Extended Essay Sources Of Iodine


By Nick English

You've likely chewed on seaweed wrapped around a sushi roll, but few Westerners would consider picking up a bag of the stuff at the grocery store. It might be time for a change: Seaweed is filled with antioxidants, calcium and a broad range of vitamins, but that doesn't begin to scratch the slippery brown surface of this fascinating food.

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Why It's Super
A member of the algae family, edible seaweed typically comes in three varieties: brown, red and green. The most commonly eaten (and researched) are the brown varieties such as kelp and wakame, followed by red seaweed, which includes nori (yep -- that's what most sushi chefs use).

While seaweed-based cuisine has a proud history in many Asian countries, Japan has made it into an art form, employing over twenty different species in their fare. In a restaurant, you're most likely to consume seaweed in a small kelp (kombu) salad, simmered into miso soup, or wrapped around a sushi roll.

At just two tablespoons per serving, it's true that seaweed isn't a realistic source of many vitamins, and its benefits can occasionally be exaggerated. Seaweed contains vitamins A and C, and is also a source of calcium, which is one of the reasons some red seaweed supplements are included as part of some treatment plans for osteoarthritis. However, serving sizes are often not large enough to get a decent boost in these nutrients.

Seaweed's best-known benefit is that it is an extraordinary source of a nutrient missing in almost every other food: iodine. Consuming healthy levels of iodine is critically important to maintaining a healthy thyroid, a gland in your neck which helps produce and regulate hormones. A malfunctioning thyroid can result ina wide range of symptoms such as fatigue, muscle weakness and high cholesterol (to name a few). In severe or untreated cases, it can lead to serious medical conditions like goiters (a swelling of the thyroid gland), heart palpitations and impaired memory.

Since manufacturers started adding iodine to salt in the 1920s and the World Health Organization adopted a worldwide salt iodization program in 1993, symptoms of extreme iodine deficiency have largely disappeared. However, for a host of reasons, including iodine-blocking chemicals in our environment, the poor quality (i.e. iodine-free) salt used in processed foods, and a general trend of salt-ophobia among health conscious folks, mild iodine deficiency is once again becoming increasinglycommon.

The trouble with mild iodine deficiency is that it can manifest very subtly. Fatigue, depression, a higher susceptibility to diseases, difficulty losing weight -- these can all result from an underactive thyroid, and if the symptoms sound a little familiar, it's not hard to test yourself. But if you're keen to avoid thyroid drama (which, by the way, is especially important if you're pregnant), noshing  on some seaweed could help: One gram of brown seaweed contains roughly five to 50 times the recommended daily intake, while red and green varieties provide slightly less (the exact iodine content depends on the water in which it's grown).

The benefits of this sea green extend far beyond basic nutrition: Research suggests seaweed can also help regulate estrogen and estradiol levels -- two hormones responsible for proper development and function of sexual organs -- potentially reducing the risk of breast cancer. In fact, some claim Japan's high seaweed consumption is responsible for the country's conspicuously low incidence of the diseases . For the same reasons, seaweed may also help to control PMS (men, rejoice!) and improve female fertility issues.

And many studies have shown seaweed is an extraordinarily potent source of antioxidants and also helps prevent inflammation, which can contribute to a host of ailments that include arthritis, celiac disease, asthma, depression and obesity.

Your Action Plan
Before adding seaweed to all of your meals, consider that -- despite it's potential benefits -- this sea vegetable can be troublesomely healthy. Ten grams (roughly two tablespoons) of dulse, a type of red seaweed, has 34 times the amount of potassium in an equally sized serving of banana -- a high enough dosage to cause heart palpitations among people with kidney problems (though it should generally be safe for those without preexisting conditions).

Similarly, while the thyroid malfunctions without iodine, research suggests too much of the stuff can have its own side effects. The answer lies, as always, in moderation -- one two-tablespoon serving of brown seaweed every week will provide a happy medium, while nori's lower iodine content means you're free to enjoy a few rolls of sushi every week, if you wish.

It's also worth remembering that if the water the seaweed comes from is contaminated (with, say, toxic metals or arsenic), the seaweed will be as well. The US Food and Drug Administration regulates commercial seaweed, and they have pretty high safety standards, but it's important to note that the FDA does not regulate supplements. So if you're taking seaweed pills (yes, they're a thing), it's important to choose a reputable brand. Speak with your physician before you decide on supplements -- the metals in some seaweed pills could send you to the hospital, and they can be especially to dangerous to pregnant or lactating women and their babies.

