Hello.
I'm Priscilla Connors from the University of North Texas.
We're here today at the home of chef instructor Jodi Duryea to see the effects of time, temperature,
and pH on edible plant pigments.
These edible plant pigments are phytochemicals, or nonessential substances found in our foods
that give us health benefits beyond those of the basic nutrients.
Hi, Chef Duryea, Thanks for inviting us into your home.
Thanks, Dr. Connors.
It's a pleasure having you here.
Would you like to tell us what you plan to do with the vegetables today?
Sure.
We're going to start with green vegetables, and that's your chlorophyll.
And we just have some examples of those vegetables.
So this is just your basic jalapeno of course.
And then you have your green bell peppers.
Zucchini, now zucchini has both the chlorophyll on the outside.
And then inside it's white, so it would be a flavonoid.
So a multipurpose plant.
It's a multipurpose phytochemical bonanza.
And this is your kale.
And again, this has both your chlorophyll and your carotenoids as pigments.
Even though you basically-- the dominant one is chlorophyll that you see.
But when you go through-- when you're actually underneath that layer of chlorophyll is the
orangey pigments, the yellow pigments.
When you cook kale, you always want to remove the stem.
That stem is very woody, lots of cellulose, very chewy.
So when you take-- you want to just cook the green part of it.
And then we have here some really lovely collar greens.
And again, your collar greens are great examples of chlorophyll.
It has really large leaves.
It's huge.
And you always want to chop your leaves up.
And again, you want to take the stem off.
So the way you-- the best way to do that is just strip the leaves right off of it.
That doesn't damage the leaf when--
Mm-mm.
--you just strip it like that?
And you can see how it's just really stringy.
And as you cook it, it becomes even stringy-er.
So this is the part you want.
And again, you want to just-- you can tear it up, or you can cut it up before you cook
it.
And then over here we have some fresh beets.
And these are starting to fall apart.
But the beets are an example of your flavonoids, your red pigment, purple pigment vegetables.
But the greens are wonderful to cook with.
They're great sauteed.
They're also really good when they're really little as a salad green.
So very nice good source of calcium.
Is there only a specific time of the year that the greens are available, or can you
get them all the time?
You can usually get green beets most of the year.
They actually grow better in cool weather, and they're usually harvested around in the
cooler temperatures.
So not solid winter, but definitely spring and fall, depending on when they were planted.
OK.
And then today what we're going to use for our demonstration are sugar snap peas.
And sugar snap peas are real sweet.
They're real crunchy.
You can eat the whole thing.
Only thing you want to try to remove with the sugar snap pea is that string that goes
around it.
Because that string, again, a little chewy.
So when you're eating them, they tend to just get caught in your teeth.
Is there a specific time of year that you get fresh sugar snap peas?
Well most the time, they used to be considered an early summer, late spring vegetable.
But nowadays you can get them most of the year.
Does it take very long to cook them?
No, your sugar snap peas usually cook within a minute or two.
You want to start with boiling water.
Why would you want to do that?
That way the heat comes back up quickly.
If you start them in cold water, by the time they get to a boil, they're going to have
lost a lot of their pigment.
And one of the primary aims when we're cooking is to retain as much color as possible.
Because that signifies you're retaining vitamins.
OK.
These sugar snap peas are going to be used to demonstrate time and pH.
The green vegetables in general you always want to cook in a full boiling pot of water.
And you want a large amount of water relative to the amount of vegetables.
Why would do that?
So again, the more water you have when you have it up at boiling when you put the vegetables
in, it's going to come much faster up to a boil.
All right.
And the idea is that you're going to retain as much chlorophyll, or the green pigment,
as possible.
And what we're going to demonstrate-- what we're going to use to demonstrate this are
two pots of boiling water.
So what we're going to do first is check our water and make sure it's neutral.
So I put the test strip, just for second.
And you can see seven pH, which is neutral.
From here, I'll take the vinegar.
And we're going to do about one ounce of vinegar per quart of water.
And hopefully, turns to about a five pH, which is a nice acid level.
And then we take baking soda and use about a tablespoon of baking soda, in again a quart
of water.
And that comes out to about a nine pH, so a nice alkali solution.
So from here I'm going to put in a good handful of the sugar snap peas.
And I'll start the timer for two minutes.
Hopefully they should come back up to a boil very quickly.
From that point, you'll see-- you already can see how initially when they enter that
boiling water they turn a nice bright green.
You compare it to the ones before they were cooked.
With chlorophyll, generally what should happen with an alkali is they actually turn a nice
brighter green.
And there are some people that will use a little bit of baking soda when they wash their
lettuces to make it a brighter green.
The downside to it is that the alkali will actually start to break down the fibers in
the vegetable, and they become mushy and soggy.
With your green vegetables in an acidic water, what tends to happen to the chlorophyll is
it leaches the chlorophyll out.
And they start to turn grayish green.
Two minutes, I'm going to set it for an additional six.
And I'll take some of-- so you can see that the alkalines stayed a nice bright green.
The ice-- we put the vegetables into an ice bath to stop the cooking quickly.
So this shocks them and removes the heat quickly so that the heat doesn't continue to cook
them.
You can see the immediate color difference.
This is with the alkali, and this is with the acid.
The alkali are much brighter.
And you can also see in terms of the firmness.
These are softer, more bendable.
They're not going to be as crunchy.
These have a little bit more body to them.
Because acid tends to make fibers stronger.
Alkali breaks them down.
So this is about six minutes into the boiling of the vegetables.
You can see again with the acid the green is becoming paler.
There's a little bit of-- around the edges there's a yellowing of the vegetables.
They're almost that kind of khaki color starting to form.
And then over here with the baking soda, the alkali, they're still a real bright green.
But their shape is getting a little softer.
The water itself is changing color.
It's becoming a much more yellower color, either from the baking soda being heated or
from the actual chlorophyll getting into the water.
So that was eight minutes.
And I'll take-- you can see as I'm taking it out that they're really falling apart,
slimy almost.
The baking soda is breaking down the fibers and making it-- and then with that acid, they're
becoming that kind of olive gray.
But they still hold their shape well.
So here you have your alkali.
And you can almost see how slimy they've become.
They've really broken down, but they have retained their really bright green color.
So chlorophyll definitely-- baking soda helps retain chlorophyll as they cook.
But unfortunately the effect on the fibers, not pleasant.
And then with the acid, when you cook a green vegetable in the acid, you can see the distinctly
olive color that you create with that.
The fiber itself stays very firm.
We've been testing the effect of cooking medium pH in chlorophyll, a green plant pigment.
Here are five samples of snow peas that demonstrate the effect, from front to back.
In the very front, our snow peas that are raw and uncooked.
In the second row on the left, the snow peas have been cooked for two minutes in an acid
environment.
On the right, they were cooked for two minutes in a basic environment.
In the third row, our snow peas on the left that were cooked for eight minutes in an acid
environment.
On the right, cooked for eight minutes in a basic environment.
This demonstrates the color change that chlorophyll experiences when exposed to an acid, which
makes it drab olive green and a base or alkaline, which helps it remain a bright green.