Sensory Attributes and Antioxidant Potential of Value-added Products of Grapefruit (Citrus paradisi)

Richika Garg1,*, Neerja Singla1, Monika Gupta2, Rohini Jain1
1Department of Food and Nutrition, Punjab Agricultural University, Ludhiana-141 004, Punjab, India
2Department of Fruit Science, Punjab Agricultural University, Ludhiana-141 004, Punjab, India.
Background: Grapefruits are one of the nutritious and most commonly consumed fruits in United States, next to oranges. Conversely, limited consumption has been reported in India due to its sour taste and bitter flavour. So, the present investigation was undertaken to produce value-added products (chiller, squash, spread and peel candy) from different varieties (Red blush, Ruby Red, marsh Seedless) with an objective to enhance its sensory acceptability. 

Methods: The four cultivars of grapefruits were procured from citrus farm of PAU, Ludhiana. Half of the fresh fruits were washed thoroughly in distilled water, peeled, sectioned into small pieces and dried in hot air oven at ±55°C. The dried fruit was then ground into fine powder and stored in the air-tight containers (27°C) for nutritional analysis whereas the other half was processed manually to formulate the value-added products in the Food Lab of the same for its sensorial evaluation. 

Result: Out of four varieties; Red blush became most acceptable for chiller and spread, whereas Ruby Red and Marsh Seedless for squash and peel candy. Prior to product formulation, nutritional parameters of varieties were analysed. They reported high amount of potassium and crude fibre i.e.111-117mg and 1.27-1.40 g/100 g. Among formulated products, ascorbic acid and antioxidant potential was highest in chiller i.e. 28.89 mg/100 g and 75.82%. Quercetin Equivalent was 77.33 (highest) in peel candy.
Grapefruit is a hybrid of pomelo (Citrus maxima) and sweet orange (Citrus sinensis) developed in the eighteenth century. In India, grapefruit remained an underutilized fruit despite being the rich source of antioxidant, vitamins and minerals and is used for the production of ethno-medicines (Barua et al., 2019). It is especially high in pectin (a soluble fibre) that helps in lowering blood cholesterol levels (Younus et al., 2008). The potassium found in grapefruit helps in maintaining bone strength as when we consume citrate it gets converted into bicarbonate, which further supports acid-base balance to lessen the potential losses of calcium from the bones. Besides fibre and micronutrients, it contains phytochemicals such as flavonoid, carotenoids, glucarates, coumarins, terpenes, limonoids and furanocoumarins. These phytochemicals, particularly the furanocoumarins have anti-inflammatory and anti-oxidative effects (Codoñer-Franch and Valls-Bellés, 2010). They also inhibit cancer cells proliferation and repair damaged DNA that would otherwise lead to the development of tumours.
Grapefruit peel being rich source of pectin is widely used for its extraction and utilizing it in the formulation of best quality food products including jams. Khan et al., 2014 using Duncan variety, extracted maximum amount of pectin (22.55%) at 120°C at an acidity levels of 1.5 pH whereas 0.41% of pectin was extracted at 2 pH, keeping the temperature same. Essential oils can also be extracted from its peel. Red Blush variety of grapefruit constituted 67 compounds; amounting 97.9% of oils Nijoroge et al. (2005). These extracted oils can be further used as flavouring agents, anti-ageing skin care products, insects repellent/ attractant, etc. Apart from this, its dried waste products can be used as cattle feed that will not only act as an effective waste manager but also diminishes the burden on environment. It can also be used for the production of bioethanol and as biosorbents for heavy metals in treatment of waste water (Khalil et al., 2022). Chaudhary et al (2017) investigated that kinnow waste on using it as a cattle feed saves the cost upto 12 percent as compared to conventional sources without altering its nutrient digestibility. Fruit and vegetable pomace can be enriched in bakery products to increase their fermentability, hydration capacity and phytochemicals, etc. (Sahni and Shere 2018). Keeping in view the various nutritional and health benefits of the fruit, efforts were made in the present study to formulate its value-added products having good sensory and nutritional attributes.   
