The pH of Lycopersicon esculentum and



The pH of Lycopersicon esculentum andHow it is Affected by CanningNancy Brim3451 Alison DriveAtlanta, GA 30319Lakeside High SchoolTenth GradeTable of ContentsBackground Information3Materials and Methods5Results6Discussion and Conclusion7Acknowledgements9Works Cited10Appendix11The tartness that distinguishes Lycopersicon esculentum, the tomato, from other vegetables is produced in part by acids. Practically all foods contain acids, either naturally or added later during processing (Gould 268). There are several important factors that seem to have an influence on the acidity of tomatoes. These include variety, maturity, handling and holding procedures prior to processing, and the processing itself (Gould 273). Does the pH of roma and plum tomatoes change once they are canned?There are many types of tomatoes. At the local grocery store, roma tomatoes, grape tomatoes, and regular vine-ripened tomatoes are all for sale. There are many varieties available to home gardeners, ranging from new hybrids to tasty heirloom varieties (Jett par. 2). Many consumers prefer tomatoes that are home grown and vine-ripened. Growing tomatoes at home is not complicated. According to William McGlynn, a horticultural food specialist, tomatoes may be harvested at the mature green stage, semi-ripe (with different amounts of red pigmentation), or fully ripe, depending on marketing requirement (4). They are very perishable and subject to surface and internal damage, and must be handled accordingly (2). Tomatoes are sensitive to chilling injury, which differs with maturity of the fruit and proper temperature management for ripening and storage are critical to maintain quality (3). Tomatoes are dependent upon growing conditions and as the variety changes, so can the conditions required.Good-quality roma tomatoes are firm, smooth-skinned and at least pink in color (Hartz and Miyao 1). Tomatoes that are partially green will ripen if left at room temperature (Hartz and Miyao 1). The plum tomato is fairly hardy and bears fruit in cooler temperatures, as well as hot, dry climates (Hartz and Miyao 2). The black plum tomato is originally from Russia (Hartz and Miyao 2). Eating either tomato after it has matured on the vine always seems to taste better than eating a store bought one.Tomatoes have a tart taste. The most adundant natural acid in tomatoes is citric acid which is also found in oranges and lemons (Wahem 1). The pH of tomatoes runs between 4.0 and 4.5 (Wahem 4). Tomatoes average a pH of 4.3 and an acidic product is considered to have a pH of 4.6 or less (Gould 273). Many vegetables go through the canning process. Food processing companies desire a lower pH to prevent microbial growth in their canned foods because the pH of a food is the controlling factor in the regulation of many chemical and microbial reactions (Gould 270). Tomato processors tend to use citric acid and fumaric acid as a chemical agent to lower pH (Gould 270). Lowering pH with additional citric acid along with heating the product allows for sterilization and thus limited or no microbial growth (Gould 271). In addition, sugars are added to keep the pH from dropping too low (Wahem 2). A pH that is too low would limit microbial growth, but might have such a sharp taste that some consumers may not like it.Microbial growth in canned foods is to be avoided. Food-borne illness is an ever-present threat that can be prevented with proper care and handling of food products (Wagner 1). It is estimated that between 24 and 81 million cases of food borne diarrhea disease occur each year in the United States, costing between $5 billion and $17 billion in medical care and lost productivity (Wagner 1). Listeria monocytogenes, one such disease causing bacteria, can grow in a pH range of 5.0-9.5 (Wagner 13). Yersinia enterocolitica is an organism that is sensitive to heat and acidity (pH 4.6) (Wagner 16). Knowing the pH of the canned food is important. To measure the acidity of a substance, you can measure its pH. According to Raymond Chang in Chemistry, the symbol pH is used for the hydrogen-ion concentration present in an aqueous solution (607). The more hydrogen ions present in a solution, the more acidic the solution is (607). The pH scale is a logarithmic scale and ranges from 1-14 (608). A pH of zero is the most acidic, pH 7 is neutral, and pH 14 is the most alkaline (608). Tomatoes are acidic and thus have a pH under 7.Tomatoes have a sharp taste and are used in a variety of recipes. Some cooks choose to use canned tomatoes instead of fresh. Cooks are also concerned about microbial growth in their foods. Thus a lower pH is preferable. If plum and roma tomatoes are compared before and after canning, a canned plum tomato will be more acidic than a fresh plum tomato and both tomato varieties will display comparable acidity after canning.Three types of tomatoes were used. The first consisted of ten small market fresh red ripe plum tomatoes. The second type consisted of ten small plum tomatoes obtained each from ten cans of Hunts All Natural Peeled California Whole Tomatoes?. The third type consisted of ten red small roma tomatoes each from ten cans of Progresso Italian Tomatoes?. Each of the thirty samples were placed in a Krups Mini Food Processor? on puree for fifteen seconds. There was no need to strain the resulting liquid because colorimetric methods were not used.A pH probe and Voltage Plotter III? software designed by Vernier? Software were used and the software was run on an Apple IIg? computer. The pH probe measures pH by relating it to the potential developed between two electrodes when immersed in a solution (Vernier 1). Strong acids are electrolytes meaning they contain ions in solution and electrolytes conduct electric currents (Gould 271). The voltage recorded by the probe is a measure of the hydrogen ion activity (Vernier 1). A pH change of 1.0 unit equals a constant change in voltage (Gould 271). The computer converts the voltage reading to a pH value (Gould 271).The pH probe was calibrated using standard buffers of 4.0 and 7.0 using the calibration built