Smoothies with improved sensory characteristics and microbial quality were developed by blending watermelon-pineapple and sweet melon – cucumber. The fruits were sorted, washed thoroughly with clean water, peeled, sliced and diced into small cubes and blended. Smoothies from blends of watermelon – pineapple (WMP) and sweet melon – cucumber (SMC) were formulated. The samples were blended in different ratios: watermelon- pineapple control (WMPC-100%), watermelon-pineapple (90:10WMP1), (80:20%WMP2), (70:30%-WMP3), (60:40% WMP4) and (50:50%-WMP5), and the same ratios were also used for sweet melon-cucumber blends respectively. The samples were analysed for organoleptic properties and microbial quality. Significant (p>0.05) differences did not exist in sensory evaluation between blends; but within samples. The result for organoleptic properties based on blend ratios for watermelon-pineapple and sweet melon –cucumber in relation to the parameters assessed, for aroma, colour, taste, flavor and general acceptability showed that samples WMP3(70:30), WMP2 (80:20%) and SMC2 (80:20%) were the most preferred. Microbial count result for watermelon-pineapple sample for total bacterial cells, total coliform and fungi count ranged from; 1.5×104 to 8.2×103, 1.5×103 to 6.4×103 and 1.1×104 to 9.2×103 cfu/ml and for sweet melon-cucumber sample, the count ranged from 1.5×104 to 9.1×105, 1.0×106 to 9.6×103 and 1.8×105 to7.9x103cfu/ml. The biochemical test revealed some microbial floral such as Bacillus, Salmonella spp, Klebsiella spp, E.coli, and Staphylococcus aureus. The overall sensory scores for smoothies containing i) watermelon-pineapple and ii) sweet melon- cucumber was very good (8.0 & 7.0) respectively. With good manufacturing practices safe smoothie beverages prepared and consumed regularly can assist in the enhancement and sustainability of household food and nutrition security.

Accepted: 22/09/2023

Published: 23/09/2023 *Corresponding Author

Obasi, Blessing Chidi

E-mail: blessed200067@ yahoo.com

Phone: 2347035852279, 2348134533991

Keywords: blends, microbial quality, smoothies, sensory characteristics, vegetable sources.

1.0 INTRODUCTION

Fruits are excellent sources of phytochemicals which are essential for human health and relished by consumers in all seasons. The perishable nature of fruits and vegetables leads to higher pre- and post- harvest losses during distribution and processing. Fruits high in acidity content and astringency have a limited scope for table consumption though they are rich in functional ingredients. Combination of two or more fruits and vegetables will develop novel flavour and taste, which help in consumer acceptance. Presently, blended beverages are available in different flavours such as strawberry, chocolate, banana, vanilla, mango, raspberry, orange, etc.

Smoothie is a thick beverage product prepared from raw fruit pulps and/or the blends. Smoothies may include other ingredients such as vegetables, water, crushed ice, fruit juice, sweeteners (such as honey, sugar, syrup), dairy products (such as milk, yoghurt, low fat or cottage cheese, whey powder), plant milk (such as coconut milk, tiger nut milk, almond nut milk, soy milk), seeds (such as celery seeds), spices (such as ginger, garlic), tea, chocolate, herbal supplements or nutritional supplements (Zavasta, 2009). Some commercial smoothies, however, have added sugar, in order to increase sweetness. In some developing countries like Nigeria, smoothies are commonly prepared on demand and sold in big shops, hotels and other relaxation spots and might depend on the combination of fruits. Recently, smoothie products have been made more convenient in that consumers can carry the product out of the point-of-purchase in packaging materials. A healthy diet should compose of an appreciable quantity of fruits and vegetables, and regular consumption of sufficient amounts to avert major chronic diseases (Maksuda, et. al., 2016). Pineapple (Ananas comosus) has an outstanding juiciness and strong flavour that balances the taste of sweet and tart. Pineapples are also very rich source of bioactive compound known as bromelain, which is associated with many health benefits (Walker, et al., 2002). Water lemon (Citrullus vulgaris) is an excellent source of pro-vitamin A and other phytochemicals such as lycopene, beta-carotene, lutein and zeaxanthin (Charoensiri, et. al., 2009 and Edwards, et. al., 2003). Cucumbers contain 95 percent water.” This makes cucumbers a great way to stay hydrated. Cucumber-based beverages are taking part in balancing electrolyte levels, in case of dehydration. Cucumbers contain several antioxidants, including vitamin C, beta carotene and as well as flavonoids, triterpenes and lignans that have anti-inflammatory properties. The anti-inflammatory compounds in cucumbers help remove waste from the body and also reduce skin irritation.

