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Improving the Safety of Pumped Food Products

Contents

1 Why Submit Foods to X-ray Inspection?

2 How Does an X-ray System Catch Contaminants?

3 Factors Affecting the Sensitivity of X-ray Inspection

4 Establishing CCP’s for an X-ray System on a Production Line

4.1 X-ray Inspection at the Beginning of the Production Line

4.2 X-ray Inspection of Processed Food

5 Applying X-ray Inspection to Pumped Food Products

6 Factors to Consider When Installing X-ray Systems

7 Typical Applications

7.1 Meat and Poultry Applications

7.2 Slurries, Semi-solids and Fluids

8 Conclusion

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Food manufacturers are under increasing consumer and legislative pressure to provide safe food. One of the tools that helps to maintain food safety is x-ray inspection.

This white paper looks at the use of x-ray inspection systems to eliminate physical contaminants on pumped food lines. It begins with a short introduction to x-ray inspection and why it’s used in the food-processing industry. It goes on to consider the factors that affect the sensitivity of x-ray inspection, the effectiveness of x-ray inspection at different points on the production line, and the ease with which the technology can be applied to production lines based on pumped product.

After reviewing the factors that production-line managers should take into account when considering installing an x-ray inspection system, the white paper suggests typical applications, and then looks at points to consider when using x-ray inspection for processed meat and poultry lines and for lines involving slurries, semi-solids, and fluids.

Contamination Detection in Pumped Foods

1. Why Submit Foods to X-ray inspection?

X-ray inspection systems keep foods safe by offering unsurpassed detection of physical contaminants. No other technology detects such a wide range of contaminants such as stone, metal, glass, bone, and high-density plastic and rubber, to name just a few.

Incorporating x-ray inspection systems into a company-wide product-safety programme helps manufacturers comply with national and international regulations, such as HACCP (Hazard Analysis Critical Control Points), as well as standards set by retailers.

Typical contaminants

2. How Does an X-ray System Catch Contaminants?

An x-ray system is essentially a scanning device. When a product passes through the x-ray system, the internal sensors capture a grey-scale image of the product. The software within the x-ray system analyses the image and compares it to a predetermined acceptance standard.

On the basis of the comparison, it accepts or rejects the image. In the case of a rejection, the software sends a signal to an automatic reject system/valve which removes the product from the production line.

X-ray image of processed chicken

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Fig 1: X-ray image of a ready meal - lots of varities of greys make it more difficult to detect a contaminant

Fig 2: X-ray image of pumped caramel - it is easier to detect a contaminant in a homogenous product

4. Establishing Critical Control Points for an X-ray System on a Production Line

To be fully effective, x-ray inspection should be part of a company-wide approach to product safety and part of a product inspection programme. Implementing x-ray inspection into such a programme helps food manufacturers to achieve compliance with standards such as HACCP.

HACCP consists of seven steps known as principles.1. Conduct a hazard analysis2. Identify critical control points (CCPs)3. Establish critical limits for each CCP4. Establish CCP monitoring requirements5. Establish corrective actions6. Establish record-keeping procedures7. Establish procedures to verify the system is

working as intended

The second of those principles – identifying the critical control points (CCPs) – helps to choose the best location to apply x-ray inspection on a production line. A CCP is a step or process that’s essential to product safety. It’s the point at which control must be applied to reduce the risk of contamination to acceptable levels.

To find out more about selecting CCPs, please read the white paper “How to select CCPs for x-ray systems” (www.mt.com/xray-whitepapers). White Paper

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3. Factors Affecting the Sensitivity of X-ray Inspection

The ease with which food contaminants can be identified by x-ray inspection depends on various factors such as product density, product thickness, and product homogeneity.

Product DensityProduct density determines the depth of grey in the grey-scale image. The denser the product, the darker the grey.

To be detectable to x-ray inspection, a contaminant has to be denser than the product in which it’s embedded. That means it will absorb more x-rays than the surrounding product, and show up on the grey-scale image as an area that’s darker than its surroundings. In other words, any contaminant with a density similar to, or less than, that of the product in which it’s embedded is incapable of being detected by x-ray inspection.

Product ThicknessAs the product thickness in the path of the x-ray beam increases, so does its overall level of absorption. That makes detection more difficult. A contaminant in a shallow layer of product flowing through a pipe is easier to detect than a contaminant hidden inside a finished sealed pack. In general, the shallower the depth of product, the better the sensitivity of x-ray inspection.

Product HomogeneityThe texture and consistency of a food product has an effect on x-ray sensitivity. A product with components of varying density, such as a ready meal, shows up in a greyscale image as a variety of greys (Fig 1). The more components there are, the wider the range of greys. Analysing the image for contaminants is harder because the software has to pick out the tell-tale dark speck of a contaminant from an image containing numerous shades of grey. The more homogeneous the product, such as liquid caramel, the easier it is to spot contaminants (Fig 2).

