1 Background

Fruits, which are the primary source of natural food, are mainly consumed fresh or ripe. Due to their high quantities of dietary fibre, vitamins, minerals, notably electrolytes; and phytochemicals, especially antioxidants, fruits are most often regarded in nutritional recommendations [1]. Fruit eating is important because it has been reported to lower the risk of various diseases, including atherosclerosis, heart and brain disorders, and cancer [2,3,4]. However, the optimum benefit of fruit may not be obtained when the safety and source of the fruits are called into question.

Food safety is one of the most pressing public health concerns in the world, especially in emerging and developing economies, and it has also become one of the most difficult societal concerns in these countries [5]. Food safety can be threatened through various activities such as poor hygiene, raw and poorly cooked food, storing fruits in unsafe temperatures, and artificial ripening of fruits [6].

Fruit ripening is a natural process in which the fruit experiences a series of chemical changes that cause it to become sweeter, colourful, soft and pleasant [7]. Ethylene is a plant hormone that causes fruit ripening and the senescence of vegetative tissues, and it has been shown to aid fruit ripening when administered exogenously [7, 8].

Although employing ethylene for ripening under controlled temperature and relative humidity conditions is the only safe and widely acknowledged method, artificial ripening agents such as ethylene gas, ethylene glycol, and calcium carbide (CaC2), can expedite the ripening process [9]. However, due to the high cost of ethylene ripening agents, the use of substitute low-cost chemicals like CaC2, despite being banned in Nigeria due to its toxic effects, and ethephon has been reported to be used illegally to artificially trigger fruit ripening in many underdeveloped nations [10, 11].

The use of artificial ripening agents has been banned in many countries around the world [12, 13] and in Nigeria [14]. In Nigeria, as well as in most parts of the world, governing bodies [such as the National Agency for Food Administration and Control (NAFDAC) and Standards Organization of Nigeria (SON)], policies, and laws have been put in place to help curb the illegal use of artificial ripening agents in ripening fruits [14, 15]. The policies and laws in Nigeria regarding the use of calcium carbide (CaC2) aim to stop its use due to its toxic effects. According to the National Agency for Food and Drug Administration and Control (NAFDAC), the use of CaC2 for fruit ripening is banned because it can produce harmful chemicals that pose significant health risks to consumers, including cancer [14, 15]. NAFDAC has warned that carbide-ripened fruits can kill and has taken steps to enforce this ban by educating the public and conducting inspections to ensure compliance. Agents such as ethylene gas, and ethephon have been approved by the authorities to aid in ripening of fruits while CaC2 was banned due to toxic effects [10, 11]. This, however, has not stopped the use of artificial agents such as CaC2 in ripening fruits. The encouragement of CaC2 use often comes from informal sources within the agricultural sector due to its low cost and rapid ripening effects. However, this practice is illegal and discouraged by health authorities. Common fruits that are often subjected to artificial ripening using agents like CaC2 include: mangoes, bananas, pawpaw (papaya) and tomatoes. Although the most common are mangoes, and bananas [9].

CaC2 use has been linked to several negative health effects in humans and to reduce fruit quality [9, 16]. The negative effects of CaC2 range from congenital effects [17] to mucosal irritation [18]. Consumers of such fruits may also suffer from nervous system illnesses, skin ulcers, and heart-related health problems because of arsenic's hypoxia-inducing effects in CaC2 [19]. Because of these facts, some nations have banned the use of CaC2 as a fruit ripening agent [20, 21]. Covert use of CaC2 to ripen fruits is common practice in African countries, including Nigeria [22, 23]. Traders of these fruits in locations where artificial fruit ripening is common have limited knowledge of artificial ripening and the risks associated with using CaC2 to ripen fruits [24, 25]. Consumers are also often unaware of the ripening method used by vendors and its effects [26].

This study presents a distinctive approach to understanding fruit safety and artificial ripening practices, particularly in the context of Ado-Ekiti, Ekiti State, Nigeria. Unlike previous research efforts, which often took a broader perspective, this study focuses specifically on the dynamics within this specific region. By delving deeply into the ripening practices of local fruit sellers and assessing the knowledge of both sellers and consumers regarding the health risks associated with calcium carbide (CaC2) use, the research offers a comprehensive understanding of the factors influencing fruit safety within the local market.

One notable aspect of this study is its integration of perspectives from both fruit sellers and consumers. By considering the viewpoints of these two key stakeholders, the research provides a holistic view of the issue, uncovering potential disparities in knowledge and practices. Furthermore, the study aims to identify knowledge gaps and misconceptions that may contribute to unsafe practices, thereby informing targeted educational interventions to enhance fruit safety awareness within the community.