In recent studies, smoothies (a form of ready-to-drink beverage) have become one of consumers’ preferred choices of drink, with suitable sensory properties in combination with nutritional benefits (Anon 2009 and Bordia, 2010). Researchers focused on developing different types of fruit-based smooth beverages/vegetable purees or smoothies made from a combination of fruits and/or vegetables to increase their contemporary value, nutritional content, and shelf life, without altering their sensory attributes (Keenan, et al;2010; Koutidou, et al; 2017). Therefore, this study aimed at the development of new smoothie formulations using watermelon, pineapple, sweet melon and cucumber as well as to investigate sensory characteristic and microbial quality of the obtained products.

2.0 MATERIALS AND METHODS

2.1 Raw materials and sources

The raw materials used in this study were water melon, pineapple, sweet melon and cucumber. They were purchased from the railway fruit market Makurdi, Benue State, Nigeria, and conveyed to the Department of Food Science and Technology, Federal University Wukari, laboratory where all the analyses were carried out.

2.2 Experimental design

The experiments were carried out based on completely randomized design (Bower, 2013) to obtain seven samples as shown in table 2.1 and 2.2

2.3 Sample preparation

2.3.1 Production of water melon-pineapple smoothie

Water melon-pineapple smoothie was produced as described in Figure 2.1. The fresh fruits of watermelon and pineapple were sorted, thoroughly washed with tap water and peeled with sterile knife and diced. The diced fruits were weighed on an electronic weighing scale and combined using the blending ratio of table (2.1) and then frozen to get a thicker and cold smoothie then blended together using an electric blender. Blending and homogenization took place within 3-5 minute.

2.4 The blending formulation on watermelon-pineapple and sweet melon-cucumber smoothie

Table 2.1: blending formulation on watermelon-pineapple smoothie.

sample code/ratio %watermelon %pineapple WMC 100 0 PSC 100 0 WMP1 90 10 WMP2 80 20 WMP3 70 30 WMP4 60 40 WMP5 50 50

KEY: WMC=watermelon control(100), PSC=pineapple control(100), WMP1=Watermelon-pineapple(90:10), WMP2=watermelon-pineapple(80:20), WMP3=watermelon-pineapple(70:30), WMP4=watermelon-pineapple(60:40), WMP5=watermelon-pineapple(50:50).

Table 2.2: blending formulation on sweet melon-cucumber smoothie.

sample code %sweet melon %cucumber SMC 100 0 CUC 100 0 SMC1 90 10 SMC2 80 20 SMC3 70 30 SMC4 60 40 SMC5 50 50

KEY: SMC=sweet melon control (100), CUC=cucumber control (100), SMC1 = sweet melon-cucumber (90:10), SMC2 = sweet melon-cucumber (80:20),

SMC3 = sweet melon-cucumber (70:30),

SMC4 = sweet melon-cucmber (60:40),

SMC5 = sweet melon-cucumber (50:50).

Fig 2.1: Flowchart for the production of water melon and pineapple smoothie

Source: (Victor-Aduloju et al; 2020).

2.5. Production of sweet melon and cucumber smoothie

Sweet melon and cucumber smoothie was produced as described in Figure 2.2. The sweet melon and cucumber was sorted and thoroughly washed with running tap water and 0.5g sodium chloride (Nacl) to remove moldy and contaminating microorganisms. Using a sterile knife, the sweet melon was cut and peeled neatly, the cucumber was sliced leaving the peels on to give the smoothie a brighter green color and more nutrients. The sliced sweet melon and cucumber was frozen to give a thicker texture without losing any flavor. The ingredients were blended using the ratio according to table 2.1, in an electric blender. Blending was done for 3-5min.

Fig 2.2: Flowchart for the production of sweet melon and cucumber smoothie

Source: (Victor-Aduloju et al; 2020).

