Article pp.168-171 du Vol.23 n°1 (2003)

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168-171 Sci. Aliments 23(1), 2003 M. de Lamballerie-Anton et al.

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High-pressure effect on the reaction between cathepsin D and bovine myofibrils

M. de Lamballerie-Anton, J. Perron, S. Jung, R. Chéret¹

Beef meat ageing occurs during chilled storage for 10-14 days and induces a distinct improvement of the organoleptic characteristics of the meat such as tenderness, jutosity, flavour, and colour. Several enzymatic systems are invol- ved in myofibrillar protein alteration. Among them lysosomal enzymes such as cathepsin D play an important role. The present experiment was focused on this enzyme which is linked with tenderness acquisition.

High-pressure processing had application for years in ceramics industries. Gene- rally, products are subjected to high-pressure in the range of 100-1000 MPa. In the 1980s, a research program begun in Japan to use high-pressure in food industry.

High-pressure processing is gaining in popularity with the North American and Euro- pean food industry where a variety of food products like fruit juices, ham, jam could be found. The principal advantage of this technology is the capacity to inactivate pathogenic micro-organisms: so shelf-life could be prolonged. Other advantages of high-pressure treatment over traditional thermal processing result in the almost complete retention of nutritional and organoleptic characteristics. Moreover the structure of molecules is affected and that induces modifications of water, proteins, polysaccharides and lipids. High-pressure treatment causes three main kinds of changes in meat: enzymatic, protein (mainly on myofibrils) and structural modifications. The mechanisms of the various effects are not yet fully understood.

The present paper describes our main results on the high-pressure effect and time on the reaction between cathepsin D and bovine myofibrils.

Activity of high-pressure cathepsin D on haemoglobin:

The Biceps femoris or Longissimus dorsi muscles are pressurised, at 2 days post mortem (10˚C), between 0 and 600 MPa. Cathepsin D extract activity was determined with haemoglobin as a substrate. The results show that high-pressure treatment had significant effect on the increase of cathepsin D activity.

This trend continues throughout storage, up to 20 days post mortem [1]. This increase of enzyme activity may be explained by the breakdown of the meat lysosomes and thus the leakage of the enzyme into the cytosol [2].

1. GEPEA, ENITIAA, BP 82225, 44322 Nantes cedex 3, France, e-mail : [email protected].

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Image analysis study of the relationship between total collagen content… 169

Moreover, our results show that cathepsin D activity determined with myofibrils as a natural substrate was increased after high-pressure treatment [3].

Figure 1

Activity of meat cathepsin D extracted from high-pressure treated meat on haemoglobin substrate

Activity of non-pressurised cathepsin D on high-pressure treated myofibrils:

When meat is pressurised, the enzymes and their substrates are submitted to high-pressure. The effect of high-pressure was studied on the myofibrils, and the ability of the cathepsin D from non-pressurised meat to hydrolyse pressurised myofibrils was evaluated.

Whatever the conditions of pressure and time, the hydrolysed fraction was higher when myofibrils has been previously high-pressure treated than with control myofibrils [2]. The activity of enzymatic extract is optimal (160% relative activity) when pressure is equal to 300 MPa and time is equal to 200 s. Then the pressure enhances myofibril sensitivity to cathepsin D. Thus, the ability of meat cathepsin D to hydrolyse high-pressure treated myofibrils was confirmed.

Figure 2

Activity of non-pressurised meat cathepsin D on high-pressure meat treated myofibrils Pressure (MPa)

200 400

600 800 100 200 400 500

100 300 500 700 900

Time (s)

Relative activity (%)

Time (s) Pressure (MPa)

0 200

400 600 800

100 200 300 400 500

100 120 140 160

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170 Sci. Aliments 23(1), 2003 M. de Lamballerie-Anton et al.

Activity of high-pressure treated meat cathepsin D on high-pressure treated meat myofibrils:

The above results show that high-pressure treatment affects the release of the enzymes from lysosome and cathepsin D activity, and that cathepsin D could hydrolyse high-pressure treated myofibrils. Also, the pressure scale had an influence on activity.

The 100% activity is equivalent to the untreated sample. The upward and downward trend of Figure 3 reminds the Figure 2, but the activity of enzymatic extract is optimal (135% relative activity) when the pressure is equal to 170 MPa whatever the time level. These activities values are even lower than with unpres- surised cathepsin D.

Above 300 MPa, the activity of cathepsin D was lower than that of the non- pressurised, so high-pressure was unfavourable to enzymatic reaction between myofibrils and cathepsin D. This could be explained by a partial denaturation of the enzyme due to high-pressure. High-pressure could also affect recognition of natural substrate.

Figure 3

Activity of high-pressure treated meat cathepsin D on high-pressure treated meat myofibrils

CONCLUSION

On one hand, the cathepsin D activity increases after a high-pressure treatment. On the other hand, the pressurised myofibrils have a greater sensitivity to cathepsin D than non-pressurised myofibrils. In both cases, the highest values occurred at a pressure of 300 MPa. When cathepsin D and myofibrils are both treated, the activity is lower. When meat is submitted to treatment, enzymatic

150 130 110 90 70

0 200

400 600

800 110 210 310 410 510

Pressure (MPa) Time(s)

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Image analysis study of the relationship between total collagen content… 171

systems and their substrates are obviously both pressurised; so these results could explain why high-pressure treatment of post rigor meat is not able to increase tenderness.

REFERENCES

1. JUNG S., GHOUL M. & DE LAMBALLE- RIE-ANTON M., 2000. Meat Science 56 3 239-246.

2. JUNG S., DE LAMBALLERIE-ANTON M, TAYLOR R.G. & GHOUL M., 2000. J.

Agric. Food Chem. 48 2467-2471.

3. JUNG S., CHAPLEAU N., GHOUL M., DE LAMBALLERIE-ANTON M., 2002. Trends in High Pressure Bioscience and Biotech- nology, Elsevier Science 541.