Chemistry 101-292 Mr. O Sullivan Lab Report Experiment #11 Determination of techniques to prevent the Browning of Cut Produce
Abstract The purpose of this experiment was to determine effective techniques to prevent the of cut produce. In a previous observational experiment one banana and one apple were cut in slices which were placed on paper plates labelled with different food additives: two acids, two bases, one vitamin C, one sugar and one salt solution. The ph levels were determined with litmus paper. One plate was reserved as a control plate. Prior to cutting produce, solutions of solid food additives were prepared for dipping. The apple and banana were bathed in each solution. Using the scientific method, the changes in color, texture and shape of the produce were observed every thirty minutes to determine if had occurred. Produce was observed for a total of one-hundred and eighty minutes to determine best method to prevent. The experiment in this report uses the results from the banana and apple experiment to determine best technique to prevent the of a potato. A potato was cut in round slices and exposed to oxygen soaked for two minutes in one Vitamin C and salt solution, and different solutions of acids. It was hypothesized that the most acidic solution would be most effective in preventing the of the produce, in other words preventing the contact of the produce with oxygen, thereby preventing oxidation. If a potato slice bathed in a strong acid is exposed to oxygen, then the of that produce will be delayed for at least one-hundred and eighty minutes, as the acidic conditions will limit reaction rate of enzymatic oxidation. It was found that data supported hypothesis as the potato slices in which was prevented were strong acid solutions. Introduction According to Marian Cothran of Lexington Community College in Kentucky, the of produce is due to, polyphenoloxidase, an enzyme that oxidizes phenolic compounds in the tissues of fruits or vegetables when reacting with oxygen in the air, causing those compounds to change color as they condense into polymers. Enzymes are proteins that function as catalysts to speed up chemical reactions. The color results from the formation of the pigments, catechols and tannins. The pigments expose the enzymes in the produce to the air which causes the enzyme to activate, hence the effect. In this case the two ways to prevent the enzyme from reacting is to inactivate it with extreme temperatures, or to prevent the produce from being exposed directly to oxygen. To freeze or heat produce will cause the enzyme to become inactive and will prevent. To prevent exposure to oxygen produce can be placed in a sealed plastic bag, cellophane wrap, and/or household solutions can be added to the surface to prevent. 2
Experiments 1 and 2 determined that the of banana and apple slices is delayed and minimized with a coating of an acidic, a salt and a vitamin C solution, more so than with base or sugar solutions. Therefore this experiment, #3, will focus on acidic solutions, yet will also include Vitamin C and salt solution as they prevented in previous experiments. It is hypothesized that if a potato slice bathed in acidic acid is exposed to oxygen; then the of produce and oxidation will be delayed and minimized. Procedure and Materials 1. Five paper plates to place produce slices were set up with the following labels: Vitamin C solution, lime juice (citric acid), lemon juice (citric acid)*, salt solution, and FruitFresh solution. *Both lemon and lime used to see if difference in acidity. 2. Lime juice and lemon juice were freshly squeezed into a bowl and placed behind labelled plate. Three teaspoons of the citrus juices were diluted with 30 ml (using a measuring cup) of warm H 2 O. Solutions of Vitamin C, salt and ascorbic acid were prepared in the following manner: a. Vitamin C- one tablet of 250 mg was crushed into powder and 30 ml of warm H 2 O was added and mixed. b. Salt solution- add 3 tsp. salt to 30 ml of warm H 2 O. c. FreshFruit solution- add 3 tsp of powder to 30 ml of warm H 2 O. 3. Two potato slices were immersed in each solution for three minutes for best results. 4. One potato slice was placed on labelled solution plate and the other in a plastic sandwich bag behind the plate. 5. Two slices were set aside for Control: on plate (no solution), another in plastic bag. 6. Potato slices were observed every thirty minutes and results recorded on data sheets. 7. At the end of one-hundred and eighty minutes top three best methods chosen and rated. 1-best, 2-good 3-ok 3
