項(xiàng)麗慧,宋振碩,張應(yīng)根,王麗麗,陳 鍵,陳 林
?農(nóng)產(chǎn)品加工工程?
茶鮮葉萎凋過(guò)程中攤青工藝對(duì)白茶品質(zhì)的影響
項(xiàng)麗慧,宋振碩,張應(yīng)根,王麗麗,陳 鍵,陳 林※
(福建省農(nóng)業(yè)科學(xué)院茶葉研究所,福州 350013)
為探明茶鮮葉萎凋過(guò)程中攤青工藝對(duì)白茶風(fēng)味品質(zhì)和生化成分的影響,在控溫除濕環(huán)境中以基于靜態(tài)攤晾于水篩加工而成的白茶為對(duì)照,在不同茶鮮葉減重率(65%、70%和75%)時(shí)對(duì)在制品進(jìn)行并篩或堆青處理。結(jié)果表明,各處理制成的白茶呈現(xiàn)出較為相似的感官品質(zhì)特征,但堆青處理相較并篩處理及對(duì)照茶樣的香氣鮮度下降而滋味甜度提高。在并篩處理中以在減重率為70%時(shí)并篩略?xún)?yōu)于在減重率為65%時(shí)并篩的白茶品質(zhì),且二者均以薄并篩處理較優(yōu)于對(duì)照茶樣。在減重率達(dá)75%時(shí)對(duì)在制品進(jìn)行相同時(shí)長(zhǎng)不同厚度的堆青處理(堆青方式:2~6篩并1筐)以厚堆處理的白茶品質(zhì)較優(yōu),而不同時(shí)長(zhǎng)相同厚度的堆青處理(堆青時(shí)長(zhǎng):2~6 d)則以短時(shí)堆青的白茶品質(zhì)為佳。不同攤青處理白茶的兒茶素類(lèi)、生物堿和主要氨基酸組分無(wú)明顯規(guī)律性差異。相較靜態(tài)/并篩工藝組,堆青工藝組茶樣中呈甜味的脯氨酸和苯乙醇、橙花醇、香葉醇等花果香成分顯著降低(<0.05)?;诓铇由M成的模式識(shí)別可將全部供試茶樣劃分成靜態(tài)/并篩工藝組與堆青工藝組2種類(lèi)群。堆青處理可通過(guò)促進(jìn)脂肪酸代謝,增加烷烴類(lèi)、降異戊二烯類(lèi)和醛類(lèi)化合物含量來(lái)有效調(diào)節(jié)白茶樣品的生化組成;橙花醇、橙花醛和香草醛等23種化合物可視為其與靜態(tài)/并篩工藝組茶樣相互區(qū)分的主要特征標(biāo)識(shí)物(群)。研究結(jié)果可為基于攤青方式的白茶風(fēng)味品質(zhì)工藝技術(shù)調(diào)控提供參考依據(jù)。
工藝;品質(zhì)控制;白茶;萎凋;攤青
白茶屬中國(guó)六大茶類(lèi)之一,其外表天然素雅、內(nèi)質(zhì)清甜爽口,且因具有良好的抗氧化、降血糖、降血脂和抑菌等功效而廣受消費(fèi)者青睞[1-3]。白茶制作主要包括萎凋和干燥2道工序,其中萎凋是形成白茶特定風(fēng)味品質(zhì)的關(guān)鍵工序[4-5]。茶鮮葉在萎凋過(guò)程中隨著水分的減少,發(fā)生復(fù)雜的生化變化,主要表現(xiàn)為游離氨基酸、咖啡堿、核苷酸和有機(jī)酸的增加,兒茶素、碳水化合物、類(lèi)胡蘿卜素、葉綠素、脂類(lèi)和脂肪酸的減少,以及可溶性糖、香氣揮發(fā)物和多酚氧化酶活性的改變[6-9]。為提高茶鮮葉的萎凋均勻度并避免葉片貼篩,在萎凋過(guò)程中常需進(jìn)行1~2次并篩,或在萎凋后期通過(guò)堆青以實(shí)現(xiàn)白茶風(fēng)味品質(zhì)的目標(biāo)轉(zhuǎn)化[10]。傳統(tǒng)并篩是在萎凋葉含水率約為30%時(shí),將2篩萎凋葉合并為1篩,待萎凋葉含水率約為25%時(shí),再將2篩合并為1篩,繼續(xù)萎凋至梗脈水分大為減少,葉片微軟,葉色轉(zhuǎn)為灰綠時(shí)結(jié)束萎凋[11]。堆青則是在萎凋葉含水率約為20%時(shí)將在制品進(jìn)行堆積,厚度約15~60 cm,歷時(shí)1~15 d[12-14]。在茶鮮葉萎凋過(guò)程施以不同并篩或堆青處理,其實(shí)質(zhì)在于通過(guò)控制攤青厚度來(lái)改變溫度、相對(duì)濕度和通氣條件等環(huán)境因素,以有效調(diào)節(jié)在制品失水速率,并促進(jìn)白茶特定風(fēng)味品質(zhì)的形成。目前國(guó)內(nèi)學(xué)者僅考察了堆青起始含水率、堆青溫度、堆青歷時(shí)等單一或其部分復(fù)合因子對(duì)白茶品質(zhì)的影響[13-16],而基于攤青工藝(并篩或堆青起始時(shí)間、攤青厚度和攤青歷時(shí))的白茶風(fēng)味品質(zhì)耦合調(diào)控卻鮮有見(jiàn)報(bào)[14]。為此,本試驗(yàn)在控溫除濕環(huán)境(20~22 ℃,55%~65%相對(duì)濕度(relative humidity,RH))中以靜態(tài)攤晾于水篩加工而成的白茶為對(duì)照,在不同茶鮮葉減重率(65%、70%和75%)時(shí)對(duì)在制品進(jìn)行并篩或堆青處理。通過(guò)白茶樣品的感官審評(píng)和色譜-質(zhì)譜聯(lián)用檢測(cè)分析,探討了茶鮮葉萎凋過(guò)程中不同攤青工藝對(duì)白茶風(fēng)味品質(zhì)和生化成分的影響,以期為改進(jìn)白茶加工技術(shù)和提高制茶品質(zhì)提供參考依據(jù)。