With the right accompaniments, seaweed can be a flavorful component with a healthy dose of antioxidants and iodine -- just try not to eat an ocean's worth.

Do you have a favorite way to eat seaweed, or do you think we should steer clear of the stuff? Let us know below!

Extended Essay on how heating extra virgin olive oil to the range of temperature between 130 ºC and 190 ºC, the standard cooking temperatures, affects its free fatty acidity, peroxide value and phenol content

How does heating extra virgin olive oil to the range of temperatures between 130 °C and 190 °C, the standard cooking temperatures, affect its free fatty acidity, peroxide value and phenol content?

Extended Essay

Candidate name: Carlos Val Mas
Date of exams: May 2015
Subject: Chemistry
Supervisor: Amber Haq
Centre number: 000817
St George’s British International School
Candidate number: 000817-0067
Word count: 3996

Abstract
Olive oil is known to have many beneficial qualities. As it is widely used for cooking in my culture, I was interested in investigating how its nutritional qualities changed when exposed to high temperatures. Therefore, I asked:
How does heating extra virgin olive oil to the range of temperatures between 130 °C and 190 °C, the standard cooking temperatures, affect its free fatty acidity, peroxide value and phenol content?
I heated four extra virgin olive oil samples each one to a different cooking temperature: 130 °C, 150 °C, 170 °C and 190 °C for 10 minutes with a deep fat fryer. I left another sample at room temperature (20 °C) as a control. For each sample I measure: the free fatty acidity (FFA) by titrating it with potassium hydroxide, the peroxide value (POV) by using an iodometric titration method, and the phenol content by observing the color change in the Iron (III) chloride test. The detailed methods are given in the appendices.
The results show that the FFA increases over all the temperatures. The POV increases when the oil is heated from 20 °C to 130 °C, and it decreases between the 130°C-190°C range due to increasing rate of secondary oxidation. Lastly, the phenol content decreases. These values are linked; the rise in quantity of FFA increases the rate of oxidation (at low temperatures this increases POV whilst at higher temperatures this will decrease POV). This oxidation produces free radicals which then reduce phenol content.
Overall, I can conclude that olive oil’s beneficial health qualities declined when heated and even toxic substances were produced. Nonetheless, the short heating period and the absence of water-rich food were flaws in my experiment’s replication of cooking conditions, leaving unresolved the effects of long heat exposure and the heating of oil with food. Word count: 299
Contents
I have chosen to section this extended essay into six parts. My introduction will allow me to present the relevant context, and in the background information I will explain the chemical theory. As my investigation involves three different tests, in the experimental procedure I will present the design, data, conclusion and evaluation of each experiment separately. The analysis of the overall results is in the general conclusion. Due to the practical nature of my extended essay, I will include an appendix with the methods, raw data and risk assessment.
Page
Introduction 4

Background information
General Olive oil overview 5-6
Chemical changes that occur when olive oil is heated which will be tested for in my investigation
Hydrolysis 7-8
Oxidation 9-10
Phenol content 11-12

Experimental procedure
Hypothesis 13
Heating olive oil 13
Control variables common for all experiments 14
Experiment 1: Free Fatty Acidity 15-20
Experiment 2: Peroxide value 21-26
Experiment 3: Phenol content 27-28

Conclusion 29-30
Bibliography 31-32

Appendix
Appendix 1: 33
Appendix 2: Methods, apparatus, materials, raw data 34-37
Appendix 3: Risk assessment 38-39

