Controlled atmosphere and refrigerated storage in cut roses ‘ Avalanche ’

In Brazil, there are few studies on cut flowers cold storage, and there is no research on the association of controlled atmosphere with flower cooling. Worldwide research in this sector is considered scarce; this requires the establishment of adequate postharvest technology, involving cold storage and controlled/modified atmosphere for cutting flowers. In Brazil, roses are the most widely cultivated cut flower and a single producer exports three pallets of this species by airfreight per week. The objectives of this work were to define the concentrations of O2 and CO2 in which cut roses ‘Avalanche’ should be submitted, defining procedures for postharvest conservation and establishing technical guidelines for the exportation of cut roses under controlled atmosphere. The experiments were carried out at 1±1 °C with the help of a flowchart to dose the gases, and the concentration of O2, CO2 and ethylene were assessed. Phase 1 experiment had O2 concentration set at 21% associated with four different concentrations of CO2, 10, 20, 30 and 40%. Phase 2 experiment had O2 at 3% associated with four different concentrations of CO2, 3, 6, 10 and 15%. The controlled atmosphere with 3% O2 and 6% CO2 associated with 1+1 °C was indicated for the storage of cut rose ‘Avalanche’.


INTRODUCTION
Brazil has prospects for being a producer and exporter of flowers and ornamental plants.The floriculture has been shown to be important in the economy and have a turnover of ca.R$ 6.5 billion per year (JUNQUEIRA and PETTZ, 2017).However, significant part of the plant production investment can be simply lost if the proper attention to stages of harvest, handling and storage of the product is not correctly dispensed.
The maintenance of postharvest quality of cut flowers is highly important in order to guarantee the producer the expected income, thus sustain the in-place production chain.The postharvest losses can reach out 50% of the total yield.Thus, investing in postharvest handling can generate a more economically and environmentally viable return than to expand the production (DIAS-TAGLIACOZZO and MOSCA, 2007).
Among the several factors, that impact on cut flower quality after harvest, adequate storage and transport at low temperature is undoubtedly the most prominent one.Storage is responsible for maintaining the balance between the distributor and the consumer market and its goal is to maintain quality for commercialization.Cold storage is a way to delay senescence and consequently extend the product life span, since respiration and transpiration rates, as well as infections, are reduced (DIAS, 2016).The use of controlled atmosphere is complementary to refrigeration, thus capable of increasing the efficiency of refrigerated storage (AKBUDAK and ERIS, 2005).
Controlled atmosphere can significantly affect postharvest quality and marketability of cut flowers.The increase in CO 2 concentration can be beneficial for product quality maintenance, being a reduction in the respiration rate the mostly observed effect (BURANA et al., 2013).An atmosphere of low O 2 concentration can also reduce the respiration rate as well and maintain the flower quality (CEFOLA at al., 2016).
To the best of our knowledge, there are no studies relying on cold storage associated with controlled atmosphere (CA) for cut flowers in Brazil.Therefore, the establishment of appropriate postharvest storage technology under refrigeration and CA for cut flowers is important to the local flower industry.
The work aim was to define the ideal gas mixture ratio for cut roses 'Avalanche' under CA and cold storage, to generate exportation guidelines for CA use and to reach the end consumer with quality.