into the software. See Appendix A for information on how the probe was calibrated. Each sample consisted of 75.0mL and each pH reading was performed from 30 seconds. The probe was held in each sample for 30 seconds prior to the first recorded value to insure a more stable reading. A rinsing of the pH probe in Kroger Distilled Water followed each sample run? to insure that no tomato puree was left on the apparatus. One value was recorded for each sample. All calculations were performed using the software Microsoft Excel? run on a MacIntosh Plus? computer.The raw data for the red ripe plum tomatoes showed pH values ranging from 4.12 to 4.46. The raw data for the canned red tomatoes showed pH values ranging from 4.27 to 4.45. The raw data for the canned red roma tomatoes showed pH values ranging from 4.17 to 4.26. For a complete table of the raw data, see Appendix B.The mean pH for the red ripe plum tomato was 4.33+/-0.10. The mean pH for the canned red plum tomatoes was 4.36+/-0.09 and the mean pH for the canned roma tomatoes was 4.20+/-0.03. The canned plum tomatoes had the highest average pH and the canned roma tomatoes had the lowest average pH. The fresh red plum tomatoes’ pH was lower than the canned version.Table One Average pH of Tomato Samples Fresh Red Canned Red Canned Red Plum Tomatoes Plum Tomatoes Roma TomatoesSample size , N101010Average pH4.334.364.20Stavdard deviation0.100.090.03Figure One illustrates that there is an overlap between confidence intervals of fresh red plum tomatoes, the canned red plum tomatoes, and the canned red roma tomatoes. This is interpreted to mean that the fresh red plum tomatoes pH values are not significantly different from the canned red plum tomatoes’ values and the canned red plum tomatoes’ pH values are not significantly different from the canned red roma tomatoes’ values.Figure One Confidence Intervals of TomatoEach standard reading differed by a value of 0.14 units. This result is not significant to the experiment because both standards differed by the same amount. Also, the coefficient of variation for both was under 1.0%All tomatoes chosen for the study were in the acidic range. When canning tomatoes, an organic acid such as citric acid is added to help control the pH and prevent spoiling. The plum tomato cultivars apparently did not need the addition of much acid during the canning process because the pH results of the canned plum tomato reveal little difference from the fresh plum tomato pH. When looking at the two varieties of canned tomatoes, the pH might be affected by the sodium hydroxide used in the peeling process that occurs prior to canning. This use of a strong base may result in an initial increase in the tomato pH which in turn would then decrease when the citric acid was adding during processing. The pH of the canned tomatoes can also be affected by the sugars naturally present in the tomatoes which can decompose upon heating in the presence of acids to give acetic, lactic, fumaric, and glycolic acids.It is possible for canned tomatoes to have a lower pH although the reason is not exclusively due to the natural pH of the tomatoes. The addition of acids and the reduction of sugars in the processing of the tomatoes also may contribute to a more acidic pH reading. Since there was no significant difference between the canned plum and canned roma tomatoes, it would appear from this small sampling that the canning process produces tomatoes within the same pH range. This seems plausible, for the goal of canning is to produce tomatoes within a certain pH range to prevent spoilage.Due to the small sample size, these results cannot be applied to the general tomato population. A much larger sample size with the representation of additional varieties would be required to make generalizations about the hydrogen-ion concentrations of plum and roma tomatoes before and after the canning process. Future research might include the pH of fresh roma tomatoes and comparing this to the canned roma tomatoes. Also, testing the pH of tomatoes that were canned at home instead of commercially processed would be advantageous.AcknowledgementsI would like to thank Professor Matson for the use of San Jose State University science 108 laboratory equipment. Works CitedChang, Raymond. Chemistry. New York: McGraw-Hill, 1994. Print.Gould, Walter A. Tomato Production, Processing, and Quality Evaluation . Westport: AVI, 1983. Print.Hartz, Timothy K., and Gene Miyao. Processing Tomato Production in California. University of California, Davis: Division of Agriculture and Natural Resources, 2003. Print.Jett, Lewis W. “Growing Home Grown Tomatoes.” Division of Plant Sciences. University of Missouri, June 2005. Web. 8 July 2005. < agguides/hort/g06461.htm>.McGlynn, William. ‘The Importance of Food pH in Commercial Canning Operations.” Division of Agricultural Sciences and Natural Resources. Oklahoma State University Cooperative Extension Service, 2000. Web. 7 July 2005. < . okstate.edu/ docushare/dsweb/Get/Document-603/FAPC-118pod.pdf>.Wagner Jr., Al B. “Bacterial Food Poisoning.” Texas Agricultural Extension Service. Texas Agricultural and Technical University, July 2002. Web. 7 July 2005. <, Ibrahim, A. “The effects of acidification and sugar addition on quality attributes of canned tomatoes.” Journal of Food Processing and Preservation. 14(2007)1-14. Print.Appendix ACalibration of the pH probeUsing the calibration built into the software, 1.81 volts was assigned to a pH of 7.0 when the probe was held in the 7.0 buffer solution. A pH of 4.0 was given to 2.61 volts when the probe was held in the 4.0 buffer solution. When a test was run using a 7.0 standard solution, the resulting pH was 7.14 +/-0.01. When a second test was run using the 4.0 pH standard solution, the resulting pH was 4.14+/-0.02. Appendix BTable TwoThirty Trials of Tomato pH Trial Fresh Red Plum Canned Red PlumCanned Red Roma Tomato Tomato Tomato14.124.274.1924.314.274.1934.424.294.2344.394.284.1954.464.294.1764.204.444.1974.394.444.2184.344.434.1894.354.254.26104.274.434.18 ................
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