Safety of Food throughout the Supply Chain

Abstract

Today, in addition to food security, food safety is very important, because one of the prominent causes of increasing diseases is changing people’s eating habits and lack of food safety along the food chain. Vegetables and fruits, in all stages of the food supply chain, are contaminated with a variety of bacteria, viruses, protozoa, and parasites. The prevalence of many diseases has been recorded in the past as a result of eating fruits and vegetables. The results of extensive research conducted in this field around the world were used in this chapter, and melon is discussed in detail as an example. Research findings show that pathogens that lodge in the skin of melon can enter the melon flesh when cut and infect it. Similarly, in hot climates, the bacteria Salmonella, Listeria, and E. coli multiply easily in melon flesh at low pH and soon reach pathogenic doses. Therefore, appropriate hygiene measures should be considered along the food chain. These hygiene measures are considered very important from the perspective that very small contamination by campylobacter, Escherichia coli, and norovirus, for example, can cause a major health problem. Highly vulnerable people include pregnant women, young children, the elderly, and the sick.

1. Introduction

Food security and food safety are two basic concepts of human nutrition and, especially recently, have played an important role in the food industry and trade worldwide. According to the Codex’s definition [1] “Food safety is the absence or presence of small amounts of hazardous substances in food that do not threaten the health of the consumer; these include microbial, chemical, and physical factors that are often not seen, such as bacteria, viruses, or chemical residues [1].

Melons (Cucumis melo L.) and watermelons (Citrullus lanatus L.) are important members of the Cucurbitaceae family. The term musk melons include various cultivars of melon. Commercial melons are evaluated based on their various characteristics, such as shape (spherical or oblong), skin color, and shape of the flesh [2]. More than 100 million tons of melons and watermelons are produced worldwide, 80% of which are from Asia. The main producer, from 2009 to 2011, is China with 60% of world production. However, the exports of this country account for only 0.13% of the total exports of the world [3]. Major exporters of melons have been reported from Mexico, Spain, the United States, and Brazil [3]. In Europe, melons are grown mainly in southern regions, such as Spain, Portugal, Italy, and Greece. In Europe, 3 million tons of watermelon and 2 million tons of different melon cultivars are produced every year [3]. Melons and watermelons are not produced in Germany [2]. Afghanistan is one of the main centers of melon production, which is currently producing 15 different varieties of melons, mainly in the northern and southern parts of the country. These varieties include Jane Tour, Zermati, Bori Kaleh, Asqalani, Sabz-Maghaz, Alishabi, Sefal-Sar, Marpost, Ghazikhani, Andalak, Qandak, Alla-Poqaq, Arkani, Arkani-Garmah, and Sard-e-Lelmi [4].

Fresh vegetables and fruits are contaminated with a variety of pathogens along the production-to-consumption chain, resulting in dangerous diseases in humans [4]. For example, melon is one of the fruits that is known among people as a fever and disease stimulator that some doctors even include this fruit in the list of patients to avoid (personal interview, August 20, 2018).

Pathogens identified in melon include Salmonella, Listeria monocytogenes, and Enterohemorrhagic Escherichia coli (E. coli) [5]. Campylobacter, E. coli, and Norovirus can cause serious diseases [5].

A report prepared for the Codex Committee in 2011 states that between 1950 and 2011, 85 cases of the melon disease were recorded [1]. Some cases of the melon disease have also been reported in Germany [2]. Melons, on the other hand, do not appear to contain substances that are harmful to health. Therefore, in this study, it was assumed that external factors cause diseases in consumers, these factors are transmitted from the skin to the inner parts of the fruit when the fruit is peeled and gets contaminated. To test this hypothesis, various relevant sources, including research reports and articles, have been studied and their key concepts have been included in this chapter. Due to production and supply conditions, melon skin is in contact with germs and parasites, especially in melons that have large and rough skin. On the other hand, disinfection of melon fruit does not include the stages of production, supply, and consumption, and therefore the fruit remains contaminated and causes health problems.

2. Methodology

This study has been done using various first-hand sources that include reports and research articles. The study materials were collected in the first step, and in terms of logical relationship with the hypothesis, were divided into three categories: (1) very relevant, (2) relevant, and (3) less relevant.

3. Findings and discussion

3.1 Microbiology and pathology

3.1.1 Bacteria salmonella

It is a gram-negative bacterium that is common in nature and can survive in it for a long time. This bacterium is found in all types of animals and is one of the most important causes of diarrhea in humans. Food, at any stage of the production-to-consumption chain, can be contaminated with this bacterium through indirect contact with human or animal feces. This pathogen can survive in or on food for several months. Even frost cannot kill it [2]. Compared to other bacteria, it can grow in a variety of conditions. This bacterium can multiply at a temperature of 7–45°C, and the higher the temperature, the more it multiplies. The ideal temperature for the multiplication of these bacteria is 37°C. Only at temperatures above 60°C does the bacterium begin to die. Multiplication of this bacterium is also possible at pH 4–5 [2].

