摘要:為獲得具有湖南地域特色、滋味醇厚較鮮爽、香氣濃郁持久的黑茶拼配原料,以櫧葉齊、桃源大葉、黃金茶1號鮮葉為原料加工得到櫧葉齊黑毛茶(Z)、桃源大葉黑毛茶(T)、黃金茶1號黑毛茶(H),并將3個(gè)黑毛茶Z∶T∶H按20∶20∶60、20∶60∶20、40∶15∶45、40∶45∶15、60∶10∶30、60∶30∶10拼配得到6個(gè)拼配茶樣,對其進(jìn)行感官審評、理化成分及香氣組分等比較分析。研究結(jié)果表明,櫧葉齊黑毛茶占比為40%、60%時(shí),拼配茶樣滋味醇厚較鮮爽、香氣濃郁持久,品質(zhì)高于單一黑毛茶及櫧葉齊黑毛茶占比為20%的2個(gè)拼配茶樣。生化分析結(jié)果發(fā)現(xiàn),櫧葉齊黑毛茶占比為40%、60%時(shí),茶樣水浸出物、沒食子酸含量更高,滋味醇厚較鮮爽;在此基礎(chǔ)上,桃源大葉占比較高時(shí),茶多酚、黃酮、總兒茶素、咖啡堿含量更高,滋味更加濃強(qiáng);黃金茶占比較高時(shí),可溶性糖含量更高,滋味更為甜醇。頂空-固相微萃取法(HS-SPME)結(jié)合氣相色譜質(zhì)譜聯(lián)用技術(shù)(GC-MS)共檢測出77種揮發(fā)性成分,基于正交偏最小二乘法判別分析(OPLS-DA)模型的變量投影重要性(VIP)共篩選出41種候選差異揮發(fā)物(VIP>1),進(jìn)一步計(jì)算其相對香氣活性值(ROAV),發(fā)現(xiàn)芳樟醇、L-α-松油醇、雪松醇、異亞丙基丙酮、藏紅花醛等13種關(guān)鍵差異揮發(fā)物(VIP>1、ROAV>1);櫧葉齊黑毛茶占比為40%、60%時(shí),高含量的藏紅花醛、苯乙醇與其高香持久的特征密切相關(guān),加入高配比的黃金茶1號黑毛茶,使得D-檸檬烯、芳樟醇氧化物(Ⅳ)含量更高,賦予了拼配茶樣的花香屬性。
關(guān)鍵詞:黑毛茶;優(yōu)化拼配;滋味品質(zhì);香氣品質(zhì);氣相色譜-質(zhì)譜聯(lián)用
中圖分類號:S571.1 文獻(xiàn)標(biāo)識碼:A 文章編號:1000-369X(2024)05-763-16
Research on Flavors and Qualities of Optimization Blending Samples of Hunan Raw Dark Teas
JIANG Ating1, LIU Qiaofang1, XIAO Juanjuan1, HE Junhui2*, GAO Bingcai2,
HUANG Jian'an1,3,4,5, WANG Kunbo1,3,4,5, LIU Zhonghua1,3,4,5, YU Lijun1,3,4,5*
1. Key Lab of Education Ministry of Hunan Agricultural University for Tea Science, Changsha 410128, China; 2. Hunan Hualai Biotechnology Co., Ltd., Anhua 413500, China; 3. National Research Center of Engineering and Technology for Utilization of Botanical Functional Ingredients, Changsha 410128, China; 4. Co-Innovation Center of Education Ministry for Utilization of Botanical Functional Ingredients, Changsha 410128, China; 5. Key Laboratory for Evaluation and Utilization of Gene Resources of Horticultural Crops, Ministry of Agriculture and Rural Affairs of China, Changsha 410128, China
