The Flavours of Plants

[Applause] w wow he hey he hey yikes that was that was great um h i I can't tell you how it feels to be here Renee colleagues uh of Rene's this has been an amazing event and the um and of course this is just part of it I I have never in my life thought that I would have the chance to smell 35 varieties of hay but that's what I did yesterday and I'm really glad I did if you get a chance as you're leaving check out the hay it's amazing um and uh I'm going to be taking you from the sublime and the poetic what was just on the table here uh back to school sorry uh to chemistry class uh my justification for that is that uh what underlies that poetry is chemistry uh plants are the sort of chemical Masters of the Universe uh they're the only creatures there are that can start with Rock and um air and sunlight and turn those materials into what was just on this table it's they're amazing creatures and what I'd like to do today is um tell you a little bit about one small part of their lives we've been hearing about all different aspects of their lives over the last couple of days I'm going to focus very much on Flavor which is the part of their lives that gives us the most pleasure uh and talk a little bit about what science can tell us about the nature of their flavor why they have these flavors why should we be so lucky as to have these amazing things to uh to n nourish ourselves with um and then I I hope along the way to uh be able to provide the the cooks in this room with a few useful pieces of information so somewhere around here here uh so don't worry I'm going to be flashing molecules on the screen there's no test at the end it's just to remind you that this is what it's all about this is what it comes down to when we taste something when we smell something when we experience the flavor these are what we're experiencing molecules and I've got just four examples water which has no taste or smell right next to it something that looks very similar same structure but one atom has been changed the the oxygen has been changed to sulfur and now you've got something that smells like eggs rotten eggs if it's too strong nice eggs if it's uh just a little hint uh acetic acid the smell of vinegar and on the right there a molecule of sucrose which is sweet sugar this is what uh this is the way we experience plants and Foods in general it's um the chemical senses uh let's see there we go so uh just a few words about uh kind of different categories of our um of our nourishment fruits are delicious so what's the recipe for the deliciousness of a fruit uh molecules and in the case of fruits it's dozens to hundreds of molecules so this is the recipe for the deliciousness of strawberry in fact this is only a partial list of the uh of the flavor compounds that are found in the strawberries fruits are amazingly complicated and I think in fact is my feeling is that fruits are sort of the the model for what cooks do when they're trying to make something delicious uh in in the background in the recesses of our brains are the example of these natural materials that are that that kind of excite so many of our receptors that uh we don't need anything else in our mouths and I I think cooking is kind of an an attempt to to create by human Ingenuity what plants have been doing for millions of years herbs and spices are a different story so where fruits are uh combinations of hundreds of different Aroma molecules and taste molecules herbs and spices tend to be characterized each one by one or a small number of taste or smell molecules and I've just shown examples here of these very common herbs and spices and the molecules that Define them um and it's it's a as I say completely different situation very simple chemistry when it comes to herbs and spices so why is that why do herbs and spices have the flavors they do is it for the same reason to attract animals to do some kind of delivery service um the answer is no and I discovered this for myself the first time when I discovered that uh herbs and spices can be characterized by essentially one molecule uh I went to the chemical uh supply houses and I ordered uh essence of th essence of oregano and there they are thol carvacrol the the flavor impact compounds of those two herbs what I wasn't expecting when I got them was the the message printed on that same label which is that they're toxic if you see uh appear harmful by inhalation in contact with skin and if swallowed which is what we're usually doing with time swallowing it uh oregano uh where's the button here it's not not there we go um corrosive causes Burns harmful by inhalation and contact with skin and have swallowed so what's going on there why are these things toxic and why do we go ahead and use them well it it has to do with uh the lives of these plants and so if you take for example Mediterranean herbs like time and and rosemary and oregano and so on uh what you find is that they evolve in a part of the world where they're pretty exposed this is typical Limestone of uh of the Mediterranean uh area and plants that manage to grow in it and there aren't that many of them are obvious to any goat that happens to be walking by uh or any slug that happens to be Crawling by in fact slugs have been a very important