according to Kokkinakis and Fragkiadakis¹¹, Strawn et al.¹², and Estrada-Acosta et al.¹³, implementation of good agricultural practices (GAPs) and good manufacturing practices (GMPs) enhances the safety of fresh produce and its value throughout the food chain. This also facilitates the implementation of Hazard Analysis Critical Control Points (HACCP), which have been developed to identify specific risks related to food processing and as risk control measures. Generally, HACCP programs are a proactive way to limit food safety risks.

On an international level, GAPs and GMPs are described in the Codex Alimentarius Commission’s code of hygienic practice for fresh fruits and vegetables¹⁴. This code helps to control microbial, chemical and physical hazards associated with all stages of fruit and vegetable production (i.e. environmental hygiene, agricultural input requirements, water for primary production, manure, biosolids and other natural fertilisers, soil, indoor facilities associated with growing and harvesting, personnel health, hygiene and sanitary facilities, equipment associated with growing and harvesting, handling, storage and transport, cleaning, maintenance and sanitation of premises and harvesting equipment).

Meanwhile, the HACCP is a tool to assess hazards and establish control systems that focus on prevention rather than rely mainly on end-product testing; it consists of seven principles as described by the Codex Alimentarius¹⁵.

To minimise the risk associated with microbial hazards of fruits, producers and processors have access to several detailed codes, guidelines and regulations, such as “The guide to minimise the microbial food safety hazards for fresh fruits and vegetables, Guidance for industry (FDA)¹⁶” “Microbiological hazards in fresh fruits and vegetables (FAO/WHO)¹⁷”; “Microbiological Risk Assessment (Codex)¹⁸ and Microbial Risk Assessment Guideline (FSIS/USDA)¹⁹”.

the best method to eliminate pathogens from produce is to prevent contamination in the first place. However, this is not always possible, and the need to wash and sanitise many types of produce remains of paramount importance to prevent disease outbreaks²⁰ and increase shelf life. As a result, different treatment methods can be applied to fresh produce, such as chemical, physical, controlled atmosphere storage and modified atmosphere packaging.

Calcium-based solutions. Calcium treatments have been used to extend the shelf life of fruits and vegetables. Calcium helps to maintain the vegetable cell wall integrity by interacting with pectin to form calcium pectate²¹. One of the most used compounds is calcium lactate, which has antibacterial properties due to its ability to uncouple microbial transport processes ²².

Chlorine (hypochlorite) chemicals are often used to sanitise produce and surfaces in produce processing facilities as well as to reduce microbial populations in water used for cleaning and packaging operations. However, there are safety concerns about the production of chlorinated organic compounds and their impacts on human and environmental safety. Liquid chlorine and hypochlorites are generally used in the 50 to 200 ppm concentration range, with a contact time of 1 to 2 min to sanitise produce surfaces and processing equipment²⁰.

Chlorine dioxide is a strong oxidising agent and a safe bactericide; it generates only a small amount of trihalomethans (THMs) as a byproduct²³. The Food and Drug Administration²⁴ has allowed the use of aqueous chlorine dioxide in washing fruits and vegetables. A maximum of 3 ppm is allowed for contact with whole produce ²⁰.

Electrolyzed water. There are two types of electrolysed water with sanitising properties: acidic electrolysed water, or electrolysed oxidising water (AEW), and neutral electrolysed water (NEW). These solutions are conventionally generated by electrolysis of aqueous sodium chloride, and an electrolysed acidic solution (AEW) or an electrolysed basic solution (NEW) is produced at the anode and cathode, respectively²². Recently, the use of electrolysed water as a sanitising agent for fresh produce has received considerable attention in microbial load reduction²⁵.

Hydrogen peroxide is a colourless gas at room temperature. Because of its high oxidation potential, it has high bacteriostatic and bactericidal properties and has gained interest as a potential disinfectant in the fresh produce industry because of its strong oxidising power. It does not react with the organic compounds present in perishables to produce carcinogenic compounds and breaks down into water and oxygen. It has gained the status of Generally Regarded as Safe (GRAS) in 1986 for some of the food commodities²⁵.

