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Robotic impact

11 June 2010

Recent changes in legislation and consumers exercising choice have reduced the options available to extend the shelflife of pre-sliced, cooked, cured meat products that are ready to eat

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The use of preservatives is being phased out in response to the demands of retailers and consumers. There is also pressure on manufacturers to increase the shelf life of their products to improve availability and reduce waste in the supply chain.

This study will look at the impact of handling techniques on the initial bacterial loadings of ham and cured meats and report on the differences between manually handled products and those handled robotically. The ready to eat meat market is a large one with sales of over £1bn per year in the UK. ( )

Setting the shelflife of fresh foods – The shelflife of fresh foods is set based on knowledge of the safe levels of bacteria that can be consumed by healthy individuals. These safe levels are set cautiously by the industry. Pathogenic organisms such as Salmonella, E.coli 0157 or Clostridium perfringens are required to be totally absent but other types of bacteria can be tolerated up to the prescribed levels. Ready-to-eat meat products are categorised as High Risk food products by the Food Standards Agency and as a result fall into an area of food that is among the tightest regulated.

In a recent survey by the FSA in the UK a proportion of ready to eat meat products were found to be on sale with unsatisfactory levels of bacteria when manufactured and at the end of their shelflife. (

Table 1. Microbiological quality of different sliced ready to eat meats

Sliced meat details

Total No. Samples

n=1484 (%)

No. Samples Unsatisfactory

n = 17 (%)

Samples with all Listeria spp.

n = 99 (%)

Samples with

L. monocytogenes

n = 55 (%)



218 (14.7)

5 (2.3)

20 (9.2)

8 (3.7)


226 (15.2)

1 (0.4)

6 (2.7)

3 (1.3)


949 (63.9)

10 (1.1)

67 (7.1)

40 (4.2)


91 (6.1)

1 (1.1)

6 (6.6)

4 (4.4)

Pre-packed & tested at end of shelf-life (n=684)


88 (12.9)

1 (1.1)

7 (8.0)

4 (4.6)


121 (17.7)

2 (1.6)

3 (2.5)

2 (1.6)


455 (66.5)

7 (1.5)

38 (8.4)

23 (5.1)


20 (2.9)






1216 (81.9)

14 (1.2)

70 (5.8)

47 (3.8)

Pre-packed product (n=1216)

Vacuum packed*

200 (16.5)

6 (3.0)

14 (7.0)

8 (4.0)

Modified atmosphere packed†

820 (67.4)

7 (0.8)

39 (4.8)

27 (3.3)

Normal atmosphere packed

101 (8.3)

1 (1.0)

12 (11.8)

9 (8.9)

Not recorded

95 (7.8)


5 (5.3)

3 (3.2)

Temperature stored/displayed

≤ 5°C

684 (46.1)

12 (1.7)

63 (9.2)

32 (4.6)

> 5 - ≤ 8°C

680 (45.8)

4 (0.6)

25 (3.6)

17 (2.5)

> 8°C (range: 9–20°C)

65 (4.4)

1 (1.5)

8 (12.3)

5 (7.7)

Not recorded

55 (3.7)


3 (5.5)

1 (1.8)

* Vacuum packaging is essentially the evacuation of air from a package that is then hermetically sealed.
† Modified atmosphere packaging is the removal of air and replacement by a strictly controlled gaseous mixture

The table above shows that 1.5% of ham packs and 1.6% of chicken packs were unsatisfactory at the end of shelf life. The technical management at these packing companies would take a cautious approach when setting the shelf life of their products to reduce the risk of these results occurring.

The setting of a shelflife for a product is carried out by the manufacturer who is stating that the food will be safe to eat at that date providing that the correct storage conditions have been applied to the product. In order to consistently meet this requirement those conditions, and initial bacterial loadings, must be strictly controlled during the slicing and packing operations.

Sources of contamination – During the large scale slicing and packing of ready to eat meat products the control of hygiene in the packing area is paramount to keeping the initial bacterial loadings under control. Typically meat is sliced on a high speed automated slicing machine and it is then placed into its pack by operatives working on the production line.

Potential sources of contamination in the slicing and packing operation are controlled by the application of rigorous hygiene to all surfaces that contact the meat product. Slicing blades, conveyors and other equipment is cleaned and sanitised on a regular basis to prevent them becoming a source of contamination. The hygiene in the packing area is actively managed and monitored to ensure that issues do not occur.

One potential source of contamination in the packing area is more difficult to monitor and manage than the hard surfaces - People are potential sources of bacteria and contamination and in a manual packing operation they come into contact with every slice of meat being packed. People carry bacteria on their skin and hair and in their noses and mouths. This bacteria is a potential source of contamination on ready to eat foods and must be controlled if the safety and shelf life of the food is to be protected or extended.

Control of contamination from production operatives – Humans are recognised in the food industry as being a large potential source of bacterial contamination of food products. This is especially the case where the operative manually handles the food product during its processing or packing operations. As you would expect, systems have been devised to minimise the risk of contamination and reduce the initial bacterial loads on the products. The initial bacterial load is a key factor in the shelf life of all fresh foods.

Typical methods used in the ready to eat meat industry to control and manage bacterial contamination from operatives

PPE – Personal Protective Equipment is used to cover as much of the operative as possible to prevent a route for contamination to occur. PPE in a high risk area would typically include – Hairnet, face mask, overall, gloves, arm bands and plastic apron and wellington boots. This PPE has to be provided at a typical cost of £3 to £4 per operator per shift. This includes the purchase cost of disposable items but also the laundry, purchase and cleaning costs for the items that have a longer use.

