Quality assurance/quality control
28 important questions on Quality assurance/quality control
What are the choices you have to make when choosing a analysis method?
- ‘Non-invasive’ vs. invasive methods
- ‘real-time’ analysis: measure while processing the foods
- General vs. specific methods
- ‘Total’ content, or composition
- Fast and easy – more prone to error vs. slow and complex – more accurate and expensive
How can you decrease the chance of errors ocuring?
- Duplicates on each level (increase accuracy)
- Calibration (increase precision)
How can you determine the dry matter / moisture content?
Drying: Oven/stove (70-100 °C, ~3 h)
- balance between efficient drying and decomposition
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Why do you want to know the dry matter / moisture content?
- to express content of compound classes (protein, fat, etc)
- to indicate stability/quality (e.g. jams)
Drying also used for convenience (shipping)
How do you determine the ash content of a product?
- Complete destruction of organic molecules
- Typically 2-10 g
- Pre-dry (see DM determination)
- Oven (550 °C, 12-18 hrs)
What are the specific properties of proteins, carbohydrates and fats that make that you can analyze them?
- Porteins contain nitrogen
- Carbohydrates have reducing ends and a refraction index
- Lipids are soluble in organic solvents.
On what two things are analysis based?
- Direct analysis - Molecular composition
- Fractionation - Solubility (e.g. in polar or a-polar solvents)
How can you ditermine the protein content?
The principle behind it is that each AA contains an nitrogen. So if you known the amount of nitrogen you are able to calculate the amount of protein.
How does dumas work?
How does kjeldahl work?
How can you calculate the conversion factor for proteins in food?
Is calculating the nitrogen conversion factor from AA a perfect method?
- No big chance of error. Due to degradation of AA over time.
- Gln/Asp is converted to Glu/Asp
- Some proteins can be bound to carbohdrate chains.
What are the non-protein nitrogens in food?
- Low-molecular weight compounds --> ammonia, betaine (sugarbeet), urea
- DNA/RNA (non-protein amino acids), present in plants
How can you correct for non protein nitrogen?
- FN,AA (g protein(AA) / g NAA; based on amino acids)
- FN,tot (g protein(AA) / g Ntot; based on dumas)
The last one takes the free AA into account
What are the different spectrophotometric assays you can do on carbohydrates?
However there are some things that might interfere with this analysis.
What is not described by the protein content?
- Protein composition (e.g. caseins/whey/soy)
- Protein modification
What are the different ways to determine carbohydrate content?
- Refractrometer, °Bx. A solution of one degree Brix gives a refraction equal to 1 gram of sucrose per 100 gram solution
- Carbohydrates (?) = 100 – lipids – proteins - ash
- Color reaction: Color intensity depends on type of sugar present Reaction in H2SO4 and reaction of HMF and furfural with phenolic compound
- Reducing sugar assay: only reducing sugars, no sucrose or polymer Oxidation of sugar by Cu ions and measuring the amount of Cu ions converted
What is not described by carbohydrate content?
- Molecular weight distributions
- Modification (e.g. degree of methylation of pectins)
- Specific composition of fibers
These properties are very relevant for techno-functional properties (jams, jellies, interactions with proteins, etc.)
What molecules does the group of lipids contain?
- Triglycerides (90%)
- Fatty acids (Saturated /Unsaturated, Cis / Trans)
- Waxes
- Sterols
How do you extract fat from your product?
- Drying (remove water)
- Grinding (fine particles): Break up all (cell wall) material, Make all lipids accessible for solvent
- Extraction: Good solvent (hexane, petroleum-ether), Low boiling point
- Evaporation (remove solvent)
How do you determine the total fat for labelling?
- First acid hydrolysis (alkaline for dairy products)
- Addition of pyrogallic acid (to avoid oxidation) --> A C11:0 triglyceride is used as internal standard
- Extraction in ether, followed by methylation Using Borofluoride (BF3) in methanol.
How do you calculate the fat content?
Be aware you have to subtract 3 water for every triglyceride. If you don't do this you have a 10% error.
How do you do a Fatty Acid composition (FAME) analysis?
- Alkaline hydrolysis (saponification) (Add NaOH in water-free methanol and centrifuge (transesterification))
- GC-FID separation and detection
What will be the order in which the fatty acids will appere on your chromatogram?
First C14 then C24.
What information is not obtained by determination of the lipid content?
- Presence of specific compounds (e.g. sterols, vitamins)
- Content of free fatty acids vs. triglycerides
- Distribution of fatty acids over the glycerol chain
How can you use infra red to determine your product composition?
- Infrared measures the absorbance a certain product has and this will be different for the different compounds. It the depends on the vibration between different molecules.
- So Absorbance = -log (I(sample)/I(reference))
- Between 300 and 100 cm-1 is the fingerprint region.
- You need to train your software to calculate the composition.
Where will you have the absorbance of carbohydrates, lipids and protiens in a infrared spectroscopy?
What is the downside of using infrared?
But more important:
The method is not absolute and has to be ‘calibrated’ for each type of product / sample!!!
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