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Rooibos anti-stress antimutagenic, anticarcinogenic, anti-inflammatory and antiviral activity

roobios

by Richard Aiken MD PhD @rcaiken

Rooibos (Aspalathus linearis) is a bush native to the Cedarberg Mountains in the Western Cape region of South Africa where it is extensively cultivated for its commercial use as an herbal tea. After harvesting, the needle-like leaves and stems can be either fermented prior to drying or dried immediately. The unfermented product remains green in color and is referred to as green rooibos. During fermentation, the color changes from green to red with oxidation of the constituent polyphenols, so the final product is often referred to as “red tea” or “red bush tea.” The non-oxidized green version, let’s call it “green herbal tea,” would be superior in antioxidants.

Rooibos possesses antimutagenic, anticarcinogenic, anti-inflammatory and antiviral activity[1], as does unfermented green herbal tea.

Rooibos is especially rich in the super-antioxidant compound quercetin. Rooibos is a source of two comparatively rare antioxidants, aspalathin and nothofagin. Aspalathin helps to modify hormones in the body and reduces the output of adrenal hormones, thus reducing stress and helping to inhibit metabolic disorders.  The antioxidant nothofagin demonstrates significant anti-inflammatory activity and neuroprotective functions[2].

As this is a tea, why not buy teabags, add hot water and drink it?  Well that’s fine, but much more expensive than bulk purchase. While the process of preparing, serving, and sipping tea can be an art, we are here interested in the nutrient value – and efficiency of preparation. Steeping in hot water extracts only a portion of the water-soluble components (such as polyphenols) of the plant, i.e., that which enters into solution if the fibrous cell walls are sufficiently disrupted by the heating process – the rest is discarded in the tea bag.

But as a food, the entire leaf can be eaten and all nutrients consumed. A dose suggested from literature studies is one teaspoon.

References

[1] Joubert, E., Gelderblom, W., Louw, A., & Beer, D. D. (2008). South African herbal teas: Aspalathus linearis, Cyclopia spp. and Athrixia phylicoides – A review. Journal of Ethnopharmacology, 119(3), 376-412. doi:10.1016/j.jep.2008.06.014.

[2] Mckay, D. L., & Blumberg, J. B. (2006). A review of the bioactivity of south African herbal teas: Rooibos (Aspalathus linearis) and honeybush (Cyclopia intermedia). Phytother. Res. Phytotherapy Research, 21(1), 1-16. doi:10.1002/ptr.1992.

World’s Healthiest Smoothie?

Where do you get your calories? Your phytonutrients?

Green leafy plants generally have a very high nutrient to calorie ratio.  This is related to the high surface to volume ratio in leaves – the sun’s energy is more available for nutrient manufacture.  However, generally leaves are rather tough and bitter, a protective defense developed by immobile plants. That’s a tough reality as the leaves of plants can provide an excellent variety of macronutrients, vitamins and minerals, and a vast array of phytonutrients.

Luckily, we don’t have to rely on leaves for our entire energy source; that would take a great deal of chewing time. Although that is precisely what our primate ancestors did for nearly 85 million years (see our new book The New Ancestral Diet).

But we don’t have that kind of time anymore, am I right? But given the powerful health benefits, how can one consume a significant amount of green leaves? The answer is food processing to assist with the chewing: smashing between stones (mortar and pestle for great pestos), cooking (laying in sun, roasting, baking, boiling, etc.) or my favorite: high speed blending.

There are some negatives to mechanical blending of fruits, green leafys and other vegetables in that the extreme disruption of cells not only releases the nutrients but allows an increased rate of oxidation of the antioxidants – but here is an important “biohack” to avoid nutrient loss that I researched “in my garage” titled Minimization of Oxidation Reaction during High Speed Blending; this is a critical consideration if you use high speed blending. I will illustrate that later in this offering.

Even so, I have found it difficult to eat more than about one pound of leaves per day (that is about seven cups of raw chopped kale, for example, providing about 200 calories).  This is partly because gathering time from the garden is significant and storage is rather a problem unless you shop every few days.  And leaves don’t freeze very well (although frozen spinach and collard greens, as examples, can be found in some supermarkets).  So, as much as you like the idea of being “powered by kale,” it ain’t gonna happen.

