Glycaemic Index

Low GI food or high GI food?
What is GI?
How is it measured?
What does it mean?
These are many other questions are addressed in AUS-e-TUTE's new glycaemic index (GI) resources.
AUS-e-TUTE Members should log-in to access the new tutorial, game, test and exam.
If you are not an AUS-e-TUTE Member you can access a "free-to-view" tutorial for evaluation purposes at https://www.ausetute.com.au/glycaemic.html

Hydrolysis of Carbohydrates

Carbohydrates like disaccharides and polysaccharides can be broken down into monosaccharides.
In the lab we use acid hydrolysis, but in your body you use enzymes to do this.
AUS-e-TUTE has just added a new tutorial, game, test and exam to help you understand these chemical reactions. Members should log-in to access these new resources (under Biochemical reactions).
If you are not an AUS-e-TUTE member you can access a "free-to-view" tutorial at https://www.ausetute.com.au/hydrolysiscarbs.html

Spud Lite?

"Spud Lite", the advertising poster said, "25% less carbs", followed in fine print by "than other potatoes".
"How strange", I thought, "I thought you ate potatoes for their carbohydrate (carbs) content so why would you want a potato with less carbohydrate?"
But then I started thinking about what this meant in terms of the chemical composition of the potato. If it contains 25% less carbohydrate, then surely that means something else must have been increased or added? Or are you just getting less potato for your money?

Typically, a traditional potato has the following approximate composition:

nutrient	% by mass
water	79
carbohydrate	17.5
protein	2
fat	0.1

 That is, 100 g of traditional potato contains about 79 g of water, 17.5 g of carbohydrate, 2 g of protein and 0.1 g of fat.

One way to reduce the percentage of carbohydrate in a potato would be to reduce the density of the potato.
If 100 g of a traditional potato had a volume of 92 mL, then the density of the potato would be 1.09 g/mL. 1 mL of traditional potato has a mass of 1.09 g and contains 17.5% by mass (0.19 g) of carbohydrate.
If "spud lite" has a lower density of potato "flesh", say 0.8 g/mL, then 1 mL of "spud lite" has a mass of 0.8 g and contains 17.5% by mass (0.14 g) of carbohydrate.
If we then compare equal volumes (sizes) of potatoes, say 1 mL of traditional potato and 1 mL of "spud lite" we find that "spud lite" contains 100 x (0.19 - 0.14)/0.19 = 26% less carbohydrate (by volume!).
But, if the density of "spud lite" is less, the % by mass composition remains the same, that is, for every 100 g of potato (traditional or "spud lite") there will be 17.5 g of carbohydrate (but the "spud lite" potato will be a bigger potato for your 100 g).

The nutrition label on a packet of "spud lite" potatoes gives the following masses per 100 g of potato:

• fat < 0.1 g
• protein 1.4 g
• carbohydrate: 8.9 g
• sugars: 1.1 g
• dietary fibre:  1.4 g

So, the total carbohydrate content is 8.9 + 1.1 + 1.4 = 11.4 g
(assuming the dietary fibre is cellulose which is also a carbohydrate).
This means that the actual mass of carbohydrate per 100 g of potato has been decreased. That is, "spud lites" are not just less dense than traditional potatoes.

 Another way to decrease the proportion of carbohydrate in your potatoes would be to increase their water content.
Imagine you have 100 g of traditional potato. This potato is made up of 79 g of water and 17.5 g of carbohydrate.
"Spud lite" contains 11.4 g of carbohydrate.

If all the lost mass of carbohydrate in the "spud lite" (17.5 - 11.4 = 6.1 g) was present as water, then the mass of water in "spud lite" = 6.1 + 79 = 85.1 g

And you, the consumer, is just paying for additional water in your potato!

Further Reading
 Experimental Design

 Carbohydrates
Proteins
Lipids (fats and oils) 
Percentage Composition
Density 

Suggested Study Questions:

1. Design an experiment to test the hypothesis that "spud lite" potatoes have a lower density than traditional potatoes.
2. Design an experiment to test the hypothesis that "spud lite" potatoes have a greater percentage by mass of water than traditional potatoes.
3.  For each serving of traditional potato given below, calculate the mass of carbohydrate consumed:
• 25 g of potato
• 75 g of potato
• 135 g of potato
4. Calculate the mass of "spud lite" you would have to consume in order to obtain
   • 1 g of carbohydrate
   • 7 g of carbohydrate
   • 21 g of carbohydrate
5. The density of potato changes as the potato ages on the shelf. The table below shows the results of an experiment in which the mass and volume of the same potato is measured and recorded every 3 days. Calculate the density of the potato on each day.

