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Week 7 & 8: Fats - Coggle Diagram

- - - - heat (from stove)
        
        Oil Reaction
        
        Isomerism of cis double bonds to trans double bonds
        
        Cyclisation of free fatty acids to form cyclic products
        
        formation of dimers, trimers, etc
        
        rancidity of oil
      - steam (from food into oil)
        
        (when heated) Hydrolysis: Mainly ester bonds
        
        Results in high formation of free fatty acids
        
        Results in rancidity of oil
      - oxygen (from aeration)
        
        FA Oxidation
        
        Causes oil to be rancid!
    - - use good quality oil (do not reuse the oil after deep frying)
      - use oil with less di- or tri- unsaturated fatty acids
  - - - Uses Wijs solution (known concentration of iodine monochloride in acetic acid, dissolved in an organic solvent) to a known amount of oil
      - Add potassium iodide solution
        
        Unreacted iodine from iodine monochloride in Wijis solution will be liberated with KI solution
        
        Unreacted iodine is then titrated with sodium thiosulphate (Na2S2O3) solution using a starch indicator
        
        Amount of iodine consumed by the double bonds can be calculated from the titration results
    - - The higher the value, the higher the degree of unsaturation
  - - - Developed for use as frying oil
      - Produced by reacting sucrose with 6-7 mols of C12-22 fatty acids in presence of catalyst
        
        Contains sucrose polyster with 6-7 mols of fatty acids
      - Cannot be absorbed in the human digestive system and therefore has no calories
    - - simulate the physical functionalities of fats for instance, creaminess and smoothness
        
        Example of carbohydrates based fat mimetics: Microparticulate cellulose
        
        Retains moisture and acts as a texturiser and stabiliser
        
        Provide mouthfeel and flow properties of fat but lacking in flavour characteristics associated with edible fats
        
        Example of protein based fat mimetics: Simplesse ®
        
        Made from whey proteins or milk and egg protein
        
        Processing involves simultaneous heating and sharing to produce small particles of coagulated proteins
        
        Provides mouthfeel of fat
- - - - Photoxidation: requires an activated oxygen to initiate the reaction
        
        Activated oxygen = oxygen in excited state = singlet oxygen
        
        Activated oxygen reacts on double bond directly
        
        The hydroperoxides formed will decompose to aldehydes and ketones
      - Enzymatic oxidation: Oxidation of linoleic, linolenic and arachidonic acids by lipoxygenase to hydroperoxides
        
        2-step mechanism:
        
        TAG in oils are converted to glycerol and free fatty acids by lipase
        
        Conversion of linoleic, linolenic and arachidornic acids by lipoxygenase into hydroperoxides
        
        Lipoxygenases: normally found in plants, eg. legumes, soybeans, wheat, potatoes and radish
        
        Blanching will inactivate the enzyme
        
        2 more items...
      - Autoxidation: Occurs when unsaturated fatty acids react with normal oxygen
        via radical mechanism
        
        divided into three steps:
        
        Initiation: Abstraction of a hydrogen from CH2 between two double bonds
        
        catalysed by light, heat or metal, example, copper
        
        Propagation
        
        Step 1
        The oil radical will react with oxygen in the air (triplet oxygen) to form a peroxyl radical
        
        Step 2
        The peroxy radical abstract a H from another lipid and form a hydroperoxide and another lipid radical and the cycle continues
        
        Hydroperoxide (Primary oxidation product): is unstable and will decompose into secondary and tertiary oxidation products
        
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        Termination: When any of the lipid, H or peroxy radical reacts with another radical
        
        Occurs only when radical concentration is sufficiently high
        
        Accelerated by using radical scavengers, like antioxidant (vit E)
    - - Nutritional quality loss
        
        Vitamins
        
        Essential fatty acids
      - Health risks
        
        Toxic compounds
        
        Growth retardation
        
        Heart diseases
      - Flavor quality loss
        
        Rancid flavor
        
        Changes of colour & texture
        
        Reduced consumer acceptance
        
        Economic loss
  - - - Add potassium iodide (KI) to a known concentration of oil
        
        The iodine liberated is titrated against a known concentration of sodium thiosulphate, Na2S2O3 using a starch indicator.
        