Humans are infected with Salmonella bacteria by eating contaminated food. But the infection can also occur through direct contact with a sick animal or human. The pathogenic dose for an adult is 104–106 Salmonella bacteria [6]. Depending on the amount of fat in the food and the immune status, even doses of less than 100 Salmonella bacteria can cause disease. After infection and the average incubation time, the first symptoms of the disease are observed after 12–36 h [6]. This bacterium causes diarrhea with abdominal pain, nausea, vomiting, and fever. In some cases, especially in vulnerable people, this bacterium causes severe illness and even death [6]. According to the Robert Koch Institute in Germany (RKI), Salmonella infected 17 people by eating melon, of which eight were hospitalized [6]. Vulnerable people include children under the age of five whose immune system has not yet been developed, adults, and those who already have a disease and are under treatment [2].

3.1.2 Listeria monocytogenes

It is a gram-positive bacterium and is a very important representative of genes Listeria. This bacterium is very common in nature and is found in soil, surface water, sewage, plants, and the digestive system of animals. This bacterium can contaminate food along with the production chain to the consumption of food, for example, during milking, butchery, vegetable or fruit collection; or cause contamination during food processing. Foods that are eaten raw have a higher risk of infection because they do not undergo any germicidal process after processing [7]. Listeria lives and multiplies in high temperatures and pH, and in a salty environment, and is a bacterium that is resilient and adapts to a variety of environmental conditions. It can multiply at 4–45°C and at pH 4.3–9. In addition, it can multiply at a salt concentration of 13% [7]. The ideal temperature for the multiplication of this bacterium is 30–37°C in neutral and slightly humid conditions, where the salt concentration is 0.5% [8].

The bacterium is transmitted to humans primarily by eating contaminated food. The dose of trauma depends on the condition of the immunity and the health of the person. According to European Union (EC) laws, ready-to-eat food is safe if the bacterial dose per gram is less than 100 calories (CFU) [6]. A healthy person does not develop a serious illness after an indication, but either develops cold symptoms or has indigestion. Unless people have a weak immune system, they can develop severe illness after several weeks of incubating the bacteria in their bodies. The bacterium causes blood poisoning, encephalitis, or meningitis, and the mortality rate from this bacterium is low. In pregnant women, it can lead to failure or premature birth and can cause irreversible disorders in infants. In Germany, 337 cases of Listeria’s disease have been reported [9]. In addition to infants, people older than 60, especially men, developed leukemia. In 2011, 147 people in the United States became infected with Listeria, and 33 of them died [10]. In this country, Listeria bacteria was found in many samples of melons. The US Food and Drug Administration (FDA) has concluded that the disease is present in the melon peel and enters the inside of the fruit through the skin and is then transmitted to humans through eating the flesh [10]. According to European Union (EC) regulations, the concentration of Listeria in prepared foods should not exceed 100 colonies per gram of food.

3.1.3 Enterohemorrhagic Escherichia coli

A gram-negative anaerobic bacterium, abbreviated as E. coli, is capable of producing the poison ciguatoxins that cause bloody diarrhea in humans. The bacterium E. coli O157: H7 causes many diseases worldwide. This bacterium is present in the digestive system of ruminants, such as cattle, sheep, goats, and deer, and is transmitted to the environment through animal feces. This bacterium was resistant to drought, frost, and acidity, which means that it can survive in soil, water, and feces for several months [2, 10].

Food is contaminated with this bacterium at any stage of the production-to-consumption chain through direct or indirect contact with the feces of an infected animal or human. This bacterium multiplies at a temperature of 8–45°C and increases with increasing temperature. The ideal temperature for the multiplication of these bacteria is 37°C. Observation of E. coli O157: H7 in 0.5, 1, and 1.5% of organic acid (HCl) indicates that this bacterium also tolerates acidic conditions [2, 10]. In one experiment, using synthetic gastric extract, E. coli O157: H7 was observed to survive at pH 1.5 and it was found that this bacterium is also resistant to strong acidity [2].

The bacterium can also be spread through direct contact or by eating contaminated food by humans. The infectious dose of this bacterium is very low, that is, 100 of them cause disease. The incubation period is 2–10 days and averages 3–4 days. This bacterium causes watery diarrhea. In some cases, it causes swelling of the intestines and causes seizures and stomach pain, producing bloody stools, and in some cases, fever. Except after the disease is in the early stages, it does not show any symptoms [10]. In young children, the bacterium causes uremic hemolytic syndrome (HUS). In some cases, kidney failure, anemia, and thrombocytopenia can occur. These severe symptoms occur in 5–10% of patients. In the acute stage, the mortality rate due to this disease factor reaches 2% [2].

3.2 Pathogenic contamination

3.2.1 Melon consumption

Melons, like many other fruits and vegetables, can be produced both in the greenhouse and outdoors. After collection, it is either packaged directly on the farm or cooled before packaging. In arid regions (such as Afghanistan) packaging on the farm is common [11]. Melons are either sold whole or sliced, and in large stores, they are sliced and wrapped in plastic, which is sometimes mixed with other fruits. In Germany, the cooling of melon slices is prohibited [11].

