microorganism

enzyme

physical and chemical effects

The principle of food freezing and preservation is to use low temperature to inhibit the growth and reproduction of microorganisms

Methods of freezing and preserving food

Most food-toxic microorganisms and fecal contaminants belong to the mesophilic group. Fecal contamination bacteria can be used as microbial indicator reagents.

Generally, food poisoning bacteria do not grow easily in environments with temperatures below 5°C. And it does not produce toxins. Once a toxin is produced, it cannot be inactivated by lowering the temperature.

Psychrotrophs in most animal foods are primarily aerobic Cooling storage combined with modified atmosphere packaging or vacuum packaging can significantly extend the storage period.

Psychrotrophs on most vegetables are bacteria or molds. The main fungi and yeasts on fruits are mold and yeast.

Decreased enzymes and slowed metabolism of substances

The drop in temperature destroys the coordination and consistency of various reactions and affects the living functions of organisms.

The viscosity of protoplasm in microbial cells increases, the water absorption of colloids decreases, the degree of protein dispersion changes, and normal metabolism is destroyed.

The formation of ice crystals will shrink the cells and increase the solute concentration, causing protein denaturation. At the same time, the ice crystals will cause mechanical damage to the cells.

temperature

Cooling speed

Combined state and supercooled state.

medium

Storage period

Alternate freezing and thawing

cooling method

Factors affecting refrigeration

Changes during refrigeration

The reverse process of reheating and cooling refrigerated food.

Packaging technology that achieves storage and preservation by controlling gas proportions.

By appropriately reducing the oxygen partial pressure and increasing the carbon dioxide partial pressure in the ambient air, the metabolic activities of fruit and vegetable products and microorganisms are inhibited and the storage time is extended.

Oxygen is reduced to 10% and carbon dioxide is increased to 10~15%.

Improved gas storage

Controlled gas storage

vacuum packaging

Moisturizing effect of controlled atmosphere storage on fruits and vegetables.

Preservation effect of controlled atmosphere storage on other products.

freezing point of food

Food freezing rules

Food freezing speed

The relationship between freezing speed and ice crystal distribution

Requirements for raw materials before freezing

Cooling consumption calculation

Freezing time prediction

Changes in food physical properties

Effect of freezing on redistribution of solutes in solution

The dangers of freeze shrinkage

Quick freezing and slow freezing

The hazards of ice crystals to food

blast freeze

contact freezing

Influencing factors

Main points

The relationship between glass state and frozen food stability

Dry consumption

Discoloration

Thawing hazards

Juice loss

How to defrost food