Chapter 2 - Food preservation and hurdle technology Flashcards
How can aw be calculated?
By calculation of the molar fraction of water in the solution:
xw = nw/(nw+ns) in mol
If the solvent is Sodium chloride, remember that the amount of moles of sodium are equal to the amount of chloride. These need to be added both to the denominator.
Is salt addition an efficient way to reduce aw?
No. You need a lot of salt to considerably reduce the water activity.
What is more effective in reducing the water activity, adding sugar or salt?
Adding salt.
Why is the theoretical reduction in aw in salt addition smaller than measured reductions?
Because the interaction of other solutes might decrease the aw even further.
Why is the theoretical reduction in water activity larger in ethanol fermentation than measured reductions?
Because the alcohol forms dimers (micelles/aggregates) so not all molecules are in the solution but only the ones on the outside of the shell.
Is moisture content the same as water activity?
No, the water activity is only determined by the reactive water. Some foods might be more hygroscopic, meaning they absorb moisture better. The water interacts with the food. Which makes it difficult for the water to react with other things. Therefore this water does not influence the water activity.
What is a chemical potential?
Particles tend to move from a higher chemical potential to a lower.
Driving force of osmosis.
What parameter is used in drying of food?
Relative humidity. Which is based on the ideal gas law PV=nRT.
RH = xw*p/pw0
pw0: partial water pressure with pure water.
How do RH and aw relate to eachother?
If the aw is reduced in the solution, the relative humidity is also reduced. Water molecules are then retained by the solvent and cannot participate in the exchange with the water phase.
What phenomenon is spray drying based on?
Hot air is used to dry the little droplets that are sprayed. The droplets are so small that the surface area is maximized.
Why is it important for Food Technologist to know the concentration of undissociated acid in the product?
Because of the weak acid principle. Weak acids partly dissociate, therefore undissociated acid is present in the product. The undissociated form can penetrate cell membrane passively. Inside the cell, it dissociated and lowers pH. Cells are exhausted by using ATP to expel the protons that are formed.
What are caustic preservations and how do they work?
A food product is dipped in a alkalic solution (NaOH/KOH). This denatures and hydrolyses the protein and inactivates MO.
Which two types of preservation occur when reducing redox potential?
1) Inhibition of aerobic bacteria.
2) Protection against chemical oxidation
How can you reduce redox potential?
- Remove oxidants (oxygen, H2O2, radicals)
- Add reductors (‘antioxidants’: Ascorbic acid)
How is waterglass used in foodpreservation?
- It is a strong reductor.
- pH 10-13
- Gel forming: physical barrier
