Lec 4a- BPK 110 Human Nutrition: Current Iss.

Transcription

1 Lec 4a- BPK 110 Human Nutrition: Current Iss. TOPICS FOR Lec 4a: 1. Introduction to Lipids 2. Lipid Structure 3. Saturated vs. Unsaturated Fatty Acid Chains 4. Phospholipids and Sterols (Other Lipids) 1

2 Learning Objectives Be able to explain the usefulness of lipids in the body and lipids in the food we eat. Be able to describe the basic structure, physical and chemical properties as well as the functions of the three types of lipids. Be able to explain where in the body and how lipids are employed to make the phospholipids, hormones plus other bioactive compounds Copyright 2018 by Nelson Education Ltd. 2

3 1. Introduction to Lipids 1a. Lipids- are family of organic compounds (recall containing carbon) that are not soluble in water but are soluble in organic solvents 1b. Types of Lipids: In food there are 3 main types of lipids that we are interested in: (i) Triglycerides** (also called triacylglycerides) (ii) Phospholipids (including lecithin) (iii) Sterols (including CholeSterol) In food, fat (lipid) is made up by 95% of (i)** and 5% of (ii) & (iii) combined 3

4 1c. Functions of Lipids in the Body Several important functions of lipids in the body: 4

5 1c. Functions of Lipids in the Body Several important functions of lipids in food: Table 5-1 Cont 5

6 (i & ii) Energy storage & energy source (iii) Secretes hormones & enzymes: *FI & EE (iv) Insulation & cushion (v) Essential Nutrients Bilayer of phospholipids *Food Intake (FI) & Energy Expenditure (EE) 6

7 2a. Lipid Structure Triglycerides (TG) = tri/gly/cer/ide (3 Fatty Acids chains + Glycerol) Synthesis & breakdown of TG by enzymes in most human tissues Glycerol = 3 carbon molecule; it is the backbone for TG Fatty Acids (FA) differ in length or # of carbons & degree of saturation Length= number of carbon atoms in the FA chain varies from about 6-8 to 22 carbons Shorter FAs tend to be liquid at room temperature 7

8 2003 Wadsworth, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license. Glycerol, a small water soluble CHO derivative + 3 fatty acids Fatty acids differ in chain length & degrees of saturation 8

9 3a. Saturated vs. Unsaturated Fatty Acid Chains Saturation equates to the number of hydrogen in FA chain that each carbon holds If each available bond from a carbon holds/bonds with a hydrogen atom then the FA chain is saturated. A saturated FA chain has a zig-zag shape (Fig 5-4) Unsaturation are points in FA chain with missing hydrogens; empty spots or points of unsaturation If 1 point of unsaturation then the FA chain is unsaturated 9

10 3b Mono-unsaturated & Poly-unsaturated Defined Unsaturation of a Fatty Acid Chain Mono-unsaturated FA= 1 point of unsaturation Poly-unsaturated FA 2 points of unsaturation in FA chain Type fatty acids incorporated into a triglyceride give a fat that is: softer (liquid) shorter-chain fatty acids more unsaturated melt at lower temperature harder longer-chain fatty acids more saturated melt at higher temperature 10

11 2 Points of unsaturation 1 Point of unsaturation zig-zag shape Each C is Missing a hydrogen 11

12 Omega 3 and Omega 6 Fatty Acids Naming of fatty acids is assigned based on where the first unsaturated/double-bond occurs. 12

13 3c. Saturation vs. Unsaturation: Degrees of Saturation e.g. s of fats & their properties: Pork Fat = room temperature = most saturated FAs Chicken fat = room temp. = less saturated FAs Safflower Oil = room temp. = mostly unsaturated FAs Generally: more unsaturation = more liquid at room temp. (~25ºC) more saturation = more solid at room temper (~25ºC) Different oils differ in their amount of unsaturation - refrigerate & look for cloudiness. > cloudiness equals a > degree of saturation 13

14 3d. Saturation vs. Unsaturation: Must Know Your Fats & Oils Fish & Vegetable Oils- generally rich in poly-unsaturated FA Some other Vegetable Oils- rich in mono-unsaturated FA e.g. Olive Oil* & Canola Oil Animal fats- mostly saturated But some plant oils have high levels of saturated FAs e.g. Coconut Oil - > saturation level than FAs in cream e.g. Palm Oil - high levels of saturated FAs * see Mediterranean Diet pages

15 2003 Wadsworth, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license. Figure 5.5 (old version) Fatty Acid Composition of Common Food Fats 15

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17 4. Phospholipids and Sterols (Other Lipids) 4a. Phospholipids = glycerol, 2 FAs & 1 phosphate group (phosphorous containing) water soluble b/c of phosphate group Functions: act as emulsifiers & disperse fat in water comprise large portion of cell membrane water loving & water hating portions e.g. Lecithin is an emulsifier found in mayonnaise (vinegar & oil) so it doesn t separate into oil/ water 17

18 4b. Sterols: 3rd subgroup of lipids of interest carbon in interconnected rings, with side chains containing hydrogen, oxygen & carbon Examples: e.g. #1 cholesterol* used by liver to produce bile e.g. #2 Vitamin D; Important for bone health e.g. #3 Sex (Steroid) hormones; important tissue building *Found in plaques in athero/scler/o/sis (artery narrowing) 18

19 Summary Lecture 4a 1. Introduction to Lipids 2. Lipid Structure 3. Saturated vs. Unsaturated Fatty Acid Chains 4. Phospholipids and Sterols (Other Lipids) 19