丑陋的外表下，是一颗富含营养的心
当果园老板伊丽莎·格林曼走过一片苹果树，看到满是凹痕有瑕疵的苹果（这些疤痕是由于对抗真菌、高温和害虫而造成的）时，她感觉到的却是一丝喜悦。她非常迷恋于果园中的这些苹果的抗压表现。她在弗吉尼亚州汉密尔顿嫁接和种植无杀虫剂的苹果，她称：这些外表丑陋的苹果，事实上可能更甜。在一项非正式的实验中，格林曼测试了有疤的和无疤的帕尔马苹果，这是一种弗吉尼亚州本地的含糖量很高的品种，格林曼发现，同一棵树上，有疤的苹果含糖量比无疤的苹果高出2%至5%。更高的含糖量意味着发酵之后酒精含量更高，可以生成更美味的苹果酒。但是，她对这些丑陋苹果的喜爱却有其他原因：它们也许营养价值更高，并且抗氧化剂含量更高。她相信压力可以帮助它们成为一种超级苹果。
歪瓜裂枣般的水果和蔬菜在今天成为了宠儿，已是越来越多商家的抢手货，而不再是被扔到垃圾填埋场。非常遗憾的是，人们每年扔掉的食物能够填满44座摩天大楼了。为什么要浪费掉这么完美的食物？从2016年4月份开始，加利福尼亚的一些全食超市开始售卖外观不怎么样但是营养丰富的农产品。但是，这些水果在努力生存的过程中，真的会产生意想不到的丰富营养吗？
人们推测，有机水果和蔬菜的情况正是如此。2014年《英国营养杂志》发表一项对343项研究【1】进行的系统回顾与荟萃分析结发现，相比于传统农产品，有机农产品的杀虫剂残留较低，而且抗氧化剂含量高出20%到40%。这些抗氧化剂包括类黄酮、酚酸、花青素和类胡萝卜素，它们都是在植物表面对害虫压力时的防卫机制产生的。作者认为，有机作物面临的压力更多，因为它们使用的杀虫剂更少。
2006年《欧洲临床营养杂志》发表另一项对传统苹果和有机苹果的研究【2】发现，有机苹果中含有更高剂量的酚类抗氧化剂和果酸。作者指出：定期吃水果可以帮助预防疾病和代谢紊乱，但是建议食用本地有机种植的品种，而不是综合栽培技术培育的品种。
丑陋水果表面的伤痕累累代表着它们成功地战胜了昆虫和感染。格林曼的理想是真正野生的苹果，一种只依靠自己自然防御机制成熟的苹果，外观的缺陷可以佐证这一点。尽管不是所有的害虫和疾病都是温和的，很多常见的苹果感染是由无害的真菌造成的。这些真菌会导致一些黑色的小疙瘩，但是这并不影响口感，也不会影响人类健康。这些小疙瘩是植物对抗自然环境中压力的结果，而这依赖于抗氧化剂。格林曼认为这些丑陋的疤痕可能代表着更高的营养价值。
格林曼或许是对的。2010年《园艺科学与生物技术杂志》发表的一项研究表明【3】，表面有疤痕的苹果含有更多抗氧化酚类化合物——苯丙素。2011年《植物生物学》发表的另一项研究【4】表明，叶子上有疤痕的苹果酚类化合物含量高出10%至20%。1976年《植物生理病理学》发表的类似研究【5】发现，叶子被真菌感染或者承受紫外线照射压力的葡萄中白藜芦醇的含量更高。2011年《生物医学中心·植物生物学》发表的日本紫菀科植物研究发现【6】，普通真菌感染也会促进这种植物中白藜芦醇的含量升高，白藜芦醇是一种抗氧化剂，具有潜在的心脏保护作用。所有的这些抗氧化剂不但会保护植物，也可能会保护食用它们的人类。
美国克莱门森大学的环境学家布莱恩·沃德称：这并不意味着人们应该抛弃传统农业，影响抗氧化剂含量的因素很多，最重要的因素是植物本身，这是基因问题，之后是土壤及其矿物含量，以及是使用的传统肥料还是有机肥料。但是，当植物面临昆虫或疾病压力时产生的这些数据确实有趣，它们生成了对人体有益的代谢物。
格林曼的观点引起了华盛顿州立大学微生物学家马丁·帕尔的兴趣。他称：人体自身的潜在保护机制可以被水果和蔬菜中的化合物激活。事实上，2015年他发表于《生理学报》的研究论文【7】提到，这些抗氧化剂或许能作为温和的压力源，启动人体的修复机制。它们激活人体细胞中的核转录因子——红细胞系相关因子2（Nrf2），它会激发超过500种基因的活动，大部分的活动都具有细胞保护功能。有证据表明，在压力下增加的其他植物化合物也可能对人体健康有好处，但是这些益处的证据还不够充足。他认为，人们与这些能产生对人体有益化合物的植物共同进化了数万年，已知的长寿饮食方法，比如传统的地中海饮食和冲绳烹调法都富含这些化合物和抗氧化剂。
因此，有机食品的园丁应该感到高兴：这种表面不完美的作物比你想象得要完美。下次就别再犹豫要不要吃表面有疤痕的水果了，记得它的体内隐藏了丰富的营养。
National Public Radio. 2016 Apr 26.