   Day	Mass (g)	volume (mL)
   1	142	130
   4	140	129
   7	138	128

6. Consider the results of the experiment above. Describe any trends that you see in the data and suggest reasons for these trends.
7. Explain what chemists mean when they refer to "carbohydrates".
8. The nutrition label on "spud lites" lists the mass of carbohydrate, sugars and dietary fibre separately. What do you think the "carbohydrate" is on this label?
9. Add together the percent by mass of all the components listed for a traditional potato.Suggest reasons for why the total percentage is less than 100%.
10. Potatoes are usually classified as high on the glycemic index (GI). What does this mean?

Sucralose and Acesulfame potassium

Artificial sweeteners,  especially aspartame, have hit the news headlines once again with PepsiCo's decision to start selling Diet Pepsi without aspartame from August 2015 in the USA. The aspartame is to be replaced by a blend of sucralose and acesulfame potassium.

Sucralose was discovered in 1976 when Shashikant Phadnis at Queen Elizabeth College was asked to "test" a chlorinated sugar compound but he thought he'd been asked to "taste" it, so he did, and found it be very sweet! Sucralose, shown on the right, is synthesised from sucrose in a number of steps in which 3 of sucrose's hydroxyl groups are substituted for chlorine atoms.
Although sucralose is about 300 times sweeter than sucrose, it is not broken down during digestion and therefore does not contribute to ingested calories (kilojoules).
Splenda is a brand name for a common sucralose-based sweetener.


Acesulfame potassium was accidentally discovered in 1967 by German chemist Karl Clauss, who found it to be sweeter than sucrose. It is not as sweet as sucralose, however, and is often used in combination with other artificial sweeteners such as aspartame or sucralose. It has the structural formula shown below:

Acesulfame potassium is currently sold under the brand names Sunette, Sweet One and Sweet 'n Safe and is found in many "sugar-free" foods such as chewing gum, jelly (Jell-O), even in alcoholic drinks.

Reference:
http://www.smh.com.au/business/retail/diet-pepsi-dumps-aspartame-as-consumer-backlash-hurts-sales-20150425-1msz1b.html

Further Reading:

• http://www.ausetute.com.au/sugars.html 
• http://www.ausetute.com.au/proteins.html
• http://www.ausetute.com.au/fungroup.html
• http://www.ausetute.com.au/intermof.html
• http://www.ausetute.com.au/skeletal.html
• http://www.ausetute.com.au/structural2D.html
• http://www.ausetute.com.au/condensedsf.html
• http://www.ausetute.com.au/molecularformula.html

Suggested Study Questions:

1. What is the molecular formula for:
   • sucralose
   • sucrose
   • acesulfame potassium
2. Draw the structural formula for sucrose and circle the hydroxyl functional groups.
3. Draw the structural formula for sucralose and
   • circle the hydroxyl functional groups in red
   • circle the halogen functional groups in green
   • circle any other functional groups blue and name them 
4. What class of compounds does sucrose belong to?
5. Draw the structural formula for acesulfame potassium and identify the functional groups.
6. Is it appropriate to call acesulfame potassium a potassium salt? Explain your answer.
7. Aspartame is the methyl ester of a didpeptide. What functional groups do you expect the aspartame molecule to have? Explain your answer. 
8. Do you expect sucralose and acesulfame potassium to be soluble in water? Explain your answer.

Sulfuric Acid and Sugar

November 28, 2014, The Canberra Times reported that, "Students were looking on as a teacher conducted an experiment involving sugar and sulfuric acid inside a cabinet when the glass container holding the acid exploded."
The experiment referred to is probably similar to the one shown in the YouTube video below in which concentrated sulfuric acid from a container is poured over sugar in a beaker.

Safety Notes

Sulfuric acid will cause permanent damage if it comes into contact with the eyes or skin. Concentrated solutions of sulfuric acid are extremely corrosive. When sulfuric acid is dissolved in water enough heat is released to make water boil! Carbon monoxide and carbon dioxide are both toxic gases. Sulfur dioxide gas is toxic in high concentration and is a severe respiratory irritant at lower concentration.Some people, especially those prone to asthma, may be especially sensitive to sulfur dioxide. In the presence of moisture, sulfur dioxide forms an acidic, corrosive solution, which in contact with the skin or eyes may lead to burns.

