water
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Food Chemistry/Food Chemistry and Analysis
Food ChemistryFood Chemistry and Analysis
Food Chemistry/Food Chemistry and Analysis
Food ChemistryFood Chemistry and Analysis• central questions‣ what is chemically present in a food ?‣ what is the behaviour of these chemicals ?
• why these questions‣ chemical quality of food products
‧ nutritional quality‧ chemical food safety‧ sensorial quality
Food Chemistry/Food Chemistry and Analysis
Food ChemistryFood Chemistry and Analysis• structure of the theoretical course‣ horizontal approach‣ major/minor components
• theory : Food Chemistry = Food Chemistry and Analysis• practicals Food Chemistry : 30 h• practicals FC&A : 60 h
Food Chemistry/Food Chemistry and Analysis
Who ?
• theory : Prof. Bruno De Meulenaer• practicals :‣ ir. Barbara Kerkaert‣ dr. ir. Frédéric Mestdagh‣MSc. Tania Cucu‣ Laurent De Smijtere‣Nathalie De Muer
Food Chemistry/Food Chemistry and Analysis
Evaluation
• practicals‣ permanent (lectures; laboratory; report)‣ periodically
‧ FC&A : open book examination‧ FC : open book examination
‣ share in total marks‧ FC&A : 33 %‧ FC : 20 %
Food Chemistry/Food Chemistry and Analysis
Evaluation
• theory‣ periodically‣ oral examination : 2 questions‣ written examination : 4-5 questions‣ share in total marks
‧ oral : 33 % (FC&A); 30 % (FC)‧ written : 33 % (FC&A); 30 % (FC)
Food Chemistry/Food Chemistry and Analysis
Evaluation-training
• test on the theory‣ chapter water + proteins
Food Chemistry/Food Chemistry and Analysis
WATER
Food Chemistry/Food Chemistry and Analysis
General properties of water
•water is a very special molecule‣ why‣ consequences
Food Chemistry/Food Chemistry and Analysis
Moisture content of foodstuffs
•see table‣ variability‣ depending upon processing‣ link to stability ?
Food Chemistry/Food Chemistry and Analysis
Interactions with water
•macroscopical : waterbinding/waterholding capacity•molecular level : kinds of water‣ bound water
‧ constitutional‧ vicinal or monolayer‧ multilayer
‣ free water•properties : see table
Food Chemistry/Food Chemistry and Analysis
Wateractivity
•definition•practical importance : availability of water•theoretical calculation : Raoult
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm
•link water activity and water content•link with kinds of water•influence of temperature
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm-influence of temperature
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm-influence of temperatureClausius Clapeyron equation
RH
Taw Δ
−=∂∂
)/1(ln
Food Chemistry/Food Chemistry and Analysis
Sorption sotherm-influence of temperature
RH
Taw Δ
−=∂∂
)/1(ln
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm-heat of sorption
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm-hysteresis
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm-modelling
M = watercontentM0 = monolayer water
Food Chemistry/Food Chemistry and Analysis
Sorption isotherm-modelling
Food Chemistry/Food Chemistry and Analysis
Characterisation of water
•water content‣ physical‣ chemical‣ fast techniques NIR
Food Chemistry/Food Chemistry and Analysis
Characterisation of water
•kinds of water – matrix interaction‣ diffusion measurements‣ di-electrical measurements
‧ dielectric relaxation (principle microwave)‧ depending upon kind of water
Food Chemistry/Food Chemistry and Analysis
Dielectrical relaxation
Food Chemistry/Food Chemistry and Analysis
Characterisation of water
•kinds of water – matrix interaction‣ diffusion measurements‣ dieclectrical measurements
‧ dielectric relaxation
‣ pulsed NMR‧ relaxation of NMR signal
Food Chemistry/Food Chemistry and Analysis
pulsed NMR
Food Chemistry/Food Chemistry and Analysis
pulsed NMR
SRC = slow relaxing components
Food Chemistry/Food Chemistry and Analysis
pulsed NMR
Food Chemistry/Food Chemistry and Analysis
Characterisation of water
•kinds of water – matrix interaction‣ diffusion measurements‣ dieclectrical measurements
‧ dielectric relaxation
‣ pulsed NMR‧ relaxation of NMR signal
‣ DSC-measurements‣ determination of water activity
Food Chemistry/Food Chemistry and Analysis
Relationship wateractivity and stability
•physical stability•chemical stability•biochemical stability•microbiological stability
Food Chemistry/Food Chemistry and Analysis
Relationship wateractivity and stability
Food Chemistry/Food Chemistry and Analysis
Relationship wateractivity and stability
•sometimes this relationship is not valid !‣ eg. hurdle theory (microbiological stability)‣ wateractivity = equilibrium, but foodstuffs are metastable‣ frozen foodstuffs:
waterdundercoole
ice
waterdundercoole
food frozenpartially
pp
pp
aw ==
Food Chemistry/Food Chemistry and Analysis
Relationship wateractivity and stability
•sometimes this relationship is not valid !‣ eg. hurdle theory (microbiological stability)‣ wateractivity = equilibrium, but foodstuffs are metastable‣ frozen foodstuffs‣ water uptake by amorphous sucrose
Food Chemistry/Food Chemistry and Analysis
Relationship water activity and stability
Food Chemistry/Food Chemistry and Analysis
Glass transition theory
•from polymer science‣ polymer theory‣ molecular mobility theory
•water acts as a plasticizer in an polymericamorphous matrix
Food Chemistry/Food Chemistry and Analysis
Fringed micel
Food Chemistry/Food Chemistry and Analysis
State diagram
Food Chemistry/Food Chemistry and Analysis
State diagram
Food Chemistry/Food Chemistry and Analysis
Tg – depending upon ?
Food Chemistry/Food Chemistry and Analysis
Glasstransistion and mobility
•WLF kinetics versus Arrhenius kinetics‣ influence of temperature on
‧ mobility‧ viscosity‧ reaction speed
Food Chemistry/Food Chemistry and Analysis
Glasstransistion and mobility
Food Chemistry/Food Chemistry and Analysis
Glasstransition and stability
Food Chemistry/Food Chemistry and Analysis
Relationship aw - glasstransition
Food Chemistry/Food Chemistry and Analysis
Relationship aw - glasstransition
sorption isotherm 23°C
for abalone (seafruit)
Food Chemistry/Food Chemistry and Analysis
Relationship aw - glasstransition