鮮葉原料采自福建茶樹(shù)種質(zhì)資源圃(27°13′57″N,119°34′31″E)種植的福云6號(hào)茶樹(shù)春季第一輪新梢,采摘時(shí)間為2021年3月,采摘標(biāo)準(zhǔn)為一芽二、三葉。甲醇和乙腈(色譜純),德國(guó)Merck公司;C7~C30正構(gòu)烷烴,美國(guó)Sigma-Aldrich公司。
萎凋環(huán)境控制和監(jiān)測(cè)裝備:KF-35GW/35356格力空調(diào),珠海格力電器股份有限公司;CH150D轉(zhuǎn)輪式除濕機(jī),廣州市森井貿(mào)易有限公司;AOTE-JS06A超聲波加濕機(jī),廣州市傲特電子科技有限公司;ROBO60T工業(yè)電熱風(fēng)機(jī),上海固途工業(yè)品銷(xiāo)售有限公司;S520-EX溫濕度記錄儀,深圳市華圖測(cè)控系統(tǒng)有限公司。
Nexera X2超高效液相色譜儀,日本Shimadzu公司;QTRAP 4500三重四極桿/線性離子阱串聯(lián)質(zhì)譜儀,美國(guó)AB Sciex公司。7890A/5975C氣相色譜-質(zhì)譜聯(lián)用儀,美國(guó)Agilent公司;手動(dòng)固相微萃取裝置和65 μm PDMS/DVB(聚二甲基硅氧烷/二乙烯基苯)固相微萃取頭,美國(guó)Supelco公司。
茶樣制備的工藝流程為鮮葉→萎凋(其間并篩或堆青)→干燥,即取約43 kg福云6號(hào)鮮葉(含水率為78.2%)[17],在控溫除濕環(huán)境(20~22 ℃,55%~65% RH)中以基于靜態(tài)攤晾于水篩加工而成的白茶為對(duì)照,在不同茶鮮葉減重率時(shí)對(duì)在制品進(jìn)行并篩處理(并篩方式:在減重率為65%時(shí)將2~6篩合并1篩;在減重率為70%時(shí)將4~8篩并成1篩),攤勻;對(duì)照和各并篩處理在茶鮮葉減重率達(dá)76%時(shí)結(jié)束萎凋。另在茶鮮葉減重率達(dá)75%時(shí)對(duì)在制品進(jìn)行相同時(shí)長(zhǎng)不同厚度的堆青處理(堆青時(shí)長(zhǎng):2 d;堆青方式:2~6篩并1筐)和不同時(shí)長(zhǎng)相同厚度的堆青處理(堆青時(shí)長(zhǎng)2~6 d;堆青方式:6篩并1筐),攤鋪勻?qū)?。萎凋結(jié)束后,將上述在制品置80 ℃烘干(1 h),并采用四分法縮分至每份約200 g,由此制得不同攤青處理白茶樣品(見(jiàn)圖1)。
注:萎凋環(huán)境:20~22 ℃,55%~65%相對(duì)濕度(RH);干燥溫度:80 ℃。實(shí)線箭頭表示萎凋過(guò)程,虛線箭頭表示干燥過(guò)程,空心箭頭表示攤青處理(并篩或堆青),中括號(hào)內(nèi)數(shù)字表示茶鮮葉萎凋減重率。水篩直徑為90 cm,初始攤?cè)~量為每篩0.5 kg;筐的規(guī)格為46 cm(Φ)*72 cm(H)。
參照GB/T 23776-2018《茶葉感官審評(píng)方法》、GB/T 22291-2017《白茶》和GB/T 14487-2017《茶葉感官審評(píng)術(shù)語(yǔ)》中的方法,由5位專(zhuān)業(yè)人員組成品質(zhì)評(píng)定小組,采用評(píng)語(yǔ)法和評(píng)分法對(duì)茶樣進(jìn)行感官審評(píng)。
非揮發(fā)性代謝物:1)提取與檢測(cè):分別稱(chēng)取供試磨碎茶樣0.100 g,用1.2 mL 70%甲醇提取液溶解后,每隔30 min渦旋一次,每次渦旋持續(xù)30 s,共渦旋6次,于4 ℃冰箱過(guò)夜。以12 000 r/min離心10 min,取上清液,用0.22 μm微孔濾膜過(guò)濾,并參照已有文獻(xiàn)方法[18]進(jìn)行超高效液相色譜-串聯(lián)質(zhì)譜(ultra performance liquid chromatography-mass spectrometry,UPLC-MS)檢測(cè)分析。為保證分析結(jié)果的重復(fù)性和可靠性,取各供試茶樣提取物混合制備質(zhì)控樣本,重復(fù)檢測(cè)3次。2)定性和定量:利用軟件Analyst 1.6.3(美國(guó)AB SCIEX公司)處理液質(zhì)聯(lián)用數(shù)據(jù),使用MultiQuant軟件(美國(guó)AB SCIEX公司)進(jìn)行色譜峰積分。保留質(zhì)控樣品中峰面積相對(duì)標(biāo)準(zhǔn)偏差(relative standard deviation,RSD)≤20%的化合物,根據(jù)樣本物質(zhì)的二級(jí)質(zhì)譜和保留時(shí)間進(jìn)行定性分析。檢索譜庫(kù):廣泛靶向代謝組數(shù)據(jù)庫(kù)MetWare database V3.3(武漢邁特維爾生物科技有限公司)。
