Mango fruit of Cultivar Langra of uniform size was harvested at 3/4th maturity stage early in the morning at a temperature of 27°C from Fruit Nursery Farm, D. I. Khan. Fruits were thoroughly washed with clean tap water and dried using a room fan at 25 oC temperature. Clean and dry fruits were irradiated at doses of 100, 150, 200, and 250 Gy in a Co60 gamma irradiator source (Izotop, Hungary) at NIFA, Peshawar having a dose rate of 8.5 kGy/hour. Fruits in control were kept un-irradiated throughout the study period. The fruits were stored at room temperature of 25.3 ± 1.4°C and RH 42 ± 2.6%. Physiological weight loss (%), firmness, TSS, vitamin C content, Acidity, and pH were determined at 2-day intervals over 8 days. Organoleptic characteristics such as appearance, taste, odor, texture, firmness, flavor, and consumer acceptability were judged by a panel of 20 volunteer judges on 9 9-point hedonic scale with number 9 being considered the best [22]. A hand refractometer (Kernco Instruments Co. Texas) was used for the measurement of total soluble solids (°Brix). Acidity was determined by neutralization reaction as described in the Association of Official Analytical Chemists [23]. A hand refractometer (Kernco Instruments Co. Texas) was used for the measurement of TSS (°Brix). Acidity was determined by neutralization reaction as described in the Association of Official Analytical Chemists [24]. The sample of unknown acidity was titrated with a standard 0.1N NaOH solution. The completion of the reaction was established using phenolphthalein as an indicator.
Three mango fruits of equal size in each irradiation treatment were separated, washed, and dried. Percent weight loss in irradiated mango fruits and control was determined by the following formula:
Total soluble solids (TSS)
Total soluble solids in irradiated mango juice and control were determined by the method of Awan (2001) [25]. A fine paste of mango fruits was prepared using a common grinder (Deuron, Model No. GL–107, Power 350 W). A drop of well-mixed juice was put on a refractometer (Brix, Atago, Japan) for TSS reading through an eyepiece mirror graduated inside.
Titrable acidity
The titrable acidity of mango juice irradiated at different doses of gamma irradiation was determined by the method of Awan (2001). A fine paste of mango juice was filtered through number 4 Whatman paper. 20 ml juice from the paste was dissolved in 80 ml distilled water in a 250 ml beaker. Three drops of phenolphthalein were put in the solution and titrated against 0.01 N NaOH till the change of color. Reading was taken and put in the following formula for acidity determination:
Where 0.01 is the dye normality of NaOH solution and 0.064 is the constant factor.
Ascorbic acid (Vitamin C)
The ascorbic acid of mango juice irradiated at different doses of gamma irradiation was determined by the method of Awan (2001). A fine paste of mango juice was filtered through number 4 Whatman paper. 20 ml juice from the fine paste was dissolved in 80 ml Oxalic acid in a 250 ml beaker. Three drops of phenolphthalein were put in the solution and then titrated against the dye till the change of color. Reading was taken and put in the following formula for ascorbic acid determination.
Where 0.1 is the dye factor or Normality of the NaOH solution
Titre is ml of dye used in the sample–ml of dye used in blank
The pH of mango juice extracted from irradiated mango fruits and control was determined by the method of Awan (2001). The pH meter was Standardized at two standards of pH 4.0 and 7.0 buffers. 5 gm pure mango juice was dissolved in 50 ml of dH2O (w/v) in a 50 ml beaker and an electrode of a pH meter was put into the solution for pH reading. The electrode was washed with distilled water from a wash bottle, dried using a piece of filter paper, and continued with the next reading.
Sensory analysis of irradiated and un-irradiated mango fruits.
Sensory evaluation of mango fruit for color, texture, flavor, and odor was done by 20 volunteers (10 males and 10 females). The volunteers belonged to agriculture research, soil conservation, food technology, water management, and agriculture extension departments. The fruits were evaluated every two days for 8 8-day storage period at room temperature. Each person was given a proforma of 9 points for evaluation with number 9 as the best. Tasteless biscuits were given for eating before sensory evaluation of mango fruit.
Statistical analysis
Statistical data analysis was carried out by one-way analysis of variance (ANOVA) in randomized complete block design (RCBD) with three replications and the means were separated by Tukey’s HSD test using Statistix 8 analytical software (version 8.1) at 5% significance level. All the results were expressed in graphs and tables in mean values with standard errors. Correlation among the fruit quality deterioration and gamma irradiation doses was also done with regression analysis using an MS Excel sheet.