Topic I. Food additives

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					I. Food additives                                                                                                                    Page 1

Topic               I.       Food additives

Reference           Chemistry – A modern view Book 2 pg. 214–226

Objectives          8.1
                    – be aware that the appearance and the flavouring of food can affect appetite (食慾)
                    – recognise that artificial colouring is used to enhance appearance of food
                    – recognise that salt, sugar, vinegar and monosodium glutamate are some chemicals used to enhance
                        flavouring of food
                    – recognise that sulphur dioxide, benzoic acid, salt, sugar, vinegar and nitrites are common food preservatives
                    – recognise the following actions of food preservatives:
                        (a) dehydration, e.g. salt, sugar
                        (b) provision of an unfavourable medium for the growth of micro-organisms, e.g. sulphur dioxide, vinegar
                        (c) towards micro-organisms, e.g. benzoic acid, nitrite
                        (d) as an antioxidant, e.g. sulphur dioxide
                    – recognise that some food additives are hazardous to health

Notes               I.                   食品添加劑)
                         Food additives (食品添加劑

                    At home, we don’t use that much of food additives. Food made at home is usually fresh and will be eaten very
                    soon. This makes them delicious and good looking.

                    Food processing in industrial scale causes change in colour of the food, loss of taste, loss of nutritional value.
                    Furthermore, the food have to be stored for a long period and is not fresh.

                    Will you buy such kind of processed food ?

                    Functions of food additives

                    In food processing industry, a lot of food additives are used to
                    1. Enhance (提高) the appetite (食慾) of customer
                         a. colour food
                         b. flavour food
                         c. enhance the texture (質㆞) of food
                    2. Replenish (補充) nutrient (養份) lost in processing food.
                    3. Preserve (保存) food and extend (增長) the shelf life (貯存限期) of food

                    I.   Types of food additives

                    Many food additives are obtained from natural product. Moreover, a lot of synthetic food additives are prepared
                    from coal tar chemical.

                    E number

                    The E number is a code used to identify food additives. This coding system is used on food manufactured in
                    European Economic Community (ECC) countries. A list of ingredients of a popular British chocolate bean label,
                    Smarties, reads like this:

                                 Ingredients: milk chocolate with lecithin (E322) as emulsifier, vanillin and
                                              flavouring, sugar, wheat flour, maize starch, colours E102 (tartrazine),
                                              E110, E124, E127, E132, D133, E171, Carnauba wax.
I. Food additives                                                                                                                  Page 2

                    Type of additive       First digit of the E    Function                Example                 Details
                    1.   Colourings        1                       to restore the          tartrazine              tartrazine is a
                                                                   original colour                                 synthetic yellow dye
                    2.   Preservatives     2                       to preserve food and    benzoic acid,           benzoic acid and
                                                                   make it last longer     sodium nitrite and      nitrite are toxic
                                                                                           salt                    towards micro-
                                                                                                                   Salt preserves the
                                                                                                                   food by dehydration
                    3.   Flavourings or    (not numbered)          to enhance favour       salt, sugar, vinegar,   MSG, a favour
                         flavour                                                           ethyl ethanoate (a      enhancer, is added
                         enhancers                                                         synthetic ester) and    to make food more
                                                                                           monosodium              appealing
                                                                                           glutamate (MSG)
                    4.   Anti-oxidants      3                      to stop fats and oils   butylated               BHA is added to
                                                                   getting oxidized and    hydroxyanisole          biscuits, butter etc.
                                                                   giving bad smell        (BHA)
                    5.   Emulsifiers and   3 or 4                  to make oil and         lecithin, gelatin (a     lecithin is added to
                         stabilizers                               water mix and alter     natural product)         ice cream, salad
                                                                   the texture of food                              dressings and
                    6. Acids and bases 5                            to control pH          sodium                   NaHCO3 is added to
                                                                                           hydrogencarbonate        canned custard
                    7. Sweeteners           4 or 6                  to sweeten food        sorbitol                 sorbitol is added to
                                                                    without using sugar                             diabetic drinks and
                    8. Nutritive            (not numbered)          to add more nutrient vitamins, minerals         Vitamin E can also
                         additives                                                                                  be used as an anti-
                                                                                                                    oxidant but it is too
                    In Britain, only 17 synthetic and 19 natural colourings are allowed in food since a lot of formerly used colourings
                    are found to be toxic. In Hong Kong, the control of the use of food additives is the responsibility of Department of

                    N.B.     salt, sugar and vinegar may be considered as food or natural food additive.

