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Name: Sasha
Status: student
Grade: 9-12
Country: Australia\
Date: Fall 2013


Question:
I am wondering what is the difference between brown glass bottles and HDPE in terms of oxidation levels on a food. Which container is going to minimise oxidation the best, please?



Replies:
Sasha,

As with most problems involving speed comparisons (a kinetics question), there are so many possible factors that, often, the best way to answer the question is by trying the experiment. Off the top of my head I can think of several factors: pre-treatment of the contents (whether any oxidizing agents have been removed or reduced), thickness of the walls of the container, exposure of the containers to ultraviolet light or heat, etc. And, unfortunately, these factors often interact. The presence of oxidizing agents within the contents become even more important if energy such as UV or heat can enter the system, for example.

So, you will need to refine the question and try to isolate a factor. For example, if you can isolate gas permeability as the only controlling factor, then it is possible to look up a table of the permeability of glass and HDPE to oxygen (the main oxidizing agent) and make a determination as to which is better. Or if you can determine that the gas permeability is negligible, and the only important factor is UV, then you can look up a table of UV transmission through glass and HDPE.

Greg (Roberto Gregorius) Canisius College


Hi Sasha,

Thanks for the question. Oxygen does not readily penetrate glass bottles or HDPE bottles. The main source of oxygen getting into the food is through the seal in the bottle cap. Cycles of heating and cooling will allow a little bit of oxygen to get into the container. This is hard to prevent--even with additional sealing by wax. However, the brown glass bottles will absorb light and thus prevent the light from activating oxygen and inducing spoilage such as making fats and oils rancid. I recommend that food be stored in the dark and in the freezer and well-sealed. This method generally makes food last the longest time with minimal storage.

I hope this helps. Thanks Jeff Grell


Hi Sasha,

Assuming sealed containers, a glass container is essentially hermetic and will not permit any oxygen entry at all. A container made of HDPE is very slightly permeable to oxygen, and over a very long period of time, can allow minimal amount of oxygen to pass through and into the inside.

But practically speaking, unless you are planning to keep the food in the containers for years, and assuming reasonably thick walls in the HDPE container (say, 3mm or more), there will be no significant difference between the two containers regarding their ability to protect food from oxidation.

Regards, Bob Wilson


Glass has much lower oxygen permeability than HDPE (less O2 will transport through the glass into the food), so it will minimize oxidation compared with HDPE.

Burr Zimmerman


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