揮發(fā)性代謝物:1)提取與檢測(cè):分別稱(chēng)取供試磨碎茶樣5.0 g,倒入60 mL棕色頂空萃取瓶?jī)?nèi),采用本色PTFE/硅膠隔墊瓶蓋密封瓶口。萃取瓶置60 ℃恒溫水浴平衡10 min,隨后將固相微萃取頭插入萃取瓶上方頂空吸附30 min,拔出后立即插入氣相色譜進(jìn)樣口中熱解吸5 min,同時(shí)啟動(dòng)儀器并按預(yù)設(shè)的儀器參數(shù)[19]進(jìn)行數(shù)據(jù)采集。為保證分析結(jié)果的重復(fù)性和可靠性,取各供試茶樣混合制備質(zhì)控樣本,重復(fù)檢測(cè)3次。2)定性和定量:預(yù)先將在氣相色譜-質(zhì)譜聯(lián)用(gas chromatography-mass spectrometer,GC-MS)數(shù)據(jù)分析化學(xué)工作站MSD ChemStation E.02.02中創(chuàng)建的供試茶樣數(shù)據(jù)文件導(dǎo)入到質(zhì)譜軟件AnalyzerPro Version 5.2.2.6441(英國(guó)SpectralWorks有限公司)中,采用相同的特征提取參數(shù)進(jìn)行質(zhì)譜解卷積(峰面積≥500,峰高≥0.1%,峰寬≥0.01 min,信噪比(S/N)=5)和化合物鑒定(置信度≥80%、保留指數(shù)誤差≤30)。剔除萃取頭和毛細(xì)管固定相流失等原因產(chǎn)生的目標(biāo)雜峰,并保留質(zhì)控樣品中峰面積RSD≤30%的化合物。檢索譜庫(kù):NIST2017譜庫(kù)和茶葉香氣成分標(biāo)準(zhǔn)品自建譜庫(kù)[20]。
采用SIMCA14.1軟件(包含Omics skin,德國(guó)Sartorius Stedim Biotech集團(tuán))進(jìn)行主成分分析(principal component analysis,PCA)、正交偏最小二乘判別分析(orthogonal partial least squares discrimination analysis,OPLS-DA)、檢驗(yàn)和火山圖繪制。使用TBtools繪制熱圖[21]。應(yīng)用ChemRICH(http://chemrich.fiehnlab.ucdavis.edu/)進(jìn)行代謝物簇富集分析[22]。
白茶樣品的感官審評(píng)結(jié)果顯示(見(jiàn)表1),各處理制成的白茶呈現(xiàn)出較為相似的風(fēng)味品質(zhì)特征,但堆青處理總體上相較并篩處理及對(duì)照茶樣的香氣鮮度下降而滋味甜度提高。在并篩工藝組中以在減重率為70%時(shí)并篩(S21、S22和S23,平均分為89.33)略?xún)?yōu)于在減重率為65%時(shí)并篩(S11、S12和S13,平均分為88.80)的白茶品質(zhì),且二者均以薄并篩處理(S11和S21)較優(yōu)于對(duì)照茶樣(CK)。此外,在早并篩和晚并篩處理茶樣均隨攤青厚度的增加而品質(zhì)有所下降。在堆青工藝組中對(duì)在制品進(jìn)行相同時(shí)長(zhǎng)不同厚度的堆青處理(S31、S32和S33a)以厚堆處理(S33a)的白茶品質(zhì)較優(yōu),且厚堆處理的白茶更顯甜香;不同時(shí)長(zhǎng)相同厚度的堆青處理(S33a、S33b和S33c)則以短時(shí)處理(S33a)的白茶品質(zhì)為佳,且堆青時(shí)間越長(zhǎng),白茶滋味越雜。
表1 不同攤青處理白茶樣品的感官品質(zhì)
注:總分=外形×25%+湯色×10%+香氣×25%+滋味×30%+葉底×10%。
Note: Total score is calculated based on a 100-point scale: appearance of dry tea (25%), brew color (10%), aroma (25%), taste (30%), and infused leaf (10%).