Abstract: In order to study how to obtain the raw materials of dark tea processing with Hunan regional characteristics of mellow and fresh taste, heavy and long-lasting aroma, Zhuyeqi raw dark tea (Z), Taoyuan-daye raw dark tea (T), Huangjincha 1 raw dark tea (H) were obtained by processing the fresh leaves of relative cultivars, and six blending tea samples were obtained by blending these three raw dark tea (Z∶T∶H) with the ratio of 20∶20∶60, 20∶60∶20, 40∶15∶45, 40∶45∶15, 60∶10∶30, 60∶30∶10. Comparative analysis of their sensory evaluation, taste quality and aroma components was also conducted. The results show that when the proportion of Zhuyeqi raw dark tea was 40% and 60%, the blended teas were mellower and fresher in taste, with heavier and longer-lasting aroma than the original raw tea and the two blends with the proportion of Zhuyeqi raw dark tea of 20%. The tea samples’ quality had significant improvement. The results of biochemical analysis show that, when the proportion of Zhuyeqi raw dark tea was 40% and 60%, the contents of water extract and gallic acid were higher, and the taste was mellow and fresh. On this basis, when Taoyuan-daye raw dark tea accounted for a higher percentage of tea, the contents of tea polyphenols, flavonoids, total catechins and caffeine were higher and the taste was mellow. When Huangjincha 1 raw dark tea accounted for a higher percentage of tea, the content of soluble sugar was higher, and the taste was sweeter. A total of 77 volatile components were detected by headspace-solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). Based on the variable importance in projection (VIP) of the orthogonal partial least squares discriminant analysis method (OPLS-DA), 41 components (VIP>1) were screened