Effect of blending, additives and storage conditions on the quality of watermelon nectar Harshata Pal, Ashis Kumar Banik and Nuchhungi Faculty of Horticulture Department of Post Harvest Technology of Horticultural Crops Bidhan Chandra Krishi Viswavidyalaya, Mohanpur-741252, India E-mail: harshata_sonai@yahoo.co.in ABSTRACT The impact of blending of nectar with coconut water, fortification with ascorbic acid and tocopherol and subsequent storage at low temperature (4-5OC) and room temperature (15-33OC) on the quality of nectar was evaluated. In most of the treatments, total soluble solids and reducing sugar content of the nectars increased during storage, whereas the total titratable acidity and lycopene content decreased. Blending and addition of tocopherol did not show improved effect on quality. Low temperature storage recorded better stability. Key words: Watermelon nectar; total soluble solid, reducing sugar, lycopene, titratable acidity, blending, additives, storage INTRODUCTION Watermelon (Citrullus lanatus) is an important cucurbitaceous crop, which is widely grown in our country and is highly relished due to its cool and thirst quenching property. The edible portion of the fruit forms about 60% of the whole fruit and juice is the major product for which the fruit is processed (Teotia et al, 1988). Watermelon juice contains a fair amount of vitamin ‘C’, Vitamin ‘A’ precursor (lycopene) and a high content of potassium, which is believed to have valuable diuretic properties (Gusina and Trostinskaya, 1974). Because of its high juice content, beverages such as nectars are the obvious choice, which will satisfy thirst, supplement nutritional requirements as well as help in stabilizing the market price. Blending of juice add variety in terms of flavour as well as nutritional value, and may result in product that possess the combined advantage of two or more fruits. Coconut water can be utilized in the processing industry for blending. Tender coconut water and pineapple juice, blended beverage can form an ideal health drink (Illaiaskutty et al, 2002). Teotia et al (1997) also observed that fortification of muskmelon RTS with ascorbic acid improved the quality of the beverage. In light of the above, the present study was carried out to prepare a stable beverage product from watermelon fruit. MATERIAL AND METHODS The experiment was conducted at the department of Post Harvest Technology of Horticultural Crops, Faculty Fig 1 Steps followed for processing of watermelon nectar of Horticulture, B.C.K.V., Mohanpur, Nadia, West Bengal. The nectars were prepared during the months of May and September 2006. Recipe The following different recipes were used for preparing watermelon nectars (Table 1) with different treatments so as to ascertain that the final product should contain 20% juice, 15% TSS and 0.3% acidity as per the Fruit Products Order specification for nectars. J. Hort. Sci. Vol. 2 (1): 38-43, 2007 Table 1. Different receipes used for preparing watermelon nectar Ingredients Watermelon nectar Watermelon juice and without blending coconut water blended (50:50) nectar Watermelon juice 200 ml 100 ml Coconut water — 100 ml Sugar 129.6 g 134.7 g Citric acid 3 g 3 g Water 667.4 ml 662.3 ml Finished product 1 litre 1 litre Treatments Control or ascorbic Control or ascorbic acid (0.25%)- 2.5 g/l acid (0.25%)- 2.5 g/l of finished product or of finished product or tocopherol- 400 mg/l of tocopherol- 400 mg/l finished product of finished product Table 2. Effect of blending, additives and storage condition on the total soluble solids (0Brix) content of watermelon nectar Blending Additives Storage Storage period (months) (watermelon juice: condition coconut water) 0 3 6 9 Effect of blending (watermelon juice: coconut water) 100 : 0 — — 16.9 17.0 17.0 17.1 50 : 50 — — 16.6 16.6 16.7 16.8 S.Em ± 0.027 0.015 0.015 0.021 CD (P=0.05) 0.079 0.044 0.044 0.063 Effect of additives — Ascorbic acid — 16.4 16.5 16.6 16.5 — Tocopherol — 16.5 16.6 16.7 16.9 — Control — 17.4 17.5 17.4 17.5 S.Em ± 0.033 0.018 0.018 0.026 CD (P=0.05) 0.096 0.052 0.054 0.077 Effect of storage condition — — RT 16.8 16.9 16.9 17.1 — — LT 16.8 16.8 16.8 16.9 S.Em ± 0.027 0.015 0.015 0.021 CD (P=0.05) NS NS 0.044 0.063 Effect of interaction 100 : 0 