Food Chemistry CHM 2962 Week 1 - Lipids Workshop Slides PDF

Food Chemistry CHM 2962 Week 1 - Lipids Weekly objectives 1. Identify classes of food lipids and fatty acids. 2. Establish the basics rules for the nomenclature of fatty acids. 3. Explore the chemical reactions of fats and oils relevant to food 4. Investigate the properties that fats and oils impa...

Food Chemistry CHM 2962 Week 1 - Lipids Weekly objectives 1. Identify classes of food lipids and fatty acids. 2. Establish the basics rules for the nomenclature of fatty acids. 3. Explore the chemical reactions of fats and oils relevant to food 4. Investigate the properties that fats and oils impart to different foods. 5. Understand methods for analysing the concentration and rancidity of fats and oils in foods. Weekly objectives 1. Identify classes of food lipids and fatty acids 2. Establish the basics rules for the nomenclature of fatty acids. 3. Explore the chemical reactions of fats and oils relevant to food 4. Investigate the properties that fats and oils impart to different foods. 5. Understand methods for analysing the concentration and rancidity of fats and oils in foods.  Recap from pre-workshop material Lipids which molecules are lipids and which are not. - The term lipids broadly defines non-polar molecules which are relevant in a biological context. - Example include sterols, non-polar vitamin molecules and of course fats and oils in food. Stearic acid General structure of sterols Cholesterol - Other non-polar molecules such as hydrocarbons are not considered to be lipids. ACTIVITY 1: Lipids - classification (a) What is the difference between oils and fats? (b) Which of the following molecules are considered as lipids? ACTIVITY 1: Discussion and feedback (a) What is the difference between oils and fats? Fats are solid at room temperature, and oils are liquid. (b) Which of the following molecules are considered as lipids? Lipids are indicated in red.  Recap from pre-workshop material One of the most common classification of fatty acids is based on the number of double bonds: - Saturated: absence of C-C double bonds - Mono-unsaturated: one C-C double bond - Poly-unsaturated: two or more C-C double bonds -6 -3 Recap from pre-workshop material ACTIVITY 2 – Part 1: Fatty acids – Melting point Would the presence of a double bond increase or decrease the melting point of a fatty acid (e.g. stearic (18:0) vs linoleic (18:1) acid)? Explain your answer. ACTIVITY 2 – Part 1: Discussion and feedback Would the presence of a double bond increase or decrease the melting point of a fatty acid (e.g. stearic (18:0) vs linoleic (18:1) acid)? Explain your answer. - Linoleic acid has a 'kink' in it (it is no longer linear). This structural feature has an impact on the melting point as a consequence of less organized packing (weaker dispersion forces) and co-alignment of molecules, and thus dispersion forces between molecules are not as strong. As a result, the melting point decreases. - Similarly, a fatty acid of the same length with two carbon-carbon double bonds will have an even lower melting point that the saturated fatty acid of the same carbon chain length. ACTIVITY 2 – Part 2: Fatty acids – Melting point Would you expect linoleic acid (cis-18:1) or elaidic (trans-18:1) to have a higher melting point i.e. the presence of which double bond will result in a higher (or lower) melting point? Explain your answer.  ACTIVITY 2 – Part 2: Discussion and feedback Would you expect linoleic acid (cis-18:1) or elaidic (trans-18:1) to have a higher melting point i.e. the presence of which double bond will result in a higher (or lower) melting point? Explain your answer. Linolelaidic, 18:2 29 (trans,trans-9,12) The presence of a trans bond preserves a higher degree of linearity in comparison to a cis double bond.  Recap from pre-workshop material Fatty Acid Nomenclature Common Semi-structural Systematic IUPAC Lipid Δx nomenclature n-x nomenclature Name formula Name Number CH3(CH2)7CH=CH( (9Z)-octadecanoic Oleic acid cis-Δ9 n-9 18:1 CH2)7COOH acid  Recap from pre-workshop material Fatty Acid Nomenclature Common Semi-structural Systematic IUPAC Lipid Δx nomenclature n-x nomenclature Name formula Name Number CH3(CH2)7CH=CH( (9Z)-octadecanoic Oleic acid cis-Δ9 n-9 18:1 CH2)7COOH acid CH3(CH2)4CH=CHC (9Z,12Z)- Linoleic H2CH=CH(CH2)7CO cis,cis-Δ9,Δ12 octadecadienoic n-6 18:2 acid OH acid ACTIVITY 3: Fatty acids – Nomenclature (a) Write the Δx nomenclature and the lipid number for the following fatty acid: (b) Draw the fatty acid with the following nomenclature: 20:3 - cis,trans,cis-Δ9,Δ11,Δ14 ACTIVITY 3: Discussion and feedback (a) Write the Δx nomenclature and the lipid number for the following fatty acid: 18:3 – cis,cis,cis—Δ7,Δ10,Δ13 (b) Draw the fatty acid with the following nomenclature: 20:3 - cis,trans,cis-Δ9,Δ11,Δ14  Recap from pre-workshop material The Chemistry - Esterification - Hydrogenation  Recap from pre-workshop material The Chemistry – hydrogenation mechanism ACTIVITY 4: Fatty acids – hydrogenation mechanism Considering the mechanism for hydrogenation of unsaturated bonds over Ni, devise a possible mechanism for cis-to-trans isomerization of unsaturated fatty acids (or any alkene) ACTIVITY 4: Discussion and feedback Considering the mechanism for hydrogenation of unsaturated bonds over Ni, devise a possible mechanism for cis-to-trans isomerization of unsaturated fatty acids (or any alkene) The manufacturer's response in the past decade to the issue of eliminating trans fats has been to find alternative plant-based fats that are naturally saturated, such as palm oil. Although recent ethical considerations around the land used to farm palm oil means manufactures will need to find other alternative going into the future.