Epic smoothie recipe for health and happiness

Okay, so we have to gather fruits and veggies from somewhere. Fortunately, most ingredients can be from organic frozen sources (fruits and non-leafy veggies).  Plus many “superfoods” – nuts, seeds, dried leaves, stems and roots, can be stored at room temperature.

My goal is a meal that is fast to prepare and has maximum nutritional impact, with high nutrient to calorie ratio.  Smoothies such as detailed here can fulfill those criteria. (note: sip and swirl in your mouth – like a fine wine – to activate the important digestive enzymes there; I make this as a morning post-workout recovery drink and there is enough left over to provide sips during the afternoon – a controlled release nutrient biohack that eliminates the need for lunch). Once home, for supper I typically prepare what I call a Buddha Bowl, consisting of whole plant based foods such as wild rice, beans, garlic, onions, spices and herbs and chopped green leaves).

My smoothie recipe usually has fresh leaves, lots of frozen organic fruits and vegetables as the base and 11 other super ingredients (see below).  As the preparation of this can still be a wee bit time consuming if done individually, I make a dozen or so preparations at a time, vacuum seal and freeze. Then for a fast super smoothie, I just add to the frozen concoction fresh green leaves (first citrus and water as I shall explain later), place in a blender (I use a Vitamix) and bingo, a most nutritious meal in a snap!

Fruits and non-leafy vegetables

For my smoothies, I primarily use a frozen source for fruits and vegetables, although if I happen to have other non-frozen ingredients in the fridge (especially if they are becoming aged), I’ll throw them into the blender.  For this recipe, I chose the follow fruits and vegetables shown below.

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The fruits I use here (shown on the left) are a mixture of organic frozen strawberries, blackberries, and blueberries from Chile and marketed by Cascadian Farms; package contents are 10 oz (284 gm) so about enough for two cups – I use one cup per smoothie.

The organic frozen vegetables are from the same distributor, consist of broccoli, cauliflower, carrots, and zucchini. Again one package is 10 oz (284 gm) and makes two cups, one of which I use for each smoothie.

The rest of the ingredients are non-frozen. I chose them for their variety of phytonutrients – they are all truly “super”:

Non-frozen superfoods for smoothie

Here is a list (no particular order) for this epic smoothie – I’ll explain why each was chosen later.

  1. Rhodiola (Rhodiola Rosea)
  2. Ashwagandha (roots of Withania Somnifera)
  3. Maca root (Lepidium meyenii)
  4. Tumeric
  5. Flax seeds
  6. Ground peppercorns
  7. Nutritional yeast
  8. Rooibos
  9. Hibiscus flowers
  10. Green tea
  11. Cacao

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Rhodiola

While some some evidence suggests that this plant may be helpful for enhancing physical performance and alleviating mental fatigue, as is the case with most plants, in particular herbs and spices, there are no definitive double blind placebo-controlled prospective studies that clearly demonstrate its efficacy.  However, it is loaded with phytonutrients such as polyphenols. It is supposedly adaptogenic, meaning that it does its good deeds without disturbing normal biologic functions.There are some claims that indicate use not only for stress and anxiety but also for depression; I’m working on fully exploring those claims; I’ll report on that at a later time.

I’m not even sure if it is an herb (plant leaf, stem, or flower used for flavoring or medicinal use) or a spice (same as herb but a root).  Various alternative names include “root,” such as the “red root” and the powder here is a deep red so I assume that it is primarily a root and therefore technically a spice.

My source for this is from Bulk Supplements (www.bulksupplements.com) – I order from Amazon and guided in my selection in part by happy consumers who have tried it and like it on some basis. Rhodiola Rosea 3% Salidroside Powder (100 grams) costs about $18.  I use a little less than one eighth of a teaspoon, about 300 mg.  I’m unsure of where this was harvested although it can grow on cold rocky slopes in the USA; it has been suggested to assist those living in very cold stressful environments such as Siberia and northern Europe. It has a shelf life of 3 or more years.

On the left is a picture of the addition to my smoothie ingredient bowl.

AshwagandhaIMG_1078

There are many claims concerning the health benefits of Ashwagandha root but most all of them are concerning reduction of adrenal stress (anxiety) and reduction of inflammation; there are many peer reviewed studies, including systematic review summaries, that are rather convincing.  Positive influences on neurodegenerative diseases such as cognitive decline and dementias are suggested.  Again, more on this in a later communication.

