Watermelon rind and its functional potential

Introduction:

In today’s market, agricultural products have its own importance and are becoming more demanding. Automation to manufacture such goods would be very helpful in growing its profitability. Watermelon is one of the growing agricultural produce in today’s market. Watermelon (Cucurbitaceae family and Citrullus lanatus species) is an important fruit widely distributed in tropical and subtropical regions. Watermelon or Citrullus Lanatus was found growing wild by Livingstone in 1854. Watermelon fruit is composed of flesh (68%), seeds (2%) and rind approximately 30% of the total mass of the fruit. It is one of the most important vegetable crops and has a broad, oval or oblong fruit shape; the skin is smooth, with dark green rind or often light green stripes which turn yellowish green when ripe with a very rich source of vitamins (Vitamin A 590 IU, Niacin 0.2mg/100 g and Vitamin C 0.77.0 mg/100g), and also serves as a great source of phytochemicals. It can also be used as an appetizer or snack for breakfasts. Citrulus lanatus is a common thirst quencher in hot summers. It has a source of carotenoid and lycopene. Lycopene is found to be protective against many types of cancers. Cucurbit seeds are a food source particularly of protein and oil. Watermelon is also known to be high in citrulline, an amino acid used to make arginine (another amino acid). During the urea cycle, arginine is used to extract ammonia from the bod. The watermelon fruit studies focused on the anti-nutritional phyto-chemical and anti-oxidant properties  also to enhance shelf-life and the fruit juice having the nutritional or quality content the rind (peels) that could facilitate their use or further use. The objective of this research work is to determine certain functional properties of the dried peel (rind) power extract with a view to harnessing it for consumption and potential industrial use. Watermelon fruit is a very pleasant fruit to eat in hot weather because it provides large amount of water and also the sweet taste is irresistible.

Total Phenolic Content in watermelon rind:

Watermelon is a fruit that member to the family of Cucumber ( Cucurbitacea ). It is huge, circular, elongated and rectangular in shape.The outside is smooth with dark green rind and when the watermelon ripe, it turns in yellowish green. It contain a large amount of Citrulin. The rind is used as vegetables and used in pickled or it is edible. Watermelon rind is fermented, mix with others and ingestable. The major phenolic content that are present in watermelon rind are Chlorogenic acid, Vanillic acid and sinapic acid.These are present in large amount in watermelon rind. Vanillin acid have high phenolic content while p-Coumaric acid and m-Coumaric acid have low phenolic content.

Phenolics	Concentration ( g )
Gallic acid	3.21-5.12
Quercitin	4.69-171.27
Caffiec acid	18.01-135.42
Vanillic acid	26.13-2317.01
Myricetine	16.18-135.18
Chlorogenic acid	115.60-1611.04
Syringic acid	ND*
p-Coumaric acid	0.50-2.51
m-Coumaric acid	1.81-14.96
Ferulic acid	ND*
Sinapic acid	113.01-241.12

The level and quantity of total phenolic content are fulfil by Avocado dry peel that give high phenolic content, higher the antioxidants volume and lower the value of fruit seed. The total phenolic content in red watermelon rind is 0.3669g and in yellow watermelon rind is 0.2273g. In commercial areas or in other way, the highest phenolic content in red watermelon was 0.0321g and in yellow watermelon was 0.0408g. The watermelon rind is dry and convert it into powder form and used in cake industries. In cakes 15% of water melon rind was used. Exchange of wheat flour by watermelon rind in cakes improved ash, fiber and phenolic contents. Watermelon rind contain nutrients and citrullin that gives it antioxidants effects and protect the human from free radical damage. Citrullin converts into arginine that are important for heart, circulatory system and immune system and relax the blood vessels.

There are four solvents are present in phenolic compounds that are present in the rind of watermelon. Ethanol, methanol, acetone and the mixtures of different solvents. These are the solvents that are extracted phenolic compounds from rind. Watermelon contain flesh, white rind and green rind. Highest phenolic content that are separated from green rind at 300°C for 30 minutes was 7626.52g and phenolic content that are separated from untreated green rind was 715.15g. The total phenolic content possessed by different methods such as Folin-Ciocalteu method, Aluminium chloride method and Free reducing antioxidant power. Methanol is more productive solvent that are used to produce highest phenolic content. At 40°C drying temperature show highest phenolic content.

Total sugar content in watermelon rind:

The sugar content that are present in watermelon rind are Glucose, Fructose and Sucrose. These sugars are more present in flesh as compared to rind. These sugars are also the source of phenolic content that present in watermelon rind. There are 30% of sugar are Sucrose that present in it. The viscosity of sucrose is decreased because of high temperature during osmotic dehydration that increase water loss by increasing diffusion coefficient in watermelon rind. The increase in sugar concentration by increasing solid gain. Higher the concentration of solid diffusion, higher the concentration of sugar.Watermelon rind have different flavors such as Vanilla, Pineapple, Strawberry, Lemon and no flavor due to the presence of sugars in watermelon rind. These flavors are used in the production of jams

The accurate composition of watermelon rind was Carbohydrate (80.75%), total sugar (0.47%) and total soluble sugar (1.42%). Functional properties of rind was water absorption capacity (7.13%), oil absorption capacity (1.65%), foaming capacity (5.65%), foaming stability (20.75%) and emulsion stability (0.28%). Quality and quantity of fruits are increased by the effect of gamma rays such as on watermelon rind. They increase fruit weight  and sugar content that are present in it. But in some cultivated plants, they decrease thickness. When sugar content increase in watermelon rind by gamma rays, inside material are not effect by this because their rind is so thick and when thickness of rind decrease, the quality of watermelon is too good to eat.

