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Team:UNITN-Trento/Project/Fruit ripening
From 2013.igem.org
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<span class="sub-subtitle">» Fruit Compression Strength Test</span> | <span class="sub-subtitle">» Fruit Compression Strength Test</span> | ||
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| - | + | A compression test determines behavior of materials under crushing loads. The specimen is compressed and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram which is used to determine elastic limit, proportional limit, yield point, yield strength and, for some materials, compressive strength. <br/> In our case we are able to make a compression test to a kiwifruit and bananas. | |
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Revision as of 15:22, 17 September 2013
Fruit ripening
We have tested several type of fruit to verify that our engineered bacteria are able to produce ethylene (cell transformed with BBa_K1065001) and methyl salicylate (cell transformed with BBa_K1065102 and BBa_K1065106) for enhancing or blocking the ripening of fruit, respectively.
The flasks containing the induced culture were kept at 37 degree in agitation and connected to a sealed jar (or a desiccator) where the fruit was exposed to either ethylene or methyl salicylate (MeSA). Negative controls were either a fruit kept in airtight jar or a fruit placed in a jar connected to a flask with non-induced cells.
Within the same experiment we used fruit assumed to be at the same ripening stage (i.e.: the same bunch of bananas).
The results obtained varied according to the fruit tested. We tested: bananas, cherry plums, cherries and heirloom tomatoes, plums, blackberries, kiwifruit, pears and others. Results were evaluated qualitatively by observing skin color changes and pulp texture or firmness.
In some cases we were able to detect different levels of fragrance, however this results were too subjective and we discarded them.
We were also able to perform a iodine coloration test on starch-containing fruit.
We also performed quantitative evaluations of ethylene effects by fruit compression strength test.
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Type of fruit Cavendish banana Duration of experiment 6 days Exposition to Ethylene 6 days Container Essicator (10.3L) |
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Type of fruit Cherry plum Duration of experiment 4 days Exposition to Ethylene 4 days Container Fruit in 1 L jar |
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Type of fruit Cherry tomatoes Duration of experiment 7 days Exposition to Ethylene 1 day Container Fruit in 0.5 L jar |
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Type of fruit Heirloom tomatoes Duration of experiment 9 days Container Fruit in 1 L jar |
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Type of fruit Cherry tomatoes Duration of experiment 8 days Exposition to Ethylene 1 days Container Fruit in 0.5 L jar |
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Type of fruit Date tomatoes Duration of experiment 7 days Exposition to Ethylene 2 day w/, 3 days w/o, 2 days w/ Container Fruit in 0.5 L jar |
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Type of fruit Blackberries Duration of experiment 7 days Exposition to Ethylene 1 day Container Fruit in 0.5 L jar |
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In summary: cell transformed with BBa_K1065001 (our ethylene producing device) successfully ripen all the fruit tested when compared to the negative control, except for a few cases (Test with Date Tomatoes) where no significant effects were observed. We believe that in the first case the experiment did not work because the temperature in the laboratory (in those days) was over 30 degrees. We know the importance of temperature on ripening of vine-rape fruit (with external color). In our specific case the too high temperature (>25°C) caused decreased activity of lycopene synthesis enzymes. [reference]
» Iodine Coloration TestStarch accumulates in apples during the growing season and is hydrolyzed to sugar in the latter stages of maturation and development (Krotkov and Helson 1946). Hydrolysis occurs in the core area first and progresses outwards (Phillips and Poapst 1952). Starch in cut sections of the fruit reacts with a solution of iodine-potassium iodide to produce a blue-black color. By relating the pattern of color development to the stage of maturation.
» Fruit Compression Strength Test
A compression test determines behavior of materials under crushing loads. The specimen is compressed and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram which is used to determine elastic limit, proportional limit, yield point, yield strength and, for some materials, compressive strength.
In our case we are able to make a compression test to a kiwifruit and bananas.
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Type of fruit Date tomatoes Duration of experiment 7 days Exposition to MeSA (BBa_K1065106) 2 day w/, 3 days w/o, 2 days w/ Container Fruit in 0.5 L jar |
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Type of fruit Blackberries Duration of experiment 7 days Exposition to MeSA (BBa_K1065106) 1 day Container Fruit in 0.5 L jar |
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Type of fruit Cherry tomatoes Duration of experiment 7 days Exposition to MeSA (BBa_K1065106) 7 days Container Fruit in 0.5 L jar |
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Type of fruit Cherry tomatoes Duration of experiment 8 days Immersion in MeSA pure 8 days Container Fruit in 0.5 L jar |
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Type of fruit Cavendish banana Duration of experiment 6 days Exposition to pure MeSA (LB-dissolved) 6 days Container Essicator (10.3L) |
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Type of fruit Cherry plum Duration of experiment 4 days Exposition to pure MeSA (LB-dissolved) 4 days Container Fruit in 1 L jar |
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Cells transformed with BBa_K1065102 and BBa_K1065106 (our methyl salicylate producing devices) did not show any difference when compared to the negative control. We were not able to determine if MeSA actually inhibited fruit ripening because the experiments were not long enough to allow ripening of the control. We demonstrated by XX that YY ml of bacteria culture (induced at O.D.600 equal to 0.6) transformed with our device produce successfully MeSA at a concentration of xx ppm in the culture medium. However, the final concentration of the inhibitor in the gas phase in the jar could be lower than the needed concentration. We are now in the process of better estimating these values.
Exposure to pure MeSA instead caused an excessive ripening when added to the culture medium while it had a toxic effect when the fruit was drenched with it. MeSA was reported to slow down ripening at high concentration (XX) and to accelerate the process at lower concentration (YY). [ref] We think that under the used conditions its concentration was above the threshold required to inhibit ripening.
