Summary Advanced biochemical anlysis of foods

ABAF lecture notes

Inhoud
Week 1..................................................................................................................................................... 2
Intro lecture – Peter Wieringa 15-03-2021 ......................................................................................... 2
Separation by gas and liquid chromatography – Wouter de Bruijn 16-03-2021 ................................ 4
Mass spectrometry – Wouter de Bruijn 18-03-2021 .......................................................................... 8
Week 2................................................................................................................................................... 15
QAQC – Peter Wieringa 22-03-2021................................................................................................. 15
Carbohydrates – Henk Schols 23-3-2021 .......................................................................................... 19
Proteins – Peter Wieringa 25-03-2021 .............................................................................................. 24
Week 3................................................................................................................................................... 29
Bio-functional carbohydrates – Henk Schols 29-03-2021 ................................................................. 29
Bioassays: Introduction and general principles – Nico van den Brink 30-03-3021 ........................... 35
Bioassays: Food safety – Nico van den Brink 01-04-3021 ................................................................. 37
Week 4................................................................................................................................................... 39
Food Fraud and Authentication – Saskia van Ruth 06-04-2021 ........................................................ 39




1

,Week 1
Intro lecture – Peter Wieringa 15-03-2021
Learning outcomes:

• Interpret results from analytical methods
• Identify errors in results from analytical methods
• Explain which analytical techniques are typically applied in different fields
• Describe the basic principles of analytical methods
• Select the analytical techniques needed to study different compounds

• Steps in analysis: Sampling (may cause some variation), sample preparation, detection and
quantification.
• Reasons for food analysis are product composition analysis, for labelling, quality assurance
and control, for research and development.
• Food safety, fraud and defence: Key marker compounds and bioassays. Also, report and
recalls.
• You cannot measure all the produced products; therefore you need to take samples.
• How to prevent error in analysis:
- What analysis methods are currently used
- How do these methods work?
- How reliable are those measurements? Confidence and how to increase confidence.
- How to draw strong conclusions.
• In this course: Product authenticity and toxicology.
• Describing the quality of the analysis: Precision and accuracy: Accuracy describes the extent
of over or underestimation of the results.




• Sampling protocols: Product → Analysis → Signal → Amount
- Random: ensure that every item in the population of the food being sampled has an
equal chance of being collected and incorporated into the sample to be analysed
- Stratified: random sampling in pre-defined subpopulations
- Selective sampling: Only in part of the subpopulations
- Convenience sampling: Only accessible etc
• Understanding levels of variation:
- Determine variation in the population: Selection of representative products to sample
- Reduce variation in each product by: Taking representative samples and increasing
sample size.
- Determine variation in analysis: Analyse samples in replicate (multiple times)




2

,• Challenges: Compound of interest:




• The detection of very small amount of analytes is difficult, the sample preparation needs to
concentrate the analyte, and remove other compounds.
• Examples of sample preparation, with precision:
- Extraction
- Precipitation
- Filtration
- Centrifugation
- Drying
- Heating
- Chemical conversion
• Detection: You don’t determine ‘proteins’, but you determine absorbance, RI, m/z, weights.




• Basics of detection method calibration:




Trick: Always re-calculate the concentration of your standards based on your calibration line.
• Other components in the sample can change the detector response. Especially in MS
presence of other compounds (co-elution) can lead to a lower signal intensity of your
analyte.
• Statistics: The normal distribution Comparing two samples:




• Comparing results: For duplicate measurements of two samples, the average values for the
two samples should at a distance of 12σ to be significantly different.


3

, • Testing for compound presence: Screening:




Identification of positive (Suspicious) samples – low precision. False positives are OK → will
be verified later in confirmation analysis. False negatives to be avoided.
• Method validation: Stronger conclusion and improved confidence in results by understanding
of the method principles, identifying sources of variation and tools to validate the method →
Schemes in the slide and knowledge clip Intro4.

Separation by gas and liquid chromatography – Wouter de Bruijn 16-03-2021
• General principles of chromatography: Detecting individual compounds after separation




• Goal: Separation of a mixture to enable analysis of individual compounds
• Method: Competition of compounds being adsorbed on the stationary phase or being
carried by the mobile phase.
• Methods: Liquid chromatography: Mobile phase which is liquid. Gas chromatography: Mobile
phase which is gas. Compounds with low affinity to the stationary phase elute early.




• Method selection and their detectors:




• Polarity intermezzo: More Acid groups/-OH/-NH2/Ether per molar mass is more polar.

4