Let’s Chew The Fat

Biology concepts – lipid, saturation, fruit, vegetable, drupe, berry, mesocarp, cotyledon, tuber, fatty acid, triglyceride

To try and get blood from a stone dates back to the 1600’s,

meaning to try and do the impossible. It was first used in a

book by Giovanni Toriano called The Second Alphabet. As far

as the turnip goes, it may relate to a story in the Bible of Cain

and Abel making sacrifices – one a vegetable and one an animal.

The vegetable sacrifice was not as appropriate since it could

not drip blood. Now we often use the phrase for the inability of

getting someone to pay money.

Did you ever hear or use the phrase, “You can’t get blood from a stone?” Sometimes the phrase goes, “You can’t squeeze blood from a turnip.” Item one - gross. Item two, where did the phrases come from? (see picture caption) Basically, they both mean the same thing. You can’t harvest something that wasn’t there to begin with. I use it with creditors – they can’t get money from me if I don’t have any.

You can’t harvest what isn’t there, so that leads to today’s question. If plants are low fat sources of nutrition, how can we use them for cooking oils? There’s corn oil, sunflower oil, cottonseed oil, canola oil, rapeseed oil, olive oil, even coconut oil. How can such low fat organisms provide us with so much fat?

Of course every cell has fats – there are the phospholipids in the cell membrane, and phytophormones made from lipids help the cells communicate and the plant respond to stimuli. Thylakoid membranes for photosynthesis have a lipid (MGDG) that normally doesn’t form a bilayer, but does in the thylakoid. Please refer to this post to show that lipids have a role in almost every cellular activity.

Unfortunately, we don’t get oil from the whole plant, just a little part of it. And even more amazing, the part we get oil from only exists for a short time in the plant’s yearly cycle. When we say vegetable oil, we really mean fruit oil.

The fruit is the part of the plant that grows from the flower after fertilization, including the seed(s). The vegetable is all the other parts of the plant, including the flower bud before it is fertilized. Now you know the true difference between fruits and vegetables.

The fat in plants is almost always associated with its attempt to reproduce itself. Part of the fruit may be fatty, the seed of the fruit may be fatty, or even the germinating plant inside the fruit could be the source of the fat.

The upper image shows the different parts of the berry fruit

avocado. The mesocarp is the part we eat and contains the

fats. The same is true for the olives below. These have had

their seeds removed and replaced with a piece of pimento.

Maybe they thought we wouldn’t notice. No, they can’t grow

them with the pimento there already, but it might be

something Bill Blazejowski could work on, like his idea to

feed mayonnaise to the tuna in the 1982 movie, Nightshift.

Let’s start with the easiest – fruits that are high fat. The oldest is the most famous – olives. The fleshy part of the fruit, the part we eat, is called the mesocarp. In olives, up to 85% of the weight of the mesocarp is fat in the form of triglycerides. Olives have been grown for eating and pressing oil since about 6000 BCE. Olive cultivation predates written language and even teenage vampire movies.

Avocados are also pressed for oil. In locales where olives are harvested part of the year, avocados can be harvested year round, so many olive oil producer make avocado oil when the olives aren’t in season. Even though we use the mesocarp of each fruit for oil, the olive is a type of fruit called a drupe, while the avocado is actually a single-seeded berry. The avocado is just about the only berry from which we harvest edible oil.

In people with metabolic and liver function changes due to diabetes or other parts of a metabolic syndrome, it is known that the monounsaturated fatty acids in olive oil help to normalize many biochemical markers of liver function in people with metabolic syndrome. A 2014 study now expands that to avocado oil. It contains many monosaturated fatty acids, and the researchers found that it has similar positive effects on biochemical metabolic markers as compared to olive oil.

Oil palm (Elaeis guineensis or E. oleifera) fruit are also high in fat. The mesocarp is pressed to make palm oil that is used for eating and cooking, especially in Africa. The seed (kernel) can also be harvested for oil, and this is called palm kernel oil. The differences between the oil from the mesocarp and from the kernel lie in their color (the fruit oil is reddish while the kernel oil is colorless) and the percentage of saturated fats. The kernel oil is higher in saturated (no double bonds) fat.

These differences have an good side for us. Palm kernel oil esters have been shown to pass the blood brain barrier (BBB, see this post) better than other oil esters. So in a 2013 study, the palm kernel esters were combined with the antibiotic chloramphenicol. The resulting emulsion showed properties that could make it useful for treating bacterial meningitis, because more of the antibiotic could be carried across the BBB.

The mesocarp of the coconut is not edible. See the fibrous

stuff being cut away from the coconut? That’s the mesocarp,

or coir. It does have other uses though. You can make good

rope from it, or perhaps you would be more interested in some

biodegradable flower pots – all made with coir.

Another type of palm oil is also used in cooking. Coconut palm oil is pressed from the flaky coconut meat that makes german chocolate cake so irresistible. But the meat isn’t the mesocarp of the coconut fruit. You wouldn’t want to eat the mesocarp of a coconut; it’s the fibrous brown covering that has to be peeled away to get to the nut.

The coconut meat is the endosperm of the seed – the more it grows, the more of the liquid endosperm (coconut milk) turns solid. It turns solid because it is more saturated fat, and like most saturated fats it is more likely to be solid at room temperature. Coconut oil is sometimes used in place of butter.

Other “vegetable” oils come from different parts of the fruit. Sunflower oil uses the entire seed, including the embryonic plant, the endosperm and skin layers – outer (exocarp) and inner (endocarp).

