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Food additive and contaminants



Food preservative and anti deterioration


1- Heat sterilization:


a- It is a best way to preserve food but can't be applied for all foods.


b- Foods that preserved by this way will deteriorate easily and very fast when exposure to the air.


- Because of the above, we need shift to use preservative, it is only tool to preserve food for long time.




Preservatives are defined as substances which have antiseptic properties under conditions of use, i.e., they are substances which inhibit the growth of microorganisms without necessarily destroying them. Effective inhibition of microbiological growth prevents spoilage of foods.


Spoilage may occur which has not relationship to the growth of microorganisms, e.g., there is spoilage which is attributed to oxidation or to the action of autolytic enzymes.


So, preservatives are more generally defined as chemical agents that serve to retard, hinder, or mask undesirable change in food.


Disadvantage for using preservatives:

1-  have a cumulative effect in adipose tissues.

2-  Prevent digestion of some kind of foods in stomach and small intestine. Ex: it has been proved that, formole present in vinegar interfere digestion of cazaine because become insoluble.




1- Natural preservatives:


Many of substances used as preservatives may in themselves be harmless, e.g., sugar, salt, nitrates, vinegar, organic fruit acids, wood smoke, hops and alcohol.


Called "common or kitchen preservatives" in contradistinction to chemical preservatives.  


It is present naturally in some foods in trace amount.



1-  Boric acid present in many plants.

2-  Salicylic acid present in Salix species.

3-  Formole present in vinegar.


2- Chemical preservatives:

 E 200-297: Benzoate E210-219, Sulphites E 220-227, Nitrates E 249-252:

1- Inorganic preservatives

The principle agents are:

Nitrates, nitrites, sulfites and sulfurous acid, borates, iodates, free chlorine, hypo-chlorites, fluorides and peroxides.

2- Organic preservatives

The principle agents are:

Benzoates, formaldehyde, salicylates, formic acid, esters of para- hydroxy benzoic acid, propionic acid and its sodium and calcium salts, thiourea and many others.

3- Sweeteners

The principle agents are:

Saccharin and dulcin.

They are very dangerous when used with food, because have high hazard to human been.

When are they used?

1-  Substitute with sucrose.

2-  Mask the decomposition or deterioration of the food state.

Boric acid:

Boric acid is usually added to butter and meats.


To detect presence of boric acid:

1- Turmeric Test:

Prepare strips of turmeric paper by soaking filter paper in an alcoholic extract of ground turmeric. Allow the paper to dry and cut into strips.



If the sample is a solid, prepare a paste of the material with water. Or add 7 ml of HCl for every 100 g of sample. Stir vigorously and dip into the mixture a piece of the prepared turmeric paper. Allow the paper to dry, give red color which is change by NH4OH to a dark blue green and back again to red by acid, boric acid is present.


2- Quantitative determination:

    (volumetric method)

Ashing the material + methyl alcohol + H2SO4 → burn boric acid, flam green color.



Present in chocolate flavored milk


1- Pour 10 drops of a solution of vanadic pentoxide in 100 ml of conc H2SO4 down the side of the test tube containing the sample. A reddish color indicates the presence of peroxides.


2- add some drops of para phenyl diamine solution to the milk give blue color is indicated the presence of peroxides.


The general means of detecting organic preservatives and sweetening agents falls into two main classes:

1-      if volatile, they may be distilled and subsequently identified, e.g., formaldehyde and formic acid.

2-      If soluble in water immiscible solvent, they may be extracted by that solvent and identified, e.g., benzoic acid, salicylic acid, saccharin.




Parahydroxy benzoic acid:

e.g., nipagin, nipasolm, nipacombin all these ester give red color with Millon's reagent.


Sorbic acid:

Is usually added to margarine and mionase.

Evaborate sample, take known amount and add mixed  of equal amounts of potassium cromate and sulfuric acid (0.3 N) in test tube  then heat on water bath for 5 minutes then add Thiobar butaric acid then heat for 10 minutes, red color is develop, is detected the presence of sorbic acid. 


Separation of organic preservatives:

Fischer method is used to separate and identify some of the most important organic preservatives and sweetening  substances. These substances are nipagin, ethyl para hydroxybenzoate, nipasol, benzoic acid, o-chlorobenzoic acid, salicylic acid, cinnamic acid, parahydroxybenzoic acid, dulcin, parachlorobenzoic acid and saccharin.

1- The extraction for all of these materials with ethyl ether.

2- The ethyl ether extracted is taken with an aqueous alkali solution.

3- The dulcin remains in the ether layer, all the other substances go into the aqueous alkaline layer.