out by this experiment, and by further calculating their relative odor activity value (ROAV), 13 key differential volatiles such as linalool, L-α-terpineol, cedrol, isopropylidene acetone and crocinaldehyde were identified (VIP>1, ROAV>1). When the proportion of Zhuyeqi raw dark tea was 40% and 60%, the high aroma and lasting characteristics were closely related to the high contents of saffron and aldehyde. Adding high proportion of Huangjincha 1 raw dark tea, the contents of D-limonene and linalool oxide (Ⅳ) were higher, which gave the floral aroma of the blending samples.
Keywords: raw dark tea, optimization blending, taste quality, aroma quality, GC-MS
黑茶是后發(fā)酵茶類,茶葉原料中的成分在微生物及濕熱作用發(fā)生轉(zhuǎn)化,形成了多種新的生物活性成分[1],具有調(diào)節(jié)糖脂代謝[2]、改善小鼠結(jié)腸炎[3]、抗癌細(xì)胞增殖[4]、緩解非酒精性脂肪肝[5]等多種保健功能。研究表明,黑茶品質(zhì)與黑毛茶原料的化學(xué)組成密不可分,黑毛茶品質(zhì)受茶樹品種[6]、地域[7]、采收季節(jié)[8]、遮陰處理[9]等因素影響。拼配作為茶葉精制不可或缺的環(huán)節(jié),是提升產(chǎn)品風(fēng)味、保持品質(zhì)穩(wěn)定的重要手段。云南機(jī)采曬青茶[10]、普洱熟茶[11]、工夫紅茶[12]等市場需求量大的茶類已有相關(guān)拼配技術(shù)的研究報(bào)道。湖南安化黑茶在大型機(jī)制壓磚車間生產(chǎn)中,進(jìn)行了毛茶的感官審評及簡單拼配,但未涉及毛茶原料優(yōu)化拼配茶樣的滋味、香氣組分分析,尚未能對黑茶品質(zhì)的轉(zhuǎn)化提供基礎(chǔ)理論性指導(dǎo)。
黑茶消費(fèi)人群日益擴(kuò)大,不同消費(fèi)群體對黑茶滋味口感提出新的需求,中老年消費(fèi)者希望黑茶存放一定時(shí)間后仍保留較醇厚的滋味,年輕消費(fèi)者希望黑茶帶有鮮爽的口感和怡人的香氣。如何生產(chǎn)出滋味醇厚較鮮爽、香氣濃郁持久、接受度更廣的黑茶,是當(dāng)今湖南黑茶企業(yè)急需解決的難題。櫧葉齊、桃源大葉為適制湖南黑茶的茶樹品種[13],其鮮葉多酚類物質(zhì)含量相對豐富[14],加工后黑茶滋味口感較濃強(qiáng),耐儲藏,但鮮爽度欠缺。黃金茶1號是湘西土家族苗族自治州選育出的地方茶樹良種,加工成綠茶滋味鮮爽,審評發(fā)現(xiàn)其加工的黑毛茶濃強(qiáng)度欠缺,但鮮爽的特征得到保留。為此,本研究選擇櫧葉齊、桃源大葉、黃金茶1號加工的黑毛茶為拼配原料,進(jìn)行系列拼配、測試分析,以期獲得滋味醇厚較鮮爽、香氣濃郁持久的黑毛茶拼配樣,為湖南黑茶加工提供理論指導(dǎo)。
1 材料與方法
1.1 試驗(yàn)材料
2023年5月底于湖南農(nóng)業(yè)大學(xué)長安教學(xué)基地,選取櫧葉齊、桃源大葉、黃金茶1號3個(gè)品種的一芽三四葉及同等嫩度的對夾葉,按照湖南黑毛茶加工工藝得到黑毛茶;常溫、避光儲存3個(gè)月后進(jìn)行感官審評、拼配優(yōu)選。櫧葉齊黑毛茶、桃源大葉黑毛茶、黃金茶1號黑毛茶分別編號為Z、T、H,6個(gè)拼配茶樣Z∶T∶H分別為20∶20∶60、20∶60∶20、40∶15∶45、40∶45∶15、60∶10∶30、60∶30∶10,分別編號為Z20T20H60、Z20T60H20、Z40T15H45、Z40T45H15、Z60T10H30、Z60T30H10。
