Introduction: (Initial Observation)
Growers of bananas, harvest their produce when it is still green. This gives enough time to growers for storage and distribution to the consumer market. As time passes, green bananas gradually turn yellow. That is the color that we usually see bananas in stores. Color change in a banana continues at home and it finally turns brown. During this change, the taste of a banana also changes.
Sugar content of fruits is usually one of the dietary concerns for consumers. You need to know how much sugar you are consuming each day, especially if you are under a restricted diet. In this project you will study bananas or any other fruit of your choice to determine its sugar content. You may choose to study the sugar contents of any specific fruit at different stages and see if the sugar content changes by the age of the fruit. You may also choose to compare different species of a specific fruit. For example you may compare the sugar content in different types of apples or different types of grapes.
Gather information about different types of sugar and how they can be identified or extracted. Read books, magazines or ask professionals who might know in order to learn about the type of sugar found in plants and fruits. Keep track of where you got your information from.
Following are samples of information that you may find on the Internet.
As a banana ripens, turning from a green to a yellow, the starch in the fruit is converted to sugar – making the banana sweeter! The best time to eat a banana is from a stage 5 to a stage 7. If your bananas are not quite at the stage you like, let them ripen a little longer. It only takes about a day for a banana to progress one-half to a full stage. Use the color chart below to help you identify the ripening stage of your bananas.
As received at your warehouse from Central and South America
First color change during warehouse processing, usually seen on the shoulder.
50% Green, 50% Yellow
Recommended color for warehouse outturn. Adjust back or ahead for delivery time, temperature, distance and retail color preferences. Consumers purchase now to enjoy later.
More Yellow Than Green
Ready for retail display. Great eye appeal and long product life. Minimum shrink for retailer.
Yellow With Green Tips
Most popular color stage for consumer purchase. Since higher temperatures speed color change, this color can be maintained longer by holding boxes in a cool area at 56° to 60°F.
Firm fruit with great eating flavor. easily bruised – handle with care.
Yellow Flecked With Brown
Sweet eating flavor. Perfect texture and consistency for blender drinks and baking
Instead of comparing different types or colors of banana, you can compare different types of carrot for their sugar contents. That will be a similar project with similar procedures.
They don’t have to be orange, carrots can come in a wide variety of colors derived from several different pigments.
Upper left is a conventional “orange” carrot. The color is due mainly to beta-carotene, with some alpha-carotene, both of which are orange pigments. Center left is a “yellow” carrot, whose color is due mainly to xanthophylls (a type of carotene). Bottom left is a “red” carrot, due mainly to lycopene (another type of carotene, also found in tomatoes), in addition to some beta- and alpha-carotene. Upper right is a “purple” carrot, due to pigments in an entirely different class, the anthocyanins. Lower right is a “white” carrot, the color of a carrot with none of these pigments.
Sucrose is a disaccharide, composed of one molecule of fructose attached to one molecule of glucose. Fructose and glucose are reducing sugars, but sucrose is a non-reducing sugar.
How to identify sugar? Is there a reagent for sugar?
The early biochemists devised analytical methods for the detection and quantification of sugars. Some of these tests (e.g., Fehling’s reagent) were based on the aldehyde or ketone groups in the sugar structures. Sometimes the test gave a color change as a metal ion was reduced to the metal itself or to an ion of lower oxidation state. In other words, the reagent oxidized the sugar while the sugar reduced the oxidation state of the ions.
Sugars form rings that involve the aldehyde or ketone group. The ring forming and opening again is reversible unless the hemiacetal or ketal hydroxyl group has become involved in another link. Rings that are locked have no aldehyde or ketone group to react (unless there are several rings, and one can open) and are non-reducing sugars. There is one glucose ring at the end of each chain in starch and cellulose, but its effect is too small to produce a positive test.
When only one sugar is present and it is a reducing sugar, one of these old tests may still be an adequate and inexpensive method for measuring a sugar concentration. For example, a flow system with a colorimeter may be used for on-line detection. However, enzymatic methods that use the specificity of the enzyme for one sugar are very common. Even better are chromatographic procedures that will measure the different sugars in a mixture.
Two main reagents used to identify or estimate the amount of reducing sugar in a liquid are Fehling’s solution and Benedict’s solution.
Simple sugars like glucose and fructose reduce Fehlings solution, giving a red precipitate from the initial blue solution; sucrose does not.
Fehling’s solution is a deep-blue alkaline solution of copper sulfate and potassium tartrate and sodium hydroxide that is used to test for sugar in the urine; solution turns reddish when sugar is present.
