5 Flashcards
Water abundance and nutritional roles
Only substance found in abundance solid, liquid and gaseous phase.
Helps control body temperature, transport nutrients/wastes and provides solution for metabolic reactions
Bonds in water
Polar covalent bond between O and Hs because of unequal sharing of electrons (O-, H+)
Hydrogen bonds intermolecular because of H(partial positive charge) with O(partial negative charge)
Surface tension
Hbonds cause surface tension which allow water to:
Cling to something as well as itself
Have a higher melting point and boiling point
Freeze faster than thaws
Form a crystalline structure in solid state
Good solvent for
sugars, starches and proteins because of Hbonds
Atmospheric pressure w/ water
Atmospheric pressure impacts boiling and freezing point: high altitude low boiling point, vice versa.
High altitude baking need to increase amount of flour and water content and oven temperature.
Impurity in water
Really frequent because great solvent
Impurity may change boiling/freezing point, physical and chemical characteristics, flavor and color, Hbonds
Examples of water content foods
F&V >70% Bread = 36% Popcorn = 4% Milk has the 88% water content Beer, tomatoes and cucumbers have >90% water content. But milk has more free water tho!
Water content - Preservation
Amount of H2O is strongly related to its perishability = because water is both a reactant and a reaction medium (leads to deteriorative chemical changes) and is a requirement for microbial growth (spoilage)
carrots and milk = 88% water but water in carrots is bound to starch so not available for microorganisms
3 types of water in food
Free water: Easily separated from food tissue, contains dissolved compounds, boils, freezes and evaporates easily
Hydrate water: loosely bound with water, must be boiled to be free of water (anhydrous). Colloidal solution.
Bound water: tied to structure of larger molecules so reacts as part of the larger molecules, does not easily freeze/boil.
Water content (texture)
F&V: rigidity of plant cells resulting from being filled with water, responsible for juiceness or crispness of harvested f&v, loss of water results in textural changes.
Meat: changes in water-holding capacity of meat proteins during freezing or heating affect texture
Fried snack foods: slight increase in water content can cause textural defects (moisten chips)
Water activity - Definition
Measure of available (mobile) water in a food system. Aw= P(t)/ Po(t) where P=partial vapour pressure of water over sample of food, Po= partial vapour pressure of pure water, t= temperature. 0 < Aw < 1.0 (pure water). How much water is available to microorganisms. Canned foods are more perishable than dried foods.
Water - Preservation techniques
Removal of water = most common and effective food preservation techniques. Dehydration/drying, concentration (removal of some), freezing. Removal of water is mostly based on water activity more than on moisture content = we try to remove free water more because they support microorganisms growth.
Functions of water in the body
Body temperature, transport nutrients/wastes, reactant in metabolism and part of body tissue.
Common pollutants
Human and animal wastes, chemicals and factory waste, garbage.
Biological: bacteria, protozoa, viruses, organic waste deplete oxygen from rivers, lakes, water supplies. Chemical: Ca+, Mg+, cause hard water which are damageable to utilities and equipment because of minerals. Acid rain changes pH of water.
Physical: garbage, plastics,etc harbor bacteria, cause physical harms and break down into toxins.
Water quality
Potable water (drinking water) is commonly supplied by municipality but usually requires further treatment to be suitable for food processing because it can be variable and we want to control that variability. Minerals present in municipal water may interact with food constituent
