The aim of the current study was to develop low-calorie nectar from snap melon and gac fruit and assess the changes in physicochemical, microbiological and organoleptic characteristics during storage at ambient (34 ± 2°C) and refrigerated conditions (5 ± 2°C) for a duration of three months. Storage of the samples in ambient and refrigerated conditions appeared to be safe from a microbiology perspective. The physico-chemical parameters of the nectar, such as pH, TSS, viscosity, and colour values, decreased, while the titratable acidity increased in the nectar during the course of storage. Moreover, ascorbic acid, phenols, β carotene, lycopene, antioxidant activity, and energy values decreased in the nectar during the storage period. In addition, the reduction in bioactive constituents was more rapid under ambient storage than in refrigerated storage conditions.
Research Article
Development of nectar from snap melon, gac fruit and steviol glycosides: changes in physico-chemical properties, antioxidant potential, sensory and microbial qualities during storage
https://doi.org/10.21203/rs.3.rs-4983838/v1
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snap melon
gac fruit
bioactives
antioxidant activity
sensory quality
microbial quality
A recent survey revealed that over one-third of the world's malnourished children reside in India [1]. Vegetables are key sources of nutraceuticals in a balanced human diet, with those from the Cucurbitaceae family being particularly beneficial. Cucurbits hold significant potential to address malnutrition among children in India. Extensive research has demonstrated that cucurbit vegetables have purgative, anti-inflammatory, anti-diabetic, and antioxidant properties. These vegetables are rich in phytochemicals, terpenoids, carotenoids, and saponins [2].
Snap melon (Cucumis melo var. momordica) (known as "Phoot" in North India, which translates to "To split") is a prominent Cucurbitaceous crop grown worldwide and is crucial for global trade. India, as a secondary center of origin, has not fully exploited this crop, which encompasses almost 40 species. Snap melon is known as Kanivellari (fruit cucumber) or Pottuvellari (split/crack cucumber) in Kerala, and is grown in the districts of Thrissur, Ernakulam, and Malappuram. Snap melon is a rich source of nutrients, including vitamin C, sugars, minerals, and dietary fiber. The ripe fruits of snap melon are known for their tendency to split or crack, which leads to high perishability and significant post-harvest losses. Therefore, it is crucial to process them into value-added products to reduce these losses.
Momordica cochinchinensis (Spreng.) commonly known as Gac in Vietnam, is a diverse cucurbit species that is widely grown in India, Malaysia, and Southeast Asia. This fruit is nutritionally unique due to its high content of carotenoids, especially lycopene and β-carotene, found in the aril (the flesh surrounding the seeds). Gac fruit is primarily used to produce gac powder and gac oil, which serve as natural colorants, nutritional supplements, and medicinal products [3]. Compared to other well-known fruits and vegetables, Gac fruit is one of the richest natural sources of carotenoids [4] [5]. Gac fruit has recently been used to make a variety of dishes, including pasteurized juice and drinks. Consequently, the food industry may find it advantageous to use Gac fruit in the production of functional beverages.
In recent times, health of humans has become a major concern globally. With the rise in health issues each year, many individuals are shifting towards healthy and natural foods. Consequently, people now seek foods that not only taste good but also contain numerous functional components. One such natural plant-derived sweetener with many functional benefits is stevia. Stevia leaves are sweet because they contain steviol glycosides, such as stevioside, rebaudioside (A–F), steviolbioside, and isosteviol. These glycosides are used commercially throughout the world to replace sugar in a variety of foods, drinks, and medications. All significant regulatory bodies worldwide have allowed the use of high-purity steviol glycosides as sweeteners, and more than 150 nations have accepted or embraced their usage in foods and drinks [6].
Blending gac fruit with snap melon could result in the creation of tasty drink with excellent organoleptic quality along with high nutritional content. Sweetening this drink with steviol glycosides will make the drink low calorie in nature. Hence the objective of the present study was to develop a functional drink rich in bioactive compounds, without synthetic preservatives and to determine the changes in the quality of the product during storage, besides adding diversity to the existing list of functional beverages from fruits and vegetables.
Sample preparation
Fresh snap melon fruits were purchased from the market, and gac fruit was collected from a farmer in its horticulturally mature stage. Fresh leaves of stevia for extraction of steviol glycosides were grown in the field maintained by the Department of Postharvest Management, College of Agriculture, Vellanikkara. Steviol glycosides were extracted from stevia fresh leaves which were sorted, and washed with tap water. They were moderately ground without agitation, followed by soaking in hot tap water at 75°C for 20 minutes, at a ratio of 200 g/L for extraction of steviol glycosides, without the use of any additional energy source (Figures 1 &2). The leaves were subsequently strained and filtered [7].
Development of nectar from blends of snap melon and gac fruit
The snap melon juice was substituted with 25%, 50%, and 75% of gac fruit aril juice, followed by addition of steviol glycosides and acid lime juice. The best combination among these was selected based on organoleptic evaluation on 9-point hedonic scale. The combination containing 75% snap melon juice and 25% gac aril juice (75% SM & 25% GF) blend obtained highest overall acceptability scores in preliminary trials and this blend was selected for the preparation of nectar. Three combinations of nectar were prepared. Conventional nectar was developed with 20% juice (75% SM & 25% GF), 15° Brix (sucrose) and 0.25% citric acid (T1). Nectar was also made from pure snap melon juice (20%), with 15° Brix (sucrose) and 0.25% citric acid (T2). For the low-calorie nectar, 20% juice (75% SM and 25% GF) was combined with stevia extract (10%) and acid lime juice (2.5%) (T3). The three formulations of nectar were pasteurized and subsequently stored under ambient (34±2°C) and refrigerated (5±2°C) conditions (Figure 6). The qualitative changes were recorded at monthly intervals for 3 months.
