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    3 - Chemical Reactions of Fat and Oils

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    sha_bee
    The document discusses several chemical reactions that can occur in fats and oils, including oxidation, hydrolysis, polymerization, and ester formation. It focuses on hydrolysis and lipolysis, explaining that the hydrolysis of ester bonds can be accelerated by heat, pressure, and water. This causes free fatty acids to be released. Oxidation reactions are also discussed, noting they can degrade flavor and are influenced by temperature, oxygen levels, and presence of prooxidants. Polymerization reactions are addressed as well, describing how small oil/fat molecules can combine into larger ones during deep frying. The impacts of deep frying processes on oils are summarized, such as darkening, oxidation, polymerization, and hydro

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    3 - Chemical Reactions of Fat and Oils

    Uploaded by

    sha_bee
    181 views16 pages
    The document discusses several chemical reactions that can occur in fats and oils, including oxidation, hydrolysis, polymerization, and ester formation. It focuses on hydrolysis and lipolysis, explaining that the hydrolysis of ester bonds can be accelerated by heat, pressure, and water. This causes free fatty acids to be released. Oxidation reactions are also discussed, noting they can degrade flavor and are influenced by temperature, oxygen levels, and presence of prooxidants. Polymerization reactions are addressed as well, describing how small oil/fat molecules can combine into larger ones during deep frying. The impacts of deep frying processes on oils are summarized, such as darkening, oxidation, polymerization, and hydro

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    fat and oil

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    3_Chemical Reactions of Fat and Oils

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    The document discusses several chemical reactions that can occur in fats and oils, including oxidation, hydrolysis, polymerization, and ester formation. It focuses on hydrolysis and lipolysis, explaining that the hydrolysis of ester bonds can be accelerated by heat, pressure, and water. This causes free fatty acids to be released. Oxidation reactions are also discussed, noting they can degrade flavor and are influenced by temperature, oxygen levels, and presence of prooxidants. Polymerization reactions are addressed as well, describing how small oil/fat molecules can combine into larger ones during deep frying. The impacts of deep frying processes on oils are summarized, such as darkening, oxidation, polymerization, and hydro

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    181 views16 pages

    3 - Chemical Reactions of Fat and Oils

    Uploaded by

    sha_bee
    The document discusses several chemical reactions that can occur in fats and oils, including oxidation, hydrolysis, polymerization, and ester formation. It focuses on hydrolysis and lipolysis, explaining that the hydrolysis of ester bonds can be accelerated by heat, pressure, and water. This causes free fatty acids to be released. Oxidation reactions are also discussed, noting they can degrade flavor and are influenced by temperature, oxygen levels, and presence of prooxidants. Polymerization reactions are addressed as well, describing how small oil/fat molecules can combine into larger ones during deep frying. The impacts of deep frying processes on oils are summarized, such as darkening, oxidation, polymerization, and hydro

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    of 16

    CHEMICAL

    REACTIONS
    OF FATS &
    OILS
    2

    CHEMICAL REACTIONS OF
    FATS & OILS
    Oxidation
    Hydrolysis
    Polymerization
    Ester formation
    Reactions during heating
    and cooking/frying
    Online lecture
    http://www.youtube.com/watch?feature=player_em
    bedded&v=nyz9tI-fCUw
    4

    Hydrolysis/ Lipolysis
    Hydrolysis of ester bonds in lipids (lipolysis)
    may occur by enzyme action (e.g., lipase) or
    by heat/moisture free fatty acids (FFA)
    5

    Hydrolysis/ Lipolysis

    Accelerated by high T, P & water, e.g., in


    deep-frying of fresh potatoes (~80%
    moisture) liberation of excessive FFA may
    result in excessive smoking (reduce smoke
    point of the oil) (1 3% FFA is tolerable)
    FFA is more susceptible to oxidation than FA
    esterified to glycerol.
    Short chain FA is responsible for undesirable
    rancid flavour (hydrolytic rancidity) in milk.
    6

    Hydrolysis/ Lipolysis
    Controlled/selective lipolysis is used deliberately to
    develop cheese flavour (ripening) & certain food,
    e.g., yogurt.
    FFA is always present in crude oil (e.g., 3-5% in
    palm oil) remove during refining (by alkali
    neutralisation/steam distillation)
    Complete hydrolysis of fats is applied on a large
    scale for the production of fatty acids for the soap
    & oleochemical industries.