Moreover, the scarcity of studies assessing the knowledge of both fruit sellers and consumers in Nigeria underscores the novelty and importance of this research. Through its rigorous examination of ripening practices and associated risks specific to Ado-Ekiti, Ekiti State, this study makes a significant contribution to the existing literature on fruit safety and artificial ripening practices.

2 Methods

2.1 Study design

This study was a cross-sectional study.

2.2 Study population and site

The study population included fruit traders in two major markets and consumers of fruits in Ado-Ekiti, Ekiti state while the study site was major fruit markets and the public around the markets in Ado-Ekiti, Ekiti state. The two major markets were Oja Oba Market and Bisi Markets.

2.3 Sample size

The total sample size for participants was determined using Raosoft® software, considering a response rate of 50% and a confidence interval of 95%. With an estimated population of 424,340 inhabitants in Ado-Ekiti as of 2019 [27], the final estimated sample size was 350.

2.4 Sampling technique

The consecutive sampling technique was used to sample the fruit sellers, while a simple random sampling technique was used to sample the consumers around the markets.

2.5 Data collection instrument

Two semi-structured questionnaires were used to conduct this study. The first questionnaire was used to assess of knowledge of health risks associated with CaC2 use in fruit ripening among fruit sellers, whereas the second questionnaire was used to assess knowledge among consumers. The first questionnaire was structured partly from inputs from similar studies by Noor et al. [28] and Ekanem et al. [25]. The second questionnaire was also semi-structured with inputs from a similar study by Eze and Asogwa [29]. The first was a 20-item questionnaire comprising two sections. The first section assessed the fruit sellers’ demographics (5 questions), while the second section assessed their practice of fruit ripening and knowledge of the health risks of CaC2 use in fruit ripening (15 questions). The second questionnaire contained 20 items and comprised three sections. The first section assessed the consumers’ demographics (5 questions), the second section assessed their frequency of eating fruits (2 questions), and the third section assessed the users’ knowledge of fruits ripening and health effects of consumption of CaC2-ripened fruits (13 questions). The knowledge of the consumers was assessed using 5-point Likert scale questions. Participants’ knowledge was categorised into Good knowledge (≥ 70% of total score), fair knowledge (50–69% of total score), and poor knowledge (< 50% of total score).

2.6 Validity and reliability of the questionnaire

The questionnaires were validated through face validity and content validity among lecturers from three departments in the College of Pharmacy, Afe Babalola University, Ado-Ekiti. The questionnaires were pre-tested on 10 fruit sellers and 10 users whose results were not included in the final analysis. The Cronbach alpha test was conducted for each section of the questionnaire and the minimum value obtained from the pre-test was at least 0.7, and this was set as a benchmark for good instrument reliability.

2.7 Data analysis

Categorical variables were also analysed as frequencies, percentages and proportions. One way Analysis of variance (ANOVA) and Independent sample t-test was used to indicate knowledge score difference with respect to socio demographic characteristics. Data collected was coded and all the analysis was done using the Statistical Package for Social Sciences version 26 (SPSS 26.0) software.

2.8 Protocol

This study was conducted from April to June 2022. Major markets in Ado-Ekiti were visited to assess fruit sellers and consumers. The sellers were then interviewed while the questionnaire for consumers was self-administered. Both written and verbal informed consent of each end user and fruit seller was sought before administering the questionnaire. In Nigeria, calcium carbide (CaC2) is commonly referred to as “carbide” among traders and farmers who use it as a ripening agent. Additionally, in Yoruba-speaking regions, it is known as “Yeye” or “Ogun Oko.” These terms are widely recognized in the context of fruit ripening. Natives of the land were part of the research team and played a crucial role in asking questions and explaining to the traders and consumers in the local dialect for those who did not understand English. This ensured effective communication and comprehension among all participants.

3 Results

3.1 Demographics of participants and fruit consumption patterns of consumers

A total of 357 consumers and 20 fruit sellers participated in this study. Majority of the participants were female for consumers (54.9%) and fruit sellers (80.0%). More than 62% (210) of the consumers were aged 18–27 years while 75% of the fruit sellers were aged between 28 and39 years. The demographics of the study participants have been summarised in Table 1. Fruits such as banana (78.3%), orange (73.0%), and apple (64.7%) were reported as mostly consumed in season by the consumers, whereas Guava (7.1%) and Berries (9.2%) were consumed less (Table 2).

