Plant materials: About 5 Kg of bitter gourd (locally named as ‘vhui korola’ or ‘ucche’), 10 Kg of brinjal (locally named as ‘pajia’) and pointed gourd (locally named ‘bombai’) were collected from the farmers’ field at Botiaghata and Dumuria, Khulna, Bangladesh. The vegetable samples were collected in the early morning and they were free from any diseases and abnormalities. The vegetable samples were similar in size accordingly.
Preparation of plant extracts: Required amount (about 1 kg) of plant materials (aloevera, garlic, onion, ginger and thankuni) were collected and blended maintaining proper sterilization practices and then filtered with the help of Whatman Filter Paper (No.2). The filtrated extracts were taken in an aluminum foil sealed beaker and stored in the refrigerator at 50C until further use (Mia, 2003). For preparing combination of the extracts, equal amount of each single extract was taken and the mixture was made 40ml. The final volume of the combinations were made 200 ml with the addition of distilled water (Mia, 2003). The combined extracts were taken to different sterilized plastic bottles with the help of funnel and were prepared for spraying purpose.
Experimental design: The experiment was laid out in a completely randomized design (CRD) with three replications of the treatments having 20 fruits of bitter gourd, brinjal and pointed gourd in each replication. Four treatments were applied on the vegetables under study including control (T1), combination of aloe vera and thankuni extract (T2), combination of garlic, onion and ginger extract (T3) and combination of aloe vera, thankuni, garlic, onion and ginger extract (T4).
Application of treatments to vegetables: The vegetable samples were placed on a sterilized surface in different groups. The untreated group was left as control. The others were treated with specific treatment through spraying.
Observations recorded: Treated vegetable samples were observed in every alternate day for physical parameters while chemical parameters were observed at 3 days interval. Data on the following parameters were recorded in the current study.
Weight loss: The weight loss was estimated by using a laboratory-grade digital weight measuring balance (AND EK600H) in every alternate day and was expressed as percentage of original weight. The percentage of weight loss was calculated by using following equation.
Percentage of weight loss (%WL) = IW-FW / IW x 100
IW = initial weight of vegetables (g)
FW = final weight of vegetables (g)
Determination of pH: In the current study, the pH of the vegetable extract was measured by using microprocessor desktop pH meter (HANNA-pH 211). The vegetable extract of 30 ml was taken into a beaker and the probe of pH meter was kept into the extract for measuring its pH. The digital meter displayed the pH reading directly (Hilderbrant, 2016).
Determination of Total Soluble Solid (% Brix) content: Total soluble solid content of vegetables was estimated by using Abbe’s refractometer (REF10/111). A drop of vegetable juice squeezed from the respected vegetable was dropped on the prism of refractometer. Percent of TSS was obtained as the direct reading from the instruction (Ranganna, 1979).
Microbial Test: Slides were prepared by taking sample from infected portion of vegetables and the microbial infection was examined through microscope. Shelf life: Shelf life for the vegetables treated with different treatments was calculated as the number of day until the score for texture and colour retains more than or equal to 3. In respect of weight loss, the number of marketable days was counted until the weight loss percentage cross the limit of 25%.
Statistical analysis: The collected data on various parameters were statistically analyzed using STAR (Statistical Tool for Agricultural Research), Version 2.0.1 (IRRI, 2013) statistical package. The means for all the treatments were calculated and analyses of variances (ANOVA) for all the parameters were performed by F-test. The significance of differences between the pairs of means was compared by Least Significant Difference (LSD) test at the 1% and 5% levels of probability (Gomez and Gomez, 1984).