Beneath An Ugly Outside, Marred Fruit May Pack More Nutrition.
Jill Neimark.
Atlanta-based writer whose work has been featured in Discover, Scientific American, Science, Nautilus, Aeon, Psychology Today and The New York Times.
When orchardist Eliza Greenman walks through a field of apple trees and gazes upon a pocked array of blemished and buckled fruits -- scarred from fighting fungus, heat and pests -- she feels a little thrill of joy. "I'm absolutely infatuated with the idea of stress in an orchard," says Greenman, who custom grafts and grows pesticide-free hard cider apples in Hamilton, Va. These forlorn, scabbed apples, says Greenman, may actually be sweeter.
In an unofficial experiment, Greenman tested scabbed and unscabbed Parma apples, a high-sugar variety native to southwestern Virginia, and found the scarred apples had a 2 to 5 percent higher sugar content than unmarred apples from the same tree. More sugar means a higher alcohol content once fermented, producing a tastier hard cider.
But she loves these ugly apples for another reason: They may be more nutritious and have a higher antioxidant content. Says Greenman: "I believe stress can help create a super fruit."
Ugly fruits and vegetables are today's pocked and scaly, dimpled, misshapen darlings -- and there is a growing movement to sell such produce, not dump it into municipal landfills. As The Salt has reported, we toss out enough food to fill 44 skyscrapers each year. Why waste perfectly good food? This April a handful of Whole Foods stores in California will sell the cosmetically marred but nutritious produce for the first time.
But does some blemished produce pack an unexpected nutritional punch -- courtesy of its own battles to survive?
We already suspect this is the case with organic fruits and vegetables. A 2014 review [1] of 343 studies found that organic produce had lower pesticide residue and a 20 to 40 percent higher antioxidant content than conventional produce. Those antioxidants include compounds such as flavonoids, phenolic acids, anthocyanins and carotenoids, all produced by plants as defense mechanisms when they are stressed by pests. The study authors suggested that organic crops may be subject to more stress because they may receive fewer pesticides, in lower doses, and with less potent killing effects.
Another study [2] of both conventional and organic apple varieties found higher antioxidant phenols and fruit acids in organic apples. The study authors noted, "The regular consumption of fruit acids is helpful in preventing illness and metabolic disorders. We recommend the consumption of regional organically grown varieties rather than of cultivars from integrated cultivation."
Ugly fruits actually bear the visible scars of their successful battles -- dimpled or scarred where they fought off a biting or gnawing insect or surface infection. Greenman's ideal is a truly wild apple, one left to its own defenses in nature -- with the cosmetic imperfections to prove it. Though not all pests and diseases are benign, she notes, a few common apple infestations are the result of harmless fungi that result in sooty "blotch" (dark patches) and fly speck (black dots), but do not harm taste or texture nor infect humans. These blotches are a result of the plant fighting off environmental insults -- relying on its antioxidant defenses to do so. Greenman suspects those unsightly scars may reflect higher nutrition.