Canola oil is pressed from the seeds of the canola plant. Canola is a plant bred from a type of rape plant, a member of the mustard family. Therefore, there's a really no difference between rapeseed oil and canola oil. The name "canola" was thought up in the 1970’s, using “Can” from Canada, because that is where it was developed, and “ola” as a term for oil. The word “rape” didn’t seem to help sales.

The top cartoon shows how the cotyledons can have different

fates. The brown oval cotyledons can become the first leaves in

epigeal growth, or can stay below ground in hypogeal growth.

Either way, they help the germinating plant get a good start. The

peanuts below show the cotyledons, the big parts we eat, as well

as the germinating plant. The red arrows point to the peanut

nibs; they’re actually the plumule and radicle (stems and root) of

the embryonic plant.

Drupe fruits like olives seem to make good oil. Drupes also include plants like peanuts and soybeans. However, these are different than olives. The fat from most drupes and whole seeds are found in the embryonic leaves, called cotyledons. They often serve as the first leaves of the baby plant, but they also store fat and carbohydrates for the germinating plant.

It occurs to me that the examples above are equal and opposite. On one hand, the fat of peanuts, soybeans, sunflowers, rapeseeds, and coconut serve to nourish the embryonic plant. Fat is a great idea for this function because it stores a large amount of energy in a small volume. Carbohydrates require water for storage, so they take up more room.

On the other hand, the fat of avocados, palm oil fruits and olives are enticements to other animals to eat the fruit. Why do the fruits “want” to be eaten, anthropomorphism aside? The answer - to disperse the seeds held within or on the fruits.

New plants do better when they are far enough away from the parent plant that they will not have to compete with them for resources and sunlight, especially since they will be smaller and in the shade. This is why seeds need to be dispersed. Nourishment for itself or nourishment for a predatory animal, these are two completely different functions for the fat, but both are held in the fruit.

The corn kernel is the fruit of the maize plant. There is starch

(glucose chains), gluten (protein) and the germ, which is the

germinating plant with a single cotyledon. The bottom drawing

shows the difference in constituents of different varieties of corn.

Sweet corn has more sugar, while dent corn has a higher germ to

endosperm ratio.

Given the high enough fat contents of the plant components described above, it makes sense that we could use them for oils. But what’s one of the most common “vegetable” oils used for both cooking and biodiesel? I’ll give you a hint – you probably enjoy some of this fat at the movies.

Yes, corn it is, both as your popcorn and the margarine you slather all over it. We already know that corn is amazing (see this post), but only 10% of corn is fat (dry it and 20% is fat). The sweet corn you eat is a special hybrid that contains more endosperm and less fat, but dent corn is the one used for making oil and feeding livestock. The corn kernel is mostly starch and glucose, but the embryonic plant has the fat. This is called the corn germ and is the only part used to make oil. The germ contains the cotyledon (called a scuttelum for corn) that stores fat for the germinating plant (get it? Germ = germinating plant)

Look at the bottom picture to see how small the germ of the corn kernel is. Because of this, it takes 40 bushels of dried dent corn kernels (at 56 pounds/bushel) to make 500 ml (0.85 lb) of corn oil! It must be cheap to grow corn because that isn’t a very good ratio, yet corn oil isn’t that expensive.

Tiger nut sedge looks a lot like a grass and is considered a weed

in many places. It was cultivated as far backs as 3000 years ago

in Egypt and has been used in cooking for just as long. The tubers

on top left can be eaten as a root vegetable, and are high in

monounsaturated fats. The dried tubers (bottom) can be ground

into flour or used as a spice. However, we might just start to grow

them for biodiesel. I’d line up to buy a tiger nut fueled car – that’s

really putting a tiger in your tank! (a 1960’s Esso gasoline slogan)

Even though this is a summer post, there’s no reason we can’t talk about an exception. Today, it’s sedge oil. The tiger nut sedge (Cyperus esculentus) is being considered as a viable source for biodiesel, but it's used in African cooking as well. Sedge plants reproduce in several ways. They have fruits, but they aren’t significantly high in fat. They have rhizomes and well, but we’re interested in their tubers (serves the same function as a potato).

The tubers are fairly high fat, and they’re a heck of a lot larger than corn germ. On a per plant basis, sedge produce much more oil, which will make C. esculentus a cheaper source of fuel if farmed on a global scale. In truth, since sedge oil comes from a part of the plant other than the fruit, it’s the only true “vegetable” oil we talked about today. I wonder - could we get oil from a turnip? Maybe that’s the blood we should be looking for.

Next week, we'll start a series of posts on just how bacteria get around using flagella. Can flagella be used to prove the existence of a universal designer?

Carvajal-Zarrabal O, Nolasco-Hipolito C, Aguilar-Uscanga MG, Melo Santiesteban G, Hayward-Jones PM, & Barradas-Dermitz DM (2014). Effect of dietary intake of avocado oil and olive oil on biochemical markers of liver function in sucrose-fed rats. BioMed research international, 2014 PMID: 24860825
 

Musa SH, Basri M, Masoumi HR, Karjiban RA, Malek EA, Basri H, & Shamsuddin AF (2013). Formulation optimization of palm kernel oil esters nanoemulsion-loaded with chloramphenicol suitable for meningitis treatment. Colloids and surfaces. B, Biointerfaces, 112, 113-9 PMID: 23974000