2.6 Analytical methods

2.6.1 Determination of pH, Titratable Acidity, Sugar Content and Total soluble Solids (TSS) of the Smoothie Samples

The pH and titratable acidity of the samples were determined using (AOAC, 2010) method. Sugar content (°Brix) was determined using a hand refractometer at 20 °C according to the method of (AOAC, 2010) and the value obtained from the reference to standard table expressed as percentage sucrose by weight (°Brix). Total soluble solid was expressed as % Total solids ¼ (W2 x 100)/W1¼ (100 – % moisture) as described by (AOAC, 2010). Where, W1: Initial weight; W2: Dried weight.

2.7 Microbiological Analysis

2.7.1 Isolation and Enumeration

Total viable bacterial cells were determined using the method as described by (Obasi et.al; 2019). Serial dilution (10 fold) was carried out (1:10, 1: 100, 1:1000…10,0000). 0.1ml of appropriate dilutions (10-2 and 10-4) was placed on various agar plates using pour plate method and incubated at 37⁰C for 18-24 hours for total aerobic bacteria and coliform count. For fungi 0.1ml amount of appropriate dilutions (10-2 and 10-4) was poured into the plates of potato dextrose agar and incubated at room temperature at 28±1⁰C for 3 to 5 days. All enumeration were expressed as colony forming unit (cfu/ml).

2.7.2 Purification and Maintenance of Microbial Isolate

Bacteria isolates were transferred into fresh agar medium of isolation and incubated at 37⁰C for 24hours. Pure colonies of bacteria were maintained and stored at 4⁰C until needed.

2.7.3 Identification and Characterisation of the Isolates

Bacteria isolates were identified and characterized based on their morphology, structures, cell shape and appearance, and biochemical tests as described by (Cheebrough, 2006; Obasi et.al; 2019). Biochemical Tests determined included- Catalase, Oxidase , Indole , Triple Sugar Ion (TSI) , Citrate Utilization Test etc.

2.8. Sensory Evaluation of the Smoothie Samples

Sensory evaluation was carried out on all the samples using the method as described by (Sukanya and Michael, 2014). The samples were coded and served to 15 – man semi-trained panelists consisting of students and staff from the Department of Food Science and Technology, Federal University Wukari, Taraba State. The panelists were asked to evaluate the samples for flavor, color, aroma, taste, and overall acceptability using a 9-point Hedonic scale, where “9” represented extremely liked and “1” represented extremely disliked. The order of presentation of the samples was randomized. Table water was presented to the panelists to rinse their mouth in-between sample testing.

2.9 Statistical Analysis

The data collected were subjected to analysis of variance in completely randomized design using the statistical package for Social Sciences Version 17.0. Means were separated using Duncan’s multiple range test with significance accepted at p<0.05 (Bower, 2013).

3.0 RESULTS AND DISCUSSION

3.1 Physicochemical Composition of Watermelon-Pineapple Smoothie and Sweet Melon-Cucumber Smoothie

3.1.1 Physicochemical Composition of Watermelon-Pineapple Smoothie

The physicochemical composition of the watermelon-pineapple smoothie blend presented in Table 3.1a showed results for pH ranging from 3.71 to 4.62, titratable acidity ranging from 2.70 to 10.50g/l, total soluble solid ranging from 0.72 to 2.96 and ˚Brix 5.00 to 14.50 respectively. The pH of the smoothie blend ranged from 4.04 to 4.62, with sample WMP1 (90:10) having the lowest and WMP5 (50:50) having the highest value. The result obtained from this study agrees with Alake et al. (2022) who had similar result. According to literature, pH range of ripe fruits is between 4.5 and 5.35, which is slightly acidic (Gbarakoro, 2021), based on their values, the results from this study fall within the range. The results obtained showed slight significant difference (p < 0.05) for all the samples. Total titratable acid is used to determine the acid content or serves as a measurement for determining the acid content of food such as fruits. The total titratable acidity (TTA) of the smoothie blend ranged from 2.70 to 8.10, with sample WMP5 (50:50) having the lowest value and WMP1 (90:10) having the highest value. The results obtained from this study were higher than the result obtained by (Uzodinma, et al; 2020) who obtained very low result from a similar study which also involved the inclusion of water melon. The higher titrable acidity values obtained in this work compared favorably with the study done by (Chaudhary, and Shanta, 2015), who also reported higher value for TTA. The total soluble solids (TSS) for the smoothie blend ranged from 1.19 to 2.96 with sample WMP5 having the lowest values and WMP1 having the highest value. Total soluble solids (TSS) are important quality indicators that relate to sweetness, often referred to as sugar index (Balaswamy, 2011).

