Effects of Ageing on Pork Quality Attributes

Ageing is one of the main factors that affect variation in tenderness. Pork tenderness increases rapidly in the first 48 hours post-mortem. In leg, nearly 100 per cent of the ageing occurs within four days post slaughter. In loin, 80 per cent of the total increase in tenderness occurs within four days, and 90 per cent within six days. Tenderness is improved further by longer ageing for up to 12 days.

• Pork ageing enhances pork flavour and overall acceptability.
• In loins, pork flavour and overall liking increase with ageing and peak at about nine days.
• It improves the blooming potential of pork and increases the ability of vacuum-packed pork to bloom.
• It has also been linked with improved water holding capacity and thus, juiciness.
• Muscles that are rich in connective tissues, such as the silverside, do not tenderise as well as muscles low in connective tissue, such as the loin. This is because the connective tissue proteins are not broken down by the enzymes active post-slaughter.

Recommendations on How to Age Pork

• BPEX recommends that loins (bone-in) should be aged for a minimum of seven days, or 14 days if they are “bone-out” (see Target Pork Quality 1; click here).
• Ageing of legs is recommended for a minimum of four days.
• The ageing rate of meat increases at high temperatures; however, to ensure meat safety, ageing is normally carried out at low temperatures (between -1.5°C and 4°C).
• Meat is normally aged in vacuum packs which helps to reduce surface drying as well as space requirements.
• Ageing in vacuum packs should be carried out at, or below, 3°C to prevent Clostridium botulinum growth and toxin production.

Post-slaughter Treatments Affecting Ageing

Pelvic suspension

Pelvic (aitch bone) suspension dramatically increases tenderness, particularly of the high value leg muscles, compared to hanging carcasses from the achilles tendon (Figure 1). By hanging from the aitch bone, the muscles of the leg are held in tension; this reduces any possible shortening and seems to accelerate the effect of ageing.

Figure 1 The effect of post-slaughter treatment on muscle tenderness

Hip suspension

Electrical stimulation

Vacuum packs

Modified atmosphere packaged (MAP) pork products

Cold shortening

Rapid chilling (without electrical stimulation) can result in muscle contraction during rigor mortis; this gives rise to tougher meat. Moreover, cold-shortened meat does not appear to benefit from ageing to the same degree so the meat remains tougher (see Target Pork Quality 3: Chilling systems; click here).

Electrical stimulation

High voltage electrical stimulation, in combination with rapid chilling, is an effective means of enhancing tenderness (see Target Pork Quality 3: Chilling systems). The ageing rate is faster in electrically stimulated carcasses than in non-stimulated carcasses, resulting in optimum tenderness being achieved sooner.

Packaging Options for Ageing

Vacuum packs

Pork is normally aged in vacuum packs, which not only controls bacterial growth but also reduces surface drying; this helps to reduce weight losses when compared to dry ageing (meat aged on the carcass or unwrapped pork). In addition, ageing in vacuum packs reduces trim losses and space requirements. Extended ageing (more than 12 to 15 weeks) in vacuum or modified atmosphere packaging (MAP) has been found to result in the development of unpleasant flavours and should be avoided.

Dry ageing

This may have positive attributes, as dried aged pork seems to display enhanced flavour. However, this practice may be linked to shorter shelf-life because of bacterial growth, and higher shrink and drying out losses.

Modified atmosphere packaging (MAP)

There is growing evidence that high oxygen packaging of meat, ie MAP, results in tougher meat with poorer flavour. It is possible that this effect is related to oxidation taking place in the high-oxygen environment. While it has not been verified in pork, it is likely that the same effect will be apparent. It is, therefore, recommended that ageing for enhanced quality is carried out prior to MAP and that the time in MAP is minimised as far as possible.

June 2012