Packaging and Produce Degradation 131
were lower under 0% O 2 than under 21% O 2 , regardless of the CO 2 concentration,
contrary to a 1.5% O 2 atmosphere, which gave results similar to those with 21% O 2.
In another study Bennik et al. [82] found that 1.5 or 21% O 2 at 8°C did not
significantly affect maximum specific growth rate or maximum population densities
of the food-borne pathogens Aeromonas hydrophila, Yersinia enterocolitica, Listeria
monocytogenes, and Bacillus cereus. Abdul-Raouf et al. [83] have reported that an
atmosphere of 3% O 2 and 97% N 2 had no apparent effect on populations of E. coli
O157:H7 inoculated onto shredded lettuce, sliced cucumbers, and shredded carrots.
Oxygen depletion does not prevent yeast growth, except in the case of strict anaer-
obiosis, which is not to be used with plant tissues [84].
As demonstrated by Vial [85], lowering O 2 from 10 to 1.5% does not significantly
reduce the total yeast and bacteria count on slices of kiwi fruit stored at 10°C for
10 d [85]. However, a strict anaerobiosis will trigger anaerobic catabolism of plant
tissue and, if the pH is neutral or slightly alkaline, can lead to Clostridium botulinum
growth [86]. But accumulation of C. botulinum toxin in the absence of visual decay
has not been reported even on mushrooms [87] and tomatoes [88]. The results of
recent studies have shown that O 2 can be used as a “hurdle” in MAP, when it is
used at concentrations above 21%. Day [89] and Barry-Ryan et al. [90] found that
high O 2 could extend the shelf life of fresh fruits and vegetables, but Kader and
Ben-Yehosua [91] failed to show such an enhancement of storability. Creation of
oxidative stress by high oxygen concentrations induces the generation of intracellular
reactive oxygen species that affect vital cell components and reduce cell viability
[92]. However, the effectiveness of these atmospheres is highly related to the anti-
oxidant capacity of the microorganisms to challenge the stress conditions, which
can even be different among the strains of the same species [93]. The study carried
out by Amanatidou et al. [92] shows that high oxygen concentrations (80% or 90%,
balanced with N 2 ) have no inhibitory effect on the in vitro growth rate of some
selected pure cultures of bacteria and yeasts (Lactococcus lactis, Leuconostoc
mesenteroides, Lactobacillus plantarum, Aureobacterium strain 27, Pseudomonas
fluorescens, Enterobacter agglomerans, Listeria monocytogenes, Salmonella enter-
itidis, Escherichia coli, and Candida sake) except Salmonella typhimurium and
Candida guilliermondii, whose growth rate and/or maximum yield were reduced
significantly under these atmospheres. Gonzalez-Roncero and Day [94] reported
similar effects of 99% O 2 on Pseudomonas fragi, Aeromonas hydropylia, Yersinia
enterocolitica, and Listeria monocytogenes. However, Jacxsens et al. [95] observed
retarded in vitro growth rates of Pseudomonas fluorescens, Candida lambica, Bot-
rytis cinerea, Aspergillus flavus, and Aeromonas caviae (HG4) under 70, 80, and
95% O 2 at 4°C, whereas Erwinia carotovora was stimulated under increasing O 2
concentrations. Wszelaki and Mitcham [96] found a 100% O 2 atmosphere to be the
most effective in reducing the mycelia growth of Botrytis cinerea at 5°C. However,
the same oxygen concentration was reported to have a stimulatory effect on Peni-
cillium decay on grapefruit [91]. When combined with high CO 2 concentrations,
hyperoxygenation becomes more effective in reducing the growth of most of the
microorganisms that were counted above [91,92,94,96,97].
Many researchers have reported a bacteriostatic effect of elevated carbon dioxide
atmospheres. Carbon dioxide (20 kPa) was reported to be effective in reducing the