The influence of controlled atmosphere storage conditions on the microbiological and sensory quality and the physiology of diced, 'ready-to-use' yellow onion was investigated. In the first experiment, diced onion was stored for 14 days at 4 degrees C and high relative humidity under a continuous stream of nitrogen containing (%O-2/%CO2): 20/0, 2/0, 2/5, 2/10 and 2/15. The tissue was sampled for microbiological and sensory analysis on days 0, 4, 9 and 14. In the second experiment, the diced onion was stored for 12 days at 4 degrees C under (%O-2/%CO2): 20/0, 2/0 and 2/10 treatments. Samples were collected on days 0, 4, 8 and 12 for physiological analysis. The following parameters were studied: mesophile and psychrotroph counts, pyruvate content (an index of flavor intensity), color, sensory quality, rate of respiration and sugar (fructose, glucose, sucrose and total sugars) content. CO2 enrichment of the atmosphere delayed diced onion deterioration. Microbial development was delayed, particularly that of che psychrotroph flora. Sensory quality was optimal under the 2% O-2/10% CO2 atmosphere. However, pyruvate and color determination showed no noticeable difference between treatments, although the period of storage significantly influenced these parameters. High CO2 and low O-2 delayed the rise in respiration and the reduction in sucrose content, as compared with the control in air. Levels of reducing and total sugars remained constant throughout storage under all treatments. Browning after cooking developed with increasing length of storage, but was delayed by storage under 10% CO2. Involvement of sugars in this disorder is discussed. This work provides a basis for the development of modified atmosphere packs which will extend the preservation of the product for 2 weeks.