It is likely helpful to ingest this substance after exercise, particularly endurance workouts or heavy lifting (supposedly helps to stimulate muscle recovery).

Also this Ayurvedic has been used to help treat insomnia.

On the left is a picture of my addition to the superfood mixture. The amount used here, suggested by the literature studies, is one half of a teaspoon, about 1600 mg.

Maca rootIMG_1080

Maca has been cultivated and grown high in the Andrean Mountains of Peru for thousands of years.

Like Rhodiola, it flourishes in extreme environments of freezing cold winds, strong sunlight, and high elevation (over 10,000 feet).  There does appear to be a correlation between plants that survive in stressful circumstances and the adaptogen effects that such plants have on the human body and mind.

The root of the Maca plant has been used for centuries as a nutritive substance that raises the body’s state of resistance to disease by increasing immunity to stress while remaining nontoxic to the recipient.

The shelf life is an amazing seven years.  Maca is powerfully abundant in amino acids, phytonutrients, healthy fatty acids, vitamins, and minerals. This superfood allegedly has the ability to increase energy and stamina, working directly on the hypothalamus and pituitary glands.

Once again, there are some indications of positive effect on mood and I am searching the literature for substantiation.

On the left shows the addition of two tablespoons of Maca powered root, the “premium” combination of Peruvian sources from this recommended source.

Turmeric

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You are more likely to have heard of this one.  Turmeric is a spice with perhaps the highest antioxidant and anti-inflammatory properties of any culinary spice – or herb. An active component of turmeric is curcumin (the pigment responsible for the bright yellow color of the spice), which may have natural antidepressant qualities and has been shown in animal studies to protect neurons from the damaging effects of chronic stress. The literature is quickly mounting support for mental health enhancement.

Turmeric suppresses pain and inflammation similar to non-steroidal anti-inflammatories. The mechanism of action is similar without the potential side effects. The health benefits derive, as for Rhodiola and Maca, from “xenohormesis” – a biological principle that explains why environmentally stressed plants produce bioactive compounds that can confer stress resistance and survival benefits to animals that consume them.

A selection, suggested from the literature, of 1 gram, equal to one teaspoon is used here.  On the left is a picture of my grating of a turmeric root used in this smoothie but this is so color intense (one should use gloves; otherwise your hands and fingernails appear yellow as a very heavy smoker).  On the right is the quantity added to our mixture.

IMG_1083Flaxseed

I am confident you know of this food and that it is most beneficial to health.  There is certainly no doubt that this food is an excellent source of essential omega-3 fats in the form of alpha-linolenic acid (known as ALA), the basic building block to other omega-3’s such as EPA (eicosapentaenoic acid), and DHA (docosahexaenoic acid).

These fatty substrates are used in several critical constructions of neuronal constituents and thus important in proper functioning of the brain.  The other major source is certain algae, a dilute source with contamination and harvesting challenges.  One could eat fish the fish livers that sequester the fatty acids form algae but that detoxifying organ contain many toxins that are unfriendly to humans, notably mercury.

Certainly much research has indicated the mental health benefits to consumption of flax seeds that I shall summarize in a later offering.

On the left I use  one tablespoon of flaxseed that contains easily a daily recommended dose.

IMG_1084Ground peppercorns

Black pepper has an ancient history of being a highly desirable but expensive spice.  It has even been used as a currency.

The Journal of Food and Chemical Toxicology reported that the compound piperine in black pepper increases the cognitive function of the brain and helps beat depression. Other studies agree, although as yet not fully accepted.  Piperine helps the body absorb curcumin and therefore enhances its antidepressant effect long-term, according to studies on rats conducted in India. There may be similar absorption assistance given to selenium, vitamin B12, and beta-carotene.

Because of its intense taste, it is typically used in small quantities and for our smoothie we use just a few “pinches” as shown to the left.

IMG_1085Nutritional Yeast

Impressive research exists that supports a positive effect of nutritional yeast on stress and related immune function resulting, for example, in a decrease for the susceptibility to the common cold. Beta glucan fiber, found in baker’s, brewer’s and nutritional yeast, helps to maintain our body’s defense against pathogens. And this is extended to improvement in mood states, related to immune vitality and emotional vitality. For endurance athletes who place significant stress upon their bodies, regular ingestion of this substance is recommended.

