lec 12 shelf life Flashcards
what does A low critical water activity (aw) suggest?
low storage stability (without a highly protective package)
what does A high critical aw suggest?
low hygroscopicity and good storage stability
what can be done to maximize
storage stability?
An increase or a decrease of the critical aw may be necessary in food formulation to maximize storage stability.
how to increase Tg?
Addition of high molar mass substances to increase Tg
how to lower Tg?
Addition of low molar mass substances to lower Tg
what is the main cause of Stickiness and caking in powders?
Main cause is plasticization of particle surfaces above Tg
where does Stickiness and caking arise from?
arises from the formation of liquid bridges between particles.
Some factors that cause liquid bridging:
* Water sorption
* Melting of compounds (e.g. lipids)
* Chemical reactions that produce liquids (non- enzymatic browning)
* Water released due to crystallization of
amorphous sugars
compare the stickiness skim milk powder with skim milk powder with hydrolyzed lactose
Stickiness Reduction:
SMP: Stickiness in regular skim milk powder can be significant, especially in conditions of high humidity or when particles are fine.
HLP: The addition of hydrolyzed lactose may reduce stickiness compared to regular SMP. Hydrolyzed lactose can alter the surface properties of powder particles, potentially reducing cohesion and adhesion between particles.
when does Structural collapse happen?
Can occur in dehydrated foods above Tg
Related to highly viscous flow
Collapse results from the structure being unable to support its own mass
give examples of Transfer of non-water compounds
-Loss of CO2 in carbonated drinks
-Sorption of flavour compounds by packaging material (flavour scalping)
Migration of substances from packaging material to the food
Polymer monomers
Plasticizers
Metals
Nanoparticles?
give examples of Crystallizations in foods
Crystallization of amorphous compounds such as sugar
Starch retrogradation
Solute crystallization in frozen foods
Recrystallization of ice during frozen storage
Colloidal instability
Creaming, flocculation, coalescence and phase separation (”oiling off”) in emulsions.
Syneresis (water release) in gels.
Macromolecule concentration
Controlling gel setting conditions
Syneresis plays an important role in starch gels due to retrogradation
Waxy starches are resistant to syneresis
how are Control of chemical changes often achieved?
by heat treatment, adjusting pH and temperature, addition of inhibiting substances
(ascorbic acid and other vitamins, sulphite etc.) minimize exposure to oxygen etc.
The measures taken depends of the deteriorative mechanism and the respective food.
what happens to food when Chemical changes via Oxidation occurs?
Involves reaction with radicals
Fats- Ranciditiy (off-flavours)
Proteins- Loss of emulsion stability, solubility, water-holding capacity, Loss of colour in fresh red meat
Pigments - Loss of colour
Vitamins – Loss of nutritional value
Flavours – Loss of flavour and/or generation of off-flavours
what is The role of light in oxidation?
The harmful wavelength depends on the absorption properties of a given food
Reactions are often related to formation of singlet-oxygen
Chlorophylls and riboflavin absorb visible light and form long-lived excited states which may react with many food components