force in the evolution of our herbs and spices so every time you enjoy something like like thyme or oregano or Rosemary you should be thanking the Slugs for forcing them to to make those chemicals so what what happens is that the plants who live in that kind of environment have to protect themselves otherwise they're just going to be eaten and some of them protect themselves with spines so there's a plant underneath there and it's grown up above itself this network of thorns that's impossible to penetrate without getting badly scratched here's a a rosemary plant that's growing out of a hole in the Limestone that you can't even see because it's plugged it so completely there's you know probably a millimeter of soil in there and it's somehow still managing to grow but it's completely exposed and the way plants that are that grow in environments like this where they're really threatened uh by being consumed by hungry animals is that they use chemistry to protect themselves so um these plants make chemical weapons they're full of them that's what makes them taste the way they taste why don't we get sick off of them why aren't they toxic to us well if you take uh a rosemary branch and put it in your mouth and chew it like a sheep it'll be toxic to you right you your your mouth will burn and if you manage to swallow it it's probably going to irritate you all the way down uh but we don't do that instead we use these materials as flavorings we make our Foods more interesting by adding complexity from these these compounds and that's why we're not so much bothered by them it also seems that for many of these compounds these plant defenses end up uh kind of goosing up our chemical defenses um now we're not trying to poison other creatures but we do have to deal with molecules like thol all the time in our diet and our bodies have developed ways of detoxifying them and getting rid of them and the more of these we have up to a certain point the better because these induce the enzymes in us that are necessary to to do a good job of that detoxification so up to a certain point it it can be actually good to get these things and again that probably reflects our Evolution along with them as uh as hunter gatherers so fruits herbs and spices um then there are the other kinds of plants that we eat uh vegetables in particular uh and the same thing turns out to be true for vegetables uh it's kind of obvious with the in the case of the onion family onion and garlic and so on it's kind of obvious in the case of the Cabbage family especially things like brussel sprouts which can be very bitter you can tell that the plant is making an effort to discourage you to eat it and part of of what's happened is in domestication is to lower the levels of those compounds to make them more palatable which may not be a good thing for our health even if it does make them easier to eat uh but it's also true of lots of other plants in our environment and plants that we now beginning to use more and more as people look around to see what's edible and what what have we been ignoring so evergreen trees for example the pinin of pine the spru of spruce those come from uh tpen that are related to the tpen in um in herbs that make um that typical evergreen forest smell those are defensive compounds we find them pleasant but the bugs that try to eat the plants don't uh clovers in lucern uh all around this site there's clover growing and in that uh hay smelling there was one bin that was nothing but lucern I think and those have a very uh special Aroma uh the aroma that comes from kumarin which is Al also found in the Tona bean and which is closely related uh chemically to vanilla so if you found as the sun kind of comes in and out it hits a a patch of vegetation out here and you end up with that kind of Sweet Sweet Clover smell that's what it's coming from it's cumarin cumarin is a defensive compound that keeps um uh bacteria and insects in and around the soil from eating those plants and it turns out that even uh the most ordinary green leafy vegetables uh their Aromas come from uh defensive compounds so it turns out that green leaves have um chloroplasts that's what makes them green those little green dots in the cells up there um and within the chloroplasts are uh molecules related to oils we don't think of of leaves as being high in fat and oil but in fact they do have a significant amount and those fats themselves don't have any Aroma those molecules are too big uh this uh molecule down here is uh the kind of fat that you find in the chloroplasts and those molecules are just too big to have any kind of Aroma or taste but if those molecules are broken down into pieces those pieces are small enough that they can give us uh an aroma sensation and that's exactly what happens whenever those leaves are broken the uh cells are damaged enzymes mix up with the chloroplasts the structural molecules are broken down into smaller pieces and that's where the smell of grass comes from when you cut the grass if you if you mow the The Greenery out here and you get that very typical green smell that's coming from from hexanal and its relatives these these breakdown products and it turns out that different families of plants have different enzymes that give you different