2.2.1 不同攤青處理白茶的主要品質(zhì)成分差異
采用UHPLC-MS和GC-MS檢測(cè)技術(shù)可從供試茶樣中分別檢出1 313種非揮發(fā)性和123種揮發(fā)性代謝物。白茶在加工過(guò)程中不炒不揉,其主要滋味成分在很大程度上保留了鮮葉原料的初始組成特征[23-24]。相較靜態(tài)/并篩工藝組,本試驗(yàn)堆青工藝組茶樣中呈甜味的脯氨酸(A31)含量顯著降低(<0.05),但各處理間兒茶素類(lèi)、生物堿及其余氨基酸組分并無(wú)明顯的規(guī)律性差異(圖2a)。已有研究顯示[25-27],烷烴類(lèi)、醇類(lèi)和醛類(lèi)等化合物是形成白茶清香、毫香特征的重要物質(zhì)基礎(chǔ)。由圖2b可看出,相比靜態(tài)/并篩工藝組,堆青工藝組茶樣的烷烴類(lèi)化合物含量明顯增加。然而其大多為無(wú)味的長(zhǎng)鏈烷烴,故對(duì)白茶特征香氣品質(zhì)的形成貢獻(xiàn)較小。此外,堆青工藝組茶樣中具有較高含量脂肪味的2,4-二烯醛(B20),而帶清新宜人花果香特征的苯乙醇(B11)、橙花醇(B24)、香葉醇(B32)和橙花醛(B38)的含量均顯著低于其他處理(<0.05),這與其相較并篩處理及對(duì)照茶樣稍欠清純的香味品質(zhì)特征較為相符。
注:變量采用UV-scaling 標(biāo)度化預(yù)處理。各成分在靜態(tài)/并篩工藝組和堆青工藝組間的差異顯著性(P<0.05)采用*表示。A534:表兒茶素;A535:(-)-兒茶素;A536:兒茶素;A595:沒(méi)食子兒茶素;A596:表沒(méi)食子兒茶素;A804:(-)-表兒茶素沒(méi)食子酸酯;A847:沒(méi)食子兒茶素沒(méi)食子酸酯;A848:表沒(méi)食子兒茶素沒(méi)食子酸酯。A15:γ-氨基丁酸;A31:脯氨酸;A38:纈氨酸;A82:亮氨酸;A84:異亮氨酸;A148:谷氨酰胺;A149:賴(lài)氨酸;A152:谷氨酸;A196:組氨酸;A231:苯丙氨酸;A269:茶氨酸;A270:精氨酸;A304:酪氨酸;A372:色氨酸。A298:茶葉堿;A356:咖啡堿。B18:十二烷;B46:二十四烷;B48:十三烷;B68:二十六烷;B72:3-甲基十三烷;B82:十四烷;B91:壬基環(huán)戊烷;B98:十五烷;B106:8-己基十五烷;B111:3-甲基十五烷;B113:十六烷。B11:苯乙醇;B15:芳樟醇氧化物IV;B24:橙花醇;B32:香葉醇;B114:雪松醇。B19:癸醛;B20:2,4-二烯醛;B22:β-環(huán)檸檬醛;B28:β-環(huán)橙花醛;B38:橙花醛;B73:2-丁基-2-辛烯醛。
2.2.2 不同攤青處理白茶生化組成的模式識(shí)別
為進(jìn)一步闡明不同攤青處理對(duì)白茶生化組成的影響,分別對(duì)供試茶樣的非揮發(fā)性和揮發(fā)性代謝物進(jìn)行多變量統(tǒng)計(jì)模式識(shí)別。主成分分析(principal component analysis,PCA)結(jié)果顯示,基于非揮發(fā)性或揮發(fā)性代謝物的模式識(shí)別均可在前2個(gè)主成分二維得分視圖中將全部供試茶樣劃分為2個(gè)類(lèi)群,即靜態(tài)/并篩工藝組與堆青工藝組(圖3a和圖3b)。與靜態(tài)/并篩工藝組對(duì)比,堆青工藝組的非揮發(fā)性和揮發(fā)性代謝物的模式分布更為集中。在并篩工藝組中以早并篩處理(S11、S12和S13)比晚并篩處理(S21、S22和S23)茶樣非揮發(fā)性代謝物的模式分布更為集中,而揮發(fā)性代謝物的模式分布則相較離散。此外,通過(guò)正交偏最小二乘判別分析(orthogonal partial least squares discrimination analysis,OPLS-DA)結(jié)果表明,基于茶樣非揮發(fā)性代謝物(模型M1)和揮發(fā)性代謝物(模型M2)能對(duì)靜態(tài)/并篩工藝組與堆青工藝組進(jìn)行更好的類(lèi)群區(qū)分(圖3c和圖3d)。M1和M2的2、2和2分別為0.722、1.000、0.779和0.486、1.000、0.764(2和2分別表示所建模型對(duì)和矩陣的解釋率,2表示模型的預(yù)測(cè)能力)。通過(guò)置換檢驗(yàn)(=200)對(duì)模型的有效性檢驗(yàn)結(jié)果顯示,M1和M2均不存在模型過(guò)擬合(圖3e和圖3f)。
2.2.3 不同攤青工藝組白茶的差異代謝物富集分析