You will notice that the reaction seems to proceed slowly at first. The reaction mixture turns yellow as the reaction begins. This reaction releases heat, it is said to be an exothermic reaction. The heat produced by the reaction then speeds up the rate of further reactions, and, in the video, this is also accelerated by stirring the mixture.

Table sugar is made up sucrose, molecular formula C₁₂H₂₂O₁₁ and structural formula as shown below:

The reaction between sucrose and sulfuric acid in which solid carbon, water vapour and heat are produced is known as a dehydration reaction  :
C₁₂H₂₂O₁₁(s) → 12C(s) + 11H₂O(g)     ΔH = -918.9 kJ mol^-1 Since the enthalpy change for this reaction is negative, the reaction is exothermic, the reaction gives off heat.
Sulfuric acid molecules have a great affinity for water, that is, sulfuric acid will readily and spontaneously dissolve in water. The water produced by the dehydration of sucrose will then be used to dilute the sulfuric acid that is present. This reaction is also exothermic.
H₂SO₄(l) → H₂SO₄(aq)     ΔH = - kJ mol^-1 The heat produced by this reaction also speeds up the rate of the dehydration reaction and subsequent dilution reactions.
Solid carbon is black, so the "black snake" is just carbon.
But what causes the carbon to "rise up" out of the beaker? This must be the result of evolving gases forcing their way through the mixture as the reaction proceeds. The gases that have been identified as products of this reaction  are:

• carbon monoxide (CO) 66% of the dry gas volume (ie, water has been condensed out)
• carbon dioxide (CO₂) 17% of the dry gas volume
• sulfur dioxide (SO₂) 17% of the dry gas volume

Since sulfuric acid does not oxidize carbon, it is most unlikely that the carbon monoxide and carbon dioxide gases are the result of a reaction between the black snake carbon and sulfuric acid. It is much more reasonable to assume that some of the sucrose undergoes dehydration by the sulfuric acid while some this sucrose (and/or some of the resulting intermediate organic products) is oxidized by the sulfuric acid to produce carbon monoxide gas and carbon dioxide gas. During this process, the sulfuric acid will itself be reduced, resulting in the formation of sulfur dioxide gas.

Reference:
http://www.canberratimes.com.au/act-news/students-treated-after-spill-in-burgmann-anglican-school-sciencbe-laboratory-20141128-11vzad.html

Further Reading:
http://ausetute.com.au/safety.html
http://www.ausetute.com.au/mmcalcul.html  
http://www.ausetute.com.au/moledefs.html
http://www.ausetute.com.au/massmole.html
http://www.ausetute.com.au/concsols.html 
http://www.ausetute.com.au/molarvol.html
http://www.ausetute.com.au/molreact.html

Suggested Study Questions:

1.  Describe two hazards in the YouTube Video.
2.  Describe the safety precautions you would take to minimize the risk of the hazards identified in question 1 above.  
3.  Why do you think the concentrated sulfuric acid is added to the sugar rather than adding the sugar to the container of sulfuric acid?
4.  In a typical experiment, 25 mL of 18 mol L^-1 sulfuric acid is added to 50 g of granulated sugar (sucrose). Calculate the amount in moles of :
   • sucrose used
   • sulfuric acid used
5. Calculate the mass of carbon that could be produced in the typical experiment given in question 4.
6. What assumptions have you made in order to calculate the mass of carbon in question 5?
7. Assume that all 50 g of the sucrose is now oxidized at 25^oC to produce carbon dioxide gas and liquid water. What is the maximum volume of carbon dioxide gas, in litres, that could be produced?
8.  Predict what you think might happen if a 50 g of granulated sugar were quickly added to 25 mL of concentrated sulfuric acid in a 100 mL conical flask that was being swirled continuously.
9. Sucrose is a disaccharide, made up of the monosaccharide glucose and the monosaccharide fructose. Starch and cellulose are both polysaccharides, that is, they are made of repeating glucose monomer units. Predict what would happen if you spilled concentrated sulfuric acid on:
   • a paper cup (cellulose)
   • a piece of raw potato (starch)
   • a cotton shirt (cellulose)
10. Design an experiment that could safely be performed in the laboratory to test your predictions in question 9.
11. Do you think that concentrated sulfuric acid will react with the monosaccharide glucose? Explain your answer using a chemical equation.
12.  Design an experiment that could safely be performed in the laboratory to test your prediction in question 11.