        The amount of hydroperoxide in the oil can then be calculated using the titration values
      - expressed as milliequivalents of oxygen per kg of fat
      - Not an accurate method – hydroperoxides are initial products, moderate value could be due to decomposition of hydroperoxides
  - - - Type of Oil: The number, position & geometry of C=C double bonds affects oxidation rate
        
        Saturated TAGs are stable at room temp
        
        Free FA react faster than TAG
        
        Conjugated double bonds are LESS reactive than non-conjugated ones
      - Degree of Unsaturation: Lipid oxidation rate increases with number of C=C double in FA
    - - Mostly phenolic compounds with bulky side chains
      - Work either by inhibiting free radical formation or scavenging the free radical
      - Ideal Antioxidants
        
        Prevent harmful physiological effects
        
        Pathological effects
        
        Carcinogenic potential
        
        Interaction with enzymes
        
        Effects on reproduction
        
        Metabolic rate
        
        No objectionable flavor, odor & color
        
        Effective at low concentration
        
        Fat soluble
        
        Readily available
        
        Economical
        
        Not absorbed by body
    - - Examples
        
        Transition metals e.g. Manganese, Iron
        
        Pro-oxidant vitamins e.g. Vit C
    - - Oxidation rate decreases with lowering Aw
        
        Rate may increase under very low Aw (<0.2) due to more readily breakdown of lipid hydroperoxides and higher efficiency of non-hydrated metal ion catalyst under such condition
        
        Rancidity becomes a major problem in dehydrated food
- - - - Saturated fatty acids :check:
        
        Trend: melting points increases as carbon number increases in fatty acids.
        
        MF (Inter-Molecular Force) strength increases with molecular size (carbon number)
        
        Structure affects MP
        
        tetrahedral in shape
        
        exist in “zig zag form”
        
        carbon bonds angle @ 109°
      - Unsaturated fatty acids :check:
        
        In 2 types
        
        In Unsaturated fatty acids with cis double bonds:
        
        Structure affects MP
        
        Carbon-carbon double bonds are 120 °, trigonal planar
        
        Cis double bonds form kinks, inefficient packing, lower melting points.
        
        Carbon-carbon single bonds are 109°, tetrahedral in shape
        
        Trend: More double bonds, more kinks
        Lower melting points
        
        Unsaturated fatty acids with trans double bonds
        
        Structure affects MP
        
        Carbon-carbon double bonds are 120 °, trigonal planar.
        
        Trans double bonds do not form kinks, “zig zag form”.
        efficient packing compared to cis double bonds, higher melting points
        
        Carbon-carbon single bonds are 109°, tetrahedral in shape.
        
        Sources of Trans Fats :check:
        
        Animal-based fats: Very uncommon, though can originate in the rumen of ruminant animals
        
        EG vaccenic acid & conjugated linoleic acid
        
        made by cooking with a very high heat, at temperatures impossible in a household kitchen
        
        a side effect of partially hydrogenating unsaturated plant fats
        
        Observation: Despite same no of carbons and double bonds, cis double bonds have lower melting points than trans double bonds.
        
        (Reason) Affected by packing of the Fatty acids in crystalline form
        
        Trend: The more efficient the packing, the higher the melting points
    - - Depends on purity, temperature, rate of cooling, presence of other crystalline nuclei, and type of solvent.
        
