Science Buddies: "Ask an Expert"

I'm doing a project on how apples and bananas affect the ripening time of a tomato. How should I quantitatively measure the "ripeness" of the tomato?

Thanks in advance,

-Lee

Hi Lee,

This sounds like a good experiment. Two of the measures often used for judging ripeness of tomatoes are color and firmness. There are a variety of ways to measure these - some might be very complicated and require specialist machinery. So depending on what grade you are in a how much equipment you have to hand you can do all kinds of things.

This area has been one of great interest to industrial food companies, such as Monsanto, over the last 15 years since researchers discovered the hormones involved in tomato fruit ripening. The food comapnies have lots of high tech ways to measure it but i think we can improvise.

If you had a high tech lab you could measure the amounts of the colored pigment molecules in the reipening tomato skin. But an easier way would be to compare the tomato skin color to a color chart by eye. You could give the colors a number scale going from green to red, with deeper reds being higher numbers. A more quantitative way would be to take a digital photograph and compare it to a digital color chart. You would want to make sure that you have a control object in the photograph so that you can calibrate the light to make sure that didn't effect the appearance of the tomato skins differently in different pictures ( i can explain more about this later if you decide to use this type of method).

For testing the firmness I think industrial labs probably have some kind of squishyness measuring machine! It would electronically measure the amount of pressure that could be applied to the tomato without bursting it. You could try using claipers to see how many milimeters the tomato can be squeezed without it causing a permenent indentation - you might have to put some kind of pads on the calipers so that the pressure is not concentrated to much in a very small area that would pierce the skin.

I would recommend picking either color or firmness and doing those experiments really well and developing a good method to test the effects of the other fruits.

Post back with your ideas about what you are going to do,

Best of luck,
Caroline

Thanks for your help!

-Lee

I agree with Caroline's excellent suggestions about color and firmness. For additional information about other properties that you could test, here is an abstract that mentions some other changes with ripening: http://taylorandfrancis.metapress.com/l ... 746055w1j2.

If time and resources allow, you could consider testing total soluble solids, acidity, and /or sugar contents.

The abstract also mentions "puncture resistance" which is typically measured with a "fruit penetrometer" with a scale of approximately 1-10 kg/cm2 (see http://www.ieindia.org/publish/ag/1205/dec05ag5.pdf). The commercially available versions of this instruments are not cheap (http://www.wagnerinstruments.com/wagner ... .php?cat=5) but you could easily make one yourself with a spring scale and a small cylinder of wood or metal.

I'm thinking about going with the firmness test, because judging the color may not always be 100% accurate. I've been to the supermarket, bought a perfectly red tomato, and still not have it taste ripe at all! (Why is that?!?)

Oh, by the way I'm a sophomore in high school.

Thanks again!