527 Dynamic CA Storage of Organic Apple Cultivars
F. Gassera and K. von Arx
Agroscope, Institute for Food Sciences Switzerland
Keywords: Malus domestica, MCP, organic production, DCA, fruit rot, fruit quality Abstract
Two new tools for improved preservation of apple quality have been developed in recent years: the treatment of apples with 1-MCP (trade name SmartFresh™) and the dynamic controlled atmosphere storage (DCA). Because of the nature of the treatment, 1-MCP may not be applied for organically grown apples, whereas DCA may be used for organic fruit. Over three years, selected hot- water treated and non-treated organic apple cultivars (‘Topaz’, ‘Ariane’, ‘Otava’) were stored under DCA-conditions in order to examine whether hot water treatment has an impact on fruit stress during DCA-storage and if DCA-stored fruit retain quality better than ULO-stored fruit during long-term storage. Furthermore, organic fruit were compared to fruit produced under “integrated production”
conditions (IP). The critical oxygen concentration (anaerobic compensation point, ACP) during DCA-storage was not influenced by previous hot-water treatment nor by the production method. However, ACP varied from year to year (e.g., for ‘Topaz’
0.20, 0.18 and 0.56 kPa O2 over 3 years), showing that yearly fluctuations of climatic conditions during production may influence fruit behaviour during storage. For
‘Topaz’ and ‘Otava’, DCA had no positive effect on fruit quality compared to ULO conditions, whereas for ‘Ariane’, DCA stored fruit retained fruit firmness and acidity better compared to fruit stored under ULO conditions. Hot-water treatment did not affect fruit quality and the incidence of physiological disorders of DCA- stored apple. Fruit rot was affected by the cultivar, ‘Topaz’ being the most susceptible cultivar and ‘Ariane’ the most resistant to fruit rot. Organic fruit were susceptible to higher fruit rot during DCA-storage than IP fruit. Compared to ULO conditions, DCA did not reduce fruit rot.
INTRODUCTION
Controlled atmosphere (CA) storage (atmosphere with reduced O2 and elevated CO2 level) has been widely used since the 1990s in Switzerland, in order to better retain quality and extend the marketing period of apples. During the years following the introduction of CA, LO (low oxygen) and ULO (ultra-low oxygen) storage were introduced, with even lower levels of oxygen in storage rooms down to 1.0% for apple storage. Furthermore, two new tools for better preservation of fruit quality have been developed since about 2000, namely the treatment of apples with 1-MCP and the dynamic controlled atmosphere storage (DCA).
The substance 1-methylcyclopropene (1-MCP, trade name SmartFresh™) is an ethylene inhibitor that blocks the ethylene-binding receptors and thus slows down the ripening and the respiration respectively of apples during storage. As a result of the reduction of fruit respiration, fruit quality, in terms of fruit firmness, total solubles and acidity, is retained better than that of non-treated apples. The application of 1-MCP was approved by the EU in 2005. 1-MCP not only maintains fruit quality during storage, but also during the shelf life and the marketing period of the fruit (Xuan and Streif, 2005;
Höhn et al., 2007). The improved quality retention during the marketing period has provided distributors with greater flexibility in the handling of apples.
The concept of dynamic controlled atmosphere storage (DCA) involves the reduction of the oxygen concentration in the storage atmosphere close to the lowest level
a franz.gasser@agroscope.admin.ch
Proc. XIth Int. Controlled and Modified Atmosphere Research Conf.
that can be tolerated by the fruit without inducing excessive anaerobic metabolism, which would affect fruit quality. Fruit respiration and thus quality loss during storage is assumed to be slowed down compared to normal ULO storage. The safe establishment of very low oxygen levels is possible – as one of several methods – by monitoring the chlorophyll fluorescence during oxygen reduction and storage: if oxygen concentrations in storage rooms fall below the critical value, the monitoring will detect the physiological stress of the fruit immediately, allowing the storage room manager to increase the oxygen concentration to a safe level (Gasser et al., 2010).
Because of the nature of treatment, organically grown apples may not be treated with 1-MCP, whereas DCA may be used for organic fruit. The consumption of organically grown apples has steadily increased in Switzerland and thus storage methods for this fruit segment have to be available. The first objective of this study was to test the DCA storage method for selected, organically grown apple cultivars, as an alternative to the application with 1-MCP. Because organically grown apples may not be treated with synthetic fungicides before harvest, there is a tendency for an increased fruit rot during storage. Organic apples are therefore very often hot-water dipped in Switzerland in order to inactivate part of rot microorganismes. The second objective of our study was therefore to examine, if hot water treatement of apples may have an adverse influence on DCA- storage.