breakdown products when the tissue is damaged so the Cucumber Aroma of cucumbers comes from Little chains that are nine carbons long instead of six in the case of hexanal um and of course uh if you've ever tasted borage uh an herb that makes these beautiful blue flowers those flowers smell exact and taste exactly like cucumber and it's because that family also has this this enzyme that gives you a uh nine carbon uh fragment instead of a six and then mushrooms it turns out the mushroomy smell of mushrooms are uh all coming from eight carbon chains of exactly the same kind they don't have chloroplasts but they have other structures in them that uh that generate these compounds so the characteristic Aromas of many of our vegetables come from these these uh breakdown products and the breakdown products are part of the plant's defensive system uh otherwise why would it be breaking down those molecules that plants generally don't do things for no good reason so if you take a plate of uh of sprouts and you spray them with hexanal which is what those Sprouts would make if they began to be eaten by uh insects or if they began to be attacked by molds and then you let them sit around for a few days if you if you've done the spraying they don't get mold at all but if you don't do the spraying they do so if you kind of pre- inoculate them with hexanal they're they're much longer lasting and in fact these breakdown products are now being used commercially as uh preservatives but natural preservatives because that's what the plant would be doing anyway uh and this is kind of a complicated diagram but but speaks to uh much of what Stephano is talking about this morning that the moment um an insect begins to bite into a leaf that damage takes place hexanal is produced and that has an immediate reaction in about a minute or less but in addition to that uh those same hexanol molecules diffuse into the rest of the leaf and act is a signal to the rest of the leaf to start making more of its defensive compounds before the caterpillar gets there and Beyond even that because the molecules are volatile some of them kind of float off of the leaf into the air where they can reach neighboring leaves on the same plant or neighboring plants and give the same message to those plants so plants do communicate with each other and they let each other know and kind of Prime each other to defend themselves against um uh predators that have just arrived on the scene now in the case of green herbs like mint um you've got both things going on you've got the essential oils that are the sort of immediate and specialized version of the defense but then if you break into the leaf you're also going to generate hex and those elements of the defense um you don't always want to do that and this is a wonderful um diagram from a a paper a few years ago studying the effects of different ways of handling an herb in order to see what kinds of uh flavor profiles you can get from exactly the same Leaf depending on how you treat it the leaf is Japanese Pepper or aano which has several different quality to it but the ones that they were looking at are not the the Buzzy numbing kind of sensation but uh the different Aromas that you can get from it and there are two different ways that you can handle Sancho in Japan one is to grind it up in a mortar or blend it or something like that but the other is to slap it you put the leaf in your hand and you spank it and then you put it into the dish uh and bartenders these days do that a lot with mint uh which is why I have mint here to to illustrate what it is you're doing if you're working with something like mint and it has these external whoops um external hairs uh and then you damage the leaf by say putting as You' make an ordinary cocktail put the leaf in the bottom of the the glass and then muddle it break it up then you're going to get the mint Aromas but you're also going to get the green Aromas from the destruction of the um of the chloroplasts uh sometimes you don't want that sometimes you want just the mint flavor and not the green flavor partly because the green flavor quickly turns into other things uh it doesn't stay fresh and green forever it begins to the the hexanal molecules react with other things in the plant and you end up with off flavors eventually so if you want just the mint Aroma what you can do is handle those mint leaves so that you only break the glands on the outside you you can take two leaves for example because most of the glands are on the bottoms of the leaves you can take two leaves put them bottom to bottom and just rub them back and forth very lightly you don't break the leaves themselves but you do break the glands then you drop them drop them in whatever you're making and you're only going to get the mint flavor and not the the green flavor uh and what the study of the Japanese pepper showed was that slapping does the same kind of thing if you uh look at the the three different lines here uh one represents what you get if the leaves are intact the dash line one if the leaves have been slapped the uh solid line and if they're crushed the dotted line so here's the intact leaves it's a little bit citrusy it's uh fresh and green to some extent Pleasant kind of generic uh flavor uh and