Ozone is efficient in reducing pathogens on fresh produce because of its strong oxidising capacity. However, using ozone as a disinfectant has disadvantages, including its instability and reactivity with organic materials. Thus, the effective elimination of microorganisms may require high concentrations, which may, in turn, cause sensory defects in fresh produce². The effectiveness of ozone treatment on microbial loads depends on several factors, such as product type, target microorganism, initial microbial load level, physiological state of the bacterial cells and zone physical state, which may explain the diversity of published results²⁶.

Quaternary ammonium compounds, commonly called “QAC”, are cationic surfactants that are able to penetrate food contact surfaces more readily than other sanitisers²². The mode of action of these compounds against bacterial cells involves a general perturbation of lipid bilayer membranes²⁷. Although they are not approved for direct food contact, QAC may only partly be useful when applied to whole produce, since the product must be peeled prior to consumption²⁰.

Organic acids (e.g. lactic, citric, acetic or tartaric acid). The antimicrobial action of organic acids is due to a pH reduction of the environment, disruption of membrane transport and/or permeability, anion accumulation or reduction in internal cellular pH²⁰. Organic acids have a potential to reduce microbial populations on fresh vegetables²⁷.

The search for data on the incidence, outbreaks, growth/survival and internalisation of bacterial pathogens in mangoes and papayas was conducted from 1986 to 2016. Electronic searches were conducted using the following scientific bases: Web of Science, PubMed, Science Direct, Scopus and data from the “Centers for Disease Control-CDC-USA”. The keywords used were incidence, isolation, prevalence, detection, growth, behaviour, survival, fruits, papayas, mangoes, internalisation, fruits, microbiological, quality, safety, outbreak.

From farm to table, there are multiple opportunities for fresh produce to become contaminated by Salmonella, Escherichia coli O157:H7, Campylobacter jejuni, Vibrio cholerae, parasites and viruses that may contaminate raw manure or unpotable water as well as animals or potentially tainted surfaces, including human hands. In addition, pathogens such as Listeria monocytogenes, Bacillus cereus and Clostridium botulinum are naturally present in the soil⁴² and may also be a problem.

An important consideration when addressing safety issues is the incidence of pathogens and outbreaks associated with particular food products⁹.The following studies show the incidence of bacterial pathogens in mangoes and papayas.

One hundred and fifty samples of fresh fruits and vegetables, collected over a period of 12 months from various localities in Karachi, Pakistan, were screened for Listeria monocytogenes. Two out of thirty samples of papaya were positive for this pathogen⁴³.

The microbiological quality of street-sold fruits in San José, Costa Rica, was analysed over a two-year period from March 1990 to March 1993. Researchers evaluated the presence of Salmonella spp., Shigella spp., Escherichia coli and faecal coliforms in several foods. The results showed that E. coli was present in more than 10% of the mango and papaya samples, while Salmonella spp. and Shigella spp. could not be isolated from these fruits⁴⁴.

Thirty samples of ripe papaya (Carica papaya) slices were collected in Calcutta, India, from itinerant roadside vendors over a three-month period. Salmonella and Vibrio cholerae results were positive in one sample each, and low levels of coagulase-positive Staphylococcus aureus were detected in 17% of the samples⁴⁵.

Bordini et al.⁴⁶analysed 100 mango samples produced in the Northeastern region of Brazil from September 2001 to May 2002 and marketed in the state of São Paulo. The authors did not observe the presence of Salmonella in any of the 33 samples of mangoes destined for export. However, Salmonella was detected in 2 out of 67 samples destined for the internal market.

The prevalence and quantity of Salmonella spp., Salmonella Typhi and Salmonella Typhimurium were identified in sliced fruits from hawker stalls and hypermarkets in Kuala Lumpur, Malaysia. Salmonella spp. and Salmonella Typhi were found, respectively, in six and three out of twenty samples of papaya and in two and one out of twenty samples of mango from hawker stalls⁴⁷.

A total of 125 samples of fresh produce were collected from major supermarkets and local markets across Singapore and characterised with respect to microbiological quality. Salmonella and E. coli O 157:H7 were absent in only ten mango samples⁴⁸.

Foodborne illness is a major public health concern worldwide in terms of the number of persons affected and the entailed economic costs². According to the WHO⁴⁹, in the year 2010, 31 foodborne global hazards caused 600 million foodborne illnesses and 420,000 deaths worldwide. Foodborne diarrhoeal disease agents caused 230,000 deaths, particularly non-typhoidal Salmonella enterica.

