Friday, February 26, 2010

Some science for raw foodists


ResearchBlogging.orgI once lived with a woman who insisted that cooking food broke down the enzymes that we so desperately need from the food.
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This same roommate also insisted that water kept at room temperature was more "alkaline" than when it was cold.  (Though this website insists that the water must have a pH = 10 to have this effect, and that if you drink it, it will clean toxins from your body. She insisted temperature alone achieved this desired effect.) 
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She was taking general chemistry at my university at the time, in my very department.  Apparently equilibrium means nothing to her... would you trust her as your doctor?  Excuse me, as your holistic natural medicine doctor who seeks to legitimize the profession by attending medical school.  I have zero beef with natural medicine, don't get me wrong, but more alkaline at room temp??  Is there a temperature dependence constant missing from H2O → H+ + OH??  F, man.  I have a beef with momos who deny the fundamentals of general chemistry.  Or who doesn't realize that the person or book that told her that might've said the pH was higher...

So, I acknowledge the health benefits of restricting the amount of processed food that one consumes, and in many fruits and vegetables, cooking does cause vitamins to leach from the greens into water, sometimes to an alarming degree.  Freezing in many cases also causes nutrient-dense foods to lose their potency.  Thanks to an article that just came out in Journal of Agricultural and Food Chemistry, we can now argue that at least eggplants do not behave the same way.  

Sample preparation:  Eggplant (the "black bell" variety) was grown in a research facility in Lodi, Italy, selected by visual inspection to be homogenous in size, color, and free from diseases or pests.  The fruits were cut into 1 cm slices and treated one of three ways - 1) kept raw (freeze-dried and lyophilized); 2) grilled on a surface of 190-210C such that the inside reached and stayed at 100C; 3) boiled in 10 min in tap water at a 1:10 fruit:water ratio such that the inside of the slices reached and stayed at 100C.  The grilled and boiled fruits were cooled for 1 minute at room temperature, then immediately frozen and lyophilized until constant weight was reached.   From these samples, 2 g samples were taken from each treatment group, treated twice with 55 mL 75% EtOH at 60C then dried with 20 mL acetone until constant weight to produce ethanol-insoluble residue, EIR.  (I bet you never thought about food sample preparation in science before, eh?)

Analytical chemical analyses:  
  • Total polyphenol index was measured with RP-HPLC and the quantity of chlorogenic acid determined, since chlorogenic acid is the predominant polyphenol found in eggplant.  Anthocyanins from the peels were quantified as well.  
  • Glycoalkaloid content (solamargine & solasonine, which you really don't want to eat in gigantic quantities as they are toxic in high doses) was determined from 0.5 g tissue treated with 95% ethanol and analyzed by RP-HPLC.  
  • Antiradical activity, signified by superoxide anions and hydroxide radicals, was determined using ESR (electron spin resonsance) spectroscopy 1 minute after generating these species via:    
    • Superoxide anions were generated by treatment of eggplant extract with 6.4 mM KO2-18-crown-6 1:1 in DMSO followed by spin trapping with 25 mM 5,5-dimethyl-1-pyrrolin-N-oxide (DMPO)
    • Hydroxyl radicals were generated by treatment of extract with 2 mM Fenton system (?) in 0.1M phosphate buffer (pH=7.4) followed by spin trapping with 10 mM DMPO
Biological assay:  Human polymorphonuclear neutrophils, which are the most common type of white blood cells (shown at the left surrounded by red blood cells), polymorphonuclear because their nuclei are often lobed -  are a type of granulocytes (dubbed so because their cytoplasms are granular in appearance).  These cells were isolated from human blood samples and chosen because when under oxidative stress, they produce oxidative species (as a good white blood cell should!) including superoxide anions, peroxides, oxygen radicals, hydroxyl radicals, and HClO, which are all considered "reactive oxidative species" (ROS).  The assay involved viewing the cells under a fluoroscence microscope to visualize the chemiluminescence produced by luminol when luminol is reacted with one of these ROS; this "luminol-amplified chemiluminescence" (LACL) assay allowed the researchers to measure oxidative bursts given off by the cells in response to varying concentrations of the eggplant extract; the fewer the bursts, the more antioxidant species the extract contains as the cells are emitting fewer ROS.

The authors found that cooking didn't affect the glycoalkaloid content, but the phenolic content was increased threefold, most likely due to greater extractability of the compounds by cooking.  The effect of the extract on the neutrophils was very marked, and the researchers were able to extrapolate that approximately 40 - 80 g of eggplant, which can be obtained in one serving, may be able to react with all the neutrophils in the body.   The following TOC graphic (black & white in the paper) shows that at higher concentration of extract, the inhibition of ROS is greater - though the concentrations needed to cause this effect are quite low.  Hope you like eggplant!  Make sure you grill the heck out of it.




  • Lo Scalzo, R., Fibiani, M., Mennella, G., Rotino, G., Dal Sasso, M., Culici, M., Spallino, A., & Braga, P. (2010). Thermal Treatment of Eggplant (L.) Increases the Antioxidant Content and the Inhibitory Effect on Human Neutrophil Burst. Journal of Agricultural and Food Chemistry DOI: 10.1021/jf903881s

8 comments:

  1. My guess on the 'alkalinity' thing is that she is misinterpreting the fact that the kw isn't constant with temperature. The pH or pOH of pure water does change with temperature. It's still neutral though, with equal amounts of H+ and OH-.

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Constructive criticism welcome; criticism for judgement's sake, not.