4- Separate the aqueous layer and then acidify. Shake with petroleum ether. The pet ether extract contains all the aromatic preservatives except parahydroxybenzoic acid and saccharin, which are insoluble in pet.ether.

5- These two substances are removed from the water layer by mean of ethyl ether.

6- It is re-dissolved in hot water, filtered and again extracted with ether and evaporated of the ether extract.

8- The identification of the crystals obtained follows by determinations of the melting point.

9- The para hydroxybenzoic acid will sublime more easily than saccharin.

10-In a simple mixture of benzoic acid and saccharin, the benzoic acid is separated from the saccharin by subliming the benzoic acid by heating on a water bath. The saccharin remains as a residue.

Antioxidants E 320 BHA and E 321 BHT  :

Fat and oils in food turn rancid when exposed to air. Synthetic phenolic antioxidants butylated hydroxyanisole and butylated hydroxytoluene, (BHA and BHT) prevent this happening but can trigger asthma, rhinitis and urticaria.


Flavouring agents (to enhance food palatability) E 620-635), Monosodium glutamate E620:

Aspartame: a low calorie sweetener can trigger urticaria (nettle rash), itchy hives and swelling of the body.


Monosodium glutamate (MSG), which can trigger the "Chinese restaurant syndrome" of burning and tightness in the chest, neck and face.


Always read all packed food labels, legislation now ensures the additives must be cleared labeled. E numbers- all additives used within the European community must have an E number.



Coloring matters in foods:

E 100-180, Tartrazine E 102, Sunset yellow E 110.

The addition of coloring matter to foods has several objectives:

1-        Foremost is used of color to increase the attractiveness and palatability of a food (not subjected to be adulterant).

2-        To achieve uniformity of product.

3-        To conceal damage, or inferiority (subjected to be adulterant).




1- Coal-tar dyes or artificial coloring matters are most common used consisting of:


a- Permitted and certified water soluble acid dyes and oil soluble dyes.


b- Non-permitted and non-certified water soluble acid dyes, water soluble basic dyes and oil soluble dyes.


Examples of artificial coloring agents are:


E 132 indigo carmine or indigotine.

E 140 chlorophyll

E 160 carotenoids

E 163 anthocyanins


E141 copper complexes of chlorophyll and chlorophyllins

E 150 caramel

E 151 brilliant black BN

E 153 vegetable carbon or carbon black.

E 171 titanium dioxide


E 131 patent blue

E 142 green S

Not allowed by government:

E 152 black 7984


E102 tartrazine

E 120 cochineal, carminic acid

E 127 Erythrosine 

All artificial colors at one stage or another in their manufacture are treated with sulfuric acid or nitric acid, both are frequently contaminated with arsenic.


2- Natural or vegetable colors, e.g., annatto and turmeric. An example of animal color is carmine from cochineal.


3- Mineral color (pigments), e.g., charcoal, lampblack, and there form of carbon are pigments used to color food other mineral colors are talc, ultramarine blue, Prussian blue and umbers.


Most of countries put a regulation laws that regulate the uses of these dyes in foods and they must be not harmful to human been and not mask the defect in food nutriment.


How to detect the presence of artificial coloring agents:


Most method is used to detect these dye is method of dying wool. When the wool is dying with these dyes, the color not remove by washing with water, otherwise, when wool is dying with natural dyes (plant), the dye is remove when washing by water.


Water soluble food colors:

1- All of the water-soluble dyes are contained sulfonates. 2- They generally can be stripped from the food by soaking in ammonia water, e.g., brilliant blue.

3- This dye is prepared by condensing 1 mole of benzaldehyde-o-sulfonic acid with 2 mole of benzylethylaniline sulfonic acid, followed by oxidation and conversion into the disodium salt.


Oil soluble colors:

1- The oil soluble dyes are belong to azo group.

2- They are insoluble in water because they have no form salt.

3- They are soluble in non polar organic solvents, e.g., orange SS, oil red XO. 




Identification of dyes by spot tests:

a- Transfer the separated coloring matter to wool or silk by boiling in ammonical solution.


b- Cut off four small pieces from the strip of dyed wool or silk thread and place in white porcelain spot plate.


c- Moisten the pieces with concentrated hydrochloric acid, concentrated sulfuric acid, 10% sodium hydroxide solution and 12% ammonium hydroxide solution, respectively. See colors, then can be detect the coloring matter. Table.


How to separate mixture of coloring agents in food:


-Nutrition food may contains more than one coloring agents.

- we can be known the presence of these coloring agents in food by using separating dye method with small pieces of wool.

- put a piece of wool in coloring solution remove it and then add another pieces of wool and so on until all pieces of wool are absorbed the dye in the solution.

So, wool extract the dye completely from solution.



