LPT 321: Meat Science (1+1)

COLD SHORTENING

• Cold shortening is an undesirable change associated with quick chilling
• Cold shortening is noticed when pre- rigor muscles, (i.e. while the pH of muscle was still above 6.2 and Adenosine Tri-Phosphate (ATP) was still present) were subjected to a temperature of below 10°C, in which the meat is very tough of meat occurred due to extreme contraction.
• Thus a pH of above 6.2 and presence of ATP is a pre-requisite for cold shortening to occur.
• The phenomenon of cold shortening was first encountered in New Zealand when rapid cooling schedules for lamb freezing were first introduced.
• Cold shortening can also occur with beef carcass and even in parts of the carcass, e.g. the loin, with fairly slow chilling.
• Cold shortening is not an important concern in the pork or poultry industry as white muscles are less prone to cold shortening.
• Cold shortening occurs due to the inability of the sarcoplasmic reticulum to sequester Ca ⁺⁺ at low temperatures (0°C - 5°C) and a decreased binding ability of mitochondria to bind Ca ⁺⁺.
• The inability of sarcoplasmic reticulum and mitochondria to bind Ca ⁺⁺ results in its spillage into the sarcoplasm and cold shortening ensues much in the same fashion as Ca ⁺⁺ triggering muscle contraction.
• This is not a serious problem in white muscles as they possess a rather better developed sarcoplasmic reticulum, in comparison to red muscles and possess fewer mitochondria than red muscles.
• The fact that white muscles also possess greater amounts of ATP, which provides energy for re-accumulation of Ca ⁺⁺ by sarcoplasmic reticulum and lesser extent mitochondria, also ensures cold shortening does not occur in white muscles.
• It can be avoided by delaying the start of chilling, e.g. for 10-12 h when the pH will be below 6.2 and the rigor will have taken place with the complete disappearance of ATP from the muscle or not chilling below 10°C in less than 10 h.
• Cold shortening can also be prevented by the use of electrical stimulation, which advances the onset of rigor, tender-stretch method of suspending carcasses and by ageing.