IB Chemistry HL Option F Food ChemistryMay 20091. Artificial food colourants have recently been linked to increased hyperactivity in children. Many foods are colourful because of the natural pigments they contain. a. Explain why naturally-occurring pigments are coloured. [1]b. State the class of pigments that give cranberries and strawberries their colour. [1]c. i. State the class of pigments that give carrots and tomatoes their colour. [1]ii. Outline why this class of pigment is susceptible to oxidation, and the effect of oxidation on this pigment. [2]2. Antioxidants occur naturally and are often added to extend the shelf life of our food.a. Define the term antioxidant. [1]b. Explain the differences between the three main types of antioxidant. Include in your answer: An example of each type of antioxidant A brief account of how it works. [6]c. Table 22 in the Data Booklet shows the structures of some antioxidants. Determine the two functional groups that are found in all of these synthetic antioxidants:2-tert-butyl-4-hydroxyanisole (2-BHA), 3-tert-butyl-4-hydroxyanisole (3-BHA) and 3,5-di-tert-butyl-4-hydroxytoluene (BHT). [2]d. Describe the step by step mechanism for the free radical reaction that causes an oily fish such as mackerel to become rancid. Include the name of each step and an equation for each step in your answer. [6]Step 1:Step 2:Step 3:3. Genetically modified (GM) foods are now widely available, although in some countries environmental groups are campaigning against them. Define the term genetically modified food and discuss the benefits and concerns of using GM foods. [5]

May 20101. Simple sugars are nutrients and are also described as monosaccharides.a. Distinguish between a food and a nutrient. [2]b. State three characteristic features of all monosaccharide molecules. [3]c. Explain the chemistry behind the non-enzymatic browning reaction that occurs when making fudge from sugar and cream. [3]2. a. Explain why pigments such as anthocyanins are coloured. [2]b. The wavelength of visible light lies between 400 and 750 nm. The absorption spectrum of a particular anthocyanin is shown below.

i. Explain what effect, if any, the absorption at 375 nm will have on the colour of the anthocyanin. [1]ii. Explain what effect, if any, the absorption at 530 nm will have on the colour of the anthocyanin. [1]c. List two factors which could alter the precise colour of a particular anthocyanin.[2]3. The structure of vitamin C is given below.

a. Refer to the structure to explain why vitamin C can exist in a +(d) form and a (l) form and explain the difference between the two forms.[2]b. The amino acid alanine is optically active. One of its enantiomers (labeled A) is represented below.

i. In the space above draw the other enantiomer of alanine (labeled B).[1]ii. Explain which of the two enantiomers (A or B) is the D isomer.[3]4. a. During oxidative rancidity hydroperoxides are formed. These degrade to produce volatile aldehydes and ketones which produce the unpleasant smells associated with food that has gone off. One way of prolonging the shelf life of food is to add the antioxidant BHT.

i. Describe two structural features of BHT which are responsible for its antioxidant properties.[2]ii. Explain how BHT can prolong the shelf life of food.[1]b. Another antioxidant is vitamin C. This works in a different way to BHT. Outline how vitamin C functions as an antioxidant.[2]

May 20111. a. Rancidity is the perception of flavours in lipids that our senses perceive as off because of a disagreeable smell, taste, texture or appearance. The processes that create the off flavours may be hydrolytic rancidity or oxidative rancidity in lipids.i. Predict the products of hydrolytic rancidity of fats.[2]ii. The hydrolysis of milk products is used in the making of cheese. State two conditions which increase the rate of hydrolysis of fats in milk.[2]iii. Potato chips are cooked in oils made from unsaturated fatty acids. Explain in terms of chemical processes why potato chips are purchased in sealed, opaque, nitrogen filled foil packs and taste best when freshly opened.[3]b. Initiation, propagation and termination steps occur in the free-radical chain mechanism during oxidative rancidity. For each step, state one related equation.[3]2. a. Antioxidants are substances that slow the rate of oxidation of foods and may also be consumed to provide health benefits. Two traditional foods with antioxidant properties are green tea and oregano. Green tea contains epigallocatechin-3-gallate (EGCG) and oregano contains rosmarinic acid. The structures of these two compounds are shown below.