Fehling’s solution (Alkaline Cupric Tartrate) is also a reagent for the presence of aldehydes (e.g., formaldehyde, HCHO)
Fehling’s solution is prepared just before use by mixing equal volumes of two previously prepared solutions, one containing about 70 grams cupric sulfate pentahydrate per liter of solution and the other containing about 350 grams Rochelle salt (potassium sodium tartrate tetrahydrate) and 100 grams sodium hydroxide per liter of solution. The cupric ion (complexed with tartrate ion) is reduced to cuprous ion by the aldehyde (which is oxidized) and precipitates as cuprous oxide (Cu2O);
Benedict’s reagent (Alkaline Cupric Citrate) is a solution of copper sulfate, sodium hydroxide, and tartaric acid. Aqueous glucose is mixed with Benedict’s reagent and heated. The reaction reduces the blue copper (II) ion to form a brick red precipitate of copper (I) oxide. Because of this, glucose is classified as a reducing sugar.
Aqueous glucose is mixed with Benedict’s reagent, a solution of copper sulfate, sodium hydroxide, and tartaric acid. The mixture is heated. Carbohydrates which react with Benedict’s reagent to reduce the blue copper (II) ion to form a brick red precipitate of copper (I) oxide are classified as reducing sugars.
Results of Benedict’s Test with Glucose, Sucrose, and Fructose
One liter of Benedict’s solution contains 173 grams sodium citrate, 100 grams sodium carbonate, and 17.3 grams cupric sulfate pentahydrate. It reacts chemically like Fehling’s solution; the cupric ion (complexed with citrate ions) is reduced to cuprous ion by the aldehyde group (which is oxidized), and precipitates as cuprous oxide, Cu2O.
How to make alkaline Cupric Citrate?
(Benedict’s qualitative reagent). With the aid of heat, dissolve 173 g of sodium citrate (C6H5Na3O7·2H2O) and 117 g of sodium carbonate (Na2CO3·H2O) in about 700 ml of water, and filter through paper, if necessary. In a separate container dissolve 17.3 g of cupric sulfate (CuSO4·5H2O) in about 100 ml of water, and slowly add this solution, with constant stirring, to the first solution. Cool the mixture, dilute to 1000 ml, and mix.
What other chemicals can be used as reagent for reducing sugar?
In addition to alkaline cupric citrate and alkaline cupric tartrate, many other complex ferric and cupric salts including tartrates, acetates, citrates and oxalates may be used for this experiment. Citric, acetic, tartaric and oxalic acids are all weak acids, so they form a weak bound with copper or Iron. This makes it easy for a reducing substance to reduce metal ions to metal itself or to an ion of lower oxidation state. We call them complex salts because they have two different metallic ions such as sodium and copper. The ratio of such elements is like you actually mixed one molecule gram of each salt.
Quick test: Cupric Sulfate/Ammonia
I have successfully used cupric sulfate solution in ammonia for this test. This is easier to prepare because you are eliminating citric or tartaric salts. Copper sulfate can be purchased from pool suppliers and hardware stores. Ammonia is used as a detergent and can be found in supermarkets. To make the solution, first prepare a saturated solution of copper sulfate. Start to add ammonia (ammonium hydroxide) gradually while stirring. initially copper hydroxide and ammonium sulfate will form and the solution turns white. As you add ammonia, copper hydroxide will dissolve in ammonia and the solution turns to deep-blue. At this time your copper-ammonia complex is ready.
Another Recipe for Benedict’s reagent.
According to “Lange’s Handbook of Chemistry” (10th ed., 1956), Lange, N. A., McGraw-Hill, NY, there are two Benedicts’ solutions, qualitative and quantitative.
|Sodium citrate (Na3C6H5O7-2H2O) – 173 g.
Sodium carbonate (anhydrous) – 100 g.
Copper sulphate.5H2O (the blue stuff) – 17.3g.
Dissolve the sodium citrate and the sodium carbonate in 600 ml of distilled water. When dissolved, dilute to 850 ml. Dissolve the copper sulfate in 100 ml of distilled water. When dissolved, dilute to 150 ml. While stirring continuously, slowly add the copper sulfate solution to the citrate/carbonate solution.
(for sugar in urine)
|Copper sulfate (pentahydrate)- 18 g.
Sodium carbonate (anhydrous) – 100 g.
Potassium citrate (K3C6H5O7-H2O) – 200 g.
Potassium thiocyanate (KSCN) – 125 g.
Potassium ferrocyanide (K4Fe(CN)6-3H2O) – 0.25 g.
Dissolve into distilled water, and make up to a final volume of 1 liter.
1 ml equates to 0.002 g sugar.
