Science Buddies: "Ask an Expert"

My daughter has completed an experiment testing the brownning of apple slices over time that have been dipped in different liquids. Qualitative analysis of the results is fairly straightforward. However, we'd like to be able to quantify it. We have photos of the slices at each step. Is there any software that measures the relative brightness of digital images?

Hi Lee,

Measuring the degree of browning on an apple surface is difficult to do, but here is a paper that describes a method using spectrophotometer in reflectance mode measured at 400 nm. The authors actually did a scan over mutliple wavelengths, but 400 nm appears to quantitiate the brown color. This article also includes a description of the chemistry of browning, which is due to enzymatic oxidation of polyphenols in the apples. Your daughter can use this information in her background section if her science board, and add the reference to the bibliography section.

http://users.ipan.lublin.pl/~akucyski/E ... z_1994.pdf

If a spectrophotometer with reflectance mode is not available, then your daughter could try homogenizing the apple slices in a blender, filtering the sample, and then measuring the absorbance of the juice at 400 nm in a regular spectrophotometer. If the school doesn't have a regular spectrophotometer, then I recommend taking the photographs and setting up a scale from 1 to 10 (no browning to darkest brown) and rating the results using this visual semi-quantitative scale.

Good luck!

Donna Hardy

Thanks Donna!

We don't have that kind of equipment so the semi-quantitative scale seems like the best bet.

I also wonder about using a light meter pointed at a computer screen image of the slice.

What do you think about that?

Thanks, Lee

Hi Lee,

A light meter pointed at the photograph is a good idea. Please let me know if this method gives a quantitative result. I'm very interested in the outcome of your evaluation.

Donna Hardy