1.2 試驗(yàn)試劑
C7~C40飽和正構(gòu)烷烴、癸酸乙酯(99.99%)為色譜純,購自上海阿拉丁生化科技股份有限公司;沒食子酸、茶堿、可可堿和兒茶素等標(biāo)準(zhǔn)品為色譜純,購自美國Sigma有限公司;乙腈、甲醇為色譜純,購自美國TEDIA公司;磷酸、碳酸鈉、福林酚、磷酸氫二鈉、磷酸二氫鉀、茚三酮、氯化鋁、蒽酮、濃硫酸為分析純,購自國藥集團(tuán)有限公司。
1.3 試驗(yàn)儀器
UV-1750型紫外-可見分光光度計(jì),日本島津有限公司;LC1260型高效液相色譜儀,美國安捷倫有限公司;手動(dòng)SPME進(jìn)樣手柄、50/30 μm DVB/CAR/PDMS萃取頭,美國Supelco公司;EPFO-984TA7CHSEUA數(shù)顯型磁力加熱攪拌器,美國Talboys公司;Technologies 7890B-5977A氣質(zhì)聯(lián)用儀,美國Agilent公司;20 mL頂空瓶,上海安譜科學(xué)儀器有限公司。
1.4 試驗(yàn)方法
1.4.1 感官審評
參考GB/T 23776—2018茶葉感官審評方法,由具有長期審評經(jīng)驗(yàn)的茶學(xué)教授和研究生共5人組成審評小組進(jìn)行密碼審評,按照外形、湯色、香氣、滋味、葉底依次給出評語及評分,對結(jié)果進(jìn)行加權(quán)計(jì)算得到總分。
1.4.2 生化成分檢測分析
茶多酚含量測定采用福林酚比色法,參照GB/T 8313—2018;水浸出物含量測定參照GB/T 8305—2013;游離氨基酸總量測定采用茚三酮比色法,參照GB/T 8314—2013;黃酮類化合物總量的測定采用三氯化鋁比色法;可溶性糖含量測定采用蒽酮比色法。
兒茶素、生物堿檢測方法參照Samanidou等[15]的高效液相色譜法,試液制備浸提方法參考GB/T 8313—2018,浸提液過0.45 μm纖維膜過濾待測。HPLC分析條件為Welchrom C18色譜柱(250 mm×4.6 mm,5 μm);流動(dòng)相A為5%乙腈甲醇溶液(V乙腈∶V甲醇=5∶95),流動(dòng)相B為0.2%磷酸,梯度洗脫,流速為0.8 mL·min-1,柱溫30 ℃,進(jìn)樣量10 μL,檢測波長278 nm。洗脫條件為0~25 min,7%~26% A;25~37 min,26%~50% A;37~39 min,50%~7% A;39~49 min,7% A。
1.4.3 揮發(fā)性成分檢測
HS-SPME富集方法參考趙靜等[16]的方法并進(jìn)行了適當(dāng)修改,使用前將50/30 μm DVB/CAR/PDMS萃取頭于270 ℃老化30 min備用;稱取2.0 g粉碎過40目篩的茶樣于20 mL頂空瓶中,上方滴入20 μL癸酸乙酯(10.9 mg·L-1),以聚四氟乙烯瓶蓋封口,80 ℃保溫,于磁力攪拌器上平衡10 min,萃取頭吸附50 min后,進(jìn)樣口溫度為240 ℃,解析5 min。
GC條件:Agilent HP-5MS毛細(xì)管柱(30 m×0.25 mm,0.25 μm),柱溫箱溫度為60 ℃,不分流進(jìn)樣,進(jìn)樣量為1 μL,進(jìn)樣溫度為240 ℃,樣品流速為1.37 mL·min-1;升溫程序?yàn)?0 ℃保留5 min,以3 ℃·min-1升至140 ℃保留5 min,再以5 ℃·min-1升至240 ℃保留10 min;載氣為高純度He。
MS條件:離子源(EI),離子源溫度200 ℃,接口溫度220 ℃,電子能量70 eV,質(zhì)荷比(m/z)掃描范圍為45~500。
