Fruit materials Locally grown banana fruits (Musa sp., AAA group, Gros Michel subgroup, var. BARI Kola-1) at mature green stage were acquired from a farmer’s field of Gazipur, Bangladesh. At the time of harvest, the temperature and relative humidity of the banana field prevailed 28±2°C and 75±5%, respectively. After harvest, banana hands were transported to the Postharvest Laboratory, Horticulture Research Centre of BARI, Gazipur and cut into fingers using a sterilized sharp knife. Fruits were then sorted and grouped based on uniformity of developmental stage, weight and size, and then randomly divided into 12 treatment groups. Upon arrival no fungicide treatment was applied for controlling postharvest diseases.
1-MCP treatment Twelve groups of 60 fruits each were treated with aqueous 1-MCP (0.1% active ingredient, AgroFresh, Inc., Rohm and Haas, Philadelphia). Solutions were prepared with granular 1-MCP at 100, 300 and 500 µg L-1 (a.i.). Quantities of 1-MCP granules containing the desired levels of active ingredient were suspended in 20 L of distilled water in 40 L plastic buckets and swirled gently with a plastic spatula until fully dissolved and then covered the bucket with its lid to protect the gas released from 1-MCP. Five minutes after preparation, banana fingers were immersed into each solution for 5, 10, and 15 min, and all treatments were completed within 30 min of 1-MCP solution preparation. A weighted and perforated plastic plate was placed on the fingers to ensure complete submerse during the emersion period. Banana fingers dipped in blank distilled water for 5, 10, and 15 min were used as control treatment. After removal from the bucket, fruit surface water was quickly dried with a table fan. The fingers were then placed into 1% perforated low-density polyethylene bags (0.03 mm thick), each containing five fingers. The treated fingers were then stored for five weeks at 20±2°C and 75±5% RH for ripening. A set of 20 fingers from each treatment was used to determine the changes in respiration rate and surface colour. The same set of fruits was used throughout the whole storage period to get unique data. The remaining 40 fingers from each treatment were used to determine the flesh firmness and different chemical attributes at different storage interval. The experiment was laid out in Complete Randomized Design replicated thrice. Data on the changes in different physicochemical parameters during storage were collected on day 0, 7, 14, 21, 28 and 35 of storage.
Determination of respiration rate: The respiration rate of banana was assayed at each measurement interval during storage. Ten fingers from each treatment were placed in 4 L airtight plastic containers equipped with septa and sealed for 2 h at 20±2°C. After incubation, 1 mL of gas sample was withdrawn from headspace by a gas-light hypodermic syringe and analyzed using a gas analyzer (CO2/O2 gas analyzer, Quantek Instrument, Model No. 902D, USA). The percentage of CO2 evolved in the container gas was recorded. Then the respiration rate was calculated based on the total gas volume in the jar, fruit surface volume, fruit weight and incubation time and expressed as mL kg-1 h-1 of CO2 evolved.
Assessment of pulp tissue firmness Firmness analysis was performed using Fruit Texture Analyzer (GUSS, Model No. GS25, SA) supported by FTA Win Software. Firmness measurement was taken as the maximum penetration force reached during the tissue breakage and determined with an 8 mm diameter stainless steel flathead probe, which penetrates in a normal direction at a cross-head speed of 5 mm S-1. Round banana slices of 25 mm thick containing both peel and pulp were cut transversely from the stem end, equatorial and blossom end of each fruit with a sharp knife. After establishing zero-force contact between the probe and the horizontally positioned fruit, the specimen was compressed 3 mm at 3 equidistant points of each slice and mean was calculated. The maximum force generated during probe travel was recorded and expressed in Newton (N).
Measurements of surface colour Banana external colour was examined with a Chroma Meter (Model CR-400, Minolta Corp., Japan). CIE L*a*b* coordinates were recorded using D65 illuminants and a 10° standard observer as a reference system. L* is lightness, a* (-greenness to +redness) and b* (- blueness to + yellowness) are the chromaticity coordinates. The a* and b* values were converted to chroma [C = (a*2 + b*2 ) 1/2] and hue angle [h° = tan-1(b*/a*)]. Before measurement, the equipment was calibrated against a standard white tile. Three readings were taken at different locations on each finger, taking five fingers from each treatment. Measurements were done in triplicate.
Measurements of ascorbic acid, total soluble solids (TSS), titratable acidity For ascorbic acid measurement, 10 g of fruit tissue was homogenized in 50 mL of 3% cold metaphosphoric acid (HPO3) using a blender for 2 min and filtered through Whatman filter paper No. 2. The clear supernatant was collected for assaying ascorbic acid by 2,6-dichlorophenol indophenol titration following the method of Ranganna (1986). Ten milliliters of aliquot was titrated with 0.1% 2,6- dichlorophenol indophenol solution until the filtrate changed to pink colour persisted for at least 15 seconds and the titration volume of 2,6-dichlorophenol indophenol was recorded. Prior to titration 2,6- dichlorophenol indophenol solution was calibrated by ascorbic acid standard solution. Ascorbic acid content was calculated according to the titration volume of 2,6-dichlorophenol indophenol and results were expressed as mg 100 g-1 fresh weight.
Again, 10 g of fruit pulp was homogenized in 50 mL of distilled water for 2 min using a kitchen blender and filtered through Whatman filter paper No. 2. The supernatant was collected in order to determine total soluble solids by using hand-held Kruss refractometer (Model HR 900, SN 1200793, brix range 0-90% at 20°C, Germany), pH by glass electrode pH meter (Delta 320, Mettler, Shanghai) and titratable acidity, which expressed as citric acid (%) was determined by titration with 0.1 mol L-1 NaOH to pH 8.1 according to the method by Ranganna (1986).
Experimental design and statistical analysis The experiment was carried out in a Completely Randomized Design (CRD) with three replications. The data were subjected to analysis of variance (ANOVA) using the CropState Statistical Software version 7.2. The results showing significant differences were then subjected to mean separation using Tukey’s Studentized Range (HSD) Test at P<0.05. Analyzed data were graphically plotted using Microsoft XL software.