We use here one heaping teaspoon of Bragg’s nutritional yeast.  This has a nutty, cheesy flavor as opposed to Brewer’s yeast that is quite bitter. This product is fortified with vitamin B12, an interesting pairing of nutritional fungal and bacterial sources.

IMG_1086IMG_1087Rooibos

Research conducted in Japan shows that rooibos, or “red tea”, possesses antimutagenic, anticarcinogenic, anti-inflammatory and antiviral activity. Rooibos is especially rich in the super-antioxidant compound quercetin. Rooibos is a source of two comparatively rare antioxidants, aspalathin and nothofagin. Aspalathin helps to modify hormones in the body and reduces the output of adrenal hormones, thus reducing stress and helping to inhibit metabolic disorders.  The antioxidant nothofagin demonstrates significant anti-inflammatory activity and neuroprotective functions.

Note this is a tea, so why not buy teabags, add hot water and drink it?  Well that’s fine but much more expensive than bulk purchase. While the process of preparing, serving, and sipping tea can be an art, we are here merely interested in the nutrient value – and efficiency of preparation. Steeping in hot water extracts water-soluble components of the plant and that which enters into solution if the fibrous cell walls are sufficiently disrupted by the heating process. As a food, the entire leaf can be eaten and all nutrients consumed. By the way a bio-hack to optimize antioxidants in tea is found in my article Synergism of Tea Plant and Citrus for Optimum Health.

A dose here suggested from literature studies is one teaspoon.

IMG_1087Hibiscus flowers

Another herbal “tea
“, Hibiscus flowers are beautiful showy red flowers that are harvested and dried as most teas.  This plant contains bioflavonoids, which are believed to help prevent an increase in LDL cholesterol, and lower blood pressure.  The research is quite clear on these effects. It may work by boosting nitric oxide production, generally an advantage for cardiovascular activities.

Again, why bother to make “tea” with this food and limit the nutrient availability when you can eat it!

I use here a heaping tablespoon for our super-mixture.

IMG_1088Green Tea

The third “tea” is Green Tea, or just “tea”.  Tea is the most consumed beverage in the world. It comes from an evergreen called Camellia sinensis. “Green” tea merely refers to the natural state of the Tea Plant; in the United States, the preferred tea is “black” tea, a less healthy oxidized version. Green tea offers incredible health benefits but is consumed mainly for its psychoactive ingredients: caffeine and l-theanine.  The stimulating effect of caffeine is modulated by the calming effect of l-theanine.

Tea is very rich in polyphenols, accounting for up to 30% of the dry weight of tea. Tea has positive effects on cognitive functioning beyond the stimulating effect from caffeine through possibly enhancing short-term plasticity in the pare-frontal brain areas.

Drinking green tea is associated with reduced mortality due to many causes, too many to mention here but includes lowering blood pressure, oxidative stress, and chronic inflammation. 

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Cocoa

Raw unprocessed cocoa is one of the richest antioxidant foods in the world. Studies indicate that cocoa has an effect on carbon dioxide levels that affect blood vessels and improve blood flow.  This has positive implications, for example, on reducing the risk of stroke.

Any form other than raw contains typically added fat and sugar and is to be avoided.

Let’s add a tablespoon of cocoa (also termed cacao) nibs.

Ingredients combined, evacuated, and frozen

Below are pictures of our dry mixture (left); also adding it to the vacuum bag (picture on the below right)

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Next a cup of the frozen fruits and a cup of the frozen vegetables are added (below)

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Then the bag is evacuated (below).  A ten-day supply was generated as shown below on the right.

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How to blend in order to maximize nutrition

The first step to blending any fruits or vegetables is to create a pH environment that slows down the oxidation of the critical anti-oxidant phytonutrients with disruption of the cellular contents as happens in all forms of processing, including high speed blending.  I have referenced above the science behind this in my article Minimization of Oxidation Reaction during High Speed Blending.The need is to provide a low pH blending fluid and citric acid in the blender prior to the introduction of the fruits and vegetables (this inhibits the activity of polyphenoloxidase that assists oxidation).