Physico-chemical analysis
pH, TSS and acidity: The pH values were measured with a standard digital pH meter. Total soluble solids (TSS) were determined using digital refractometer (Atago, Japan), with results expressed in degree Brix (°Brix). Titratable acidity was assessed using a standard alkali solution (0.1N NaOH) with phenolphthalein as indicator, and the results were presented as a percentage [8].
Colour values (L*,a*,b*): A Minolta CM-3600D spectrophotometer (Konica Minolta Sensing, Inc., Osaka, Japan) was used to measure the samples' color in terms of L*, a*, and b*. The light was provided by a D65 lamp as standard. The JAYPAK 4804 application (Quality Control System, Version 1.2) examines the color values based on the CIELAB color space. In color values, L* represents lightness, a* denotes redness/browning, and b* denotes yellowness.
Viscosity (cP): Viscosity is measured by using low-viscosity model viscometer (Ametek Brookfield DVE viscometer, USA) with four spindles and a narrow leg.
Viscosity in cP (mPa*s) = Dial reading x factor
Ascorbic acid (mg/100g): The ascorbic acid content was measured using a titrimetric method with 2,6-dichlorophenol indophenol dye (DCPIP), with the sample extracted with 3% metaphosphoric acid. The endpoint was reached when the excess unreduced dye turned rose pink in the acidic solution [9].
Total phenolics (mg/100g): The total phenol content was determined using the Folin-Ciocalteu reagent (FCR) following the method described by Asami et al. [10]. In this process, phenols in the sample react with phosphomolybdic acid in an alkaline medium to form a blue-colored compound. The spectrophotometer was set to 650 nm, and the color intensity was measured against a blank reagent.
β carotene and lycopene (mg/100g): The β-carotene and lycopene content in the samples were analyzed using the method outlined by Vieira et al. [11]. The sample was mixed with a solvent mixture of acetone and hexane in a 4:6 (v/v) ratio. The mixture was then centrifuged for one minute at 15,000 rpm. To determine the amount of β-carotene and lycopene in the sample, absorbance (A) values at 453 nm and 505 nm were recorded, and the quantification of carotenoids was done by using the following equations.
Cβ-carotene = 4.624 x A453 – 3.091 x A505
CLycopene = 3.956 x A453 – 0.806 x A505
Antioxidant activity (DPPH) ( values): The sample's antioxidant activity was estimated using DPPH (2,2-diphenyl-1-picrylhydrazyl) reagent by the method prescribed by Tansku et al.[12]. Different volumes of standards and samples were pipetted, followed by the addition of 2.8 ml of methanol and 0.2 ml of DPPH (50µM) reagent to each. The mixture was homogenized and left in the dark for 20 minutes. Absorbance at 517 nm was measured using a UV-Visible 1800 spectrophotometer from Shimadzu, Kyoto, Japan. The antioxidant activity of the sample was evaluated based on its ability to inhibit DPPH radical absorption. The percentage of DPPH inhibition was calculated using the following formula.
Energy values (kcal): The energy value of the sample was determined by multiplying the amounts of protein [8], fat (Soxhlet extraction), and carbohydrates by factors of 4, 9, and 4, respectively.
Energy (kcal) = (Carbohydrate x 4) + (Fat x 9) + (Protein x 4)
Microbiological analysis (Bacteria, fungi, yeast): Microbiological quality was assessed by counting the total number of microorganisms (CFU). All analyses were performed in triplicate in each of the packaged sample.
Sensory analysis: A panel of fifty people from different age groups was selected to rate the nectar on a 9-point hedonic scale according to appearance, colour, flavour, taste, aftertaste, body/consistency, aroma, and overall acceptability. A score of 5.5 or higher was considered acceptable [13]. Panelists scored the samples according to their degree of acceptability using a nine-point hedonic scale in order to assess the sensory qualities.
Statistical analysis: For testing each quality parameter, five replication were taken and the data was expressed on the basis of mean and standard deviation (SD). A two-way analysis of variance (ANOVA) was done using completely randomised design (CRD).
Physico-chemical analysis
Snap melon and gac fruit were harvested at the horticultural mature stage, and their proximate composition was recorded and presented (Table 1.). Snap melon had the highest moisture content of 95.38% and titratable acidity of 0.64%. Gac fruit aril recorded highest total soluble solids content of 7.5°Brix, pH of 5.78, ascorbic acid content of 44.8 mg/100g, total phenolic content of 95 mg/100g, β carotene and lycopene content of 1.23 and 1.63 mg/100g respectively. β carotene and lycopene was not detected in snap melon. The radical scavenging activity IC50 value (DPPH) of snap melon was 14.66 µg/mL, while that of gac fruit was 8.94 µg/mL.
The initial pH values of nectar varied significantly from 2.69 to 4.56 (Table 2.) among the treatments. Also, pH values decreased significantly during the storage period. The treatment T3 recorded the highest pH of 4.56, followed by T1 at 2.69. T2 which was the nectar developed from pure snap melon juice sweetened with sucrose had the lowest pH of 2.48. The rate of decrease in pH was more rapid in ambient storage than refrigerated condition.