The total sugar content of sucrose, fructose and glucose are 24-91mg. The sugar are divided into sucrose, fructose and non-dominated groups. Total sugar content is inversely proportional to the high percentages of sucrose and fructose that are present in watermelon rind. Watermelon rind are use to make candy that are very tasteful due to the normal amount of sugars content that are present in watermelon rind and also use in making sugar syrups. In this using different levels of sugars that present in it to improve the sweetness and flavor of candy and sugar syrups.

Anti-Nutrient Components:

Saponin, alkaloid, tannins, phenols, flavonoid, cyanide, oxalate and phytate are the anti-nutrient contents of watermelon rind. Potassium permanganate titration method, iron chloride titration method and folin-ciocalteau method were use to determined the contents of oxalate, tannins and phytate. Decrease in the level of oxalate 92-96% for dried samples and 49-64% for roasted samples. Decrease in phytate levels 58-76% and 73-82% for dried and roasted samples. Decrease in tannins levels 15-35% and 23-38% for dried and roasted samples

Watermelon rind candies:

Osmotic dehydration method is used to prepare the watermelon rind candy. This process involves to slow down the soaking of syrup before drying at 50°C for 14, 18 and 20 hours. This drying effected on the moisture content of candy. Watermelon rind candy was dried for 14 hours. Candy products have no bacterial growth with longer shelf life because they contain 60-70% sugar and 0.4-0.6% water activity. Firming agents, preservatives, blanching and prickling are used in the production of watermelon rind candy. In starting, the moisture content is 15.6-16.15%, sugar content 79.78-81.63%, reducing sugar 55.56-58.71% and acidity is 0.54-0.88% are present in watermelon rind candy. Watermelon rind candy are packed in polyethylene pack.

                          Sensory scores of watermelon rind candy at different treatments    

Formulation	Color	Body	Texture	Taste	Overall
A	7.6	7.4	6.8	7	7.2
B	6.8	7.2	6.8	6.6	6.8
C	8.4	8.6	8.6	8.6	8.6
D	6.8	6.4	6.8	6.2	6.4

Only rind was used in preparation of candy. Green rind removed while white flesh is blanched in boiling water. After blanching cubes of rind dipped in the syrup that made with sugar, pectin and citric acid. The viscosity or thickness is increased by dip in syrup.

Watermelon rind Pickles:

The watermelon rind pickle was wet through lime, brine and water. Titrable acidity is 0.0094, pH 0.0042, color 0.0153, texture 0.0373 were different but viscosity 0.6603, total solids 0.1175 and moisture 0.2519 were not different. Thick and crispy rind are used in the production of pickle and the thickness was 10mm. Sweet and salty pickles were produced from watermelon rind and the white rind are used for this purpose (mesocarp).

Pickles added spices to meals and snacks. The mixture of spices, sugar and vinegar with watermelon rind for pickling gives texture, blurry and sweet-sour flavor. Fermented pickles, Fresh pickles, Fruit pickles and relishes are the types of pickles. By changing in amount of vinegar in pickles, we prevent the growth of Clostridium botulinum that are the type of food poisoning. The number of nitrites and nitrates in watermelon rind pickles as to potential human dietary health relevance. The method of pickling are time-consuming and include three steps: 1-Rind preparation and soaking pretreatment, 2-Brine preparation and 3-Canning and preserving method. The pH of product is below 4.6 by adding high amount of acid in brine to stop the growth of Clostridium botulinum.

Utensils, scales, jars, lids and water-bath canner are used in the production of pickles. Wash the rind with cold water and cleanup the jars properly. Pickle require heat treatment to kill microorganisms and to inactivate enzymes that cause spoilage and effect on texture, flavor and color.

Dehydrated wafers of watermelon rind:

Only rind was used in preparation of wafer. Green rind removed while white flesh is blanched in boiling water. After blanching cubes of rind dipped in the syrup that made with sugar, pectin and citric acid. The viscosity or thickness is increased by dip in syrup.

Osmotic dehydration method is used to prepare the watermelon rind dehydrated wafers. This process involves to slow down the soaking of syrup before drying at 50°C for 14, 18 and 20 hours. This drying effected on the moisture content of wafer. Watermelon rind wafer was dried for 14 hours. Wafer products have no bacterial growth with longer shelf life because they contain 60-70% sugar and 0.4-0.6% water activity. Firming agents, preservatives, blanching and prickling are used in the production of watermelon rind wafer. In starting, the moisture content is 15.6-16.15%, sugar content 79.78-81.63%, reducing sugar 55.56-58.71% and acidity is 0.54-0.88% are present in watermelon rind wafer. Watermelon rind wafer are packed in polyethylene pack.