The present experiment was carried out at Postharvest Processing Lab of the Department of Horticulture, Patuakhali Science and Technology University during the period from 01 July to 15 August, 2016 to study the post-harvest storage life and quality changes of Banana cv. Amritosagor as influenced by promising postharvest treatments of lemongrass extract.
Experimental material Hands of mature green banana color index 1 (green) were brought from a commercial orchard located at Dumki. Banana fruit which is free from physical injury, insect or pathogen infection as well as more or less similar in size (200-250 g) were selected for the experiment.
Design of experiment The experiment was organized in a completely randomized design (CRD) with five replications including five bananas in each replication at ambient condition. Three treatments were imposed on banana fruits under the experiment where fruits treated with distilled water were indicated as control groups (T1), fruits treated with fungicide dipheniconazol® 0.5ml/litre considered as positive control (T2) and fruits immersed with 20% lemon grass extract oil (T3) were considered as post-harvest treatment.
Preparation of lemon grass extracts (Hydrodistillation) The lemon grass extracts were prepared and applied on the fruit samples at postharvest analysis laboratory, Department of Horticulture, Patuakhali Science and Technology University. Two hundred grams of freeze dried samples were subjected to hydrodistillation. The hydrodistillation was carried out by using the Clevenger equipment at 100°C for 6 hours in glass Dean and Stark apparatus modified to allow the lowest phase return. The oil with water mix was added, to trap the condenser, through the top of the condenser. Later oil with water mix was collected every hour. Then, a few amounts of hexane was added through the condenser. The mixtures were combined and dried over anhydrous Na2SO4 for 24 hours and then filtered (it was filtered with 0.001 millimeter micropore filter paper). Finally, yellowish essential oil extracts were found which were stored at 4°C for further use.
In vitro screening of plant essential extract against C. musae mycelium linear growth and spore germination The inhibitory effects of lemongrass (Cymbopogon citrates) essential oils were tested in vitro on mycelial growth of C. musae. Preliminary screening was carried out according to Arrebol et al. (2010). The Petri dish with 9 cm diameter was poured with potato dextrose agar (PDA) media. The lemon grass extracts were dispersed to PDA media immediately before it was filled into the Petri dish at a temperature of 25-30°C. The concentrations of lemon grass extract were tested and 20% extracts were optimized to mix up with the media. The controls included the same quantity of distilled water was added with PDA media. The test fungus (anthracnose of banana) was inoculated immediately after preparation of the petri dishes by placing it in the centre of each plate. A 5 mm diameter disk of the test fungus cut with a sterile cork borer from the periphery of actively growing cultures on PDA plates. The petri dishes were incubated in the dark chamber at a temperature of 25°C. Mean growth rates fungal mycelia were observed. Fruit samples were placed on a sterilized surface in three groups having five replications for each treatment and the extracts were sprayed over the fruit according to the treatments in vivo condition.
Methods of treatment application Randomly selected twenty five fruits were dipped into the lemon grass extract (20%) solution for three minutes to ensure that enough quantity of extract being absorbed by the fruit surface. The treated fruits were subjected to air dry at room temperature (26±20C). In case of fungicidal treatment, five litres of distilled water was taken in a bowl and 2.5 ml of Diphenoconazol® solution (Trade name: Score, Synzenta Bangladesh Limited) was added. The selected fruits were then individually dipped in this prepared fungicidal solution for three minutes to ensure that enough quantity of solution being absorbed. In case of distilled water treatment, each fruit was then individually dipped into the sterilized distilled water for three minutes and allowed to dry for ten minutes. Each of the treated fruit was wrapped with 70 g offset paper and held at 26±2ºC and 80±5% RH for 15 days. Every three days, five fruits represented five replications for each treatment were used for the determination of physicochemical properties of the treated fruits. Data were documented on 0, 3, 6, 9, 12 and 15 days of storage (26±2ºC and 80±5% RH).
Parameters studied The physic-chemical characteristics of treated fruits such as color changes, pulp pH, Total Soluble Solids (TSS), Titratable Acidity (TA), total sugar, reducing sugar, non- reducing sugar, ascorbic acid content, disease incidence (percentage of fruits infected) and disease severity were studied in the present experiment.
Methods of studying physico-chemical parameters The changes in peel color of fruits were determined by visual observation changes in peel of the treated fruits were determined. The pH of fruit juice was recorded by using an electric pH meter. The pH meter was standardized with the help of a buffer solution as described by Ranganna (1994). TSS content of banana pulp was measured by using Abbe's Refractometer. A drop of banana juice squeezed from the fruit pulp was dropped on the prism of the Refractometer. Temperature corrections were made by using the methods described by Ranganna (1994). The sugar content of treated fruits of each treatment was estimated by the procedures, described by the Ranganna (1979) with using following formula:
Total sugar (%) = Reducing sugar (%) + Non-reducing sugar (%)
Statistical analysis The data which was taken on different days after storage on various parameters were statistically analyzed using MSTATc statistical package. The means for all the treatments were calculated and analyses of variances (ANOVA) for all the parameters were performed by F-test. The significance of the difference between the pairs of means was compared by the least significant difference (LSD) test at 1% and 5% levels of probability.