Nondestructive and Continuous Monitoring of Oxygen Levels in Modified Atmosphere Packaged Ready-to-Eat Mixed Salad Products Using Optical Oxygen Sensors, and Its Effects on Sensory and Microbiological Counts during Storage


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The objective of this study was to determine the percentage oxygen consumption of fresh, respiring ready-to-eat (RTE) mixed leaf salad products (Iceberg salad leaf, Caesar salad leaf, and Italian salad leaf). These were held under different modified atmosphere packaging (MAP) conditions (5% O2, 5% CO2, 90% N2 (MAPC—commercial control), 21% O2, 5% CO2, 74% N2 (MAP 1), 45% O2, 5% CO2, 50% N2 (MAP 2), and 60% O2, 5% CO2, 35% N2 (MAP 3)) and 4 °C for up to 10 d. The quality and shelf-life stability of all packaged salad products were evaluated using sensory, physiochemical, and microbial assessment. Oxygen levels in all MAP packs were measured on each day of analysis using optical oxygen sensors allowing for nondestructive assessment of packs. Analysis showed that with the exception of control packs, oxygen levels for all MAP treatments decreased by approximately 10% after 7 d of storage. Oxygen levels in control packs were depleted after 7 d of storage. This appears to have had no detrimental effect on either the sensory quality or shelf-life stability of any of the salad products investigated. Additionally, the presence of higher levels of oxygen in modified atmosphere packs did not significantly improve product quality or shelf-life stability; however, these additional levels of oxygen were freely available to fresh respiring produce if required. This study shows that the application of optical sensors in MAP packs was successful in nondestructively monitoring oxygen level, or changes in oxygen level, during refrigerated storage of RTE salad products.

Practical Application

The use of a nondestructive form of oxygen determination in food packaging is described using optical oxygen sensors. Information obtained by this method can give valuable data on the level of oxygen in atmospheres generated in packaging applications and its effect on quality, sensory, and shelf life in ready-to-eat salad products. This method will have benefit for use in quality control and postpackaging assessment.