Many other factors can affect the sensitivity of an x-ray system. To find out more about the factors limiting the sensitivity of detection, please read “The X-ray Inspection Guide” (www.mt.com/xray-guide).

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4.2 X-ray Inspection of Processed Food

When installed during or after the food processing or before the filling process x-ray inspection of pumped products is ideal as they tend to be homogeneous; their texture and density are much more uniform. And since the product is already flowing through a pipe, it can easily be presented for inspection in shallow depths by narrowing the gauge or altering the cross-section of the pipe.

X-ray systems for pumped products can be used at different stages on a production line depending on the identified CCP, ensuring the best location to detect contaminants in pumped products on the production line.

5. Applying X-ray Inspection to Pumped Food Products

Pumped products typically include meat and poultry as well as slurries, semi-solids and fluids at any stage prior to final packaging.

Connecting x-ray inspection equipment to an existing piped production line isn’t complicated. Standard fittings are used to attach the pipe through which the pumped products passes to the manifold of the x-ray machine. The manifold typically tapers the round production-line pipe to a rectangular-shaped inspection window with an equivalent throughput volume. The rectangular section is where the x-ray beam scans the flowing product. The depth of product at this point is typically between 35mm to 50mm. When the software detects a contaminant, it diverts the product from the pipe via a reject diverter valve.

A typical x-ray pipeline system

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Once the CCPs on a production line are identified, other factors such as practicality and cost-effectiveness need to be taken into account to select the ideal location for an x-ray system. There are occasions where it would be necessary to install more than just one x-ray system on the production line and that’s why there is no single solution that’s right for every production line.

For this white paper we will only focus on the inspection of pumped food products.

4.1 X-ray Inspection at the Beginning of the Production Line

Detection levels are typically better in the early stages of the production process where unprocessed pumped product can be presented in a shallower depth and with a more uniform texture. As the line progresses, the nature of contaminants can change too. Each processing step can introduce new contaminants, or break existing contaminants down into smaller, less detectable pieces.

X-ray inspection of ground meat

At each stage of the production process, the value of the product increases. For that reason food manufacturers find it more cost-effective to reject contaminated product before it’s been processed or sealed in its final packaging.

Catching contaminants early is not just more efficient in terms of reduced product waste and costs, it also helps prevent damage to processing equipment caused by big contaminants, which could in turn introduce more contaminants. Additionally when installed early in the production process it can serve as a check on suppliers’ quality control.

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6. Factors to Consider When Installing X-ray Inspection

Product passing through a pipe performs slightly differently to product travelling on a conveyor. To make the most of x-ray inspection, you need to take the following factors into account:

Air BubblesAir bubbles in a pumped product are tiny voids – zones containing no product. Voids absorb fewer x-rays so they appear as lighter areas on grey-scale x-ray images. The contrast at the edges of these lighter areas can trigger the x-ray software into thinking that it detected a contaminant, causing false rejects. Since air bubbles reduce the depth of grey, they could lighten the colour of any contaminants directly behind or in front. That makes the contaminants harder to detect.

Air bubbles are common in pumped meat and poultry appications but are not difficult to eliminate with the right x-ray system design. A vacuum filler pump, for example, generates a constant, homogeneous flow with minimal air bubbles.

Slurries and other viscous products do not normally contain air bubbles when pumped through a pipe.

Speed VariationsA well-designed x-ray system will automatically adapt to changes in the flow rate of the customer product. It adjusts the scan speed and the associated reject timing in accordance with a speed signal from the production-line pump.

Location on the Production LineAs mentioned previously, x-ray inspection can be applied anywhere on a production line containing pumped products. But the earlier you apply it, the better. The value of rejected product is lower, plus you may be able to recover the product and feed it back into the line after removal of the contaminants.

A very common location is at the start of the production process when product value is low and the risk of contaminants from incoming raw product is at its highest. Using x-ray inspection at this stage also lets you monitor suppliers’ quality control.

7. Typical Applications

A huge range of processed food products pass through pipelines. Typical applications could be:

Meat and Poultry

whole muscle; minced meats for sausages, pies and pasties; pâtés

Bakery jams; syrups, cake mix and fillings

Dairy butter; ice cream; yoghurt; curd

Fruit and Vegetables

purées; mousses; compotes; juices; smoothies; chopped fruit and vegetables

Fish and Seafood

fish spread, processed fish for ready-meals

Confectionery melted chocolate; nougats; toffees

Ready-Meals sauces; soups; pie fillings

We can divide these food products into two broad classes: (1) meat and poultry, and (2) slurries, semi-solids, and fluids. We’ll look at them separately.