The results showed a significant difference (p < 0.05) among the samples. The ˚brix for the smoothie blend ranged from 4.73 to 8.50 with WMP1 (90:10) having lowest value and WMP5 (50:50) having the highest value. The brix content obtained in this study was similar to those obtained for fruit pulps/juices as reported by (Balaswamy, 2013), especially for the major samples used in this study pineapple. The brix indicate the degree of sweetness and the presence of the sugar present in the fruit (Balaswamy, 2011). The result showed significant difference (p < 0.05) for all the samples in this study.

Table 3.1a: Physicochemical Composition of Watermelon-Pineapple Smoothie

Sample code pH TTA TSS ˚BRIX WMC 3.71c±0.01 10.50a±0.14 2.02c±0.01 5.00d±1.41 PSC 4.55a±0.36 4.05e±0.07 0.72e±0.12 14.50a±0.71 WMP1 4.04bc±0.19 8.10b±0.14 2.96a±0.04 4.73d±0.39 WMP2 4.16abc±0.23 4.80c±0.14 2.62b±0.02 5.75cd±0.35 WMP3 4.21ab±0.13 4.46d±0.20 1.30d±0.18 7.50bc±0.71 WMP4 4.29ab±0.01 4.10e±0.14 1.21d±0.01 7.50bc±0.71 WMP5 4.62a±0.02 2.70f±0.14 1.19d±0.01 8.50b±0.71

Values are mean ± standard deviation of the physiochemical composition. Means within each column not followed by the same superscript are significantly different (p ≤ 0.05) from each other using Duncan multiple range test.

Key: WMC: watermelon control (100%), PSC: pineapple control (100%), WMP1: watermelon-pineapple (90:10%), WMP2: watermelon-pineapple (80:20%), WMP3: watermelon-pineapple (70:30%), WMP4: watermelon-pineapple (60:40%), WMP5: watermelon-pineapple (50:50%).

3.1.2 Physicochemical Composition of Sweet Melon-Cucumber Smoothie

The physicochemical composition of the sweet melon-cucumber smoothie blend presented in Table 3.2b showed results for pH ranging from 3.31 to 5.17, titratable acidity ranging from 0.81 to 10.58g/l, total soluble solid ranging from 1.47 to 3.74 and °Brix 2.25 to 5.23 respectively.

The pH value indicates the acidic or basic content of a particular substrate, the pH ranged from 3.31 to 4.19, with sample SMC5 (50:50) having the lowest pH value and SMC1 (90:10) having the highest pH value. The results obtained showed significant difference (p < 0.05) among the samples. Similar pH ranges from 6.75-0.15 were obtained in the work done by (Balaswamy, 2021] that developed smoothies from selected fruit pulps/ juices. By the addition of cucumber to the sweet melon, it reduced the acidic content of the smoothie as shown in Table 3.2b. The total titratable acidity (TTA) of the smoothie blend ranged from 7.47 to 10.58, with sample SMC1 (90:10) having the lowest value and sample SMC5 (50:50) having the highest value which is in agreement with the work of (Balaswamy, 2021) who obtained low acidity for fruit pulps/juices for sweet melon as observed also in this study. The results showed significant difference (p < 0.05) among the samples. TSS for SMC blends ranged from 1.79 to 2.84 where SMC5 (50:50) had the lowest value and SMC1 (90:10) had the highest value. The results showed a significant difference (p < 0.05). The ˚brix for the smoothie blends ranged from 3.50 to 5.23. Where sample SMC5 (50:50) had the lowest value and sample SMC1 (90:10) had the highest value. The brix indicates the degree of sweetness and the presence of the sugar in the fruit. Sweet melon generally has more (content) natural sugar when compared to cucumber and the result obtained in this study for sample SMC1 (5.23) compared favourably with the report of (Balaswamy, 2021) who obtained a value of 5.93 for fruit pulps/juices from sweet melon sample.