Introduction
From a young age I have helped my grandfather harvest olives and bring them to the press. I had always thought that this oil was very healthy: its antioxidants lower risk of cancer and its mono-unsaturated fatty acids reduce low density lipoproteins (bad cholesterol) levels which cause heart disease. (I will explain in the background information). Recently, however, I read articles claiming these beneficial qualities decreased with temperature. I was interested in experimenting whether temperatures of 130 °C to 190 °C produce a detrimental chemical change to olive oil. These temperatures were chosen as cooking, chemically speaking, involves maillard reactions between sugars and amino acids which occur readily between 140 °C and 165 °C. (See appendix 1).
As my investigation focuses on nutritional and health aspects, I decided to test the following variables: free fatty acidity (FFA) as it gives the measure of the amount of hydrolysis; peroxide value (POV) as it shows the amount of primary oxidation and consequently the amount of toxic secondary oxidation products formed; and phenol content as it is the major antioxidant present in olive oil. (I will explain these in the background information.) Furthermore, POV and FFA are continuous variables which allow me to numerically analyze the data and compare it with reference values.
From all the above-mentioned comes my research question: How does heating extra virgin olive oil to the range of temperatures between 130 °C and 190 °C, the standard cooking temperatures, affect its free fatty acidity, peroxide value and phenol content?
1.1 Relevancy of experiment:
Knowledge on olive oil’s possible loss of health benefits is especially relevant in my home country Spain as 12.6 kg are consumed on average per person per year. The question is becoming more pertinent as world olive oil production has doubled since 1990 . Greater information on this topic could trigger consumers to purchase more heat resistant oils to cook at high temperatures (see comparison of oils in appendix 2) or use lower temperature cooking techniques.
Background information
General olive oil overview
2.1.1 Olive oil is the lipid obtained when the fruit of the Olea europaea plant is pressed. It is composed mainly of triglycerides.
A triglyceride is an ester composed of glycerol and three fatty acids. Although the exact composition of fatty acids in olive oil varies by cultivar, time of harvest or extraction process, the standard amounts are:
Oleic acid (55% to 83%), monounsaturated omega-9 fatty acid

linoleic acid (3.5 to 21%), polyunsaturated omega-6 fatty acid viii
Palmitic acid (7.5% to 20%), saturated fatty acidvii
viii
Stearic acid (0.5% to 5%) saturated fatty acidvii
viii
α-Linolenic acid (0 to 1.5%). Polyunsaturated omega-3 fatty acidvii
viii

2.1.2 Olive oil is an important source of Omega-3 and omega-6, two essential fatty acids that the body cannot synthesize. The terms Omega-6 and Omega-3 refer to the position of the first double bond relative to the terminal –CH3 group.
2.1.3 Fatty acids are classified according to the number of double bonds.
Saturated: no double bonds
mono-unsaturated: One double bond
Poly-unsaturated: multiple double bonds
2.1.4 The saturation of the fatty acids affects their melting point. Unsaturated fatty acids have kinks in their hydrocarbon chain as the carbon-carbon double bond angle is 120°. These kinks don’t allow the triglycerides to be packed closely together resulting in weaker van der Waals forces and consequently low melting points. As olive oil’s fatty acids are predominantly monounsaturated and polyunsaturated, it is a liquid at standard ambient conditions.

2.2__Chemical changes that occur when olive oil is heated which will be tested for in my investigation:

2.2.1 Hydrolysis:
2.2.1.1 Definition: Hydrolysis is the splitting of chemical bonds by the addition of water. First, the water molecule dissociates: H2O (l) H+(aq) + OH-(aq)
Then, the nucleophile (a nucleus-seeking agent such as OH- attacks the carbon of the carbonyl group (C=O).
The ester bond breaks and produces a carboxylic acid (fatty acid) and a diglyceride. The process repeats until a glycerol and three fatty acids are obtained.
Figure 2: Showing the hydrolysis of a triglyceride

2.2.1.2 Effect of temperature
The dissociation of water is an endothermic reaction; the greater the temperature, the more water will dissociate into its ions and thus the nucleophilic substitution will occur.
Additionally, with higher temperature there will be greater rate of collision and more of these colliding particles will have the necessary activation energy for to break the ester bonds between glycerol and fatty acids.

2.2.1.3 Other factors
Harvesting damage, delays between harvesting and extraction, fungal diseases, careless extraction methods, and storage conditions all affect hydrolysis.

2.2.1.4 Measurement:
Hydrolysis is measured by the amount of free fatty acids produced (specifically oleic acid).

Free fatty acidity (FFA: the measure of oleic acid in g per 100 g of oil.
Thus a rise in FFA means more hydrolysis has occurred.
As hydrolysis also causes an organoleptic (odor and flavor) deterioration as one tastes fatty acids more than triglycerides, the olive oil industry uses FFA classify oil’s commercial grades.

The International Olive Council (regulating 98 % of production) has the following standards:
Extra virgin olive oil: Max FFA of 0.8 g/100g
Virgin olive oil: Max FFA of 2 g/100g
Ordinary virgin olive oil: Max FFA of 3.3 g/100g

2.2.1.5 Nutritional implications
The glycerol and free fatty acids formed during frying have little relevance, as they are similar to those originating from the digestion through the action of pancreatic lipase in the body.

