Spinach stored under a range of CO2-containing
atmospheres was reported to show important increases in ammonia concentrations (Cantwell et al., 2010). However, in our study,
ammonia was not the only compound associated with the development of off-odours as those leaves stored in MAP without CO2 also
developed off-odours despite the low ammonia content. Increases
in ammonia have been associated with senescence symptoms
when spinach was stored in air or in CA with elevated CO2 levels
(Martínez-Damian and Cantwell, 1999). In our study, we observed
that ammonia accumulation was not the only cause of leaf senescence as baby spinach with the lowest content of ammonia showed
the highest tissue damage and leaf senescence. Ammonia can be
toxic to plant cells (Toivonen, 1997), although in our study, baby
spinach exposed to moderate O2 with CO2 showed clearer symptoms of cell damage, in agreement with the accumulation of toxic
molecules such as free radicals causing the early phase of senescence (Wagstaff et al., 2007). The senescence effect in baby spinach
could be attributed more to oxidative metabolism as differences
between MAPs were related to O2 levels.