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Evaluation of Watermelon (citrullus Lanatus) Juice Preserved with Chemical Preservatives at Refrigeration Temperature

M. K. Alam
Department of Food Processing and Engineering, Chittagong Veterinary and Animal Sciences University, Khulsi, Chittagong, Bangladesh

M. M. Hoque
Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet, Bangladesh

S. Morshed
Department of Applied Chemistry and Chemical Technology, Chittagong Veterinary and Animal Sciences University, Khulsi, Chittagong, Bangladesh 5Department of Applied Food Science and Nutrition, Chittagong Veterina

F. Akter
Department. of Physical & Mathematical Sciences, Chittagong Veterinary and Animal Sciences University, Khulshi, Chittagong-4202, Bangladesh

K. N. Sharmin
Department of Applied Food Science and Nutrition, Chittagong Veterinary and Animal Sciences University, Khulsi, Chittagong, Bangladesh

Abstract/ Executive Summary:

This study was done to analyze the effect of chemical preservatives on watermelon juice. Ten different samples of pasteurized watermelon juices with different chemical preservatives, termed as T1, T2, T3, T4, T5, T6, T7, T8, T9, T10 , were made which were stored at 4 - 15°C for three months. T1 and T2 were rejected soon due to spoilage. pH decreased from 5.094 to 4.017 and minimum pH content was reduced in T10 (7.87%), while maximum in T1 (57.55%). The total soluble solids (TSS) increased from 17.460% to 18.980% with maximum in T1 (51.67%) and minimum in T7 (4.88%). Reducing sugar was increased from 15.650 to 17.500% with maximum in T10 (18.22%) and minimum in T2 (5.90%). Minimum microbial load was observed in T10 (0.20cfu/ml) and maximum in T1 (>24 cfu/ml) in case of coliforms; minimum in T10 (78×105 cfu/ml) and maximum in T1 (258×105 cfu/ml) in case of total viable bacteria and same results (minimum in T10 and maximum in T1) were shown in case of fungal count. E.coli was found in T1, T2, T3 and T4 and some bacteria was found in SS agar (especially Salmonella) in T1, T2, T3 and T5. Among all the treated juice samples T10 was most effective in maintaining the sensory and nutritional quality during storage.

Keywords: Watermelon juice; Pasteurization; Sugar; Sodium benzoate; Potassium sorbate.

Location: Department of Food Processing and Engineering, Chittagong Veterinary and Animal Sciences University

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity:

Objectives:

The present study is selected to determine the chemical properties (pH, TSS, reducing sugar) and to analyze the microbiological characteristics during storage time.

Methodology:

Fresh mature watermelon were purchased from local market in Sylhet with uniform in color and size and stored at 250 C. The fruits were thoroughly washed with distilled water to remove dirt, dust, pesticide residues and then rinds were washed with pure ethanol to remove micro flora on the surface of the fruit prior to juice extraction. All glassware and knives were autoclaved at 121°C for 45 min and all other equipment was sanitized with hypochlorite prior to usage. The watermelons were cut into quarters and the flesh was scooped out and cut into small cubes. The cubes were placed in a laboratory scale juice processor. The extracted juice was then centrifuged and filtered. The filtered juice was placed in autoclaved screw-top glass bottles. The filtered watermelon juice, in screw-top glass bottles, was pasteurized in a covered water bath with high temperature short time (72oC for 15s) (Precision Water bath 180 Series, Chicago, IL). The treatments were made as pasteurized watermelon juice {Treatment one, T1 (control)}, pasteurized watermelon juice +20% sucrose (T2), pasteurized watermelon juice +0.1% sodium benzoate (C6H5COONa) (T3), pasteurized watermelon juice +20% sucrose +0.1% sodium benzoate (C6H5COONa) (T4), pasteurized watermelon juice +0.1% potassium sorbate (CH3-CH=CH-CH=CH=COOK) (T5), pasteurized watermelon juice +20% sucrose+0.1% potassium sorbate (CH3-CH=CH-CH=CH=COOK) (T6), pasteurized watermelon juice +0.05% sodium benzoate (C6H5COONa) +0.05% Potassium Sorbate (CH3-CH=CH-CH=CH=COOK) (T7), pasteurized watermelon juice +20% sucrose +0.05% sodium benzoate (C6H5COONa) +0.05% potassium sorbate (CH3-CH=CH-CH=CH=COOK) (T8), pasteurized watermelon juice +0.1% sodium benzoate (C6H5COONa) +0.1% potassium sorbate (CH3-CH=CH-CH=CH=COOK) (T9), pasteurized watermelon juice +20% sucrose +0.1% sodium benzoate (C6H5COONa) +0.1% potassium sorbate (CH3-CH=CH-CH=CH=COOK) (T10) and stored at refrigeration temperature (4-15°C) for a period of three months.Chemical analysis Inolab digital ph meter was used for pH determination. The Nelson-Somogyi method was used for the quantitative determination of reducing sugars. The reducing sugars when heated with alkaline copper tartrate reduce the copper from the cupric to cuprous state and thus cuprous oxide is formed. When cuprous oxide is treated with arsenomolybdic acid,the reduction molybdic acid to molybdenum blue takes place. The blue color developed is compared with asset of standards in a colorimeter at 620nm. The total soluble solids (TSS) were determined by using oven drying method [8].Microbial analysis: Total coliform count was performed by using most probable number technique (MPN). Total viable count by using nutrient agar media [9], total fungal count by using rose bengal agar [10], E.coli confirmation test by using eosin methylene blue agar, and Salmonella confirmation test by using SS agar were done after preparing and treating the juice.Statistical analysis: The data obtained was subjected to statistical analysis using RCBD (Randomized Complete Block Design) and the means were compared by using LSD (Least Significance Difference) test [11]. For all the analyses, the alpha error was set at 0.05%.

Source of Information: J. Sci. Res. 5 (2), 407-414 (2013)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Finally from the study it can be concluded that pasteurized juice with 20% sucrose, 0.05 or 0.1% sodium benzoate and 0.05 or 0.1% potassium sorbate were considered most acceptable by taking into account some chemical properties (pH, TSS, and reducing sugar content) and by consideration of the microbial load on comparison with other samples with three months storage.

Knowledge Management: Journal