定性分析:利用NIST 20標(biāo)準(zhǔn)譜庫對GC-MS分析得到的色譜峰進(jìn)行人工解析,通過正構(gòu)烷烴標(biāo)準(zhǔn)品的保留時(shí)間計(jì)算出保留指數(shù)(RI),再與數(shù)據(jù)庫中的RI進(jìn)行比較,定性標(biāo)準(zhǔn)為相似度80%以上,且RI相差小于10。
定量方法[17]:通過計(jì)算待測揮發(fā)物與癸酸乙酯的峰面積之比,使用歸一法進(jìn)行相對定量(假定各揮發(fā)物的絕對校正因子為1.0)。
相對香氣活性值(ROAV)用來評價(jià)單個(gè)揮發(fā)性化合物對整體香氣的貢獻(xiàn)[18-19],計(jì)算公式如下:
OAVi=Ci/OTi
ROAVi=100×OAVi/OAVmax
式中,OAVi表示揮發(fā)性化合物i的氣味活性值;Ci表示揮發(fā)性化合物i的相對含量;OTi表示揮發(fā)性化合物i的氣味閾值;OAVmax為揮發(fā)性化合物中最高的氣味活性值。
1.5 數(shù)據(jù)處理
試驗(yàn)3個(gè)重復(fù)取樣、3次平行測試,數(shù)據(jù)用平均值±標(biāo)準(zhǔn)差( ±SD)表示;使用Excel 2019對數(shù)據(jù)進(jìn)行統(tǒng)計(jì)分析;采用IBM SPSS statistics 19.0軟件進(jìn)行顯著性分析;使用WPS 2019教育版、SIMCA-P 14.1軟件、聯(lián)川生物云平臺(www.omicstudio.cn/tool)進(jìn)行香氣的多元統(tǒng)計(jì)數(shù)據(jù)分析及相關(guān)圖形繪制與處理。
2 結(jié)果與分析
2.1 茶樣的感官審評分析
感官審評結(jié)果發(fā)現(xiàn),3個(gè)黑毛茶及6個(gè)拼配茶樣感官品質(zhì)特征差異明顯(表1)。櫧葉齊黑毛茶香氣最為持久、但湯色欠亮;桃源大葉黑毛茶干茶條索粗壯、香氣較低、但滋味醇厚;黃金茶1號黑毛茶帶花香、滋味鮮爽欠醇厚。6個(gè)拼配茶樣整體表現(xiàn)為色澤黑褐、條索更顯緊結(jié)、勻齊,高火香、栗香濃郁持久,湯色黃亮,滋味醇厚且鮮爽回甘,葉底暗黃泛青、明亮,評分較高。櫧葉齊黑毛茶占比為60%的Z60T30H10茶樣栗香濃郁、持久。黃金茶1號黑毛茶占比為60%的Z20T20H60茶樣香氣較持久、冷后帶花香。桃源大葉黑毛茶占比60%的Z20T60H20茶樣滋味最為苦澀,而Z20T20H60、Z40T15H45、Z60T10H30、Z60T30H10這4組桃源大葉黑毛茶占比較少的茶樣整體更顯鮮爽,說明桃源大葉黑毛茶占比多的茶樣可能澀感更強(qiáng)。6個(gè)拼配茶中,櫧葉齊黑毛茶占比為40%和60%的4個(gè)茶樣滋味濃強(qiáng)較鮮、香氣濃郁持久,整體表現(xiàn)較優(yōu)。
2.2 茶樣的生化組分分析
由表2可知,6個(gè)拼配茶樣中,櫧葉齊黑毛茶占比為60%的Z60T30H10茶樣水浸出物含量最高(39.48%)、可溶性糖含量最低(4.15%)。桃源大葉黑毛茶占比為60%的Z20T60H20茶樣茶多酚、黃酮含量最高(18.63%、0.86%),游離氨基酸含量最低(4.61%)。黃金茶1號黑毛茶占比為60%的Z20T20H60茶樣中可溶性糖含量最高(4.90%);水浸出物、茶多酚、黃酮含量均最低(38.96%、16.05%、0.81%),但仍高于黃金茶1號黑毛茶的含量。
由表3可知,6個(gè)拼配茶樣中,桃源大葉黑毛茶占比為60%的Z20T60H20茶樣非酯型兒茶素、酯型兒茶素、總兒茶素含量最高,分別為53.76、84.25、138.01 mg?g-1,但仍低于桃源大葉黑毛茶。黃金茶1號黑毛茶占比為60%的Z20T20H60茶樣沒食子酸含量最低,但仍高于黃金茶1號黑毛茶。桃源大葉黑毛茶占比為10%的Z60T10H30茶樣咖啡堿、非酯型兒茶素、酯型兒茶素、總兒茶素含量均最低,分別為25.38、43.96、70.19、114.15 mg?g-1。