Benedict’s Quantitative Reagent
In about 600ml of hot water dissolve
- 200g of sodium citrate
- 75g sodium carbonate
- 125g potassium thiocyanate
In about 100ml of water dissolve
- 18g of copper sulphate.6H2O .
When the solutions have cooled mix them together stirring constantly. Add
- 5ml of 5% potassium ferrocyanide then make up to 1L..
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to compare the sugar contents of green, yellow and brown bananas.
Which banana has a higher sugar content? Yellow or brown?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
- Independent variable is the color of banana.
- Dependent variable is the sugar content.
- controlled variables are the the experiment procedures and environmental conditions.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following is a sample hypothesis.
The sugar in a banana increases as the banana turns to yellow and then brown. My hypothesis is based on my gatherd information about photosynthesis and production of starch in plants. Starch later breaks down to simple sugar by the action of enzymes. As time passes more starch will break down to sugar.
This is another hypothesis:
The sugar content in green, yellow and brown bananas are the same. My hypothesis is based on my gathered information that fruits have no way of getting additional water and nutrients after they are separated from the tree.
What do you think? What is your hypothesis?
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Sugar in fruits is a simple sugar known as fructose. Simple sugars are reducing substances and can react with oxidizers. For example a simple sugar such as fructose or glucose may reduce a metal ion to metal itself or to an ion of lower oxidation state. So we can use a metallic salt as a reagent and determine the amount of sugar by color change or the amount of precipitation. In other words, the reagent oxidizes the sugar while the sugar reduces the oxidation state of the ions.
In this experiment the sugar quantity is determined using the alkaline copper method (Benedict’s solution) which gives a color after it reacts with the sugar. Comparison to the amount of color produced by known sugar concentrations (standard curve) can be used to determine its exact concentration; however, we will not measure the exact concentration here. We only compare the colors to determine which banana contains the most or the least amount of sugar.
Fructose and glucose are reducing sugars so reduce the copper compound in Benedict’s reagent to copper.
For this experiment you need to have some Benedict’s solution. You may purchase benedict’s solution or you may make it yourself as described here.
To prepare Benedict’s reagent, dissolve 34.6 g of hydrated sodium citrate and 20.0 g of anhydrous sodium carbonate (or 23.4g of the monohydrate) in 160 ml of distilled water by heating. Filter the solution, if necessary. Add to it a solution of 3.46g of cupric sulfate (CuSO4.5H2O) dissolved in 20 ml of distilled water. Dilute to 200 ml total volume.
If you don’t have sodium citrate, make it yourself. Dissolve one mole (192 grams) citric acid and 3 mole (120 grams) caustic soda in water and let it crystallize.
What other ways do you know for making sodium citrate?
- Prepare and peal off your banana samples. At least one banana of each type (Green, yellow, brown).
- Use a blender to liquefy each banana for 2 minutes. Add 200 ml of water and continue blending for another one minute. Wash the blender before starting each new sample.
- Use cheese cloth to filter each banana shake separately.
- Label 3 beakers with Green, Yellow and Brown for three types of banana that you test.
- Fill up each beaker with 100 mL of clear filtered juice of one type of banana as labeled.
- Add 5 ml of Benedict’s solution to each beaker. Stir the solution and heat it up in a hot water bath for 15 minutes.
- Compare the color and precipitation of copper hydroxide in all 3 beakers to determine which one contains more sugar.
Notes: While heating the samples, make observations every minute and note how the colors changes. Very dilute reagent or excess amount of reagent may reduce the accuracy of your results. Repeat your experiment with different amounts of reagent and compare the results.
To measure the amount of precipitants, you need to filter them (using centrifuge or filter papers), let them dry and weigh them.
You can also measure and record the height of precipitants in a test tube and use it as an indication of the amount of precipitants in that test tube.
Make a graph:
Create a bar graph to visually present your results. Make one vertical bar for each color of banana (Green, Yellow, Brown). The height of each bar will indicate the relative amount of sugar, represented by the weight or the height of precipitation in the tube.
Materials and Equipment:
List of material can be extracted from the experiment section. The final list of material depend on your final experiment design.
Benedict’s solution or a material set for that are available at ChemicalStore.com.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
If you do any calculations for this project, write your calculations in this part of your report.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Visit your local library in the section dedicated to food chemistry or organic chemistry. Look for books that discuss formation of sugar in plants, types of sugar, and methods of measuring sugar. In certain industries where the sugar compound is well known, physical properties of a liquid solution may be used to estimate the sugar content. Such physical properties include density, viscosity and refraction index. While getting familiar with such methods, you must not use them and you should only focus on chemistry techniques for your project.