To investigate the possible reasons for fruits, such as tomatoes, becoming softer and squashier as they ripen.
Research on squashy tomatoes
Aim:
To investigate the possible reasons for fruits, such as tomatoes, becoming softer and squashier as they ripen.
Research:
Pectin's are extracted from the cell wall with hot water or dilute acid or calcium chelators. They are the easiest constituents to remove from the cell wall. They form gels (i.e., used in jelly making). They are also another diverse group of polysaccharides that is particularly rich in galacturonic acid (galacturonans = pectic acids). Pectic polysaccharides can be cross-linked by dihydrocinnamic or diferulic acids.
Although most pectic polysaccharides are acidic, others are composed of neutral sugars including arabinans and galactans. The pectic polysaccharides serve a variety of functions including determining wall porosity, providing a charged wall surface for cell-cell adhesion (middle lamella), cell-cell recognition, pathogen recognition and other.
In plant cells, Pectin is linked to cellulose to form protopectin, which has the ability to absorb large amounts of water. Cellulose gives the supporting tissues their rigidity, whilst the pectic components give the plant its flexibility.
In industry and at home, Pectin is well known for its gelling, thickening and stabilizing properties. Today, it is used in such diverse applications as yoghurt, confectionery and acid milk drinks. It has the image of a natural product and has acknowledged nutritional benefits. For all those reasons, new uses are constantly found for Pectin in the food industry, and also in pharmaceutical and cosmetic applications.
Pectinase can be found within the lysosome organelle of a plant cell, and these can be activated by the gas ethylene, which is produced by plant respiration. Pectinase breaks down pectin, a polymer found primarily in fruits. The result is a rapid release of liquid of the cell contents. The control will yield a small amount of juice but it is very obvious from this experiment that an enzymes speeds up a reaction. The boiled pectinase shows that heat will denature the enzyme, yielding results similar to the control. Pectinase is inexpensive and keeps in a refrigerator for at ...
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Pectinase can be found within the lysosome organelle of a plant cell, and these can be activated by the gas ethylene, which is produced by plant respiration. Pectinase breaks down pectin, a polymer found primarily in fruits. The result is a rapid release of liquid of the cell contents. The control will yield a small amount of juice but it is very obvious from this experiment that an enzymes speeds up a reaction. The boiled pectinase shows that heat will denature the enzyme, yielding results similar to the control. Pectinase is inexpensive and keeps in a refrigerator for at least two years.
Pectinases are produced during the natural ripening process of some fruits, where together with cellulases, they help to soften their cell walls. These enzymes are also secreted by plant pathogens such as the fungus and the soft-rot bacterium, as part of their strategy for penetrating the plant host cell walls. In fact, the products of such enzyme assaults act as a signal, which induces, uninfected cells to defend themselves
Recent research has come to the conclusion that, Like all soft fruit, tomatoes are usually picked while they are still under-ripe (i.e. green), and then treated with ethylene (a natural ripening gas) to turn them red. This approach ensures that they remain firm during transportation and storage, thus avoiding softening and loss of product. Tomatoes turn soft, and ultimately rot, when an enzyme (polygalacturonase or pectinase) that is naturally found in the fruit breaks down the cell walls.
Switching off most of the polygalacturonase enzyme production, allowing pectin levels to remain high, and the tomatoes to soften more slowly has produced both of these genetically modified tomato products. To achieve this, researchers removed the gene that codes for polygalacturonase, copied it and then reinserted the copy back into the plant, but backwards (a genetic modification technique termed 'anti-sense' technology), which 'switches off' the polygalacturonase enzyme. Because the rate of softening has been slowed, the modified tomatoes can remain longer on the vine to develop their full flavour (and colour).
In order to stop fruits from becoming soft and squashy, and to preserve them as long as possible, we could store the fruit at low temperature, pickling in vinegar, food irradiation. Enzymes can be inactivated by heat, which is the reason for blanching vegetables; or cold temperatures below 40 degrees F can inactivate them, which is the reason for placing vegetables under refrigeration.
Bacteria also produce enzymes that break down food and allow them to obtain nutrients through their cell walls. Therefore, lowering the temperature reduces the rate of enzyme action as well as the rate at which bacteria can multiply. Refrigeration increases the time required to spoil food.
As the number of bacteria increases, the amount of enzymes produced increases. Higher temperatures can cause increased enzymatic activity. With large numbers of bacteria and high temperatures, a food will spoil very rapidly. When bacterial contamination is high and the storage temperature is low, a food will keep for a moderate period of time; when the bacterial contamination is low and the storage temperature high, food will keep for a moderate period of time. However, if the contamination of bacteria is low and the storage temperature kept low, the food product will have the longest possible shelf life.
The second way in which to preserve the fruit for as long as possible is by putting it within vinegar. Not many enzymes can work in acid conditions. Vinegar is a dilute solution of ethanoic acid. Soaking fruits in vinegar makes the pH unsuitable for those enzymes with which microorganisms carry out external digestion (because they need a near-neutral or alkaline PH in which to work).
The final way in which to preserve the fruit is by large doses of ionising radiation break down molecules in food and release ions. Ionising radiation kill the microorganisms in food increase the time that it will keep without soiling but they do not destroy poisonous toxins that may have been produced in the fruit.
Within plant respiration, a gas is produced which helps the ripening of fruits, and this gas is ethylene. Ethylene can promote ripening in tomatoes, bananas, citrus, pineapples, dates, persimmons, pears, apples, melons, mangos, avocados, papayas and jujubes - a clear indication that the action of ethylene is general and widespread amongst a number of fruits. It is clear that ethylene is a ripening hormone - a chemical substance produced by fruits with the specific biological phenomenon of accelerating the normal process of fruit maturation and senescence.
After fertilization, the young fruit goes through a short period of cell division, which is then followed by a rapid period of growth as these cells enlarge. During the final stages of growth and development, the tomato fruit reaches its full size and is now mature. This period of growth and development, from fertilization to development of the mature fruit, requires about 45-55 days, depending on the cultivars and the season. During the growth and development period, there are many chemical and physical changes occurring that have an impact on fruit quality and ripening behaviour after harvest. Ripening is the final stage of the maturation process when the fruit changes colour, and develops the flavour, texture and aroma that makes up what we define as optimum eating quality. The biological agent that initiates this ripening process after the fruit is mature is naturally produced ethylene - this simple plant hormone described and understood over 40years ago. While there are other factors involved in this "triggering" of the ripening process by ethylene, it is essentially a universal ripening hormone. When this internal concentration of naturally produced ethylene increases to about 0.1 - 1.0 ppm, the ripening process is irreversibly initiated. The process may be glowed, but it cannot be reversed once it is truly under way. So, here is the key point: additional and externally applied ethylene, provided prior to the time that the naturally produced internal concentration reaches the required 0.1 - 1.0 ppm level, will trigger or initiate - "promote" if you will - this natural ripening process at an earlier time.
Uday Patel