化學(xué)相似度富集分析(ChemRICH)是一種基于化學(xué)相似性而非稀疏生化知識(shí)注釋的統(tǒng)計(jì)富集方法[22]。通過(guò)ChemRICH富集分析結(jié)果表明,堆青工藝組與靜態(tài)/并篩工藝組茶樣的差異代謝物顯著富集于脂肪酸類(lèi)、烷烴類(lèi)、萜烯類(lèi)和黃酮類(lèi)等代謝物簇。堆青工藝組中的大多數(shù)不飽和脂肪酸類(lèi)(9,12-十八碳-6-烯酸、9-氧代-十八碳-12-烯酸、二氫獼猴桃內(nèi)酯、亞麻酸甲酯、共軛(9,11)亞油酸和-亞麻酸等)、烷烴類(lèi)(十四烷、9-甲基二十二烷、壬基環(huán)戊烷、3-甲基十三烷、8-己基十五烷和十六烷等)、飽和脂肪酸類(lèi)(丙戊酸和十一烷酸等)、降異戊二烯類(lèi)(-紫羅蘭酮和-紫羅蘭酮等)和醛類(lèi)(2-丁基-2-辛烯醛、癸醛和2,4-二烯醛等)化合物含量高于靜態(tài)/并篩工藝組茶樣,大部分甘油酯類(lèi)(2--亞麻酸甘油酯和2-亞油酸甘油酯等)、芹菜素類(lèi)(新西蘭牡荊苷II和新西蘭牡荊苷等)和二肽類(lèi)(-脯氨酸--亮氨酸和5-氧代脯氨酸等)化合物含量低于靜態(tài)/并篩工藝組茶樣,而近半數(shù)黃酮類(lèi)(6-甲氧基-2-(2-苯乙基)色酮、3′,4′,7-三羥基黃酮、花旗松素-3′--葡萄糖苷與山奈酚-3--阿拉伯糖苷、高良姜素、山奈酚-3--刺槐糖苷-7--鼠李糖苷、芹菜素-5--葡萄糖苷、異牡荊黃素-4′--葡萄糖苷、山奈酚-7--鼠李糖苷等)、萜烯類(lèi)(香葉基丙酮、1-咖啡酰---葡萄糖與橙花醇、香葉醇等)和吲哚類(lèi)(-乙酰--色氨酸與2-(3-吲哚基)噻唑等)化合物則發(fā)生或增或減的含量變化(圖4)。
2.2.4 不同攤青工藝組白茶的主要差異代謝物篩選
為獲得區(qū)分靜態(tài)/并篩工藝組與堆青工藝組茶樣的主要差異代謝物,以O(shè)PLS-DA模型的變量投影重要性(variable importance in project,VIP)、檢驗(yàn)顯著性和差異倍數(shù)值(fold change,F(xiàn)C)為篩選條件(VIP>1、<0.05和|log2FC|>0.5),可從供試茶樣已檢出1 436種化合物中篩選出12種非揮發(fā)性和11種揮發(fā)性代謝物(圖5)。其中2種萜類(lèi)化合物(橙花醇(B24)和橙花醛(B38))、2種鄰苯二甲酸酯類(lèi)化合物(鄰苯二甲酸二異辛酯(A758)和鄰苯二甲酸二(2-乙基己基)酯(A759))和4種其他化合物(異抗壞血酸(A276)、鄰磷酸膽堿(A319)、鳥(niǎo)苷3′,5′-環(huán)單磷酸(A695)和大黃酚-1-O--D-葡萄糖苷(A771))在堆青工藝組中的含量顯著低于靜態(tài)/并篩工藝組(<0.05);4種烷烴類(lèi)化合物(3-甲基十三烷(B72)、1-十四烯(B80)、十四烷(B82)和十六烷(B113))、2種醛類(lèi)化合物(香草醛(A185)和2-丁基-2-辛烯醛(B73))和9種其他化合物(2-甲基-3-氧代辛酸(A264)、3-吲哚乙酰胺(A267)、9-(阿拉伯糖基)次黃嘌呤(A472)、9-羥基-10,12-十八碳二烯酸乙酯(A635)、油酰單乙醇胺(A636)、未知化合物1(B49)、2,3-二氫-4-甲基-呋喃(B62)、二氫獼猴桃內(nèi)酯(B103)和未知化合物2(B104))在堆青工藝組中的含量顯著高于靜態(tài)/并篩工藝組(<0.05)。
注:非揮發(fā)性代謝物采用lg轉(zhuǎn)換和Par-scaling標(biāo)度化數(shù)據(jù)預(yù)處理;揮發(fā)性代謝物采用lg轉(zhuǎn)換和UV-scaling標(biāo)度化數(shù)據(jù)預(yù)處理。2:的解釋率2:模型的預(yù)測(cè)能力。
Note: The nonvolatile metabolites are pretreated with lg transformation and Pareto scaling, and the volatile metabolites are pretreated with lg transformation and unit variance scaling.2: the interpretability ofvariable.2: the predictability of the model.
圖3 基于供試白茶樣品生化組成的模式識(shí)別
Fig.3 Pattern recognition of biochemical compositions in white tea samples
注:采用柯?tīng)柲陕宸?斯米洛夫檢驗(yàn)(K-S檢驗(yàn))計(jì)算富集分析P值,每個(gè)節(jié)點(diǎn)表示一個(gè)發(fā)生顯著改變的代謝物簇;節(jié)點(diǎn)大小表示每個(gè)代謝物簇中代謝物的數(shù)量;節(jié)點(diǎn)顏色表示堆青工藝組比靜態(tài)/并篩工藝組增加(紅色)或減少(藍(lán)色)的化合物比例,紫色節(jié)點(diǎn)表示發(fā)生或增或減的代謝物簇。O=FA_13_1、OH-FA_18_3_2和O=FA_19_1為脂肪酸類(lèi)氧化產(chǎn)物。
