The experiments were conducting in the Post harvest Technology Division of Bangladesh Agricultural Research Institute, Gazipur in the year of 2013-2014 and 2014-2015. Yard long bean were harvested from a farmer’s field of Pubail, Gazipur and transported to the post harvest laboratory of Bangladesh Agricultural Research Institute, Gazipur within one hour. Matured and fresh yard long bean which were free from diseases and visual defects were identified and washed with distilled water, then dried in air. Yard long bean was cut into 20 mm pieces. Water blanching was performed in hot water at temperature ranges from 90 to 950C, cool the product in distilled water and vacuum packing was done. Finally, the product was storage at the laboratory deep freeze (-18OC) available for homestead use. The experiment was started from the month of May in each year and the products were stored for the next 4 months and the shelf life studies were continuing after 1 month interval.
Treatments
There were eleven (11) treatments are:
T1 = control
T2 and T3 = blanching at 900 C and 950 C for 2 min, respectively
T4 and T5 = blanching at 900 C and 950 C for 4 min, respectively
T6 and T7 = blanching at 900 C and 950 C for 6 min, respectively
T8 and T9 = blanching at 900 C and 950 C for 8 min, respectively
T10 and T11 = blanching at 900 C and 950 C for 10 min, respectively
Measurement of ascorbic acid, total soluble solids (TSS), pH and titratable acidity: Ascorbic acid measurement, 10g sample 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-dichlorophenolindophenol titration following the method of Ranganna (1986). Ten milliliters of aliquot was titrated with 0.1% 2, 6- dichlorophenolindophenol solution until the filtrate, changed to pink colour persisted for at least 15 seconds and the titration volume of 2, 6- cichlorophenolindophenol was recorded. Prior to titration 2, 6- dichlorophenolindophenol solution was calibrated by ascorbic acid standard solution. Ascorbic acid content was calculated according to the titration volume of 2, 6- cichlorophenolindophenol and results were expressed as mg 100gm-1 fresh weight. Again, 10g sample 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 measure total soluble solids using a digital refractometer (Model NR151) and expressed as percentage, pH using a glass electrode pH meter (Delta 320, Mettler, Shanghai) and titratable acidity 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).
Measurement of β-carotene: The estimation of β-carotene was done by the extraction of 3g product sample with acetone (Fisher Scientific Ltd., Uk) and petroleum ether. It was further purified with acetone, metabolic KOH and distilled water. The resulting solution was filtered with anhydrous sodium sulphate and read on a spectrophotometer (T-80, PG Instrument Ltd., UK) at 451 nm against petroleum ether as a blank. A standard graph was plotted using synthetic crystalline β-carotene (Fluka, Germany) dissolved in petroleum ether and its optical density measured at 451 nm (Alasalvar et al. 2005).