i. Explain why both EGCG and rosmarinic acid have antioxidant properties.[1]ii. List two health benefits of consuming foods such as green tea and oregano.[2]b. Anthocyanins are naturally occurring pigments responsible for the colour of blueberries and cranberries. The structures of two forms of anthocyanins are show in Table 22 of the Data Booklet.i. Using the abbreviations QB for quinoidal base and FC+ for flavylium cation, state an equation to describe how pH affects the colour of anthocyanins.[1]ii. Suggest why blueberries should not be stored in aluminum cans.[2]c. Compare the structures of the natural pigments, chlorophyll and heme B using Table 22 of the Data Booklet.[4]3. Carvone is a member of a family of compounds called terpenoids. Carvone occurs in two enantiomeric forms. (S)-(+)-carvone is the principal component of caraway seed oil and (R)-()-carvone is the principal component of spearmint oil.a. Identify the chiral centre in carvone, with an asterisk, *.[1]

b. Explain the meaning of the R and S notation and how this differs from the d and l notation.[2]c. The structure represented is (S)-(+)-carvone. Explain how this has been deduced.[2]

May 20121. Most foods are complex mixtures and many components of them are nutrients.a. State an example of a food that is not a nutrient and use this to explain the difference between these two terms.[3]b. Anthocyanins, carotenes and porphyrins are coloured substances found in foods. Their structures are shown in Table 22 of the Data Booklet.i. Identify the common feature in their structures that results in these compounds all being coloured and explain this on a molecular level.[3]ii. Under certain conditions, anthocyanins are converted into a colourless carbinol pseudobase, an example of which is shown below.

In terms of its structure, explain why the pseudobase is colourless even though the anthocyanin is coloured.[1]c. The absorption spectrum of -carotene is shown below.

In this spectrum, explain why carotenes have their typical colour.[2]d. There are distinct differences between the solubilities of anthocyanins and carotenes. Describe these and explain the differences in terms of their structures.[3]2. Rancidity limits the shelf life of foods containing oils and fats.a. Rancidity can occur as a result of two separate processes. State these processes and explain the difference between them.[3]b. Substances such as THBP (2,4,5-trihydroxybutyrophenone) and TBHQ (tert-butylhydroquinone) are often added to slow down rancidity. Explain how additives such as THBP and TBHQ delay rancidity.[2]c. State the name of one naturally occurring substance which has a similar effect in slowing down rancidity. Identify a food that is rich in this and state an additional health benefit thought to arise from its regular consumption.[3]Compound:Food:Benefit:3. Texture is an important feature of food. Various dispersed systems have distinctive textures.a. Describe what is meant by the term dispersed system.[1]b. Identify the phases of the two components of an emulsion.[1]c. Emulsifiers such as lecithin are frequently used to prevent the separation of emulsions. One compound of lecithin has the structure shown below.

Explain how emulsifiers, such as this, stabilize emulsions. [3]

May 20131. Antioxidants occur naturally (such as vitamin C) or can be synthetic.a. Define the term antioxidant.[1]b. i. Identify an element that is a common naturally occurring antioxidant.[1]ii. State one food in which this antioxidant can occur.[1]c. The structures of three synthetic antioxidants, 2-BHA, 3-BHA and BHT are given in Table 22 of the Data Booklet. Another synthetic antioxidant is THBP whose structure is shown below.

i. Deduce which of these four antioxidants contain the phenol group.[2]ii. Deduce whether THBP contains the tertiary butyl group or not.[1]iii. Suggest the function of the tertiary butyl group in antioxidants.[1]2. The food industry uses food-grade dyes and pigments to increase the appeal of food products.a. State the difference in terms of solubility between a dye and a pigment.[1]b. The pigment associated with the olive-green colour of the outer shell of the American lobster is astaxanthin, shown below. When cooked the lobster changes to a red colour.

