Preparation of liquid food sample for analysis
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Transcript of 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
Removal of co-extractives
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.
Removal of co-extractives
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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