2.2.2 Oxidation:
2.2.2.1 Definition:
Oxidation is the degeneration of lipids involving oxygen through a free radical reaction. A free radical is an atom, molecule, or ion that has unpaired valence electrons or an open electron shell, and therefore is very chemically reactive.
Oxidation is composed of two stages:
Primary oxidation (formation of hydroperoxides)
Initiation:
The carbon-hydrogen is broken through homolytic scission in UV light: R-H→R·+H·
Propagation:
The resulting radicals react with oxygen forming peroxide radicals: R·+ O2→ROO·
These react with the hydrogen radical from the initiation stage to form a hydroperoxide.
ROO·+ H·→ROOH
Secondary oxidation (breakdown of hydroperoxides):
As seen in figure 9 , during secondary oxidation, the hydroperoxide undergoes homolytic (requiring UV light) β-scission (splitting of carbon-carbon bond) into free radicals RO· and OH·. These can then react to form aldehydic acids (polymer with 1 aldehyde and one carboxylic acid), diacids, ketones and hydroxyacids.
2.2.2.2 Effect of temperature
Oxidation is accelerated as more particles will be colliding successfully (with the necessary activation energy for the reaction to occur). Therefore, at high temperatures, the hydroperoxides formed during primary oxidation are decomposed much more rapidly. Also, due to lower oxygen pressure, many radicals (R·) produced in the initiation will react directly to form non-oxygenated dimers (R-R).
2.2.2.3 Other factors
Unsaturation increases oxidation as the double bonds in the fatty acid weaken the C-H bonds on the adjacent carbon atoms and makes H removal easier.
Hydrolysis also increases oxidation as free fatty acids oxidize faster than triglycerides. C. Dobarganes, the director of the ‘Instituto de la Grasa’, explained to me that free fatty acids have greater mobility and are more polar compared to triglycerides. Additionally, she said that triglycerides are harder to oxidize as it is more difficult for oxygen to attack their sn2 position (2nd carbon).
Measurement
The peroxide value (POV) : the amount of peroxide oxygen per 1 kilogram of fat or oil.
The POV is expressed in milliequivalents (meq). This is the defined as the amount of substance which will react with one mole of hydrogen ions (H+) in an acid–base reaction (mols x valence).
(N.B. 1 meq O2=; because 1 meq of O2 =1 mmol/2= 0.5 mmol of O2, where 2 is valence).

2.2.2.5 Nutritional implications
The aldehydes produced in secondary oxidation are toxic and are related to neurodegenerative diseases. Some of the low molecular aldehydes may also produce pathological effects in liver or thymus if ingested in high concentrations

2.2.3 Phenol content:
2.2.3.1 Definition
Olive oil contains phenolic compounds; chemical compounds consisting of a hydroxyl group (—OH) bonded to a benzene ring. The average total phenol content in olive oil is 500mg/kg.
There are two different types:
Hydrophilic phenols: phenolic alcohols and acids, flavonoids, lignans and secoiridoids.
Flavonoid polyphenols: They have a 15 carbon skeleton which consists of two phenyl
(6 carbon) rings and a heterocyclic ring: C6-C3-C6.
2.2.3.2 Antioxidant capacity
Phenols reduce free radicals by getting oxidized themselves.
The hydroxyl group in phenols is a good hydrogen donor. The hydrogen then reacts with the free radicals, R•, and a radical form of the antioxidant, PO• is produced .
R• + POH → R-H + PO•
These radicals produced, PO•, can also remove further free radicals in a termination reaction.
R• + PO• → RPO (formation of phenolate ion)
PO• + PO• → PO-PO (formation of dimer)

2.2.3.3 Effect of temperature
Many phenols get evaporated at high temperatures. For example, tyrosol evaporates at 158 °C and hydroxytyrosol evaporate at 174 °C .
More importantly, at higher temperature there is greater oxidation which means more free radicals. The phenols will get oxidized and will no longer be recognized as phenols but as phenolate ions or dimers.

2.2.3.4 Other affecting factors
Olive Variety
Time of Picking: green olives have more polyphenols than ripe olives.
Processing: When olives are in contact with water, hydrophilic phenols are lost in diffusion.
Refining: Using filters to reduce acidity will decrease antioxidant content.
Time stored: Polyphenol levels decreases during storage time.

