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Lipids : 


Structure & Biological Importance : 

Structure & Biological Importance

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Importance of Food Lipids Food Quality - Flavor, aroma, texture, mouth feel - Safety Nutritional - energy source - cell structures - essential fatty acids Biological - vitamins A, D, E, & K (fat soluble) - cell membrane characteristics - cholesterol for Vit. D3, corticosteroids, bile acids - signaling molecules, e.g. eicosanoids

Background : 

Background Lipids (fats) include a diverse range of compounds that have nonpolar groups that make them relatively insoluble in water (hydrophobic) Three major classes: Simple lipids – FA, TG, Waxes Compound lipids – Phospholipids, glycolipids, lipoproteins Derived lipids - Sterols

Simple Lipids : 

Simple Lipids

Fatty Acids : 

Fatty acids are what make lipids energy rich Lipids are “2.25” times more energy-rich than carbohydrate and protein Carbon Hydrogen Oxygen Lipid 77 12 11 Starch 44 6 50 Fatty Acids Carbons metabolized for energy

Fatty Acids : 

Fatty Acids Long carbon chains that contain a methyl group (CH3) at one end and a carboxyl group (COOH) at the other Characterized by: # of carbons (chain length) # of double bonds (degree of unsaturation) Location and orientation of these bonds (non-conjugated, conjugated; cis, trans)

Nomenclature and Structure : 

Saturated – single bonds Nomenclature and Structure Unsaturated – double bonds R1 C R2 C C C C R1 C R2 C C C C

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C C C H C H H H H trans C C H H C H H C H H cis Nomenclature and Structure H

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Fig. 5-1, p. 132

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Chemical Hydrogenation of Vegetable Oil

Melting point : 

Melting point MP ↑’s w/ chain length & degree of saturation Short chain FA or unsaturated FA = liquid at RT Long chain FA or saturated FA = solid at RT

Trans-fatty Acids : 

Trans-fatty Acids Animal fats and foods with partially hydrogenated vegetable oils can contain trans-fatty acids

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0 10 20 30 40 50 60 70 trans Fatty Acids % of all fatty acids 1 - 8 % RUMINANT FAT 0 10 20 30 40 50 60 70 Double Bond Position 40 - 60 % PHVO trans Fatty Acids % of all fatty acids % of Total trans Fatty Acids

Trans-fatty Acids : 

Trans-fatty Acids Animal fats and foods with partially hydrogenated vegetable oils can contain trans-fatty acids Increased consumption of partially hydrogenated vegetable oils is associated with increased risk of heart disease

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Willet et al., 1993 Trans Fatty Acids and Coronary Heart Disease Other studies have also shown that the positive association between TFA and CHD risk can be explained entirely by the intake of TFA from vegetable sources: Ascherio et al. (1993) Bolton Smith et al. (1996) Gillman et al. (1997) Pietinen et al. (1997)

Dietary Sources of Trans Fatty Acids (TFA) : 

Dietary Sources of Trans Fatty Acids (TFA) US situation: 5.8 g/d or 2.6% of daily calories

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conjugated C C H H C H C H non-conjugated H H C C C H H C H C H Nomenclature and Structure

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cis-9, trans-11 CLA linoleic acid trans-11 18:1 Double bonds: cis vs. trans

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cis-9, trans-11 CLA linoleic acid trans-11 18:1 Double bond pairs: non-conjugated vs. conjugated

Conjugated linoleic acid (CLA) : 

Conjugated linoleic acid (CLA) Considered a bioactive fatty acid Provides an additional health benefit beyond standard nutritional value of a food product Studied for numerous health effects Cancer prevention (c-9, t-11 CLA) Atherosclerosis prevention (c-9, t-11 CLA) Weight management (t-10, c-12 CLA) Predominantly found in ruminant products and also available in health supplements

Fatty acid nomenclature : 

2009 Cengage-Wadsworth Fatty acid nomenclature Delta () system - length, number/ position of double bonds double bond indicated by # of 1st C involved in bond from COOH end Omega (ω) system - Double bonds counted from omega (methyl/CH3) end

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2009 Cengage-Wadsworth Linoleic acid nomenclature

Essential FA : 

Essential FA Linoleic (LA) 18:2 n-6, -linolenic (ALA) 18:3 n-3 Humans cannot desaturate beyond 9C Lack ∆12 & ∆15 desaturases (in plants) Deficiency symptoms ↓ growth, dermatitis, kidney lesions, death, neurological abnormalities DRI: None for total fat AI for Linoleic= 11-17 g/d; -linolenic = 1.1-1.6 g/d

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Essential FA

Essential FA : 

