Making sense of oxygen migration using sensors

Packaging Professional magazine
10 Sep 2012
processed cheese in plastic packaging

A discreet oxygen sensor that can be incorporated within a pack at the
point of filling or sealing, to monitor oxygen throughout storage, may
offer a longer shelf-life for cheese.

Oxygen is detrimental to the quality of many commercially available cheeses, so it is important to control oxygen levels in MAP or vacuum packs. 

The presence of oxygen around oxygen-sensitive products, such as cheddar cheese, can result in aerobic microbiological spoilage. It can also promote rancidity through interaction with polyunsaturated fats, thereby affecting palatability, and causing discolouration. ‘In theory, the lower the oxygen content the higher the quality and the longer the life’, explains researcher Joseph Kerry of University College Cork, Ireland. 

To resolve this, the team placed an oxygen sensor onto laminate films prior to forming, filling and sealing, and followed oxygen levels within individual cheese packs. The vacuum-packed cheddar cheeses were monitored for typical oxygen levels at 4°C with optical sensors pre-fitted to PP and PET packaging laminates. The oxygen levels present in packs immediately after packaging were 3% on average. Further ingress of oxygen into all packs occurred over storage time, with levels ranging from 3.6% to 8.2% after six days. 

‘In properly packaged cheddar cheese that has been vacuum packaged, you would expect to have oxygen levels below 0.5%. The desire is to have even lower levels present. Therefore, the oxygen levels we found show the dramatic effect of oxygen ingress within packs once package containment has been lost.’ Using the information obtained from the oxygen sensors, the team detected leakage problems in specific areas of the cheese packs. ‘Examination of these package areas by microscopy revealed that pin-holing was occurring in the laminate films as the cheese packs were being formed. Modifications to the manufacturing line were implemented and further analysis using oxygen sensors demonstrated that no further pin-holing occurred, resulting in optimisation of cheese quality,’ adds Kerry. 

He notes that the oxygen sensor can monitor both increases and decreases in oxygen levels, and can be used in numerous food applications, from processed meats to fresh fruit and vegetable products. The technology will come particularly useful in instances where cheese packs possess poor seals, are gas-flushed incorrectly or lose containment over time due to using materials that have inadequate barrier properties, or are physically damaged during forming, allowing oxygen to migrate. ‘Oxygen sensors are relatively new to the packaging market and consequently have received little attention as of yet, but new systems are becoming available. We have been using this technology for the past 10 years in Ireland within various facets of the Irish food and beverage industry,’ says Kerry. 

Currently, the sensors operate over wide pH and temperature ranges and are capable of reading oxygen levels at 0.1–100%. Kerry said that to date, there is no food manufacturing process or product that interferes with the optimal functioning of the oxygen sensors. 

The next phase of research will investigate the use of new sensing materials that can be used to enhance signalling, reduce cost and assist in disguising the sensor’s presence within packs. 

However, even with promising lab results, Kerry adds that regulations can stifle smart packaging technology getting to market. ‘In order for smart packaging technologies to be taken up industrially and embraced by retailers, EU bodies responsible for curtailing the development of innovative forms of packaging need to comprehend that, while we continue to constrain smart packaging development in Europe, the rest of the world leads the way. We need to encourage adoption and application. The movement of food and beverage products over longer distances is increasing food prices and the ever-growing demand for higher quality, more convenient and longer shelf-life food products, which justifies the use of such technologies.’