2.2.3.5 Nutritional implications
Phenols prevent of a number of free radical caused degenerative diseases such as:
Cancer
Cardiovascular disease

3. Experimental Procedure
3.1 Hypothesis:
Due to increased kinetic activity I expect oxidation and FFA to increase. A rise in FFA would further increase oxidation as it occurs faster on free fatty acids. Consequently, at high temperatures, the phenol content will decrease as phenols will both reduce more free radicals and get evaporated. Increasing oxidation will trigger an increase in POV until a certain temperature, after which it will decrease due to a higher rate of hydroperoxide formation (primary oxidation) than decomposition (secondary oxidation).
3.2 Heating olive oil
3.2.1 Type of olive oil:
Extra virgin olive oil from a local organic grower. This ensures that it contains no other substances.
3.2.1 Summary of method for heating olive oil:
I heated four 100 ml extra virgin olive oil samples, each one to a different cooking temperature: 130 °C, 150 °C, 170 °C and 190 °C for 10 minutes with a deep fat fryer. I left another sample at room temperature (20 °C) as a control. After heating oils, I stored them in a dark refrigerator to prevent oxidation and hydrolysis.
3.2.2 Adaptation of method:
As the school didn’t have an isomantle, I first used a hot plate. However, this didn’t let me control the temperature and it didn’t heat the oil homogeneously. Therefore, used a deep fryer which auto-regulated to stay at a specific temperature.
3.2.3 Evaluation of method:
Weakness Improvement
Although the deep fryer would automatically stabilize at a temperature, there was some fluctuation. Hence I used a ± 5 °C as the uncertainty. The use of an isomantle would provide a stable temperature. This would allow the conditions to be controlled for all of the temperatures.
3.3 Control variables common for all 3 experiments:
Name of variable
(possible errors) Value it was controlled at Possible effects of not controlling variables
Temperature of reactants 20 °C (room temperature) Temperature affects rate of the reactions due to increased kinetic energy of particles and also shifts equilibriums (specifically relevant for ionization of water in titrations.
The glassware I used was calibrated at 20°C so temperatures different to this would have caused inaccurate measurements.
Speed and time at which it was swirled. I specified the time in each method. When swirling I used same magnetic stirrer. When shaking, I tried to be as consistent as possible although this still had human error. Greater swirling or shaking increases motion of particles and thus their chances of collision. Rate of reaction increases.
Ambient light I did all trials with the same lighting. The colors in the titrations, or Iron (III) chloride test would appear different.

3.4 Experiment 1 (Free Fatty Acidity)
3.4.1 Variables:

Independent variables: Temperature to which oil is heated for ten minutes.
Dependent variables: Titer of potassium hydroxide for solution to become colorless.
Specific Control variables:
The end point in the titration is when the pink color lasts more than 30 seconds. This is still susceptible to human error.
3.4.2 Explanation of method

Free fatty acids are non-polar so I used propan-2-ol to dissolve them. Then I titrated the solution with alkali potassium hydroxide solution using phenolphthalein as an indicator. Oleic acid behaves like a weak acid as it has the carboxylic acid group (-COOH). It will react with potassium hydroxide until a neutral solution is reached:
C18H34O2 (aq) + KOH (aq) K + C18H33O2 (aq) + H2O (l)

Phenolphthalein changes color 8.2 . Figure 10 shows that the pH of the reaction changes rapidly (from 7 to 11) close to the equivalence point. Thus, phenolphthalein is a suitable indicator as its uncertainty is acceptable.

3.4.3 Results
Note: The raw data for this experiment is found in appendix 2
In order to calculate the FFA I used the following formula:
Free acidity=█(@ 100× T/1000 × M x 282.4)/w
Where:
100 is used as FFA is measured as g in 100 g of oil
T is the volume in ml of KOH solution used (in dm3)
M is the molarity of the KOH solution (0.25 mol / dm3)
W is the weight of the sample of oil in grams (10 g)
282.4 is the molar mas of oleic acidxxxiii
For example, at 20°C, the FFA calculation given that the titers at each trial are:
Trial 1: 0.6→((0.6/100*0.25*282.5))/10=0.423=0.4
Trial 2: 0.8→((0.8/100*.25*282.5))/10=0.564=0.6
Trial 3: 0.9→((0.9/100*.25*282.5))/10=0.6345=0.6
Average FFA=((0.423+0.564+0.6345))/3=0.5405= 0.5
STD deviation= 0.1076 =0.1
STD error=0.1076/(√3)=0.06