Table 1 Demographics of fruit sellers and consumers
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Table 2 Consumption frequency of fruits by consumers
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3.2 Fruit ripening practices and methods used by fruit sellers

Some of the methods commonly used by the fruit sellers to aid fruit ripening were the use of CaC2 (50%), natural ripening (100%), packaging in polythene bags (80%), and keeping in a cool dry place (100%) (Table 3).

Table 3 Fruit ripening methods identified and used by fruit sellers
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3.3 Knowledge of fruit sellers and consumers on the health effects of calcium carbide-ripened fruits

For the fruit sellers, 60% (12) reported that CaC2 can cause cancers in consumers whereas 7 (35%) stated that CaC2 makes fruits soft and causes bacterial infections. Only 15% recognised that CaC2 can cause cough, chest tightness and stomach upset in the consumer. Overall, 90% of the fruit sellers had poor knowledge of the health effects of CaC2-ripened fruit consumption in humans. This is summarised in Table 4. Over 37% (125) of the consumers agreed that most fruits ripened with CaC2 appear ripened but are usually raw inside and taste sour whereas 0.9% (3) strongly disagreed that chest and abdominal burns could result from eating chemically ripened fruits. Ninety-three (27.6%) consumers strongly agreed that the use of CaC2 to ripen fruits can make them overly soft and encourage the growth of infectious bacteria, and 13 consumers disagreed that eating CaC2-ripened fruits can cause diarrhoea. One hundred and seventy-three (51.3%) consumers had poor to fair knowledge of CaC2 ripened fruit consumption health effects. This is summarised in Table 5.

Table 4 Knowledge of the health effects of calcium carbide-ripened fruits among fruit sellers
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Table 5 Knowledge consumers on the health effects of calcium carbide-ripened fruits
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There was a significant difference in knowledge scores based on age (p = 0.012), marital status (p = 0.019), and gender (p = 0.013) among the consumers but none among the fruit sellers (Table 6).

Table 6 Differences in knowledge scores based on the demographics of fruit sellers and consumers
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4 Discussion

The increased global demand for ripe fruits and the quest to boost profits have resulted in the unhealthy usage of hazardous chemicals such as CaC2 in fruit ripening in developed and developing countries [17, 30, 31]. This study assessed the ripening practices of fruit sellers and the knowledge of the health risks associated with CaC2 use in artificial ripening of fruits among fruit sellers and consumers in Ado-Ekiti.

Fruit ripening is a genetically designed, highly coordinated process of transition from unripe to ripe in order to produce an appealing edible fruit [32]. These edible fruits are grouped into climacteric and non-climacteric fruits [33]. In this study, the majority of the fruit consumers interviewed indicated consumption of climacteric fruits. This is similar to the findings obtained from studies conducted in Lagos [34] and Ibadan [35]. This could be because of ease of ripening of climacteric fruits at home even after they have been plucked. Non-climacteric fruits have a nearly constant or gradual drop in respiration rate until senescence, with little or no increase in ethylene production [36].

The fruit sellers in this study identified and stated that natural ripening, packaging in bags, use of CaC2, and use of other fruits were methods of fruit ripening. This is similar to the results from studies in Ilorin [23] and Uyo [25], where these methods were identified as common methods of fruit ripening among fruit sellers. Fruit sellers are likely to use these fruit ripening procedures, including artificial ripening, to meet the increasing demand for fruits both in and out of season, without knowing the health effects of some of these methods.

Artificial fruit ripening has been deemed unsafe because of health concerns [13, 24]. In this study, 50% of the fruit sellers admitted to use CaC2 to ripen their fruits. This is higher than the findings from a similar study conducted in Uyo, where 25% of the fruit sellers used CaC2 to ripen their fruits [25]. CaC2 is widely used to ripen fruits, particularly in underdeveloped nations such as Nigeria. The rationale for its use is that when water is added, ethylene is formed.

Calcium carbide exposure is also carcinogenic to various organs, including the liver, kidney, lung, and gastrointestinal tract [37, 38], and may also damage the immune system [39]. The fruit sellers stated that CaC2 is associated with cough (15%), chest tightness (15%), cancer (60%), skin damage (10%), and headache (5%). This is in tandem with findings from a study in Nigeria where 27.1%, 36.7%, 19.6%, 22.1%, and 13.6% of traders knew that CaC2 is associated with cough and chest tightness, stomach upset, headaches, skin damage, and frequent thirst respectively [25]. Similarly, in a study in Malaysia, 7.5%, 1.5%, 0.5%, 2% and 0.5% of their respondents knew that the use of CaC2 for fruit ripening causes cough, chest tightness, skin damage, frequent thirst, and headache, respectively [28]. There was an overall poor knowledge among the majority of the fruit sellers, similar to studies in Nigeria [25] and Malaysia [28].

