想吃美味番茄？那就远离冰箱
在你买了番茄装进购物袋里拿回家的功夫，它就已经跟过去不一样了。不管你买的是李子番茄、樱桃番茄，还是纯种番茄，要想吃到味道最好的番茄，就得自己采摘，然后当场吃掉。那是因为番茄的味道，由糖、酸和几种被称为挥发物的化学物质构成，自它从藤上被摘下来的那一刻开始，就在逐渐减弱。现在你能做的只有一件事：让它远离冰箱。
2016年10月17日，美国《国家科学院院刊》在线发表佛罗里达大学、浙江大学、康奈尔大学、美国农业部的研究报告，发现番茄在大多数冰箱保持的温度下保存时，会发生不可逆转的基因变化，由此永远失去它们的一些味道。
该研究将两个品种的番茄（纯种番茄和一种更常见的现代品种）储存在41℉（约合5℃）的温度下，之后再将它们转移到室温（68℉，约合20℃）下。对番茄在低温下的内部变化进行研究后，发现这种亚热带水果进入了休克状态，在低温储存一周后发生了损失极大的变化。恢复室温后，哪怕只有一天，番茄中一些产生其味道挥发物的基因便不再起作用，而且无法恢复。
就像是一首交响乐，去掉小提琴和木管乐器，还能听到乐声，但它已经不一样了。再将小提琴加回去，也还是不对。你需要那30种或更多的化学物质像交响乐一样平衡组合在一起，才能有一个好味道的番茄。
根据作者的建议，如果能买到新鲜的番茄，就在室温下进行保存，以便保持它们的风味，而且最好在买回家一周内将它们吃完。如果看到杂货店老板将它们储存在温度很低的冰箱里，就告诉他们不要那么做。
但是，该研究的意义似乎主要在于学术方面。普通美国人每人每年平均会吃掉将近20磅（约合9公斤）新鲜番茄。此外，尽管研究人员、企业和农民全都竭力产出更美味的番茄，但有些因素还无法控制。
毕竟，大多数反季节番茄刚开始成熟，可能就被人从藤蔓上摘了下来。它们被储存、测量大小、划分等级，并与其他番茄一起被装箱，每箱重25磅。接着，它们要在一个湿度和温度都受到控制的房间里（不低于55℉）待上2～4天，吸收一种用于催熟的气体（乙烯），随后被装上一辆控温的卡车，运往一个仓库。在仓库里，它们被重新包装，重新拣选，并送到食品杂货店。在那里，如果需求量不大或者空间有限，它们会被放在一台冰箱里储存，等到你买下它们的时候，可能已经过去一个星期甚至十天了。
佛罗里达番茄委员会负责人说：它或许永远也无法媲美你在自家后院种的、经过八九十天自然成熟的番茄，但比石头汤强。冬季里，美国多达一半的新鲜番茄是由该委员会供应的。
在寒冷的月份里，是不是该忍受没有番茄的饭菜呢？纽约蓝山餐厅及石谷仓蓝山餐厅多次获得詹姆斯·比尔德奖的大厨说建议：冬天别吃番茄，从商店里买番茄干来用，也可以在夏天制作番茄酱并妥善储存，做好番茄酱并装在罐子里，可以吃上一整个冬天。
Proc Natl Acad Sci U S A. 2016 Oct 17. [Epub ahead of print]
Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation.
Zhang B, Tieman DM, Jiao C, Xu Y, Kunsong Chen, Fe Z, Giovannoni JJ, Klee HJ.
Horticultural Sciences, Plant Innovation Center, Genetics Institute, University of Florida, Gainesville, FL 32611; Laboratory of Fruit Quality Biology/Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Zhejiang University, Hangzhou 310058, People's Republic of China; Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, NY 14853; US Department of Agriculture-Agricultural Research Service Robert W. Holley Center for Agriculture and Health, Cornell University, Ithaca, NY 14853.
Significance
Cold storage is widely used to extend shelf-life of agriculture products. For tomato, this handling results in reduced flavor quality. Our work provides major insights into the effects of chilling on consumer liking, the flavor metabolome and transcriptome, as well as DNA methylation status. Transcripts for some key volatile synthesis enzymes and the most important ripening-associated transcription factors are greatly reduced in response to chilling. These reductions are accompanied by major changes in the methylation status of promoter regions. Transient increases in DNA methylation occur during chilling. Our analysis provides insight into the molecular mechanisms of tomato fruit flavor loss caused by chilling.
Abstract
Commercial tomatoes are widely perceived by consumers as lacking flavor. A major part of that problem is a postharvest handling system that chills fruit. Low-temperature storage is widely used to slow ripening and reduce decay. However, chilling results in loss of flavor. Flavor-associated volatiles are sensitive to temperatures below 12℃, and their loss greatly reduces flavor quality. Here, we provide a comprehensive view of the effects of chilling on flavor and volatiles associated with consumer liking. Reduced levels of specific volatiles are associated with significant reductions in transcripts encoding key volatile synthesis enzymes. Although expression of some genes critical to volatile synthesis recovers after a return to 20℃, some genes do not. RNAs encoding transcription factors essential for ripening, including RIPENING INHIBITOR (RIN), NONRIPENING, and COLORLESS NONRIPENING are reduced in response to chilling and may be responsible for reduced transcript levels in many downstream genes during chilling. Those reductions are accompanied by major changes in the methylation status of promoters, including RIN. Methylation changes are transient and may contribute to the fidelity of gene expression required to provide maximal beneficial environmental response with minimal tangential influence on broader fruit developmental biology.
DOI: 10.1073/pnas.1613910113