significantly correlated between the constituents except total free amino acids and EGC contents. Moisture content was highly significantly correlated with ph, Hunter b, total Nitrogen, EC, EGCG and ECG, while ph and Hunter b value were almost significantly correlated with other items except one or two only. This results indicated that the contents of physicochemical constituents changed with different roasting temperature and time. Conclusions and Suggestions The experiments were conducted to discover the effect of different heating methods on the roasting process for Poachung tea. The effects of far infrared radiation roasting with different temperature and time were studied and compared the results from using electric roasting. The moisture and ph of tea from EHR were lower than the tea form FIRR with the same roasting conditions. The tea infusion with EHR were more yellowish and brighter than that the tea samples from FIRR. The data of folin and EGC contents with FIRR were higher and lower than the tea samples from EHR, respectively. The other phenolic constituents were not significantly different between these two methods. As using the higher roasting temperature, the moisture, phenol, folin, EC, ECG, and EGCG contents and ph of FIRR samples decreased. In the meantime, the caffeine content and yellowish (Hunter b value) color of tea infusion increased with no significant changes

9 遠紅外線烘焙溫度與時間對包種茶品質之影響 23 Table 5 Correlation coefficients between *, **, *** significant at p<0.05, p<0.01, p<0.001, respectively

10 24 農業機械學刊第 17 卷第 2 期 2008 年 6 月 for Hunter L value (brightness) and Hunter a value (redness), as the roasting temperature was increased. As the roasting time is longer, the values of moisture content phenol, total free amino acids folin, EGCG and ECG contents and ph and Hunter a value decreased. The other constituents and color did not significantly change. Therefore, the FIRR did show the effect to improve the tea quality by comparing the results of EHR. The study does prove the effect of the far infrared heating on the tea roasting. The potential of using far infrared heating to roast tea is possible. At this study, the main objective is to discover the effect on the tea quality. Since the price of energy goes up dramatically, the effect of energy saving for a new processing process is getting to be more important. Therefore, in addition to the effect on the tea quality, the benefit of energy saving of FIRR should be further studied. References 1. 伊藤利昭川口將德 遠赤外線加熱の原理と食品工業への應用 ヅセパンフードサイエス 11:39 2. 橋口真典 1986 遠赤外線殘殺菌裝置利用によとる包裝食品の保存技術 食品加工技術 6(3): 西沢健治 1986 遠赤外線の食品への利用 食品加工技術 6(3): American Association of Cereal Chemists St. Paul, MN, USA. 5. Chen, Chih-Chung, Shin-Hwei You, Ji-Bin Sun, and Chu-chin Chen Effects of firing on the quality of Oolong tea infusion. New Food Industry 23(2): Ou, S. M, Y. S. Tsai and R. H. Chang Evaluation and comparison of methods for the determination of phenolic compounds in Parchung tea. Taiwan Tea Research Bulletin 7: Ruan, I. M Re-drying and roasting of tea. Tea Extension Newsletter 6: Ruan, I. M., R. H. Chang, and L. F. Chang Effects of different roasting temperature and time on chemical components and quality of Paochung tea. Taiwan Tea Research Bulletin 8: Shyu, Y. S Re-drying and roasting of Paochung tea. Tea Newsletter 3: Shyu, Y. S., Y. S. Tasi, R. H. Chang, K. F. Kuo, and J. C. Lin Studies on the improvement of charcoal baking for Paochung tea, I: effects of different baking methods and time on the sensory quality and chemical composition of Paochung tea. Taiwan Tea Research Bulletin 17: Shyu, Y. S., Y. S. Tasi, R. H. Chang, K. F. Kuo, and J. C. Lin Studies on the improvement of charcoal baking for Paochung tea, II: effects of different baking temperature and time on the sensory quality and chemical composition of Paochung tea. Taiwan Tea Research Bulletin 20: Shimizu, k Technical subjects on application of far infrared ray to food industry. The Food Industry 29(5): Sugiyama Application of far infrared ray heating to food industry. The Food industry 29(5): Stone, H. and Sidle, J Sensory Evaluation Practices. Academic press. Orlando. Florida. USA. 15. Tanaka, T Characteristics and application of semi-raw noodle manufacturing system using far infrared ray, The Food Industry 29(5): l35. 收稿日期 :2008 年 5 月 14 日修改日期 :2008 年 6 月 10 日接受日期 :2008 年 7 月 6 日