袁梓洢 1，尹保凤 1，邓丽莉 1,2,*，曾凯芳 1,2
（1.西南大学食品科学学院，重庆 400715；2.重庆市特色食品工程技术研究中心，重庆 400715）
摘 要：色泽是果蔬采后主要的感官品质之一，它是消费者判断果蔬成熟度、新鲜度、商品可接受度及营养价值的重要参数。决定果蔬采后色泽的主要色素有叶绿素、类胡萝卜素和花色苷，它们的代谢使果蔬呈现红、橙、黄、绿、蓝、紫等多种颜色。果蔬采后常发生的褪绿、褐变、黄化和白化等转色现象，也与果蔬色素代谢过程密切相关。研究果蔬采后色素代谢及其调控具有重要意义。本文综述了物理因子、化学因子和生物技术等在调控果蔬采后色素代谢方面的作用和机理，旨在为采后果蔬色泽的有效调控提供一定的理论参考。
关键词：果蔬；色素；叶绿素；类胡萝卜素；花色苷；调控
袁梓洢, 尹保凤, 邓丽莉, 等. 果蔬采后色素物质代谢调控研究进展[J]. 食品科学, 2016, 37(17): 236-244. DOI:10.7506/ spkx1002-6630-201617040. http://www.spkx.net.cn
YUAN Ziyi, YIN Baofeng, DENG Lili, et al. Ad vances in regulation of pigment metabolism in postharvest fruits and vegetables[J]. Food Science, 2016, 37(17): 236-244. (in Chinese with English abstract) DOI:10.7506/spkx1002-6630-201617040. http://www.spkx.net.cn
色泽、香气、风味、果形、质地是果蔬主要的感官品质，其中色泽是果蔬采后最基本、最重要的外观品质，它的深浅度、光泽度和均匀度直接影响果蔬的商品价值。果蔬色泽不仅影响消费者对果蔬的可接受度，同时也是消费者判断果蔬成熟度、新鲜度及营养价值的重要参数 [1-4]。不同种类、品种果蔬呈现的色泽主要由其所含色素物质的种类、含量、各色素含量间的比例决定 [5-6]。此外，果蔬采后贮藏过程中，伴随成熟衰老进程的到来，转色现象普遍发生，如黄化 [7]、褪绿 [8]、褐变 [9]和香蕉高温“绿熟” [10]等现象。这些都与果蔬色素的代谢密切相关。因此，研究采后果蔬色素代谢及其调控具有重要意义。本文综述了物理因子、化学因子和生物技术等因素对采后果蔬色素及色泽的调控作用，以期为采后果蔬色泽的有效调控提供一定的理论参考。
果蔬中的叶绿素由叶绿素a和叶绿素b组成。其中，叶绿素a呈蓝绿色，叶绿素b呈黄绿色 [11]。果蔬组织采后叶绿素的代谢主要涉及叶绿素的降解。目前研究发现的叶绿素的降解途径主要有酶降解和光降解两种途径。酶降解途径是以叶绿素a为中心的降解途径。叶绿素的光降解途径目前研究较少，过氧化物酶（peroxidase，POD）与该代谢路径联系紧密，但此代谢活动发生位置不明确，可能在类囊膜中，也可能在亚细胞内 [12]。当酚类物质和H 2O 2存在时，叶绿素a会被POD氧化成无色的低分子化合物 [13]。另外，光照条件下，在脂氧合酶（lipoxidase，LOX）作用下，植物衰老过程积累的大量游离不饱和脂肪酸形成的自由基能使叶绿素氧化成无色化合物 [14]。LOX作用的脂质氧化引起的膜完整性丧失也加速叶绿素含量下降 [11]。
类胡萝卜素按其分子组成分为含氧类胡萝卜素（叶黄素类）和不含氧类胡萝卜素（胡萝卜素类） [15]。叶黄素类主要有叶黄质、β-隐黄质、玉米黄质、紫黄质、新黄质、辣椒红素、辣椒黄素等；胡萝卜素类主要有α-胡萝卜素、β-胡萝卜素、ζ-胡萝卜素、番茄红素、八氢番茄红素、六氢番茄红素等 [16-17]。不同类胡萝卜素呈现不同的颜色，果蔬中各种类胡萝卜素组成比例的变化赋予了不同果蔬特有的颜色 [16]。