IMG_1102IMG_1105 On the far left is a picture of my Vitamix; next to it is about one cup of filtered water and one lemon, quartered with skin and seeds intact. The next picture is of the blending of water and whole lemon until it is smoooth.

The rest of the contents of the smoothie can now be added without fear of reducing the nutrient value by the high speed blending.  Go ahead and blend at the highest speeds for as long as you wish. I like “smooth” smoothies so I typically add plenty of filtered water and blend at the highest setting for about 30 – 45 seconds.

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Next I take a heaping cup of frozen chopped spinach. and add that to the pH adjusted solution.

 

 

 

Finally the addition of the vacuumed sealed super-nutrient mixture that was prepared and frozen earlier.

The mixing of all ingredients is shown to the left (my foot, lower left, is “grounding” – hey, can’t hurt).  The whole mixing process takes about 5 minutes.

 

To your health

IMG_1119Well that’s it.  The taste of this particular concoction is “nutritious”.  I wouldn’t say it is “delicious”, but certainly palatable.  I’m mainly interested in long-term happy survival here, not culinary flavor optimization – that is for special occasions, this is for frequent consumption.

Note my “green smoothie” isn’t green, instead has a reddish brown color.  That is a result of the berries and most of the super herbs, spices, and teas that have a red or brown color. Not pretty perhaps, but pretty great nonetheless.

I welcome comments and suggestions.  Think you can beat this smoothie for health impact? Let me know!

 

 

 

Biohack your Tea with Lemon or Lime

SNAPPLE_LEMON_TEA_16

Tea is the most consumed beverage in the world.  It comes from an evergreen called Camellia sinensis. The health benefits of “tea” is generally appreciated but what is not known to many is how to maximize those benefits. It’s all about the degree of oxidation.

“Green” tea merely refers to the natural state of the Tea Plant; in the United States, the preferred tea is “black” tea.  Black tea is green tea that is partially oxidized.  While this has certain flavor advantages, much of the health benefits of green tea is lost. So-called white tea is just young green tea and does not have the phytonutrients density as the mature green tea.

Tea processing

Whenever the tea leaf is fragmented, there is a disruption of cellular contents.  The cellular contents of tea with sought-after health benefits are a class of compounds called polyphenols, particularly catechins.  These are present in the cell’s vacuoles; when they come into contact with the polyphenol oxidase in the cell’s cytoplasm, after cellular disruption, the polyphenol is deactivated.

When tea leaves come into contact with water, particularly at higher temperatures, cell walls are partially disrupted and soluble cellular contents enter solution.  Entrained and solubilized oxygen then can oxidize the polyphenols catalyzed by the enzyme polyphenol oxidase and health benefits are reduced.

But we can do something to minimize that regrettable situation.

Effect of acidity

The optimum pH for polyphenol oxidase activity varies but is around  7. However, the enzyme  activity rapidly decreases at more acidic pH values as provided by citrus fruits such as lemons or limes .

Chemical Inhibition

It has been shown that complete inhibition of polyphenol oxidase activity is found with an ascorbic acid solution .

Citric acid also can inhibit  activity, although not as strongly as ascorbic acid . Citric acid exists in much greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits.

How do you take your tea?

Mention should be made of the best way to consume any plant is by eating it, not just consuming that which solubilizes in water.  Bulk green tea leaves are quite inexpensive (see an example here) and can be, for example, be added to green smoothies for optimum nutrition.  The same oxidative penalties may arise though – see a study I wrote on reducing that problem here.

Here’s how to make a better cup of hot tea

Boil water. Remove from heating source and add the juice from a fresh lemon or lime.  Then add tea bag or infuser or raw green tea leaves.  Do this for each individual cup of tea – do not store.

Nootropic Caffeine

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Why is it that aqueous extracts of the Tea Plant is the most consumed beverage in the world? It’s not the taste – it’s because it’s psychoactive.

The compound responsible is theanine – found only in the Tea Plant and a certain fungus (Bay Boleet). Theanine modulates the psychostimulant effect of caffeine, further increasing focus but also with a calming that has been shown to increase alpha waves in the brain – similar to meditative states (Nobre at al.).

Therefore there may be cognitive and anxiolytic properties of theanine in the presence of caffeine and possible as an isolated extract.

