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Lecture 4

Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols.doc

20 Pages

Health Studies
Course Code
HLTH 230
Jeffery Lalonde

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Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) Intro • well balanced diet requires some fat -usually there is an abundance trend in 80s to avoid fat - even now low fat or fat free products • • fat provides mouth feel • fat soluble vitamins • fats are mad of C, H, O (like carbohydrates) linked to poor health • -too much/too little/too much of some kinds of fat lipids -family of compounds that include: -Triglycerides -Phospholipids -Sterols -characterized by their insolubility in water fats -lipids that are solid at room temperature oils -lipids that are liquid at room temperature A Chemical Overview 1. Every triglyceride contains 1 glycerol molecule and 3 fatty acids 2. Fatty acids may be 4 to 24 carbons long -18 carbon fatty acids are the most common in foods 3. Fatty acids may be saturated or unsaturated -unsaturated fatty acids may be monounsaturated or polyunsaturated 4. Of special importance in nutrition are polyunsaturated fatty acids known as Omega-3 and Omega-6 5. The 18 carbon polyunsaturated fatty acids linoleic (Omega 3) and linoleic acid (Omega 6) are essential fatty acids Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) Fatty Acids fatty acid: organic acid (a chain of carbon atoms) with: -acid group (COOH) at one end -a methyl group (CH3) at the other end saturated fatty acid: fatty acid carrying the max. # of hydrogen atoms saturated fat: fat composed of triglycerides where most fatty acids are saturated -mainly in animal fats (butter, cheese, cream, ice-cream) -also in coconut oil, palm oil unsaturated fatty acid: fatty acid that has at least 1 double bond and therefor lacks hydrogen atoms monosaturated fatty acid: fatty acid that has one double bond and therefor lacks 2 hydrogen atoms Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) polyunsaturated fatty acid: fatty acid that lacks 4 or more hydrogen atoms and has 2 or more double bonds between carbons omega 3 fatty acid: has its first double bond 3 carbons away from methyl end omega 6 fatty acid: has its first double bond 6 carbons away from methyl end An impossible chemical structure : -cannot exist -2 of the carbons have only 3 bonds each, but every carbon MUST HAVE 4 BONDS the 2 carbons form a double bond to make Oleic acid Oleic acid - 18-carbon, monosaturated Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) Linoleic acid - 18-carbon, polyunsaturated (lacks 4 hydrogens, has 2 double bonds) Length of fatty acid carbon chain • most naturally occurring fatty acids contain even numbers of carbons (up to 24 carbons long) • 18 carbon fatty acids are abundant in our food supply • Stearic acid = “simplest” 18 carbon fatty acid b/c bonds are all the same between carbons -saturated, no double bonds Length of fatty acid carbon chain • long chain fatty acids: most common fatty acids in diet -12 to 24 carbon -found in meat, seafood, vegetable oils • medium chain fatty acids: 6-10 carbons • short chain fatty acids: less than 6 carbons -found in mainly dairy products Triglycerides • approx. 95% of lipids in foods • approx. 99% of lipids in body • free fatty acids are uncommon in foods/body • lipids usually in form of triglycerides formed by a series of condensation reactions (fig. 5-3) (like 2 monosacharrides bonding to • make disacharrides in terms of carbohydrates) -hydrogen atom from glycerol joins with hydroxyl group from a fatty acid -molecule of water is formed -bond is formed between glycerol and fatty acid -fatty acid + glycerol = condensation reaction Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) Degree of Unsaturation • effects both -firmness of fatty acid -stability of fatty acid *remember: unsaturated fatty acids lack hydrogen atoms and have at least 1 double bond • firmness: -generally affected by: saturation: increase degree of unsaturation, decrease firmness length of carbon chains: decrease carbon chain length, decrease firmness -the shorter the chain, the less firm the fatty acid will be ex.