Postharvest application of antagonistic bacteria (Bacillus cereus strain PSTU HORT-10) on the storability and quality of banana. The postharvest application of antagonistic bacteria on banana fruit was conducted to investigate the significance differences among the treatments on the storability and quality of banana fruits. Experimental site The experiment was conducted at the “Postharvest processing and analysis unit of Postharvest laboratory”, Department of Horticulture, PSTU. Experimental materials Matured, green, approximately uniform size banana fruits without visible defects were brought from local market. The fruits were then carefully handled to avoid mechanical injury. The fruits were then carefully transported to post-harvest laboratory. 24 fruits were selected in each treatment and total no. of fruits was 72. 8 fruits represented each replication for each was used for determination of physio-chemical characteristics. Design and Layout of the experiment Bacillus cereus strain PSTU HORT-10 (antagonistic bacterium) was selected as treatment for this study compared with other treatments, which were: 1) Treatment (antagonistic bacterial suspension): Cell suspension of the best antagonistic bacterium 2) Positive control: Diphenoconazol solution at the rate of 0.5 ml/L of water (Trade name: Score, Syngenta Bangladesh Limited) 3) Negative control: Sterilized distilled water.
Methods of treatment application Fruits were randomly selected from the experimental fruit lot. Each of the fruits was washed in running tap water for removing any surface contamination followed by distilled water. The fruits were placed on the table of the laboratory at ambient condition to allow air dry at room temperature (26±2C). The postharvest treatments were applied to the fruits as per the following methods.
Preparation of bacterial suspension (Treatments) For bacterial suspension treatment, the banana hands were immersed into prepared aqueous bacterial suspension which bacterial colony showed antagonism performance in this experiment and kept for 10 minutes before placing on the paper placed on the table in the laboratory at ambient condition. Preparation of Diphenoconazol solution (Positive control) Five litres of distilled water was taken in a bowl and 2.5 ml of Diphenoconazol'P solution (Trade name: Score, Synzenta Bangladesh Limited) was added. Twenty four fruits were randomly selected from the experimental fruit lot. The selected fruits were then individually dipped in this prepared fungicidal solution for three minutes to ensure that enough quantity of solution being absorbed. The treated fruits were allowed to air dry for a period of ten minutes.
Immersed in Sterilized distilled water (Negative control) Twenty four fruits were randomly selected from experimental fruit lot. Each fruits was then individually dipped into the sterilized distilled water for ten minutes and allowed to dry for a period of ten minutes. The banana fruits were randomly selected for the post-harvest treatments. After the applications of treatments, the fruits were wrapped by 70gm offset paper and stored at 28+2c and 66 to 74% relative humidity. During the entire storage period, the fruits, used for the experiments, were keenly observed but data were collected until the disease severity become 30%. Data were recorded at 3days interval.
Atmospheric condition of storage room The temperature and relative humidity of the storage room were recorded daily during the study period with a digital thermo hygrometer (Wet and dry bulb hygrometer, Zeal, G.H. ZEALTA). The minimum and maximum temperatures during the study period of the storage room were 26 c to 30 c, respectively. The minimum and maximum relative humidity was 80% and 90%, respectively Physical characteristics of treated fruits The physical characteristics of treated fruits such as total weight loss, peel firmness, external peel color, pulp to peel ratio, sensory evaluation of ripe fruits were studied in the present experiment.
Determination of color The peel color of the leather was determined using an Android Application Software namely “On Color Measure” (developed by PotatotreeSoft, Version 3.0) equipped with an aim pointer. It provides the easiest way to store the information of each color detection. Color measurements were done at each face of leather and a mean value was obtained. The leather color determination was expressed in chromaticity values of Red (R*), Green (G*) and Blue (B*). For measuring the color the camera was aimed at the target color point and clicked on crosshair pointer and moved it to any place on the screen. The dashboard displays the information of the color detected. Grab button was clicked to capture the screen image and saved all the detailed color information including RGB, HSV, color names, hex code and screen images.
Chemical characteristics of treated fruits The Chemical characteristics of treated fruits such as total anthocyanin content of peel and the carotenoid content, soluble acid concentration (SSC), pH, Reducing sugar content, Non-reducing sugar content, ascorbic acid content of fruit pulp were studied ion the present experiment.
Determination of soluble solid concentration (SSC) The soluble solids concentration of banana will be determined by using a digital refractometer. The remaining of the filtrated juice from TA determination was used to measure the SSC of the fruit pulp. Before measurement, the refractometer will be calibrated with distilled water to give a 0% reading. About 1-2 drops of the filtrate was placed on the prism glass of the refractometer to obtain the % SSC reading. The readings were multiplied by dilution factor to obtain an original % SSC of the pulp tissues. Since differences in sample temperature could affect the measurement of SSC (Boourne, 1992), each of the reading was standardized to a temperature of 200 by adding 0.28% to obtain % SSC at 270.
Preparation of sample 50 ml fruit juice mixed with 100ml of distilled water and 5ml of neutral led acetate solution and then kept for ten minutes and the mixture was homogenized. Then the blender material was transferred to a 250ml volumetric flask. The volume made up to the mark with distilled water. The solution was then filtered.
Determination of total invert sugar 50ml of purified solution (filtered) was taken in a 250ml conical flask. 5ml citric acid and 50ml distilled water added to it. The conical flask containing sugar solution boiled for inversion of sucrose and cooled. The solution was transferred to a 250ml volumetric flask and neutralized by 1N NaOH using phenolphthalein indicator. The volume was made up to the mark with distilled water. Then the mixed Fehling’s solution was titrated using similar procedure followed as in case of invert sugar (reducing sugar) mentioned earlier. The percentage of total invert sugar was calculated by using the formula used in incase of reducing sugar.