花青素是一类广泛存在于果蔬中的水溶性色素，属类黄酮化合物。花青素不稳定，常与戊糖类、甲基戊糖和己糖类结合形成花色苷 [18]。花色苷是以葡萄糖为前体，苯丙氨酸为直接前体经一系列酶催化反应合成的 [19]。稳定态的花色苷一般存在于植物细胞的液泡中 [20-21]。
2.1 光照对采后果蔬色素代谢的调控
不同的光质、光强、光照时间对果蔬色素代谢的调控不同。目前，自然光、紫外线、脉冲光、发光二极管（light emitting diode，LED）光在调控果蔬色素代谢上的研究均有报道。如紫外线有效抑制贮藏果蔬叶绿素的降解和黄化程度 [22]；紫外线B波段诱导中国红沙梨果实花色苷合成 [23]；脉冲光增强红熟番茄果实的红色，促进花色苷、番茄红素、α-胡萝卜素和β-胡萝卜素积累 [6]；660 nm LED红光使柑橘果实β-隐黄质积累 [24]，而450 nm LED蓝光提高番茄果实的着色和红色度 [25]；红光LED和蓝光LED处理促进葡萄果实花色苷含量的增加 [26]；紫外线C波段和红光处理显著提高番茄红素含量 [27]等。但光照促进果蔬色素降解的作用也有报道。如红辣椒中类胡萝卜素在光诱导下发生“光漂白”现象 [28]；光照处理后西兰花的黄化现象被诱导等 [29]。
光照对采后果蔬色泽的调控可能与光受体和光信号转录因子有关 [30]。光敏色素互作因子（phytochrome interacting factors，PIF）家族的光信号转录因子在黑暗条件下积累抑制类胡萝卜素的合成和有色体的形成 [31]。基因向光素2（phototropin，FaPHOT2）可能与草莓果实对蓝光的感应有关。草莓果实基因FaPHOT2表达水平随花青苷含量增加而增加。敲除FaPHOT2导致 花青苷含量降低，而其过表达导致果实花青苷的积累 [32]；另一方面，光处理影响色素代谢过程中相关酶活性和基因的表达 [22,24]。紫外线B波段处理后，葡萄浆果中花青苷合成关键基因黄酮醇合酶（flavonol synthase，FLS1）和类黄酮糖基转移酶（flavonoid glycosyltransferase，UFGT）基因表达上调，果实花青苷含量的增加 [33]。白光处理通过抑制红肉马叙葡萄柚八氢番茄红素脱饱和酶（phytoene desaturase，PDS）基因和ζ-胡萝卜素脱饱和酶（ζ-carotene desaturase，ZDS）基因的表达导致β-胡萝卜素含量显著降低 [34]。蓝光通过上调温州蜜柑和夏橙中八氢番茄红素合酶（phytoene synthase，CitPSY）基因的表达量促进果实类胡萝卜素积累，而红光对这两种果实的CitPSY基因表达无影响 [35]；也有研究表明红光通过诱导温州蜜柑CitPSY、CitPDS、CitZDS、β-环化酶（lycopene β-cyclase 1，CitLCYb1）、CitLCYb2、β-羟化酶（β-carotene hydroxylase，CitHYb）和玉米黄素环氧酶（zeaxanthin epoxidase，CitZEP）基因的表达，诱导果实β-隐黄质积累 [24]。
光照也通过对转录因子的调控调节果蔬花色苷的代谢。光照通过激活转录因子FaMYB10的表达水平提高草莓天竺葵素-3-O-葡萄糖苷和矢车菊素-3-O-葡萄糖苷的合成 [36]。果实采收前一周，转动果实改变其向阳面，果实转录因子MdMYB10基因和7 个花青苷合成相关的结构基因表达量均上调 [37]。泛素化E3连接酶组成型光形态建成1（ubiquitin E3 ligase constitutive photomorphogenic1，MdCOP1）、下胚轴延长因子5（elongated hypocotyl 5，MdHY5）、MdMYB22和MdMYBs都是苹果果皮中受紫外线B波段诱导的基因，紫外线B波段诱导的果实花青苷的积累发生在这些基因表达升高以后。