A. C. Nobre, A. Rao, and G. N. Owen. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr, 17(suppl – 1):167-168, 2008.

Minimization of Oxidation Reaction during High Speed Blending

by Richard Aiken MD PhD (Twitter @rcaiken)

There has been some concern as to the effect of high-speed mechanical blending on the nutrient value of fruits and vegetables. The main concern is that rupture of the cell walls and organelles within the plant cell releases nutrients but vigorously exposes them to atmospheric oxygen with potentially deactivating oxidation reactions.

Conclusions

There is a significant amount of oxidation that occurs during blending bananas. The oxidation reaction is slowed somewhat by blending at slower speeds but even then significant oxidation occurs. Reduction of the temperature, an increase in acidity and particularly the chemical influence of ascorbic acid apparently stops the catalysis of DOPA by PPO and therefore its oxidation.

Discussion

Although this experiment was specifically performed on a fruit with the major phenolic component DOPA, the results might be extended to other phenolic-containing plants. If so, it is recommended prior to general blending of plants, that a cold water solution containing a fruit with a high ascorbic acid content and low pH (lemons, oranges, limes as examples) be blended at high speed. Subsequently, general blending can be achieved with other additional plant foods at high speed minimizing oxidation.

Blender mechanical properties

There are two primary physical processes that work to mechanically break down the cell wall of plants, releasing nutrients: shear forces and cavitation.

Shear forces are created by the high-speed impact of the food with the blender blades. This includes direct cutting by the blade itself as well as shearing by application of high kinetic energy of the particulate matter moving through surrounding medium and striking other particles and the container.

Cavitation is caused by the Bernoulli effect – the same principle behind air flight – planes and helicopters and why boats can sail faster against the wind than with the wind. The speed of the blades in fluid cause a decrease in pressure above the blades equal to the vapor pressure of the fluid, similar to boiling. Bubbles form on the blades (assuming a fluid component), are flung away and implode causing very powerful shockwaves that further break down even the smallest of remaining particles.

Polyphenoloxidases (PPO)

The enzymes in the class PPO appear to reside in the plastids of all plants and are released when the plastid cell membrane is disrupted. PPO is thought to play an important role in the resistance of plants to microbial and viral infections and to adverse climatic conditions.

Phenolic compounds are responsible for the color of many plants and impart taste and flavor. They are important antioxidants.

In the presence of oxygen from air, the enzyme catalyzes the first steps in the biochemical conversion of phenolics to produce quinones, which undergo further polymerization to yield dark, insoluble polymers referred to as melanin. This is the same melanin that determines darkness of human skin and hair. In plants, melanin forms barriers and has antimicrobial properties that prevent the spread of infection in plant tissues.

Note enzymatic browning is considered desirable for the color and taste of tea, coffee and chocolate.

Phenolic substances in plants

There are many phenolic (or polyphenolic) compounds in fruits and vegetables. Epidemiological studies and associated meta-analyses strongly suggest that long term consumption of diets rich in plant polyphenols offer protection against development of cancers, cardiovascular diseases, diabetes, osteoporosis and neurodegenerative diseases[1].

Polyphenols can be divided into many different subcategories, such as anthocyans and flavonoids. Flavonoids are formed in plants from the aromatic amino acids phenylalanine and tyrosine. Tyrosine also synthesizes DOPA (3,4-dihydroxyphenethylamine) that forms dopamine.

Many plants synthesize dopamine to varying degrees. The highest concentrations have been observed in bananas, levels of 40 to 50 parts per million by weight.

Effect of acidity

The optimum pH for PPO activity has been shown to be 7 (dopamine substrate). However, the enzyme displays high activity between pH 6.5–7.5 and the activity rapidly decreases at more acidic pH values[2].

Effect of temperature on PPO stability

Heating at 60 degrees for 30 minutes reduces the enzymatic activity by 50%; heating at 90 degrees C completely destroys the enzyme. The optimum temperature for maximum activity is 30 degrees C (86 degrees F).

Chemical Inhibition of PPO

It has been shown that complete inhibition of PPO activity is found with as low as 0.8 mM ascorbic acid[3]. Ascorbic acid, also known as vitamin C, acts as an antioxidant because it reduces the initial quinone formed by the enzyme to the original diphenol.

