Preservation of food by Reducing Water Activity

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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