        TAG with three of the same fatty acids has 3 basic polymorphs:
        
        β’-Polymorph Form
        
        Orthorhombic packing
        
        Hydrocarbon chains in zig zag pattern, stacked perpendicular to each other, at an angle of 70°
        
        Lifetime of 60s to years
        
        Both α and β’ are metastable (unstable) and eventually convert to β form
        
        β’ forms are desirable in preparation of shortenings and margarine
        
        β-polymorph form
        
        Most stable polymorph
        
        Parallel or Triclinic packing array
        
        Hydrocarbon chains are tilted at 70°
        
        Example of oil that crystallises in β form are soybean oil, peanut oil, corn oil, olive oil, coconut oil and safflower oil.
        Examples of fats that crystallise in β form are cocoa butter and lard
        
        Cocoa butter: Natural fat with unusual physical properties
        
        Fatty acids on TAG are only stearic acid (S), palmitic acid (P) and oleic acid (O)
        
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        α-Polymorph Form: Fatty acid chains are arranged in a disordered or heaxagonal packing array
        
        Most unstable of all the three polymorph – has short lifetime of ~60s
        
        Converts to β’ polymorph after ~60s
        
        Occurs during rapid cooling
        
        Application
        
        The incorporation of air, plasticity and consistency, and solid-liquid ratio are important characteristics of shortenings.
        
        These physical characteristics in turn depend upon the polymorphic forms of the fats used and the methods of preparation.
        
        Plasticity and consistency, as well as solid-liquid ratio, depends on the melting range, proper tempering is required to form the mixed crystals required for a broad melting range.
  - - - From unsaturated fatty acids to saturated acids
        
        Advantages:
        
        Prolong shelf life of oils – Double bonds are reactive – oxidises readily to form rancid and off flavour tastes
        
        Increase melting points of oils – removal of double bonds results in more efficient stacking
        
        Disadvantage: Trans fats increase levels of LDL cholesterol and lower levels of HDL cholesterol, thus increasing the risk of coronary heart disease.
        
        Why are Trans Fats not degraded?
        
        Enzymes are specific, will only metabolise cis fatty acids into prostaglandins and leukotrienes
        
        Trans fatty acids cannot be metabolised by enzymes
        
        Not useful for the human body!!
      - Can be Partial hydrogenation: Hydrogenation process is stopped when the oil reaches the proper consistency for its application :check:
        
        Partially Hydrogenated Oil
        
        Eg. Sunflower oil partially hydrogenated to form sunflower spread
        
        used in food for many reasons
        
        Partial hydrogenation increases product shelf life and decreases refrigeration requirements.
        
        Partially hydrogenated oils have the right consistency to replace animal fats such as butter and lard at lower cost.
        
        They are also an inexpensive alternative to other semi-solid oils such as palm oil.
        
        Partially hydrogenated plant oils can be used to replace animal fats in foodstuffs for adherents to the dietary rules of Kashrut (kosher) and Halal, and for vegetarians and vegans.
        
        Unreacted double bonds will isomerise to form trans double bonds!
- - - - Structure: contains a glycerol with three fatty acids
        
        Different triacylglycerols will have different fatty acids attached to it
        
        2 components
        
        Glycerol :red_cross:
        
        Has three OH groups
        
        OH groups form ester linkage with fatty acids
        
        The carbons are described by specific numbering (sn)
        
        Fatty Acids
        :check:
        
        Belongs to carboxylic acid functional group
        
        R = long chain of hydrocarbons, usually about 12 – 18 carbons
        
        R can be saturated or unsaturated
        
        Types
        
        Saturated vs unsaturated
        
        Saturated FA: no C-C double bonds,
        
        1 more item...
        
        Unsaturated FA: – fatty acids with C-C double bonds
        
        2 more items...
        
        Length of FA chains
        
        Short-chain (<6 C)
        
        2 more items...
        
        Medium-chain (6-12 C)
        
        Long-chain (>12 C)
        
        Very long-chain (>22 C)
    - - With polar head (hydrophillic) and two hydrocarbon tails (hydrophobic)
        
        Head group – phosphate group esterified with inositol (cyclohexane), ethanolamine, OH group of aa serine
    - - Properties
        
        Malleable at room temp
        
        Melt above 45 °C (113 °F) to give a low viscosity liquid
        
        Insoluble in water but soluble in organic, non-polar solvents
        
        Biosynthesized by both plants & animals
        
        Plants secrete waxes as a way to control evaporation and hydration, especially in warm climates
        
        Examples of wax: Beeswax (honey bee), earwax (human ear), spermaceti (sperm whale), jojoba oil (seeds of the jojoba bush), soy oil (soybean)