Enzymatic Browning is a natural occurrence that mainly takes place in a wide range of fruits and vegetables “1”. When a fruit or vegetable is bruised, cut, or peeled, they start to darken quickly due to the development of brown melanin. The brown melanin arises due to the oxidation of phenolic compounds present in the fruits. One of the common fruits where enzymatic oxidation takes place is in the apples. Enzymatic oxidation is not automatic, but instead, it follows a series of steps“1”. Most apples contain an enzyme known as polyphenol oxidase (phenolase). Phenolase has additional components such as catecholase, crelose activity, and some small traces of copper. When an apple is sliced into pieces, it releases phenolase from its cell, exposing it to oxygen“1”. It then reacts with atmospheric oxygen, catalyzing the biochemical conversion of phenolic compounds to o-quinones. The formed o-quinones are converted to colorless precursors, leading to the formation of a brown-colored substance. The Brown secondary mater is what is, on most occasions, known as melanin. Drago (2016) note that the rust-like reaction occurs on the surface of the apples since those cells have been broken, and this process often releases phenolase and other enzymes that can easily react with atmospheric oxygen “1”. As a result, phenolase is the compound that plays an active role in enzymatic browning especially when it is exposed to oxygen.
Description of my observation
The exposure of enzymes to atmospheric oxygen is the first step that initiates the browning process. When analyzing the apple in the experiment, five pieces out of six were placed in different solutions, including vinegar, water, baking soda, lemon, and magnesia milk. One of the observations made is that for greater enzymatic browning to occur, an ideal or favorable environment should be provided. Most reactions take place at a temperature of around 37.5 degrees “2”. However, when the temperatures are high, the enzymes may be denatured, preventing a reaction. When the temperature is reduced, it reduces the rate of a reaction; however, it does not completely hinder the reaction from taking place“2”. Understanding these concepts is key towards understanding why browning may be intense in some of the sliced apples while it may be mild in some. Based on my observation, the sliced apple that was placed in the water had a bit of browning due to the following reason. Placing the apple in water restricts the amount of oxygen that comes in contact with phenolase. As a result, this act temporarily inhibits the formation of melanin. However, as time progressed, it would begin to brown slowly. Later on, the browning would subside due to the evaporation of water or the presence of traces of oxygen. This explains why the apple placed in water was not intense.
The apple that was placed in lemon also experienced slight browning because of the decreased PH levels. As a result, the citrus juice in the lemon would result in the removal of metal ions in the enzymes, phenolase would be restricted, and this would prevent browning “5”. Additionally, the enzymatic browning was not intense in vinegar, an aspect that may have resulted from the inability of phenolase to react with oxygen efficiently in an acidic medium “5”. There was intense browning in the sliced apple that was placed in magnesia milk. Magnesium is one of the active ingredients in Magnesia milk. As a result, when the sliced apple was placed in magnesia milk, the magnesium reacted with oxygen, hence donating one of its electrons to it. After the oxygen received one of the electrons, it oxidized magnesium, meaning there was an addition of oxygen “3”. Due to the addition of oxygen, it catalyzed the reaction, leading to the brown substance forming at a faster rate. This observation can be directly observed on the piece of apple after it was removed from the magnesia milk: intense browning had taken place.
Purpose of Control Experiments.
Having a control in any scientific study is an important factor. A control constitutes an element that often remains unchanged or unaffected with the other variables in the experiment. Most experimenters use controls since it can be used as a benchmark or a point of reference when making comparisons with findings from a given study “4”. As a result, most controls are often held constant throughout the experiment. When analyzing this experiment, the inclusion of the solutions to test enzymatic browning may play a role in influencing the final outcome. However, with the inclusion of control, it aids in minimizing the effects of factors other than the one that is being tested “4”. Without including a control in this experiment, it would be impossible to ascertain if the experiment is working. As a result, using it helps assure the experimenter that the treatment being given is working and is not being influenced by other things outside the experiment“4”.
The absence of controls in any scientific experiment makes it impossible to have a basis of understanding if the obtained results was due to the variable being tested or was due to some external factors“4”. Based on the advantages associated with controls, every experiment should incorporate it since it forms the basis of comparison.
In conclusion, enzymatic browning is a natural phenomenon occurring in different vegetables and fruits, especially when cut or bruised. The reaction of phenolase and oxygen leads to the formation of melanin on the surface of the apple. To ensure that enzymatic reaction is minimized, cut fruits should not be exposed to oxygen.
References.
- Singh, B., Suri, K., Shevkani, K., Kaur, A., Kaur, A., & Singh, N. (2018). Enzymatic browning of fruit and vegetables: A review. Enzymes in food technology, 63-78.
- Quevedo, R., Pedreschi, F., Bastias, J. M., & Díaz, O. (2016). Correlation of the fractal enzymatic browning rate with the temperature in mushroom, pear, and apple slices. LWT-Food Science and Technology, 65, 406-413.
- Tang, T., Xie, X., Ren, X., Wang, W., Tang, X., Zhang, J., & Wang, Z. (2020). A difference of enzymatic browning unrelated to PPO from physiology, targeted metabolomics, and gene expression analysis in Fuji apples. Postharvest Biology and Technology, 170, 111323.
- Li, X., Ding, P., & Rubin, D. B. (2018). Asymptotic theory of rerandomization in treatment–control experiments. Proceedings of the National Academy of Sciences, 115(37), 9157-9162.
- Sariri, R., & Ghafoori, H. (2017). Antioxidant and anti-tyrosinase activity of lime extracts. Biosciences Biotechnology Research Asia, 6(2), 545-550.