紫外线B波段处理诱导上游光信号因子MdCOP1基因的表达，并通过结合MdMYBs启动子区域，激活转录因子MdHY5信号通路，最终导致苹果果皮红色的形成 [33]。苹果MdMYB1蛋白在光处理条件下积累，而黑暗条件下则通过一个依赖于泛素化途径发生降解。MdCOP1基因是黑暗条件下MdMYB1蛋白泛素化反应和降解过程中必需的 [38]。此外，苹果中B-box蛋白（constans-like 11，MdCOL11）也参与紫外线B波段和温度诱导的果皮花青苷生物合成。其诱导的信号反应可能涉及转录因子MdHY5和MdMYBA基因的参与。MdHY5和MdCOL11基因也可能通过结合花青苷生物合成相关基因启动子区域的G-box，直接调控这些基因的表达 [39]。
此外，光能促进果蔬内源激素（生长素、细胞分裂素、赤霉素等）的生成调控果蔬的色素代谢 [25]。红光LED夜间照射处理后，葡萄果皮内源脱落酸（abscisic acid，ABA）、ABA氧化产物红花菜豆酸含量，以及生物合成关键基因类胡萝卜素裂解双加氧酶（9-cis epoxycarotenoid dioxygenase，VvNCED1）基因和脱落酸8’-羟化酶（abscisic acid 8’-hydroxylase，VvCYP707A1）基因表达量均增加 [26]。
2.2 温度对采后果蔬色素代谢的调控
果蔬中不同色素物质对温度的响应不同。对花色苷而言，其降解过程符合一级反应动力学方程，一般随着贮藏温度上升，花色苷降解速率越快 [40]。花青苷的积累与季节的温度相反。低温季节花青苷和飞燕草素积累增强，单糖苷花青素积累，但随着季节温度的升高，其含量降低并伴随二糖苷花青苷含量的增加 [41-42]。温度对不同果蔬的类胡萝卜素代谢的调控方式不同。4 ℃、6 h的低温冷激处理促进克莱门汀蜜橘果实类胡萝卜素的积累和叶绿素的降解 [43]。高温使番茄的番茄红素合成减少 [44]，但高温能促进“Cara Cara”脐橙积累类胡萝卜素和转色 [45]。但在柑橘果实乙烯褪绿反应中，虽然高温条件下褪绿反应启动更快，但与低温相比，高褪绿温度条件下，果实积累的色素种类不同，导致果实呈现不同颜色。65 °F和75 °F条件下，果实快速积累玉米黄质和β-柠乌素（橙色素），形成高度着色的果实。而85 °F条件下，β-柠乌素的积累受到抑制，导致果实橙色变浅 [46]。20/15 ℃或25/15 ℃交替处理比持续的20 ℃和25 ℃褪绿处理得到的柑橘果实颜色更好 [47]。果实对温度的这种敏感性可以解释商业褪绿条件下和生长在热带地区柑橘果实着色差的现象 [48]。
温度调控采后果蔬色素代谢的可能机理是温度影响了色素代谢相关酶活性和基因表达。高温或热处理显著降低苹果果皮花青苷合成相基因的表达量，而低温通过上调花青苷生物合成相关基因的表达，促进果实花青苷的积累和着色。热处理快速降低调控苹果果实红色形成的R2R3 MYB转录因子（MYB10）的表达水平。一个晚上的低温就足以激发MYB10基因的大量表达 [49]。从苹果中分离得到受冷诱导的碱性螺旋-环-螺旋蛋白（basic helixloop-helix，bHLH）的成员之一MdbHLH3，其通过其N末端的两个区域（氨基酸1～23和186～228）特异的与转录因子MdMYB1互作。随后MdbHLH3基因结合到花青苷生物合成相关二氢黄酮醇-4-还原酶（dihydroflavonol-4-reductase，MdDFR）基因和MdUFGT基因，以及MdMYB1基因的启动子区域，启动这些基因的表达。此外，MdbHLH3基因可以经过转录后修饰，增强其启动子结合能力和转录活性 [41]。当紫外线B波段结合17 ℃低温处理苹果时，MdCOP1、MdHY5、MdMYB22和MdMYBA等基因的表达和花青苷的积累均增强 [33]。
