Food Analysis
Introduction
Chemical & Physical Properties
Nutritive value
Functional Characteristics
Acceptability of the products
Quality Management
R&D Purpose
Quality Assurance
Food Composition
Ensure quality & safety of food supply
Validity of Conclusion
Proper selection and preparation
Appropriate calculations and interpretation of data
Changes of sample
Evaporation, absorption of moisture, evaporation
of volatile or lipid oxidation
Enzymic action
Actions of microorganisms
Reliability of Analysis
Specificy
Sensitivity
Accuracity
Precision
Repeatability
Reproducibility
Moisture
Oven Drying
Heated under specific conditions -> constant weight,
calculation based on loss of weight
Thermal energy used
Influenced
Time & temp of drying
Type of oven used & conditiond
Type of sample
Types of oven
Convection & Forced Draft Oven
Vacuum Oven
Microwave Oven
Infrared (IR) Drying
Advantages: Precise
Easy to use and cheap
Disadvantages: Time consuming
Destructive
Unsuitable for some type of food
Distillation Method
Co-distilling the H2O with a high boiling point solvent that immiscible with H2O, distilled water is condensed,collecting the mixture, measure the volume of water
Dean & Stark Method
Immiscible solvents with higher boiling point that H2O
Reflux Distillation
Solvent less dense (toluen) or more dense (tetrachloroethylene) than H2O
Advantages: Suitable for low moisture
Cheap, easy to set up & operate
Disadvantages: Destructive
Time consuming
Karl-Fischer Method
Based on reaction involving reduction of iodine by sulfur dioxide in the presence of H2O
Any H2O remains reacts with iodine, produce colourless solution
If all H2O have been used up, additional iodine -> dark-red brown (end point)
Crude Fiber
Acid & Alkali
Chem/Enzyme - Digestion of CHO, protein and lipid
Indigestable -> fiber -> weight -> ashed -> cooled
-> weight
Sample digested with H2SO4 & NaOH
Disadvantages: Only measure Cellulose & Lignin
Not calculate all fiber
Not get specific amount
AOAC Method
Isolate fibre -> selective ppt -> weight
From TDF
1) Duplicate of dry & defatted
Enzymatical (alpha-amylose, amyloglucosidase & protase
Total fiber -> add 95% ethanol -> filter (soluble & insoluble)
Insoluble: collected by filtration
Soluble: add 78% ethanol, filtre
2) Duplicate of ash content
Englyst Cumming Method
Defatted sample -> heated with hot H2O, gelatinized starch
Enzyme added -> digest starch & protein
Pure ethanol -> ppt fibre separate from digested solution (centifugration)
Fibre hydrolysed by conc. H2SO4 -> breakdown starch into monosaccharide
Conc. monosaccharide -> use colorimetrically / chromatographycally
Theander-Marlett Method
Free sugar & lipid extracted by alcohol and hexane
Starch -> removed by enzymatic degestion
Fiber fractions -> hydrolyzed with H2SO4
Sugar content gravimetrically measure (Lignin)
Carbohydrates
Chemically
Titration: Lane-Eynon Method
Reducing sugar + copper sulfate react with alkaline tartrate, boiled + methylene blue (indicator) -> coloured solution, titrated -> decolouration of indicator
Disadvantages: Not stoichiometric
Cannot distinguish different
type of reducing sugar
Gravimetric: Munsun-Walker Method
Oxidation CHO + heat, excess copper sulfate and alkaline tartrate -> ppt of copper oxide
Amount of ppt = conc. of reducing sugar
Modification: excess alkaline copper citrate with sodium carbonate. Reduction, excess copper citrate + potassium iodide, titrates with sodium thiosulfate
Advantages: More reproduceable
and accurate
Colorimetric: Somogyi-Nelson Method
Modification of Munsun-Walker and Lane-Eunon Method
Heated with alkaline copper tartrate add reduce copper -> cupros oxide, treated with arsenomolybdate reagent -> intense, stable blue-colour solution
Abs is determined
Advantages: Applicable for low
containing CHO
Physically
Polarimetry
To measure chiral susbtance
To measure the angle that plane polarized light is rotate on passing through a solution
Disadvantages: Unable to analyzed mixture of
CHO
Refractive Index
Measure content of dissolves solids
in sugars solutions
Calculation of CHO by difference
Total CHO: 100 - (% moisture + % protein
+ % fat + % ash)
Disadvantages: Inaccurate result for CHO
Incomplete digestion or extraction of food constituents
Does not differentiate between available and non-
available CHO
Ash
Dry Ashing
Weight (sample), burned off without flame, heated, cooled, weighing (ash)
Presence of oxygen
Advantages: Safe
No added reagent
Large number of crucible can be handle at once
Disadvantages: Time consuming
Loss of volatile elements at high temp
Interaction between mineral and crucible
Wet Ashing
Oxidation by HNO3 and HCLO4, heated up slowly, continue boiling -> colourless, cooled, add 50% HCL, diluted with distilled water