                    Summary of food additives with E number

                    Food Colours
                    E102 Tartrazine yellow
                    E110 Orange Yellow S
                    E124 Ponceau 4R (red in processed strawberries)
                    E131 Patent Blue V
                    E142 Green S (green in processed peas)
                    E211 Sodium benzoate
                    E220 Sulphur dioxide
                    E223 Sodium metabisulphite
                    E236 Methanoic acid
                    E260 Ethanoic acid (the important chemical in vinegar)
                    E280 Propanoic acid
                    E300 Ascorbic acid (Vitamin C)
                    E321 BHT (butylated hydroxytoluene), used in crisps
                    E322 Lecithin (also used as emulsifier)
                    E330 Citric acid
                    Emulsifiers, stabilizers and thickeners
                    E410 Carob bean gum
                    E440 Pectin, which helps jams to set
                    E466 Sodium carboxymethylcellulose
I. Food additives                                                                                                                   Page 3

                    A. Artificial colouring

                         Artificial colouring is added to processed food to make the appearance more appealing. For example,
                    chlorophyll starts to disintegrate once the green plant is harvested. Green S (E142), an artificial colouring, is used
                    to colour the processed peas green.

                    B. Flavourings and flavour enhancers

                    Sugar, salt and vinegar are commonly used natural flavourings. They add taste to food. Furthermore, many
                    synthetic esters are used as artificial flavourings because of their pleasant smells.

                    MSG (monosodium glutamate) is not a flavouring, it has tasteless. However, it is a flavour enhancer which
                    increases the sensitivity of taste buds (味蕾) and makes the taste of food more appealing (吸引).

                    C. Preservative

                    Spoilage of food is caused by the growth and reproduction of micro-organism. Micro-organism produces many
                    toxic metabolic waste and may causes food poisoning. To preserve food, micro-organisms are either killed or
                    their growths are inhibited (抑制抑制).

                    There are many kinds of micro-organism including different bacteria, mould and yeast.

                    Some food preservatives are natural e.g. salt, sugar, vinegar and some of them are artificial e.g. sulphur dioxide,
                    benzoic acid, sodium nitrite.

                    Different food preservatives work according to different principles.

                    (a) Dehydration
                        e.g. salt, sugar
                        Salting and sugaring remove the water from the food by osmosis. Micro-organisms do not grow well in the
                        dehydrated condition. Therefore, salted or sweetened food is preserved.

                    (b) Provision of an unfavourable medium for growth of micro-organisms
                        e.g. vinegar, sulphur dioxide
                        Preserving by immersing in vinegar is called pickling. Micro-organisms do not grow well in acidic
                        In making of wine, SO2 is added into the fruit juice to suppress the growth of wild yeast and other micro-
                        organisms. SO2 is also widely used to preserve dry fruit and fruit juice. SO2 is both acidic and toxic to
                        bacteria which helps to kill micro-organisms and is also an anti-oxidant. It prevents air from oxidizing the

                    (c) toxicity towards micro-organisms
                        e.g. benzoic acid, nitrite
                        Benzoic acid is widely used in soft drink because it would be converted into non-toxic substance in human
                        body. However, the concentration should not be higher than 0.1 percent otherwise it would be toxic to human
                        as well.
                        Nitrite is used to cure meat. It inhibits the bacterial growth and also gives a pink colour to the meat.
I. Food additives                                                                                                                  Page 4

                    Common food additives
                    Additives            Function                    Working principle                                    不良反應)
                                                                                                         Adverse Effect (不良反應
                    Colourings           enhance appearance          Adds colour to food                 Some may cause hyperactivity
                    MSG                  flavour enhancer            Makes taste buds more sensitive     Causes allergy, chinese
                                                                                                         restaurant syndrome
                    Ester                flavouring
                    BHA / BHT            antioxidant
                    Vitamin C or E       antioxidant / nutrient
                    SO2 / Na2SO3         antioxidant /               *toxic to micro-organism            irritant to respiratory system
                    Sodium benzoate      *preservative               *toxic to micro-organism
                    Sodium nitrite       preserve and *curing        toxic to micro-organism / *react    stomach cancer / anemia (貧
                                         meat                        with protein                        血)
                    Sugar / Salt         *preservative /             *dehydrate the micro-organism       diabetes (糖尿病) / high blood
                                         flavouring                  by osmosis                          pressure
                    Vinegar              *preservative /             *inhibit growth of micro-
                                         flavouring                  organism by an acidic medium

