BIOO211 LabAssignment Rui ZHANG3 Essay

Submitted By Remeycn
Words: 1904
Pages: 8

Activities Part A

In this experiment I use apple as test item, and choice bottle water, lemon juice, white vinegar and sodium bicarbonate solution as anti-oxidant test solutions.

Control group
Group A
Group B
Group C
Anti-oxidant test item
Water
Lemon juice
White vinegar
Sodium bicarbonate solution
PH of anti-oxidant test solution
7
2
4
8
Observation colour of the cut surface soon after cutting
Plastic cling wrapped at room temperature
After 15mins
1
0
0
2
After 30mins
2
0
1
3
After 1hr
3
0
2
4
After 24hrs
4
1
3
5
Plastic cling wrapped in the refrigerator
After 15mins
0
0
0
1
After 30mins
1
0
0
2
After 1hr
2
0
1
2
After 24hrs
4
0
2
4
Key:
0=no browning 1=slight browning
2=less than half-coved light browning 3=half-covered light browning
4=total light browning 5=completely dark browning

Activity questions

1. In this experiment I use apple as test object, and choose lemon juice (pH=2), White vinegar (pH=4) and Sodium bicarbonate solution (pH=8) as anti-oxidant item. Water (pH=7) is used as the control object. According the table, all group have a trend of turning brown besides Group A (lemon juice). Objects in the room temperature shows it was turning brown faster and deeper than the object in refrigerator. Group A (lemon juice) barely changes the colour over the period of whole experiment. The apple coved with Sodium bicarbonate solution displayed the most browning in the all test objects of this experiment in the end.
(Word 103)

2. The experiment result indicates the order of anti-oxidants ability is lemon juice > white vinegar > water > bicarbonate solutions. The browning of apple slices are due to oxidation, but an enzyme called polyphenol oxidase from apple tissue can speed up the processing (scientific American 2008). Polyphenol oxidase is sensitive to extremes of pH because it interferes with weak ionic bonds that hold its 3D structure together (JVC’s Science Fun 2011). This is why low pH solutions can brown apple slowly than the other test items. Comparing with other test solution, bi-carbonate solution seems speed up the browning, because the bi-carbonate has high pH that contains higher amounts of oxygen.
(Word 112)

3. Polyphenol oxidase is the major cause of enzymatic browning in most of plants (FOOD-INFO 2015). In the experiment, all pH<7 test solutions can slow down the process of polyphenol oxidase. From pH5 to 9 is the pH range which most proteins, and therefore enzymes, are active only within. Adding citric, ascorbic or other pH lower than 4.0 acids slows down the enzyme activity (FOOD-INFO 2015). Low temperature can also slow down the reaction in the all test objects. There are two ways that temperature can affect an enzyme. One is a direct influence on the reaction rate constant, and the other is in thermal denaturisation of the enzyme at elevated temperatures. The polyphenol oxidase enzyme activity shows inhibited When temperatures below 7°C, but the enzyme is not inactivated (FOOD-INFO 2015).
(Word 135)

4. Free radical refers to a molecule compounds under light, heat or other external conditions, the occurrence of a covalent bond formed by homolytic having unpaired electron of an atom or functional group (Lobo et al. 2010). Free radicals can be produced through normal metabolic in the human body. It can also be formed from outside of human body like: by smoking, exposure to X-rays, environmental pollution, and industrial chemicals (Lobo et al. 2010). Free radical is highly active, once it form it can start chain reaction, like dominoes. We need contain free radical to maintain the vitality of the energy transfer, to kill bacteria and parasites and also to participate eliminate toxins (Lobo et al. 2010). If the body cannot balance free radical, a condition called oxidative stress will be happened. It will harm lipids, proteins and DNA of body and leads a number of human disease, such as heart attract, stroke and cancers (Lobo et al. 2010). Antioxidants can safely interact with free…