Ascorbic acid RT 16.8 17.0 17.2 17.0 100 : 0 Ascorbic acid LT 16.8 16.8 16.8 16.9 100 : 0 Tocopherol RT 16.4 16.6 16.7 16.9 100 : 0 Tocopherol LT 16.4 16.4 16.5 16.6 100 : 0 — RT 17.8 17.8 17.6 17.7 100 : 0 — LT 17.8 17.8 17.7 17.7 50 : 50 Ascorbic acid RT 16.0 16.1 16.2 16.2 50 : 50 Ascorbic acid LT 16.0 16.1 16.1 16.0 50 : 50 Tocopherol RT 16.8 16.7 16.8 17.2 50 : 50 Tocopherol LT 16.8 16.9 16.7 17.0 50 : 50 — RT 17.0 17.2 17.3 17.6 50 : 50 — LT 17.0 17.0 0.037 17.2 S.Em ± 0.067 0.037 0.108 0.053 CD (P=0.05) NS 0.108 0.108 NS RT = Room temperature (150-310C) LT = Low temperature (40-50C) NS = Non-significant J. Hort. Sci. Vol. 2 (1): 38-43, 2007 39 Stable beverage product from watermelon TSS content of extracted watermelon juice - 10.2°Brix TSS content of watermelon juice: coconut water mixture - 7.5°Brix Acidity of watermelon juice - 0.02% Acidity of watermelon juice: coconut water mixture - 0.02% Total soluble solids was determined using an Erma hand refractometer. Titratable acidity, reducing sugar and lycopene content were estimated following AOAC (1984). Statistical analysis was carried out according to Gomez and Gomez (1983). Completely Randomized Design was followed for data interpretation. Sensory evaluation The samples were evaluated by a panel of ten judges for three quality parameters viz., colour, taste and flavour with a possible scores of 40, 30 and 30, respectively. RESULTS AND DISCUSSION Total soluble solids (TSS) TSS content during storage increased (Table 2) more prominently in the nectar blended with coconut water compared to the unblended samples. Storage under low temperature condition (4°-5°C) showed less change in TSS content as compared to the room temperature (15°-33°C) stored samples. The unblended watermelon nectars fortified with ascorbic acid and stored under low temperature condition (4°-5°C) showed minimum change in TSS content during storage whereas the unblended watermelon nectar with tocopherol treatment and stored under room temperature condition (15°-33°C) showed maximum change in TSS content during the nine months of storage. The increase in soluble solid content of the nectars during Table 3. Effect of blending, additives and storage condition on the reducing sugar content (%) of watermelon nectar Blend Additives Storage Storage period (months) (watermelon juice: condition coconut water) 0 3 6 9 Effect of blending (watermelon juice : coconut water) 100 : 0 — — 8.26 8.41 8.57 8.73 50 : 50 — — 8.05 8.20 8.40 8.58 S.Em ± 0.019 0.006 0.021 0.003 CD (P=0.05) 0.057 0.018 0.062 0.009 Effect of additives — Ascorbic acid — 8.22 8.32 8.49 8.58 — Tocopherol — 7.66 7.88 8.11 8.28 — Control — 8.59 8.72 8.86 9.10 S.Em ± 0.024 0.007 0.026 0.004 CD (P=0.05) 0.071 0.022 0.076 0.012 Effect of storage condition — — RT 8.17 8.37 8.63 8.86 — — LT 8.14 8.25 8.34 8.45 S.Em ± 0.019 0.006 0.021 0.003 CD (P=0.05) NS 0.018 0.062 0.009 Effect of interaction 100 : 0 Ascorbic acid RT 8.69 8.83 8.78 9.24 100 : 0 Ascorbic acid LT 8.69 8.71 8.28 8.82 100 : 0 Tocopherol RT 7.80 8.04 8.02 8.51 100 : 0 Tocopherol LT 7.80 7.98 8.82 8.17 100 : 0 — RT 8.21 8.58 8.24 9.22 100 : 0 — LT 8.21 8.35 8.14 8.47 50 : 50 Ascorbic acid RT 7.76 7.92 7.97 8.28 50 : 50 Ascorbic acid LT 7.76 7.82 8.08 8.02 50 : 50 Tocopherol RT 7.52 7.81 7.90 8.43 50 : 50 Tocopherol LT 7.52 7.71 9.24 8.08 50 : 50 — RT 8.89 9.02 9.07 9.53 50 : 50 — LT 8.89 8.95 0.052 9.20 S.Em ± 0.048 0.015 NS 0.008 CD (P=0.05) NS 0.043 0.024 RT = Room temperature (150-310C) LT = Low temperature (40-50C) NS = Non-significant storage may be attributed to partial hydrolysis of complex carbohydrates (Awan et al, 1980). Similar observation in storage of squashes of orange, lemon and bael fruits were reported by Jain et al (1984). Reducing sugar The reducing sugar content of watermelon nectars showed an increasing trend during storage irrespective of the treatments and storage conditions (Table 3). However, this change was slightly higher in the blended watermelon nectars as compared to the unblended materials. Fortification with ascorbic acid showed lesser change in reducing sugar as compared to those fortified with tocopherol or without fortification (control). The change in reducing sugar was also comparatively slower under low temperature storage