a little bit Woody and then if you slap them you actually get much more citrus more floral about the same fresh green U more pleasant because the other Aromas have gone up uh so you've you've really accentuated the the citrusy quality but then if you crush them you end up with a huge boost in what they call undesirable grassy which I think is just uh way too much of the of the fresh green and fresh beginning to turn into stale so depending on how you handle the leaves you can get very different uh qualities out of them okay um shifting now from herbs and spices and what happens when you slap them to uh uh things that have to do more with the way plants are grown both in agriculture and in the wild and why their qualities are different so it turns out that uh I mentioned the the herbs that can have very different uh uh profiles growing in in close but different places because there may be more slugs over here than there are over there or on the The Mountaintop and the the valley it turns out that a single plant can undergo that kind of change when it's growing right next to another one so in a study of the differences between conventionally and organically raised bok choy they found that uh an ordinary in conventional agriculture because you're Protec ing the plants from Attack by insects uh they have a certain level of uh these defensive compounds of various kinds if you let the insects in uh of course they the leaves look terrible but in fact uh at least judging by flavor and by uh defensive compounds they're actually much richer than they would have been in the conventional agriculture moreover what they found was that if if in organic agriculture the plants are not attacked by insects the plants that are not attacked by insects more resemble the conventionally grown plants than they do the attacked organically grown plants in other words stress by insects is uh in a way a good thing because it induces more defensive compounds more flavor compounds more antioxidants and things like that in the the vegetable so uh as I say that may look terrible and it may look unappetizing and you probably wouldn't want to put a whole Leaf of that in a garuu but uh it would be a shame to throw it out because there's a lot of good stuff in there um a slightly better piece of news about uh trying to get the best out of uh produce raised in um in agriculture is that you can in fact fool plants into thinking that they're being attacked by insects when they're not so you can get the same kind of effect as I just showed you in that previous slide but without the leaf being eaten and it turns out that um fungi so disease-causing organisms in plants and insects which also attack plants their their structures are built out of a material called kiten uh which is not found in any other animals and it's not found in plants themselves it's also found in crustation uh uh sea creatures because Crustaceans and uh and land insects are very closely related so all these things contain this substance in them called kiten for the plant the presence of kiten is a sign that it's about to be attacked by either uh fungus or an insect and so the moment it detects any sign that there's kiten in the vicinity it uses that as a signal to start making defensive compounds so it turns out that what you can do is take any of those materials but it's easiest to use uh crustations because there are a lot more of them and their uh their exoskeletons are are more substantial grind up those exo exoskeletons treat them so that some of the kiten is soluble and you get something called kyosan spray kyosan on the soil or on the developing seed or on the growing plant and you end up inducing those same defenses the enrichment of flavor the enrichment of antioxidants without the plant actually being attacked by insects which is a pretty cool effect it's only been known for a few years it really hasn't even begun to be exploited uh this is is not meant to make you oops not meant to make you think that uh that these plants which have been treated are somehow better than these because they're they actually don't look that good any of them they've all been grown in a laboratory just to demonstrate that growth is enhanced in the presence of these um elicitors of defenses uh and this is a a practical way to make more flavor in in vegetables and herbs uh and then it also turns out that physical stress growing plants in um uh restricted water conditions or in high salt conditions even though it ends up making the plants dwarfed because they don't grow as well the plant that does grow is again much much richer in defensive compounds flavor uh carotenoids the uh B um uh vitamin A uh and B vitamins as well again because plant feels as though it's under stress it's putting more of its effort into protecting whatever uh tissues it's able to to make so uh those are a few interesting things and I think useful things to know about the the chemistry of flavor and plants uh again as the speakers have said we're we're just beginning to understand these amazing creatures and seems to me that uh the more we stop and pay attention to them smell them chew them get to know how many there are uh the better we'll be able to um make use of these amazing uh partners of ours on this planet thanks