She may be right. One study [3] showed that an apple covered in scab has more healthy, antioxidant phenolic compounds, called phenylpropanoids, than a scab-free apple peel. Another study [4] showed that apple leaves infected with scab have 10 to 20 percent more phenolic compounds. Similar research [5] has found high levels of resveratrol in grape leaves infected with fungi or simply exposed to the stress of ultraviolet light. A study [6] of Japanese knotweed, a plant with a long tradition of use in Chinese and Japanese herbal medicine, found that infection with common fungi boosted its resveratrol content as well. Resveratrol is an antioxidant that's been well-studied for its potential cardio-protective action. All these antioxidants protect both plants, and probably the humans who eat them.
This does not mean that we should turn away from conventional agriculture, or make hard and fast assumptions about crops, says environmental biologist Brian Ward, of Clemson University. "There are so many factors contributing to antioxidant content," says Ward, who oversees research in both conventional and organic agriculture. "The most important factor is the plant itself -- and the variety. That's genetic. Then there is the soil, its mineral content, and whether conventional or organic fertilizer is used. But yes, there is some interesting data that when plants are stressed by insects or disease, they produce metabolites that are good for us."
Greenman's insight intrigues microbiologist Martin L. Pall, professor emeritus at Washington State University. Pall says that our own innate, potent protective mechanisms can be activated by compounds in fruits and vegetables. In fact, he suggests in a recent research paper [7], those antioxidants may serve as mild stressors that kick our repair mechanisms into high gear. They activate a molecule in our cells known as Nrf2, which itself can trigger the activity of over 500 genes, most of which have cell-protective functions.
"This is certainly true of compounds like resveratrol," he says. "That part of the story is pretty clear." He says there's intriguing evidence that other plant compounds that increase under stress may be good for our health, too, but those benefits are not as well-documented.
Pall contends that we have co-evolved for eons with plants whose compounds benefit us. He points out that known longevity diets -- such as the traditional Mediterranean and Okinawan cuisine -- are rich in exactly these compounds and antioxidants.
So, backyard organic gardeners, rejoice: Your imperfect produce may be more perfect than you thought. Next time you hesitate over a flawed fruit, remember that it may be a hardy survivor bearing hidden nutritive gifts.
参考文献
Barański M, Srednicka-Tober D, Volakakis N, et al. Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses. Br J Nutr. 2014;112(5):794-811. DOI: 10.1017/S0007114514001366 http://journals.cambridge.org/abstract_S0007114514001366
Hecke K, Herbinger K, Veberic R, et al. Sugar-, acid- and phenol contents in apple cultivars from organic and integrated fruit cultivation. Eur J Clin Nutr. 2006;60(9):1136-1140. DOI: 10.1038/sj.ejcn.1602430 http://www.nature.com/ejcn/journal/v60/n9/full/1602430a.html
Slatnar A, Mikulic-Petkovsek M, Halbwirth H, et al. Response of the phenylpropanoid pathway to Venturia inaequalis infection in maturing fruit of 'Braeburn' apple. J Hortic Sci Biotech. 2010;85(6):465-472. DOI: 10.1080/14620316.2010.11512699
Mikulic-Petkovsek M, Slatnar A, Stampar F, et al. Phenolic compounds in apple leaves after infection with apple scab. Biol Plant. 2011;55(4):725. DOI: 10.1007/s10535-011-0176-6
Langcake P, Pryce RJ. The production of resveratrol by vitus vinifera and other members of the vitaceae as a response to infection or injury. Physiol Plant Pathol. 1976;9:77-86. DOI: 10.1016/0048-4059(76)90077-1
Kovárová M, Frantík T, Koblihová H, et al. Effect of clone selection, nitrogen supply, leaf damage and mycorrhizal fungi on stilbene and emodin production in knotweed. BMC Plant Biol. 2011;11:98. DOI: 10.1186/1471-2229-11-98
Pall ML, Levine S. Nrf2, a master regulator of detoxification and also antioxidant, anti-inflammatory and other cytoprotective mechanisms, is raised by health promoting factors. Sheng Li Xue Bao. 2015;67(1):1-18. DOI: 10.13294/j.aps.2015.0001