than under room temperature storage J. Hort. Sci. Vol. 2 (1): 38-43, 2007 40 Harshata Pal et al Table 4. Effect of blending, additives and storage condition on the titratable acidity (%) of watermelon nectar Blend Additives Storage Storage period (months) (watermelon juice: condition coconut water) 0 3 6 9 Effect of blending (watermelon juice : coconut water) 100 : 0 — — 0.45 0.43 0.38 0.34 50 : 50 — — 0.41 0.39 0.36 0.31 S.Em ± 0.002 0.003 0.005 0.002 CD (P=0.05) 0.006 0.007 0.016 0.006 Effect of additives — Ascorbic acid — 0.45 0.42 0.40 0.36 — Tocopherol — 0.39 0.37 0.33 0.27 — Control — 0.45 0.43 0.38 0.35 S.Em ± 0.002 0.003 0.007 0.303 CD (P=0.05) 0.006 0.007 0.020 0.008 Effect of storage condition — — RT 0.43 0.40 0.36 0.30 — — LT 0.43 0.42 0.39 0.35 S.Em ± 0.002 0.003 0.005 0.003 CD (P=0.05)! NS 0.007 0.016 0.007 Effect of interaction 100 : 0 Ascorbic acid RT 0.45 0.42 0.38 0.32 100 : 0 Ascorbic acid LT 0.45 0.44 0.42 0.41 100 : 0 Tocopherol RT 0.40 0.38 0.29 0.24 100 : 0 Tocopherol LT 0.40 0.39 0.34 0.28 100 : 0 — RT 0.51 0.48 0.41 0.37 100 : 0 — LT 0.51 0.49 0.44 0.40 50 : 50 Ascorbic acid RT 0.46 0.41 0.38 0.32 50 : 50 Ascorbic acid LT 0.46 0.44 0.42 0.38 50 : 50 Tocopherol RT 0.39 0.35 0.32 0.26 50 : 50 Tocopherol LT 0.39 0.37 0.35 0.30 50 : 50 — RT 0.40 0.38 0.34 0.29 50 : 50 — LT 0.40 0.38 0.35 0.33 S.Em ± 0.005 0.006 0.014 0.006 CD (P=0.05) NS NS NS 0.017 RT = Room temperature (150-310C) LT = Low temperature (40-50C) NS = Non-significant which is in agreement with the findings on watermelon juice made by Chahal and Saini (1999) and also on mango nectar by Sahni and Khurdiya (1989). Increase in reducing sugar during storage was observed in watermelon juice by Bawa and Bains (1977) and also in muskmelon RTS (Teotia et al, 1997). The increase in reducing sugars during storage may be attributed to hydrolysis of non-reducing sugars to reducing sugars, and a higher storage temperature and acidity accelerated the process of hydrolysis (Sahni and Khurdiya, 1989). Among all the treatments, there was minimum increase in reducing sugar content in the unblended watermelon nectar which was fortified with ascorbic acid and stored under low temperature (4°-5°C). Maximum increase in reducing sugar content was recorded in the watermelon nectar blended with coconut water and fortified with tocopherol and stored at room temperature (15°-33°C). Total titratable acidity The total titratable acidity of the watermelon nectars decreased throughout the period of storage for six months irrespective of the treatments and storage conditions (Table 4). The decrease in acidity of the nectars during storage was more rapid in the nectars with coconut water than in unblended samples. There was a significant difference in acid levels during storage with addition of different additives. The addition of ascorbic acid showed a slower lower change in the acid content as compared to the control and the tocopherol treatment showed a rapid increase in acidity during storage. Low temperature storage (4°-5°C) a significantly reduction in acid content as compared to the room temperature storage (15°-33°C). Least change in total titratable acidity was recorded in the unblended watermelon nectar with ascorbic acid fortification and storage under low temperature for nine J. Hort. Sci. Vol. 2 (1): 38-43, 2007 41 Stable beverage product from watermelon months. Bawa and Bains (1977) also observed a slight decrease in acidity of stored watermelon juice. Lycopene content The lycopene content of the watermelon nectars decreased during storage for nine months both under low temperature (4° - 5°C) and room temperature (15° - 33°C) conditions (Table 5). The rate of decrease in lycopene content was slightly lower in the unblended watermelon nectars than those blended with coconut water. The nectars under room temperature storage (15° - 33°C) also showed slightly higher rate of decrease in lycopene content as compared to the nectars under low temperature storage (4° - 5°C). Gowda and Jalali (1995) also reported decrease in lycopene content of watermelon juice in storage. Lycopene is the dominant pigment found in watermelon juice which is responsible for the red colour (Huor et al, 1980). Table 5. Effect of blending, additives and storage