water Flashcards
roles for water in food system
A carrier of nutrients and waste
(2) A reactant and a reaction medium
(3) A stabilizer of biopolymer configuration
Texture is often associated with
moisture
The amount of water, its location and its interaction with the
chemical components in a food product is extremely important
from the standpoint of acceptability and
stability
Why is water so unusual?
two oxygen lone electron pairs left
in two of the sp3 orbitals. They produc electron rich regions
structure of water
In the liquid phase, water is considered to have “transitional”
structure, termed ”flickering clusters” - regions of threedimensionally hydrogen-bonded water molecules somewhat
similar in structure to ice
Number of clusters … with temperature but the number of
molecules per cluster …
increases and decreases
influence of ionic compounds in water
ionic compounds are dissolved in water. It forms a hydration shell which neutralize the charge of the respective ions
Essentially, a hydration shell forms around each ion to … the
charge of the respective ions
NEUTRALIZE
influence of H bonding compounds
H bonds compounds are also capable of disrupting the struture of water
inflence of nonpolar substances
form clathrate compounds - semicrystalline form
what is the eutectic point
solution can become concentrated to a point at which the remaining water will co crystallize with solute crystals to form and grow
type IV water
Aw= 1
pure water
type III water
Aw = 0.99-0.80
water entrapped in the tissue matrix
microorganism can grow
type II water
Aw= 0.80-0.25
microbial growth is halted
type I water
Aw= 0.25 - 0
Water that you cannot remove. strong H bonds
what is desorption
slow process, with moisture gradually
decreasing until the food is in equilibrium with its environment
what is adsorption
dry food is placed in a wet environment
what is moisture sorpton isotherm
process where a food is dried completely and placed into an enclosed chamber above a saturated salt solution
what is hyteresis
is when the curve in agraph will depend if you loose water (desorption) or if you are gaining it (adsorption)
what are the fcators of concern of water activity
(1) Enzymatic reactions
(2) Lipid oxidation
(3) Hydrolytic reactions
(4) Non-enzymatic browning
(5) Various forms of microbial growt
control of water activity
remove water
convert free water to bound water
freeze the food
what are the 3 classes of food dispersion
(1) True solutions (or molecular dispersions)
(2) Colloidal dispersions
(3) Suspensions
what are the characteristics of true solution
(1) The molecules and ions are present in their lowest subdivision.
(2) The particles are <0.1 µm in diameter.
(3) The solution formed is transparent.
(4) The solution has high osmotic pressure
(5) The solution passes through parchment membranes
characteristics of colloidal dispersions
- don’t pass a parchment membrane
- reduced osmotic pressure
- translucent
- may aggregate to form gels
