1 Introduction

Fruits are essential component of a healthy diet. They contain a variety of phytonutrients which has been linked with numerous health benefits including enhancing the immune system [1]. They may be consumed in their raw form or processed into juice. The juice may either be consumed immediately or further processed and packaged locally or by fruit juice companies to extend the shelf life.

Freshly prepared fruit juice as being considered healthy, may not be the case in some instances due to contamination by microbes [2]. Commonly found microorganisms in street juice include, Pseudomonas spp., Staphylococcus spp., Vibrio cholerae, Escherichia coli, Salmonella Typhi [3]. Factors that may contribute to microbial contamination of fruits juice ranges from contamination of fruits from the farm, handling, processing, packaging, and transportation, [4].

When fruits meant for juice production are poorly handled, the contamination can be transferred to the juice. During the juice production process contamination can be due to unhygienic environment, food flies, airborne dust, extended preservation without proper pasteurization and refrigeration, and contaminated source of water especially for locally made ready to drink and packaged fruit juice [5].

Aside microbial contamination, fruit juices can be contaminated with metals [6, 7], residues from pesticides [8] and many other contaminants harmful to human health. Antimicrobial residues is another contaminant that has raised concerns in the food value chain especially food of animal origin [9]. In plant food, antimicrobial residue such as oxytetracycline has been reported in vegetables like cabbage [4]. Antimicrobials are applied on some fruits such as apple. For instance, streptomycin is given to apple trees during blooming (bloom) to suppress fire blight in countries such as in New Zealand where it is permissible [10]. When juice is made from such fruits, the juice may be contaminated with antimicrobial residues. The continuous consumption of antimicrobial residue contaminated foods may lead to the emergence of antibiotic resistance pathogens which can affect humans. This is especially important because an identical wide host-range of plasmids harbouring antibiotic resistance genes have been discovered in plant and human pathogens [11, 12]. Also, a recent study in India, recorded 80% of bacterial strains isolated from orange juice samples to be drug resistant [13]. However, these antimicrobials (antibiotics) are only required for the control of plant bacterial diseases, for example, pear and apple fire blight and peach bacterial spot [14]. Antimicrobial residue (antibiotics) may be introduced into fruit through the water used for irrigation or manure applied on the farm. According to Kumar et al., [15], organic crops are likely to be contaminated with antibiotics because of exposure to antibiotic residues found in manure. Furthermore, a study by Amarasiri et al., [16], reported that antimicrobial residues, antimicrobial-resistant bacteria, and antimicrobial resistant genes (ARGs) can all be widely distributed in water. In Ghana, antimicrobial residue contamination is typically found in animal and food products such as meat and milk, vegetables, honey, and uptake of antibiotics from irrigation water [17,18,19]. Research on microbial quality of food conducted in the Northern region, Tamale, are mainly on beef, ready-to-eat vegetable salad and raw milk [20,21,22]. Report by Saba and Gonzalez-Zorn [23], reported on the limited data on microbial quality in fruit in Tamale. Fruits and its products are ready to eat without heating and can pose health risks to consumers when unhygienically handled. Thus, this study was conducted to determine the microbial load in locally and industrially processed fresh fruit juice, and to determine, if any, the presence of antimicrobial residues in these fruit juices.

2 Materials and methods

2.1 Study area

Fruit juice samples were obtained in Tamale, the capital city of the northern region of Ghana. Tamale is estimated to have a land size of about 646.90180 Km2 located within latitude 9° 25′ 58.5084'' N and longitude 0° 50′ 54.4272'' W. The Metropolis shares boundaries with Central-Gonja to the South-West, Sagnarigu West and North, Mion District to the East and East-Gonja to the South [24]. Microbial analysis of all fruit juice samples was carried out in the microbiology section of the Spanish Laboratory complex of the University for Development Studies, Nyankpala campus situated within the Tolon District. The Tolon district geographically lies between longitudes 0° 53′ and 1° 25′ West and latitude 9° 15′ and 10° 02′ North [25].

2.2 Sample collection

Prior to sample collection, a purposive and snowball survey was conducted to determine the number of local fresh juice sales point within the Tamale metropolis. All 25 reported sales point for local fresh fruit juice were considered for sample collection in this study. Fresh fruit juice samples were collected in sterile plastic Ziploc bag. Three industrially processed fruit juice were collected as control.

A total of 28 fruit juice samples were collected based on two categories: 25 locally processed fresh fruit juices which were obtained from catering services sold from dispensers (watermelon, watermelon-ginger, pineapple, pineapple-ginger, pineapple-sugarcane, tamarinda-ginger and mango) and three (3) industrially processed fruit juices which were obtained from shelves of supermarket. Out of the seven varieties of the local fresh juice, three (watermelon ginger, tamarind ginger, and pineapple sugarcane) was each sold at only one sale point. The other four varieties of local fresh juice (Watermelon (4 sale point), Pineapple (6 sales point) Mango (4 sales point), and Pineapple ginger (8) were collected from at least four different sales points. The collected samples were kept in an air-tight box containing ice packs and transported to the Spanish Laboratory Complex of the University for Development Studies for analysis.