Data, Observations, Results The following tables represent experimental data obtained during the experiment. Tables will specify quantity of H 2 O used for dilutions as well as denote observations visible due to the rate of reaction with oxygen measured in thirty minute intervals for three hours. These changes are important to determine best technique to prevent of producing and oxidation reaction. Table 1. Potato Data Solution (A-no bag) (B-Bag) No solution Control A No solution Control B Vitamin C - A Vitamin C- B Lime Juice- A Lime Juice- B Lemon Juice-A Lemon Juice-B Salt Solution-A Salt Solution-B Time (in minutes) 30 min. 60 min. 90 min. 120 min. 150 min. 180 min. in middle & edges Less than no bag bleeding of skin, light brown patch Light uniform all over Less than no bag, spots around bleeding; same as More in same areas More No change No change Veins darkening; white powder on edges Wavy brown veins visible Darker Darker less than bag More No change No change Two spots of light brown patches Same spots, No change No change No change Browning like control, less than Vit. C, less than control control Browning, potato is wet Browning increase, water is released in bag Freshfruit- A Freshfruit acid-b Note: Experiment was conducted at room temperature. 4
It was observed from Experiments 1 and 2 which gave same results of, that acids prevented more than bases did. It was also observed that base solutions such as Baking Soda and Milk of Magnesia promoted of the produce. It can be assumed that solutions with a base ph (above 7.0) will promote enzymatic and oxidation of the produce. It can then follow that acids are more effective at preventing. Surprisingly, salt and sugar solutions worked quite well to prevent in apples and bananas, but did not work on the potato. The salt solution actually caused the potato to secrete water it had absorbed during the dipping (perhaps related to osmosis and diffusion). Perhaps the concentration of salt was not high enough to interfere with chemical reaction in the potato in this experiment. It was also observed that the main difference between Freshfruit and Vitamin C, which both contain ascorbic acid, is that FreshFruit contains ascorbic acid AND citric acid. Also, a very slight difference was seen between of solutions outside of a bag and inside of the bag. In solutions where occurred, the in the plastic bag was less than for the slice without it. However, in the case of lime juice (citric acid) and Freshfruit no change in color was observed. Also this experiment included both lime and lemon juice as lime has a more bitter taste leading one to wonder if it is slightly more acidic than a lime. Litmus papers for ph level specific tests were not available. Discussion & Conclusion Determination of the of produce was approximated with human sight and six observations over a three hour period. It must be emphasized that two minutes passed between each observation station (solution) which could provide slight inaccuracy in the results. This 5
experiment could be improved if each solution was done individually, however the whole process would be more time consuming. After analyzing experimental data, the hypothesis can be accepted due to the fact that acidic solutions had favorable results in preventing the of the potato slice. From table 1 it can be observed lime juice and fresh fruit had no appear on the potato slice, both inside and outside of the plastic bag. It is known that increases with direct contact to oxygen; however some food additive solutions can be used to prevent this. From the experiments performed it can be concluded that the of produce increases with a higher ph in bases and as time increases. The of produce decreases with low ph solutions such as acids, with acids with lowest ph having the best results. Browning is the result of the reaction between oxygen and the produce pigment, also known as oxidation. If oxidation can be prevented by applying an acidic solution to the potato slice, than it can be assumed that the acidic solution prevents or limits the reaction rate of pigment oxidation. This supports the hypothesis stated. It can be suggested that for future experiments on a more effective way to calculate rate of color change () or rate of reaction be used. Color observations are useful but could be supported by a numeric value of the rate of reaction of in acids, bases and vitamin C. It can also be suggested that instead of trying one fruit for multiple different solutions, one solution, i.e. salt water solution, could be tested on four different fruits to see if a variation in results is visible. This experiment has scientific errors as a regular cooking measure cup was used to estimate 30 ml of water. A more precise measuring instrument such as a graduated cylinder could improve this aspect of the experiment. It would also have helped to know the concentrations of the acids and bases being used on the produce to accurately define which acids work best and that variation in preventing are due to differences in strength. 6
Since concentrations of acids and rate of reactions could not be calculated a numerical value for percent error cannot be obtained. Top three techniques to prevent are Freshfruit as #1-best; Lime juice (citric acid alone) as #2, and Vitamin C (ascorbic acid alone) as #3. It should also be observed that the concentration of ascorbic acid in the 250 mg Vitamin C pill might have been less than the concentration of ascorbic acid found in FreshFruit powder. Finally, determining when the begins, changes or ends is not very accurate with the human eye. A microscopic view of the color change and computer analysis could have provided very specific and scientific results. 7