                    1.   Other methods of preserving

                    a) Canning (製罐製罐)
                    Food is cooked or semi-cooked and then canned. The can is then heated again to kill the germs inside.

                    b) Drying (乾燥 or Dehydration (脫水       脫水)
                    Use sun or oven to dry food directly or use salt or sugar to dehydrate the food by osmosis. Both methods remove
                    the water, which is essential to the micro-organism.

                    c) Freezing (冷藏
                    Low temperature freeze all of the water and slow down the metabolic activity of the bacteria.

                    d) Freeze-drying (冷乾 冷乾)
                    Drying is done at a very low temperature. This preserves the favour of the food. For example, the instant coffee
                    powder is made in this way.

                    e) Irradiation (輻射輻射)
                    The food is irradiated with gamma ray, x-ray or electrons to kill the bacteria. Irradiation also delays ripening of
                    fruits and vegetables.

                    D. Hazards of using food additives

                    1.   Allergies
                         Monosodium glutamate (MSG) can cause symptoms such as thirst, headache, a burning sensation, chest pain
                         and discomfort in the abdomen. This is called ‘Chinese restaurant syndrome’.

                    2.   Hyperactivity
                         Some colourings are suspected to cause over activity of children. This affects their ability to concentrate and

                    3.   Long-term illness
                         Nitrite can cause lowering of blood haemoglobin, malnutrition and suspected to be carcinogenic.
I. Food additives                                                                                                                     Page 5

                    Advantages and disadvantages of using food additives

                                          Advantages                                                 Disadvantages

Glossary            appetite        coal tar      E number        colourings       preservatives       flavourings
                    flavour enhancers         monosodium glutamate (MSG)           Anti-oxidants        emulsifiers       stabilizers
                    sweeteners         micro-organism        dehydration       vinegar        pickling       benzoic acid        nitrite
                    cure         canning       drying      freezing       freeze-drying       irradiation       allergies
                    hyperactivity        carcinogenic       chromatography         chromatogram
Past Paper          95 I 3
Questions           95 I 7 a iii
                    98 I 3 a
                    99 I 7 b iv

95 I 3
3        Some of the ingredients present in a certain brand of cheese sticks are as follows:                                      6
         benzoic acid, corn meal, cheese, monosodium glutamate (MSG), sunset yellow (E110), vegetable oil
         Which of the above ingredients are food additives ? Suggest ONE function for each of the food additives.
         Monosodium glutamate (MSG): flavour enhancer / to enhance (increase) flavour (taste)               1 + 1 marks
         (DO NOT accept MSG is flavouring)
         Benzoic acid: preservative / toxic to (can kill) micro-organisms (bacteria)                        1 + 1 marks
         Sunset yellow (E110): Colouring / dye                                                              1 + 1 marks
         (3 marks for the correct choice of 3 food additives; if more than 3 substances are chosen, deduct 1 mark for each
         wrong answer. 3 marks for the correct function of the chosen food additives)
C        This question was generally well answered except that some candidates wrongly thought that MSG is a
         flavouring. In fact, MSG acts as a flavour enhancer.