condition on the lycopene content (mg/100 ml) of watermelon nectar Blend Additives Storage Storage period (months) (watermelon juice: condition coconut water) 0 3 6 9 Effect of blending (watermelon juice : coconut water) 100 : 0 — — 564 517 457 423 50 : 50 — — 396 363 326 293 S.Em ± 0.373 0.479 0.497 0.437 CD (P=0.05) 1.086 1.396 1.447 1.274 Effect of additives — Ascorbic acid — 488 453 394 367 — Tocopherol — 463 418 375 344 — Control — 487 449 405 362 S.Em ± 0.456 0.587 0.608 0.536 CD (P=0.05) 1.329 1.711 1.771 1.561 Effect of storage condition — — RT 479 444 388 354 — — LT 479 436 394 361 S.Em ± 0.373 0.479 0.497 0.437 CD (P=0.05) NS 1.396 1.447 1.274 Effect of interaction 100 : 0 Ascorbic acid RT 581 549 408 402 100 : 0 Ascorbic acid LT 581 543 517 486 100 : 0 Tocopherol RT 538 492 441 403 100 : 0 Tocopherol LT 538 481 432 397 100 : 0 — RT 572 523 481 425 100 : 0 — LT 572 517 464 423 50 : 50 Ascorbic acid RT 396 357 331 291 50 : 50 Ascorbic acid LT 396 363 321 289 50 : 50 Tocopherol RT 388 361 324 299 50 : 50 Tocopherol LT 388 341 303 278 50 : 50 — RT 403 385 345 302 50 : 50 — LT 403 372 331 297 S.Em ± 0.919 1.174 1.217 1.071 CD (P=0.05) NS 3.422 3.546 3.121 RT = Room temperature (150-310C) LT = Low temperature (40-50C) NS = Non-significant Sensory quality Data presented in Table 6 revealed that the sensory quality of watermelon nectars of different treatments maintained acceptable quality during the entire period of storage for nine months at low temperature condition (4o - 5o C). However, under room temperature condition (15o to 33o C) the quality was maintained upto six months of storage only. The quality rating of watermelon nectars of different treatments decreased with increase in duration of storage. The unblended watermelon nectar with ascorbic acid treatment stored under low temperature condition showed maximum quality rating of 91 at nine months of storage. The watermelon nectar with different treatments maintained higher scores of quality ratings i.e., above 70 at nine months of storage at low temperature. J. Hort. Sci. Vol. 2 (1): 38-43, 2007 42 Harshata Pal et al Thus, the total soluble solids and reducing sugar content of nectars increased during storage, whereas the total titratable acidity decreased. On the other hand, the lycopene content of the nectars decreased during storage irrespective of the storage condition. Blending watermelon with coconut water juice and supplementation with toopherol did not improve quality. ACKNOWLEDGEMENT We are thankful to Dr. A. K. Banik, Chairman of my Advisory Committee and other associates in the project. REFERENCES A. O. A. C. 1984. Official methods of analysis, 14th edition. Association of official Agricultural Chemistry, Washington D.C. pp 16. Awan, J. A., Folaye, C. A. and Okaka, J. C. 1980. Effect of bottle colour and storage conditions on the quality of soursap (Annona muricata). J. Food Sci. Technol., 17: 251-53. Bawa, A. S. and Bains, G. S. 1977. Integrated processing of watermelons for juice and seed. Ind. Food Packer, 31: 12-15. Chahal, G. S. and Saini, S. P. S. 1999. Storability of juice from New Hybrid watermelon variety. Ind. Food Packer, 53: 12-17. Gomez, K. A. and Gomez, A. A. 1983. Statistical procedures Table 6. Effect of blending, additives and storage condition on sensory quality scores of watermelon nectar Blend Additives Storage Scores of sensory quality at different storage period (watermelon juice: condition (months) coconut water) 0 3 6 9 100:0 Ascorbic acid RT 97 95 88 48 100:0 Ascorbic acid LT 97 97 95 91 100:0 Tocopherol RT 96 90 87 43 100:0 Tocopherol LT 96 96 93 85 100:0 - RT 97 92 85 47 100:0 - LT 97 97 94 83 50:50 Ascorbic acid RT 83 77 72 24 50:50 Ascorbic acid LT 83 83 82 71 50:50 Tocopherol RT 84 75 70 43 50:50 Tocopherol LT 84 84 81 70 50:50 - RT 84 77 70 29 50:50 - LT 84 84 81 71 RT = Room temperature (150-310C) LT = Low temperature (40-50C) for Agricultural Research. An IRRI Book, John Wiley and Sons, New York. Gowda, I. N. D. and Jalali, S. 1995. Studies on juice making from watermelon fruits. Ind. Food Packer, 49 : 33-41. Gusina, G. B. and Trostinskaya, L. O. 1974. Watermelon juice with pulp. Konserv. i Ovoschesuch. Prom., 3: 17-18. Huor, S. S., Ahmed, E. 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