注:圖a橫坐標(biāo)表示兩白茶樣本組間各代謝物峰面積均值的倍數(shù)變化(fold change,F(xiàn)C);縱坐標(biāo)表示t檢驗(yàn)的P值;與靜態(tài)/并篩工藝組相比,堆青工藝組中顯著上調(diào)的代謝物標(biāo)為紅色,顯著下調(diào)的代謝物標(biāo)為藍(lán)色,無(wú)顯著差異的代謝物標(biāo)為綠色。其中被標(biāo)記的化合物為主要差異代謝物(VIP>1、P<0.05和|log2 FC|>0.5)。圖b每行表示不同的代謝物,每列表示不同攤青處理白茶樣品,其中變量采用UV-scaling 標(biāo)度化預(yù)處理。A185:香草醛;A264:2-甲基-3-氧代辛酸;A267:3-吲哚乙酰胺;A276:異抗壞血酸;A319:鄰磷酸膽堿;A472:9-(阿拉伯糖基)次黃嘌呤;A635:9-羥基-10, 12-十八碳二烯酸乙酯;A636:油酰單乙醇胺;A695:鳥(niǎo)苷3′, 5′-環(huán)單磷酸;A771:大黃酚-1-O-β-D-葡萄糖苷;A758:鄰苯二甲酸二異辛酯;A759:鄰苯二甲酸二(2-乙基己基)酯。B24:橙花醇;B38:橙花醛;B49:未知化合物1;B62:2, 3-二氫-4-甲基-呋喃;B72:3-甲基十三烷;B73:2-丁基-2-辛烯醛;B80:1-十四烯;B82:十四烷;B103:二氫獼猴桃內(nèi)酯;B104:未知化合物2;B113:十六烷。
不同萎凋環(huán)境(溫度和濕度)將明顯影響茶鮮葉的失水速率,且通過(guò)特定的控溫除濕環(huán)境可實(shí)現(xiàn)白茶風(fēng)味品質(zhì)特征的有效調(diào)控[28]。已有研究表明,茶鮮葉萎凋減重率45%~60%為其多酚及兒茶類(lèi)氧化[29-30]和白茶香氣品質(zhì)形成的重要發(fā)展階段[10]。本試驗(yàn)在茶鮮葉萎凋減重率為65%~75%時(shí)設(shè)計(jì)了6種并篩和5種堆青處理,結(jié)果發(fā)現(xiàn)相比對(duì)照茶樣,堆青處理相較并篩處理對(duì)白茶風(fēng)味品質(zhì)和生化組成模式的影響更為明顯。兒茶素類(lèi)、氨基酸、生物堿等非揮發(fā)性代謝物是茶湯的主要呈味物質(zhì)[31-32]。除脯氨酸外,不同攤青處理白茶的主要滋味成分無(wú)顯著差異,這與各處理具有較為相似的風(fēng)味品質(zhì)特征基本相符。但堆青工藝組中的大多數(shù)脂肪酸類(lèi)化合物含量高于靜態(tài)/并篩工藝組茶樣,且大部分甘油酯類(lèi)、芹菜素類(lèi)化合物和近半數(shù)的黃酮類(lèi)化合物含量趨向降低。這表明堆青處理促進(jìn)了在制品中甘油酯的水解,并產(chǎn)生脂肪酸的累積。脂肪酸不僅是白茶香氣成分的重要前體物質(zhì)[33],也是引起茶葉酸敗的主要成分[34]。堆青工藝組中呈脂肪味的2,4-二烯醛含量顯著高于其他處理茶樣,其主要來(lái)源于脂肪酸氧化[35-36]。因此,在堆青過(guò)程中需關(guān)注脂質(zhì)氧化程度,以避免產(chǎn)生不良風(fēng)味。此外,芹菜素類(lèi)、黃酮類(lèi)化合物的氧化減少亦可在一定程度上降低堆青工藝組茶樣的苦澀滋味[37-38]。香葉醇、十六醛、庚醛、壬醛和5-乙基-6-甲基-3-庚烯-2-酮等與白茶新鮮氣息密切相關(guān),芳樟醇、呋喃型芳樟醇氧化物、香草醛、苯乙醛、-紫羅蘭酮和香豆素等則是白茶呈現(xiàn)甜香的主要特征香氣成分[25,35]。在茶鮮葉萎凋過(guò)程中,類(lèi)胡蘿卜素裂解雙加氧酶催化類(lèi)胡蘿卜素形成-紫羅蘭酮和-紫羅蘭酮等降異戊二烯類(lèi)物質(zhì)[39]。堆青工藝組茶樣中香草醛、-紫羅蘭酮和-紫羅蘭酮等顯著高于其他處理,而香葉醇的含量均顯著低于其他處理(<0.05),其與堆青工藝組茶樣香甜度較高而鮮度下降的香氣品質(zhì)特征較為相符。陳維等[14]研究發(fā)現(xiàn)苯甲醛、苯乙醇和苯乙醛等隨堆青時(shí)長(zhǎng)增加而上升,而正己醇、(,)-2,4-己二烯醛和辛醛在堆青后普遍降低。本試驗(yàn)結(jié)果顯示2-丁基-2-辛烯醛、二氫獼猴桃內(nèi)酯和1-十四烯等在堆青后增加,苯乙醇、橙花醇、香葉醇和橙花醛等花果香成分減少。這可能與本試驗(yàn)選用的鮮葉原料、堆青方式和檢測(cè)方法等存在差異有關(guān)[20,40]。綜上可見(jiàn),選擇適當(dāng)?shù)亩亚嗵幚矸绞?,通過(guò)控制脂質(zhì)氧化和促進(jìn)清甜花香物質(zhì)的釋放將有望為改善白茶風(fēng)味品質(zhì)提供新的解決方案。
1)不同攤青工藝制成的白茶呈現(xiàn)出較為相似的白茶風(fēng)味品質(zhì)特征,但堆青工藝組相較靜態(tài)/并篩工藝組茶樣的香氣鮮度下降而滋味甜度提高,且在茶鮮葉萎凋減重率達(dá)75%時(shí)將6篩(水篩直徑為90 cm,初始攤?cè)~量為0.5 kg/篩)在制品合并為1筐(直徑=46 cm、高度= 72 cm),堆青2 d后的攤青處理可獲得較優(yōu)的白茶品質(zhì)。