Initial TSS of the different types of nectar varied from 1.45 to 16.78°Brix. The TSS of sucrose-sweetened nectar was significantly higher than stevia-sweetened nectar. The treatment T1 recorded highest TSS of 16.78 °Brix followed by T2 at 16.62 °Brix. The treatment T3 which was sweetened with steviol glycosides had significantly lower TSS of 1.45 °Brix. TSS values of nectar showed a decreasing trend during storage period (Table 2). The decrease in TSS was more rapid under ambient storage than refrigerated storage.
Nectar developed from different combinations had initial titratable acidity values ranging from 0.28 to 0.56%, as indicated in Table 1.b. Treatment T2 developed from pure snap melon juice had the highest acidity level of 0.56% followed by T1 of 0.51%. T3 made with snap melon juice and gac fruit aril, sweetened with steviol glycosides had a significantly lower titratable acidity of 0.28%. Titratable acidity of nectar showed generally an increasing trend during storage (Table 2).
Colour values (L*,a*,b*): Instrumental colour values for L*, a* and b* differed between the types of nectars (Table 3). L* (99.31) value was higher for the nectar made solely from pure snap melon juice (T2), and a* (1.20) and b* (7.23) values were higher for the treatment (T3) containing gac fruit aril and steviol glycosides in it. During the storage period L* values decreased in the nectars. The a* and b* values also varied significantly.
Viscosity (cP): The viscosity of the nectars ranged from 24.70 cP to 52.68 cP (Table 1). The viscosity of the nectar containing gac fruit aril and sweetened with stevia (T3) was 52.68 cP, which was significantly higher than the 24.70 cP viscosity of the nectar made from pure snap melon (T2). Viscosity of the nectar decreased significantly during the storage period.
Ascorbic acid (mg/100g): The ascorbic acid content of all treatments varied significantly. According to Table 2, treatment T3 developed from snap melon and gac fruit aril sweetened with steviol glycosides had significantly higher ascorbic acid content of 41.14 mg/100g which was followed by T1 at 27.42 mg/100g. Treatment T2 developed from pure snap melon had the lowest ascorbic acid content of 19.42 mg/100g. The ascorbic acid content of nectars decreased significantly during the storage period (Table 2). The rate of deterioration of ascorbic acid content was slower under refrigerated condition than ambient storage.
Total phenolics (mg/100g): The total phenol content of nectar varied significantly (Table 2). The highest was in treatment T3 developed from snap melon and gac fruit aril sweetened with stevia extract (57.14 mg/100g) which was followed by treatment T1 developed from snap melon and gac fruit aril sweetened with sucrose (45.00 mg/100g). T2 developed from pure snap melon juice had the lowest phenol content (26.42 mg/100g). Phenols decreased during the storage period (Table 1.b). During storage, nectar stored under refrigerated condition retained phenols better than the samples held under ambient condition.
β carotene and lycopene (mg/100g): The β carotene content ranged from 0.082 to 0.135 mg/100g\(\:\:\) and lycopene content ranged from 0.179 to 0.189 mg/100g in the nectar (Table 2). Treatment T3, developed from snap melon and gac fruit aril sweetened with steviol glycosides had the highest β carotene and lycopene content of 0.135 mg/100g and 0.189 mg/100g respectively. The lowest β carotene and lycopene content was recorded in treatment T1 developed from snap melon and gac fruit aril sweetened with sucrose of 0.131 mg/100g and 0.179 mg/100g respectively. β carotene and lycopene content was not detected in nectar prepared from pure snap melon without gac fruit aril (T2). β carotene and lycopene content showed a decreasing trend during storage (Table 2). The deterioration of β carotene and lycopene was slower under refrigerated storage than under ambient storage.
Antioxidant activity (DPPH) (\(\:{\text{I}\text{C}}_{50}\) values): T3 developed from snap melon and gac fruit aril sweetened with steviol glycosides recorded highest radical scavenging activity (DPPH) of 2.47µg/mL, followed by T1 at 3.20 µg/mL. T2 developed from pure snap melon juice recorded the lowest antioxidant activity of 6.03 µg/m. The antioxidant activity of nectar showed a declining trend during storage (Table 2). The reduction in antioxidant capacities was more prominent under ambient storage.
Energy values (kcal): The energy value varied significantly between the nectar combinations (Table 2). Energy values of nectar sweetened with sucrose (T1, T2) was significantly higher than the nectar sweetened with steviol glycosides (T3). T1 recorded the highest energy value of 109.48 kcal followed by T2 at 70.64 kcal. T3 recorded the lowest energy value of 55.88 kcal.
Microbiological analysis (Bacteria, fungi, yeast): Variation in microbial population in the nectar was not significant (Table 4). The bacterial population was initially observed in all treatments. The highest bacterial population was observed in treatment T1 (0.36 x 104 CFU/ml). The fungal population was not observed in any of the treatments. Yeast populations were observed in all the treatments with the highest population in treatment T2 (0.36 x 104 CFU/ml). During the storage period bacterial, fungal and yeast populations increased in the nectars. The lowest bacterial, fungal and yeast populations were observed in treatment T3 developed from snap melon and gac fruit aril sweetened with steviol glycosides.