3.1 植物激素对采后果蔬色素代谢的调控
植物激素在采后果实色素代谢中仍然发挥重要作用。在延迟成熟的锦橙突变体材料中，果实着色延迟伴随着类胡萝卜素和ABA代谢途径上CsPSY、CsNCED1、CsABA8ox基因表达下调，茉莉酸（jasmonic acid，JA）、茉莉酸甲酯（methyl jasmonate，MeJA）代谢途径上LOX基因、丙二烯氧合酶（allene oxide synthase，AOS）基因、茉莉酸-O-甲基转移酶（jasmonic acid carboxyl methyltransferase，JMT）基因和茉莉酸受体冠菌素不敏感1（coronatine insensitive 1，COI1）基因表达下调 [50]。
3.1.1 乙烯对采后果蔬色素代谢的调控
乙烯在调控果蔬色素代谢过程中有重要作用，乙烯能加速果蔬叶绿素降解以及类胡萝卜素和花色苷的积累，从而促进采后果蔬的转色。但乙烯的作用效果会受乙烯浓度、果蔬成熟度、贮藏温度等多个因素的影响。高乙烯浓度和成熟度较高的辣椒转色越快 [51]。不同成熟度的草莓也表现了该特点 [52]，但乙烯处理后，不同成熟度的伏令夏橙的转色效果与上述结果相反 [53]。
外源乙烯调控采后果蔬色素代谢的机理涉及多个方面：一方面，可能与处理果蔬内源乙烯的生物合成和信号传导途径有关。外源乙烯能够诱导乙烯合成相关基因1-氨基环丙烷-1-羧酸（1-aminocyclopropanecarboxylic acid，ACC）合成酶（ACC synthase，ACS）基因和ACC氧化酶（ACC oxidase，ACO）基因表达、ACO酶活性变化，增加内源乙烯生成量，诱导叶绿素的代谢 [54]。外源乙烯能诱导草莓 [52]、苹果 [54]等果蔬中乙烯受体基因的表达。在番茄果实中，通过RNA干涉技术（RNA interference，RNAi）减少乙烯响应因子（ethylene response factor 6，SlERF6）的表达，提高了果实中类胡萝卜素和乙烯水平 [55]。另一方面，乙烯影响果蔬色素代谢相关酶活性和基因的表达。乙烯通过激活夏橙叶绿素酶基因表达及其蛋白活性诱导叶绿素分解 [56]。乙烯加速椪柑果实褪绿的过程中，叶绿素a/b结合蛋白基因（chlorophyll a/b binding protein，CitCABs）的表 达水平降低，从而促进了结合态叶绿素分子向游离态的转化。而叶绿素降解相关基因：叶绿素酶（chlorophylase，CitChlase）和叶绿素b还原酶（chlorophyll b reductase，CitNYC）基因转录水平的增加则进一步促进了叶绿素的降解。而采用能够延缓乙烯褪绿效果的赤霉素处理，抑制了乙烯诱导的类胡萝卜素生物合成相关基因的表达和八氢番茄红素、六氢番茄红素及β-橙色素的积累 [57]。西兰花中脱镁叶绿酸a水解酶（pheophytinase，PPH）基因、脱镁叶绿酸a加氧酶（pheophorbide a oxygenase，BrPAO）基因表达受乙烯的影响 [58]。但乙烯的各种调控机理不是相互独立的，它们存在一定的关联性。外源乙烯处理鸭梨发现PbPPH基因、乙烯信号转导途径和内源乙烯的生成同时发生，不过调节三者之间的中间因子仍不明，需要进一步研究 [59]。此外，乙烯也能影响果蔬色素代谢相关细胞器结构的变化 [60]。
3.1.2 脱落酸对采后果蔬色素代谢的调控
