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From: Food Quality & Safety magazine, August/September 2007

MAP Your Food

New technologies for oxygen monitoring provide noninvasive, real time, passive, in-situ monitoring of the flush chamber/package

by Devinder Saini, PhD

The food industry continuously changes based on consumer demand and economic realities. Most recently, the industry’s focus has been on food safety, quality, and shelf life. One of the responses to these concerns within the food industry has been the increased use of Modified Atmosphere Packaging (MAP).

Exposure of food products to the atmosphere causes oxidation of the product, resulting in decreased shelf live, loss of flavor, and discoloration. MAP reduces the amount of oxygen to which the product is exposed. This is accomplished by flushing the package with nitrogen or CO2 prior to sealing, creating an internal package environment of less than 0.5% oxygen. In order for a MAP package to meet the objective, there must be good packaging materials with oxygen barriers, a good flush of the package before sealing, and a good seal for package integrity.

While the development and evaluation of packages and packaging materials has been going on for centuries, real-time monitoring of MAP processes is now available. One method is through the MAP 1000 System, developed by OxySense, Inc. Earlier the OxySense 4000B system allowed packaging laboratories to monitor oxygen levels inside the package without having to destroy the package to do so. The newer systems also allow the operator to have real-time, noninvasive monitoring, control, and documentation of the flush cycle.

Optical Sensing

Oxygen in packages is typically monitored by extracting a sample of the atmosphere from the package or flush chamber, which is then taken to an instrument that makes the measurement. The sample is extracted automatically using a vacuum system with long hoses/tubes. The drawback to this type of system is that it does not provide real-time information, is intrusive and does not provide documentation of the flush cycle. The vacuum system can easily break down, or the sampling tube can easily be clogged, leading to unreliable data readings and resulting in stoppages of the packaging line.

New technologies provide noninvasive, real time, passive, in-situ monitoring of the flush chamber/packages. With this system, there is no sample extraction, no vacuums or hoses. One such system, the OxySense MAP 1000, has two components—the Master Controller (the box) and the OxySentry Sensor—and no moving parts, meaning limited maintenance. Oxygen is measured directly in the chamber or package using the solid state optical sensor.

Optical sensing allows measurements without disturbing the environment in which they are being made. The act of sensing does not consume the oxygen. This is different from the conventional sensors as they consume the oxygen during measurement and alter the environment in which they are being used.

Based on Fluorescence Quenching of Dye

The optical oxygen sensing method used in one of the new technologies the OxySense MAP 1000 is based on the fluorescence quenching of a dye immobilized in a gas permeable hydrophobic polymer (a patented formulation that can stand high temperatures, oils, and other harsh environments).

The dye absorbs light in the blue region of the spectrum and fluoresces in the red region of the spectrum. The presence of oxygen quenches the fluorescent light from the dye, resulting in a change in the emitted intensity as well as its lifetime as function of oxygen concentration. The change in the lifetime can be calibrated to provide very accurate oxygen measurements. The change in the oxygen concentration can be calibrated resulting in a very accurate oxygen sensor, which is totally passive (does not consume oxygen to make the measurement). The fluorescence decay curves for various oxygen concentrations are shown.

The accuracy of measurements made by this optical sensing method has been compared with measurements made by a gas chromatograph and show a high degree of correlation. These tests were independently conducted and show better than 99% correlation with GC in light and dark conditions.

Simple, Reliable Measurements

The MAP 1000’s instrument box contains all the electronics and is, in effect, the controller. The separate OxySentry sensor can be configured and customized to the individual production lines such as machines with flush chambers, form fill and seal machines.

This instrument’s specifications make it ideal for use by the food, beverage and pharmaceutical industries:

  • Operating Range: 0-30% O2
  • Detection Limits: 0.03% O2
  • Accuracy: 5% of the reading
  • Minimum Response Time: <0.2 seconds
  • Operating Temperature: 32°-140°F (0-60°C)

Taking measurements using MAP 1000 is simple and reliable. The OxySentry attaches to the inside wall of the flush chamber, a fiber-optic bundle is attached to the sensor through the wall of the chamber, and the other end of the bundle is attached to the MAP 1000 instrument, which can be placed in any location.

Once the instrument is activated, measurements are made automatically and displayed on a screen. The instrument is operated via the touch screen, which displays the oxygen concentration and has features including user settable alarm levels, a digital or analogue output signal and local Ethernet connectability.

Additional features include:

  • A totally passive sensor that does not alter the measurement environment;
  • Real-time continuous measurements;
  • Factory calibrated;
  • Fast response;
  • Automatic data logging; and
  • Monitoring of every flush fill cycle.

The real-time measuring capability of this instrument makes it possible, for the first time, to monitor the oxygen concentration on every flush and fill cycle of the packaging machine. That feature coupled with the automatic logging facility allows the user to track the oxygen concentration in every package and improves the efficiency of the packaging process.

Improved Packaging Line Efficiency

The OxySense MAP 1000 system provides an innovative, online oxygen monitoring/control system for use with vacuum/gas flushed MAP systems. Such systems can help improve the packaging line efficiency.

The system is totally passive and can rapidly and accurately provide measurements of oxygen concentration within the fill chamber. It provides real-time measurements of residual oxygen concentration. The near-instantaneous response time (<0.2 second) means quick response and reduced loss from substandard fill atmospheres.

Because the system uses direct and passive measurement (as opposed to a system that draws a gas sample from the chamber prior to measurement), the Map 1000 provides information unobtainable using conventional instruments and allows food manufacturers and packers to improve the quality of their products leading to better customer satisfaction.

Dr. Saini is vice president and chief scientist of OxySense, Inc. Reach him at info@oxysense.com.

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