LPT 321: Meat Science (1+1)

UNDESIRABLE CHANGES IN FREEZER STORAGE OF MEAT

Freezer burn

• Freezer burn is an extension of  surface desiccation associated with freezing.
• It occurs on the outer surface of imported frozen offals, like kidneys livers.
• Freezer burn is attributed to loss of moisture from the outer tissues; it may be seen where a carcass is stored close to opening of a cold air duct.
• The meat or offals have a brown withered discolouration.
• Storage temperature influences both the rate of desiccation and the development of freezer burn. This can be prevented by using suitable packaging.

Bone darkening

• Bone darkening is a condition, which develops when young poultry is frozen and thawed.
• Organoleptic properties of the muscle are not affected, but the brown to black appearance of the long bones and the surrounding muscles results from leaching of haemoglobin out of the bone marrow.
• Subsequent oxidation of the red haemoglobin to methaemoglobin produces the dark colour. Bone darkening is a problem only in young birds for two reasons.
  • First, more haemoglobin is present in the bone marrow of young, rapidly growing birds.
  • Secondly, incomplete calcification of the bones allows the haemoglobin to escape from the marrow cavity.

Recrystallization

• Recrystallization is an important physical change which may take place during frozen storage, resulting in translocation of water and consolidation of the unfrozen soluble water molecule tend to migrate from small to large crystals.
• This migration is promoted by fluctuating storage temperatures.
• Many workers have found that fluctuating temperatures result in moisture loss and quality deterioration.

Thaw rigor

• When prerigor meat is frozen, a severe type of rigor mortis ensues during thawing.
• The shortening so produced may be 60 to 80% of the original length of the unrestrained muscle.
• Although shortening is less in a muscle attached to skeleton, the condition results in tough meat and heavy drip losses.