Ciara McDonnell
Teagasc Walsh Fellow PhD student
Dr Paul Allen
Principal Research Officer, Department of Food Chemistry and Technology, Teagasc Food Research Centre, Ashtown, Dublin.
Dr James Lyng
Senior Lecturer, School of Agriculture and Food Science, University College Dublin, Belfield, Dublin

Meat curing is the most ancient food preservation technique dating back to 3000BC. Curing techniques have evolved into different methods such as wet-curing, injection-curing and dry-curing. Salt (NaCl) is the most important of all cure ingredients as it improves shelf-life, flavour, juiciness and tenderness.

Regardless of the method used to cure meat, diffusion of NaCl into the complex meat matrix is slow, taking up to two days per kilogram for traditionally-cured products. While injection-curing is fast, it produces lower quality cured pork products. The meat curing industry would benefit from a novel processing technology that could produce high-quality products under accelerated processing conditions.

Power Ultrasound

Power ultrasound is a technology that can lead to increased mass transfer through the mechanism of cavitation. Cavitation is the implosion of microscopic gas bubbles due to pressure fluctuations at a very high frequency (>20kHz). This violent bubble implosion could create microscopic channels in the meat matrix for increased diffusion and improved quality.

Increased mass transfer through the application of ultrasound has already been proven in food matrices such as cheese, apples and strawberries; however research on meat is lacking. The technology is certainly viable for industrial application. It was first used in the 1960s for cleaning and has since been applied industrially for homogenisation, emulsification and degassing. As an added advantage, the technology works with excellent energy efficiency (more than 85 per cent).

Reducing Curing Time

A research collaboration between Teagasc Food Research Centre Ashtown and University College Dublin has assessed the potential for ultrasound to reduce meat curing time.

Salt and moisture uptake acted as an indicator for accelerated processing. Quality attributes such as pH, colour, texture profile analysis, cook loss and water holding capacity, were also analysed. Protein denaturation and hydration were assessed by differential scanning calorimetry (DSC) and low-field nuclear magnetic resonance (LF-NMR), respectively.

Samples were treated with ultrasound intensities of 50, 75 or 100W per square cm for 10, 25 or 40 minutes in a specially designed treatment vessel with an ultrasound probe (550W).

There was a tendency for NaCl content to increase with power input (intensity × time). Moisture content was significantly increased by 100W per square cm for 10 or 25 minutes. There was no effect on the pH or the total colour difference of samples.

Ultrasound caused a significant reduction in cohesiveness and gumminess of samples, however, hardness and chewiness are considered to be more important sensory traits for ham and these were not affected.

Myosin denaturation (indicated by DSC) occurred in samples treated with the highest power output (100W per square cm for 40 minutes) but this effect was not evident at a depth greater than 2mm from the surface.

Myosin is the most important protein for water-binding within the meat fibre, thereby affecting juiciness, so its denaturation should be avoided. However, as the denaturation only occurred on the surface of the samples, no changes in water-holding capacity, water mobility or distribution were evident.

To date, results indicate that power ultrasound can reduce processing times by accelerating NaCl diffusion, without any detrimental impact on the end product. Work is currently underway on a pilot-scale production of sonicated hams for sensory trials.

April 2013