以上結(jié)果表明,拼配茶樣中,櫧葉齊黑毛茶占比40%、60%時(shí),水浸出物含量表現(xiàn)較高水平;隨著桃源大葉黑毛茶占比增加,茶多酚、非酯型兒茶素總量、酯型兒茶素總量均呈明顯升高趨勢,茶湯滋味愈發(fā)濃強(qiáng);黃金茶1號黑毛茶高比例拼入,使得茶樣的可溶性糖含量更高,茶湯的回甘度增加。
2.3 茶樣的揮發(fā)性組分分析
通過HS-SPME-GC-MS對3個(gè)原黑毛茶及
其6個(gè)拼配茶樣(n=3)中揮發(fā)性成分進(jìn)行檢測,共鑒定出77種揮發(fā)性成分,碳?xì)浠衔?8種、醇類16種、酯類9種、酮類5種、醛類6種、含氮化合物7種和其他化合物6種(表4)。
將茶樣中揮發(fā)性成分進(jìn)行對比,由圖1A可知,9個(gè)茶樣中共有的揮發(fā)性成分有14種,為苯乙醇、芳樟醇及其氧化物等;拼配后,櫧葉齊黑毛茶占比為40%的Z40T15H45、Z40T45H15茶樣中特有2種揮發(fā)性成分,分別為3-甲基十五烷、2-乙?;量瑱饺~齊黑毛茶占比60%的Z60T10H30、Z60T30H10茶樣特有4種揮發(fā)性成分,分別為二十烷、十八烷、十七烷、2-氯乙酸十四酯。由圖1B可知,櫧葉齊黑毛茶、桃源大葉黑毛茶、黃金茶1號黑毛茶分別檢測出37種、48種、36種揮發(fā)性成分;而拼配后的茶樣揮發(fā)性成分種類多于以上3個(gè)原黑毛茶;櫧葉齊黑毛茶占比為20%的Z20T20H60、Z20T60H20茶樣分別定性出39種、41種揮發(fā)性成分;占比為40%的Z40T15H45、Z40T45H15茶樣分別定性出51種、50種揮發(fā)性成分;占比為60%的Z60T10H30、Z60T30H10茶樣分別定性出57種、56種揮發(fā)性成分。由此可見,隨著櫧葉齊黑毛茶占比增加,揮發(fā)性成分種類呈上升趨勢。
不同種類揮發(fā)性成分含量的熱圖顯示(圖1D),6個(gè)優(yōu)化拼配茶樣中醇類含量最高,Z40T45H15茶樣的碳?xì)浠衔?、醇類、酮類和醛類含量較高,Z40T15H45茶樣的酯類含量最高,Z60T10H30和Z60T30H10茶樣的含氮化合物較高。拼配茶樣的香氣組分及含量分布比單一黑毛茶更均勻,櫧葉齊黑毛茶占比較高的拼配茶樣含氮化合物含量更高,櫧葉齊黑毛茶和桃源大葉黑毛茶占比較高的拼配茶樣碳?xì)浠衔?、醇類、酮類和醛類含量均更高,櫧葉齊黑毛茶和黃金茶1號黑毛茶占比較高的拼配茶樣酯類含量更高。
2.4 茶樣的差異揮發(fā)性成分篩選和ROAV分析
對3個(gè)黑毛茶及其6個(gè)拼配茶樣的揮發(fā)性成分含量進(jìn)行主成分分析(PCA),結(jié)果如圖2A所示,擬合系數(shù)為R2X[1]=0.845,R2X[2]=0.683,模型質(zhì)量較好。同時(shí)采用聚類分析(HCA)對PCA所得主成分進(jìn)行聚類(圖2B),結(jié)果表明,6個(gè)拼配茶樣與3個(gè)黑毛茶分成兩個(gè)明顯的大類,3個(gè)黑毛茶之間差異明顯;拼配茶樣中櫧葉齊黑毛茶占比為60%的Z60T10H30和Z60T30H10聚為一類,黃金茶1號黑毛茶占比較高的Z20T20H60與Z40T15H45、桃源大葉黑毛茶占比較高的Z20T60H20與Z40T45H15分別聚類。感官審評結(jié)果發(fā)現(xiàn),Z60T10H30和Z60T30H10茶樣具有香氣濃郁持久的特征,Z20T20H60與Z40T15H45茶樣冷后帶花香,Z20T60H20和Z40T45H15茶樣香氣稍欠。
基于PCA和HCA不同拼配茶樣及黑毛茶的分布結(jié)果,將9個(gè)茶樣分成3組(桃源大葉黑毛茶單獨(dú)為一組;櫧葉齊黑毛茶與黃金茶1號黑毛茶為一組;6個(gè)拼配茶樣為一組),建立正交偏最小二乘法判別(OPLS-DA)模型(圖3A),本研究模型理論上解釋變異(R2Y)和預(yù)測能力(Q2)值分別為0.906和0.950,均接近1,說明模型較好。對建立的模型進(jìn)行200次的置換檢驗(yàn)(圖3B),結(jié)果顯示,Q2回歸線與垂直軸的截距小于零,說明模型不存在過擬合,認(rèn)為OPLS-DA模型具有較好的驗(yàn)證效果。在OPLS-DA判別模型基礎(chǔ)上,以VIP值>1、P<0.05為標(biāo)準(zhǔn)共篩選出碳?xì)浠衔?5種、醇類11種、酯類3種、酮類4種、醛類5種、其他化合物3種等41種差異揮發(fā)性成分,咖啡堿、2,6,10-三甲基十三烷、異胡薄荷醇的VIP值較高,分別為1.41、1.30、1.27。
