This Investigatory Project won first place at the Intel Philippines Regional Science Fair Region VIII. This earned the top 6 place at the Intel Philippines Science Fair National Category held at the University of the Philippines Diliman on February 15 to 17, 2010.
Tomatoes sold on the market have most probably passed through various treatments to prolong their shelf life.
This study aimed to investigate the firming effect of tawas, lime, and refrigeration on tomatoes. The exposure time and stage of ripeness (unripe, half ripe, ripe, and overripe) of the tomatoes used were varied. It was found that the effect of the four treatments (tawas-water solution, lime-water solution, refrigeration, and room temperature) on the firmness of tomatoes varied according to the degree of ripeness upon treatment and time of observation.
Consumers may not know it but the tomatoes they buy could have already passed through several treatments. Some vendors soak ripe tomatoes in tawas or alum solutions in order to maintain the firmness of the tomatoes. The amount of alum involved varies, but usually 1/4 kilo of alum is mixed with 30 liters of water. Soaking time runs for about half a day. Aside from tomatoes, vendors also soak wilting carrots, radish, sliced unripe jackfruit, and bean sprouts in tawas solution.
Foreign countries such as the United States have already recommended the use of lime as the better alternative to tawas to keep pickled fruits and vegetables crisp. Tawas could induce a bitter taste and has a level of toxicity. Aside from alum and lime, there is already a common middle-class household practice of refrigeration to preserve food. Thus, it had now become very interesting to find out the comparative effect and limitation of these three methods in keeping ripe tomatoes firm.
Definition of Terms
Tomato: the fruit of the plant Solanum lycopersicum, reclassified Lycopers icon lycopersicum, Lycopersicum esculentum, or kamatis in Filipino.
Tawas or alum: also known as aluminum potassium sulfate
Tawas-water solution: made by dissolving 1/4 teaspoon of tawas (0.6 grams) in 568 ml of water, resulting to a concentration of 0.105 percent
Lime: calcium hydroxide, also called apog
Lime-water solution: made by dissolving 1/8 cup of lime (13.25 grams) in 568 ml of water, resulting to a concentration of 2.33 percent
Firmness: the denseness or solidity of an object; a measure of the tomato's hardness as sensed by compressing or touching the tomato with the fingers; was rated from 1 to 4, with 4 being the firmest
Shelf life: the length of time a product can be stored without deterioration occurring
Materials and Method
The study used 48 tomatoes (12 unripe, 12 half ripe, 12 ripe, and 12 overripe) of the improved Pope variety that were produced in Nueva Ecija. They were of the same sizes and were selected randomly from newly opened crates. Their stage of ripeness was distinguished by their color and firmness. From each of the four groups (unripe, half ripe, ripe, and overripe), the tomatoes were again randomly selected to form four subgroups (each subgroup contained three tomatoes). Each subgroup was also randomly assigned to receive different treatments (immersion in alum-water solution, lime-water solution, refrigeration, or storage at room temperature).
The study used culinary measuring cups and spoons, an electronic weighing scale (Custom CS-240, capacity of 240 g, graduation of 0-120g/0/g), graduated cylinders (1 liter and 50 ml), home refrigerator, two thermometers (one was placed inside the refrigerator and the other in the room where the tomatoes were kept), and plastic containers that served as vats for the tawas and lime solutions. The tomatoes were observed or evaluated through time for nine times (hours 6, 24, 30, 54, 78, 102, 126, 150, and 174). The appearance and changes in the tomatoes during the various observations were photographed using a digital camera.
Temperature readings were noted during observation time. Firmness was evaluated qualitatively by touch and comparatively ranked: from 1 to 4, with 4 as the firmest. Firmness was evaluated and ranked after 6, 24, 30, 54, 78, 102, 126, 150, and 174 hours. Evaluation was done per group and it was done by choosing the firmest in each subgroup. Evaluation was also done to the subgroups of tomatoes subjected to soaking treatments. It was basically done to compare the effect of the different soaking times.
The results for each group of tomatoes, the different treatments and the soaking time are summarized and presented in the following line graphs.
Overripe tomatoes soaked in the tawas-water solution were the firmest. Lime-soaked tomatoes were generally second best up to hour 54 but their firmness dramatically declined as time progressed. Later observations showed that the tomatoes kept in the refrigerator and at room temperature were firmer than the lime-soaked ones. By hour 102, the lime- soaked overripe tomatoes were the least firm (Figure 1).
Ripe tomatoes refrigerated or treated in tawas or lime solutions were firmer than those tomatoes kept at room temperature. But their relative firmness changed over time. Lime-treated ripe tomatoes were the second firmest, followed by those kept in the refrigerator. The least firm were those kept in room temperature (Figure 2).
Refrigerated and tawas- or lime-treated tomatoes we;.e firmer than those kept in room temperature. However, there are differences in their relative firmness. Those treated with lime were the firmest; next were the tawas-treated; followed by the refrigerated; and last were the tomatoes kept in room temperature. The results were consistent throughout the nine observations (Figure 3).
Refrigeration and tawas and lime treatments made unripe tomatoes firmer compared to tomatoes stored in room temperature. Unripe tomatoes responded best to the tawas-water solution. Although lime-soaked tomatoes were as firm as the tawas-treated after 30 hours of soaking, the former became less firm two days after (Figure 4).
The tawas-water solution was more effective for unripe and overripe tomatoes, while lime-water solution was more effective for half ripe and ripe tomatoes (Figure 5). The tomatoes soaked in the lime-water solution had a white powdery coating on their skin which was difficult to wipe off.
Conclusions and Recommendations
The taivas-water solution was more effective for overripe tomatoes. The overripe tomatoes that were refrigerated and kept in room temperature became firmer than the lime-soaked ones. Lime-water solution was the most effective for ripe tomatoes, followed by tawas treatment, then refrigeration, and lastly room temperature. For half ripe tomatoes, the firmest were the lime-treated tomatoes, followed by the tawas-treated, then by the refrigerated tomatoes, and last were the tomatoes stored in room temperature. For unripe tomatoes, tawas treatment was the best.
For the effect of soaking time, it was greater with longer soaking period (30 hours). Refrigeration worked bes, for overripe, ripe, and unripe tomatoes. Keeping overripe and ripe tomatoes in room temperature made them last longer than treating them with tawas or lime-water solution.
Further studies should be done to investigate the effect of the firming agents to different varieties of tomatoes, if the tawas used is food grade, and if the results will be the same using other types of tomatoes.
Ingrid G. Sievert
Maria Shiela S. Cemanes
Princess Michelle B. Gabornes
Mrs. Lily Ann A. Bidua
Leyte National High School