EFFECT OF VAPOUR HEAT TREATMENT ON PENICILLIUM DIGITATUM (PERS.) SACC. CITRUS SINESIS (L.) OSBECK.

Abstract

Sweet orange (Citrus sinesis) is consumed all over the world. It is an excellent source of vitamin C which is a powerful antioxidant that helps in building the body immune system. However, the activities of microorganisms especially fungi have reduced its production, storability and market values which makes it less available in season and out of season. Penicillium digitatum is one of the most common postharvest pathogens of orange fruits. The objectives of this project are to test different temperature-time protocols of vapour heat on oranges infected by P. digitatum (green mould) in order to identify treatments that will control green mould on oranges. Spore suspension of P. digitatum was inoculated on freshly harvested oranges which were later subjected to vapour heat treatment at 55oC and 60oC for 5 to 40 minutes at 5 minute intervals. The treated oranges were arranged in completely randomized design in five replicates and stored at 28o ±2oC and 95% relative humidity. Disease severity assessed every 48 hours showed that treatment at 55oC for 5- 20 minutes did not preserve orange fruits for up to 10 days, although they showed less severity compared with control. Treatment at 55oC for 40 minutes preserved orange fruits for 10 days only while treatment for 25 minutes at 55oC controlled the disease on orange fruits for more than 60 days. Treatment for 35 minutes at 55oC controlled P. digitatum for up to 70 days. Fruits treated at 60oC for 5 minutes showed symptoms of rot before control. On 14th day of storage, the level of rot on the fruit exposed for 5 minutes at 60oC in comparison with the control was the same but fruits exposed for 10- 25 minutes at 60oC showed lesser disease severity when compared with control. Treatment for 30 – 40 minutes at 60oC showed no symptoms of the diseases up to 70 days of storage. This research showed that vapour heat treatment at 55oC for 35 minutes and 60oC for 30 – 40 minutes was able to control the growth of Penicillium digitatum on infected oranges for 70 days of storage.