Four varieties of marketable sized (weight ranging from 200-250 g) grapefruit namely Ruby Red, Red Blush, Flame and Marsh Seedless were procured from the Department of Fruit Science, Punjab Agricultural University, Ludhiana, Punjab and were brought to Food Analysis Laboratory of Department of Food and Nutrition. Other ingredients used for the preparation of different products, such as sugar, salt, powdered black pepper, citric acid crystals, benzoic acid, lemon, calcium hydroxide and sodium benzoate were purchased from the local market of Ludhiana and were stored at room temperature (27°C). The fruits were then peeled, sectioned into small pieces and dried in hot air oven at ±55°C. The dried fruit was then ground into fine powder with the help of pestle and mortar and stored in the air-tight containers at ambient temperature (27°C) for nutritional analysis such as proximate composition, total sugars, reducing and non-reducing sugars, minerals (potassium and calcium), vitamin C, total flavonoids and antioxidant potential by DPPH radical scavenging method. All the proximate parameters were analysed using methods described in Association of Official Analytical Chemist (AOAC, 2000). Moisture content was carried out in a hot air oven at a temperature 105°C for 8 hours. The crude protein was estimated by kjeldhal method using Kjelplus (SUPRA- LX VA) in which nitrogen content was estimated and was then multiplied with the factor 6.25 for protein estimation. The crude fat was evaluated by Soxhlet extraction method using SOCS PLUS (SCS 6). The ash content was evaluated by igniting the sample in a muffle furnace at a temp. 550°C for 4 hours. Carbohydrate was calculated by difference method:
 Crude fiber was also estimated by the method described in Association of Official Analytical Chemists (AOAC, 2000) by using FIBRA PLUS (FES 6). The calorific value of grapefruit varieties was estimated by multiplying the percentages of carbohydrate, protein and fat with their physiological fuel value i.e. 4, 4 and 9, respectively. Total sugars and reducing sugars were estimated by the method described in AOAC, 2000. Whereas, non-reducing sugar was calculated by subtracting reducing sugars from total sugars. Minerals namely potassium and calcium were determined by method given in AOAC (2003). Vitamin C content was evaluated by using 2, 6-dichlorophenol indophenol dye which gives blue colour on reduction by ascorbic acid and it was read in spectrophotometer (ELICO SL 177) at 500 nm (AOVC, 1996). For the analysis of flavonoids and antioxidant potential, the methanolic extract was prepared. For the analysis of flavonoids, absorbency was read at 415 nm against the blank (Zhishen et al., 1999). For the analysis of antioxidant potential the sample was evaluated by DPPH (2, 2-diphenyl-1-picrylhydrazyl) method. The discoloration of DPPH was read at 517 nm against blank (Tadhani et al., 2007). All the samples were analysed in triplicate.
For the formulation of the products various sensory trials were conducted in the Food Laboratory of PAU, Ludhiana to standardize the recipe of all products. Standardized amounts of ingredients and methods of preparation of grapefruit products (Chiller, squash, peel candy and spread) have been mentioned in Table 1. Each product was prepared from four different grapefruit varieties and for sensory evaluation it was served to semi-trained panel (n=30) of Departments of Food and Nutrition, Food Science and Technology and Fruit Science of PAU in a well-lit laboratory of the Department of Food and Nutrition during day time and to the untrained panel (n=50) of local consumers to check the consumer acceptability. The panel was provided with the single product (30 ml each) at a time along with water in order to prevent the interference of different flavours. They were asked to report their sensory preferences in a given datasheet. The acceptance sensory test using a nine-point Hedonic rating scale was performed for several sensory attributes such as texture, appearance, flavour, taste and overall acceptability (Nicolas et al., 2010). Based on the results of this evaluation, the most acceptable variety from each product was selected and it was further evaluated for their proximate composition. The detailed experimental design of this study is given in Fig 1.

Table 1: Formulation of value-added products of grapefruit varieties.

Fig 1: Experimental of formulation and nutritional evaluation of value-added grapefruit products.

