Science Buddies: "Ask an Expert"

In researching artificial preservatives, I found that many of them contain antioxidants that absorb oxygen molecules and prevent rancidity. My question is: what about antioxidants that occur naturally in fruits and plants? Can they have the same effect of inhibition on the oxidation process as the antioxidants in artificial preservatives such as BHT or propyl gallate? For my science project, I am comparing the effectiveness of naturally occurring antioxidants with synthetic (artificial) preservatives. For my IV, I am planning to use an antioxidant fruit extract, antioxidant rosemary extract and food grade Butylated Hydroxytoluene. The fruit antioxidant extract that I ordered online provided a ratio of 1-2 drops for every 8-16 ounces of water (it’s purpose is for fortifying water). The food-grade BHT I ordered online did not provide direction on ratio for application in food or otherwise.

I am trying to find a way to develop a standardized approach to measuring these three different mediums and the right amount to apply (not just guess). Can you help?

Hi mariaplayspiano,

Very interesting project idea!

One common way standardizing amounts is chemistry experiments is to use the same number of moles for the chemicals under comparison. That approach won’t work here because the extracts are mixtures of unknown amounts of various chemical compounds from the natural materials.

Instead, my suggestion is to use a standard weight for the extracts and the BHT. Please note that the extracts may be dissolved in water. For example I found one fruit extract online that stated it had 360 mg of extract ingredients per mL of solution. If that is the case with your extract materials I suggest using the appropriate volumes of extracts to get the same weight of extract ingredients.

To get an estimate of a reasonable weight to use, you might want to research BHT. The following link indicates that up to 0.01% BHT can be added to foods:

https://en.wikipedia.org/wiki/Butylated_hydroxytoluene

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman

Thank you for replying! It was very helpful.

I did a preliminary test on avocado samples with each of the antioxidant extracts: BHT, rosemary extract, and pomegranate extracts, and a control to observe whether or not the antioxidants actually did inhibit or slow down the oxidation process. I ran into a couple of issues.

The pomegranate extract has a very pigmented dark hue to it that imitates the brown that an avocado gets when it undergoes oxidative stress. The rosemary extract actually started out clear, but within a matter of minutes the extract itself turned a dark brown color as well. My initial idea was just to measure browning on the avocado but I am worried that I won’t be able to differentiate between the extract and the browning of the avocado. Is there any other way for me to measure oxidation besides browning? I read in various science journals that many food scientists measure thiobarbituric acid-reactive substances (T BAR) or peroxide values ( PVs) as an indicator of oxidation, but I am not sure I can replicate that or if it’s even applicable to what I’m trying to find.

Thanks again,
Maria

Hi mariaplayspiano,

Great idea on your preliminary experiment! How much of the colored extracts did you apply to the avocado samples? My thought is that if BHT is effective at a 0.01% application level (that’s 10 mg of BHT added to 100 g of avocado), then you might try a similar level of application of the rosemary and pomegranate extracts. Despite being colored, the small amounts of extracts added might not influence your color observations.

I’m not familiar with testing the effectiveness of antioxidants. But I did find a couple of review articles that list several test methods in addition to the ones you mentioned.

http://ucce.ucdavis.edu/files/datastore/608-46.pdf

http://nfscfaculty.tamu.edu/talcott/cou ... veness.pdf

I don’t think that any of the methods listed can be done outside of a laboratory equipped for that kind of work. Perhaps other contributors to this forum can suggest some suitable ideas for testing avocado oxidation.

I hope this helps. Please post again if you have more questions.

A. Norman