In the USA, in 2013, the Centers for Disease Control and Prevention (CDC) reported 818 foodborne disease outbreaks, resulting in 13,360 illnesses, 1,062 hospitalisations, 16 deaths and 14 food recalls (CDC, 2013)⁵⁰. In the developing world,2epidemiological data on foodborne diseases remain scarce. Even the most visible foodborne outbreaks often go unrecognised, uninvestigated or unreported and may only be visible if connected to major public health or economic impacts⁴⁹.

According to the Brazilian Ministry of Health⁵¹, from 2007 to 2016, 6.848 outbreaks were related to the consumption of contaminated food, with 121.283 illnesses, 17.517 hospitalisations and 111 deaths. Fruits and food were responsible for 0.6% of the outbreaks, while the number of non-identified foods related to the total of the outbreaks is still as high as 66.9%.

The following reported outbreaks are related to the consumption of mango and papaya contaminated by bacteria. A large outbreak of food poisoning occurred in September 1996 and involved at least 116 workers at a shipyard in Jurong, Singapore. Four samples of cut watermelon, pineapple, papaya and honeydew melon were tested positive for Salmonella weltevreden⁵². In 1998, an outbreak caused by S. Oranienburg, with nine cases and three hospitalisations, occurred in a private home in Washington state and was associated with the consumption of fresh imported mangoes purchased from a particular grocery chain⁵³. In December 1999, the first reported outbreak of salmonellosis with mangoes in the United States occurred. Seventy-eight patients from 13 states were infected with Salmonella Newport. Fifteen patients were hospitalised and two died. The mangoes had been imported from a single farm in Brazil⁵⁴. Another outbreak in 2001 of S. enterica, associated with the consumption of imported mangoes from Peru, occurred in the United States. The serotype was Saintpaul; 26 cases were reported⁵⁵. In 2003, an outbreak due to the consumption of mangoes contaminated with S. saintpaul in a restaurant/delicatessen occurred in California, US, with 17 cases⁵⁶. During the period from October 2006 to January 2007, an outbreak with 26 cases of Salmonella Litchfield infection occurred in Australia. This was the first Australian Salmonella outbreak associated with the consumption of papaya⁵⁷. A total of 106 individuals were infected with Salmonella Agona in 25 states in the US from January 1 to August 25, 2011; no deaths were reported. This outbreak was related to eating fresh, whole imported papayas from Mexico⁵⁸.

During August 2012, a multistate outbreak of Salmonella Braenderup in the USA occurred due to the consumption of imported mangoes from Mexico. A total of 127 persons were infected; 33 were hospitalised, but no deaths were reported. From July to August 2012, a similar strain of S. braederup caused 21 illnesses in Canada; the infection was linked to mangoes from Mexico⁵⁹. In 2013, a multistate (4) outbreak occurred in the USA due to the consumption of papaya contaminated with S. Thomson, resulting in 13 cases, 6 hospitalisations and 1 death⁶⁰. In 2014, two outbreaks due to the consumption of mango contaminated with Salmonella were reported in the USA, one multistate and the other in the state of Connecticut, each with four illnesses and one hospitalisation⁶¹.

All cited outbreaks were caused by Salmonella spp. Other pathogens, such as L. monocytogenes, are not sufficiently established as relevant fruit juice-borne pathogens in the scientific literature, as compared to Salmonella and E. coli O157:H7. However, this pathogen is of concern in fresh fruits and fruit juices, due to its ability to survive under a variety of adverse conditions. The reason why there are no reports of listerioses linked to the consumption of fruit or fresh juices, in contrast to the variety of outbreaks related to other enteropathogens, is unclear³.

Physical barriers, such as skin or rind, do not necessarily prevent the contamination of produce, because cutting and slicing eliminate this protection and microbes can invade the internal tissue. In addition, bacterial microorganisms from contaminated washing water can enter fruits and vegetables under certain conditions^45,62. Mangoes and papayas are tree fruits with similar processing procedures on the farm⁵⁷. For example, at least three salmonellosis outbreaks may have been caused by the same mechanism through the immersion of warm papaya/mango in cooler water, resulting in a pressure difference between the produce core and the surrounding water, which allowed Salmonella present in the water to enter the fruit, generally through the area around the stem^54,55,57.