The majority of consumers reported that eating fruits artificially ripened with CaC2 can cause health problems such as chest and abdominal burns (70%), liver disease and cancer (70.6%), diarrhoea (67.3%), and stomach cramps and vomiting (65.9%). These findings are in tandem but slightly higher than those obtained in a study by Eze and Asogwa [29] where the consumers stated diarrhoea (60.5%), liver disease (53.0%), stomach and vomiting (63.6%), as well as chest and abdominal burns (54.4%). The majority of the participants showed fair to poor knowledge of health issues associated with the use of CaC2 in fruit ripening, similar to the study in Rivers state, where the majority showed average knowledge [29].

The significant difference in mean scores among consumers based on age suggests that younger consumers (aged 18–27 years) tend to have a higher level of knowledge regarding artificial fruits ripening compared to older age groups. This finding contradicts the notion that younger individuals, especially those in their late teens and early twenties, are less likely to be health-conscious and actively seek information about healthy eating habits [40].

Among fruit sellers, although not statistically significant, there seems to be a trend where middle-aged sellers (aged 28–39 years) have a slightly higher mean score compared to other age groups. This trend might be attributed to their longer exposure to the fruit-selling business, potentially leading to a better understanding of consumer preferences and market demands.

The significant difference in mean scores among consumers based on marital status indicates that single consumers tend to have a higher level of knowledge or preferences regarding fruits compared to married or divorced/separated consumers. This finding may be attributed to the fact that single individuals often have more autonomy over their dietary choices and may be more inclined to prioritize health-conscious behaviours [41]. Among fruit sellers, although not statistically significant, there appears to be a similar trend where single sellers have a slightly higher mean score compared to other marital status categories. This trend could be explained by the flexibility and independence that single individuals may have in managing their fruit-selling businesses, allowing them to cater more effectively to consumer preferences.

The significant difference in mean scores among consumers based on gender suggests that female consumers tend to have a higher level of knowledge or preferences regarding fruits compared to male consumers. This is quite dissimilar to a similar study which males showed better knowledge than females [29]. Our study finding however, is consistent with existing literature indicating that women often exhibit greater interest in and awareness of health-related topics, including nutrition and dietary choices [42, 43]. Among fruit sellers, gender did not significantly influence mean scores, indicating that both male and female sellers may possess similar levels of knowledge. Strategies should be put in place to engage more males when disseminating health-related information on the artificial ripening of fruits.

5 Limitations

The limitation is that the study was conducted in major markets in Ado-Ekiti, which could make the results non-generalizable. Further studies can be explored by measuring the impact of educational intervention on the knowledge of the public on the health risks associated with artificial fruit ripening. However, these findings can serve as background to future studies with a wider scope and coverage. While the assessments of the importance of assessing the frequency and circumstances of CaC2 use among traders to provide accurate and responsible risk communication is crucial, these assessments were not conducted in the current study. Thus, we suggest future research being conducted on frequency and level of use of CaC2 for fruit ripening among traders, future research to tailor risk communication to accurately reflect actual risk levels, thereby avoiding unnecessary fear and panic among consumers; and also studies to explore the awareness of unauthorized use of CaC2 among traders in Nigeria. Understanding traders' motivations and constraints will allow future studies to address the root causes of unauthorized use and to develop more effective educational and regulatory strategies. Also, the insights gained from these assessments in future studies will be used to design interventions which will aim to promote safer ripening practices, increase awareness about the risks of unauthorized agents, and support traders in transitioning to approved methods.

6 Conclusion

This study identified common fruit ripening practices among the fruit sellers. There was an overall poor knowledge shown by fruit sellers but fair to poor knowledge shown by the fruit consumers on the health risks associated with CaC2 use in the artificial ripening of fruits. While certain demographic factors such as age, marital status, and gender appear to influence the knowledge regarding the health risks associated with CaC2 use in the artificial ripening of fruits among consumers, these factors may have limited impact on fruit sellers' knowledge. These findings provide valuable insights for marketers, policymakers, and health educators aiming to promote healthy fruit consumption and improve public health outcomes. Further research is warranted to explore the underlying factors driving these demographic differences and to develop targeted interventions tailored to specific consumer segments.