Table 3.2b: Physicochemical Composition of Sweet Melon-Cucumber Smoothie

Sample pH TTA TSS BRIX SMC 5.17a±0.01 0.81f±0.01 3.74a±0.01 4.25a±1.06 CUC 3.59bc±0.02 6.79e±0.01 1.47g±0.01 2.25 a±1.06 SMC1 4.19b±0.69 7.47d±0.02 2.84b±0.01 5.23 a±1.09 SMC2 3.47c±0.04 8.81c±0.01 2.74c±0.01 5.00 a±1.41 SMC3 3.41c±0.01 9.38b±0.04 2.68d±0.04 5.00 a±1.41 SMC4 3.41c±0.01 9.41b±0.01 2.15e±0.01 4.00 a±1.41 SMC5 3.31c±0.02 10.58a±0.04 1.79f±0.02 3.50 a±0.70

Values are mean ± standard deviation of the physiochemical composition. Means within each column not followed by the same superscript are significantly different (p ≤ 0.05) from each other using Duncan multiple range test.

Key: SMC (100): sweet melon control, CUC (100): cucumber control, SMC1: sweet melon-cucumber (90:10), SMC2: sweet melon-cucumber (80:20), SMC3: sweet melon-cucumber (70:30) SMC4: sweet melon-cucumber (60:40), SMC5: sweet melon-cucumber (50:50).

3.2 Sensory Evaluation

3.2.1 Sensory evaluation for watermelon-pineapple smoothie

A sensory evaluation aims at measuring consumer’s sensory perception of products as well as the effective, emotional responses that arise from this perception (Delarue, 2022). The result presented in Table 3.3a shows the sensory evaluation of watermelon-pineapple smoothie.

Taste ranged from 6.47-7.60. The highest value was WMP3 (7.60) followed by WMP5 (7.27) and the least value recorded was WMP4 (6.47). The high rating of taste for WMP3 could be as a result of the substitution of pineapple. The result obtained from this study is similar to the findings of Teleszko and Wojdyło, (2014) and Nowicka et al., (2016) where sweeter products were more accepted when compared to other less sweet samples (varied ratio) and this is because pineapple have more sugar in the base of the fruit.

The values for aroma ranged from 6.67 to 7.33. Based on the samples analyzed, the lowest value was WMP1 (6.67) and the highest values were obtained from samples WMP2, WMP3 and WMP5 (7.33) respectively having the highest rated aroma value which may be because pineapple has an outstanding juiciness and strong flavour that balances the taste of sweet and tart. Pineapples are also very rich source of bioactive compound known as bromelain, which is associated with many health benefits (Walker et al. 2002, in Uzodinma et al., 2020). The results were not significantly different (p < 0.05).

The ratings for color by the panelists ranged from 7.07 to 7.40. The highest rating for colour was sample WMP1 (7.40) for the varied samples while WMP4 (7.07) had the least value. The control sample PSC (7.93) was the most appealing by the panelist because generally, pineapple has an acceptable colour used in liquid beverage such as juice as a result of the presence of (lycopene) alpha-carotenoid Uzodinma, (2020). The results were not significantly different (p < 0.05).

The general acceptability of watermelon-pineapple smoothie showed that sample WMP2 (7.73) was most preferred by consumer followed by WMP5 (7.33), WMP1 (7.07), WMP3 (7.07) and the least was WMP4 (6.60) respectively. There was a significant difference (p < 0.05) between the samples.

TABLE 3.3a: Mean Sensory Score of Watermelon-Pineapple Smoothie

Sample

Code Taste Aroma Colour Flavor General

Acceptability WMC 6.87a±1.51 6.93a±1.53 7.80a±1.21 7.00a±1.36 7.47ab±1.25 PSC 7.27a±1.95 7.60a±1.12 7.93a±1.28 7.07a±1.27 7.89a±1.19 WMP1 7.00a±1.51 6.67a±1.35 7.40a±1.50 6.73a±1.49 7.07ab±1.49 WMP2 7.00a±1.07 7.33a±1.05 7.33a±1.23 7.27a±0.90 7.73a±0.96 WMP3 7.60a±1.12 7.33a±1.04 7.33a±1.40 6.93a±1.49 7.07ab±1.44 WMP4 6.47a±0.99 6.73a±1.22 7.07a±1.22 6.93a±1.44 6.60b±0.91 WMP5 7.27a±1.16 7.33a±1.23 7.33a±0.90 7.13a±1.30 7.33ab±0.81

Values are mean ± standard deviation of 15 panelists. Means within each column not followed by the same superscript are significantly different (p < 0.05) from each other using Duncan multiple range test.

