Water Activity in Food Preservation

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Presentation transcript:

Water Activity in Food Preservation -solutions -ions -properties of water

Salts are IONIC COMPOUNDS -Ions form between metals and nonmetals. -All atoms will react until the atoms have 8 electrons in their valence (outer) shells. -Watch the animation of sodium reacting with chlorine to form table salt, sodium chloride (NaCl): http://www.visionlearning.com/library/module_viewer.php?mid=55 -Other examples of ionic bonding: http://www.teachmetuition.co.uk/Chemistry/Chemicalstructureandbonding/ionic_bonding. htm

Properties of Water http://www.northland.cc.mn.us/biology/Biology1111/animations/hydrogenbonds.html Water molecule

Water Activity (Aw) and Free Water in Water as a Solvent http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html Dissolving animation Water Activity (Aw) and Free Water in Food Preservation http://physioweb.med.uvm.edu/bodyfluids/osmosis.htm Water activity osmosis (follow links to sample problems) http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf Salt and free water

REVIEW QUESTIONS What holds ionic compounds together (example: salts?) Water is a molecule with polar covalent bonds. What does polar mean? Why is water such a good solvent for salts? What does Aw stand for? How can the water activity be decreased? Water moves or diffuses from an area of high water activity to an area of low water activity. -At the beginning of the meat experiment, where was the water activity the highest: inside of the meat or outside in the bag? -Would water move from inside meat to outside bag, or from bag into meat? WHY?????