-polyunsaturated veg. oils are generally liquid at room temp -saturated animal fats are firm at room temp -Palm oil and cocoa butter have F-A 12 carbons or shorter -> softer than animal fat b/c of shorter chain -Beef tallow is primarily made of F-A 18 carbons in length • stability oxidation: process of substance combining with oxygen -oxidation of fats produces variety of chemical compounds that smell and taste rancid (fat is spoiled) -which fats are most prone to oxidation? -polyunsaturated fats spoil more readily due to decreased stability of double bonds -saturated fats are the most resistant to oxidation we needed to find a way to make polyunsaturated fats more stable Protecting fat-containing products against rancidity 1. Protect fats from environment -sealed in air tight containers and refrigerated out of light (expensive) 2. Add antioxidants -antioxidants compete for oxygen and protect oil -ex. BHA, BHT, vitamin E -Butylated hydroxyanisole (BHA) butylated hydroxytoluene (BHT) 3. Hydrogenation -saturating some or all of points of unsaturation by adding hydrogen Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) Hydrogenation/Trans fats hydrogenation: chemical process -> hydrogens are added to monounsaturated/ polyunsaturated fatty acids -reduce number of double bonds -makes fats more saturated (solid) and more resistant to oxidation Advantages of hydrogenation? 1. Protects against oxidation by making polyunsaturated fats more saturated -Commercial benefit: increases shelf life 2. Alters texture of food by making liquid vegetable oils more solid -Commercial benefit: improved food texture (flaky pie crust, spreadable margarine, creamy pudding) *in hydrogenation, double bonds switch sides -> creation of trans fatty acids How are Trans-fatty acids formed? • polyunsaturated fat is rarely hydrogenated completely during processing • fat is generally partially hydrogenated -> some double bonds remain • double bonds change from cis formation to trans formation • small amount of trans fats are naturally found in milk and meat products -ex. conjugated linoleic acid -CLA is not counted as Trans Fat on Food labels in Canada Cis double bonds • -most common double bonds in nature -hydrogens next to double bond are on the same side of carbon chain • Trans fatty acids -found naturally in small amounts in milk and meat Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) -hydrogens next to double bond are on opposite sides of the carbon chain Trans Fat • increased trans fat intake linked to increased LDL cholesterol (“bad cholesterol”) • consumption of trans fat also decreases HDL cholesterol (“good cholesterol”) • limiting trans fat can improve blood lipids and lower risk of heart disease What is being done in Canada? June 20, 2007, the Minister of Health announced that Health Canada adopted the following recommendations of the Trans Fat Task Force : • Limit the trans fat content of vegetable oils and soft, spreadable margarines to 2% of the total fat content • Limit the trans fat content for all other foods to 5% of the total fat content, including ingredients sold to restaurants. • Minister called on the food industry to achieve these limits within two years. • Companies and food manufacturers are encouraged to replace trans fats with healthier trans fats with saturated fats.rated and polyunsaturated fats and to not replace • To ensure that the industry is making progress in meeting the 2% and 5% limits of the Monitoring Program.anada will closely monitor the actions of the industry via the Trans Fat Comparison of Dietary Fats • Primarily saturated fatty acids: -coconut oil, butter, beef tallow, palm oil, lard • Rich in monosaturated fatty acids: -olive oil, canola oil, peanut oil • Rich in omega-6 polyunsaturated fatty acids: -safflower oil, sunflower oil, corn oil, soybean oil, walnut oil, cotton seed oil • Rich in omega-3 polyunsaturated fatty acids: -flaxseed oil, fish oil Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) FIGURE 5-5 should know which is highest in each of them! *coconut oil, olive oil, safflower oil 3 classes of Lipids #1 Triglycerides: lipids composed of 3 fatty acids attached to a glycerol 1) Provide energy 2) Insulate body - fat is a poor conductor of heat 3) Natural shock absorbers providing a cushion for bones and organs #2 Phospholipids: compound similar to triglyceride but has a phosphate group and a nitrogen containing compound in place of one of the fatty acids Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) -ex. Lecithin FIGURE 5-8 Why is Structure important? -phospholipids are soluble in both water and fat -fatty acids make it soluble in fat -phosphate group allows it to dissolve in water Use of Phospholipids in food industry? -used as emulsifiers (to mix with water) in products like mayonnaise + chocolate bars -Lecithin is most commonly used What are some of the natural richest food sources of lecithin? -eggs, liver, soybeans, wheat germ, peanuts Important roles of Phospholipids in the body 1) Part of the cell membrane that allows fat soluble substances