Analysis Of Food. 1-Introduction. Food analysis is the discipline dealing with the development, application and study of analytical procedures for characterizing the properties of foods and their constituents Characteristics of food, include their composition
-one of the most important reasons for analyzing food to ensure that they are safe
-Food considered to be unsafe because it may contains:
1- harmful micro organisms (Salmonella) .
2- toxic chemicals (pesticides).
3- extraneous matter(glass, wood, metal, insects and matter)
So analytical techniques must be of high sensitivity to detect low levels of harmful material
a- most foods are compositionally complex material
Made up of a variety of different chemical constituents
b- Composition depends upon the property that is of interest to the analyst e.g.:
specific atoms :C,H,N,O,S,Na,…etc
specific molecules : water, sugar,….
Specific substances : milk, flour, butter,….
Types of molecules : fats, proteins, carbohydrates, minerals
a- Molecular structure(~1-100nm)
type of molecules present
b- Microscopic structure (~10nm-100 μ m)
food can be observed by microscopy (not by unaided eye)
eg emulsion droplets, fat crystals, protein aggregates,...
c- Microscopic structure (~> 100 μm) food can be observed by the unaided eye) eg sugar granules , raisons, chocolate chips food….
Thus food must be carefully designed so that they have the required physicochemical properties over range of environmental conditions
Analytical techniques are needed to test physicochemical properties
Some of the criteria that are important in selecting a technique are:
Simplicity of operation
Specify : a measure of ability to detect and quantify a specific components within a food material even in the presence of other similar components eg fructose in presence of sucrose or glucose
A food analyst has to select an appropriate fraction of the whole material which is one of the most important stages of food analysis , and can lead to large errors when not carried out correctly
5. 1- Making Samples Homogeneous
1- Mechanical devices e.g., grinder, mixers ,slicers , blenders
2-Enzymatic method e.g., professes, calluses, lipases
3- chemical methods e.g., strong acid , strong bases.
Microbial Growth and Contamination
Proteins are important constituents of food, they are major source of energy.
Amino acids are the basic structural units of proteins. An amino acid is a compound that contains at least one amino group(-NH2) and at least one carboxyl group (-COOH)
1- Food is digested with strong acid (H2SO4) to oxidize any nitrogen in the oxidation state -3 to NH4SO4
N(food) (NH4) 2SO4
2- HgO is added as a catalyst to ensure complete oxidation.
3- Nitrogen in oxidation states other than -3 (nitro, azo- are oxidation to N2 resulting an error , salicylic acid is added as a reducing nitrogen to -3 state.
4- The ammonium sulphate is then converted into ammonia gas by heating with sodium hydroxide
6-The excess HCL is then titrated with standard
1 Mole HCL=1Mle N=14 gN
7-A blank sample is usually run at the same time as the material being analyzed to into account ay residual nitrogen take may be present into the reagent used to carry out the analysis.
8- the continent of protein is equivalent to the amount of nitrogen found
F= conversion factor =100( % Nin food protein)
A conversion factor of 6.25(equivalent to 0.16g nitrogen per gram of protein) is used for many application this is an average value, each protein has a different conversion factor depending on its amino-acid composition
1- Methods using UV-visible spectroscopy
2- Infrared spectroscopy : near infrared (NIR)λ region is 800-2500nm, it penetrates deeper into the food sample giving a more reprehensive analysis.
3- NMR Spectroscopy : protein content by measuring area under a peak in a NMR chemical shift spectra that correspond to the protein fraction.
1-these methods use either the natural ability of proteins to absorb (or scatter) light in the UV-Vis reason of the electromagnetic spectrum
They chemically or physically modify proteins to make them absorb or scatter light in this reason
2- Calibration curve of absorbance or turbidity verses protein consecration
The density of a protein is greater than that of the most other food components, and so there is an increase in density of a food as its protein content increase.
The refractive index of an aqueous solution increases as the protein concentration increases
1-Separation due to Different Adsorption characterization Ion exchange chromatography .
2-Separation due to size difference . Size exclusion chromatography
3- Separation by electrophoresis
These metals can be determine gravimetrically or by atomic absorption methods.
Mercury in mushroom
Mercury in fishes
2- benefits of fish: high in protein, law in saturated fat and high in unsaturated fat
3- most people are exposed to mercury via food
4- fish takes up mercury from steams and oceans as they feed, this mercury is the most toxic form ,methyl mercury. It binds to there tissue protein (muscles)
6-organic form I dangerous (methyl mercury) .
7- inorganic mercury is converted to organic mercury by anaerobic bacteria at the bottom of lakes streams
8- small aquatic animals consumes the organic mercury, and in turn eaten by larger life form.
9-as the elements move up to the food chain , forms microbes to the fish then to large animal as swordfish, mercury becomes more concentrated.
11-mercury levels differs from one species of fish to the next , according to fish, size, location, habitat and age.
12- fish contains higher levels of mercury includes , shark , swordfish , barramundi,…
13- fish contains lower levels of
Mercury includes, lobster, salmon and canned tuna.
1. Atomic Absorption Methods
2. Dithizone Colorimetric Procedure
3. Neutron Activation Analysis
1- It is the most commonly used method.
2- wet oxidation process.
3- Hydroxylamine hydrochloride is added to reduce the remaining oxidizing material from wet oxidization. 4-Mercury is extracted from solution using Dithizone in chloroform.
5- Copper can interact with thiazone causing interference
formed while copper Dithizone remains in CHC13
7- The aquophase containing mercury-thiosulfate is again oxidizes by H2SO4 or HNO3 and mercury is extracted with in CHC14
8- Mercury – dithionate is determined spectrophotometrically at 490nm
Low cost, simplicity, senility.=
Interference of copper.
Total carbohydrate content of food is calculated by difference ,rather than analyzed directly .
Thus the constituents in food (proteins, fats water, ash, alcohol) are determined individually , summed and subtracted from total weight of the food.
Total cryohydrate =
100(weight in grams(protein, fat, water, ash, alcohol) in 100 grams of food
A- Paper chromatography
b- high performance liquid chromatography
Example separation of fructose , orbital ,scarce and lactose
Fats are hydrolyzed using an alkali such as(NaOH), the alcohol is liberated and also salts of fatty acids (soaps)
2- The amount of free acids presents gives an indication of the age and quality of fats
3- Acids value :is the number of milligrams of KOH requires to neutralize the free acid present in 1gm fat.
1-The milk sample is prepared by mixing 10ml of milk 10ml, of 28%ammonium hydroxide, 25 ml petroleum ether and 25ml diethyl ether.
3- 5ml water is added then 2N HCL till pH is about 2 is reached.
4- Separation was carried out using Gas Chromatographic (G . C) method.
6- The column is then programmed from 130-200 ˚C Nitrogen is used as carrier gas.
7- This method is effective, rapid, accurate quantitative results were easily obtained
The flavor of the food, can be natural or artificial flavoring
Due to the high or unavailability of natural flavor extracts most commercial flavoring are nature-identical which means that they are the chemical equivalent of natural of natural flavors but chemically synthesized rather than being extracted from the source material
Acetic acids: gives vinegar its sour taste and distinctive smell
Citric acids: found in citrus fruits and gives then them their sour taste.
Lactic acids: found in various milk product and give them rich tartness
Malic acids:found in apples that gives them their sour/taste.
Tartaric acids:found in grapes and wines and gives them a tart taste
Dr. Lateefa alkhateeb