ABA是非呼吸跃变型果实成熟过程中最重要的激素，与果实色素代谢密切相关。在脐橙和夏橙果皮破色期，果皮ABA含量达到峰值，随着果实的完全着色ABA含量下降。“Pinalate”脐橙中（Navelate脐橙芽变品种，ABA缺失突变体），ζ-胡萝卜素去饱和过程部分受阻，导致果实中早期合成的线性胡萝卜素积累，果皮叶黄素和ABA合成减少，环化和氧化类胡萝卜素比例减少，使果实颜色由橙黄色变成黄色 [61]。内源ABA的积累和外源ABA处理都能促进乙烯的合成或增加果实对乙烯的敏感性，影响果实的色素代谢 [62-63]。ABA处理显著诱导红灯甜樱桃花青苷的合成，而ABA生物合成抑制剂去甲二氢愈创木酸（nordihydroguaiaretic acid，NDGA）处理阻止了花青苷的合成。ABA合成关键基因PacNCED1的沉默也导致无色果实的形成 [64]。ABA处理后，温州蜜柑、夏橙和Lisbon柠檬总类胡萝卜素含量均显著下降，但每种果实中各种类胡萝卜素单体的响应不同 [35]。
ABA级联反应由ABA受体、二级信使、蛋白激酶和各种转录因子构成，协同调控包括色素代谢在内的果实成熟相关反应的发生 [65]。一般，外源ABA通过调控采后果蔬类胡萝卜素和花青苷代谢相关基因的表达，影响果蔬色素的代谢。如ABA处理诱导花青苷合成苯丙氨酸解氨酶（phenylalnine ammonialyase，VvPAL）基因、肉桂酸-4-羟化酶（cinnamate-4-hydroxylase，VvC4H）基因、查耳酮异构酶（chalcone isomerase，VvCHI1）基因和VvCHI2基因的变化 [66]；诱导温州蜜柑中CitPSY、CitPDS、CitZDS、CitLCYb1、CitLCYb2、CitHYb、CitZEP、CitNCED2、CitNCED3基因显著上调等 [35]。但外源ABA处理时间、浓度、果蔬成熟度会对其作用效果有影响 [67]。此外，在采后果蔬色素代谢的调控过程中，ABA和光、温度等因子具有交互作用。光照和ABA均能通过激活转录因子FaMYB10基因的表达调控花色苷的生物合成 [36]。ABA生物合成抑制剂处理和RNAi介导的ABA生物合成基因镁螯合酶H亚基/ABA受体（Mg-chelatase H subunit /ABA receptor，FaCHLH/ABAR）的下调表达，与ABA处理具有相反的作用。FaMYB10基因在光和ABA响应和花青苷合成过程中作为信号转导中间体起作用。PacMYBA基因在ABA调控的红樱桃花青苷生物合成过程中也具有重要作用 [64]。
3.1.3 赤霉素（gibberellins，GAs）对采后果蔬色素代谢的调控
GAs对不同果蔬的作用效果不同。GA有利于夏橙果实返青 [68]，GAs能延缓克莱门柚外观色泽变化，相应色素代谢脱镁叶绿酸a加氧酶和八氢番茄红素合酶基因的表达下调 [69]。但GAs处理却能明显增加葡萄浆果花色苷的含量 [70]，可能与GAs处理对果实糖代谢的调控有关 [71]。外源GA处理能引起温州蜜柑、夏橙、Lisbon柠檬3 个品种柑橘汁胞类胡萝卜含量显著降低。但3 个品种中对外源GA处理产生响应的类胡萝卜素和代谢相关基因不同 [35]。
此外，多种植物激素对采后果蔬色素代谢的调控存在交互作用 [72]。如乙烯诱导的柑橘果实褪绿过程伴随着果实ABA含量的急剧增加 [73]；采前使用二氧代钙（赤霉素的抑制剂）处理蜜橘、橙子、柠檬，采后再用乙烯处理后发现蜜桔、橙子果皮色泽增强，叶绿素含量下降，类胡萝卜素含量增加 [4]。此外，番茄果实类胡萝卜素的积累受生长素-乙烯平衡的调节。乙烯前体ACC或者生长素抑制剂2-（对-氯苯氧）-异丁酸（p-chlorophenoxy isobutyric acid，PCIB）处理果实，均能加速果实的转色，番茄红素、α-、β-和δ-胡萝卜素的积累和β-叶黄素和叶绿素b的消失。而使用吲哚乙酸（indole-3-acetic acid，IAA）处理延缓果实番茄红素的积累和叶绿素a的减少 [74]。
3.2 NO对采后果蔬色素代谢的调控
