Effect of cold storage and ozone treatment on physicochemical parameters, soluble sugars and organic acids in Actinidia deliciosa
Introduction
The kiwi fruit was introduced to the world market from New Zealand in 1950s. The export of fresh fruit led to rapid expansion and in 2006 kiwi fruit production in France was estimated at over 78,000 tons, representing 7% of worldwide production (FAO, 2005). In Corsica, kiwi fruit production is a dynamic agricultural activity and represents 10% of the French total (Eurostat, 2006). Kiwi fruit represent a source of antioxidant substances, which may intervene in the prevention of pathologies. Due to its composition, sensory characteristics and stability during preservation, the kiwi fruit has great potential for industrial exploitation (Cano Pilar, 1991, Soufleros et al., 2001).
The storage of fruit is very important for its quality, in particular its organoleptic flavour properties. The storage period for the fresh kiwi fruit market is about 4–6 months (Antunes and Sfakiotakis, 2002, Crisosto and Kader, 1999). During this storage period, rotting causes serious economic losses. Botrytis cinerea has been identified as the major fungal pathogen, causing soft rot decay during post-harvest storage (Lee, Lee, Park, Hur, & Koh, 2001). Different storage methods are used for the conservation of fruits and vegetables: air storage, controlled freezing-point storage at 0 °C, modified atmosphere packaging storage, controlled atmosphere storage (Antunes and Sfakiotakis, 2002, Das et al., 2006), and ozone-enriched atmosphere storage (Tzotzakis, Borland, Singleton, & Barnes, 2007). Ozone can be a good alternative sanitizer for fresh fruits and vegetables (Han, Floros, Linton, Nielsen, & Nelson, 2002; Yousef, Kim, & Dave, 1999). It destroys micro-organisms by progressive oxidation of vital cellular components (Das et al., 2006).
Different storage methods have various effects on the quality of fruit. For example, Brix and reducing sugar increase during storage at 0 °C, while the firmness of the Hayward variety decreases (Manolopoulou & Papadopoulou, 1998). Brix is considered to be an important factor in terms of quality at the eating stage (Lallu et al., 1989, Tavarini et al., 2008). Flesh firmness is reduced after cold storage and soluble solid contents increase significantly over 6 months at 0 °C (Tavarini et al., 2008).
Kiwi fruit flavour can be affected by a number of components, including sugars and organic acids. The flavour depends essentially on the balance between sugars and non-volatile organic acids. The most important kiwi fruit sugars are glucose, fructose and sucrose (Soufleros et al., 2001). Glucose and fructose concentrations increase gradually from the earliest stage of fruit development until harvesting. Organic acids are one of the important factors influencing fruit flavour (Chen, Liu, & Chen, 2009) and they accumulate at the early stages of fruit development (Zhao, Li, Jiang, Wang, & Yang, 2007). The most important organic acids contained in the kiwi fruit are citric, quinic and malic (Nishiyama, Fukuda, Shimohashi, & Oota, 2008).
In recent years, there has been increasing interest in the production of kiwi fruit due to its vitamin C content and high antioxidant capacity (Cassano et al., 2006, Tavarini et al., 2008). The kiwi fruit is beneficial for certain health conditions (Cano Pilar, 1991, Carvalho and Lima, 2002, Tavarini et al., 2008). Kiwi fruit contains more ascorbic acid than citrus fruits (Nishiyama et al., 2004, Soufleros et al., 2001). Some authors (Adorisio et al., 1990, Das et al., 2006, Lombardi-Boccia et al., 1986, Manolopoulou and Papadopoulou, 1998, Selman, 1983) have recorded significant reductions in vitamin C concentrations during cold storage. In particular, the vitamin C concentration of the Hayward variety changed from 200 to 37 mg/100 g fresh weight after 6 months of cold storage (Tavarini et al., 2008). No study has been carried out to investigate kiwi fruit quality as a result of ozone treatment storage. The objective of this work is to compare kiwi fruit quality as a result of two storage methods – air storage at 0 °C and ozone treatment – over a period of 7 months, in order to define the best storage method. We studied various parameters: physicochemical parameters (weight, firmness, pH, total acidity, reducing sugar, Brix), B. cinerea contamination, organic acids, soluble sugars and vitamin C.
Section snippets
Plant material
Kiwi fruits (Actinidia deliciosa var. Hayward) were randomly collected on a plantation at Fiumorbu in Corsica (France). One hundred and fifty kiwi fruits were harvested on November 1st 2006. After sampling, the kiwi fruits were placed in an icebox and kept cool during transportation to the laboratory. At the laboratory, half the fruit was placed in a chamber at 0 °C and the other half in an ozone treatment storage chamber. Different analyses were performed over seven consecutive months, at 0, 7,
Evolution of physicochemical parameters during storage (cool storage and ozone treatment)
During storage, the kiwi fruits underwent compositional changes. Fig. 1 presents the evolution of various physicochemical parameters during ripening as a function of storage method (cold or ozone treatment). The weight of the fruits decreased considerably during ripening (Fig. 1, Tukey test, p < 0.05). After 7 weeks of ripening in both the 0 °C and the ozone treatment chamber, the decrease was about 3.5%. Jourdain, De Taffin, and Coquinot (1982) observed a decrease of 1.7% over the same time. The
Conclusion
Several conclusions can be drawn from this study:
- (i)
The Corsican kiwi can be stored for a 7-month period in either cold storage or using the ozone treatment. Firmness remained between 1.5 and 0.5 kg/0.5 cm2 during storage in both types of chamber.
- (ii)
Ozone treatment storage significantly decreased Botrytis contamination. It was shown to be able to deactivate the B. cinerea pathogens in the kiwi fruit.
- (iii)
The Corsican kiwi fruit is characterised by high concentrations of citric and quinic acids and its main
Acknowledgements
The authors are indebted to the European Community for partial financial support (PIC INTERREG IIIA).
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