    Triglyceride + Water heat Glycerol + 3 FFA


    Oxidation
    Oxidation reaction of an oil/fat (at the double
    bond) with oxygen in the air adversely affect the
    flavour of the fat/food oxidative rancidity.
    8

    Oxidation

    Autoxidation oxidation induced by air at


    room temperature radical chain process.
    Products containing fat with a higher
    proportion of unsaturated fatty acids are
    more prone to oxidation.
    Rate of oxidation with T, O2, presence of
    light & contact with pro-oxidants (e.g. copper)
    9

    Polymerization
    Reaction whereby small molecules of oil/fat
    combine to form much larger molecules.
    This may occur at points of unsaturation on fatty
    acid chains (preceded by oxidation) or at the
    ester bond.
    Can occur in deep frying of foods accelerated
    by frying at too high a T (> 177 C) in the
    presence of O2.
    Polymerisation also causes viscosity & if
    allowed to proceed can result in foaming of the
    frying oil.
    10

    Deep frying a process of cooking involving the


    direct heat transfer of heat from oil to cold food
    Applications: frying of french fried potatoes,
    seafoods, poultry, doughnuts, etc.
    Food placed in hot oil is heated quickly to the
    point where water is vaporised the resulting
    steam causes a boiling action in the oil;
    this boiling action aeration in the oil
    oxidation with the formation of
    hydroperoxides
    11

    Changes in oil during frying (cont.)


    The peroxides (being very unstable) decompose
    via fission, dehydration & formation of free
    radicals to form a variety of volatiles (VDP) &
    nonvolatile decomposition products (NVDP).
    The VDP are constantly being removed by the
    evolving steam.
    The NVDP (polymers, dimers, trimers) are mainly
    formed via oxidation reactions removed from the
    frying oil via absorption by the food being fried/by
    deposition on frying kettle part/filtration.
    Solubilisation of components from food being fried
    e.g., coloured compounds
    12

    Changes/Reactions During Deep Frying


    1. Darkening of the frying oil protein accelerates colour
    darkening > starch; breadings high in reducing sugars
    darkening
    2. Oxidation - as frying T ; presence of prooxidants
    (Fe & Cu); presence of antioxidants (e.g. BHA/BHT)
    minimise oxidation.
    3. Polymerisation can cause foaming, gumming
    (methyl silicone at 0.5 2 ppm can reduce foaming)
    4. Hydrolysis/development of free fatty acids rate of
    hydrolysis increases with more water in food, higher
    frying T, slower turnover (replacement with fresh oil) &
    food loading (amount of food being fried).
    13

    FFA Development During Deep Frying

    High potato
    rate
    % Free Fatty Acids

    Low potato
    rate
    zero rate

    Hours of frying
    14

    Foam Development During Deep Frying

    Low potato rate


    zero rate
    % Foam Height

    High potato
    rate

    Hours of frying
    Changes during deep-fat frying
    Steam, volatiles, antioxidants

    AERATION ABSORPTION VAPORIZATION

    oxygen steam
    FOOD
    OXIDATION HYDROLYSIS
    SOLUBILIZATION FFA, diglycerides,
    hydroperoxides
    (conjugated dienes) glycerine,
    colored compounds
    monoglycerides

    FISSION DEHYDRATION FREE RADICALS

    alcohols ketones dimers,trimers,


    epoxides, alcohols,
    aldehydes
    hydrocarbons
    acids hydrocarbons
    HEATING dimers, cyclic compounds
    Changes/Reactions During Deep Frying

    16

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