i. Identify the class of pigment to which astaxanthin belongs.[1]ii. Explain why the properties of pigments in the shell of a live lobster can lead to colour variation (for example, from olive-green to orange).[1]iii. Explain how the colour of astaxanthin changes to red when cooked.[2]3. The Maillard reaction is the basis of non-enzymatic browning and involves the reaction between carbohydrates and proteins.a. The first step of this reaction involves a condensation reaction between a reducing sugar, such as glucose, and an amino acid.i. Using RCHO to represent glucose and H2NR to represent an amino acid, deduce the structural formula of the product.[1]ii. Identify the other product of this reaction.[1]b. Other than condensation, state the name of one type of reaction involved in the other two steps of the Maillard reaction.[1]4. The structure below shows an enantiomer of -ionone, which has a raspberry flavour.

a. Identify the chiral centre in the structure above with an asterisk (*).[1]b. Explain what is meant by the R, S notation and how this is different to the +(d) and (l) notation.[2]c. Deduce whether the enantiomer shown is R or S and explain your answer.[2]d. Another enantiomer of -ionone has a different flavour. Suggest a reason for this difference.[1]e. Two other optical isomers which have an effect on flavour are +(d) and (l) limonene. State the flavour associated with each enantiomer.[1]+ (d) limonene: (l) limonene:5. Auto-oxidation is the chemical process responsible for the rancidity of butter.a. Using RH as the formula for the fat in butter, state three equations associated with the reaction of RH with oxygen, resulting in the formation of hydroperoxides.[2]b. In this process the hydroperoxides act as intermediates. State why they degrade and rearrange to other compounds and identify a functional group in thesecompounds.[1]

May 20141. The formula of linoleic acid is given in Table 22 of the Data Booklet.a. Identify the structural formula of the triglyceride formed when three molecules of linoleic acid react with one molecule of glycerol (propane-1,2,3-triol),CH2OHCHOHCH2OH.[1]b. State the other product formed during this reaction.[1]c. Explain why the triglyceride formed from linoleic acid and glycerol is a liquid and not a solid at room temperature.[2]d. Describe how the triglyceride formed from linoleic acid and glycerol could be converted into a saturated fat and give any necessary conditions.[2]e. Other than the fact that it is a solid at room temperature, discuss two advantages and two disadvantages of a saturated fat compared to unsaturated fat or oil.[4]Advantages:Disadvantages:

2. Describe how the following additives can prolong the shelf life of food:a. sodium benzoate and benzoic acid.[1]b. potassium nitrite and potassium nitrate.[1]3. Lycopene occurs naturally in tomatoes and is responsible for their red colour. Lycopene is a known antioxidant and some people believe that it is effective at preventing prostate cancer. Its structure is shown below.

a. i. Lycopene is a hydrocarbon. State the class of naturally occurring pigments to which it belongs.[1]ii. Outline why lycopene is a coloured compound.[1]iii. The UV/VIS spectrum of lycopene is shown below.

Explain why it is coloured red.[1]iv. Antioxidants can be divided into three main types. Lycopene is a reducing agent and acts as an antioxidant by removing or reducing the concentration of oxygen. Others, such as BHT (3,5-di-tert-butyl-4-hydrotoluene), inhibit the formation of free radicals or interrupt the propagation of free radicals. Explain how the third type of antioxidants functions and give one example.[2]b. i. Describe how a fatty acid, RH, undergoes oxidative rancidity. Your answer should state the names of the three different steps and include one equation for each step.[3]ii. Explain how an antioxidant such as BHT is able to inhibit the formation of free radicals during the oxidative rancidity of a fatty acid.[2]4. Your school is holding a debate on the benefits and concerns of genetically modified (GM) food. Several speakers have argued the benefits of GM foods and included such factors as enhanced taste, resistance to disease and increase in crop yields. Discuss three arguments you would use to highlight the concerns of using GM foods.[3]