I also calculated the uncertainty for my each FFA value.
As the uncertainty for the titer is ±0.2 cm3, the % Uncertainty of my first trial= (±0.2 cm^3)/(0.6 cm^3 ) = ±33.3%
As the uncertainty for the mass of oil is ±0.1 ml, the % Uncertainty of mass of olive oil= (±0.1 ml)/(10 ml) =±1%
To find the uncertainty of the FFA value, one adds the two % uncertainties:
% Uncertainty of FFA= ±33.3% ±1%=±34.3%
One then multiplies the % uncertainty with the value:
Unc. of FFA=±34.3% * 0.4 (meq/kg)= ±0.1372= ±0.1 (1dp) (meq/kg)
I then averaged this value with the uncertainties of the other two trials at20°C.
The FFA results of all of the trials with their respective average % uncertainty are seen in the following table. The specific table regarding uncertainty calculations is in appendix 2.
Table 1: Table showing processed data of free fatty acidity titration and the calculation of free acidity with their statistical measures
Temperature to which oil was heated ±5°C Titer
(±0.2cm3)
FFA
(g oleic acid/100 g oil)
Average FFA
(g oleic acid/100 g oil)
STD Deviation
STD Error Average uncertainty of FFA
±g/100 cm3 oil

20
0.6 0.4 0.5 0.1 0.1
0.8 0.6 0.06
0.9 0.6
130 1.1 0.8 0.7 0.1 0.06

0.1
0.9 0.6
0.8 0.6
150 1.2 0.8 0.8 0.1 0.06

0.06 0.1
1.0 0.7
1.3 0.9
170 1.9 1.3 1.3 0.1 0.04

0.20 0.2
1.8 1.3
2.0 1.4
190 2.7 1.9 1.6 0.4 0.20

0.2
2.3 1.6
1.7 1.2
Graph 1:

Graph 2:

3.4.5 Analysis:
According to both graph 1 and 2, the FFA value increases as temperature rises. The FFA rises from a value of 0.5 to 1.5. However, there is little increase between the 20 °C sample (0.5) and the sample heated to 130 °C (0.7). This shows that significant levels of hydrolysis began around the 130 °C mark. In fact, the main increase is between 150 °C to 170 °C (0.8 to 1.3).
The IOC sets a maximum FFA value of 2 for virgin olive oil. In my experiment, the values were below this value. There are two reasons which explain this: the exposure time of the olive oil to the heat was short and there was little water in the oil compared with the amount introduced by foods when fried. Water is necessary for hydrolysis to take place.
3.3.6 Evaluation of Free acidity test:
Weaknesses Improvements
The uncertainties in this test were considerable (from 9% to 22%). However, data points do not overlap on graph. To reduce error when determining end point, I could use a colorimeter. I could also use a pH sensor instead of a titration. This would be more precise. However, if badly calibrated, this could cause considerable systematic errors.
3 trials are too few In order for STD deviation and error to be statistically relevant I should have done 30 trials minimum.

Accuracy: I believe the data is mostly accurate as the value of FFA obtained for the 20 °C is 0.5. This is in line with the IOC regulation of S4O62- + 3 I-

The starch indicator forms a deep blue color clathrate (lattice containing different molecules) with the triiodide (I3-). When the iodine molecule is reduced into iodide ions I- , the clathrate is decomposed so the color disappears. This is the titration point.

3.5.3 Adaptation
The AOCS recommended the use of chloroform; a solvent not permitted by school health and safety regulations. So, I consulted with the University of Jaen’s Department of Olive studies who suggested using 2,2,4 Trimethylpentane instead. This chemical was also risky, however, I contacted the Chemistry Advisor at CLEAPPS and he saw no significant hazards.