2.3 Microbiological analysis

Culturing of samples was carried out as previously describe by Mahale et al., [26], with some modification. Briefly, 10 ml of each local fresh fruit juice was pre-enriched in 90 ml of 0.1% peptone water and incubated at 37 °C for 6 h. This was followed by five levels (101 to 10–5) serial dilutions in 0.1% peptone water. 100 µl of each dilution factor were inoculated on MacConkey (MCA; HiMedia, Mumbai, India) and Salmonella –Shigella (SS) media and spread using sterilized glass beads. The plates were incubated at 37 °C for 24–48 h. Identical morphologically red-pink colony with bile precipitate on MacConkey agar, which was gram negative bacilli was subjected to biochemical test.

Whilst on SS agar, identical morphologically straw-coloured colonies with black centres, which was gram negative bacilli was also subjected to biochemical test.. The confirmed E. coli or Salmonella spp. colonies were then aseptically picked and streaked on nutrient agar and incubated at 37 °C for 24 h to obtain pure culture isolates for stock.

2.3.1 Biochemical identification of E. coli and Salmonella spp.

Biochemical identification of E. coli and Salmonella spp were performed as previously described by Kar et al., [27] with some modifications. Briefly, Isolates were subjected to Citrate, Catalase, Indole, Tripple sugar iron (TSI) test. E. coli is characterised as citrate-negative, catalase-negative,indole-positive, and TSI showing; Acid/Acid, Gas positive ( +) and H2S negative (−).

Whilst Salmonella is characterised as citrate-positive, catalase-negative, indole-negative and TSI showing; Alkaline/Acid, Gas positive (+) and H2S positive (+).

2.4 Antimicrobial residue detection

Antimicrobial residues detection was performed on all 28 samples using rapid qualitative screening method. it was performed using the PremiTest kit (R- Biopharm AG, Germany) following the manufacture’s instruction. Briefly, 100 μL of each fresh local fruit juice sample was pipetted into the ampoules labelled with the fruit juice sample codes. The ampoules with the respective fruit juice samples were pre-incubated at room temperature for about 20 min, before ampoules were gently inverted to dispense the fruit juice samples. The residual fruit juice samples in the ampoules were carefully removed by filling and emptying ampoules with deionized water thrice. This was followed by inversion of the ampoules on tissue paper to drain any remaining water. The test ampoules were then wrapped in aluminium foil provided by the manufacturer and incubated in a water bath at 64 °C until the control changed colour from purple to yellow [19].

2.5 Statistical analysis

The data on microbial count were entered into Microsoft Excel (2016) for processing and analysis. The data were summarised using the descriptive statistical analysis. Oneway ANOVA test was performed to compare significant difference in average count. The results were presented using tables and figures. A P value of ≤ 0.05 is considered significant.

3 Results

3.1 Occurrence of bacteria isolates

Escherichia coli was recorded in 22 (88%) out of the 25 locally processed fruit juice sampled whilst Salmonella spp was detected 10 (40%) out of the 25 sampled local fruit juice recorded (Table 1).There was no E. coli or Salmonella detected in the industrially processed fruit juices.

Table 1 Occurrence of bacteria isolates in locally made fruit juice samples
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3.2 Microbial load profile of the fruit juice samples

The detectable E. coli count recorded for locally made fresh fruit juice ranged from 1.33 × 103 CFU/ml to 9.23 × 104 CFU/ml with a mean count of 1.74 × 106 CFU/ml. Salmonella spp. count also ranged from 3.33 × 102 CFU/ml to 9.53 × 105 CFU/ml in the locally processed juices with a mean count of 9.87 × 105 CFU/ml. There was no detectable E. coli and/or Salmonella spp count in some of the local fresh fruit juice samples (Adiditional file 1: Table S1). Also, none of the industrially processed juice included as control recorded detectable E. coli and/or Salmonella spp count (Additional file 1: Table S2).

3.2.1 E. coli load in different local fresh fruit juice samples

Three local fresh fruits juice each sold at only one sales point which included; Watermelon ginger, tamarind ginger and Pineapple sugarcane recorded E. coli count of 6.43 × 104, 0.00 × 100, and 2.67 × 103 respectively (Figure 1A).