The survival and/or growth of pathogens on fresh produce is influenced by the organism, produce item and environmental conditions in the field and thereafter, including storage conditions. In general, pathogens will survive, but not grow on the uninjured outer surface of fresh fruits or vegetables, partly due to the protective character of the plant´s natural barriers (for example, cell walls and wax layers). In some cases, pathogen levels will decline on the outer surface⁹. One exception is the study conducted by Bordini et al.⁴⁶, which reported that the number of Salmonella present on mango rind surfaces depended on the storage temperature; at 22^oC, an increase up to 2.30 logs was observed, while at 8^oC, no significant variation occurred.

Microorganisms can grow and survive on mangoes and papayas, as shown in the following studies. The ability of five strains of enteropathogenic bacteria (Shigella sonnei, S. flexneri, S. dysenteriae, Salmonella derby and S. typhi) to survive and grow on sliced jicama, papaya and watermelon was investigated. Small increases in the numbers of Shigella species occurred on inoculated papaya after storage for only 2 h at 25–27^oC, and an increase of about 1.4 in 6 hours at room temperature was observed for S. typhi inoculated on this fruit. Both microorganisms could grow on papaya stored at temperatures of 22–27^oC⁶³.

Castillo and Escartin⁶⁴ studied the survival of Campylobacter jejuni on sliced watermelon and papaya. The populations on papaya cubes inoculated with this microorganism survived for at least 6 h. The percentage of survivors at 6 hours of storage ranged from 7.7 to 9.4. Decreases in count were substantial at 2 h of storage.

Yegeremu et al.⁶⁵ studied the fate of Salmonella species and E. coli in fresh-prepared orange, avocado, papaya and pineapple juices. They observed that S. typhimurium and S. choleraesuis could proliferate in papaya juice when stored at ambient temperatures. Salmonella typhimurium reached counts as high as 10⁹ CFU/mL in 24 h, steadily increasing until 48 h. Salmonella choleraesuis reached its maximum count (10⁸ CFU/ml) at 24 h, with a slight decrease thereafter. Counts of both Salmonella species increased by one log unit in 24 h at 4^oC, but did not exceed 10⁵ CFU/ml throughout the storage time.

Penteado and Leitão^66,67 investigated the growth of L. monocytogenes and S. enteritidis in papaya pulp. For L. monocytogenes, maximum populations of about 5, 4 and 7 log units were reached at temperatures of 10, 20 and 30^oC, respectively, at the end of the incubation periods. Generation times (g) of 15.05, 6.42 and 1.16 were obtained and decreased as the temperatures increased. The same authors observed maximum populations of 10⁸ CFU/g for 24- and 48-hr incubation periods and generation times of 16.61, 1.74, and 0.66 hrs at incubation temperatures of 10, 20 and 30^oC, respectively.

Mutaku et al.⁶⁸ evaluated the growth potential of E. coli O 157:H7 in fresh juices of papaya, pineapple and avocado. In papaya juice, counts of the test strains increased at varying rates at both storage temperatures, ambient (20–25^oC) and refrigeration (4^oC).

Bordini et al.⁴⁶ studied Salmonella enterica behaviour in mangoes stored at temperatures of 8 and 22^oC for 24 and 144 h and observed that mean population numbers increased in the rind, stem, middle and blossom end of the fruits at 22^oC, over a period of 24 h, with values of 0.53, 1.16, 1.47 and 1.36 logs, respectively. With an incubation period of 144 h, the values were 1.84, 1.74, 2.30 and 2.30, respectively. At an incubation temperature of 8^oC, the increase in the number of bacteria was smaller: 0.59 log in the stem end, 0.82 log in the middle side and 0.80 log in the blossom end after 24 h of incubation and 0.21, 0.22 and 0.47 log, respectively, after 144 h. At the rind surface, there was a decrease in the number of bacteria: 0.41 log MPN/g after 144 h.

