polyphenols

Recently, I was on the phone with a mentor and we were discussing hedgerows (my new pet project, aside from brewing all sorts of alcohol). With some of the species I mentioned, I was told that livestock would eat them down to nothing and render the hedgerow useless. After having a few tree species rejected, I frustratingly asked: “What if I planted my hedgerows with invasives like multi-flora rose, then?!”

Without any hesitation, my mentor said: “Invasives like multi-flora rose are very delicious to many animals, like my goats. You might be suggesting invasive plants for your hedgerow because they are vigorous and seem to outcompete everything else, but try to think about vigor from another perspective. If plants with high vigor are also the most sought after by animals, don’t you think that vigor might be an evolutionary trait to survive browse?”

This is the first time I’ve heard this perspective on invasives and I’ve really enjoyed thinking about it. After some minimal research, I found out that the subject is still debated today by ecologists as the “plant vigor hypothesis.” Generally speaking, vigorous plants have higher nutrient densities than non-vigorous plants, so herbivores are more prone to eat them. However! If the very vigorous cultivars are able to put on a bunch of girth, many herbivores aren’t able to eat the whole thing because of their jaw size.

This, of course, has got me thinking about apples. Here’s why.

In many essays on this blog, I’ve talked about how I consider many cider and heirloom cultivars to be very vigorous as compared to most of the grocery store cultivars. Vigorous cultivars are harder to prune, occupy more space (so less trees per acre), have issues with vegetative vs fruit bud proportions, etc. In general, they are harder to grow. After reading more about this “plant vigor hypothesis,” I wonder if there is a connection between vigor and nutrient density in apples cultivars?

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From an evolutionary standpoint, a correlation between vigor and nutrient density makes sense to me. Many wild crab apples in the US have much higher tannins (aka polyphenols, which =nutrition density) than cultivated varieties. This is from the many lifetimes spent co-evolving with insects and herbivores who are trying to eat them. From observing crabapples in the “wild” and planted in landscapes, it seems as if many trees have low vigor and perhaps this is because they have evolved to have an unpalatable deterrence for animals and humans alike?

In hard cider, many of the wild crabs are too much for our palates to handle and though very nutritious, they will cause a harsh and likely negative consumer experience. So what have we done? Over time, cider drinkers/makers/apple growers have selected cultivars to grow which are palatable to the consumer, but also contain enough tannins (or polyphenols, or natural defense) to give the cider some substance. Could it be that in selecting not-so-astringent apple cultivars for eating/drinking, we’re unknowingly selecting for more tree vigor? If the apple cultivar hasn’t evolved enough to deter herbivores through astringent taste, then do genetics dictate that it must rely on vigor to survive?

These sorts of questions make me excited and I’ll keep learning about these processes in order to try and uncover different management ideas that don’t involve regulating vigor through the use of dwarfing rootstocks, black magic hormonal potions like Apogee (which converts vegetative buds into fruiting buds), and planting in light soils. All of those management aspects, I suspect, are making the vigorous cultivars less vigorous/more fibrous/less nutrient dense.

Thoughts to be continued, but in the meantime here are a few off the top of my head:

Thought 1: Pruning extremely vigorous varieties like an herbivore in order to get faster fruit set?

Thought 2: Continuing to fruit explore to find mixes of wild x cultivated which hit high nutrient densities, palatability, and lower vigor. (I’m writing a fruit exploring book about how to do this at the moment)

Thought 3: Making crabapples a significant part of my home breeding program.

It seems like it has rained every day for the past month in the Champlain Valley of New York and Vermont. Combined with 70-80 degree temperatures, the fungal population couldn’t be happier. It’s like one continual fungal feast over here, and I couldn’t be more psyched. Why? Because I’m absolutely infatuated with the idea of stress in an orchard.

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In A Radical Orchardist: Part One (which I encourage the reader to read before pursuing this essay), I re-introduced my thoughts about how apple scab, a fungal disease, increases the brix (sugar content) of the apple, which translates into a higher alcohol content once fermented. For hard cider purposes, I thought, perhaps we shouldn’t be spraying-late season fungicides for cosmetic fungal diseases like apple scab, since lingering fungicide residue has been known to kill the ferment (the yeasts) in the wine and cider realms. I also re-introduced the idea of managing apple scab as a value-added disease for cider apples, a thought that is about as radical as it gets these days in the apple world. A thought that I’m still excited to explore and understand in order to embrace it or dismiss it.

This year, I’ve been actively looking for scientific research on the effects scab has on apples, from a nutritional standpoint. I want to know how the apple reacts to scab; What does that fight look like? Does a stressing agent like apple scab bring about super fruits? This research is slow, mostly due to the fact that I don’t have access to any scientific journals, but it’s progressing and has me optimistic. The following is a report on my findings and thoughts.

Stress: The New Bittersweet?

My journey started when I found a paper about the effects of apple scab on the peel of an apple. The article, which can be found here and simply broken down here, stated that a peel covered with scab lesions is higher in polyphenols than one not covered in scab. What’s the big deal? Quite a bit, actually. This is a big deal.

Phenols, such as chlorogenic acid (as seen in the top graph), are classified as antioxidants, meaning that they tend to prevent or neutralize the damaging effects of free radicals in the body. Free radicals are chemicals that have the potential to cause damage to cells and tissues in the body. Many of the phenols mentioned in the paper above are related to resveratrol (the polyphenol found in red wine which got a lot of news a while back for making wine drinking a life-saving activity). When researched in the skin of non-scabby red apples (aka: what you see in a grocery store), they were found to contain powerful antioxidant capacities, along with anti-cancer, anti-inflammatory, and cardio-protective properties.

