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