MATERIALS AND METHODS
Over three years (2010-2012), selected hot-water treated and non-treated organic apple cultivars (‘Topaz’, ‘Ariane’, ‘Otava’) were stored under DCA-conditions in order to examine whether hot water treatment has an impact on fruit stress during DCA-storage and if DCA-stored fruit retain quality better than ULO-stored fruit during long-term storage. Furthermore, organic fruit were compared to fruit produced under “integrated production” conditions (IP), originating from the same orchard.
Hot Water Treatment
Hot water treatment was applied by dipping one box per DCA-condition (Table 1) with about 12 kg of apples in a hot water bath kept at 52°C during 150 s. Due to the high volume of the water bath, water temperature remained constant during the treatment.
DCA Storage
DCA trials were performed on fruit originating from the same orchard of Agroscope in Wädenswil (Switzerland), grown under organic and integrated production conditions. Fruit were harvested at the commercial harvest date. Trials were carried under various DCA conditions as described in Table 1 in small containers (10-11 kg of apples per container), connected to a flow-through system (Gasser et al., 2003, 2010). ACP (anaerobic compensation point) was controlled by monitoring the respiratory quotient (RQ), calculated based on respiration measurements, as well as by the hourly measurement of the chlorophyll fluorescence (F-α) using the “Harvest Watch” system (Satlantic Inc., Halifax, N.S., Canada). Apples were kept dark-adapted during the storage tests.
Quality Measurements
Fruit quality was determined at the time of harvest and at the end of the storage period and the shelf life respectively by measuring fruit firmness, total soluble solids, titratable acidity and fruit weight with a Pimprenelle instrument (SETOP, Cavaillon, France). Four replicates with 5 fruit each removed from storage containers were analyzed immediately and four replicates with 5 fruit each were stored for a subsequent shelf life period at 20°C for 7 days in normal atmosphere before being analyzed. Statistical analyses were performed using XLStat Pro V2011.204 (Addinsoft, Andernach, Germany). All experiments were performed in replicates as mentioned above and results are displayed as mean ± standard deviation. Significant differences between means were
determined by analysis of variance (ANOVA) using Tukey’s/Duncan’s post hoc tests for pairwise comparisons of means (p<0.05).
For the estimation of the starch index after harvest, 20 fruit were cut in halves across the equator, dipped for 30 s in an iodine solution (10 g potassium iodide + 3 g iodide/L H2O) and air dried at 20°C for 5 min. The color patterns appearing after the iodine treatment were compared to the color reference charts (CTIFL, France). Fruit rot at the end of storage was determined by counting the number of decayed apples in the DCA- containers.
RESULTS AND DISCUSSION
ACP Level as Influenced by Cultivar, Production Method and Hot Water Treatment DCA test containers were first held for one week at ULO conditions as described in Table 1 and were then exposed to oxygen reduction at a low rate of 0.2 kPa per week.
Figure 1 shows a typical example of the time course of RQ and the chlorophyll fluorescence during DCA storage of ‘Topaz’ apples in function of the oxygen level in the storage atmosphere. RQ and Fα both showed the same reaction to the step-wise oxygen reduction, illustrating that the measurement of the chlorophyll fluorescence reflects the respiratory behaviour of fruit. After the ACP was reached, the oxygen concentration was increased by about 0.1 to 0.3 kPa above the critical value in order to allow safe storage until the end of the storage period (7-8 months).
Table 2 shows the ACP level determined for all tested cultivars over 3 years. The critical oxygen concentration (anaerobic compensation point, ACP) during DCA-storage was not influenced by previous hot-water treatment as shows the comparison of organically grown apples with and without hot water treatment. This finding is quite important since most of the organic apples in Switzerland are hot water treated before storage. Production method (organic/IP) had either no effect on the level of ACP. The example of ‘Topaz’ shows that the ACP may vary considerably over the years (0.20, 0.18 and 0.56 kPa over the 3 years), showing that yearly fluctuations of climatic conditions during production may influence fruit behaviour during storage.
In the storage season 2009/2010, apples of the cultivar ‘Topaz’ originating from a later harvest date (1 week after commercial harvest) were also tested under DCA conditions (data not shown). They exhibited exactly the same ACP levels as the first pick listed in Table 2.
Fruit Quality
For ‘Topaz’ and ‘Otava’, DCA had no positive effect on fruit quality retention compared to ULO conditions, whereas for ‘Ariane’, DCA-stored apples retained fruit firmness and acidity better compared to fruit stored under ULO conditions (Fig. 2). In contrast to our results, Lafer (2009) found in his experiments with organic ‘Topaz’ in Austria, that DCA improved quality retention in terms of fruit firmness and titrable acidity compared to CA-stored fruit. In addition, the incidence of physiological disorders was reduced under DCA-conditions. However, quality retention during storage seemed to be quite variable depending on the origin of the fruit.
Another important question is, wheter hot water treatment has a negative impact on fruit quality or even enhances the incidence of physiological disorders. In our experiments over 3 years, no physiological disorders could be detected for DCA-stored
‘Topaz’, ‘Otava’ or ‘Ariane’, and no significant differenc could be shown between treated and not-treated fruit with regard to fruit firmnes and titrable acidity (data not shown).
