Preservation of food by Reducing Water Activity
Yeasts and molds
some can grow at low aw ( 0.60-0.62)
X.bisporus can germinate at aw 0.605
Zygosaccharomyces rouxii grow at aw 0.65
How to decrease water activity
concentrating
adding solute and eliminating water
adding solute to the food system
sugar
salt
drying
drying depends on temperature and pressure conditions
sun drying
hot air drying
hot vacuum drying
freeze drying
lyophilization
Effects of drying on microbes in food
young cultures are more senstive to drying than old cultures
more microorganism are destroyed during freezing than during dehydration
the goal
no food-poisoning organisms be allowed
except low no of Clostridium perfringens
coliform count of dried food should be 0
produce dried food with a total count of < 100000/g
endospores, yeasts, molds and many gram -ve and +ve survive
not lethal
many are recovered
Subtopic
Principles
drying lowers the moisture content
activities of microorganism are inhibited
microorganism and enzyme need water to be active
