The experiment was carried out at the laboratories of the Departments of Horticulture and Biochemistry of Bangladesh Agricultural University, Mymensingh during May to September, 2016. The experimental litchi fruits were taken out from the local growers of Ishurdi, Pabna. The maturity of the litchi fruits was ascertained by the comparative smoothness of epicarp and flatness of tubercles.
Experimental materials: The commercially momentous litchi variety namely ‘Bombai’
‘Bombai’: This is vital commercial cultivar of Bangladesh. Litchi fruits are almost heart shaped. Ripening commences from the last week of May. The color at maturity is pointed out as yellow-green background with red tubercles. The average weight of fruit varies from 15-20g. Fruit pulp has satisfactory flavor and is soft, greyish white, juicy, sweet to sour in taste. Regarding weight, the ratio of rind, pulp and seed is 12.11:70.08:16.8. Ghosh et al. (1987) found that the average weight of litchi fruit was 19 g which consisted of 19.9% seed, 62.2 % pulp, 17.9% skin, on the basis of weight. They also narrated that the fruit pulp contained 17.7% total soluble solids, 0.42% acidity and 11.0% sugars.
Experimental treatments: Total 8 treatments are implemented in this experiment. The experiment was consisted of 2 factors. Factor A: Temperature T1: Ambient temperature T2: Low temperature (4 ºC) Factor B: PP bags (Polypropylene bag), size: 36cm X 24 cm P1: Control (unwrapped) P2: 50µ PP bag P3: 75µ PP bag P4: 100µ PP bag.
Experimental design: The two factors experiment was implemented in a completely randomized design with three replications of 8 fruits at each. Randomly selected a total of 192 fruits of more or less similar shape and size and free of visual diseases symptoms were used.
Application of postharvest treatments: Among 8 fruits in each replication of each treatment 4 fruits were marked to investigate disease incidence, disease severity and the remaining 4 fruits were kept unmarked conditions for destructive sampling to examine dry matter content, TSS, Titratable acidity, pulp to peel ratio and pulp pH.
Methods of studying Parameter: (A) Pulp to peel ratio- The fruits were peeled at the 3rd, 6th and the 9th days of storage. After separating, the peel and pulp weights were taken individually by using an electric balance and the pulp to peel ratio was calculated. Then the pulp was used for other chemical analysis.
(B) Dry matter content- Ten grams of fruit pulp was taken in a Petridis from each treatment and replication. The Petridish was placed in an electric oven preset at 80°C for 72 hours until constant weight was attained. It was then cooled in desiccators and weighed again. Percent moisture content was calculated according to the following formula: Moisture content (%) = IW-FW / IW x100
Where, IW = Initial weight of pulp (g), FW= Final weight of oven-dried pulp (g).
Percent dry matter content of the pulp was calculated from the data obtained during moisture estimation using the following formula; Dry matter content (%) = (100%-% moisture content)
(C) Total soluble solids- Total soluble solid (TSS) content of litchi pulp was estimated by using Abbe's Refractometer. A drop of litchi juice squeezed from the fruit pulp was placed on the prism of the refractometer. Then TSS was obtained from direct reading of the instrument. Temperature corrections were made by using temperature correction chart that accompanied the instrument.
D) Pulp pH- Preparation of standard buffer solution pH -7 and pH-4 buffer tablet BDH (chemicals Ltd., Poole, England) was dissolved in water and made up to the mark of 100 ml with distilled water.
Extraction of fruit juice: For the determination of pulp pH, 5 g of fresh pulp was taken in a conical flask containing 10 ml of distilled water. Then the pulp was crushed thoroughly in a mortar and pestle and extract was filtered through two layers of cloths.
Procedure: The pH meter (Hanna) was standardized by using buffer solution of pH -7 and pH-4 when correction for temperature was also taken into consideration. On completion of calibration the electrode was washed twice with distilled water, rinsed with litchi juice and dipped into the juice. The pH was recorded.
(E) Titratable acidity- Titratable acidity of litchi pulp was determined according to the method mentioned by Rangana (1979). The following reagents were used for the determination of titratable acidity. 1. Standard NaOH solution (0.1N) 2. 1% phenolphthalein solution.
Extraction of litchi juice: Ten grams of fresh litchi pulp was homogenized with distilled water in a blender. The blended materials were boiled for 1 hr under refluxing. The whole mass was than cooled, filtered and transferred to a 100 ml volumetric flask and the volume was made up to the mark with distilled water.
(F) Disease incidence- Disease incidence refers to the percentage of fruits infected by disease organisms. The fruits were critically examined for the appearance of disease symptoms. The first count was made at the 2 nd day of storage. The diseased fruits were identified symptomatically. The disease incidence was calculated as follows: Disease incidence (%) = Number of infected fruits / Total number of fruits under study x 100
(G) Disease severity- Disease severity refers to the percentage diseased portion of infected fruit. The infected fruits of each replication of each treatment (varieties) were observed to determine percent fruit area infected and was measured based on eye estimation. The mean values regarding infected fruit area were calculated, presented, and discussed.
Statistical analysis: The collected data were statistically analyzed by Analysis of Variance (ANOVA) test. The means of different parameters were compared by least significant difference (LSD) as described by Gomez and Gomez (1984). For percentage data arcsine transformations were carried out to satisfy the assumption of ANOVA.