Statistical analysis
Mean and standard deviation for the different parameters were computed. Analysis of Variance (ANOVA) was employed following CRD and Statistical Analysis Tool Pack and SPSS 16 (statistical package for the social sciences). Least significant difference at 5% was calculated using SAS (Statistical Analysis System, version 9.3 for windows) software for the comparison among the parameters. Percentage preferences of local consumers were estimated while selecting the most acceptable variety from each product.
Proximate analysis of fresh grapefruit varieties
Moisture content in different varieties of grapefruit ranged between 89.5-90.21 g/100 g. Ash is the non-gaseous, non-liquid residue left after the combustion which estimates the total mineral content of sample and in fresh edible parts of grapefruit it ranged from 0.90-1.50 g/100 g (Table 2). The carbohydrate content in grapefruit was 7 g/100 g as reported by Paul and Shaha (2004), the value being close to that reported for all the varieties of grapefruit (Table 2). The crude fibre was in the range of 1.27 (Marsh Seedless) -1.40 g/100 g (Ruby Red) and carbohydrate content was found to be in the range from 6.49 (Flame) to 7.31 g/100 g (Marsh Seedless). The calorie value of different grapefruit varieties ranged from 29.66- 32.44 kcal/100 g.

Table 2: Proximate composition of fresh grapefruit varieties (on DW basis) and its formulated products (g/100 g).

Sensory characteristics of formulated products
The formulated products were subjected to sensory evaluation and the mean overall acceptable scores of the most acceptable varieties have been depicted in web diagram (Fig 2). The chiller prepared from Red Blush variety got higher scores for taste, texture, flavor and overall acceptability by the panel of semi-trained judges and was also preferred by 69% of the untrained panel (n=50). For squash, spread and peel candy; ruby red, red blush and marsh seedless varieties got higher overall acceptability with consumer preference of 75, 73 and 78 percent, respectively.

Fig 2: Overall Acceptability of most acceptable grapefruit varieties of the formulated products.

Mineral content, total sugars (reducing and non-reducing) and Ascorbic acid of grapefruit varieties and its products
Potassium and calcium content of grapefruit varieties and products have been depicted in Table 4. Among products, peel candy had significantly higher amount of minerals. Reducing and non- reducing sugars ranged between 5.39- 5.72 g/100 g among four varieties of grapefruit (Table 3). However, among the formulated products, peel candy had the highest amount of total sugar (56.90- 57.37 g/100 g) and chiller had the lowest (11.47-11.90 g/100 g) with no significant varietal difference in the products. Amongst the varieties, flame variety had the highest amount of reducing sugar i.e. 3.98 g/100 g. Amongst the products, peel candy had the highest amounts (25.0-26.0 g/100 g). Total and reducing sugar was 32.84 and 8.18 percent in lemon cordial (Helali et al., 2008) and 68.54 and 22.40 per cent in peel candy of sweet orange (Bisht 2017).

Table 4: Minerals and antioxidant properties of grapefruit varieties and its formulated products.

Table 3: Total sugars (reducing and non- reducing) in grapefruit varieties (g/100 g on FW basis) and its formulated products.

Citrus fruits are primarily rich in ascorbic acid and are major contributors to antioxidant activity of fruit. It scavenges the free radical by donating its own electron and breaking the chain reaction of free electrons and thus protecting the other molecules from oxidation ascorbic acid, in fresh grapefruit varieties was present between 33.03±0.3- 34.73±2.33 mg/100 g with highest content in Marsh Seedless and lowest in Ruby Red variety (Table 4). Among grapefruit products, chiller reported maximum amount of it (21.75±0.61-28.89±0.34 mg/100 g).

Total flavonoids and DPPH radical scavenging activity (% Inhibition)
In grapefruit varieties flavonoids ranged from 68.08±2.49 (Flame) to 75.07±1.52 mg QE/100 g (Marsh Seedless). Among grapefruit products, peel candy had the maximum amount (72.28±0.72-77.33±0.33 mg QE/100 g). The results of antioxidant potential was in comparison with the study of Muzykiewicz et al., (2019) who evaluated the highest antioxidant potential in the white grapefruit extracts by DPPH method. Antioxidant activity of fresh grapefruit varieties was found to be ranging from 75.44±1.50 to 78.40±3.20 per cent. In grapefruit products, the maximum % inhibition was observed in chiller i.e. from 70.99±0.11 to 75.82±0.45 (Table 4).
It can be concluded that the grapefruit can be used to make value added products with minimal processing at household level to harness the nutritional and health benefits of this fruit. The present effort can be considered a good initiative to enhance the consumption of this nutritionally rich fruit, which otherwise is not being used upto the mark due to its bitter and sour taste.

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