STANDARDIZATION AND CHARACTERIZATION OF VALUE ADDED WATERMELON JUICE (Citrullus lanatus) READY-TO-SERVE BEVERAGE

An experiment was conducted to study the feasibility of blending pineapple and watermelon juice in different ratio for preparation of blended RTS beverage. The formulated RTS beverages were evaluated for various chemical, organoleptic and microbial qualities. The titrable acidity, ascorbic acid, total soluble solids (TSS) and total sugars of freshly made RTS beverages increased while pH decreased with the increased concentration of pineapple juice from 10-30%. Tukey’s test results revealed that, the mean scores for all assessed organoleptic characters varying significantly (pH0.05) in the freshly made pineapple blend watermelon RTS beverages. The formulated beverage with 80:20 watermelon and pineapple juice was found to be superior in quality and could be stored at 30±1°C for a minimum period of three months without any significant changes in quality attributes.


INTRODUCTION
Fruit and Vegetable sector has much potential to contribute to increase the level of national income, export revenue, generate new employment opportunities, increase farm income and enhance the nutrition and health of the people. The potential for cultivating fruit and vegetable crops for the domestic and export markets is high. Sri Lanka's per capita consumption of fruits and vegetables remains far below the required average daily intake. According to Medical Research Institute (2011), the daily per capita requirement of fruits for a balanced diet should be 30-40g (edible portion), which is approximately equivalent to 25-40 kg fresh fruit per head per year.
Consuming fruits and vegetables of all kinds has long been associated with a reduced risk of many lifestyle-related health conditions. Watermelon (Citrullus lanatus) is an important cucurbitaceous crop, whose fruits serve as a dessert to the common people in summer. These fruits are available in May to June in the markets throughout Sri Lanka.
Watermelon is consumed as a fresh fruit and for its dry seeds. The watermelon fruit contains 93% water, with small amounts of protein, fat, minerals, and vitamins. The major nutritional components of the fruits are carbohydrates, especially sugars (6.4g/100g), vitamin A (590 IU), and lycopene (4,100μg/100g, range 2,300-7,200), an anticarcinogenic compound found in red flesh watermelon (USDA Nutrient Database, 2009). Only a few studies have dealt with drying of watermelon, mainly with osmotic dehydration of the pulp (Falade et al., 2007) and spray-drying of the juice (Quek et al., 2007).
Pineapple (Ananas comusus) belongs to the family of Bromeliaceae.
The fibrous flesh of pineapple is yellow in colour and has a vibrant tropical flavour that balances the tastes of sweet and tart. It is an excellent source of vitamin C which is required for the collagen synthesis in the body. It is also available in the same season from May to June of which watermelon are available in Sri Lanka.
Juice blending is one of the best methods to improve the nutritional quality of the juice. It can improve the vitamin and mineral content depending on the kind and quality of fruits and vegetables used (De Carvalho et al., 2007). Apart from nutritional quality improvement, blended juice can be improved in its effects among the variables, thus it cannot depict the net effects of various parameters on the reaction rate. Moreover, one could think of a new product development through blending in the form of a natural health drink, which may also be served as an appetizer. The watermelon fruit juice blend that could lower the risk of cardiovascular disease has been created by Cyril et al. (2009).
Polyphenols are found in fruits as diverse in red watermelon. Their beneficial effect on health is well known, with a diet rich in polyphenols correlating with a reduced risk of cardiovascular disease.
According to the Sri Lanka Standard Institute specifications, RTS fruit beverage should not exceed its total acidity more than 1% (as anhydrous citric acid). The fruit and sugar content should not be less than 5% by mass and preservatives should not exceed the limit of Sulphur dioxide (70 ppm) and benzoic acid (120 ppm). Adding preservatives such as Sulphur dioxide and benzoic acid can increase the shelf life of RTS beverages. Colouring matter and clarifying agents can be added to the product, to increase attractiveness and addition of flavouring ingredients is allowed only in the product prepared by using mango.
Therefore, this research was carried out to formulate an acceptable quality of RTS beverage using watermelon and pineapple at different combinations considering SLS requirements and to assess the chemical, organoleptic and microbial qualities of pineapple blend watermelon RTS beverage after formulation and during storage.

MATERIALS AND MEEHODS
Undamaged, disease free, healthy, mature and ripe watermelon (Variety -Thillina) and pineapple (Variety -Mauritius) fruits were purchased from the Commercial Horticultural Farms of the Department of Agriculture, Sri Lanka.

Juice preparation
Fruits were washed with clean running water to remove dust particles and to reduce the microbial load on the surface of the fruits. Peeled pineapples were crushed with mixer cum juicer for the extraction of juice. Watermelons were cut with the help of stainless steel knives into pieces and seeds were removed manually. The fleshes were passed through the juicer for extraction of juice. Six formulations were prepared by mixing watermelon juice and pineapple juice in different ratios with sugar, acidity as anhydrous citric acid and 70 ppm of potassium metabisulphite (KMS). The amount of added sugar, citric acid and potassium metabisulphite were kept as same for each treatment.
The prepared beverages were filtered through the strainer (200 µm) to get a clarified juice and filled in previously sterilized glass bottles (200 ml) leaving 2.5 cm head space and sealed airtight by crown corking covered with aluminium foil. Then the bottled juice were sterilized at 105°C for 10 min and cooled to room temperature of 30±1°C.
The following treatment combinations were formulated: Ascorbic acid content of beverages was titrimetrically estimated by indophenol dye method. The pH was determined by an Electronic pH meter (Mettler Toledo, UK). Lane-Eynon method was performed to determine the total sugar content of the formulated beverages.
Hand-held refractometer (ATAGO-S-28Emodel) was used to estimate the total soluble solids (TSS) and the values were expressed as °Brix.
The analyses were replicated thrice.