Now, take those phenolic values from the skin of the non-scabby red apple and multiply them by at least 3+ times. That new value is one coming from an apple with scab infection. To further push this point, this article suggests :

The way in which orchards are managed can influence the amount of phenolics, as shown by Veberic et al. (2005), who reported that organically grown apples had somewhat higher amounts of phenolics as compared with traditionally grown apples. These authors concluded that this is probably because organically grown apples face more stressing conditions, for synthetic fertilizers and pesticides are not used.

Folks, this is superfood status and at the very least, people should try to source ugly organic apples and eat the peels. Research says that doing so might save your life someday.

Now, to project these findings onto cider…

What makes a cider apple a cider apple? The quick universal answer most people know is that it’s in the tannin. Tannin is a collection of phenols such as chlorogenic acid, phloridzin, epicatechin and the procyanidins (source). Only the procyanidins are considered “true tannins” because they have the ability to tan things like animal hides and give the drying sensation we recognize as astringency (aka: the sensation you get when you stick an acorn in your mouth). For the most part, bittersweet apples have the most tannins, or phenolics, and dessert apples have the least.

https-::books.google.com:books?id=jZvqBwAAQBAJ&lpg=PA622&dq=plant%20polyphenols&pg=PA829#v=onepage&q=apple&f=false

A bittersweet apple, taken from this Serious Eats article, is described below:

If there is one style of apple prized above all others by American cider makers, it’s the bittersweet apple. Affectionately referred to as a “spitter,” these apples are low in acid, high in tannin, and impart the classic flavor of finer French and English ciders. At first bite, most would consider bittersweet fruit inedible. But what is ill suited for the fruit bowl is ideal for the cider press.

For the most part, America’s high acid, high sugar apple crop provides all the fuel for fermentation and puckering power necessary for a great cider. But what that fruit lacks is tannin—the molecules that impart astringency and provide a cider’s texture—and bittersweet apples fill this void.

https-::books.google.com:books?id=lATkBwAAQBAJ&lpg=PA106&ots=76WFijiMHz&dq=%22tetrameric%20procyanidin%22%20apple&pg=PA105#v=onepage&q=%22tetrameric%20procyanidin%22&f=false(image)

Ignore the yellow highlighting, and the column about gelatin

I hope your wheels are turning like mine were, but in case not, let me break it all down for you.

Cider apple varieties are known for their higher levels of phenolics, because those phenolics (aka tannin) distinguish them from dessert fruit. Those phenolics involved in making a cider apple a cider apple are also the same phenolics that increase in concentration when the apple is stressed with apple scab. If you refer to Figure 1 above, you’ll also see that in addition to high levels of polyphenols, a bittersweet apple is one with a higher brix. Let me remind this audience that this whole Radical Orchardist series started with the deletion of an article I wrote about how apple scab increases the brix in apples.

I’m no chemist, but it seems to me that stress has the potential to send some dessert varieties into the realm of a bittersweet. Now, how about stressing a cider apple? Is the increase in phenols due to stress worth it to the cider maker and the consumer? This study says that phenols in hard cider are absorbed, metabolized, and excreted by humans. Meaning, we’re getting the nutrients.

phenolic content of apple leaves, healthy vs infected with scab. http://www.sipav.org/main/jpp/volumes/0108/010807.pdf

It makes sense to me. When stress occurs, the apple’s response is to pump the site of infection/attack full of phenolics (see graph to the right) . Look no further than your forest’s edge to find wild, highly evolved, inedible tannic crabapples that serve my point. The crabapples have evolved to contain these phenolics without provocation. The lesser-evolved dessert varieties, however, may need to be provoked through varying degrees of stress in order to produce a more nutrient-dense product, or one that more resembles a bittersweet cider apple.

What does this mean for management? Back in the first A Radical Orchardist essay, I irritated a few folks with the question:

What is a cider apple? Sure, you can have all the old French and English varieties like Dabinett, Frequin Rouge, Tremletts Bitter, Norfolk Beefing, etc, but if they are managed the same as dessert apples…are they really cider apples? I don’t think so.

And I still don’t think so. I believe that growing cider apples requires a completely different mindset than growing dessert fruit in order to make high quality, nutrient-dense, healthy organic hard cider. To me, a part of being a cider orchardist involves learning how to balance stress within the orchard through organic means. What do I need to give the tree in order to replenish the expense of fighting off an infection? What is the tipping point of too much stress? I whole-heartedly believe that these, plus many more, are the questions we should be asking. Imagine a world where the value of an apple comes not from its looks, but from its nutrient content. That’s what I’m aiming for with stress, and I believe there is value in that.

Please, those of you who are researchers…prove me wrong. I have admitted to the fact that I’m no chemist, and without academic ties, its completely reasonable that my understanding is flawed from the free book snippets and articles I find online. Send me a response with accessible PDFs, I’ll make sure to post it in a follow-up essay with reasons why I agree or disagree. Hopefully some great questions will come out of it and some university or private foundation somewhere will want to investigate.

In the meantime, the take home message is to #eatuglyapples and #drinkuglyapples. Embrace the scab, avoid the rot and challenge the status quo.

Postscript: Earlier in this essay, I included the following phenolics to define tannin. They were chlorogenic acid, phloridzin, epicatechin and the procyanidins. From this article, it states that apples infected with scab had:

6.5 times more phloridzin than a healthy apple.
chlorogenic acid can be found in the first graph of this essay
epicatechin levels are in the following graph:
procyanidans are flavanols, which are widely cited by research papers to be the reason why some apple varieties are resistant to scab.