2)不同攤青處理白茶的兒茶素類(lèi)、生物堿和大部分氨基酸組分無(wú)明顯規(guī)律性差異。相較靜態(tài)/并篩工藝組,堆青工藝組茶樣中呈甜味的脯氨酸和苯乙醇、橙花醇、香葉醇等花果香成分顯著降低(<0.05)。靜態(tài)/并篩工藝組與堆青工藝組茶樣的生化組成模式存在明顯的類(lèi)群區(qū)分。
3)堆青處理可通過(guò)促進(jìn)脂肪酸代謝,增加烷烴類(lèi)、降異戊二烯類(lèi)和醛類(lèi)化合物含量來(lái)有效調(diào)節(jié)白茶樣品的生化組成;橙花醇、橙花醛和香草醛等23種化合物可視為其與靜態(tài)/并篩工藝組茶樣相互區(qū)分的主要特征標(biāo)識(shí)物(群)。
4)茶鮮葉萎凋過(guò)程中生化成分的變化受鮮葉原料特性、加工環(huán)境條件、技術(shù)干預(yù)措施等諸多因素的影響,今后尚需考慮開(kāi)展基于不同茶樹(shù)品種、芽葉嫩度和采摘季節(jié)等因素的多批次生產(chǎn)試驗(yàn),由此系統(tǒng)揭示攤青工藝對(duì)白茶風(fēng)味品質(zhì)影響的一般性規(guī)律。
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Effects of the leaf-spreading process on the quality of white tea during the withering of fresh tea shoots
XIANG Lihui, SONG Zhenshuo, ZHANG Yinggen, WANG Lili, CHEN Jian, CHEN Lin※
(,,350013,)
This study aims to investigate the effect of the leaf-spreading process on the flavor quality and biochemical components of white tea during withering. Under the indoor air conditions preset at 20-22 ℃ and 55%-65% relative humidity (RH), the static withering on bamboo sieves (0.5 kg fresh leaves per sieve: diameter () = 90 cm) was used as the control (Immobility). Tea samples were acquired by thin or thick piling-up, namely Bingshai or Duiqing when the weight loss rate of fresh tea shoots reached 65%, 70%, and 75%. The results showed that there were the similar sensory qualities in all tea samples. However, the freshness of the aroma decreased, and the sweetness of the taste increased in the white tea samples with Duiqing, compared with the Immobility and Bingshai. The quality of tea samples with the late Bingshai (4 to 8 sieves of work in process (WIP) merged into 1 sieve when the weight loss rate arrived at 70%) was slightly better than those with the early Bingshai (2 to 6 sieves of WIP merged into 1 sieve when the weight loss rate reached 65%). Furthermore, the best sensory qualities of the tea samples were produced from the thinnest Bingshai than Immobility. The best quality white tea sample was acquired with the thickest Duiqing (6 sieves of WIP merged into 1 basket) when treated for the same length of time (2 days) and different thicknesses (2 to 6 sieves of WIP merged into 1 bamboo basket: diameter () = 46 