Milk degrading when exposed to light

Factual Questions
1

My friend claimed today that milk is better in opaque containers because when exposed to light, the milk is somehow degraded. Nothing on Snopes about this. Googling turns up some studies, but they seem to originate from trade groups who might have an axe to grind.

Anyone know anything about this?

2

A whole range of foods are affected by light. Two well known ones are beer and olive oil. Both gain bad tastes when exposed to light, and this is the prime reason they are (or should be) sold in dark glass bottles. In both cases there are specific chemical reactions that are triggered by light, that cause bad flavours to arise. Milk, and milk product flavours are highly sensitive to oxidation of lipids and fatty acids, and a photochemical reaction that can do this will quickly lead to the presence of a slightly rancid taste. Some proteins may also be cleaved, and you can get cabbage like smells. None of these reactions make the food “bad” in the sense that it has gone off. Although sometimes the taste changes are similar. But the tastes can reach a point where the milk is clearly affected and the palate decides it is degraded.

3

Thanks. How long would it take to notice these effects? I’ve bought milk in clear plastic for years and never noticed anything of the sort.

4

Hmm, I wonder if this is what’s going on with my milk. I live in a small town with only one supermarket, and because the store brand is about a dollar cheaper per gallon, I always buy that. About a third of the time, the milk has an off flavor and smell, even when it’s ten days before the sell-by date, and even when another half gallon bought the same day with the same date is fine.

It’s not bad enough to throw it away, but it’s bad enough that I keep it to the side to use for oatmeal, because I put so much cinnamon in my oatmeal that it overpowers everything else.

5

I just put mine in the fridge, which is dark inside.

6

Whenever I look in mine, it seems to be all lit up.:stuck_out_tongue:

7

Hood brought out their “LightBlock” jug a few years ago, with much fanfare. I fail to see how it can make much of a difference over the lifetime of a gallon of milk, most of which is spent in a dark refrigerator.

8

I can remember this being a thing like, 30 years ago maybe, early 80s. Some study claimed that UV from florescent lights (like in convenience stores) depleted the nutritional value of milk stored in translucent plastic jugs compared to milk in cartons. For a brief period after some places were selling two half-gallon cartons bundled together at the same price as the gallon jugs because of this.

Must have been junk science cause it didn’t last.

9

UHT milk is in light (and UV) proof tetra-pak to ensure it doesn’t degrade due to light.
Note this is for UHT milk - meant to be good for a year after purchase…
Its the effect of lots (17) of days worth of light being tested.
It is important.

A 1994 book mentions why

Summary, it could degrade - taste bad, develop a funky colour, and be less nutritious.

10

IT IS VERY TRUE that light exposure affects the flavor of milk and other dairy products. The flavor developed is called “oxidized flavor”. This flavor is undesirable but many consumers are already used to drinking milk with oxidized flavor due to the prevalence of clear milk jugs. The flavor is developed due to a number of factors:

  1. Riboflavin- Milk is a a very good source of riboflavin and this vitamin is a “photosensitizer”, meaning that it can get excited in the presence of light and create many unstable oxygen species that can begin creating radicals or molecules with unpaired electrons from fats and proteins present in milk. This creates peroxides which further degrade to many other smaller molecules that have a low threshold ( a little bit present and we can detect them) and very bad taste (descriptors used are burnt feathers, grassy, fatty, paint-like, etc).
  2. Unsaturated fats in milk- this is usually affected by the type of feed the cows consumed ( grass fed cows are more susceptible to this defect due to the increase in unsaturated fats). More unsaturated fats equal more double bonds and these bonds are more likely to get attacked by the unstable oxygen species.
  3. Prooxidants naturally occurring in milk such as iron, copper, or even some vitamins such as Vit E and Vit c (if present in very high concentrations). These prooxidants can also initiate the development of oxidized flavor to the fact that they can easily donate or receive electrons.

These are only a few of the factors that give rise to this flavor defect, there are many others.
Clear plastic jugs do not protect from this defect, white block containers help a bit but do not protect 100% either. The yellow containers provide better protection but they are not easy to find.
I am a graduate student at Iowa State University and my research involves understanding the effect of light and metal on the development of oxidized flavor in milk.
If you want more information regarding this issue, visit this page by the University of California, it can help explain this issue in more detail:
http://drinc.ucdavis.edu/dairyp/dairyp3.htm