preparation of liquid food sample for analysis

PREPARATION OF LIQUID FOOD SAMPLE FOR ANALYSIS

Considerations

FOOD

• Edible materials

• Essential body nutrients

• Required for life and growth, such as proteins, carbohydrates, fats, vitamins, or minerals.

Moisture content

• Affects the extent of sample heterogeneity.

Considerations

Post-mortem or postharvest physiological changes

• Affects the extent of sample heterogeneity.

Enzymatic changes

• Result in appreciable changes of certain food components(CHO & N components).

• Inactivate food enzymes by denaturation in boiling methanol-water or ethanol-water mixtures

Produce small, discrete primary and secondary samples

• Representative of the entire food material, with minimal error.

How does foodstuffs are classified?

General classification of food samples according to their content

How much sample for analysis?

To measure minute quantity of compound of interest.

Large quantity For the macro

analysis of gross food components.

To measure crude fat, crude protein, crude fibre, or ash.

Small quantity

Food pretreatment

Removal of extraneous matter

Sample reduction

Determination of moisture content

Removal of co-extractives

Food pretreatment

• By filtration or separated by centrifugation.

• Sediment present in liquids such as beer, wine, juice, or cooking oil.

Removal of extraneous matter

Food pretreatment

• To obtain smaller subsamples

• Used as a representative analysis of the whole

• Methods include mechanical grinding, mixing, agitating, stirring, macerating,

pulverizing, mortar and pestle, mechanical high-speed beaters or blenders,

etc.

Sample reduction

Food pretreatment

• Affect the chemical and physical nature of the foodstuff.

• Important in terms of food quality.

• Affects food freshness, preservation, and resistance to deterioration.

Determination of moisture content

Food pretreatment


Interferences in sample extracts

Generation of emulsions

Contamination or plugging of equipment

Masking of the analytical signal for the

target analyte

Increase in the method limit of detection

Sample turbidity

Food pretreatment

• Removed during a post-extraction clean-up

• Passing the liquid extract through a clean-up column for sorption or

filtration of the interferences.

• Analyte enrichment.


Sample preparation

Step 1

• Sample dilution

Step 2

• Evaporation

Step 3

• Distillation

Step 4

• Microdialysis

Step 5

• Liquid-Liquid Extraction(LLE) or Lyophilization

Techniques for sample preparation

Techniques Advantages Disadvantages

Dilut ion • Simple

• Cheap

• High throughput

• No cleanup

• No enrichment

Filtrat ion • Simple

• Fast

• No enrichment

• Potential analyte binding

Centr i fugat ion • Simple cleanup

• High throughput

• No enrichment

• Cumbersome

Liquid-Liquid

Extract ion (LLE)

• Best non-chromatographic cleanup

• Enrichment

• Cumbersome

• Expensive

• Lots of solvent usage

Solid Phase

Extract ion (SPE)

• Best cleanup and fast

• Enrichment

• Easy to automate

• Many sorbents available for cleanup

• May need multiple steps

• Not well understood

Liquid-Liquid Extraction(LLE)

Solid Phase Extraction(SPE)

Membrane techniques

Membrane techniques

Non-Porous membrane technique

Supported Liquid Membrane

extraction (SLM)

Polymeric Membrane

Extraction (PME)

Membrane-Extraction with a Sorbent Interface

(MESI)

Microporous Membrane Liquid-Liquid Extraction

(MMLLE)

Porous membrane technique

Dialysis

END

Reference

Sampling and sample preparation for food analysis by Meredith S.S. Curren and Jerry W. King

Basic food microbiology by George J Banwart

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