Food Analysis

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Food Analysis

Protein Analysis

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

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

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

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

Crude fat

Non-solvent Extraction Method

Detergent Method

Milk + ionic detergent (Dioctyl sodium phosphate) Add Hydrophilic polyoxyethylene detergent Fat is measured volumetrically

Advantages : Non corrosive properties

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

Babcock Method

H2SO4 + milk, shaken until homogeneous, centrifuged, submerged into H2O Addition of hot H2O (isolate fat), measure volumetrically

Disadvantages : Charring effect of sugar

Solvent Extraction Method

Mojonnier Method

Extracted with mixture of ethyl & pet-ether Extracted fat is dried - constant weight Modified : use acid pre-treatment (HCL) - flour

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

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

Vitamin

Vitamin B3

Niacin + Cynogen bromide -> coloured complex

Disadvantages: Toxic reagent

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 C

Flurometric Method

Ascorbic acid oxizide by O-phenylenediamine -> dehydroascorbic acid ( fluroscent quinoxaline)

2,6-dichlorophenolindophenol Titrimetric Method

L-ascorbic acid oxidize by indicator dye -> dehydroascorbic acid End point, unreduced dye -> rose pink for 10 sec

Vitamin A

HPLC Method

Involve in chromatographic separation and quantitative at 325nm

Colorimetric Method

Vitamin A + antimony trichoride -> unstable blur colour, read at A620nm

Disadvantages: Cannot differentiate ratinol isomers and retinal esters

Ash

Alkalinity of Ash

Ash + HCL, warn on steam bath, cool, titrate HCL with NaOH (methly orange as indicator)

Acid Soluble

Add HCL to total ash, boil, filter, wash with hot H2O, dried furnace until constant weight

Water Soluble & Water Insoluble

Ash, diluted with H2O, boil, filter with hot H2O, muffle furnace, weight (insoluble)

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

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

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

Carbohydrates

Physically

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

Refractive Index

Measure content of dissolves solids in sugars solutions

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

Chemically

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

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

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

Crude Fiber

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)

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

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

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

Moisture

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)

Distillation Method

Advantages: Suitable for low moisture Cheap, easy to set up & operate Disadvantages: Destructive Time consuming

Reflux Distillation

Solvent less dense (toluen) or more dense (tetrachloroethylene) than H2O

Dean & Stark Method

Immiscible solvents with higher boiling point that H2O

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

Oven Drying

Advantages: Precise Easy to use and cheap Disadvantages: Time consuming Destructive Unsuitable for some type of food

Types of oven

Infrared (IR) Drying

Microwave Oven

Vacuum Oven

Convection & Forced Draft Oven

Influenced

Type of sample

Type of oven used & conditiond

Time & temp of drying

Heated under specific conditions -> constant weight, calculation based on loss of weight

Thermal energy used

Introduction

Reliability of Analysis

Reproducibility

Repeatability

Precision

Accuracity

Sensitivity

Specificy

Changes of sample

Actions of microorganisms

Enzymic action

Evaporation, absorption of moisture, evaporation of volatile or lipid oxidation

Validity of Conclusion

Appropriate calculations and interpretation of data

Proper selection and preparation

Food Composition

Ensure quality & safety of food supply

Quality Management

Quality Assurance

R&D Purpose

Chemical & Physical Properties

Acceptability of the products

Functional Characteristics

Nutritive value