MATERIAL AND METHODS
Rose stems 'Avalanche' were harvested in the late afternoon and transported the following morning to the Postharvest Laboratory.The stems were divided into 20 random batches and placed in 32L acrylic vessels, each vessel contained twelve stems.The vessel lid had 2 holes, one for the controlled air mixture entry and another to the exit, allowing the gas concentration adjustments.The gas mixtures were generated with the help of a portable flowboard made according to Calbo (1989).
Phase 1 experiment had stems stored at 21% O 2 associated with 4 different concentrations of CO 2 , i.e. 10, 20, 30, 40%, the difference to 100% was supplemented with nitrogen.Both control and flowboards were kept in chambers at 1 ± 1 o C for 7, 14, 21 days.After each storage period, the batch of each treatment was withdrawn and transferred to 25 o C and 70% RH for quality evaluations according to Dias et al. (2016), which included flower quality assessment, botrytis occurrence and foliage quality.
Phase 2 experiment had stems were stored at 3% O 2 and this time, 4 different concentrations of CO 2 were used, i.e. 3, 6 and 10, and 15%.Supplemented nitrogen was used to complete 100% and the experiment was for 7, 14 and 21 days followed by CA conditions removal and quality assessment as previously mentioned.
The control samples in both experiments were subjected to atmospheric air after passing through solutions of 10% CaCl 2 and 5% KMnO 4 , to remove CO 2 and C 2 H 4 .Chromatographic analyzes were performed to certify the desired gas concentrations was enforced.The experimental design was completely randomized with 4 treatment replicates containing 12 stems.
The assessment was made by taking 1 mL samples from the vessel and injected into a Varian 3400® Gas Chromatograph, equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD) for the analysis of O 2 , CO 2 , N 2 and C 2 H 4 present in the sample.Column, injector, FID and TCD temperatures were respectively 80, 120, 250 and 200 o C, and the gas flows were 20 mL min -1 for the helium used as entrainment gas, 30 mL min -1 for hydrogen, 300 mL min -1 for synthetic air and 20 mL min -1 for TCD reference gas.The results of the metabolic activity of the roses were obtained in area and converted into mg CO 2 kg -1 h -1 and μL C 2 H 4 kg -1 h -1 .
The data was subjected to one way ANOVA and the means compared by the tukey test at 0.05 significance level with the help of SISVAR software (FERREIRA, 2011).

Phase 1
The concentrations of 10, 20, 30 and 40% of CO 2 associated to 21% O 2 were not effective regardless of storage time.The weight loss was approximately 35% and no significant differences were observed between treatments.All treatments presented flower quality similar to those shown in Figure 1.The flower quality curves (Figure 1A) and the incidence of Botrytis cinerea curves (Figure 1B) were close to or below the control.The foliage quality did not exhibited significant differences between treatments and high CO 2 concentrations showed a deleterious effect on the leaves (Figure 1C).

Phase2
Considering that when using a CA with 21% O 2 associated with 10% and 20% of CO 2 (phase 1) presented similar quality outcome to the control, and a detrimental effect of the 30% and 40% CO 2 concentrations, the concentration of O 2 was reduced to 3% and associated with the lower concentrations of CO 2 , i.e. 3, 6, 10 and 15%.
The results presented in figures 4 to 12 indicate that the best treatment was a CA containing 3% O 2 and 6% CO 2 .The fresh weight loss, at this phase, was also around 35% and did not show differences between treatments.
After one week of CA storage (Figure 2 ), the effects of this treatment differs little from the others, including the control, and did not show significant differences between treatments.after being kept for 1 week under controlled atmosphere with 21% O 2 and 3, 6, 10 and 15% CO 2 .Statistical analysis showed no significant differences (p≤0.05) between the treatments.
However, after 2 weeks (Figure 3) and mainly 3 weeks (Figure 4), there was a positive effect of the CA containing 3% O 2 and 6% CO 2 on the overall assessed quality when compared to the control.This CA concentration was associates to higher flower quality, longer green foliage and minor Botrytis cinerea incidence, indicating that this is an adequate condition for cut rose storage.

Figure1.
Figure1.Flower quality (A), Botrytis cinerea incidence (B) and foliage quality (C) of cut rose 'Avalanche' after being kept for 1 week under controlled atmosphere with 21% O 2 and 10, 20, 30 and 40% CO 2 .* (C) The 10% curve coincides with the values of 20% one and the 30% curve coincides with the values of 40% one.

Figure 2 .
Figure 2. Flower quality (A), Botrytis cinerea incidence (B) and foliage quality (C) of cut rose 'Avalanche'after being kept for 1 week under controlled atmosphere with 21% O 2 and 3, 6, 10 and 15% CO 2 .Statistical analysis showed no significant differences (p≤0.05) between the treatments.

Figure 3 .
Figure 3. Flower quality (A), Botrytis cinerea incidence (B) and foliage quality (C) of cut rose 'Avalanche' after being kept for 2 weeks under controlled atmosphere with 21% O 2 and 3, 6, 10 and 15% CO 2 .(C) Control and 10% CO 2 treatment lines overlap the graph.Different letters indicate significant differences (p≤0.05) between the treatments.