Results:
Note: The raw data for this experiment is found in appendix 2
In order to calculate the POV, I used the following formula:
POV= ((T-T_(0))*c*1000)/2
T = Titer of sodium thiosulfate solution
T0 = Titer of sodium thiosulfate solution in the blank test
c =molarity of the sodium thiosulfate solution
m = mass of oil sample (2g)
For example, at 20 °C, and given that the blank titer for this titration is 0.1 cm3, the POV calculations values for each trial were:
Trial 1: Titer= 0.9 →T-T0 =0.9-0.1 cm3= 0.8 → POV= ((0.8 cm^3*0.05 mol)/(dm^3*1000))⁄2g =20.0 meq/kg=
Trial 2: Titer= 0.8 →T-T0 = 0.8-0.1= 0.7 → POV= ((0.7 cm^3*0.05 mol)/(dm^3*1000))⁄2g =17.5 meq/kg
Trial 3: Titer= 0.9 →T-T0 = 0.9-0.1= 0.8 → POV= ((0.8 cm^3*0.05 mol)/(dm^3*1000))⁄2g =20.0 meq/kg
I then found the average POV value:
Average POV =(20+17.5+20)/3=19.166= 19.2 meq/kg
To understand dispersion of the data, I calculated:
STD Deviation= 1.443375673= 1.4 STD error= 1.44337/√(3)= 0.833333333= 0.8
I also calculated the uncertainty for each POV value. For the first trial I did the following calculation:
As the uncertainty for the titer is ±0.2 cm3 and the uncertainty for the blank titer is ±0.02 cm3,
Then, the % Uncertainty of (T-T0)= (±0.22 cm^3)/(0.8 cm^3 ) = ±27.5%
As the uncertainty for the mass of oil is ±0.1 g, the % Uncertainty of mass of olive oil= (±0.1 g)/(2 g) =±5%
To find the uncertainty of the peroxide value, one adds the two % uncertainties:
% Uncertainty of POV= ±27.5% ±5%=±32.5%
One then multiplies the % uncertainty with the POV value calculated:
Unc. of POV =±32.5% * 20 (meq/kg)= ±6.5 (meq/kg)
I then averaged this value with the uncertainties of the other two trials at 20 °C.
((6.5+6.4+6.5))/3= ±6.5 (meq/kg)
The specific table regarding all uncertainty calculations is in appendix 2.
All he POV results with their respective average % uncertainty is seen in the following table.
Table 1: Table showing the blank titration value
Blank titration (T0) cm3 ±0.02 0.10

Table 2: Table showing the peroxide value for each temperature with the average % uncertainty (meq/kg)
Temp. ±5 °C Titer of KOH ±0.2 cm3
Titer-blank titer
(T-T0)
±0.22 cm3
Concentration of Na2S2O3 (mol/dm3) mass of oil
±0.1 g POV (meq/kg) Average Peroxide Value
(meq/kg) STD Deviation STD error Average uncertainty of Peroxide Value
(±meq/kg)
20 0.9 0.8 0.05 2.0 20.0 19.2 1.4 0.8
0.8 0.7 17.5 6.5
0.9 0.8 20.0
130 1.5 1.4 35.0 35.0 0.0 0.0 7.3
1.5 1.4 35.0
1.5 1.4 35.0
150 1.4 1.3 32.5 29.2 3.8 2.2 7.0
1.1 1.0 25.0
1.3 1.2 30.0
170 0.8 0.7 17.5 19.2 1.4 0.8 6.5
0.9 0.8 20.0
0.9 0.8 20.0
190 0.8 0.7 17.5 15.0 2.5 1.4 6.3
0.6 0.5 12.5
0.7 0.6 15.0

Graph 3:

Graph 4:

