15 September 1995

Shock way to add tenderness

By Harry Hope

PORK loin tenderness is improved by high voltage electrical stimulation (HVES) to the carcass immediately after slaughter.

The effect, combined with rapid chilling, can be similar to that obtained by a further eight days ageing time before retail sale.

The Meat and Livestock Commission (MLC) recognises that the cost of ageing pork is a hurdle to the widespread acceptance of its "pork blueprint". This recommends boneless loins are aged for at least 12 days before retail sale to enhance tenderness.

Benefits of ageing

Keen to find a way of achieving the benefits of ageing without the need for extending ageing time beyond that which happens naturally in the distribution chain, the MLC decided to explore the potential benefits of electrical stimulation, building on work on HVES by Bowes of Norfolk and the University of Bristols Division of Food Animal Science (DFAS).

A series of five MLC-funded research projects were carried out by DFAS followed by three trials with Bowes of Norfolk to pave the way for commercial acceptance.

Trial conclusions were that HVES generally led to a substantial improvement and reduced variability in pork loin tenderness, as great as that obtained by a further eight-day ageing time.

But HVES can increase drip loss and paleness associated with the pale, soft, exudative (PSE) condition in pigmeat, unless rapid chilling is also applied.

Project work confirmed the ideal procedures to use for electrical stimulation. It requires the use of a high voltage system with special electrical characteristics and a defined time of application. It works best when linked with rapid chilling, preferably crust freezing.

One Bristol trial involved six contrasting post-slaughter treatments. These were compared using 300 carcass sides from 150 animals. Measurements included weight loss during cooling, drip loss from chilled cuts, meat colour and tenderness.

The likely economic benefits of rapid chilling were confirmed by treatments E and F (see box) where evaporation weight loss in chilling was reduced from about 2.3% for the slow chill rates, to about 1.8% for rapid chilling. For a carcass of average weight this means that rapid chilling could save of 0.3kg in carcass weight.

Compared with the 1C chill (C), the HVES treatments (D and F) tended to be very slightly paler and show a little more drip loss. The use of rapid chilling without HVES tended to reduce drip loss of the topside muscle but not the loin.

Rapidly chilled unstimulated carcasses in treatment E were substantially tougher and showed greater variation in toughness than treatments A, B and C, but both HVES treatments produced the most consistently tender meat, irrespective of chilling system.

Compared with 1C chilling (C), rapid chilling alone (E) increased toughness in four-day aged loin by 7%. But the combination of HVES and rapid chilling (F) reduced it by 9%, giving a reduction from treatment E to F of 15%.

Ageing reduced loin muscle toughness for all treatments except C. Excluding treatment C, the reduction in toughness moving from four to 12 days ageing averaged 6%.

The first automatic on-line HVES system for pigs in Britain, and possibly the world, is now operating at Bowes of Norfolk.