Cyclodextrin

Researchers at Temple University's Water and Environmental Technology (WET) Center have been investigating the use of cyclodextrins in the treatment of waste water.
Cyclodextrins are made up of sugar molecules, bonded together to form a ring. An example of the structure of a cyclodextrin, alpha-cyclodextrin which is a 6-membered sugar ring, is shown below:

Cyclodextrins can be used in water treatment because they can bond to substances such as toxic organic compounds or heavy metals and hold them inside the ring structure. Owing to the many polar OH functional groups, cyclodextrins are water soluble, but the researchers have produced insoluble materials by coating a thin layer of cyclodextrin on sand, glass, silica and filter paper. Doing this allows the absorbent material to be collected, washed and re-used.

Reference:
Temple University (2013, September 24). New adsorbent is more effective and environmentally friendly for treating wastewater. ScienceDaily. Retrieved September 30, 2013, from http://www.sciencedaily.com­ /releases/2013/09/130924174152.htm

Further Reading
Carbohydrates: http://ausetute.com.au/members/sugars.html 
Functional Groups: http://ausetute.com.au/fungroup.html
Solubility: http://ausetute.com.au/intermof.html

Zeolites: http://ausetute.com.au/members/zeolites.html
Polymers: http://ausetute.com.au/members/polymers.html 

Suggested Study Questions:

1. What does the "cyclo" part of the name in cyclodextrin refer to?
2. Use the structure above to determine the molecular formula for alpha-cyclodextrin.
3. Use the molecular formula to determine the empirical formula for alpha-cyclodextrin.
4. Calculate the percentage composition of alpha-cyclodextrin.
5. Draw the structure of alpha-cyclodextrin and locate and identify the functional groups.
6. Use a diagram to explain how alpha-cyclodextrin dissolves in water.
7. Use a diagram to explain how alpha-cyclodextrin could be used to remove lead ions from water.
8. Draw the structure of alpha-cyclodextrin an clearly identify all 6 of the sugar molecules making up the structure. 
9. Activated carbon is commonly used to remove contaminants from water. What benefits do you think there might be in using cyclodextrin-derived absorbant materials instead of activated carbon? 

Tasty Chemistry

Taste refers to the ability to detect the flavour of substances. We receive tastes through sensory organs called taste buds which are concentrated on the upper surface of the tongue.
Among the 50 or so cells in each taste bud there are cells responding to each of the five tastes:

• sweetness
• bitterness
• sourness
• saltiness
• umami-ness or savoriness
  

Sweetness is often associated with foods rich in simple carbohydrates such as glucose and sucrose, but many compounds taste sweet. Examples include the amino acids alanine, glycine and serine as well as the glycosides glycyrrhizin (found in licorice root) and stevioside (from the Stevia rebaudiana shrub). Even some inorganic compounds, such as beryllium chloride and lead acetate, taste sweet.

Bitterness is perceived by many people to be unpleasant. It helps prevent us ingesting toxic substances. A bitterant is the chemical that makes a substance taste bitter. Examples of bitterants are sucrose octaacetate which is used as an inert ingredient in pesticides and herbicides, and, brucine which is a bitter alkaloid closely related to strychnine that is found naturally in a number of plant species.

Sourness is the sensation evoked by substances that are acidic such as lemons and pickles. The acids we ingest release protons which enter the cell and cause a direct, detectable, electronic response.

Saltiness is the taste produced by the presence of alkali metal cations such as Na⁺ and K⁺. The less sodium-like the ion is, the less salty the sensation will be, eg, Rb⁺ and Cs⁺ ions are larger than Na⁺ ions so they do not taste as salty.

The umami taste is due to the detection of the carboxylate anion of glutamic acid, a naturally occurring amino acid found in meat, cheese, and other protein-rich foods. Glutamates, the salts of glutamic acid, easily ionize resulting in the same carboxylate anions and therefore producing the same umami taste. As a consequence, glutamates are often used as flavour enhancers, the most common of which is monosodium glutamate (MSG).

Further Reading
Carbohydrates (sugars)
Amino Acids
Properties of Acids and Bases

Study Questions

1. Name the 3 elements common to all carbohydrates.
2. What is the structural difference between molecules classified as monosaccharides and those that are classed as disaccharides or polysaccharides?
   
3. Is glucose an example of a monosaccharide, a disaccharide or a polysaccharide?
4. Is sucrose an example of a monosaccharide, a disaccharide or a polysaccharide?
5. What elements are common to all amino acids?
6. What functional group or groups must a molecule contain in order for it be classified as an amino acid?
7. Draw the structures for glycine, alanine and serine. Identify the functional groups present in each molecule.
8. A number of amino acids are said to taste sweet, but acids generally are said to taste sour. Can you explain these apparently contradictory statements?