The oxidation levels of bananas

How do the different oxidation levels of bananas by the number of days affect the sugar (C12H22O11) content of a banana, measured using a refractometer by percentage (%)?

I. Background Information
As we see a banana transform from its green color to a yellow color and then all the way to a brown-black color, this process is known as fruit ripening. Fruit ripening is a coordinated process of transforming fruits from unripe to ripe stages. A series of physical and chemical changes take place in bananas during ripening that converts it to edible fruit. During the ripening process, the starch, which is the main component of unripe bananas, is transformed into sugars (commonly sucrose). Unripe bananas contain around 80% starch weighted dry, and the fully ripe bananas will end up with less than 1% starch. The proteins in the bananas will create certain chemical reactions that transpire quicker than normal. So the amylase breaks down the existing starch in unripe bananas to produce simple sugars and hence is accountable for increasing the sweetness/ sugar content of ripe bananas. Ripe bananas can reach up to a total of 20% sugar content.

The ripening process is also triggered by ethylene (C2H4), an odorless organic compound, with carbon to carbon double bond structure, and a gaseous hormone that causes fruit to ripen. Bananas produce ethylene in response to the environment as it reacts with open-air oxygen. As bananas ripen, it releases more ethylene gas in the air to form carbon dioxide and water. These products can then aid in the ripening process of bananas. The chemical reaction for this would be C2H4 (g) + 3 O2 (g) → 2 CO2 (g) + 2 H2 O (l). As the gas diffuses easily, it is able to travel through nearby fruits, in this case, are the other bananas going to be tested on. The gas causing the ripening will then soften the surface of the banana, converting starch into sugars.

As for the browning process of the bananas that can be seen as they sweeten over time, they involve the oxidation with oxygen in the atmosphere of compounds, inside the banana flesh. The oxidation is then catalyzed by polyphenol oxidase, a copper-containing metalloprotein, found in bananas. This oxidation process produces quinone (C6H4O2), an organic compound leading to the conversion of brownings in bananas. The oxidation acts as a “rust” forming pigments on the surface of the bananas.

The methodology of measuring the amount of sugar present in the banana is also a critical step. The commonly used instrument to measure sugar content is known as a refractometer. This instrument will consider the higher amount of sugar present in the banana, causing it to bend a beam of light. The unit to measure the amount of sugar in a dissolved solution is known as degrees Brix. A 15° Brix solution consists of 15 grams of sugar in every 100 grams of solution. A few drops of liquid extracted from the bananas will be placed on the refractometer’s glass, and the reading of the degree Brix on the scale visible through the eyepiece will be seen. Solutions containing a greater sugar content will cause more refracting light which will then be reflected on the scale.

If the time of a banana’s ripening process is increased, then it will result in higher sugar content. It can be explained that the increasing amount of time allows more starch broken down into sugars, and letting ethylene to pass through and expose the bananas with this gas, causing more oxidation to occur, and hence more sugar will be transformed in the fruit.

Variable Description
Independent variable Time: number of days
(1 day, 2 days, 3 days, 4 days, and 5 days), The independent variable of the experiment will be mainly emphasized on the different amount of days that will be affecting the level of ripeness of the bananas. This will be done by ensuring that the experiment will take place over 5 days, letting one banana to be tested on each day.

So as we start with 5 unripe bananas, the first day will require only one of the bananas to be tested on. As the second day goes by, the same procedure will be done, and so on until the fifth day. This will allow us to see how much sugar concentration increases gradually over time. The very first banana should result in the weakest sugar concentration while the last banana should be the one to result in the highest sugar content.
Dependent variable Amount of sugar (C12H22O11) content present

As bananas go through various ripping stages, they will tend to have increased sugar content over time. The sugar content will be measured by using a refractometer, as it will be able to analyze the sugar percentage contained in the tested fruit. The liquid from the banana will be extracted and dropped onto the surface of the refractometer. This instrument will then include a scale showing the results in degree Brix, with the uncertainty of ± 0.1.

No. Controlled Variables Significance Solution

  1. Location The different locations where the bananas are stored could impact the ripping process as the air circulation in the area could differ. To ensure accuracy, all the bananas will be placed in the same location.
  2. Temperature Temperature differences may also affect each banana as a lower or higher temperature could either quicken or slow down the ripening process. To avoid possibilities of errors, the temperature where the bananas will be placed will be at room temperature, specifically around 22°c (more less).
  3. Time Tested The inconsistent duration of when each banana will be tested during the day could project a higher or lower sugar concentration that it should actually be, impacting the accuracy of the experiment. The testings will be conducted at the same time of the day, every day for the course of five days.
  4. Amount The amount of extracted liquid banana to be placed in the refractometer may affect the readings, hence it should be persistent to avoid misreadings. The amount of liquid banana extracted that will be taken to be tested on will remain the same, which is 0.2 mL each trial. A dropper/pipette will be used to help measure the liquid.
  5. The instrument used (refractometer) If the instruments used are not consistent with only one, it could result in inaccuracy as different instruments may have different uncertainties. Only one refractometer will be used throughout the experiment to allow consistency.