including vitamins and hormones to move easily in and out of cell 2) Act as emulsifiers helping keep fats suspended in blood and body fluids Benefits of Lecithin supplements? • Lecithin is made by liver (non-essential, does not need to be supplemented) • primarily hydrolyzed in intestine by lecithinase, leaving little to reach the tissues in tact • large doses may cause GI distress, sweating, and loss of appetite #3 Sterols: compounds containing a four ring carbon structure with any of a variety of each side chains attached FIG 5-10 • present in foods derived from both plants and animals • cholesterol: only significant amounts of cholesterol in food derived from animals Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) -vegetarians would not have cholesterol • phytosterol: also called plant sterols -plant-derived compounds that have structural similarities to cholesterol -lower blood cholesterol by competing with cholesterol for absorption -include sterols and stanols Roles of Sterols Sterols in the body include: • Bile acids - help in preparing fat for digestion • Sex hormones (ex. testosterone) • Adrenal hormones (cortisol) • Vitamin D • Cholesterol -Cholesterol can serve as a starting material for these compounds -Cholesterol is a structural component of cell membranes Cholesterol • found in animal food - not significant amounts in plant sources manufactured in the liver which makes 800-1500mg per day (endogenous production) • • body generally makes more cholesterol (endogenous) than what is eaten (exogenous) • Cholesterol is harmful when it forms deposits on the artery walls that contribute to plaque formation (plaque leads to atherosclerosis) *Cholesterol is not a bad thing in bad foods *is a compound made by the body (and eaten) and used by the body *“Good cholesterol” is not a type of cholesterol in food, but refers to HDL cholesterol which is a way the body transports cholesterol atherosclerosis: type of artery disease -> plaques on inner walls of arteries --------------------------------------------------------------------------------------------------------------------------- Diet and Lifestyle Recommendations (2006) Scientific Statement from American Hrt Ass. Phytosterols • lower cholesterol levels by up to 15% • maximum effects are observed at phytosterol intakes of approx. 2 grams/day currently widely available in US - have just been made available in Canada • -Margarine -yogurt drinks • margarine pulled from shelf in Canada in 2001, back in 2010 • now found in yogurt drinks and margarine in Canada • plant sources very high in kcal -sesame seeds 400mg sterols/100g-600kcal -wheat germ 400mg sterols/100g-360kcal -brazil nuts 95mg/100g-656 kcal Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) -Becel Pro Active - 2g/25ml - 75 kcal (easiest way to get phytosterols) *really hard to get from plant sources *to get full 2g/day of phytosterol, you will have to eat a lot of sesame seeds -> too many calories --------------------------------------------------------------------------------------------------------------------------- Digestion of Lipids • each day, GI tract receives approx. -50-100g triglycerides -4-8g phospholipids -200-350mg cholesterol • lipids are hydrophobic (water-fearing) • enzymes to digest fats are hydrophilic (water loving) GOAL: keep fats mixed in watery fluids of GI tract dismantle triglycerides into small molecules that body can use (monoglycerides, fatty acids, glycerol) Lipid Digestion: Mouth • hard fats melt at body temp lingual lipase • -released by salivary glands at the base of tongue -efficiently digest short and medium chain fatty acids in milk -very important for infants -plays minor role in adults Lipid Digestion: Stomach • strong muscular contractions help prevent fat from floating on top of other stomach contents • churning grinds solid pieces into finer particles, disperses fat into small droplets lingual lipase -acid stable (can continue to keep working in stomach) gastric lipase -begins to break down fat droplets -works best in acidic environment of stomach -works primarily on outside long chain fatty acid leaving diglyceride and free fatty acid (only a minor role in fat digestion) Lipid Digestion: Small Intestine • most hydrolysis of TGs take place in small intestine • fat particles pass from stomach into small intestine • chyme in small intestine signals release of CCK • release of CCK triggers gallbladder to release bile • Bile Lecture 4 - The Lipids- Triglycerides, Phospholipds, and Sterols (Chapter 5) -contains bile acids made in liver from cholesterol
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