Effect of chitosan coatings on the physicochemical characteristics of Eksotika II papaya (Carica papaya L.) fruit during cold storage
Introduction
Papaya (Carica papaya L.) is one of the most important fruit crops grown in the tropical and sub-tropical regions of the world. Being a climacteric fruit, papaya has a short postharvest life, thus, research has focused on minimising postharvest losses in order to prolong shelf life. The postharvest storage procedures for papaya help to minimise the quality deterioration from the decomposition processes (Rohani, Zaipun, & Norhayati, 1997).
The introduction of a high yielding and good quality Eksotika II papaya hybrid has gained popularity in domestic as well as export markets. However, the short storage life limits the export of papaya in refrigerated sea containers. Air freight is expensive and shipping in refrigerated containers and modified atmosphere packaging cannot yet offer sufficient storage life without the use of fungicides. Moreover, prolonged storage at low temperatures may damage the fruit physiologically (Maharaj & Sankat, 1990). If these limitations are minimised, the farmers and exporters of papaya fruit can earn maximum profits and capture a larger share of the world market. Alternative methods that prolong the postharvest storage life of papaya during shipping are required.
Recently, there have been increased efforts to discover new preservative compounds derived from natural sources (e.g. carnauba, paraffin, shellac, beeswax and chitosan), having no known effects on human health (Vargas, Pastor, Chiralt, McClements, & González-Martínez, 2008). It is thought that coating the fruits with preservative compounds reduces the rate of respiration by creating a modified atmosphere around the fruits, thereby retarding ripening and senescence. Chitosan, which has a chemical structure close to that of cellulose, has long been known to protect perishable foods from deterioration by reducing dehydration and respiration, maintaining the textural quality (No, Meyers, Prinyawiwatkul, & Xu, 2007). Chitosan coatings for storing strawberry, tomato, mango and carrots have been developed (Chien et al., 2007, Durango et al., 2006, Muñoz et al., 2009). Indeed, chitosan is often considered to be the ideal preservative coating for fresh fruit because of its excellent film-forming and biochemical properties (El-Ghaouth, Smilanick, & Wilson, 2000). Furthermore, chitosan has been approved by the United States Food and Drug Administration (USFDA) as a food additive, and has passed the toxicological tests (Hirano et al., 1990). Although there has been some research into the use of chitosan as a preservative in some tropical fruit (El-Ghaouth et al., 2000), there has yet to be any published study on the use of chitosan coatings to maintain the quality and extend the shelf life of Eksotika II papaya.
Therefore, the aim of this study was to elucidate the potential of chitosan coatings on the extension of the storage shelf life of Eksotika II papaya fruit, and also to investigate the influence of different concentrations of chitosan coatings on the gaseous exchange and quality attributes of the papaya fruit during cold storage.
Section snippets
Plant material
Mature-green papaya fruit of colour index 2 (green with trace of yellow) were obtained from a local exporter, Exotic Star (M) Sdn Bhd, Sg. Chua, Kajang, Selangor, Malaysia, on the same day of harvesting. The cultivar ‘Eksotika II’ fruit of uniform size (400–500 g), shape and maturity and free from any indication of mechanical injury, insect or pathogenic infection, were selected for the experiment.
Preparation of chitosan solutions and application of treatments
Locally prepared shrimp shell chitosan (95% deacetylated) was obtained from the chitin-chitosan
Weight loss
The weight loss appeared to be the major determinant of storage life and quality of papaya fruit. Fig. 1 shows that chitosan coatings significantly (P ⩽ 0.05) reduced the weight loss of the papaya fruit during storage compared to the control. The weight loss decreased with increasing chitosan concentrations. The minimum weight loss was observed in the chitosan treatments of 1.5% and 2.0%.
The slower rate of moisture loss from the chitosan coated fruits may be attributed to the additional barrier
Conclusions
In conclusion, the present study shows that chitosan, as a preservative material, could delay the ripening process by inhibiting the respiration rate in the Eksotika II papaya fruit. This suggests that chitosan not only maintains firmness but also improves the postharvest quality during cold storage and also suggests that chitosan is promising as an edible coating to be used in commercial postharvest applications for prolonging the storage life of the Eksotika II papaya.
Acknowledgements
We would like to thank the Ministry of Science, Technology and Innovation, Malaysia for financial support under IRPA Grant No. (01-02-04-0061-EA001), and Universiti Putra Malaysia, Serdang for using its laboratory facilities. We are grateful to Exotic Star (M) Sdn Bhd, Kajang, Selangor for providing the Eksotika II papaya fruit. We are also obliged to Dr. Daniel R. Smith for many helpful comments on earlier versions of this manuscript.
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