内源NO和外源NO对果蔬的色素代谢有一定的调控作用。成熟度越高的果蔬，NO的释放量越少，乙烯释量却升高；同时内源NO释放量与果蔬成熟过程中叶绿素含量变化有一定的关系 [75]。外源NO处理能延缓果蔬的色泽变化和成熟衰老进程。目前已广泛用于芒果 [76]等果蔬中，且不同种类果蔬有不同的最优NO处理浓度、时间和温度。NO调控果蔬色素代谢机制主要与其对乙烯代谢的调控相关。它能通过调控乙烯生物合成相关基因和信号转导基因的表达，抑制乙烯的生成和信号转导 [77]。NO也能影响色素代谢相关酶的活性。
3.3 糖类物质对采后果蔬色素代谢的调控
糖类是类胡萝卜素和花色苷生物合成的物质基础，而且糖类物质可作为一种信号分子影响色素代谢。高浓度糖可以抑制葡萄多酚氧化酶（polyphenol oxidase，PPO）的活性，防止变色；还可使色素代谢相关的基因黄烷酮-3-羟化酶（flavanone-3-hydroxylase，F3H）基因、UFGT基因等表达发生变化 [78-79]。另外，果糖、葡萄糖和蔗糖处理都能促进葡萄浆果花色苷的积累，但果糖和葡萄糖处理效果优于蔗糖 [20]。蔗糖和甘露醇处理显著提高温州蜜柑、夏橙、Lisbon柠檬汁胞总类胡萝卜素、隐黄质、反式-紫黄质、顺式紫黄质和叶黄素，但3 个品种中对外源GA处理产生响应的类胡萝卜素和代谢相关基因不同，表明不同糖类物质调控果实色素代谢的机制存在差异 [35]。
3.4 1-甲基环丙烯（1-methylcyclopropene，1-MCP）对采后果蔬色素代谢的调控
1-MCP对果蔬色素代谢的调控作用受贮藏温度、处理浓度、果实成熟度等因素影响。冷藏温度条件下，1-MCP处理西兰花的叶绿素含量变化明显慢于20 ℃贮藏条件 [80]。不同浓度1-MCP结合冷藏能延缓苹果色素降解，且低浓度1-MCP效果更好 [81]。但高浓度的1-MCP有效地延缓绿熟番茄果实色泽、番茄红素和叶绿素含量的变化 [3]。1-MCP作用效果存在也组织特异性 [82]。另外，1-MCP处理方式也可能影响其对果实色泽的影响，番茄和桃子都需要进行重复或持续多次1-MCP处理才能抑制其 色泽的变化，这可能与果实中新的乙烯受体合成有关 [83]。1-MCP调控采后果蔬色素代谢的机理可能与其对果蔬内源乙烯和乙烯信号转导途径的调控有关 [84]。另外，也可能与其对色素代谢相关酶活性和基因表达水平的调控有关。1-MCP处理能影响西兰花贮藏过程色素代谢相关酶（PPO、LOX、POD）的活性 [85]。京白梨和翠绿梨色素代谢中PAO基因、NYC基因和滞绿蛋白（stay-green protein，SGR1）基因表达下调，叶绿素降解延缓 [60]。此外，1-MCP对果蔬色泽代谢的作用效果可能与CO 2含量有关，但至今该机理存在争议，还不明确 [86]。
生物技术的发展使人们对果蔬色素物质代谢调控的认识由宏观现象深入到微观的基因调控上。果实类胡萝卜素、花青苷等色素物质的生物合成均在转录水平受到调控。利用病毒诱导的基因沉默（virus induced gene silencing，VIGS）和RNAi等生物技术，通过对色素物质代谢途径上关键基因或关键转录因子的调控，可以在一定程度上实现对果蔬组织色素代谢方向和比例的调控，从而改变果蔬的颜色表型。如将从细菌或/和高等植物中提取的番茄红素β-环化酶（lycopene β-cyclase，LeCYB）基因导入番茄基因组中，使果实的类胡萝卜素合成途径更多地引至β,β-分支，相应β,ε途径受阻，果实呈现橙黄色 [87-88]。叶绿素降解关键基因LeSGR1沉默得到果肉表型为绿色的番茄（LeSGR1滞绿体） [89]。通过VIGS技术沉默番茄ABA生物合成和氧化分解关键基因SlNCED1和SlCYP707A2，导致成熟SlNCED1-RNAi-处理的番茄果实颜色变为橙色 [90]。通过RNAi抑制番茄果实中APETALA2转录因子（SlAP2a）的表达，得到深橙色的番茄果实 [91]。嵌合抑制型转基因番茄EFR.B3-SRDX中EFR.B3-SRDX基因的过表达导致果实色素积累减少，果实由野生型的红色转为橙色 [92]。此外，通过RNAi介导的基因沉默技术沉默番茄果实延伸复合蛋白2-类似基因（elongator complex protein 2-like gene，SlELP2L），导致番茄果皮叶绿素的显著积累和类胡萝卜素含量的下降，形成深绿色果实 [93]。
