Plant material and growth condition The investigation was carried out during the years of 2016-2017 on sweet orange grown and maintained in the Fruit Research Farm, Horticulture Research Centre, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur. Seven years old healthy tree of three sweet orange varieties viz., BARI Malta-1, BAU Malta-1, BAU Malta-3, and five lines viz., CS Jain-001, CS Jain-002, CS Jain-003, CS Ram-001, and Variegated Malta were selected for this study. This experiment was laid out in a Randomized Complete Block (RCB) design with three replications.
Fruit sampling Randomly collected mature fruit samples of different sweet orange genotypes were subjected to the Post Harvest Technology Division laboratory, BARI for determining the physicochemical properties. For each fruit character, ten fruits were collected randomly and observations were recorded on each fruit separately.
Fruit physical attribute Parameters like fruit length, fruit diameter, the thickness of mesocarp, the width of epicarp at the equatorial area, and diameter of fruit axis were recorded using Digital Vernier Calipers where the number of segments was counted manually. The juice was collected from pulp and weighted by an electric balance. Then juice (%) was calculated using equation 1.
Fruit chemical attribute Immediately after the collection of physical parameters, the pulp was rapidly separated, squeezed and filtered the juice to determine the fruit quality, including total soluble solid (TSS), pH of juice, titratable acidity (TA), sugar, β-carotene and ascorbic acid. The total soluble solids content of fully mature fruits was recorded with a handheld refractometer (Atago Co. Ltd., Japan). The pH of the juice was estimated by a hand pH meter.
TSS and juice pH measurement A handheld refractometer (Atago Co. Ltd., Japan) was used to record total soluble solid content of fully mature fruit. The pH of the juice was estimated by a hand pH meter.
Titratable acidity (TA) The titratable sweet orange pulp acidity was determined by the method of Rangana (1979). Ten milliliters of juice extracted from pulp was taken in a 250 ml conical flask. Two or three drops of the indicator phenolphthalein were applied to the flask and vigorously shaken. It was then titrated instantly with 0.1 N NaOH solutions from a burette till a stable pink color appeared. From the burette reading, the volume of NaOH solution for titration was registered. The titration was done in triplicate percent titratable acidity was calculated by using the formula.
Determination of Fehling’s factor Sugar content was determined by the method ascribed by (Rangana, 1979). The Fehling solution was standardized by combining the same quantity of Fehling’s solution A and Fehling’s solution B in the beaker then 10 ml of this mix solution was taken into a 250 ml conical flask and 25 ml double distilled water was added to it. On a hot plate, the conical flask containing the mixer solution was heated and three drops of a solution for methylene blue indicators were added. A standard sugar solution was used to titrate the mix solution. Decolorization of the indicator showed the endpoint. Fehling’s factor was calculated by using the formula.
Sample preparedness About 50 g of fresh sweet orange pulp was blended along with distilled water in a blender. The merged materials were then filtered and transferred to a 100 mL volumetric container, and distilled water provided the volume. One hundred milliliters of the filtrate was taken in a 250 ml volumetric flask. Approximately 5 ml of 45% neutral lead acetate solution was added to it and shaken and after 10 minutes, 5 ml of 22% potassium oxalate solution was added to the flask and the volume was made up to the mark with distilled water.