2. Material and methods
2.1. Localization, plant material and treatments application
The experiments were carried out over two years in the
postharvest research center of the Federal University of Santa
Maria, Brazil. In the first year (2012) the plant material composed
of ‘Royal Gala’ apples and in the second year (2013) ‘Galaxy’ apples
were used as the plant material. In the two years, fruits were harvested
in a commercial orchard, located in Vacaria, RS, Brazil. Right
after harvest, fruits were transported to the postharvest research
center and experimental samples were performed, with 25 fruits
each. The treatments tested in the first year were: (1) controlled
atmosphere storage (CA) with 1.2 kPa O2 + 2.0 kPa CO2; (2)
dynamic controlled atmosphere by chlorophyll fluorescence +
1.2 kPa CO2 (DCA-CF) and (3) ultralow oxygen storage with
0.4 kPa O2 + 1.2 kPa CO2 (ULO). On the second year, we tested a
fourth treatment composed by initial low oxygen stress (ILOs) +
ULO, in addition to those previously mentioned. The ILOs were
applied during one day (0.05 kPa of O2). Each treatment was composed
of four replicates, of 25 fruits each. Fruits were maintained at
temperature of 1.0 C during the storage period. The relative
humidity was 94 ± 1%.
2.2. Controlled atmosphere setup and maintenance
In order to obtain the desired atmospheric condition the CA
chambers (180 l) were flushed with nitrogen until they reached
the pre-established oxygen level. This procedure was carried out,
aiming to reduce fruit metabolism as fast as possible. The carbon
dioxide level was obtained by accumulation in the storage chamber
due to fruit respiration.
During the storage time, the oxygen and carbon dioxide levels
were determined and corrected daily with the aid of an automatic
CA control system. The equipment compared the oxygen and carbon
dioxide levels to a set point. If the oxygen level was lower than
the set point, O2 was injected up to the desired concentration. The
same was used for carbon dioxide correction. Generally the CO2
level was above the desired concentration and the excess was
automatically absorbed with a lime scrubber. In the DCA-CF the
oxygen partial pressure was monitored and corrected according
to the methodology proposed by Prange et al. (2007) and maintained
between 0.35 and 0.45 kPa.
2.3. Fruit quality evaluation
After nine months of storage plus seven days of shelf life, fruits
were submitted to quality analysis. The quality analysis were
performed in four replications of 25 fruits each. The following
physical, chemical and biochemical analysis were carried out