Sensory analysis: The sensory evaluation of nectar from snap melon and gac fruit aril revealed that treatment T1 developed from snap melon and gac fruit aril sweetened with sucrose was the most accepted one among the three treatments of nectar, based on organoleptic qualities (Figs. 3, 4 & 5). T1 exhibited the highest levels of acceptance in terms of appearance, colour, flavor, taste, aftertaste, body/consistency, aroma and overall acceptability. T1 obtained an overall acceptability score of 7.7, followed by T2, developed from pure snap melon sweetened with sucrose of 7.5. T3, developed from snap melon and gac fruit aril sweetened with steviol glycosides, had the lowest overall acceptability of 5.5 among the nectars. The nectar treatments sweetened with sucrose obtained the highest overall acceptability scores compared to the nectar sweetened with steviol glycosides. The overall acceptability scores of nectars, along with other parameters, reduced throughout the storage period.
| Parameters | Snap melon | Gac fruit |
|---|---|---|
| Moisture content (%) | 95.38 | 90.43 |
| Titratable acidity (%) | 0.64 | 0.25 |
| TSS (°Brix) | 1.2 | 7.5 |
| pH | 4.52 | 5.78 |
| Ascorbic acid (mg/100g) | 26.4 | 44.8 |
| Total phenolics (mg/100g) | 40 | 95 |
| β carotene (mg/100g) | ND* | 1.23 |
| Lycopene (mg/100g) | ND* | 1.63 |
| Anti-oxidant activity (IC50 Values) (µg/mL) | 14.66 | 8.94 |
ND-Not detected*
| Parameters | Storage condition | Storage time (months) | T1 | T2 | T3 | CD | S.Em |
|---|---|---|---|---|---|---|---|
| pH | Initial | 0 | 2.69b | 2.48b | 4.56a | 0.29 | 0.10 |
| Ambient | 1 | 2.48b | 2.46b | 3.97a | 0.41 | 0.14 | |
| Refrigerated | 1 | 2.67b | 2.52b | 4.26a | |||
| Ambient | 2 | 1.74c | 1.58c | 2.97b | 0.41 | 0.13 | |
| Refrigerated | 2 | 1.98c | 1.69c | 3.51a | |||
| Ambient | 3 | 1.64b | 1.51b | 2.77a | 0.66 | 0.22 | |
| Refrigerated | 3 | 1.87b | 1.54b | 3.09a | |||
| Total soluble solids (°Brix) | Initial | 0 | 17.18b | 18.11a | 1.45c | 0.45 | 0.15 |
| Ambient | 1 | 16.32c | 16.67bc | 1.22d | 0.49 | 0.16 | |
| Refrigerated | 1 | 16.90b | 17.50a | 1.25d | |||
| Ambient | 2 | 15.75b | 15.20c | 0.95d | 0.42 | 0.14 | |
| Refrigerated | 2 | 16.85a | 16.12b | 1.15d | |||
| Ambient | 3 | 14.15bc | 12.50c | 0.70d | 1.68 | 0.56 | |
| Refrigerated | 3 | 15.85a | 15.67a | 1.05d | |||
| Titratable acidity (%) | Initial | 0 | 0.51a | 0.56a | 0.28b | 0.09 | 0.03 |
| Ambient | 1 | 0.57a | 0.63a | 0.38b | 0.13 | 0.04 | |
| Refrigerated | 1 | 0.54a | 0.60a | 0.34b | |||
| Ambient | 2 | 0.66ab | 0.76a | 0.47bc | 0.19 | 0.06 | |
| Refrigerated | 2 | 0.70a | 0.73a | 0.38c | |||
| Ambient | 3 | 0.76a | 0.82a | 0.54bc | 0.19 | 0.06 | |
| Refrigerated | 3 | 0.73ab | 0.75a | 0.51c | |||
| Ascorbic acid (mg/100g) | Initial | 0 | 27.42b | 19.42b | 41.14a | 8.54 | 2.87 |
| Ambient | 1 | 21.42bc | 16.66c | 30.95a | 9.42 | 3.17 | |
| Refrigerated | 1 | 26.18ab | 19.04bc | 33.30a | |||
| Ambient | 2 | 15.03c | 14.19c | 21.23abc | 7.70 | 2.59 | |
| Refrigerated | 2 | 23.00ab | 17.69bc | 26.54a | |||
| Ambient | 3 | 12.06b | 6.89c | 16.37a | 4.26 | 1.43 | |
| Refrigerated | 3 | 18.09a | 15.51ab | 18.95a | |||
| β carotene (mg/100g) | Initial | 0 | 0.131a | ND | 0.135a | 0.039 | 0.013 |
| Ambient | 1 | 0.039bc | ND | 0.050bc | 0.020 | 0.007 | |
| Refrigerated | 1 | 0.058b | ND | 0.084a | |||
| Ambient | 2 | 0.032c | ND | 0.043bc | 0.014 | 0.005 | |
| Refrigerated | 2 | 0.050ab | ND | 0.062a | |||
| Ambient | 3 | 0.014b | ND | 0.022ab | 0.010 | 0.003 | |
| Refrigerated | 3 | 0.024a | ND | 0.028a | |||
| Lycopene (mg/100g) | Initial | 0 | 0.179a | ND | 0.189a | 0.058 | 0.019 |
| Ambient | 1 | 0.065ab | ND | 0.059ab | 0.031 | 0.011 | |
| Refrigerated | 1 | 0.077a | ND | 0.089a | |||
| Ambient | 2 | 0.049c | ND | 0.067bc | 0.023 | 0.008 | |
| Refrigerated | 2 | 0.077b | ND | 0.103a | |||
| Ambient | 3 | 0.021b | ND | 0.034ab | 0.017 | 0.006 | |
| Refrigerated | 3 | 0.037a | ND | 0.050a | |||
