Effects of elevated concentrations of CO2 in modified atmosphere packaging on the quality of prickly pear cactus stems (Opuntia spp.)

We have tested the effects of passive and semi-active modified atmosphere packaging (MAP) on the postharvest life and quality of flattened stems or cladodes of the prickly pear cactus (Opuntia spp.), called "nopal or nopalitos" in Mexico stored at 5 degreesC. In semi-active MAP, we injected elevated partial pressures Of CO2 (20, 40 or 80 kPa) in the packages immediately after sealing. Passive MAP (where no CO2 was added) had an atmosphere of up to 8.9 kPa O-2 and 7 kPa CO2 after 35 days of storage at 5 degreesC. Semi-active atmospheres with initial CO2 pressures of 40 or 80 kPa increased the losses in texture, weight, chlorophyll content, dietary fiber content and color. Passive MAP and semiactive MAP with 20 kPa CO2 significantly decreased the losses in the above-mentioned parameters, and also decreased the microbial counts (total aerobic mesophiles (AeM), mold and yeasts), but slightly increased the total anaerobic mesophiles (AnM) counts. The microorganisms identified were Pseudomonas, Leuconostoc, Micrococcus, Bacillus, Ruminicoccus, Absidia, Cladosporium, Penicillium and Pichia. Therefore, fresh prickly pear cactus stems can be stored for up to 32 days in MAP with < 20 kPa CO2 without significant losses in quality nor any significant increase in microbial counts. (C) 2003 Elsevier B.V. All rights reserved.