7.1 Meat and Poultry Applications

Typical pumped meat and poultry products include ground meat, sausage meat, and poultry trims such as breast fillets and thigh meat. Bone contaminants are by far the most common ones, although lead or steel shot (buck shot), needles, and teeth are also common. Depending on the pumped meat or poultry application, x-ray inspection can detect metal down to 0.8mm, and calcified bone and tooth down to 2mm. The maximum pipe diameter for meat applications is 75mm (3 inches) because narrower pipes make it easier to identify fragments of bone.

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Since chicken bones are less dense than red meat bones, they’re harder to detect. The density of chicken bone tends to be closer to that of the chicken meat in which it lies. On a grey-scale image, the difference between the grey of the meat and the grey of the bone is less marked.

Let’s look at some important points to consider when using x-ray inspection for pumped meat and poultry applications:

• High volume throughput of up to 9 tonnes an hour.

• Contaminants will be removed before adding further value to the product through processing.

• Rejected product could be reworked and reused (depending on the application).

• Reject portion sizes are larger than for a conveyorised x-ray system because the pipeline reject mechanism can’t isolate a single item such as a chicken breast fillet.

• Faster flows increase reject portion sizes – up to 1kg to 1.5kg (2lb to 3lb) of rejected product when running at 9 tonnes an hour through a 76mm (3-inch) pipe.

• High rejection rate due to frequency of bone contaminants in meat and poultry products – an acceptable reject level needs to be defined.

7.2 Slurries, Semi-solids and Fluids

X-ray inspection is especially useful for products that cannot be sieved. These are for example products such as textured fruit purées and yoghurts containing fruit chunks. Sieving removes physical contaminants by catching anything that’s too big to fit through the sieve mesh and is used mainly for liquid applications like milk. X-ray inspection of pumped products is a good alternative for catching physical contaminants where sieving can’t be used.

The contaminants within slurries, semi-solids, and fluids are varied. Depending on the application, x-ray inspection can detect metal down to 0.8mm, glass and stone down to 2mm, and dense plastic down to 4mm. The maximum pipe diameter for these more fluid applications is 100mm (4 inches).

Contaminated slurries, semi-solids, and fluids are typically rejected from the pipe through a diverter ball valve. The ball valve automatically removes contaminated product without creating a back pressure in the system.

The sanitary design of an x-ray system inspecting slurries, semi-solids, and fluids is very important. For more efficient cleaning aseptic x-ray inspection systems are available. An aseptic design incorporates steam-cleaning ports for destruction of pathogenic bacteria growth. For dairy applications, there are x-ray inspection systems that are certified to 3-A Sanitary Standards.

Let’s look at some important points to consider when using x-ray inspection for slurries, semi-solids and fluids:

• High volume throughput of up to 18 tonnes an hour – larger than for meat and poultry because pipeline diameters are typically greater and fluids can travel faster through pipes.

• Contaminants will be removed before adding further value to the product through processing.

• Rejected product can be reworked and reused (depending on the application).

• Faster flows increase reject portion sizes – up to 5kg or more of product when running at 18 tonnes an hour through a 100mm (4-inch) pipe.

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8. Conclusion

For many years, x-ray inspection has proven its effectiveness at eliminating contaminants from processed and packaged food products. The effectiveness of x-ray inspection systems depends on the product density, thickness and homogeneity of the inspected product.

Since pumped products tend to be more homogeneous, it’s easy to adjust their depth by altering the size or shape of the pipe through which they flow. That makes pumped products an ideal application for x-ray inspection, offering food manufacturers excellent levels of contaminant detection.

Pumped products on a food processing line tend to occur early in the production process before a manufacturer has added further value to the product through processing and packaging. Since product value is lower at this point, this location is very common for x-ray inspection system for removing contaminants.

Early removal of contaminants has two other advantages: it protects valuable processing equipment from damage further downstream, and it serves as a check on suppliers’ quality control.

Installing x-ray inspection equipment on a pumped production line is a simple process. A pressure vacuum pump will eliminate air bubbles especially in meat and poultry applications. A well-designed x-ray inspection system can also automatically change the scanning speed and the reject timings to match the customer’s flow rate.

X-ray inspection is a versatile technology that’s suitable for the inspection of a wide range of pumped food products on CCPs on a food processing line. It helps maintain product safety and brand reputations, and can protect valuable equipment from damage.

For more information

Mettler Toledo Ltd64 Boston RoadBeaumont LeysLE4 1AWLeicesterTel. 0870 066 3150Fax. 0116 236 6399Email: pi.mtuk@mt.com

Subject to technical changes©03/2011 Mettler-Toledo Safeline X-ray Ltd.Printed in the UK

www.mt.com/safeline-xray

Further Information about X-ray Inspection FREE Technical GuideMake an informed decision

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