| Total phenolics (mg/100g) | Initial | 0 | 45.00a | 26.42b | 57.14a | 12.49 | 4.20 |
| Ambient | 1 | 38.75b | 18.75d | 42.50b | 4.01 | 1.35 | |
| Refrigerated | 1 | 42.50b | 26.25c | 47.50a | |||
| Ambient | 2 | 26.25b | 12.50d | 27.50b | 4.71 | 1.58 | |
| Refrigerated | 2 | 33.75a | 21.25c | 37.50a | |||
| Ambient | 3 | 8.75cd | 6.25d | 12.50bc | 4.37 | 1.47 | |
| Refrigerated | 3 | 22.50a | 13.75b | 25.00a | |||
| Viscosity (cP) | Initial | 0 | 45.38b | 24.70c | 52.68a | 5.40 | 1.81 |
| Ambient | 1 | 39.67c | 22.37d | 48.20a | 3.49 | 1.17 | |
| Refrigerated | 1 | 43.32b | 23.75d | 50.97a | |||
| Ambient | 2 | 35.50c | 20.92d | 44.00ab | 4.27 | 1.43 | |
| Refrigerated | 2 | 40.10b | 21.62d | 47.75a | |||
| Ambient | 3 | 31.25c | 18.07d | 39.00b | 4.59 | 1.54 | |
| Refrigerated | 3 | 36.70b | 19.62d | 43.72a | |||
| Antioxidant activity (\(\:{\text{I}\text{C}}_{50}\:\)values) (µg/mL) | Initial | 0 | 3.20b | 6.03a | 2.47b | 0.88 | 0.29 |
| Ambient | 1 | 5.29b | 9.94a | 4.33bc | 2.04 | 0.68 | |
| Refrigerated | 1 | 3.42bc | 8.95a | 2.46c | |||
| Ambient | 2 | 6.41b | 11.71a | 4.99bc | 2.17 | 0.73 | |
| Refrigerated | 2 | 3.78c | 11.82a | 3.65c | |||
| Ambient | 3 | 9.76c | 22.75a | 4.80de | 3.58 | 1.18 | |
| Refrigerated | 3 | 7.63cd | 16.51b | 3.36e | |||
| Protein (gm/100g) | Initial | 0 | 1.32a | 1.01b | 0.55c | 0.29 | 0.10 |
| Ambient | 1 | 0.92 | 0.77 | 0.62 | NS | 0.09 | |
| Refrigerated | 1 | 0.92 | 0.90 | 0.57 | |||
| Ambient | 2 | 0.85b | 0.70bc | 0.55c | 0.25 | 0.08 | |
| Refrigerated | 2 | 1.87a | 0.62bc | 0.55c | |||
| Ambient | 3 | 0.60 | 0.72 | 0.57 | NS | 0.07 | |
| Refrigerated | 3 | 0.72 | 0.47 | 0.45 | |||
| Carbohydrate (mg/100g) | Initial | 0 | 16.71a | 13.14b | 10.85c | 1.81 | 0.61 |
| Ambient | 1 | 10.00b | 7.50c | 6.75c | 1.78 | 0.60 | |
| Refrigerated | 1 | 12.50a | 10.97ab | 7.50c | |||
| Ambient | 2 | 7.25b | 6.25bc | 5.50c | 1.42 | 0.47 | |
| Refrigerated | 2 | 10.50a | 7.00b | 9.50a | |||
| Ambient | 3 | 6.50bc | 5.25c | 4.50c | 2.15 | 0.72 | |
| Refrigerated | 3 | 9.00a | 5.50c | 8.00ab | |||
| Fat (gm/100g) | Initial | 0 | 4.18a | 1.55b | 0.92c | 0.19 | 0.06 |
| Ambient | 1 | 2.50b | 1.37c | 1.75c | 0.50 | 0.17 | |
| Refrigerated | 1 | 3.12a | 1.50c | 2.57b | |||
| Ambient | 2 | 2.45a | 1.02c | 1.62b | 0.34 | 0.11 | |
| Refrigerated | 2 | 2.40a | 1.17c | 1.80b | |||
| Ambient | 3 | 2.60a | 0.95c | 1.07c | 0.37 | 0.12 | |
| Refrigerated | 3 | 2.05b | 1.05c | 1.75b | |||
| Energy value (kcal) | Initial | 0 | 109.48a | 70.64b | 56.16c | 7.55 | 2.54 |
| Ambient | 1 | 66.20b | 45.47d | 45.25d | 7.86 | 2.64 | |
| Refrigerated | 1 | 81.72a | 61.10bc | 55.47c | |||
| Ambient | 2 | 57.85b | 37.72d | 37.02d | 6.32 | 2.12 | |
| Refrigerated | 2 | 68.80a | 56.40b | 46.68c | |||
| Ambient | 3 | 51.55a | 31.85b | 30.57b | 9.45 | 3.18 | |
| Refrigerated | 3 | 57.35a | 49.65a | 39.55b |
ND* - Not detected NS* – Not significant
| Parameters | Storage condition | Storage time (months) | T1 | T2 | T3 | CD | S.Em | |
|---|---|---|---|---|---|---|---|---|
| Colour values | L* | Initial | 0 | 88.72b | 99.31a | 86.00b | 8.00 | 2.69 |
| Ambient | 1 | 88.44b | 96.35a | 82.63d | 2.64 | 0.89 | ||
| Refrigerated | 1 | 88.74b | 98.33a | 85.34c | ||||
| Ambient | 2 | 84.58bc | 92.30a | 79.90d | 3.70 | 1.24 | ||
| Refrigerated | 2 | 85.53b | 94.32a | 81.20cd | ||||
| Ambient | 3 | 81.87bc | 90.19a | 73.54d | 2.67 | 0.90 | ||
| Refrigerated | 3 | 83.62b | 90.94a | 80.79c | ||||
| a* | Initial | 0 | 1.20a | -0.02b | 0.86a | 0.46 | 0.15 | |
| Ambient | 1 | 0.570b | 0.042c | 0.475b | 0.27 | 0.09 | ||
| Refrigerated | 1 | 0.495b | 0.075c | 1.060a | ||||
| Ambient | 2 | 0.210ab | 0.050b | 0.470a | 0.30 | 0.10 | ||
| Refrigerated | 2 | 0.400a | 0.065b | 0.420a | ||||
| Ambient | 3 | 0.705ab | 0.055c | 0.905a | 0.61 | 0.20 | ||
| Refrigerated | 3 | 0.760ab | 0.160bc | 0.920a | ||||
| b* | Initial | 0 | 7.23a | 1.02b | 5.25a | 2.22 | 0.74 | |
| Ambient | 1 | 4.17b | 1.71c | 7.05a | 0.77 | 0.26 | ||
