X-ray technology for routine analysis of fat in meat

X-ray analysis is well known from medical applications and security scanners at the airport, but perhaps not so well known in food production.

The short wavelength of X-rays allows them to penetrate all sorts of materials. Some of the X-rays get absorbed and the rate of absorption depends on the density of the material encountered. For instance, the femur in your leg shows up because it absorbs more X-rays than the surrounding flesh and, likewise, those nail scissors that you forgot to take out of your hand baggage absorb at lot rays and will show up strongly against other items.

The X-ray advantage
X-ray is just one of three main options for testing fat content in meat.

The classical reference analysis is the Soxhlet method. A sample of meat is weighed, the fat is extracted from the sample and weighed, and the fat is calculated by dividing the weight of the fat by the weight of the sample. 

Another option is NIR.  As discussed on our NIR technology page, Near Infrared is a much faster and more convenient alternative to the reference method. A sample is simply plucked from a production line and tested in a matter of minutes. 

X-ray is even faster, but the big difference compared to NIR is in the way it can measure entire batches of meat as they pass through the instrument on a conveyor belt, just like your bag at the security check.

This gives a complete and continuous measurement of entire batches of meat which is particularly useful given the inhomogeneous nature of meat. For example, a batch of meat trimmings will consist of some cuts that have a lot of fat and others that are leaner. Measuring everything gives an accurate assessment of the total fat content allowing effective sorting and segregation leading to better quality and improved profitability in subsequent processing.  

DEXA X-ray and how it works 
When it comes to measuring fat in meat, a form of the technology called dual energy X-ray Absorptiometry (DEXA) is particularly useful.

The simple version is that meat is passed through the analyser on a conveyor belt, exposed to X-ray rays and its absorption of those X-rays is detected and measured.  The result is displayed on a screen. The data can also be fed to a factory control system, for example, when building bins of trimmings with an automatic tray-sorting system.  More on this in the video here. 

The main elements of a DEXA X-ray system are an X-ray generator, a sensor and conversion unit which converts the X-ray energy to light and image processing technology to calculate the result.

DEXA X-ray works by measuring the absorbency of two x-ray energy spectra.

• An X-ray generator projects two specific X-ray energies (a high energy and a low energy) through the meat passing through the analyser on a conveyor belt. 

• The X-rays that pass through the meat are detected by a detector, consisting of a scintillator, converting x-rays to visible light, and a line of light sensitive diodes, converting light into an electrical current.

• The electrical current is digitized and fed to a computer. 

• Image processing algorithms use the data to map the relative ratio of energy absorbed at different points in the product.

• This data map is used to determine the average fat content of the scanned material.

Grading of cuts
With x-ray technology it is possible objectively to grade whole cuts such as pork bellies and pork hams into uniform categories, which is not achievable via the traditional visual inspection. The grading is based on fat measurement and can be combined with image recognition. 

The benefits of this technology apply for manufacturers of bacon, producers of dry ham products and other manufacturers of finished meat products based on whole meat cuts. Suppliers of raw meat cuts can also ensure that deliveries are to specification (size, length, width, thickness), fat-content and without foreign objects.

Is X-ray harmful to food or for the operators using analysis equipment? 
Exposing food to X-rays and placing X-ray equipment on the production floor in a meat plant naturally raises questions about the harmful nature of X-ray. 

Irradiated food does not become radioactive and the minimum level of radiation used when radiating food to kill bacteria, is more than a hundred thousand times higher than the level used in meat plant X-ray equipment. The meat products do not require special labelling after analysis.

The radiation level of X-ray inspection equipment used in meat plants is comparable to low level medical procedures used on humans. There are very strict rules for the design, construction, installation and test of X-ray apparatus, enforced by the local authorities. X-ray machines in meat plants, provided they are operated according to instructions, are safe to operate and are safe for the operators working in the vicinity of the machine. In this respect, the instruments used in meat plants can be compared with the baggage scanners known from every airport around the world.