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A coloured view of beef

TResearch Spring 2022

By integrating information from different datasets, Teagasc has successfully published the world’s first collection of protein biomarkers (biological measures of a biological state) for dark-cutting beef, improving understanding of what leads to this colour defect.

Colour is an important characteristic of meat quality and a key visual cue that influences our purchasing decisions. Shoppers consider darker beef to be more undesirable, and are therefore much more likely to reach for the brighter coloured beef that’s on display. Because of this clear preference, dark-cutting carcasses are usually discounted during meat grading and downgraded in value, leading to economic losses.

Often the colour of meat is simply influenced by exposure to air or packaging conditions, but it can also be a result of a colour defect called Dark, Firm and Dry (DFD) meat. In the past, knowledge on DFD meat has been limited and its causes not well-understood.

To address this gap in knowledge, Teagasc has undertaken research to define the underlying biochemical pathways that lead to the change in colour. The hope is that a better understanding of the defect will reduce its prevalence, therefore minimising waste from quality beef, and improving the efficiency and subsequent profits of the beef sector.

Causes of dark-cutting beef

The conversion of muscle to meat after slaughter usually results in a decline of pH levels, but when the pH level of muscle remains high, DFD meat can occur. This leads to a high ultimate (final) pH (pHu), and prevents the muscle from developing the bright-red colour typically seen when a cut surface is exposed to oxygen.

Mohammed Gagaoua, Marie Skłodowska-Curie Career-FIT Fellow Researcher at Teagasc and project lead, says: “A lack of muscle glycogen (energy storage) at the point of slaughter is considered a key causative factor for DFD meat. And nutritional status and physical and psychological stress close to slaughter are considered key causes of low glycogen.

“Many countries use pHu as a key reference to determine DFD meat. However, the thresholds differ significantly. It’s also worth noting that dark-cutting beef has been observed where the pHu is within the normal range, but the cause for this is less evident.”

Over the past decade, hundreds of thousands of samples have been tested by researchers under given conditions – including the large-scale study of proteins (proteomics). Comprehensive analysis of proteins has generated significant datasets, which has allowed Mohammed and his colleagues to integrate and analyse information across data types, and gather proteomics data on the quality defect.

Finding patterns in data

The project team’s key objectives were to identify the main molecular signatures and to shortlist robust biomarkers of dark-cutting beef.

“Merging the findings of studies and data-mining (finding patterns in large datasets) have enabled us to examine and compare datasets across a range of meat quality studies, in our search for both the underlying mechanisms influencing the DFD meat trait, and a suite of candidate biomarkers,” says Mohammed.

“We applied this approach to proteome studies on dark-cutting beef by gathering papers and datasets of high-pHu versus normal-pHu, with a number of other determined factors.”

Eight eligible studies were chosen, which, notably, showed strong disparity when it came to common protein biomarkers. Despite this, 10 were identified, and the features within them that were considered important to the occurrence of dark-cutting beef were revealed.

Analysis confirmed the importance of muscle contraction in dark-cutting beef development, followed by the regulation of apoptosis (the process of programmed cell death used during early development to eliminate unwanted cells), carbohydrate biosynthetic (the production of a chemical compound by a living organism) and protein folding (where the protein becomes biologically functioning).

Across the studies, the loss of oxygen related to energy metabolism after death was also an important common process, but the muscle system of the animal remained the major influencing factor.

“The importance of the physical structure was evident,” explains Mohammed, “therefore, we believe that the extent to which muscle protein loses its shape and ability to perform its function may play a role in oxygen diffusion and myoglobin status. These are both known to be influenced by mitochondrial functionality (the ability to convert energy from food into a form that cells can use).”

Supporting future research

The project team uncovered a number of important findings through its work, and as a result published the first-known collection of protein biomarkers. This innovative database may serve as a reference for future studies, and it has also highlighted a number of areas in need of greater research.

“Our research has shown that there is no unique major pathway underpinning dark-cutting, which instead can be the result of varying interactions along several pathways,” says Mohammed.

“Importantly, it has also shown us the areas that need more research and investment, so that we can continue to improve knowledge around the dark-cutting condition and support the beef industry in becoming as efficient as it can be.”  


The project team has created the world’s first collection of biomarkers for dark-cutting beef, made up of 130 candidate biomarkers.

What is dark-cutting beef?

Dark-cutting is the term used for meat that doesn’t bloom or brighten when it is cut and exposed to oxygen, leaving it dark in colour. 

While safe to eat, dark-cutting beef can have:

  • a high water holding capacity, causing the meat to lose moisture during cooking and become dry
  • reduced shelf life – the moisture and increased pH level cause bacteria to grow quicker
  • a sticky texture.


We’d like to give special thanks to all the co-authors of this study. 


Mohammed Gagaoua acknowledges the funding support received from the Marie Sklodowska-Curie grant agreement number 713654 under the project number MF20180029.


Mohammed Gagaoua
Marie Skłodowska-Curie Career-FIT Fellow Researcher – Food Quality and Sensory Science Department
Teagasc Food Research Centre, Ashtown, Dublin.

Anne Maria Mullen
Principal Research Officer – Food Quality and Sensory Science Department
Teagasc Food Research Centre, Ashtown, Dublin.

Declan Troy
Assistant Director of Research
Teagasc Food Research Centre, Ashtown, Dublin.

To find out more about this work, you can read the peer reviewed article by the authors at this link.