Key: WMC: watermelon control (100%), PSC: pineapple control (100%), WMP1: watermelon-pineapple (90:10%), WMP2: watermelon-pineapple (80:20%), WMP3: watermelon-pineapple (70:30%), WMP4: watermelon-pineapple (60:40%), WMP5: watermelon-pineapple (50:50%).

3.2.2 Sensory evaluation for sweet melon-cucumber smoothie

The result of the sensory rating for the smoothie blend of sweet melon-cucumber is shown in the Table 4.4b. Taste ranged from 5.67 to 7.33. The highest rating by the panelist was recorded for sample SMC2 (7.33) and the least value was for sample SMC4 (5.67). The result obtained from this study in terms of taste is in agreement with the work done by Balaswamy, et al., (2013) who had a similar result (7.8). The result showed significant difference (p < 0.05).

Sweet melon is largely sought for due to its sweet refreshing fruit Harini and Nithyalakshmi. (2017). Also, Allwood et al., (2014) reported that the flavor and aroma of the fruit is dictated by the amount of volatile organic compounds present in it. Aroma ranged from 5.93 to 6.73. SMC5 had the highest value and sample SMC4 had the lowest. The result showed a significant difference (p < 0.05). Colour ranged from 5.86 to 6.93. Sample SMC4 had the lowest value and sample SMC1 had the highest compared to other samples. The result is not significantly different (p < 0.05). Flavour ranged from 5.80 to 6.80. Sample SMC5 had the lowest and SMC2 had highest value. The flavour of food ultimately determines its acceptance or rejection even though its appearance may evoke initial response Ojinnaka and Nnorom, (2015). The results were not significantly different (p < 0.05).

The general acceptability of the control (SMC) is expected and might be due to higher sweetness as indicated by the ºbrix value. Based on the various blends sample SMC2 (7.00) was the most preferred in relation to all the parameters assessed. The result was not significantly different (p < 0.05).

TABLE 3.3b: Mean Sensory Score of Sweet melon-Cucumber Smoothie

Sample

Code Taste Aroma Colour Flavor General

Acceptability SMC 7.07a±2.60 7.60a±1.12 7.07a±2.02 6.87a±2.03 7.33a±1.91 CUC 6.27ab±1.94 6.73ab±1.62 6.20a±1.57 5.80a±1.70 6.33a±1.88 SMC1 7.07a±1.44 6.60ab±1.35 6.93a±0.96 6.67a±1.59 6.93a±1.49 SMC2 7.33a±1.05 6.60ab±1.50 6.80a±1.01 6.80a±1.78 7.00a±1.25 SMC3 6.13ab±1.13 6.53ab±1.13 6.33a±1.63 6.07a±1.49 6.53a±1.13 SMC4 5.67b±1.29 5.93b±1.39 5.86a±1.64 6.00a±1.36 6.20a±1.26 SMC5 6.33ab±1.84 6.73ab±1.33 6.13a±1.88 5.80a±1.52 6.33a±1.80

Values are mean ± standard deviation of 15 panelists. Means within each column not followed by the same superscript are significantly different (P < 0.05) from each other using Duncan multiple range test.

Key: SMC: sweet melon control (100%), CUC: cucumber control (100%), SMC1: sweet melon-cucumber (90:10%), SMC2: sweet melon-cucumber (80:20%), SMC3: sweet melon-cucumber (70:30%), SMC4: sweet melon-cucumber (60:40%), SMC5: sweet melon-cucumber (50:50%)

3.3 Microbial Load

3.3.1 Total aerobic plate count (TAPC) of bacterial cells (cfu/ml) for watermelon-pineapple smoothie

The result presented in table 3.4a showed the total aerobic plate count (TAPC) of the bacterial cells, coliform and fungi counts for the watermelon-pineapple smoothie. The total bacteria cells, coliform and fungi count(cfu/ml) for samples analyzed at different ratios included watermelon control (WMC:100%), pineapple smoothie control (PSC:100%), watermelon pineapple (WMP:90:10, 80:20, 70:30, 60:40 and 50:50%) ranged from 1.5×104 – 8.2×103 , 1.5×103 – 6.4×103 , 1.1×104 -9.2×103 cfu/ml respectively.