95 I 7 a iii
7a        The label on a bottle of 'Effervescent Calcium' tablets is shown below.

        (Relative atomic masses: C = 12.0, O = 16.0, Ca = 40.0;
        Molar volume of gas at room temperature and pressure = 24.0 dm3)
    iii On the label, some words are missing in the second warning statement. Complete the second warning statement, 2
        beginning with the word 'Keep'. Explain your answer.
        (Keep) out of moisture (water) / (keep) in a dry place.                                                  1 mark
        Reason: The amount of active ingredients will decrease / the tablet will lose function / the active ingredients of
        the tablet will react in the presence of water.                                                              1 mark
I. Food additives                                                                                                              Page 6
         (Keep) out of heat / (keep) in a cool place                                                          (1)
         Reason: at high temperatures, vitamin C deteriorates / CaCO3 undergoes decomposition / the amount of active
         ingredients will decrease / the tablet will lose function.                                           (1)
         Keep away from sunlight                                                                              (1)
         Reason: Vitamin C may decompose. (CaCO3 does not decompose under sunlight).                          (1)
         (The warning statement and the reason must match each other.)
C        This was an open-ended question. Most candidates could not give the correct reason for keeping the tablets in a
         dry place.

98 I 3 a
3        Consider the following substances:
         sodium benzoate, sodium chloride, sodium hypochlorite, sodium hydrogencarbonate, sodium hydroxide, sodium
         sulphite and monosodium glutamate
3a       Which substance is commonly used for preserving fish ? Briefly explain its action.                                3

99 I 7 b iv
7b iv Explain why vinegar can be used as a food preservative.                                                 (9 marks)

90 28
    D   28 Which of the following are important uses of sulphur
           (1) as a food preservative
           (2) as a bleaching agent in the paper industry
           (3) in the manufacture of sulphuric acid
           A. (1) and (2) only
           B. (1) and (3) only
           C. (2) and (3) only
           D. (1), (2) and (3)

95 25
    C   25 Which of the following methods is NOT used to preserve
           food ?
           A. adding salt
           B. adding vinegar
           C. adding aqueous ammonia
           D. storing at a low temperature

96 16
    C   16 Which of the following methods can be used to separate the
           colourings in brown chocolate beans ?
           A. filtration
           B. crystallization
           C. paper chromatography
           D. fractional distillation

96 26
    A   26 Which of the following pairs is WRONGLY matched ?
              Food              Preservative
           A. sausage           monosodium glutamate
           B. meat              sodium nitrite
           C. fruit juice       benzoic acid
           D. pickled papaya vinegar

96 43
    A   43 Which of the following statements concerning the use of
           sodium sulphite as a food additive are correct ?
           (1) It is toxic to bacteria.
           (2) It is an antioxidant.
           (3) It is a flavour enhancer.
           A. (1) and (2) only
I. Food additives                                                                                                 Page 7
              B. (1) and (3) only
              C. (2) and (3) only
              D. (1), (2) and (3)

97 22
    B      22 Which of the following statements concerning the
              compound, CH3COOCH2CH3, is correct ?
              A. It is a food preservative.
              B. It has a pleasant smell.
              C. Its systematic name is methyl ethanoate.
              D. It is an electrolyte.

97 26
    C      26 Which of the following statements concerning food
              additives is correct ?
              A. A food additive with an E number of 102 can be used
                  as a sweetener in candies.
              B. Sodium benzoate can be used as a flavour enhancer in
                  potato chips.
              C. Sodium nitrite can be used to inhibit the growth of
                  bacteria in bacon.
              D. Synthetic esters can be used to enhance the appearance
                  of fruit juice.

97 46
    A      46 Sugar can be used as a preservative for fruits.             Sugar can act as a dehydrating agent.

98 8
       C   8   Monosodium glutamate is used
               A. to prevent food from being oxidized by air.
               B. to kill bacteria in food.
               C. to enhance the flavour of food.
               D. to improve the appearance of food.

98 43
    A      43 Which of the following substances are commonly found in
              canned grapefruit juice ?
              (1) citric acid
              (2) benzoic acid
              (3) ethanoic acid
              A. (1) and (2) only
              B. (1) and (3) only
              C. (2) and (3) only
              D. (1), (2) and (3)

99 14
    A      14 Which of the following adverse effects associated with
              excessive intake of food additives is correct ?
                  Food additive                 Adverse effect
              A. tartrazine (a yellow           causing hyperactivity
              B. sodium nitrite                 causing stomach ulcer
              C. monosodium glutamate           causing cancer
              D. sodium chloride                causing allergy

99 23
    B      23 Which of the following combinations is correct ?
                 Food additive               Function
              A. sodium benzoate             flavour enhancement
              B. sugar                       dehydration
              C. monosodium glutamate        sweetening
              D. vinegar                     antioxidizing