Unit 9D?
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moisture sorption isotherm
having a graph with relative humidity and water content examines how a food product behaves as a function of RH change in weight in relation to RH
relationship between Aw and RH
Aw= RH/100
When we deal with foods do we say RH or Aw
Aw
how to create moisture sorption isotherm?
measure the change in weight as a function of RH set up a series of hermetically sealed chambers containing different saturated salt solutions difference in weight- water lost or gain of moisture due to atmosphere in chamber?
why do you need to specify the temperature on these graphs?
hotter air can hold more mass of moisture need to specify the temperature
what does MSI graph tell you?
1) expected moisture sorption behaviour 2) can indicate the effect of temperature 3) allows one to determine the expected Aw of a product at a specific temperature and RH which is the point where no absorption or release of moisture occurs 4) predict the final moisture content
what is important in predicting product stability
Aw
other factors affecting the drying process
1) reducing pressure ( under vacuum) reduces the temperature difference required in any drying process as the BP of water is reduced 2) latent heat (enthalpy) of evaporation 3) makeup/structure of the product
Pasteurization vs blanching?
animal based product (P) and vegtables (B)
Sulfiting
soaking food in sodium bisulphate and water for 10-30 mins
Sulfuring
exposing fruits to fumes from buying sulphur for up to 4 hours ex) dried apricots- to keep bright orange colour
Drum drying *
rotating heated drums
spray drying
very small drops of the food are sprayed into the top of a head chamber and tower and dehydrate best for powdered milk
vacuum drying
heated trays or shelves called platens transfer heat in vacuum chamber expensive highest quality
freeze drying
dehydofreezing expensive used for high end products maintains best flavour
concentration *
lower shipping costs because less volume and extended shelf life
the open kettle
frequent stirring take a long time not best choice
heat evaporation method
enter and leaves the evaporator
filtration method
small particles pass through files isolating and concentrating
green peas must be soaked in sodium bisulphate solution before dehydration to eliminate enzyme activity? T or F
F- rich in thiamine, which is sensitive to sodium bisulphate
for every 15 degree change in temperature, air holds how much more moisture?
twice as much
does sulphiting extend or shorten drying time?
extend
why do you sulphite
to control enzyme activity
does sulphuring extend or shorten drying time what are other advantages?
shortens, inhibits old growth and repels insects