The total bacteria count for all the samples were within the maximum acceptable level for any fruit juice as listed in the microbiological criteria for foodstuffs by Gulf Standards (2000) which is 1.0 × 104 cfu/ ml. Generally smoothie production which do undergo pasteurization have been reported to have a total bacterial count above 102 margin by Uzodinma et al., (2020). However, the results obtained from this study did not surpass the Commission Regulation (EC) No. 2073/2005 on microbiological criteria for foodstuffs for unpasteurized fruits and vegetable juices (ready-to-eat).

The coliform count ranged from 1.5×103 to 6.4×103cfu/ml with sample WMP5 (50:50) having a higher count which could be as a result of non-pasteurization. The high coliform count did not exceed 1000 cfu/ml of the sample since it is within the maximum acceptable level for any fruit smoothie (Gulf Standards 2000; Anon, 2005).

The fungi count ranged from 1.1×104 to 9.2×103cfu/ml with sample WMP3 (70:30) having highest count of which agrees with the food safety and standard authority for microbial limit for fruit juice and fruit nectar FSSAI, (2011).

Table 3.4a: Total aerobic plate count (TAPC) of bacterial cells (cfu/ml) obtained from watermelon-pineapple Smoothie

Sample code Ratio Total bacteria count(cfu/ml)

Coliform count

Fungi count WMC 100 1.7×104 1.6 x104 3.6×103 PSC 100 5.3×103 1.6×104 6.4×105 WMP1 90:10 2.1×104 1.7×104 3.0×103 WMP2 80:20 1.5×104 1.5×103 1.3×104 WMP3 70:30 8.2×103 5.3×103 9.2×103 WMP4 60:40 6.3×103 6.0×103 1.1×104 WMP5 50:50 8.1×103 6.4×103 1.4×104

Key: WMC: (100%) watermelon control, PSC: pineapple control (100%), WMP1: watermelon-pineapple (90:10%), WMP2: watermelon-pineapple (80:20%), WMP3: watermelon-pineapple (70:30%), WMP4: watermelon-pineapple (60:40%), WMP5: watermelon-pineapple (50:50%).

3.3.2 Total aerobic plate Count (TAPC) of bacterial cells (cfu/ml) for sweet melon-cucumber smoothie

The result presented in table 3.4b showed the total aerobic plate count (TAPC) of the bacterial cells, coliform and fungi counts for the sweet melon-cucumber smoothie. The total bacteria cells, coliform and fungi count (cfu/ml) for samples analyzed at different ratios include sweet melon control (SMC:100%), cucumber-smoothie control (CUC:100%), sweetmelon-cucumber (SMC:90:10, 80:20, 70:30, 60:40 and 50:50%) ranged from 1.2×104 to 8.0×103 for total bacterial count, 1.3×104 to 7.0×105 coliform count and fungi count 1.8×105 to 7.9×103 respectively.

The total bacterial count did not surpass the Commission Regulation (EC) No. 2073/2005. The counts were below the maximum acceptable level for any fruit juice/smoothie as listed in the microbiological criteria for foodstuffs by Gulf Standards (2000) which is 1.0 × 104 cfu/ ml. for all the samples assessed.

The coliform count ranged from 1.3 x104 to 9.6×103 cfu/ml. Sample SMC5 (50:50), SMC4 and SMC1 were within the acceptable limit for coliform count in any microbiological criteria for

juices and smoothies. Sample SMC3 was above the acceptable limit for coliform count, but SMC2 had no growth.

The fungi count ranged from 1.8×105 to 7.9×103cfu/ml. The total fungi count of the non-pasteurized smoothies did not exceed the maximum acceptable level for any fruit juice as listed in the microbiological criteria for foodstuffs by (Gulf Standards 2000 and Uzodinma et al., (2020).

