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Fruit: When You're Ripe, You're Right

based on 4 ratings
Author: Maxine Levaren

Sometimes the most common situations can spawn great project ideas. For example, did you ever wonder why fruits bought at the same time ripen at different speeds?

Well, for her science project, Shannon Gonzalez decided to find out. Her project display is shown in the figure below.

Figure: Project display for “Fruit, when you are ripe, you are right.”

Hypothesis

I believe that pears will ripen at different speeds due to their environmental conditions.

Independent variables

  • Temperature
  • Light

Dependent variables

  • Refractive index, the ratio of the velocity of light in a vacuum to the velocity in a medium
  • Condition of pears

Controls

  • Pears used
  • Process of testing

Experimental groups

  • Group B: 15 pears refrigerated
  • Group C: 15 pears at room temperature
  • Group D: 15 pears in dark areas
  • Group E: 15 pears at natural outdoor temperature

Control groups

Group A: 15 pears immediately after purchase

Materials

  • 75 unripe pears
  • Scalpel
  • Glass test tubes
  • Ohaus balance (a digital scale)
  • Distilled water
  • Sorvall Mc 12v (used to create centrifugal force to squeeze juice from a piece of fruit)
  • 5–40 micro liter finnpipette, a device used to dispense liquid
  • Pipette tips
  • Refractometer, used to measure the turning of a light or sound wave
  • 95 percent ethanol solution
  • Paper
  • Tape
  • Permanent marker
  • Scissors
  • Journal/log

Procedures

  1. Divide the 15 unripe pears into five groups, with each group containing three pears.
  2. Label each group, for example: A1, A2, and A3 . . . E1, E2, E3.
  3. Prepare fruit for testing and place in glass test tube.
  4. Weigh the test tube on the Ohaus balance to determine the amount of distilled water that must be placed in the empty tube for balance.
  5. Place an empty glass tube on the Ohaus balance.
  6. Place both tubes on opposite holes in the Sorvall Mc machine.
  7. Set the Sorvall Mc 12v at maximum speed (1200 rpm) at 2 minutes.
  8. Remove tubes, extract the pear juice with a device called a finnpipette set at .10 microliter.
  9. Get refractive index, using refractometer.
  10. Repeat Steps 2 through 8 with all samples in group A.
  11. Repeat Steps 3 through 10 with group B pears (refrigerated).
  12. Repeat Steps 3 through 10 with group C pears (room temperature).
  13. Repeat Steps 3 through 10 with group D pears (in dark area).
  14. Place group E pears on a windowsill where they can be exposed to the natural outdoor temperature and repeat Steps 3 through 10.
  15. Leave the pears in their given conditions for a week and observe the ripening process (appearance and feeling).
  16. Average all the readings for groups A, B, C, D, and E.

Results

Comparing the averages for all the pears, I found that they ripened in the following sequence (fastest to slowest):

  • Group E: natural outdoor temperature
  • Group D: darkened area
  • Group C: room temperature
  • Group A: immediately after purchase (control group)
  • Group B: refrigerated

Conclusions

The hypothesis was correct because all the pears ripened at a different rate due to their different environments. The refrigerated fruit had the lowest refractive index because refrigeration stopped the production of ethylene, a hydrocarbon gas that makes fruits ripen. The fruits that weren’t placed in the refrigerator began to ripen because hydrolases (substances that cause the chemical reaction of a compound with water) broke down the chemicals found inside the pears.

These chemical changes also caused external evidence of ripening. When the chemicals and acids broke down, sugar was produced, which increased the juiciness of the fruit, and produced a scent. The breakdown of chlorophyll also contributed to the fruit’s discoloration.

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