| Refrigerated | 1 | 4.72b | 0.40d | 7.05a | ||||
| Ambient | 2 | 2.25c | 1.02c | 6.14a | 1.50 | 0.50 | ||
| Refrigerated | 2 | 3.99b | 1.82c | 4.58b | ||||
| Ambient | 3 | 4.48a | 1.62b | 7.11a | 2.64 | 0.88 | ||
| Refrigerated | 3 | 5.04a | 7.11a | 6.36a | ||||
| Parameters | Storage condition | Storage time (months) | T1 | T2 | T3 | CD | S.Em | |
|---|---|---|---|---|---|---|---|---|
| Microbial population | Bacteria (104 CFU/ml) | Initial | 0 | 0.36 | 0.26 | ND | - | - |
| Ambient | 1 | 4.00 | 8.50 | 4.00 | - | 0.82 | ||
| Refrigerated | 1 | 4.25 | 3.25 | 2.75 | ||||
| Ambient | 2 | 5.25 | 9.25 | 5.75 | - | 0.71 | ||
| Refrigerated | 2 | 4.50 | 5.75 | 4.25 | ||||
| Ambient | 3 | 6.00 | 11.00 | 7.25 | - | 0.82 | ||
| Refrigerated | 3 | 4.00 | 7.75 | 4.50 | ||||
| Fungus (104 CFU/ml) | Initial | 0 | ND | ND | ND | - | - | |
| Ambient | 1 | 2.75 | 3.25 | 1.00 | - | 0.43 | ||
| Refrigerated | 1 | 1.75 | 3.00 | 0.75 | ||||
| Ambient | 2 | 3.25 | 3.75 | 2.50 | - | 0.22 | ||
| Refrigerated | 2 | 2.75 | 3.25 | 2.25 | ||||
| Ambient | 3 | 4.25 | 4.50 | 3.50 | - | 0.31 | ||
| Refrigerated | 3 | 3.00 | 4.00 | 2.50 | ||||
| Yeast (104 CFU/ml) | Initial | 0 | 0.26 | 0.36 | ND | - | - | |
| Ambient | 1 | 4.75 | 3.75 | 2.50 | - | 0.50 | ||
| Refrigerated | 1 | 3.75 | 2.00 | 1.50 | ||||
| Ambient | 2 | 9.50 | 4.25 | 5.25 | - | 1.03 | ||
| Refrigerated | 2 | 4.00 | 3.25 | 2.25 | ||||
| Ambient | 3 | 8.50 | 5.00 | 7.00 | - | 0.96 | ||
| Refrigerated | 3 | 1.75 | 3.75 | 5.00 | - | |||
ND* - Not detected NS* – Not significant
pH has a strong influence on sensory and microbial qualities of the product. The low-calorie nectar exhibited higher pH values compared to nectar sweetened with sucrose, likely due to the higher pH level of stevia extract. Balaswamy et al. [14] found that the pH of stevia aqueous extract was higher than that of fruit juices. Similar findings were reported by Reale et al. [15] on low-calorie apricot nectar and Jabeen et al. [16] in guava drink, noting that beverages sweetened with stevia had higher pH values than those sweetened with sucrose. During storage, a consistent decrease in pH was observed across the treatments of snap melon and gac fruit nectar, a trend also noted by Kausar et al. [17] in cucumber-melon drink and Majumdar et al. [18] in ash gourd-mint leaves juice. TSS plays a significant role in sensory quality which determines the marketability of the product. A significant difference was noted between the TSS of nectar sweetened with steviol glycosides and the one sweetened with sucrose. The TSS of nectar sweetened with steviol glycosides was lower than that of the sucrose-sweetened nectar, likely because stevioside does not contribute to the total soluble solids (TSS) [19]. The decrease in TSS during storage could be attributed to the breakdown of carbohydrates, particularly sugars, into acids by microorganisms. Similar reductions in TSS during storage were observed by Singh and Gaikwad [20] in bitter gourd-lemon functional RTS beverage and Habib and Iqbal [21] in mixed vegetable juice from tomato, cucumber, and pumpkin. A notable difference in acidity levels was observed between nectar sweetened with steviol glycosides and the one sweetened with sucrose. This difference may be attributed to the higher pH of stevia extract. Similar findings were reported by Sharma and Thakur [22] in their study on low-calorie bitter gourd-aonla blended squash. An increasing trend in titratable acidity was observed in all treatments of snap melon and gac fruit nectar during storage. This rise in acidity can be linked to the decline in pH of the product. Similar conclusions were drawn by Gomez et al. [23] in Indian blackberry nectar and Kausar et al. [17] in cucumber-melon functional drink. Sabahuddin et al. [24] found that the increase in acidity during storage was more pronounced when the low-calorie herbal beverage was stored at higher temperatures compared to low-temperature storage.
