Science Fair Project:

Measuring Sugar in Fruit Using a Refractometer

2.8 based on 40 ratings

Research Questions:

  • How does a fruit become ripe?
  • What happens chemically when a fruit ripens?
  • How does the sugar content compare between ripe and unripe fruit?
  • Why are unripe fruits mealy and ripe fruits sweet?

The ripening of fruit is a complex procedure. Release of ethylene gas triggers whole families of enzymes, including amylases, kinases, hydrolases and pectinases to work their magic and neutralize acids, form anthrocyanins that give colors to fruit, and soften hard, inedible fruits into toothsome, delicious ones. One critical element of the ripening involves the conversion of starches to sugars. Farmer use refractometers to use monitor this process and measure sugar content. This helps them know when to harvest crops.

You can use a refractometer to measure sugar content in upripe and ripe bananas and evaluate how important the formation of sugars is in the ripening process. If other unripe fruits are available, expand this study to include these other fruits.

Materials:

  • Unripe bananas – (purchase the same day you start the experiment)
  • Refractometer
  • Graph paper

Experimental Procedure

  1. Select five green, unripe bananas that are nearly identical with respect to size and color.
  2. Read the directions for using the refractometer.
  3. Cut a three-inch length off one banana and mash it with a fork or run in through a blender or juicer.
  4. Put the banana pulp from the three-inch section into a cheesecloth and squeeze out a few drops of liquid.
  5. Test the liquid that you extracted using the refractometer. Record your results, noting the date, the fruit, the appearance of the fruit and the sugar content.
  6. Repeat steps 3 through 5 at least once with the remainder of the banana. All of these readings are your “Day One” results. Average them together.
  7. Repeat steps 3 – 6 for the next four days. By day five, you should have no more bananas.
  8. Graph your results. The y-axis can represent the refractometer readings and the x-axis can represent time.

Terms/Concepts: Ripening; Ethylene gas; Enzymes; Conversion of starches to sugars; Brix meter (refractometer); Abscission zone

References:

Books

Stuppy, Wolfgang and Rob Kesseler. Fruit: Edible, Inedible, Incredible. Firefly Books, 2008

McGee, Harold. On Food and Cooking: The Science and Lord of the Kitchen. Collier Books (1984)

Websites

Chemistry Lab Techniques: Refractometry

http://www2.ups.edu/faculty/hanson/labtechniques/refractometry/intro.htm

Ross Koning: Fruit Ripening

http://plantphys.info/plants_human/fruitgrowripe.shtml

Author: Cy Ashley Webb
Disclaimer and Safety Precautions

Education.com provides the Science Fair Project Ideas for informational purposes only. Education.com does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against Education.com that arise thereof. In addition, your access to Education.com's website and Science Fair Project Ideas is covered by Education.com's Privacy Policy and site Terms of Use, which include limitations on Education.com's liability.

Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.

How likely are you to recommend Education.com to your friends and colleagues?

Not at all likely
Extremely likely