A hidden cost of the PPE requirement in High Risk areas is often missed but can have a significant impact. The sourcing, storage and control of PPE can be a major cost in large factories. The management of changing areas and locker rooms is significant and adds to the overall impact of the control of potential contamination from human sources.

Hand washing and personal hygiene – The training and control of people is a major area of activity in food businesses. The hand washing and personal hygiene regimes within high risk packing areas are vital to the minimisation of bacterial contamination risk. In a manually packed environment the food contact surfaces include the hands of the operators as well as the conveyors and other equipment. It is the hands that are likely to spread contamination throughout the area if the disciplines are not well managed.
Hands have particular issues when it comes to maintaining them as a hygienic food contact surface.

Hands can be difficult to clean because the surface is soft and contains pores that entrap bacteria. Hand sanitation is also difficult because the chemicals that can be used need to be mild and not attack the skin surface. These issues are helped with the use of gloves to provide a barrier but these too are not easy to keep clean over the period of a shift. The final issue around hands is the temperature.

Typically the surface temperature of a gloved hand in a refrigerated area will be 20 to 22 c and this has an incubation effect on any bacteria on the surface of the glove. In the space of 4 hours the number of bacteria can double leading to potential contamination of all products handled. This risk is often managed by a “glove changing procedure” to prevent the build up of bacterial numbers.

The productivity effect of bacterial controls – All of the bacterial risks mentioned above can be controlled and minimised with good manufacturing practices but this will often have an impact on productivity. Getting dressed in PPE and maintaining good hand hygiene are non value added activities in the packing of ready to eat meat products and as such this activity needs to be minimised.

The management of good hand hygiene in a high risk, ready to eat packing facility is a major drain on resources. Management time is taken in establishing the disciplines and auditing systems are often employed to ensure those disciplines are being maintained. Return to work interviews, health monitoring and random hand swabs of High Risk packing staff are often employed as part of a strategy to reduce the risks involved in handling ready to eat products. Most factories would exclude operators from their High Risk areas if they had a cold or sore throat. People who have been absent from work through sickness are often excluded from food contact to minimise risk while their samples are checked. Some companies have systems where people returning from foreign holidays are required to be checked for pathogenic bacteria before being allowed into the high risk areas of the factory.

The effect of environmental temperature – We have already seen the impact of hand temperature on the potential growth of bacteria to higher numbers. The other aspect of temperature is that of the environment. In hand packed operations the environmental temperature is likely to be around 10 to 12 degrees C. This temperature is used to try and create a working environment that is not so severe that it impacts on the comfort or dexterity of the people handling the product but also offers some degree of protection from bacterial growth on the surfaces.

Product slicing tends to be at a temperature of between -5 and zero degrees. It was noticed during the project that factories using robotic handling could operate at a lower target temperature of 5 to 8 degrees C. This maintains tighter control over the bacterial growth on the food contact surfaces and this leads to lower initial loadings of bacterial during the packing operation.

Fig – Listeria species have optimal growth rates that occur at 30 to 35 c. It can be seen that, even at low temperatures, the growth rate can double with only small changes in temperature. From a microbiological point of view there are great advantages if a product can be processed and packed at low temperature. This can have a significant impact on initial bacterial loads and therefore shelf life.

Seal Integrity – impact on shelf life. Most sliced ready to eat meat products in the UK are packed in either a vacuum or a modified atmosphere to extend the shelf life of the product. The impact of vacuum or modified atmosphere techniques is significant in extending the safe life of products by up to 20 days compared to the same product packed in air. Both Vacuum and MAP systems rely on the seals of the pack being well made to keep out oxygen and as a result restrict bacterial growth and extend shelf life. Recent work on the integrity of heat seals in the food industry has revealed that the biggest cause of heat seal failure is the entrapment of food in the seal or the contamination of the seal area with food prior to sealing. The placement of sliced ready to eat meat products into packages is an opportunity for the seal area to become contaminated.
The unregulated actions of human operators filling packs are an area where contamination can occur. This is especially the case with under trained operators or where manufacturing speeds are being increased to try and improve output and reduce costs. The speed of operation means that errors caused by misjudgements or fatigue can cause the seal on the pack to not be correctly formed and as a result shelf life of that product will be greatly effected.

Conclusions –

The use of robotic methods to handle pre-sliced, ready to eat, meat products presents the user with the opportunity to reduce initial bacterial loadings and as a result it is possible to extend the shelf life of the product. The reduced initial loadings can be achieved by more robust and consistent levels of hygiene on the food contact surfaces, a better control of the high risk environment through the greatly reduced number of people in the area and finally through the opportunity to reduce ambient temperatures to a level that would not otherwise be sustainable.
The use of automated pick and place robots in place of human operators offers the following potential hygienic advantages –
The gripper that forms the food contact surface will be at low temperature and not at body temperature. This will reduce the rate of bacterial growth on the contact surface when compared to hand operations.
The gripper can be designed to present less opportunity for bacterial harborage and growth when compared to a hand or even a gloved hand.
The gripper will be made of materials that can be effectively cleaned and sanitised in a manageable way when compared to the systems required to maintain control over a hand washing régime.

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