Fig. 1
figure 1

A graph showing E. coli count in different type of local fresh fruit juice each sold at only one sales point. No viable count is recorded in tamarind ginger with the highest count recorded in watermelon ginger. B shows graph of mean E. coli count in different local fruit juice each sold in at least four sales points. Highest count is recorded in Pineapple and the least count recorded in Pineapple ginger

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Four local fresh fruit juice each sold at more than three sales point: Watermelon (4 sale point), Pineapple (6 sales point) Mango (4 sales point), and Pineapple ginger (8 sales point) recorded mean E. coli count of 4.13 × 104, 1.71 × 105, 5.98 × 104 and 3.60 × 104 CFU/ml respectively (Figure 1B). Statistical analysis of local fruit juice sold in at least four sales points showed no significant difference in E. coli count between the different local fresh fruit juices (Table 2).

Table 2 Shows the statistical comparism of the different local fresh fruit juice each sold in at least four sales points
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3.3 Antimicrobial residue profiling

There were no antimicrobial residues detected in any of the 28 samples, both locally and industrially processed juice samples tested negative.

4 Discussion

4.1 Microbial quality

Despite the potential benefits derived from fruit juice consumption, safety and quality of these juices have become of concern in both industrially processed and locally produced juices. Contamination of fruits and its products can occur from harvesting, through fruit juices processing to sales points. Hence, fruit juices have recently been identified as “emerging vehicles” for foodborne illnesses caused by bacterial pathogens [28, 29].

Results of the current study showed that all the industrially processed fruit juice samples were devoid of both E. coli and Salmonella spp. unlike the locally processed fruit juice that recorded both microorganisms. Both E. coli and Salmonella spp. has previously been isolated in fruits [30]. The two bacterial genera enumerated has been identified as the leading cause of foodborne diseases [31, 32]. The results of the industrially processed samples are consistent with Addo et al., [33], that recorded the absence of Salmonella and any other coliform in imported fruit juice samples. With regards to the local fresh fruit juice, the recorded prevalence of E. coli (88%) and Salmonella (40%) in the current study contradict Addo et al., [33], where all freshly prepared fruit juice samples tested negative for E. coli. However, it is in line with De Jesús et al., [34], who recorded the presence of E. coli and Salmonella in 85% of fresh orange juice samples, and also corroborates Bikala and Kadire [35], work where E. coli (81.25%) Salmonella (62.5%) were isolated in fresh juice samples Additional file 1: Table S2.

In terms of E. coli count, whilst no viable count is recorded for the industrial fruit juice, the recorded average load for local fresh fruit juice in this study was above the acceptable limit of 1 × 102 Cfu/ml specified by the Ghana Standards Authority (GSA) [36, 37]. The observed difference in bacterial load between the local fresh fruit juice to industrial juice in this study is similar to the report by Rahman et al., [38], where total viable bacterial count was found to be greater in most fresh juices (2.4 × 104 Cfu/ml than in commercially packaged juices (3.2 × 103 Cfu/ml).

In this study, difference in E. coli count is recorded in the different types of local fruit juice. Local fresh pineapple juice recorded the highest count whilst local fresh Pineapple ginger juice recorded the least count. It is unclear whether pineapple ginger mix has some antimicrobial properties. Interestingly, tamarind ginger from only one sales point recorded no viable count. It is unclear whether this can be attributed to possible antibacterial property of the mix. The variation in the microbial load of these freshly prepared fruit juices could imply how fruits handled by specific vendors/processors has a substantial impact on the level of microbial contamination [30]. It is unclear whether the processing could be a contributing factor for the observed variations for this study.

Adherence to safety standards, which includes the use of safe water, hygienic practices, pasteurisation, efficient packaging and routine microbial quality check by most industries could account for the low or the observed no viable count of E. coli and Salmonella spp. in the industrial fruit juice. Therefore, adapting such good practices could improve the quality of locally produced fresh fruit juice.

4.2 Antimicrobial residues

To enhance crop yields, the agricultural business (including crop cultivation and livestock production) faces hurdles. As a result, the use of antibiotics in livestock and antimicrobials on some disease-causing bacteria in fruit trees, are now common [9]. Antimicrobial in these fruits can be transferred to fruit juices.

Antibiotic residues have been linked to the usage of antimicrobial residue-contaminated manure in a number of studies [39, 40]. According to Kumar et al.,[15], organic crops are likely to be infected with antibiotics due to exposure to antibiotic residues found in manure. Taylor and Reeder [41], discovered no evidence of antibiotic use on crop plants in Africa, including Ghana. In this study, antimicrobial residues were absent in all 28 samples examined. This corroborate with Taylor and Reader’s report [41].

5 Conclusion

Majority of the locally processed fresh fruit juices were contaminated with E. coli and a fewer number of samples were contaminated with Salmonella spp. However, the industrially processed juices were devoid of contaminations for both microorganisms. Also, the microbial load for E. coli was above the recommended. Interestingly, antimicrobial residues were absent in all fruit juices sampled, both industrially and locally processed juices.

Although fruit juices boost the immune system of consumers, it can also harm humans if they are contaminated with foodborne pathogens. To avoid outbreaks of food-borne disease, the quality of the fruit juices should be monitored through regular surveillance to determine microbial and antimicrobial residue quality.