Pectin Methyl Esterase in Vegetables
Grade Level: 6th - 8th; Type: Chemistry/Food Science
The goal of these experiments is to learn about pectin methyl esterase (PME) and pectin in plants.
- What is pectin methyl esterase?
- Where is PME found in the plant? What does it do chemically?
- What are the benefits of the PME to the plant?
- What does enzyme activation mean?
Pectin methyl esterase (PME) is an enzyme found in the cell wall of plants. Scientists believe that it exists in all plants because it has been found, in varying quantities, in every plant examined so far. The gene that codes for PME has also been identified. Chemically, this enzyme catalyzes the de-esterification of pectin. Researchers are unsure how this benefits the plant. However, the presence of PME benefits humans. When vegetables are heated to 120 degrees Fahrenheit, the enzyme becomes activated. The texture of the cell wall becomes stiff – and remains stiff even when subject to boiling for long periods of time. Vegetables that contain significant amounts of PME can be subjected to the high temperatures and long boiling times necessary for canning without making the vegetables mushy and unappetizing.
- Four green beans, tablespoon of peas, 1 stalk celery, 1 carrot, 1 piece brocilli
- Sauce pan
- Access to a stove
- Cut up the vegetables into bite-size pieces and put them in a bowl. Add the fresh peas to the bowl.
- Put four cups of water into a medium-to-large saucepan and heat to boiling.
- Turn the heat down to a low simmer and plunge the vegetables into the water. Let the vegetables boil for 45 minutes.
- Remove the vegetables from the water. Drain them and let them cool on a baking sheet.
- Closely inspect the vegetables. Which retains its color the best? Which retained its structure the best? Gently squeeze the vegetables between your fingers. Try to rate which retained its texture the best. Try to think of other foods that retain their texture to this extent. What would happen if you boiled bread or cheese for 45 minutes? What would happen if you cut up an apple or a pear and boiled it for 45 minutes? Can you speculate which has the most PME?
- Call your local county agricultural extension office to see if they can provide you with data on PME content of various vegetables.
Terms/Concepts: Enzyme; Enzyme Activation; Cell Wall; Pectin methyl esterase (PME)
- McGee, Harold, On Food and Cooking: the Science and Lore of the Kitchen. McMillan Publishing (1984).
- PDFcast.org: Isolation and study of a ubiquitously expressed tomato pectin methylesterase regulatory region http://pdfcast.org/pdf/isolation-and-study-of-a-ubiquitously-expressed-tomato-pectin-methylesterase-regulatory-region
- New Insights into Pectin Methylesterase Structure and Funtion http://www.cell.com/trends/plant-science/abstract/S1360-1385%2807%2900096-9
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