II. Apparatus

  1. Bananas (unripe; 1 per increment for 3 trials, so 5 large bananas total)
  2. Cheesecloth
  3. Glass bowl
  4. Pipette/ dropper
  5. Metal fork
  6. Metal knife (use with safety)
  7. Refractometer

III. Procedure and Safety

  1. To start, provide five unripe bananas. The bananas should be as similar in size and color (green) as possible. The first reading must start with bananas that are unripe.
  2. Prepare the refractometer that will be used. Read the directions and understand how to use it.
  3. Take one banana, and carefully cut off 5 cm of it using a knife. (Note: Starting on the first day with the unripe banana and continuously ripening, over the course of 5 days.)
  4. Place the chopped piece of the banana into a plate or a bowl, and mash it with a fork until completely smooth.
  5. Prepare a small cheesecloth, and lay it on a flat surface.
  6. Take the mashed banana mixture and gently pour it onto the cheesecloth.
  7. Grab the cheesecloth, and begin squeezing the mashed banana until a good amount of liquid has been gathered into a small bowl.
  8. Using a pipette, measure 1 mL of the banana liquid and place it onto the refractometer.
  9. Proceed to read the sugar content of the banana.
  10. Record the data. Ensure to collect the trial number, the day tested, condition of the banana, and the sugar concentration.
  11. Repeat steps 4 to 8 with the remaining amount of banana, for two more trials. (Make sure to use a separate cheesecloth to maintain accuracy.) There should be a total of three readings of the banana.
  12. Repeat steps 3 to 10 with the remaining 4 bananas as they ripen each day.
  13. Perform the trials 2 more times. (There should always be a total of 3 trials per banana and per day.)

Safety Consideration
No. Situation The risk How to minimize the risk/ avoid it?

  1. Chances of the materials breaking
    If we do not handle the glass bowl carefully, there will be a chance of it accidentally falling and breaking since it is made out of glass. Those small glass pieces are very hazardous as they are very small and sharp. So if not handled properly, it might lead to injuries in the case of the glass pieces getting in contact with our bearskin. To avoid any possibilities of this situation from happening, the glass bowl that will be used in this experiment must be handled very carefully. Ensure to place it in a safe area or nowhere near the edges of a table in order to prevent it from falling off the table or the surface worked on.
  2. Beware of heavy equipment
    Materials/ equipment such as the refractometer may be heavy. It also has chances of falling over the working area and possibly breaking. To prevent any damage caused by the heavy materials used in this experiment, make sure that the refractometer is placed on a safe surface and not on the edge of the table at all times.
  3. Not using any safety equipment when conducting the experiment
    If safety equipment is not used when conducting the experiment, it may lead to injuries from the metal knife. To refrain from any incidents that may be caused when conducting the experiment, ensure to use all the safety equipment before starting the experiment. Use gloves, a lab coat, gloves, and other necessary equipment.

IV. Data Collection and Processing
a) Raw Data

Quantitative Observations
Independent variable: Different oxidation levels measured by days Dependent variaSugar concentration of banana
Unit: ° Brix
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5
Day 1 16.2 15.8 16.0 15.8 16.0
Day 2 18.0 18.4 18.0 18.0 18.2
Day 3 20.4 20.2 20.2 20.0 20.4
Day 4 21.4 21.0 21.2 21.2 21.2
Day 5 22.2 22.2 22.4 22.2 22.6

Qualitative Observations

  1. Day by day, the observed surface of the banana visibly darkens. It gradually went from a green color, yellow, and all the way to dark brown.
  2. The smell of the bananas each day also differed. It started off very bland and ended very sweet smelling.
  3. The extraction of ‘liquid’ from the bananas was getting easier each day due to the flesh softening.

Processed Data
b) Calculating the averages of the sugar concentration of banana
[(Trial 1 + Trial 2 + Trial 3+ Trial 4 + Trial 5) / 3]

  1. Day 1 = (16.2 +15.8 + 16.0 +15.8 +16.0) / 3
    = 15.96 ° Brix
  2. Day 2 = (18.0 + 18.4 + 18.0 + 18.0 + 18.2) /3
    = 18.12° Brix
  3. Day 3 = (20.4 + 20.2 + 20.2+ 20.0 + 20.4) / 3
    = 20.24° Brix
  4. Day 4 = (21.4 + 21.0 + 21.2 + 21.2 + 21.2) /3
    = 21.20° Brix
  5. Day 5 = (22.2 + 22.2 + 22.4 + 22.2 + 22.6) / 3
    = 22.32° Brix

c) For taking uncertainty for average
[(Maximum data – Minimum data) / 2]

  1. Day 1 = (16.2 – 15.6) /2
    = ± 0.3
  2. Day 2 = (18.2 – 17.6) / 2
    = ± 0.3
  3. Day 3 = (19.2 – 18.8) / 2
    = ± 0.2
  4. Day 4 = (20.4 – 19.8) / 2
    = ± 0.3
  5. Day 5 = (22.4 – 21.8) / 2
    = ± 0.3

d) Graphs

As seen in the graph, by plotting the degree Brix obtained from the spreadsheet, against time measured by the number of days, an increase in the sugar concentration of the bananas can be seen throughout. From day one to three, the graph seems to be increasing consistently, at approximately 2° Brix each day. This shows how the ethylene (C2H4) within the banana is reacting more gradually with the oxygen around it, causing the rate of reaction of its ripening to increase. This then aids the breaking down of the cell walls and the conversion of starch to sugar, and hence yielding a higher sugar concentration. However, progressing to day four and five, it seems that the formation of sugar in the bananas are slowing down. This indicates that the bananas have also been oxidized to the point where there is less starch to convert to sugar, and so the trend continues to increase but at a lower rate, at about 1° Brix each day. Overall, a positive linear correlation can be seen, The higher the time, the higher the change in sugar content

V. Conclusion

VI. Analysis
Sources of Error and Improvements

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