Table 3.4b Total aerobic plate count (TAPC) of Bacterial Cells (Cfu/ml) obtained from sweet melon-cucumber smoothie

Sample code Ratio Total bacteria count(cfu/ml) Coliform count (MCA) Fungi count (PDA) SMC 100 9.1×105 7.0×105 5.6×103 CUC 100 2.1×104 1.6×104 7.3×103 SMC1 90:10 1.5×104 1.4×104 1.8×105 SMC2 80:20 1.7×104 NG 5.3×103 SMC3 70:30 1.8×106 1.0×106 7.7×103 SMC4 60:40 2.1×104 1.3×104 3.2×103 SMC5 50:50

1.9×104

9.6×103 7.9×103

Key: SMC (100): sweet melon control,CUC (100): cucumber control, SMC1: sweet melon-cucumber (90:10), SMC2: sweet melon-cucumber (80:20), SMC3: sweet melon-cucumber (70:30), SMC4: sweet melon-cucumber (60:40), SMC5: sweet melon-cucumber (50:50).

3.3.3 Morphological and Biochemical Characteristics of Bacterial Strains Isolated from Watermelon-Pineapple and Sweet Melon-Cucumber Smoothie Blends

The microbial flora for watermelon-pineapple and sweet melon-cucumber smoothies as shown in Figure 3.1 and 3.2.Watermelon-pineapple isolate revealed the following species Salmonella spp 12.96%, Klebsiella pneumonia 12.96%, Staphylococcus aureus 12.96%, E.coli 11.11%, Enterobacteriaceae 11.11%, Proteus vulgaris 9.255, Pseudomonas spp 7.40%, Klebsiella spp 7.40%, Micrococcus 5.56% and Bacillus 3.70%, while sweet melon-cucumber showed the species of the microbial flora which includes Salmonella spp 12.19%, Klebsiella pneumonia 14.63%, Staphylococcus aureus 17.07%, E.coli 17.07%, Enterobacteriaceae 17.07%, Proteus vulgaris 7.31%, Klebsiella spp 7.31%, Bacillus 4.87% and Shigella 2.43% respectively.

The presence of pathogenic Escherichia coli, and Staphylococcus aureus usually constitute a direct proof of faecal contamination of irrigation water (Cheesbrough, 2006). The identified non-lactic acid bacteria (E. coli, Bacillus species and Proteus species) reported in this study has also been reported by other authors (Onovo et al., 2007).The Enterobacteriaceae family mostly involves harmless bacteria, some of them contribute to food spoilage or exist as foodborne pathogens (Edelstein, 2014). The bacterial contamination of plant origin in food as revealed in this study may occur through fertilizers with animal manure, soil, and irrigation water, as well as washing, handling, and processing vegetables or fruit during the postharvest period (Berger et al., 2010) (Seo and Matthews 2014).

Fig 3.1: Prevalence of microorganisms isolated from watermelon-pineapple smoothie blends

Fig 3.2: Prevalence of microorganisms isolated from sweet melon-cucumber smoothie blends

4.0 CONCLUSION AND RECOMMENDATION

Smoothies could be prepared and preserved by blending various tropical fruits and vegetables without any addition of external sweetener. Smoothies based on fruits and vegetables viz., blends of watermelon-pineapple and sweet melon-cucumber in this study were organoleptically acceptable. Smoothies containing: watermelon-pineapple (WMP) and sweet melon-cucumber (SMC), WMP1: (90:10%), WMP2: (80:20%), WMP3 and (70:30%) and SMC1: (90:10), SMC2: (80:20), SMC3: (70:30) respectively were found to be best combinations in terms of sensory score (˃7.0). A variety of smoothies can be prepared depending on availability of seasonal fruits/vegetables leading to new product development. The microbial counts since it was not above the allowable limit by Commission Regulation (EC) No. 2073, may not pose any threat to the health and safety of consumers.

Disclosure of conflict of interest

No conflict of interest to disclose.

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Cite this Article:

Obasi, BC; Odoh, PI (2023). Organoleptic Properties and Microbial Quality of Smoothies Produced from Watermelon-Pineapple and Sweet Melon–Cucumber Blends. Greener Journal of Agricultural Sciences, 13(3): 186-197.

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