Essential Oils and Chitosan Applications to Protect Apples against Postharvest Diseases and to Extend Shelf Life

Abstract

Apple fruits are susceptible to pathogenic fungi such as Botrytis cinerea and Penicillium expansum which are responsible for significant pre- and postharvest fruit losses. Given the strong restriction in the use of synthetic agrochemicals, especially during the postharvest phase, alternatives are currently sought for a more sustainable management of apple storage. The antifungal activity of thyme, clove, anise, camphor, and juniper essential oils (EOs) was evaluated with in vitro tests and the minimum inhibitory concentration (MIC) was determined. Thyme and anise EOs showed a MIC value of 0.5 and 1 mL L−1 against B. cinerea, respectively. A MIC of 0.5 mL L−1 was found for clove EO against P. expansum. Camphor and juniper EOs were found to be less effective. Although in those experiments the antifungal activity of EOs was proven, when EOs were applied in in vivo conditions they did not demonstrate the same effectiveness. In order to preserve EO inhibitory performances, edible coatings combining polysaccharide matrices (chitosan, arabic gum, and xanthan gum) with EOs were tested. After considering consistency, uniform coverage of the fruit surface, and antifungal properties of the matrix, chitosan was identified as the most suitable component for EO encapsulation. Treatments with chitosan in combination with thyme EO on apple fruits (cv. ‘Braeburn’) showed inhibitory effects on infection caused by B. cinerea (−48% of infected wounds compared to untreated). Similarly, clove EO combined with chitosan reduced the Penicillium infections in apple cv. ‘Golden Delicious’ by 62%. These results therefore suggest the effectiveness of the use of EOs encapsulated with chitosan for the control of postharvest diseases of apple fruits during storage.