3.5.5 Analysis:
In graph 4, there is a considerable rise in POV from 19 meg/kg to 35 meg/kg, between 20 °C and 130 °C, and a decrease from 35 meq/kg to 15 meq/kg, between 130 °C and 190 °C. I assume that the decrease in POV above 130 °C is caused by an increase in secondary oxidation compared to primary oxidation. (See oxidation of lipids pathway) A paper by the AOCS (American Oil Chemists Society) specifically states that after 150 °C hydroperoxides become mostly absent.
Graph 3 shows a linear trend line. This suggests that secondary oxidation is directly proportional to temperature.
There are some assumptions I made when drawing the trend lines in the graphs: I assumed that the peak in POV occurred close before 130 °C, I did not know specifically at which temperature. Therefore, the trend line is not fully accurate.
3.5.6 Evaluation of POV method:
Precision
Weaknesses Improvements
Due to inaccurate methods such as the endpoint determination in the titration, the uncertainties were between ±20.7% and ±42.4%. A potentiometric endpoint determination could be used or a spectrophotometric determination of the I3- chromophore.
3 trials are too few For STD deviation and error to be relevant I should have done 30 trials.
Accuracy:
Although I am not able to calculate a percentage error as there is no ‘standard’ olive oil, my results were accurate because extra virgin olive oil should have a POV less than 20 meg/kg at 15 °C . My result was 19 meg/kg at 20 °C. The blank titration (V0) is accurate as the blank titer should be below 0.05 cm3 when using 0.1 M Na2 S2O3. As I used a concentration of 0.05M, a blank titer of 0.08 cm3 is acceptable.
3.6 Experiment 3: Phenol Content
3.6.1 Variables:
Independent variables: Temperature to which oil is heated for ten minutes.
Dependent variables: Color of solution when Iron (III) chloride is added
3.6.2 Explanation of method
The Iron (III) chloride test
The phenolic compounds in the oil will react with iron (III): 3 C6H5OH + FeCl3 → Fe(OC6H5)3 +3HCl
The electromagnetic influence of the phenol splits the incomplete d-orbitals of the iron. With light, the electrons get excited from the lower to the higher energy sublevel and a photon of green light is absorbed. Consequently, the complementary color (violet) is seen.
3.6.3 Adaptation of method
The original method used dichloromethane as a solvent. As this was too hazardous I substituted it with a water-ethanol mix. As most phenols in olive oil are hydrophilic this was still effective.
3.6.4 Results
Temperature to which oil was heated ± 5 °C 20 °C 130°C 150°C 170°C 190°C
Image of oil
3.6.5 Analysis
Although the color observed was not violet, as the olive oil is green, the paling of color with as temperature rises shows a decrease in phenol content. There is also a significant decrease in phenol content between 150 °C and 170 °C.
3.6.6 Evaluation of Ferric (III) chloride test:
Weaknesses Improvements
Iron (III) Chloride test provides qualitative results. Hence, it is not as precise. I could use the Folic-Ciocalteau assay. This is still colorimetric but, it is more precise.
For quantitative data to be obtained, spectroscopic techniques could be used. I could also use a colorimeter. However, the school lab did not have the necessary apparatus.

Accuracy:
My results are in line with a study that reported that at temperatures of 177˚C, about 60% of the dihydroxyphenols in extra virgin olive oil are lost after 10 minutes. Additionally, my results are supported by the fact that phenols get evaporated at high temperatures.

4. Conclusion
How does heating extra virgin olive oil to the range of temperatures between 130 °C and 190 °C, the standard cooking temperatures, affect its free fatty acidity, peroxide value and phenol content?
I hypothesized that increased kinetic activity would cause oxidation and FFA to increase. A rise in FFA would further increase oxidation as it occurs faster on free fatty acids. Consequently, at high temperatures, the phenol content will decrease as phenols will both reduce more free radicals and get evaporated. Increasing oxidation will trigger an increase in POV until a certain temperature, after which it will decrease due to a higher rate of hydroperoxide formation (primary oxidation) than decomposition (secondary oxidation).
My hypothesis was proved correct by my results. In graph 1 FFA increases throughout and in graph 2 POV increased between 20 °C and 130 °C but decreased from 130 °C to 190 °C. Decreasing POV shows that stronger (secondary) oxidation occurred so it can be concluded that both hydrolysis and oxidation increased. The Iron (III) chloride test demonstrated a decrease in phenol content with temperature.
The biggest changes in all three tests occurred between the 150 °C to 170°C mark. This shows the relationship between the values. It also provides a temperature above which it is unrecommendable to cook.
From a health view point, it can be concluded that secondary oxidation does accelerate at temperatures above 130 °C. The aldehydes produced in secondary oxidation are toxic. Additionally, the phenol content also decreases, thus, the beneficial antioxidants olive oil is famous for are lost. The increase in FFA does not have health implications as free fatty acids are safe to eat. Nonetheless, it makes the use of top quality (low FFA) olive oil for cooking unnecessary.
Regarding taste and smell, when the POV Is between 30 and 40 meq/kg, a rancid taste is noticeable . As the POV at 130 °C was 35 meq/kg, it can be concluded that heating the oil to 130 °C and above for ten minutes would produce a rancid taste in the oil.
Unresolved questions:
I did not consider the effect of heating the oils with food. This is important because the conditions of cooking should have been realistically replicated.
It would also be interesting to investigate the effect of repeated exposures to heat (refrying). This is relevant as frying oil is often reused.

5. Bibliography

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