A Tough Nut To Crack
February 6, 2015
Nuts seem to be popping into more and more cuisine lately. Mediterranean and Asian diets make heavy use of nuts while yogurts and salads often come with some nuts mixed in.
There’s a good reason for this. On top of being the quickest way to ruin a perfectly good brownie (yuck!), nuts are full of Omega-3 fatty acids, vitamin E, fiber, unsaturated fats and many more beneficial compounds. Walnuts boast one of the lowest saturated fat to total fat ratios in the nut world and contain hundreds of nutritional compounds.
But for every human-health-altering compound, or phytochemical, scientists have discovered in the walnut, another remains hidden, and many more have yet to be fully studied. That is why N.C. State University nutrition researcher Mary Grace developed a new technique for extracting phytochemicals from walnuts.
Now this may not seem like a big deal, but efficiently isolating these compounds allows researchers to study each one in depth to see exactly what health benefits might be hidden inside the hard shells.
This is also by no means a simple task. Isolating each phytochemical without chemically altering it is a task akin to dismantling a house without breaking anything and making separate piles for tiles, floor boards, pipes, nails, drywall, etc. without any information as to how the house was built. Walnut researchers do not even have the luxury of a juice they can squeeze out to get a productive start on the research like fruit researchers do.
Despite all of those challenges, Grace was able to come up with this recipe for deconstructed walnuts:
- Shell walnuts.
- Crush nuts into a fine powder.
- Add liquid hexanes to walnut powder and mix well. Strain mixture ensuring all liquid is removed and set remaining powder aside. Evaporate hexanes from liquid component to isolate walnut oil. Set oil aside. (Chemists call that mix-and-strain process an extraction, as in the hexanes dissolved the walnut oil and extracted it from the powder.)
- Extract powder with mixture of 4:1 mixture of methanol (often found in paint and varnish stripper) and water. Discard remaining powder and evaporate methanol from liquid mixture.
- Mix ethyl acetate (antifreeze) into water. Let sit until ethyl acetate and water separate water layer from ethyl acetate layer, which chemists do like this. Freeze-dry ethyl acetate layer to get a mixture of walnut chemicals.
- Repeat the liquid-liquid extraction from step 5 using butanol (a component in some renewable fuels) and the water layer left over from step 5. After separation, set aside water layer and freeze-dry butanol layer to get a mixture of different walnut chemicals.
- Purify components of the ethyl acetate mixture and butanol mixture using high-speed counter current chromatography, which involves dissolving the freeze-dried chemical mixtures and passing those solutions over a rapidly moving stream of a different solvent. The rapid stream will pluck out the chemicals in the mixture one at a time, based on how well they dissolve into the stream.
- Store each component separately.
While it does not sound as appetizing as a walnut salad, Grace’s recipe makes 13 separate fractions of phytochemicals, and repeating step 7 with a few of those fractions gave a grand total of 20 phytochemicals, including two new compounds.
This process may also seem complex, but it can efficiently separate the compounds in walnuts to the point where food scientists and nutritionists can independently study the effects each one has on the body.
That sort of efficiency lends a great deal of credibility to agencies like the FDA who control what claims doctors and food producers are allowed to make about the health benefits of food. It’s one thing to say that walnuts can help do X, Y and Z, but it’s a much different thing to say Praecoxin-A methyl ester, a chemical commonly found in walnuts, does X, Y and Z.
Grace’s research was published in the journal Food Chemistry.
— Daniel Lane
Daniel Lane covers science, engineering, medicine and the environment in North Carolina.