Test Apple Maturity

Introduction: (Initial Observation)

Apples are a very popular fruit that have many uses. Apples are turned into apple juice and apple cider, made into apple pies, and turned into apple jelly and Apple Jelly Cake!.

Chemicals extracted from apples include malic acid and pectin that are used for medicinal and food applications. Apples and apple juice can also be fermented to produce alcoholic beverages.

Farmers need to know when their apples are ready for harvest. They need to know it in advance so they can plan for hiring helpers, renting trucks and selling their products. In this project we will investigate a scientific method of doing that.

Information Gathering:

Find out about plant growth, photosynthesis and the production of starch and sugar in plants. Read books, magazines or ask professionals who might know in order to learn about the changes that happen inside apple while it matures and ripens. Keep track of where you got your information from.

Following are samples of information that you may find:

History and Background Information:

The native home of the apple is not certain, but it has been guessed that they originated in the Middle East more than 4,000 years ago. Humans have been eating apples for over 750,000 years! Early settlers, who brought apple seeds with them, introduced the apple to America. The apple is a fruit of the temperate zones and only reaches perfection in their cooler regions. Analyses of apples show us that they contain about 85% water. The amounts of sugars and malic acids in each variety determine the balance of sweetness and tartness in the fruit. Unpeeled apples have plenty of nutrients just under the skin. They are a good source of potassium, folic acid, and vitamin C. A medium apple, approximately 5 ounces, has only 81 calories and 3.7 grams of fiber from pectin, a soluble fiber. A medium apple supplies 159 mg of potassium, 3.9 mcg of folic acid, 7.9 mg of vitamin C, and 9.6 mg of calcium. Additionally, there are trace amounts of B vitamins, iron, magnesium, and zinc.

Predicting Harvest Date Windows for Apples

The Starch Index (SI) method is probably the best way to judge fruit maturity without expensive equipment. The SI technique measures the starch to sugar ratio, which is directly correlated with the maturity of fruit. Therefore, the SI index is an inexpensive way to assess the degree to which fruit have converted starch to sugar. Secondly, because SI is a reliable indicator of relative fruit maturity, SI testing can help you determine if the harvested fruit should be placed in cold storage, or marketed immediately.

Immature ‘Jonathan’ apples, harvested 8/31/99, SW Michigan, starch index 2–3

Here is our quick and simple testing technique in a nutshell:

• Equipment consists of a one quart hand-operated spray bottle filled with SI solution, a pocketknife, and a Starch Index chart.
• It’s most important to use the chart and begin sampling and testing the fruit at least two weeks before anticipated harvest to get a baseline on the maturity.
• The procedure is simple—pick a sample of apples that appear ready to harvest, based on size, color, days after full bloom, and taste. Spray the SI solution on fruit sliced in half at the equator, wait one to one and one-half minutes, and then make your readings based on the SI chart. The whole process is portable, quick, simple, and saves SI solution compared to dipping individual apple in a solution filled pan.

Mature ‘McIntosh’ apples ready for CA storage, harvested 8/31/99, SW Michigan, starch index 4–5

Three critical ingredients—fruit color, fruit size, and SI measurement must be considered when deciding when to pick and how to store. Overlooking any one ingredient could spell the difference between profit or loss for any year’s harvest.

Somewhat over-mature—but still good for fresh eating—’Honeycrisp’ apples, harvested 8/31/99, SW Michigan, starch index 6–7

Source…
Jon Clements, Michigan State University and Win Cowgill, Rutgers Cooperative Extension

Apples naturally contain a carbohydrate known as starch. As apples ripen, the amount of starch decreases as it turns to sugar. Starch is converted to sugar near the core of the apple first and gradually expands towards the skin. Apples are ripe and sweet when most of the starch becomes sugar. An iodine test is a simple way to see whether an apple is ripe and mature. Iodine is a common solution used for medicinal purposes with wounds and cuts. It is commonly applied to cuts and wounds to clean and disinfect.

The image to the right right is a sample chart. The iodine solution has created a dark area where starch is present.

Question/ Purpose:

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 use starch pattern in an apple to test it’s maturity or estimate it’s maturity date.

A specific question for this project is:

Does storage temperature affect apple maturity? (The specific question, identifying variables, Hypothesis and the experiment number 2 are only for higher grades.)

Identify Variables:

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 storage temperature.

Dependent variable is the apple maturity (measured using starch index method).

Constants are light, the type of apples and the experiment method.

Hypothesis:

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.

Since the amount of starch in apple will decrease as apple becomes more mature, we will be able to test the maturity and estimate the maturity date.

My hypothesis is that “Apples mature faster in higher temperatures.”.

Experiment Design:

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.”

