I recently received a question about bananas.
Is it true that a full ripe banana with dark patches on the skin produces TNF (tumor necrosis factor) which has the ability to combat abnormal cells? Therefore the riper the banana the better the anti-cancer quality. Please enlighten us.
Very interesting question,
I actually did some research online and found this Japanese journal article, and what I can say is that I am actually quite skeptical. There are a few reasons for my skepticism.
1. This is actually a mice model. Many people outside of the scientific community have no idea how mice model results have failed to transpose to humans.
2. The banana extract is given intravenously to mice. Anybody with some biology in high school will understand that taking things orally and intravenously can be totally different. If the Japanese scientists found that there are increase in immune cells in the mice, I would argue that anything that is injected intravenously would somehow induce the immune response against this xenobiotic, hence the proliferation of immune cells.
From a food scientist point of view, again I am skeptical that the black part of the bananas are producing TNF. Why?
1. We understand the blackening of bananas as one of the two mechanisms:
• The diminishing of carotenoids, hence exposing black pigments or
• The aggregation of compounds, creating a mass of black pigments, hence covering up the indigenous yellow pigments.
I am more inclined towards the latter. We also know that banana emits ethylene constantly (Yes, banana is an ethylene producing machine, so if you want to ripen whatever fruit, just put it in a bag with bananas, and yes if you put it one day longer, everything will rot, haha!). So the black pigments are actually signs of cell death. Just like when you put your bananas in the refrigerator. Bananas are so chill-liable, that once exposed to even refrigeration temperature (4 degrees Celsius or 39.2 degrees Fahrenheit), oxygen transfer across the cell membrane becomes impaired, so your banana dies and becomes black.
2. Even if bananas produce TNF, how likely is it to survive your stomach acid and digestive proteases in your gastrointestinal tract and still is able to be absorbed into your bloodstream intact as TNF? We all know that TNF is a protein complex, and most protein complex diminishes into smaller units to aid transfer into the bloodstream.
All in all, I just think that this needs more research. We can either do an oral challenge in mice model again, or simply do a human study (It’s not like you’re feeding them arsenic, you’re feeding them banana extract, duh!)
So, if you think you should eat black bananas versus yellow bananas, you are wise. It’s not because it produces TNF, it’s because it’s sweeter and tastier (because most starch have broken down to simple sugars by now).
Author: Ben Yeap, M.S., Coalescence Food Scientist