香氣成分含量的高低并不能作為判定茶葉香氣的特征依據(jù),單個(gè)揮發(fā)性成分對整體香氣的貢獻(xiàn)還取決于其氣味閾值,因此根據(jù)定性定量結(jié)果及相關(guān)文獻(xiàn)對篩選出的41種差異性成分進(jìn)行ROAV計(jì)算[18,20-24]。當(dāng)ROAV>1則認(rèn)為該組分對茶樣香氣具有貢獻(xiàn),ROAV>10則認(rèn)為該組分對茶樣香氣貢獻(xiàn)極大。由表5所示,共篩選出13種關(guān)鍵化合物,呈花香的芳樟醇、呈柑橘香的D-檸檬烯、呈木香的雪松醇和藏紅花醛等4種組分對茶樣香氣貢獻(xiàn)極大;其中櫧葉齊黑毛茶、黃金茶1號黑毛茶合并占比較高的Z40T15H45和Z60T10H30茶樣中ROAV>1的化合物分別有12種和11種,較其他茶樣更豐富。
櫧葉齊黑毛茶占比達(dá)60%的Z60T10H30和Z60T30H10茶樣中藏紅花醛、苯乙醇的ROAV大于其他拼配樣;櫧葉齊黑毛茶占比為20%的Z20T20H60和Z20T60H20茶樣中呈辛辣味的異亞丙基丙酮的ROAV分別高達(dá)95.58、96.82。黃金茶1號黑毛茶占比為60%的Z20T20H60茶樣中呈柑橘香的D-檸檬烯、呈甘草香的紫羅烯、呈泥土香的月桂醇和呈花香的芳樟醇氧化物(Ⅳ)ROAV值均最大,分別為8.64、2.94、5.49、4.23,推測以上化合物與拼配茶的花香屬性有關(guān)。桃源大葉黑毛茶占比較高的Z20T60H20和Z40T45H15茶樣中呈丁香的L-α-松油醇、呈木香的雪松醇、呈花香的芳樟醇和呈油脂香的壬醛ROAV均較大,其中Z20T60H20茶樣中呈薄荷香的異胡薄荷醇、呈辛辣味的異亞丙基丙酮ROAV均最大,分別為4.30、96.82。由此可知,拼配茶樣中桃源大葉黑毛茶占比增加,其L-α-松油醇、芳樟醇等香氣成分含量更高,但香氣組成更單一;櫧葉齊黑毛茶和黃金茶1號黑毛茶占比較高時(shí),香氣組分種類更豐富、含量更協(xié)調(diào);其中,櫧葉齊黑毛茶占比增加,藏紅花醛和苯乙醇含量更高、異亞丙基丙酮含量更低,香氣更持久;黃金茶1號黑毛茶的拼入,具有花果香特征的D-檸檬烯和紫羅烯含量更高,為茶樣增添了多元的香氣屬性。
3 討論
拼配是改善茶產(chǎn)品風(fēng)味品質(zhì)的重要手段,并能保證大批量茶產(chǎn)品品質(zhì)的穩(wěn)定性。劉學(xué)艷等[10]將機(jī)采的秋季曬青茶進(jìn)行拼配,成功獲得了滋味濃醇回甘、帶花香和蜜香的成品茶;張杰等[11]對云南不同地區(qū)的熟茶進(jìn)行拼配,發(fā)現(xiàn)以西雙版納地區(qū)的普洱熟茶作為主要的拼配茶樣時(shí),所得成品茶的滋味更為醇厚。本研究發(fā)現(xiàn),櫧葉齊適合作為黑毛茶拼配的基礎(chǔ)原料,加入滋味醇厚微苦的桃源大葉及滋味鮮爽欠厚的黃金茶1號黑毛茶,得到的優(yōu)化拼配茶滋味醇厚較鮮爽、香氣濃郁持久,理化檢測及香氣組分分析結(jié)果也印證了以上結(jié)論。
本研究結(jié)果顯示,黃金茶1號黑毛茶可溶性糖含量顯著高于其他茶樣,黃金茶1號黑毛茶占比越高,拼配茶樣滋味回甘愈強(qiáng);Yu等[25]研究發(fā)現(xiàn),茶樣中可溶性糖能提高茶湯鮮度和甜度,緩解苦澀味。桃源大葉黑毛茶中,茶多酚、簡單兒茶素及酯型兒茶素含量明顯高于櫧葉齊黑毛茶和黃金茶1號黑毛茶,其占比增加,拼配茶樣滋味的醇厚度和苦澀感增加。龔華春等[26]研究發(fā)現(xiàn),桃源大葉茶多酚含量明顯高于櫧葉齊,以其為原料加工的工夫紅茶的品質(zhì)風(fēng)味較好。由此可知,拼配茶樣中可溶性糖、茶多酚、兒茶素類物質(zhì)含量豐富,與黑茶的滋味品質(zhì)密切相關(guān)。