Strawn and Danyluk⁶⁹ reported growth of Salmonella on cut mangoes stored at 23 ± 2^oC and survival at 4 ± 2^oC, regardless of initial inoculum concentrations. Population level was a factor at 12 ± 2^oC, with Salmonella growth only at the high (5 log CFU/g) and medium (3 log CFU/g) inoculum levels. Escherichia coli O157:H7 grew rapidly on fresh-cut papayas at 23 ± 2^oC and 12 ± 2^oC and survived throughout the shelf life of cut, refrigerated papayas. Similarly, Salmonella grew rapidly on fresh-cut papayas at 23 ± 2^oC and 12 ± 2^oC and survived throughout the shelf life of refrigerated fresh-cut papayas (4 ± 2^oC). Inoculum levels had no effect on Salmonella behaviour in cut papaya. Both microorganisms can survive on frozen cut mangoes and papayas for at least 180 days.

Barbosa et al.⁷⁰ inoculated mango slices with S. aureus and L. monocytogenes (10⁷ CFU/g), and the viable cell numbers exhibited a reduction of only one log unit after six days of storage for S. aureus, while being constant at 10⁷ CFU/g for L. monocytogenes over the same period.

Penteado et al.⁷¹ studied the growth of S. enteritidis and L. monocytogenes in mangoes pulp at different temperatures and incubation times. At 25^°C, the authors observed an increase of about 4.8 cycles log^-1 after 48 h of incubation and a maximum population of 7.6 log units for S. enteritidis, while L. monocytogenes exhibited an increase of about 6 cycles log^-1, with a maximum population of 8.6 log for the same temperature and period of incubation. At 10^oC, no growth could be observed for S. enteritidis. For L. monocytogenes, an increase of about 4 cycles log^-1was observed, with a maximum population of 7 log units after 200 h. At 4^oC, both bacterial populations survived for eight days. At -20^oC, S. enteritidis was able to survive for five months, while L. monocytogenes could still be recovered after eight months.

Ma et al.⁷² studied the behaviour of Salmonella spp. on fresh-cut tropical fruits, such as dragon fruit, banana, starfruit, mango, pineapple, guava and wax apple, at 28 and 4^oC at four inoculum levels: 0.1, 1.0, 2.0 and 3.0 log CFU/g. The population of Salmonella in mango remained equal to the initial inoculum level after six days of storage at 4^oC for all fruits tested. At 28 ± 2^oC/two days, there were increases of 0.11, 0.51 and 0.56 for inoculation levels of 0.1, 2.0 and 3.0, respectively, and a decrease of -0.39 for the inoculation level of 1.0 log CFU/g.

Table 1 shows the important factors to consider when conducting a bacterial growth study in fresh mango and papaya, including inoculation, storage conditions, incubation temperature and time, type of microorganism and pH. Along with storage temperature, pH is cited as the principal determinant of bacterial growth on fresh fruits. Many acidic fruits do not support the growth of human pathogens and even inactivate them^73,74.

Table 1
Growth and survival of pathogenic bacteria on mango and papaya.

S¹ = Stem end; M² = Middle; B³ =Blossom end; R⁴ = Rind

The chemical and biochemical composition of mango varies with cultivation, variety and stage of maturity. The major constituents of the pulp are water, carbohydrates, organic acids, fats, minerals, pigments, tannins, vitamins and flavour compounds^76,77.

Fruits can be divided in two groups: those with pH ≤ 4 (high-acid fruits), where the growth of microbial pathogens is unlikely to occur, and those with a pH above 4 (low-acid fruits), where microbial growth is more likely (e.g. mango and papaya)⁸. Variation in pH exists among varieties, growing conditions and processing methods⁷⁷, as in the case of the Dashehari mango cultivar. During ripening, the pH rose from 3.0 to 5.2⁷⁸, demonstrating the importance of determining pH when conducting a growth study.

Papaya has low acidity when compared to other tropical fruits, which is a nutritional advantage, as it allows its consumption by people sensitive to fruit acids; however, this low acidity is a problem faced by processors, because high pH values favour enzymatic activity and microbial growth⁷⁹.

As shown in Table 2, variation in pH occurs in both fruits, depending on the variables mentioned, which is of paramount importance when conducting studies related to the behaviour of microorganisms in this food.

Table 2
pH values of mangoes and papayas.

* E-mail: analucia.penteado@embrapa.br