参与果实正调控花青素合成 的转录因子主要源于MYB和bHLH家族。MYB转录因子和ABA在果实花青苷生物合成过程中发挥重要作用。从红灯甜樱桃中分离得到的R2R3-MYB转录因子PacMYBA通过与一些花青苷相关的bHLH转录因子相互作用，激活花青苷生物合成相关基因：二氢黄酮醇-4-还原酶（dihydroflavonol-4-reductase，PacDFR）、无色花色苷双加氧酶（leucoanthocyanin dioxygenase，PacANS）和PacUFGT基因的启动子。通过VIGS技术抑制转录因子PacMYBA的表达，导致甜樱桃果实中红色色素的缺失 [64]。在荔枝果实中转录因子LcMYB1控制果实的花青苷合成，仅在有花青苷积累的组织中检测到LcMYB1基因的表达。ABA和阳光照射促进其表达，而氯吡苯脲和套袋抑制其表达和花青苷合成，LcUFGT可能是其调控的目标结构基因 [94]。紫色花椰菜中，MYB-bHLH-WD40转录复合体调控bHLH基因的表达，bHLH可能是控制花青苷生物合成中的关键点。BoMYB2和各种BobHLHs基因特异性地调节后续的花青苷合成途径相关基因的表达 [95]。
三大色素物质赋予果蔬多种色泽，其代谢是采后果蔬组织生理活动的重要组成部分。近年来，叶绿素、类胡萝卜素和花色苷的合成及降解途径都已比较明晰，代谢相关的机理也从一般现象的解释到酶、蛋白质稳定性、结构再延伸至分子水平。通过物理、化学、生物等因子的单一或结合调控，一方面可以改善果蔬着色效果（包括色素物质的含量、组成及比例的定向调控等），提高其外观品质和经济价值；另一方面可以使果蔬更好的护色（包括滞绿体的出现、黄化、褐变调控等），从而增加果蔬产品的市场竞争力。另外，一些果蔬突变体（如橙黄色的番茄果实等）的出现极大丰富了果蔬色泽，满足消费者对果蔬产品的不同需求。不过，三大色素代谢途径中一些酶的作用仍存在质疑，叶绿素和类胡萝卜素可通过类异戊二烯途径进行合成，两者的交叉性仍需解决；叶绿素降解和花色苷合成都经历了细胞部位的转移，转移机制不明且两者的转移是否具有关联性？此外，由于果蔬的结构特征使得采后果蔬的色素代谢不同于植物，其代谢过程更加复杂多变。对果蔬色素调控手段而言，物理、化学、激素因子和生物技术的方式多样但各自有缺陷，仍需进一步研究各种调控因子结合是否具有1＋1＞2的模式。同时仍需掌控众多因子的主次之分，从而达到更好的调控效果。
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Advances in Regulation of Pigment Metabolism in Postharvest Fruits and Vegetables
YUAN Ziyi
1, YIN Baofeng
1, DENG Lili
1,2,*, ZENG Kaifang
1,2
(1. College of Food Science, Southwest University, Chongqing 400715, China; 2. Chongqing Engineering Research Center of Regional Food, Chongqing 400715, China)