Fruit and vegetable beverages are first judged by the visibility or colour and appearance which plays a crucial role in marketability. The colour values of all treatments varied significantly. The L* value was higher for nectar made from pure snap melon juice, while a* and b* values were higher for nectar containing gac fruit aril and steviol glycosides. The absence of gac fruit aril and stevia extract likely contributed to the higher L* value in nectar made from pure snap melon juice, while their addition likely increased the a* and b* values. These color values were similar to those found in the study by Wirivutthikorn [25] in tofu milk supplemented with gac fruit aril powder. During storage, L*, a*, and b* values generally showed a decreasing trend with slight variations. Similar trends were observed in the studies by Eissa et al. [26] in fruit drinks and Cortellino and Rizzolo [27] in functional drinks based on ricotta cheese whey and fruit juices.
Viscosity indicates the consistency of the product which is a direct indication of the dissolved solutes in the drink. Nectars sweetened with steviol glycosides showed higher viscosity than those sweetened with sucrose. The increased viscosity in nectar containing gac fruit aril and stevia extract might be due to reduced water activity. Wirivutthikorn [28] reached similar conclusions in their study on corn milk beverages with added gac fruit aril, as did Peasura and Sinchaipanit [29] in their research on guava nectar sweetened with stevia. During storage, the viscosity of nectars decreased. This reduction in viscosity can be linked to the decline in TSS. Similar observations were made by Wojdyło et al. [30] in quince fruit juice and Oszmianski et al. [31] in shampion apple juice.
Ascorbic acid is a strong antioxidant, supplied primarily through diet, of which plant-based products are of much importance. Nectar sweetened with stevia exhibited higher ascorbic acid content compared to nectar sweetened with sucrose. This increased vitamin C level may result from the combined effect of gac fruit aril and stevia extract, both of which are sources of ascorbic acid. Lemus-Mondaca et al. [32] noted that fresh stevia leaves contained vitamin C. The reduction in ascorbic acid content during storage could be due to its oxidation into dehydroascorbic acid, and ascorbic acid is also sensitive to heat. Similar findings were reported by Gomez et al. [23] in Indian black berry nectar and Gupta et al. [33] in bottle gourd nectar.
Phenolics is a group of compounds with strong antioxidant properties. Tannins, catechins, quercetin are some of the phenolic compounds found in fruits and vegetables. The total phenol content was higher in nectar sweetened with steviol glycosides compared to those sweetened with sucrose. Nectar containing both gac fruit aril and stevia extracts had even higher phenol content. Ahmed et al. [34] noted the presence of phenols in aqueous extract of stevia. During storage, phenol content decreased in all treatments of snap melon and gac fruit nectar. Decline in phenols may be due to oxidative degradation. Similar findings were reported by Sharma et al. [35] on aloe vera-aonla blended functional squash and Palamthodi et al. [36] on ash gourd/bottle gourd beverages blended with jamun in their studies.
β-carotene and lycopene are antioxidants responsible for bright hues of red, orange and yellow colours. The nectar containing gac fruit aril and steviol glycosides had higher levels of β-carotene and lycopene. In their study, Gupta et al. [37] found that β-carotene was the primary bioactive compound in the leaves of Stevia rebaudiana. β-carotene and lycopene were not detected in the nectar made solely from snap melon juice without gac fruit aril. The degradation of β-carotene and lycopene during storage could be due to photo-oxidation. Additionally, carotenoids can be converted into isomers during storage, resulting in their degradation. Low-temperature storage resulted in better retention of β-carotene and lycopene. Similar findings were reported by Baç et al. [38] in tomato pulp and pink grapefruit juice and Nhung et al. [39] in gac fruit oil made from gac aril.
