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Recently while visiting a shop with electronics I saw a fridge with a huge advertisment sticker going more or less like this:

There's blue light source in this fridge so there will be less bacteria inside and your fruits will have larger quantities of vitamins.

Can it be true? How can dead (picked, transported and refrigerated) fruit produce more vitamins? How does blue light affect this?

Furthermore I thought that only UV light kills bacteria.

Therefore my question is: how much truth was on that sticker?

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  • $\begingroup$ Until proven by the manufacturer, I would see this as an unsubstanciated marketing claim. $\endgroup$ – Chris Oct 16 '17 at 8:44
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    $\begingroup$ Fruits and vegetables are generally not dead. Most fruit contains seeds, which will grow if planted. (Aside from those bred to be seedless or sterile.) Many vegetables, e.g. potatos & onions will likewise grow, and sometimes will sprout even in the refrigerator. $\endgroup$ – jamesqf Nov 15 '17 at 19:32
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Maybe a little bit?

There are two claims here, so let's talk about them individually. I'm not sure how this light is being produced (probably LED), but it'll have a wavelength somewhere between 400 and 500 nanometers.

Reduced bacterial presence:

The intrinsic antimicrobial activity of blue light is well documented. Although the mechanism is not entirely understood and widely debated, the commonly accepted hypothesis is that the blue light triggers the production of reactive oxygen species like singlet oxygen that are highly toxic. However, this has only been observed under high-power light sources, and low levels of light may actually increase bacterial activity. What counts as a high-power source, you ask? The number from this article is $\frac{10mW}{cm^2}$. For a fridge with an internal surface area of >1 meter, such a power source should draw at least 100 W. Given that normal refrigerators use draw 100-200 watts, you'd essentially be doubling your electrical bill for the fridge.

It should also be noted that the above is a best-case scenario. As soon as you add anything to the fridge, you'll reduce the intensity and thus the effectiveness of the light source. Also, the light is unlikely to be on all the time- it probably turns on when you open the door and turns off when you close it. While this helps a lot with power use, it minimizes the effect of the blue light, which is constantly on in experiments.

Larger quantities of vitamins

There's no (reliable) evidence of light of any kind actually creating vitamins, so what the sticker suggests is that it doesn't degrade the vitamins already present as quickly as other kinds of light.

There's a good article here that discusses the stability of various vitamins. It's worth noting that most of these vitamins and essential amino acids are much more likely to be destroyed by cooking than light, which is probably why the fridge focuses its claim on fruits, which are less likely to be cooked.

There's very little research that I was able to find about the effect of different wavelengths of light on the stability of various vitamins, but as a whole I remain fairly skeptical that there's any notable difference. Most experiments that do study degradation of vitamins under light subject pure vitamins to high-intensity light for several days- unlikely to happen in your fridge.

TL;DR:

A claim like this shouldn't be a major factor in your buying decision. The effects of the blue light are probably negligible given the conditions in your fridge, but if you've got two very similar choices this feature could act as a nice tiebreaker. Besides, there's a lot to be said about how cool blue light looks and the confirmation bias present in your purchase.

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  • $\begingroup$ wooooooowwwwww :O $\endgroup$ – user46147 Dec 17 '17 at 12:33
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Light's pulse perturbs the surrounding medium. If the surrounding medium is a living thing, it perturbs the living thing.

The higher the energy of light, the faster the light's pulse; the faster the light's pulse, the shorter the wave-length; the shorter the wave-length, the larger number of compressions ("machine-gun shots") per unit of distance that the perturbation (wave) travels; the larger the number of machine-gun shots, the larger the damage.

Blue light has more energy than green light (which has more energy than red light) but less energy than UV light. Hence, blue light is less efficient than UV light. Some bacteria are more sensitive to light than others; the less sensitive, the higher the energy light is needed to achieve a comparatively same antibacterial effect.

A long-term exposure of bacteria to light---that is damaging to the bacteria but does not kill them all---can lead to a selection of resistant mutants.


https://www.ncbi.nlm.nih.gov/pubmed/29046782

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Good question. Asian fridge moguls want to shine blue light on your chopped fruit, mostly, rather than save your life from a hazardous food.

Some research by National University of Singapore studied the effect of visible blue light diodes on some bacteria although not fungi which makes the fruit go moldy (mould propagation in apples is a common bio practical study).

The bacteria studied are not fruit surface bacteria. they are gut and skin bacteria.

The study did not test if fruit last longer in blue light. it just exposed gut and necrotizing bacteria to blue light.

You may get less E-Coli and salmonella, which is weird because you would have a very unwholesome fridge to have a E-Coli danger from it. fruit is not only consumed by bacteria. Salmonella dangers exist inside certain eggs, which is a dark environment. Fruit practically can't transmit major illnesses like S.Aureus, they live in different environments than fruit and are endemic to humans, but fruit do contain a lot of microorganisms necessary for their fermentation and to break them down.

Blue light perhaps increases your appetite too. https://www.sciencedaily.com/releases/2014/06/140602115916.htm

The raw scientific research for it from 2015 is not for funghi or yeasts, and it doesn't penetrate a steak properly, so it's fairly misleading marketing.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

  • $\begingroup$ And how would the blue light help the salad or make people less greedy? $\endgroup$ – skymningen Oct 16 '17 at 9:31
  • $\begingroup$ I found more qualified research which states that blue light can increase your appetite. previously I had read the opposite statement. good comment. sciencedaily.com/releases/2014/06/140602115916.htm $\endgroup$ – com.prehensible Oct 16 '17 at 9:44
  • $\begingroup$ That is actually something that makes a little sense to me, as in general, I have always heard that blue makes people "more comfortable". Some people eat more when they are comfortable, while others eat less, though. $\endgroup$ – skymningen Oct 16 '17 at 11:40
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    $\begingroup$ "fruit is not consumed by bacteria" Can you support this with a source? $\endgroup$ – anongoodnurse Oct 16 '17 at 13:28
  • $\begingroup$ I'll rephrase it.. fruit is not ONLY consumed by bacteria. ask your local fungicide toting farmer. can you support a motion that suggests that fruit treated with antibiotics will not develop fungal and yeast decomposition? if not, the result is the same. The science does not protect fruit from funghi. let's just say that no one puts antibiotics on their fruit to prevent rotting. They industrially use fungicides. $\endgroup$ – com.prehensible Oct 17 '17 at 5:32

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