cm, height () = 72 cm) of Duiqing at the weight loss rate of 75%. Additionally, the WIP was preferred for the shortest duration (2 days), if treated with a different length of time (2 to 6 days) at such thickness of Duiqing. Although no regular changes were seen in the contents of catechins, alkaloids, and the main free amino acids among different treatments, the levels of proline (sweet) and some floral fruit components (phenylethanol, nerol, and geraniol) were significantly reduced in the white tea samples from the Duiqing process group, compared with the Immobility/Bingshai process group. The biochemical pattern recognition showed that all white tea samples were divided into two groups, i.e., Immobility/Bingshai and Duiqing process groups. The Duiqing process effectively regulated the biochemical compositions in the white tea samples, with an increase in the content of fatty acids, alkanes, norisoprenoids, and aldehydes. The 23 chemical compounds (such as nerol, citral, and vanillin) were considered the most important markers to distinguish them from each other. These findings can provide a strong reference to regulating the flavor quality of white tea using leaf spreading.
processing; quality control; white tea; withering; leaf-spreading
2022-11-05
2023-01-30
福建省自然科學(xué)基金項(xiàng)目(2020J011364);福建省屬公益類(lèi)科研院所基本科研專(zhuān)項(xiàng)(2019R1029-5和2020R1029008);福建省農(nóng)業(yè)科學(xué)院科技創(chuàng)新團(tuán)隊(duì)項(xiàng)目(CXTD2021004-2)
項(xiàng)麗慧,助理研究員,研究方向?yàn)椴枞~生物化學(xué)與分子生物學(xué)。Email:xlh1991@foxmail.com
陳林,博士,研究員,研究方向?yàn)椴枞~加工、茶葉生物化學(xué)及綜合利用。Email:chenlin_xy@163.com
10.11975/j.issn.1002-6819.202211049
TS272.7
A
1002-6819(2023)-07-0266-09
項(xiàng)麗慧,宋振碩,張應(yīng)根,等. 茶鮮葉萎凋過(guò)程中攤青工藝對(duì)白茶品質(zhì)的影響[J]. 農(nóng)業(yè)工程學(xué)報(bào),2023,39(7):266-274. doi:10.11975/j.issn.1002-6819.202211049 http://www.tcsae.org
XIANG Lihui, SONG Zhenshuo, ZHANG Yinggen, et al. Effects of the leaf-spreading process on the quality of white tea during the withering of fresh tea shoots[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2023, 39(7): 266-274. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.202211049 http://www.tcsae.org
農(nóng)業(yè)工程學(xué)報(bào)2023年7期