Abstract：Color is one of the main sensory qualities of fruits and vegetables, and it is also a crucial parameter for consumers to judge the maturity, freshness, commercial acceptability and nutritional value of fruits and vegetables. Color diversity in postharvest fruits and vegetables is due to the differential accumulation of three main classes of pigments: chlorophylls, carotenoids and anthocyanins. The classical red, orange, yellow, green, blue or purple coloration of fruits and vegetables is due to the metabolism of those pigments. Besides, the color change phenomena of postharvest fruits and vegetables, such as degreening, browning, yellowing and whitening, are also closely related to the metabolism of pigments. Hence, it is important to understand pigment metabolism and its regulation in postharvest fruits and vegetables. This paper summarizes the effects of physical factors, chemical factors and biotechnology on the coloration of postharvest fruits and vegetables, and the underlying mechanisms are also reviewed in this paper, aiming to provide theoretical references for furt her research on the general rule and regulation of pigment metabolism in postharvest fruits and vegetables.
Key words：fruits and vegetables; pigments; chlorophylls; carotenoids; anthocyanins; regulation
DOI：10.7506/spkx1002-6630-201617040
中图分类号：S609.3
文献标志码：A
文章编号：1002-6630（2016）17-0236-09
收稿日期：2015-10-01
基金项目：国家自然科学基金青年科学基金项目（31401540）；重庆市博士后科研项目特别资助项目（Xm2014106）；
“十二五”国家科技支撑计划项目（2015BAD16B07）
作者简介：袁梓洢（1991—），女，硕士研究生，研究方向为果蔬采后生理。E-mail：yuanziyi010@163.com
*通信作者：邓丽莉（1983—），女，讲师，博士，研究方向为果蔬采后生理与生物技术。E-mail：denglili_361@163.com
引文格式：