1 / 19

Module 4. Lipids

Module 4. Lipids. Food Chemistry 2 ND Food Technology. Table of Contents. Introduction Classification Fatty acids Gliserides Phospholipids Unsaponifiables Emulsions & emulsifiers Physical properties of oils & fats Cocoa butter & confectionary fats Heated fats - frying.

rune
Download Presentation

Module 4. Lipids

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Module 4. Lipids Food Chemistry 2 ND Food Technology

  2. Table of Contents • Introduction • Classification • Fatty acids • Gliserides • Phospholipids • Unsaponifiables • Emulsions & emulsifiers • Physical properties of oils & fats • Cocoa butter & confectionary fats • Heated fats - frying

  3. 1. Introduction • Difficult to give definitions – too many different types – usually water-insoluble organic compounds found in biological systems • Either hydrophobic (non-polar) or amphipathic (polar and non-polar regions) • Types of lipids for domestic & industrial purposes • Oils, margarine & butter, dripping, lard, shortening, tallow, waxes • General characteristics: • Oily & greasy feel (leaves greasy spot on filter paper) • Not easily mix with water (float on water) • Dispersed in detergent, hot water or alcohol

  4. 2. Classification • Origin • Animal • Mammal depot fat (lard, tallow), milk fat (ruminant), marine (fish oil) • Marine – eicosapentanoic (EPA), docosahexaenoic (DHA) – in tuna, sardines – mostly unsaturated – biomedical advantages for human body • Veg • Seed oils (canola), fruit coats (olive oil), kernel oils (coconut oil) • Visible / invisible • Visible – lard, butter, margarine, shortening, cooking oils • Invisible – fat in eggs, meat, poultry, fruits, veg, grain • Based on melting point: • Fats – solid / semisolid @ room temp (usually animal origin - margarine) • Oils – liquid (melting point) below room temp (usually plant origin - sunflower oil)

  5. 2. Classification • Based on structure: Basic lipid components Quantitative Phospholipids Hexoses Sphingosine Sterols Glyserol Fatty acids Fatty alcohols Phosphoric acid amino alcohols Fatty aldehydes Sterol esters Mono-, di-, tri glyserides Cerebrosides Sphingomyelin Phosphatidyl esters Plasmalogens Glyceryl ether Waxes Ether esters

  6. 3. Fatty acids • Simplest lipids – fatty acids, formula: R-COOH (R is a hydrocarbon chain, COOH is a carboxyl functional group) • Fatty acids differ from each other by: • Length of hydrocarbon tail • Degree of unsaturation (no. of double bonds) • Sat. are waxy at room temp. • Unsat. Are liquid at room temp. • Less double bonds, longer carbon tail → higher melting temp • Positions of double bonds • Essentiality – essential fatty acids (e.g. oleic, linoleic, linolenic) – not produced by body, only from plant origin – usually unsaturated • Common names – for frequently used fatty acids • IUPAC naming: • Carboxyl carbon named C-1, remaining carbons named sequentially • Carbon adjacent to carboxyl named , rest also followed by greek letters ( refers to carbon farthest from carboxyl group) • No carbon-carbon double bond – saturated, at least 1 double bond - unsaturated

  7. 3. Fatty acids • IUPAC naming: • 1 double bond – monounsaturated, 2/more double bonds – polyunsaturated • Positions of double bonds indicated by Δn (n indicates the lower-numbered carbon of each double bond • Shorthand notation: uses 2 numbers seperated by colon, e.g. arachidonate: Eicosatetraenoate No. of C-atoms in fatty acid 20:4 Δ5,8,11,14 Common name Double bond positions No. of C-C double bonds

  8. 3. Fatty acids • NB – draw structures if IUPAC name is given, Tables 2.2, 2.3, p37-38 • 2 types of double bonds: • Cis – Hydrogens on same side of bond – causes bending of hydrocarbon chains • Bending prevents close packing of hydrocarbons → cis unsaturated fats lower melting point • Trans – Hydrogens on opposite sides of bond - mostly saturated fats – higher melting point – more stable • Draw structures indicating difference between cis & trans!

  9. 4. Gliserides • A 3-carbon alcohol – usually combines with fatty acids (esterification) • Glyseride also neutral lipid – do not carry any charge • When 1 carbon is esterified with fatty acid → monogliseride, when 2 C’s esterified with fatty acid → digliseride, etc. • Glyserol has plane of symmetry (2 of 4 constituents around central carbon is identical) - monogliserides – 2 structures – enantiomeres (chiral) (Fig. 2.7, p. 47) • Saponification number: the reaction of a product with a weak acid / base • The basis of the soap-making industry • Saponification number (S.N.) – index of degree of esterification • The higher the degree of esterification, the higher the S.N. • Used as quality control tool in oils & fats industry • Lipids that do not have gliserides will not saponify • Lipids can thus also be classified into saponifiable and non-saponifiable

  10. 4. Gliserides • Hydrogenation: Chemical reaction by addition of hydrogen to double bonds of unsaturated acyl groups • For conversion of oils to fats (e.g. production of margarine • Results in a decreased susceptibility to oxidative deterioration • Reaction: gaseous hydrogen + liquid oil + solid catalyst (Ni) react under agitation in closed vessel • Hydrogenation not usually completed • May be selective (H2 added first to most unsaturated fatty acid) or non-selective • Selectivity increased by increasing hydrogenation temp • Iodine number: reaction of iodine with double bonds • Amount of iodine used indicates the amount of unsaturation remaining