Microbial Test
The prepared beverages were studied for microbial quality and safety.
The total microbial load was calculated by standard plate count method. The standard plate count was done according to the method described by Arachchi (2003) in raw mango RTS beverages.

Sensory Evaluatio
In sensory evaluation, the samples were subjected to nine-point hedonic scale test and the acceptability of samples was judged by 11 trained panelists to determine sensory preference. The sensory characteristics such as colour, flavour, taste, thickness and overall acceptability of the RTS beverages were judged by the panelists.

Shelf Life Evaluation
RTS beverages were subjected to storage studies at room temperature for a period of 3 months by drawing samples at bimonthly intervals to evaluate changes in chemical, organoleptic parameters and microbial spoilage.

Statistical Analysis
Data obtained in chemical analysis were subjected to Analysis of Variance (ANOVA) and mean separation was done with Duncan's Multiple Range Test (DMRT). Descriptive statistics was done on sensory attributes and the means were compared using the Tukey's test (p<0.05).

Titrable Acidity
According to the Sri Lanka Standard Institute Specifications, the limits of acidity for RTS preparation are 0.3-1% as anhydrous citric acid (SLS 729:1985). The titrable acidity of the RTS beverage samples varied significantly and increased from 0.16 to 0.42% with increase the concentration of pineapple juice from 10 to 30% as shown in Figure 1.
This can be attributed partly to the contribution of the inherent acid naturally present in the pineapple juice. Pineapple is acidic, which 87 % is citric acid and 13 % is malic acid. According to Samson (1986), the fresh pineapple juice has 0.7-1.6 g citric acid /100 ml.
Note: The values are means of triplicates Vertical bars indicate the standard errors.

Ascorbic Acid
Note: The values are means of triplicates Vertical bars indicate the standard errors.
Ascorbic acid is an essential nutrient for humans because it aids in the synthesis of collagen in addition to protecting against oxidative damage. Watermelon juice contains 5.81 mg/100 ml of ascorbic acid (Patil, 2000). The ascorbic acid content increased significantly from 5.64 to 15.63 mg/100 ml with an increase in the concentration of pineapple juice from 10 to 30% in the RTS beverage formulations (Figure: 2). These findings are reported that maximum ascorbic acid (15.9 mg/100 ml juice) was recorded in RTS beverage with 70% watermelon juice and 30% pineapple juice.  The results generally showed that the higher acidity, lower pH of pineapple RTS beverages. Similar study conducted by Awsi Jan and Dorcus (2012) found that there is a corresponding reduction in pH as the acidity increased in pineapple Juice blend with carrot and orange juice.

Total Sugar
Sugars, acids and their interactions are important to sweetness, sourness and overall acceptability in RTS beverages. The minimum total sugar content (as sucrose) for RTS preparation is 5% (SLS 729:1985). Sugars, acids and their interaction are important to sweetness, sourness and overall acceptability in RTS beverages. As shown in Figure: 3, the total sugar content of watermelon was 5.25%.
Schmidt et al, (2005) found that the watermelon juice contained 32.2% fructose, 9.3% glucose, and 27.1% sucrose for a total of 68.6% of sugars on a dry matter basis.
Note: The values are means of triplicates. Vertical bars indicate the standard errors. According to DMRT, the total sugar significantly (p<0.05) differed between each treatment. The treatment T6 had highest mean value and the treatment T1 (RTS beverage with 100%watermelon juice) had a least mean value at 5% level of significance.

Total Soluble Solids (TSS)
TSS:Acid ratio is often better related to palatability of the fruits than either sugar or acid alone. The recommended TSS for commercial RTS production is 15°Brix (SLS 729: 1985).

Microbial Test for Freshly Made RTS Beverages
In the freshly made beverages, no bacterial growth was observed immediately after formulation. Therefore, there was no total plate count in these samples. Carter et al. (2007) reported that many products that could safely be maintained sterile by pasteurization process alone could be doubly preserved by the addition of potassium metabisulphite.
The sulphite inhibits yeasts, moulds and bacteria (Doughari and Elmahmood, 2007). Therefore, the heat treatment was sufficient to destroy initial microbial load in the formulated fruit drinks.

Sensory qualities of Freshly Made RTS Beverages
Sensory evaluation was made through panel of 11 trained judges. The panel evaluated colour, flavour, taste, thickness and overall acceptability. A 9-point hedonic scale was used for this purpose. As shown in Figure: 4, the sensory evaluation of the RTS beverage revealed that, there were significant differences between the treatments as the concentration of pineapple juice was increased from 10 to 30% for colour, flavour, taste, thickness and overall acceptability at 5% level of significance according to General Linear Models (GLM).

CONCLUSION
Based on the chemical analysis of the freshly made RTS beverages, there were significant increase in titrable acidity, ascorbic acid, total sugar and total soluble solids (TSS) and a significant decrease in pH with the increase in the concentration of pineapple juice from 10 to 30% in RTS beverages. According to the microbial test, the total plate There was no drastic effect on the quality of the product due to microbial growth in three months at ambient temperature. Therefore, it is safe for consumption upon three months of storage. The sensory analysis revealed that, there were significant (p˂0.05) differences for the organoleptic characters between the treatments. According to Tukey's test, the highest overall acceptability was observed in the RTS beverage with 80% watermelon juice and 20% pineapple juice. The RTS beverage with 100% watermelon juice had low organoleptic characters and overall acceptability than the other RTS beverages.
Therefore, the RTS beverage formulated with 80% watermelon juice and 20% pineapple juice is the best combination for the commercial preparation of pineapple blend watermelon RTS beverage without any significant changes in the nutritional, chemical and sensory characteristics with extended shelf life.