Experiment 1:

Test apple maturity

Introduction: As apples ripen, starch stored in their flesh is gradually converted to sugar. The starch-iodine test is a way of visually assessing the progress of this conversion. Iodine reacts with starch to form a blue-black compound, therefore apples that still contain lots of starch are stained black when sprayed with an iodine solution; apples that are more mature will show little or no black stain.

Procedure:

1. Use a shallow glass pan. Pour some iodine solution into this pan to a depth of 5-8 mm.
2. Cut each apple in half across the core. Soak the cut surface of the stem half in the iodine solution for one minute. The stem can serve as a convenient handle.
3. Remove the stem halves from the test solution and place them cut surface up, to drain.
4. Score each fruit by comparison with the appropriate reference chart and calculate the average score for each lot of apples.

Experiment 2:

Test apple maturity rate at different temperatures

Warning: Adult supervision and support is required for this experiment.

Introduction: Apples with high starch contents or starch-iodine test score of 3 or 4 are usually stored a few months prior to being shipped to the market. During this period apples ripen and get to the starch iodine test score of about 5 to 7. In this experiment we will determine if the storage temperature affects the apple’s maturity.

Procedure:

1. Get 20 same size, identical, immature apples and divide them in 4 groups of 5. Immature apples may be picked directly from the trees or purchased from a local farmer or farmers market. Place each group in a separate paper bag or box. Label the bags as “startup”, “Cold”, “Warm”, and “Control”. Use paper bags or boxes so the samples will not get light but will be able to exchange air and moisture with their environment.
2. Open the bag labeled “startup” and immediately test the apples in this bag for their starch contents as described in the previous experiment. Score each apple in this group using the sample chart provided in the gathering information section. Calculate and record the average score for this group.
3. Place the bag labeled cold in a refrigerator.
4. Place the bag labeled warm in a warm place. Set the temperature of the warm place at about 40ºC or 105ºF. You may find a warm place in your home or create a warm place by safely placing an electric heater inside a small metal cabinet. Electric heaters have built-in thermostat that adjust the temperature.
5. Keep the bag labeled control at room temperature.
6. After 3 or 4 weeks open the bags labeled “cold”, “warm”, and “control ” one at a time and test them for their starch contents as described in the previous experiment. Score the apple in each group using the sample chart provided in the gathering information section. Calculate the average score for each group.
7. Record your results in a table like this:

You may finally use the above results table to draw a bar graph. Each bar may be labeled with the group name (startup, cold storage, room storage, warm storage). The height of each bar will be the starch index. (Note that a higher starch index really means less starch and more sugar. So as the bars get taller, the apple is more mature)

Materials and Equipment:

Materials used in this project are:

1. 25 immature apples (for both experiments)
2. 250 mL Iodine tincture (iodine solution)
3. Shallow glass pan or plastic tray
4. Watch, clock or timer

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.

Evaluating Test Results

Apples will show the starch-iodine test scores starting from 1 and ending at 9 over several weeks during the fall season.

Apples destined for long-term controlled atmosphere (CA*) storage have to be picked early and therefore require a lower starch-iodine test score.

Apples destined for immediate fresh market and processing plant can be picked later and therefore require a higher starch-iodine test score.

In general, apples with starch-iodine test scores of 1, 2, and 3 are considered immature. Apples with scores of 4, 5, and 6 are considered mature. Apples with scores of 7, 8, and 9 are considered over mature. Normally, apples with a starch-iodine test score of 3 or 4 are good for long-term CA* storage.

*CA stands for controlled atmosphere

Calculations:

After you score the apples in each group, you will need to calculate the average score for that group. To do that add all the scores from that group and divide the results by the number of apples in that group.

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.

Possible Errors:

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.

References:

Now do some research on the fruit, apple. Gather information and learn about them by reading books, magazines, and websites. For a start, try the links below.

http://www.vegparadise.com/highestperch39.html – Apple at a Glance

http://en.wikipedia.org/wiki/Iodine – Iodine

http://www.ifr.bbsrc.ac.uk/public/FoodInfoSheets/applefacts.html – Apple Facts

http://www.nsapples.com/ – Nova Scotia Apples

http://www.bouquetoffruits.com/fruit-facts/apple-facts.html – Apple Fruit Facts and Information

http://fruit.coafes.umn.edu/apples/starch-iodine.PDF

Ontario Ministry of agriculture and food

DISCLAIMER:

Although most of the experiments in this web-site are regarded as low hazard, author and publisher expressly disclaims all liability for any occurrence, including, but not limited to, damage, injury or death which might arise as consequences of  the use of any experiment(s) listed or described here. Therefore, you assume all the liability and use these experiments at your own risk!