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The trouble with ageing

from Beef CRC - Beef Bulletin SUMMER 2010

BRAHMAN NEWS MARCH 2011 Issue #170

The relationship between carcass temperature, ageing and ultimate tenderness was a critical discovery during the development of MSA.

It transformed some of the myths about postslaughter handling into hard fact, and has become a critical piece of knowledge underpinning MSA reliability.

Beef CRC scientists already knew that the temperature of a carcass in the hours after slaughter affected how quickly and how well the meat tenderised, but were unsure how much warmth was ideal, and for how long it should be present.

Professor John Thompson (pictured), Adjunct Professor of Meat Science, University of New England said tenderness through ageing is caused by enzymes called proteases, which break down tough protein chains in the meat.

"The warmth of the meat affects how fast proteases work. Beef CRC researchers found how long it takes before they stop working," he said.

To assess the situation, researchers used striploins from 15 dairy-cross cattle and subjected them to various treatments.

The only constant was that lactic acid levels in all cuts were allowed to reach a pH of less than 5.6, to avoid confusing the effects of pH with the effects of temperature.

In two basic treatments, meat was held at either 37°C or 15°C until the correct pH was reached, and then aged at 1°C for 21 days.

Three other treatments were also applied. Cuts were held at 15°C until the correct pH was reached, and then reheated in a 37°C water bath for either 21, 85 or 205 minutes before being aged for 21 days in the chiller.

"The results were telling us that we were onto something," said Professor Thompson.

"The meat subjected to 37°C heat to bring down pH levels reached the required acidity three times faster than meat at 15°C."

At the same time, tenderness, measured as shear force, of the meat subjected to higher temperatures was 13 per cent better than the 15°C treatment on the first day.

By Day 3 however, the rapid tenderising of the 37°C treatment had stopped, while the 15°C treatment continued to gain in tenderness up to Day 12, when it was about 20 per cent more tender than the meat subjected to higher temperatures.

Professor Thompson said they discovered that very little was gained by reheating the meat.

"Basically it had reached its ultimate pH by the time it was reheated, and tenderness was not affected enough to warrant the extra treatment," he said.

Professor John Thompson

"What the experiment taught us was that the higher the temperatures after slaughter, the faster the activity of the enzymes that degrade protein and contribute to what we call tenderness."

But enzyme activity burns out more quickly, too, so that ultimately greater tenderness is achieved by letting the enzymes work more slowly, over a greater length of time.

However, if ageing is not a requirement, the experiment also showed that a degree of tenderness can be reached faster under warmer post-slaughter temperatures.

The knowledge has subsequently been used to refine the MSA pH/temperature window, a critical point in every MSA pathway.