Mark more than one color change gradually in dying wool (first to end piece of wool).  


Natural coloring agents:

The most common used for dying foods are:

1-   caramel

2-   curcuma

3-   safran

4-   chlorophyll

5-   red wood


How to detect the presence of natural dyes:

Natural coloring agents are isolated from solution of nutrient by acidification using HCl and then extracted by amyl alcohol (wash with water 2 times) then evaporated on water path to get residue. Dissolve the residue in 50% alcohol then fractionated with pet ether (2 times). Then diluted alcohol layer with acidified water (equal volume), shake with amyl alcohol, evaporate, residue. Dissolve residue with water and then detect coloring agents according to its type.   


1- Detect caramel:


1- Marsh test:

Caramel color is insoluble in Marsh reagent which consists of 100 ml of pure amyl alcohol, 3ml of syrupy phosphoric acid and 3 ml of water. Thus this reagent provides a means of detecting caramel.



6 ml of sample, add 6 ml of alcohol and mix. Add 15 ml of the Marsh reagent and shake the mixture gently for 2', avoiding the formation of emulsion. Allow the layers to separate completely. A colored aqueous layer indicate the presence of caramel.

2- take concentration solution of sample, add 15 ml of paraldehyde. Then add few drops of alcohol with shake give black precipitate.


2- Detect safran:

Take  the concentrated solution, pass glass rod wetted by sulfuric acid, directly, give unstable blue color converted to red then black.


3- Detect curcuma:

Take  the concentrated solution, evaporated on w.b. put filter paper containing few drops of Boric acid solution, on top of beaker, the filter paper change to cherry red after drying when add a few drops of ammonia converted to greenish blue color.


Beet dye in tomato products:

Occasionally beet juice or the coloring matter of beets, betanin, is used to intensify the color of tomato products like tomato sauce, puree, and catsup. This can be detected by utilizing the differences in solubility of the normal pigments of tomato and that of betanin.


Extract the normal coloring matter of tomato products from an aqueous suspension or solution with amyl alcohol. Betanin remains in the aqueous solution. Put in a piece of tannin mordanted cotton and dye the betanin on the cotton. A terra cotta shade is produced.


Minerals colors

1- The use of mineral colors in foods is very small because many of them are poisonous.

2- These mineral colors are called pigments.

3- Mostly are organic substances combined with metals or metallic salt and are considered with mineral colors because of their metallic content.

4- e.g., of pigments are lampblack, Prussian blue, talc, umbers and ultramarine blue.

5- These may all be identified by the usual tests for metals and other elements as e.g., carbon in lampblack and sulfur in ultramarine blue.

6- Certain natural coloring matters such as chlorophyll derivatives contain metallic elements as magnesium.


Food contaminants

1- Microbial contamination:

- The high level of contamination is expected because of the improper methods of collecting, storing and marketing.

- Microbiological examination include the detection of pathogenic micro-organism such as Staphylococcus aureus, Escherichia coli, Salmonella spp, Shigella spp and Psedudomonas aeruginosa. 


Pharmacopoeial requirements:

German heath authorities have created two categories of herbal drugs with respect to microbial contamination.


Limits per drug category




Aerobic bacteria

Yeasts and moulds


Other enterobacteria












A: the preparation for topical use that contain dried herb.

B: other preparations for internal use that contain dried herb.

Staphylococcus aureus and Pseudomonas aeruginosa must not be present in internal preparations and in a limit of 102 CFU/g in herbal tea mixtures.


2- Microbial toxins


a- Bacterial endotoxins:

Man is very sensitive to their pyrogenic activity with pyrogenic symptoms, such as a rise in temperature, headache, joint pain and restless. An IV  dose 3ng/kg body weight to young healthy adult is sufficient to produce such effect. The pyrogenic potency varies with specific origin of the endotoxins. E.coli endotoxin has been shown to be the most potent one. The European pharmacopeia requires that all parenterals with a volume over 15 ml be tested for the absence of pyrogens. Injections with smaller volume are incapable of production a pyrogenic reaction. The endotoxins may be due to contamination of the main botanicals or due to the secondary contamination during the manufacturing process. Bacterial count more than 104 CFU/ml can produce endotoxins.    

b- Mycotoxins:

Heavy contamination of herbal materials with yeast and moulds resulted in growth of mycotoxin producing fungi under inappropriate drying procedure and storage.


Important toxins occurring in food and feeds are aflatoxins, patulinm ergot alkaloids, ochratoxin and zearlenone.


They varies in their structure and toxicity to liver whereas ochratoxins are nephrotoxic.


Daily intake of 2-6 mg aflatoxins (30-90 ug/kg) over a period of several weeks can be sufficient to produced fatal hepatitis.


