FDSC 300 Lecture Notes - Lecture 6: Muffle Furnace, Hydrogen Peroxide, Alkalinity
Document Summary
Water activity water activity is the ratio of the vapor pressure of water in a food (p) to the vapor pressure of water po) at the same temperature and barometric pressure. aw=p/po. Not all water present in food are available for microbial growth, physical properties and chemical and enzymatic reactions. Aw below 0,85 is cut off point for pathogenic microbial growth in canned food. Relationship between moisture content and water activity is not linear. Measurement of water activity: measuring the vapour pressure of the headspace after the closed system containing food sample attains equilibrium. The water will migrate out of the sample into the container headspace, or vice versa, until the aw of the food and the relative humidity of the headspace equilibrate. Detectors-dew point measurement, electric hygrometer sensors (including capacitance and electrolyte sensors), direct measurement of manometric pressure, tunable diode laser sensors and freezing point determination. Temperature is an important factor, usually the assays is conducted at 25 celsius.