Radical scavenging properties of fruits and vegetables are influenced by the level of bioactive compounds present in them. The nectar containing both gac fruit aril and stevia extract exhibited higher radical scavenging activity (DPPH) compared to other nectars. This increased activity can be attributed to the higher levels of antioxidants from the gac fruit aril and stevia. Similar changes in antioxidant activities were observed by Wirivutthikorn [28] in corn milk beverages with added gac fruit aril. Ahmed et al. [34] found that aqueous extract of stevia could enhance antioxidant activity. During storage, the antioxidant activity (DPPH radical scavenging activity) decreased in all treatments of snap melon and gac fruit nectar. Similar trends were reported by Gomez et al. [23] in Indian blackberry nectar and Sharma et al. [40] in low-calorie beverage from bitter gourd and kiwifruit.
The energy values of nectars showed significant variation. Nectars sweetened with steviol glycosides had notably lower calorific values compared to those sweetened with sucrose. Reduced sweetness and TSS levels in stevia-sweetened nectar could account for lower energy values. Similar findings were reported by Barakat et al. [41] in low-calorie fruit nectars. During storage, the calorific values of nectar decreased, with a more rapid decline observed under ambient storage conditions compared to refrigerated storage. This decrease in energy value during storage could be due to the degradation of carbohydrates and other metabolites by microbes. Additionally, sweetening nectar with stevia led to a reduction in its calorific value. Similar reductions in energy values were observed by Sharma et al. [40] in low-calorie beverage from bitter gourd and kiwifruit and Sharma et al. [42] in apricot and aloe vera based low-calorie beverage.
According to FSSAI (Food Safety and Standards Authority of India) regulations in India, the total microbial count must not exceed 25 CFU/ml, total coliform count (TCC) must be absent in 100 ml, and the total yeast count must not exceed 2 CFU/ml. Stevia-sweetened nectar had a lower microbial population than nectar sweetened with sucrose. Stevia's antibacterial properties may be the cause of the lower microbial load in stevia-sweetened nectar. Rodríguez-Rico et al. [43] in melon (Cucumis melo L.) juice found similar results in their study. The aqueous extract of stevia leaves shows strong antibacterial properties against a range of microorganisms, according to Ibrahem et al. [44]. In the present study during the storage period, there was an increase in the populations of bacteria, fungi, and yeast. In their respective studies, Minh [45] in cucumber (Cucumis sativus var. conomon) juice and Sharma et al. [48] in low-calorie apple-whey-based RTS beverage noted a comparable rise in the microbial count.
The organoleptic scores of nectars sweetened with sucrose were substantially higher than those of nectars sweetened with stevia. Comparable outcomes were noted by Wafaa et al. [46] in natural drinks sweetened by stevia. This could be due to the reduction in flavour and colour of the nectar. Additionally, over the course of the three-month storage period, the organoleptic ratings dropped. In their respective investigations, Sharma et al. [35] on low-calorie aloe vera-aonla blended functional squash and Salaria and Reddy [47] on RTS beverage from muskmelon (Cucumis melo L. variety ‘Sarda’) saw a comparable decline in the overall acceptability score during storage. Organoleptic property is directly related to the marketability of the product, of which flavour and colour are the most important criteria.
Gac fruit and snap melon work well together to produce value-added products such as nutraceutical nectar. By adding value, farmers can improve their income and ensure that products made from these underappreciated fruits will be available all year round. Even though the combination of nectar sweetened with stevia was high in antioxidant activity, β-carotene, phenolics, ascorbic acid, and lycopene, the nectar sweetened with sucrose had superior overall acceptance scores. During the storage period of nectar, it was noticed that the nectars stored in a refrigerator preserved their phytochemical components better than their counterparts at room temperature. Additionally, stevia extract can be used to sweeten nectar, making it appropriate for usage for diabetic patients. The quality of nectar combinations was judged satisfactory based on a sensory evaluation performed using a 9-point hedonic scale during the duration of the three-month storage period. For up to ninety days, the nectar can be stored at room temperature or in a refrigerator without any synthetic preservatives.
Amb Ambient
AOAC Association of Official Analytical Chemists
CD Critical difference
CFU Colony-forming unit
DCPIP 2,6-dichlorophenol indophenol dye
DPPH 2,2-diphenyl-1-picrylhydrazyl
FCR Folin–Ciocâlteu reagent
IC5O Half maximal inhibitory concentration
Kcal Kilocalories
MAS Months after storage
Ref Refrigerated
RTS Ready-To-Serve
S.Em Standard error of the mean
SM and GF Snap melon and Gac fruit
TSS Total Soluble Solids
Acknowledgements
The authors are indebted to the technical support provided by the staff of the Department of Postharvest Management, College of Agriculture, Kerala Agricultural University, Vellanikkara, Thrissur, during the analysis of the samples. Thanks are extended to the Farmers who provided with snap melon and gac fruit for research analysis.
Authors’ contributions
ARS contributed to manuscript writing, methodology and research analysis. SG contributed to the conceptualization and editing of the manuscript. SJ and BK contributed to quality analysis and data preparation. All authors read and approved the final manuscript.
Funding
The fund for the research was received from the Directorate of Research, Kerala Agricultural University, Thrissur, Kerala [Grant number: R7/66317/2022 dated 27.10.2022]
Data availability statement
Data sharing is not applicable to this article as no datasets were generated or analysed during the current study
Conflict of interests
The authors state that they have no conflict of interest
Ethical statement
The study was reviewed and deemed exempt by the Directorate of Research, Kerala Agricultural University Institutional Review Board
Informed consent
Informed consent was obtained from all individual participants included in the study
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No competing interests reported.