利用HS-SPME-GC-MS技術(shù)對6個(gè)拼配茶樣及黑毛茶進(jìn)行分析,共檢測出77種揮發(fā)性成分。碳?xì)浠衔锖痛碱愂瞧磁洳铇又兄饕膿]發(fā)性組分。陳慧等[27]對黑毛茶進(jìn)行控溫渥堆研究,發(fā)現(xiàn)的揮發(fā)性成分種類及組成與本研究基本一致;碳?xì)浠衔镏袑诓柘銡庥休^大貢獻(xiàn)的一般為烯烴類,其與醇類共同提升了拼配茶樣的木香和花香屬性。含氮化合物多與茶的“烘焙香”屬性相關(guān)[28],Li等[29]研究發(fā)現(xiàn),湖南茯磚茶干燥后含氮化合物的含量大幅增加,本研究發(fā)現(xiàn)櫧葉齊占比60%的拼配茶樣含氮化合物含量更高,茶樣的高火香、栗香更明顯。醛類與茶葉的“青氣”屬性有關(guān)[22],對拼配茶樣的花香產(chǎn)生一定的掩蓋作用,本研究中,桃源大葉黑毛茶占比越高、醛類含量越豐富,而黃金茶1號黑毛茶占比60%時(shí),拼配茶樣醛類含量較低,與香氣審評表現(xiàn)基本一致。酯類呈現(xiàn)明顯的花果香[18],拼配茶樣中黃金茶1號黑毛茶占比較高時(shí),酯類更為豐富,進(jìn)一步提升了拼配茶的花果香屬性。
以VIP>1、ROAV>1為標(biāo)準(zhǔn)篩選出芳樟醇、L-α-松油醇、雪松醇、異亞丙基丙酮、藏紅花醛、D-檸檬烯、紫羅烯、苯乙醇、月桂醇、1-辛烯-3-醇、芳樟醇氧化物(Ⅳ)、壬醛等13種揮發(fā)性組分,這些組分對拼配茶香氣的形成有重要作用。櫧葉齊黑毛茶占比為40%和60%時(shí),拼配茶樣中呈玫瑰香的苯乙醇和呈木香的藏紅花醛表現(xiàn)出較高水平,這可能是櫧葉齊黑毛茶占比高的茶樣香氣更顯愉悅、高長的主要原因。湯依鈺等[30]對櫧葉齊黑毛茶進(jìn)行香氣組分分析發(fā)現(xiàn),苯乙醇對其花香特征有重要貢獻(xiàn);藏紅花醛來源于類胡蘿卜素,在干燥過程中由藏紅花素糖苷鍵斷裂形成[31],是白茶中木香、花香的來源之一[32]。黃金茶1號黑毛茶占比高時(shí),具有花香、果香屬性的香氣組分芳樟醇氧化物(Ⅳ)、D-檸檬烯和月桂醇含量高于其他拼配茶樣;芳樟醇氧化物(Ⅳ)是黑毛茶加工過程中糖苷水解產(chǎn)生的一種反吡喃型氧化物[33],參與黑茶花香、脂香的形成[24];Xue等[22]研究發(fā)現(xiàn),呈橘香的D-檸檬烯對茯磚茶花果香有重要貢獻(xiàn),本研究發(fā)現(xiàn)其只在黃金茶1號黑毛茶占比大于30%的拼配茶樣中被檢測到,可見黃金茶1號中該組分的豐度較高。桃源大葉黑毛茶占比高的拼配茶樣中,芳樟醇、壬醛、L-α-松油醇、雪松醇、1-辛烯-3-醇等香氣組分含量更高,但對整體的香氣貢獻(xiàn)不突出,可能是因?yàn)椴煌銡饨M分之間呈現(xiàn)拮抗作用,使氣味強(qiáng)度降低或消失[34];花香型的芳樟醇是湖南黑茶加工原料的主要賦香物質(zhì)[35],對茯磚茶菌花香、花香和薄荷香的形成均有重要貢獻(xiàn)[29],在9個(gè)茶樣香氣成分中ROAV最高;L-α-松油醇、壬醛等香氣組分對拼配茶的辛辣味有重要貢獻(xiàn),通常在黑毛茶渥堆過程中產(chǎn)生[27];桃源大葉黑毛茶為湖南的地方大葉種茶樹資源,Wen等[36]研究發(fā)現(xiàn),呈蘑菇香的1-辛烯-3-醇能緩解大葉種黑毛茶原料在渥堆中產(chǎn)生的刺鼻氣味,使得桃源大葉黑毛茶占比高的拼配茶中沒有不愉快的香氣。
綜上所述,櫧葉齊黑毛茶占比為40%和60%的拼配茶滋味醇厚較鮮爽、香氣濃郁持久,兼顧了桃源大葉黑毛茶滋味濃強(qiáng)和黃金茶1號黑毛茶口感鮮爽的優(yōu)點(diǎn)。后期可針對這3個(gè)茶樹品種在湖南不同地域、不同生態(tài)種植條件以及不同加工方式下,開展其黑毛茶滋味、香氣品質(zhì)的差異性對比研究,為湖南優(yōu)質(zhì)、特色黑茶的加工提供理論指導(dǎo)。
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