Advantages: Minerals stay in solutions
No loss from mineral volatilization
Disadvantages: Hazardous
Corrosive reagent
Low Temperature
Organic matter oxidized in a reduce temperature (150 C)
Using stream of excited oxygen (vacuum is applied)
Advantages: Less chance of losing trace minerals
Utilization of O2 as sole reagent
Disadvantages: Small sample capacity
Expensive equipment
Water Soluble & Water Insoluble
Ash, diluted with H2O, boil, filter with hot H2O, muffle furnace, weight (insoluble)
Acid Soluble
Add HCL to total ash, boil, filter, wash with hot H2O, dried furnace until constant weight
Alkalinity of Ash
Ash + HCL, warn on steam bath, cool, titrate HCL with NaOH (methly orange as indicator)
Vitamin
Vitamin A
Colorimetric Method
Vitamin A + antimony trichoride -> unstable blur colour, read at A620nm
Disadvantages: Cannot differentiate ratinol
isomers and retinal esters
HPLC Method
Involve in chromatographic separation and quantitative at 325nm
Vitamin C
2,6-dichlorophenolindophenol Titrimetric Method
L-ascorbic acid oxidize by indicator dye -> dehydroascorbic acid
End point, unreduced dye -> rose pink for 10 sec
Flurometric Method
Ascorbic acid oxizide by O-phenylenediamine -> dehydroascorbic acid ( fluroscent quinoxaline)
Vitamin B1
Thiochrome Flurometric Method
Thiamine digest with sulphuric acid and treated with phosphate
Potassium fericyanide/H2O2 oxidised in alkaline solution, extracted with iso butyl alcohol -> Thiochrome (blue colour)
Vitamin B3
Colorimetric Method
Niacin + Cynogen bromide -> coloured complex
Disadvantages: Toxic reagent
Crude fat
Solvent Extraction Method
Goldfisch Method
Sample - in an extraction ceramic thimble
Solvent - added in boiling flask
> 4 hrs extraction, air-drying overnight
brief oven-drying, remaining is weight (fat)
Advantages : Faster & more Efficient
Disadvantages : Incomplete extraction / channeling of solvent
Soxhlet Method
Same method as Goldfisch
Solvent - built up in extraction chamber (5-10 mins),
soaking the sample, siphon back to the boiling flask.
4-6 hrs
Advantages : Increase the efficiency
Disadvantages : Time consuming
Mojonnier Method
Extracted with mixture of ethyl & pet-ether
Extracted fat is dried - constant weight
Modified : use acid pre-treatment (HCL) - flour
Non-solvent Extraction Method
Babcock Method
H2SO4 + milk, shaken until homogeneous, centrifuged, submerged into H2O
Addition of hot H2O (isolate fat), measure volumetrically
Disadvantages : Charring effect of sugar
Gerber Method
Milk + H2SO4 and Amyl alcohol, carefully inverted
centrifuged and incubated in water bath (5 mins)
Fat content read directly from the tube
Advantaged : Wider application for dairy products
Simpler and faster
Detergent Method
Milk + ionic detergent (Dioctyl sodium phosphate)
Add Hydrophilic polyoxyethylene detergent
Fat is measured volumetrically
Advantages : Non corrosive properties
Protein Analysis
Kjedahl Method
Digestion: Add with H2SO4 and catalyst (Potassium sulfate
/ Copper (II) sulfate). Nitrogen -> Ammonia
Neutralization: Ammonia + NaOH -> NH3 (gas)
Distillation: NH3 + H3BO3 (excess boric acid) -> NH4 + H2BO3 (Borate ion)
Titration: H2BO3 + H -> H3BO3
Amount of protein calculated volume of H used to react with borate ion
Advantages: Accurate & good reproducibility
Simple
Inexpensive
Disadvantages: Corrosive reagent
Not measure true protein
Time consuming
Biuret Method
Cupric ions complexed with peptide bonds
under alkaline conditions -> violet-purplish colour
Biuret reagent: Copper sulfate, NaOH, Potassium sodium tartrate -> mixed with protein
Abs of the mixture is read at 450nm against blank reagent
Advantages: Rapid test
Not detect N from non-peptide or non-protein
Few substance interfere with the biuret reaction
Disadvantages: Low sensitivity
Not an absolute method
Opalescence could occur
Lowry Method
Combines Biuret reagent with Folin-Ciocalteau phenol reagent
which react with tyrosine & trytophan residue -> gives bluish colour
Biuret reagent added, incubated at room temp for 10 mins,
freshly prepare Folin reagent added, mixed & incubated -> Abs read at 650nm
Advantages: Relatively simple
Very sensitive
More specific
Disadvantages: Colour is not propotional to protein conc.
Reaction interfere with sucrose, lipids
interfered with high conc. of reducing sugar
Dye Binding Method
Sample is mixed with known excess amount of ionic dye,protein bind the dye (form insoluble complex), unbound soluble dye determine by abs
Aionic sulfonic acid dye ; acid orange 12, orang G, Amindo black 10B
Advantages: Not measure non-protein N
No corrosive reagent
More precise
Disadvantages: Not sensitive
Non-protein components bind
with dye
Proteins differ in basic amino
acids content