Fruit Rot during Storage
As shown in Figure 3, fruit rot was affected by the cultivar, ‘Topaz’ being the most susceptible cultivar and ‘Ariane’ the most resistant to fruit rot. This finding corresponds to the experience in practice, where ‘Topaz’ is in general the most susceptible cultivar to fruit rot. Organic fruit exhibited a higher fruit rot during DCA-
storage than IP fruit. A result, which may be well explainded by the fact, that IP fruit are treated before harvest with synthetic fungicides which have a long-term effect on the growth of microorganisms even during storage, whereas organic fruit cannot be treated with such substances. Compared to ULO conditions, DCA did not reduce fruit rot, a result which is in contrast to those of Lafer (2009), who found less fruit rot in DCA-stored
‘Topaz’ apples than in CA control fruit.
In the context of these DCA storage tests, the previous hot-water treatment had no distinct effect on the incidence of fruit rot, with the expection of ‘Topaz’ stored in the storage season 2009/2010. This is suprising, because our experiments showed that fruit rot may effectively be reduced by hot water treatment (Good et al., 2012). Hot-water treatment did not affect fruit quality and the incidence of physiological disorders of all DCA-stored cultivars (no further data shown).
CONCLUSIONS
This study shows that DCA may be used for organic apples, but that the improvement of quality retention during storage depends mainly on the cultivar. Hot water treatment exerted no additive stress effect on the fruit kept under DCA-conditions.
This would allow operators of storage facilities to continue with the routine hot-water treatment of organic apples before storage. With regard to fruit rot, no distinct effect of DCA could be recognized. In Switzerland, Austria and other European countries, the DCA storage is the preferred method for the long-term storage of organic pome fruit.
However, the improvement of quality retention during storage is probably not as consistent as it is for the application of 1-MCP.
Literature Cited
Gasser, F., Dätwyler, D., Schneider, K., Naunheim, W. and Höhn, E. 2003. Effects of decreasing oxygen levels in the storage atmosphere on the respiration of ‘Idared’
apples. Acta Hort. 600:189-192.
Gasser, F., Eppler, T., Naunheim, W., Gabioud, S. and Bozzi Nising, A. 2010. Dynamic CA storage of apples: monitoring of the critical oxygen concentration and adjustment of optimum conditions during oxygen reduction. Acta Hort. 876:39-46.
Good, C., Gasser, F. and Naef, A. 2012. Heisswasserbehandlung von Kernobst.
Schweizer Zeitung für Obst- und Weinbau 24:10-14.
Höhn, E., Baumgartner, D., Crespo, P. and Gasser, F. 2007. Reifesteuerung und Apfellagerung mit 1-Methylcyclopropen (MCP). Agrarforschung 14(5):188-193.
Lafer, G. 2009. Dynamische CA-Lagerung: erste Praxiserfahrungen mit Bio-Topaz in der Steiermark. Besseres Obst 12:18-21.
Xuan, H. and Streif, J. 2005. Effect of 1-MCP on the respiration and ethylene production as well as on the formation of aroma volatiles in ‘Jonagold’ apple during storage. Acta Hort. 682:1203-1210.
Tables
Table 1. DCA storage conditions applied over 3 years (storage temperature 1°C) (O2: initial oxygen level before oxygen reduction).
Production method Hot water treatment
Topaz Otava Ariane
CO2 O2 CO2 O2 CO2 O2
Organic (ULO control) - 1.5 1.0 1.5 1.5 1.0 1.5
Organic (DCA) - 1.5 1.0 1.5 1.5 1.0 1.5
Organic (DCA) + 1.5 1.0 1.5 1.5 1.0 1.5
IP1 (DCA) - 1.5 1.0 1.5 1.5 1.0 1.5
1 Integrated production.
Table 2. Level of ACP (kPa O2) for selected cultivars determined over 3 years (stepwise oxygen reduction of 0.2kPa per week, beginning with the initial oxygen content).
Production method Hot water treatment
Topaz Otava Ariane 09/10 10/11 11/12 11/12 10/11
Organic (ULO control) - - - -
Organic (DCA) - 0.21 0.18 0.56 0.45 0.15
Organic (DCA) + 0.20 0.15 0.56 0.44 0.15
IP1 (DCA) - 0.21 0.15 0.56 0.44 0.15
1 Integrated production.
Figures
Fig. 1. Time course of RQ and F-α during dynamic CA storage of ‘Topaz’ apples (storage season 2011/2012, HT = hot water treatment).
Fig. 2. Comparison of DCA-stored organic apples with and without hot water treatment with organic apples stored under ULO-conditions (control) over 3 years (R = after removal from storage, SL = after shelf life).
Fig. 3. Influence of cultivar, storage method and hot water treatment on fruit rot during storage (7-8 months).