Citric acid also can inhibit PPO activity, although not as strongly as ascorbic acid[4]. Citric acid exists in much greater than trace amounts in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits. The concentrations of citric acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes[5].

Reaction catalyzed by PPO in Bananas

Dopamine has been reported as the major natural occurring substrate in banana pulp and the fastest and most important reactant in the production of melanin (darkening)[6].

EXPERIMENT

Measurement of PPO Activity

 PPO activity was determined by visualization of browning on a scale 0 – 5, where 5 is darkest noted and 0 is no noted darkening.

Organic bananas (PLU-94011) at ripening stage 5 (yellow peel with green tip) were used for this study.

Experimental Results

Direct blending high-speed one minute

The first trial was blending three bananas directly in the Vitamix blender, first at slower speeds, then when mixed, at high speeds for 60 seconds. A significant vortex formed.

B first high speedThe result is shown here.

Note this picture was taken within 15 seconds of the end of the blending. Already a browning is seen. I will assign a darkness scale of 4 to this, where 5 is the darkest of any of the trials at prolonged time scales.

Blending with water shield low-speed short time

The next trial used two bananas with a water shield (room temperature). It was attempted to keep the bananas under water during the blending and the vortex was mechanically disturbed. The mixture was blended for about 30 seconds on an intermediate to low setting.

The result, just after blending, is shown below on the left, compared to the first trial, now after about 15 minutes.

B first and second

I shall assign a darkening scale of 2 to this mixture.

After about a half hour, the two trials have the following appearance.

B first and second later

The first trial remains at a score of 4 while the second trial has darkened to a 3.

High-speed blending at cold temperature and with lime juice

The juice of a single lime was added to ice cold water. Lime was chosen as the pH of lime juice is quite low (2.0 – 2.4) and the ascorbic acid content is high. Bananas were then introduced. The mixture was then blended at high speed for about 60 seconds. The result, appearing on the far left in the picture below indicates a “0” on the darkness scale.

 B all three

The first trial is in the middle and has reached a score of “5”, while trial 2 is a “4” after about an hour and a half.

Further high-speed blending with ice water and lime

The last trial was the same as the third except the mixture was further subjected to an additional 90 seconds of high speed blending (for a total of 150 seconds). This trial appears second from the left in the picture below. The third trial has now begun to separate after about a half hour but there is negligible browning.

B all four

Taste and flavor

Trial #1’s taste was bland; also a scum formed on the top of the glass. Trial #2 tasted much better initially but lost taste with time.

Trials #3 and #4 were far superior – strong banana taste but the citrus was evident and tangy. This remained the case after several hours.

The browning (oxidation) results are summarized on this table:

Elapsed time after blending, minutes 0 30 90
Trial type                Darkening score
1. high-speed blending, 60 sec 4 4 5
2. low-speed blending under water, 20 sec 2 3 4
3. high-speed cold water blending with lime, 60 sec 0 0 1
4. prolonged high-speed blending with lime, 150 sec 0 0 1

 

 

References

[1] Pandey, K. B., and Rizvi, S. I., (November 2009), Plant polyphenols as dietary antioxidants in human health and disease, Oxid Med Cell Longev 2(5), 270–278.

[2] Chaisakdanugull, C., and Theerakulkait, C. (2009) Partial purification and characterization of banana[Musa (AAA Group) ‘Gros Michel’] polyphenol oxidase, International J of Food Science and Technology 44, 840-846

[3] U ̈ mit U ̈ nal, M. (2007). Properties of polyphenol oxidase from Anamur banana (Musa cavendishii). Food Chemistry, 100, 909–913.

 

[4] Purification and characterization of polyphenol oxidase from banana (Musa sapientum L.) pulp.

  1. P. Yang, S. Fujita, M. Ashrafuzzaman, N. Nakamura, N. Hayashi

J Agric Food Chem. 2000 July; 48(7): 2732–2735.

[5] Penniston KL, Nakada SY, Holmes RP, Assimos DG; Nakada; Holmes; Assimos (2008). “Quantitative Assessment of Citric Acid in Lemon Juice, Lime Juice, and Commercially-Available Fruit Juice Products” . Journal of Endourology 22 (3): 567–570.

[6] Palmer, J. K. Banana polyphenol oxidase: Preparation and properties. Plant Physiol. 1963, 38, 508-513.