The main aflatoxins produced by A. flavus are B1 and B2 where as A. parasiticus produces two additional aflatoxins G1 and G2, they give intense blue and green fluorescence respectively.


Human and animals can be exposed to aflatoxins by direct consumption of aflatoxin contaminated food and feed.


The most potent aflatoxin group is aflatoxin B1 which has been shown to have teratogenic and embryotoxic properties.


Aflatoxins can be acutely toxic, carcinogenic, mutagenic, teratogenic and immuno-suppressive to most mammalian species.


The united states FDA stated that the upper limit of aflatoxin content of peanut butter should not exceed 20 ug/g. A maximum daily dose of 10 ng/kg bw is in agreement with human data on the hepato-carcinogenicity of aflatoxins.

Established and potential method to reduce the microbial contents of herbs. There are 3 methods:

1-   gaseous treatment with ethylene oxide

2-   heating

3-   gamma irradiation

3- Pesticides:

Pesticides are compounds used for protection of plants against certain damaging.


Biological classification:

1-   Insects (insecticides).

2-   Fungal diseases (fungicides),

3-   weeds (herbicides) and

4-   rodent (rodenticides).


These compounds influence the biochemical processes in plants as well as toxicological process in living organisms. Therefore, the influence of pesticides on metabolic processes in humans is an important aspect of adverse effects of these compounds.


Chemical classification:

1-   chlorinated hydrocarbons e.g., aldrin, dieldrin, endrin, DDT (dichloro diphenyl trichloro ethane)

2-   chlorinated phenoxyalkanoic acid herbicides.

3-   Organophosphorus pesticides e.g., parathion

4-    Carbamate insecticides e.g., carbaryl. Fungicides e.g., maneb.

5-   Inorganic pesticides: aluminum phosphide, calcium arsenate and lead arsenate.

6-   Plant derived pesticides: tobacco leaf, nicotine, pyrethrum, rotenoids.


Only the chlorinated hydrocarbons and related pesticides and few organophosphorous pesticides retain a long residual action in environment leading to contamination of plants which have not been treated.


The general toxicity of chlorinated HC insecticides is CNS stimulation and/or depression depend on the compound and dose.


Organophosphate insecticides:

The largest group of pesticides used nowadays. Occupational exposure to organophosphate occurs mainly in agricultural workers who mix or apply pesticides as well as who work with crops containing pesticide residues.

Compared with organochlorine pesticides, OP degradation in the environment is very fast. Their stability in the environmental media is calculated in months. While organochlorine pesticides persist for years in the environment.


Determination of total chlorine and phosphorous:

Preparation of the samples:

1-    reduce the plant material to fine powdered and extract with a mixture of 350 ml of water and complete to 1000 ml of acetonitrile. Pesticides are mostly soluble in this solvent.

2-    It is necessary to transfer the pesticides to light petroleum. For pesticides containing chlorine further purification is seldom required, but for those containing phosphorous, further purification may be necessary by chromatography on floisil column, eluting with mixtures of light pet. And ether.


a- determination of chlorines:

it is based on the displacement of thiocyanate ion from mercuric thiocyanate by chloride ion, in the presence of ferric ion, a high colored ferric thiocyanate complex is formed and measure the absorbance at 460nm using water as a blanck.


b- determination of phosphates:

the phosphomolybdate method is based on the reaction of phosphate ions with ammonium molybdate to form a molybdophosphate complex, which is reduced to form a strongly blue colored molybdenum complex. The intensity of blue colored is measured spectrophotometrically at 820nm using water as blank.


Determination of heavy metals:

Heavy metals such as cadmium and lead present in soil, and subsequently, plants are considered potential hazardous contaminants in the biosphere to human health. Relatively low doses of lead and cadmium over long period can lead to malfunction of organs and chronic toxicity. Other toxic metals include, mercury and arsenic. Occupational and medicinal exposures to mercury and arsenic products have been associated with lung, skin and visceral cancers.

Determination of arsenic:

Certain weight of the plant material is treated in a flask with oxidizing mixture of nitric and sulfuric acids until all organic matter is destroyed, then ammonium oxalate is added to expel nitrogen oxide. The filtered solution is made to a certain volume with distilled water in a volumetric flask. The stain produced with this solution is compared with the stain from a standard arsenic solution, from which the amount of arsenic in plant sample can be calculated.


Determination of lead:

Can be determined colorimetrically, either by precipitation of the colloidal lead sulphide in alkaline solution or by dithizone (it is form a colored complex with lead that is insoluble in water, soluble in organic solvents) potassium cyanide is added during the reaction to prevent other metals from forming similar complexes with dithizone.







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