  11. 5. Phospholipids • Present in animal fats (lard, beef tallow), crude vegetable oils (cottonseed, corn, soybean oil), fish • Can be removed from fats & oils by refining, neutralization, bleaching, deoderization → oil free from phospholipid • Phospholipid removed from soybean oil used as emulsifier (in chocolates!) • Carry a charged group • Components: • Diglyseride (fatty acids of diglyseride can vary in different sources) • Esterified to phosphate group (derived from strong acid - H3PO4) • Esterified to a nitrogen-containing base (choline, inositol, ethanolamine, serine) • Draw structures of phosphatidylcholine (lecitin), phosphatidylethanolamine (cephalin), phosphatidylserine, phosphoinesitides (p. 52) • Amphipathic: • Hydrophobic (lipophilic) portion (tail) - due to long fatty acid tails of diglyseride • Hydrophilic portion (head) - due to charged base & phosphate also partially charged

  12. 6. Unsaponifiables • Unsaponifiable fractions in fats are: • Sterols (most NB) • phytosterol in plants & cholesterol in animals • Solids with high melting points • Flat molecules with all trans bonds • Are compounds containing perihydrocyclo-penteno-phenanthrene nucleus + rings • Cholesterol structure (fig. 2.12, p. 54) • Also terpenic alcohols, aliphatic alcohols, squaline, hydrocarbons

  13. 7. Emulsions & emulsifiers • Emulsion: a heterogeneous system consisting of one immiscible liquid intimately dispersed in another one, in the form of droplets with diameter over 0.1µm (milk, salad dressing) • Usually 2 phases – oil & water • If water continuous phase & oil dispersed phase – oil-in-water (O/W) type • If reversed – W/O type • Most common - phospholipids • Emulsifiers • surface agents that give stability to emulsions • Reduce interfacial tension between air-liquid & liquid-liquid interfaces • Due to molecular structure – contain hydrophilic (polar) & hydrophobic (non-polar) properties • Action of emulsifiers enhanced by stabilizers • Macromolecules e.g. starch & proteins • HLB system – numerical value for relative simultaneous attraction of emulsifier for water & oil (e.g. low HLB tend to form W/O emulsions) • Additional functions: modify physical characteristics of potato products, pasta, antifirming effect to improve shelf life of bread

  14. RAPID + heat + volume LIQUID SOLID - volume - heat SLOW 8. Physical properties of oils & fats • Oils & fats – mixtures of triglyserides • Fats semisolid at room temp – plastic fats • Solid characteristic is result of presence of some crystallized triglyserides • Fats have range of triglyserides at different melting points • Fat liquifies upon heating (all triglyserides in liquid state) • Upon cooling - higher melting fractions become crystallized, insoluble - ↑ in solid fat content

  15. 8. Physical properties of oils & fats • Above changes used to determine • melting point • Affected by chain length, unsaturation, configuration around double bond • solidification temp, • solid fat content • Dependent on temperature • Measure with dilatometer by melting expansion of fats upon heating – gives approximation of solid fats contents – reported as SFI • Lately – measure with NMR (nuclear magnetic resonance) – gives true solid fat contents – reported as SFC • (Look at Fig. 2.39, p. 85) • Cooling • Slow cooling – nucleation min, large crystals form • Supercooling – nucleation high, small / mixed crystals form • Fats do not form a glassy state like water does! • Crystal size - 0.1-0.5µm, sometimes 50µm • large crystals are grainy, 3 dim. Network, giving rigidity to product, holds the liquid portion of the fat

  16. 8. Physical properties of oils & fats • Polymorphism: • Existence of more than 1 crystal form ( , , ‘) • Cause – different patterns of molecular packing in fat crystals • Plastic range of fats: • in a relationship between SFC and hardness, there is narrow range of solids that results in a product that neither too hard nor too soft, e.g. shortening (requires extended plastic range)

  17. 9. Cocoa butter • Natural fat with unusual physical properties • High content of monounsaturated triglyserides • 3 major fatty acids – palmitic, oleic, stearic • Chocolate has desirable ‘snap’, glossy, melt smoothly in mouth, no greasiness on palate • High SFC at room temp, steep decline as temp reaches human body temp → al liquified, no waxiness • Special tempering procedure needed to produce desired polymorphic form • 50-60°C for 1h → cool to 25-27°C, to initiate crystallization → heat to 29-31°C → cool to 5-10°C • After long storage / extreme temperatures – chocolate shows ‘bloom’ – greyish covering on surface (unsuitable for consumption) caused by most stale crystal • Confectionary / specialty fats can replace cocoa butter – CBS’s & CBI’s

  18. 10. Heated fats - frying • Heating during processing (120-270°C) involve hydrogenation, physical refining, deodorization • Changes: • Randomization of glyseride structure • Dimer formation • Cis-trans isomerization • Formation of conjugated fatty acids of polyunsaturated fatty acids • No air contact, thus no oxidization • Deep frying (food heated by immersion in hot oil) @ 160-195°C • Lower temp → takes too long & food takes up too much oil • High temp → oil deterioration (food & oil being fried)

  19. 10. Heated fats - frying • (NB - Fig. 2.23, p. 68 / notes!) • Steam given off – remove volatile antioxidants, free fatty acids, other volatiles • Presence of steam – hydrolysis → produce free fatty acids & partial glyserides • Air contact – autooxidation, formation of degradation products (free radical & proxide mechanism • Lipid soluble colour components of food lipids leach into the frying oil • Final products – aldehydes, alcohols, ketones, which eventually polimerise • Suitability of fat for frying depends on ‘inherent stability’ • Calculated from level of unsaturated fatty acids & relative reaction rate with O2 • The higher the inherent stability, the less suitable for frying • Oils used for deep frying must be of high quality • Harsh conditions during frying • Must provide long shelf life of product

More Related