Essential FA Humans are unable to synthesize fatty acids that have double bonds in the omega-3 or omega-6 positions Omega-3 EFAs Eicosapentaenoic acid (EPA): coldwater fish Docosahexaenoic acid (DHA): coldwater fish Alpha-linolenic acid (ALA): flax, walnut, soybean oils Omega-6 EFAs Linolenic acid (LA): animal fats, sunflower oil Gamma-linolenic acid (GLA): sunflower oil

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Glycerol backbone, and 3 fatty acids Major lipid class in grains Main lipid store in animal tissues Diverse range of fatty acids Triglycerides

Digestion & Transport of Dietary Lipids : 

Digestion & Transport of Dietary Lipids

Recommended Lipid Intake : 

Recommended Lipid Intake Less than or equal to 30% of calories from total fat Less than or equal to 10% of calories from saturated fat No more than 300 mg of cholesterol

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Small amount of lipid digestion occurs in the mouth and stomach Bile is produced in the liver, stored in gallbladder and aids in digestion in small intestine Pancreatic lipase released in small intestine and breaks down TG into FA and glycerol Unabsorbed fat is metabolized by bacteria in the large intestine The majority of dietary lipids are TG and need to be digested before they can be absorbed Digested lipids and bile form micelles which are absorbed across the intestinal cell wall Inside the intestinal cell, fatty acids are reassembled into TG and packaged as chylomicrons for transport to tissues Adapted from Visualizing Nutrition

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Fat Digestion in the Small Intestine Pancreatic lipase breaks down TG Bile salts solubilize the fatty acids and form micelles Fatty acids are repackaged as chylomicrons for transport to tissues

Absorption : 

Absorption Diffusion →

Lipoproteins : 

Lipoproteins Required for transport of lipid in the blood Composed of proteins, polar lipids (phospholipids), cholesterol, triacylglycerol. Classified according to density Chylomicrons Very low density lipoproteins (VLDL) Intermediate density lipoproteins (IDL) Low density lipoproteins (LDL) High density lipoproteins (HDL)

Lipoproteins : 

Lipoproteins Chylomicrons carry cholesterol and TGs from intestine to body Very-low-density lipoproteins (VLDLs) carry cholesterol and TGs from liver to body Low-density lipoproteins (LDLs) carries cholesterol from liver to body cells High-density lipoproteins (HDLs) carry cholesterol back to the liver

Fat Replacers : 

Fat Replacers

Fat Replacers : 

Fat Replacers Food fats can be reduced, diluted or replaced Caloric reduction can assist with weight control Several fat replacers are compared in Table 3.13

Carbohydrate-Based Fat Replacers : 

Carbohydrate-Based Fat Replacers These are plant polysaccharides Maltodextrin, modified starches Cellulose gels Carrageenan Hydrolyzed oat flour Energy value is 0-4 kcal/g Acceptable for cooked items (not fried) Safe

Protein-Based Fat Replacers : 

Protein-Based Fat Replacers These are proteins blended with gums to form gels Microparticulated milk (Simplesse) or egg protein (K-Blazer) Isolated soy protein Energy value is 1.3-4 kcal/g Acceptable for products not heated highly Safe

Fat-Based Fat Replacers : 

Fat-Based Fat Replacers Modifying fatty acid composition can reduce caloric content Salatrim (Short And Long chain Acid TRIglyceride Molecule): used in chocolates 5 kcal/g A synthetic fat molecule with 6-8 fatty acids attached to glucose Olestra: used for chips Nonnutritive

An olestra molecule : 

An olestra molecule

Olestra Problems : 

Olestra Problems A warning label is required on products containing Olestra Olestra may cause abdominal cramping and loose stools Olestra inhibits the absorption of vitamins and other nutrients

Pharmaceutical inhibition of fat absorption : 

Pharmaceutical inhibition of fat absorption Orlistat – blocks pancreatic lipase activity

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Blocks actions of gastric and pancreatic lipase

Energy Metabolism : 

Energy Metabolism Metabolism refers to the chemical reactions that take place within the body Energy metabolism refers to the way that the body uses energy nutrients (carbohydrates, lipids, proteins) Water, vitamins and minerals do not contribute energy directly

Using Energy Values : 

Using Energy Values Knowing energy values allows one to calculate the caloric values and percentages of nutrients in foods One calorie equals the amount of energy required to raise one gram of water one degree Celcius One kilocalorie equals the amount of energy to raise 1 kilogram of water one degree Celcius

Energy values of nutrients used by the body : 

Energy values of nutrients used by the body Carbohydrates 4 kcal/g Fats 9 kcal/g Proteins 4 kcal/g Alcohol 7 kcal/g

Summary : 

Summary Macronutrients provide calories (energy) for body functions Lipids are the most energy dense macronutrient Fatty acids are classified by chain length as well as the number, position and orientation of double bonds Physical and biological properties of fatty acids are diverse Digestion of fatty acids is a complex process requiring repackaging of the fatty acids to make them water soluble

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