According to estimates by the European Food Safety Authority [12], about 7% of European citizens consume melons [12]. It has also been observed that melons are consumed by all age groups, including children and the elderly, due to their deliciousness [13].

3.2.2 Contamination of melon fruits

Melons are grown on the ground. They need warm, sunny weather and moist soil. Due to the size and weight of its fruits, the fruits are in contact with the ground and are easily contaminated with pathogens, either through contaminated soil or water [14]. Studies in Mexico and the United States show that irrigation is a major cause of contamination [14]. Another study, conducted in Texas, USA, found that irrigation water was contaminated with 9.4% Salmonella bacteria [15]. Insects are also carriers of pathogens [16]. A study by Lopez-Velasco et al. [16] found that Salmonella could also enter plants through roots; they concluded that the possibility of root infection was not high and skin contamination was the main cause.

The fruit part that is in contact with the ground is a special area for contamination with bacteria and fungi. To reduce this contamination, the ground is covered with plastic, or fruits are placed in plastic bags. Another way to reduce contamination is to roll (turn over) the fruit repeatedly. This is done by the hands and if the hands are not clean, it will cause more contamination [17].

Contamination also occurs during collection and transfer, for example, by infected people. After harvesting, the fruits are cooled by air or water, in both cases, there is a possibility of contamination and spread of contamination [18]. Clean melons are also contaminated, especially when washed in the basin [18]. In a study by Duffy et al. [19], which compared washed and unwashed melons, it was found that washed melons were contaminated with Salmonella, because contaminated surfaces, as well as contaminated fruits, caused contamination of other fruits. Similarly, the Salmonella bacterium was observed in samples taken from cold storage [20].

To keep the fruit cool during transfer, ice is placed around it, which is usually melted and this causes the contamination of clean fruits [19]. All stages of melon production require human labor. The germs survive on the skin of the melon [17]. In particular, coarse skin is a good place to protect germs from washing and disinfection [18]. The larger the skin of the melon, the more germs it contains (Figure 1) [2].

Figure 1.

Showing the food supply chain.

3.2.3 Presence of pathogens in melon

In one observation, out of a total of 366 cantaloupe melons, 16 were contaminated with pathogenic microbes. Salmonella was observed in eight specimens, and Shigella in four specimens, while E. coli was not observed in this specimen [10]. In another study by the Austrian Institute of Technology [1], it was observed that the presence of Salmonella in melons is different [1]. In Mexico, 12 out of 55 samples were infected with Salmonella. In Nigeria, three out of every 50 melons were infected with Salmonella bacteria. In addition to Salmonella, other microbes, such as Staphylococcus aureus, Enterobacter aerogenes, and Klebsiella pneumoniae, were also observed [4]. In 2000, Castillo et al. [5] collected 950 samples of melons from Texas and 300 samples from Mexico; 0.5% of the samples were from Texas and 0.3% from Mexico were contaminated with Salmonella [10], respectively. Salmonella was also found in watermelons imported from Costa Rica and Brazil. In Germany, out of 406 samples, three melons were contaminated with Listeria.

3.3. Durability and growth of pathogens in the skin and flesh of melon

Pathogenic bacteria in melon skin survive for a long time and multiply [2]. The number of E. coli O157: H7 bacteria increases by more than 100 times in one square centimeter of melon skin and a temperature of 25°C in 4 days [4]. The large, rough skin of a melon provides a multiplication space for germs. Salmonella formed a biofilm in the skin of the cantaloupe melon at 20°C after 2 h, and the bacterium increased by 200% at room temperature for 24 h [2]. Table 1 shows the amount and timing of the multiplication of Listeria and Salmonella bacteria in melons and watermelons at different temperatures. It is observed that the proliferation of bacteria has increased in proportion to the temperature; by increasing the temperature from 10 to 30°C, the largest number of these bacteria is produced in the shortest time.

Pathogen	Temperature (°C)	Watermelon		Cantaloupe
		Lag phase (h)	Generation time (h)	Lag phase (h)	Generation time (h)
Listeria monocytogenes	10	24a	13.03a	24a	7.12a
	20	18b	2.17b	6b	1.72b
	30	4c	1c	4b	0.84b
Salmonella enteritidis	10	24a	7.47a	24a	7.31a
	20	None	1.6b	none	1.69b
	30	2c	0.51c	2c	0.69c

Table 1.

Lag phases and generation times of Listeria and Salmonella bacteria in watermelon and melon [4].

Ukuku et al. [19], in their study, found that the number of aerobic bacteria in the flesh of the cantaloupe was higher than the number of these bacteria in the flesh of the honeydew melon. The microbes in the skin are transferred to the melon flesh during slice cutting [19, 21]. Due to the low acidity of the melon flesh, the bacteria survive and multiply rapidly. Listeria and Salmonella bacteria started multiplication at room temperature after 2 h [19], and the researchers also reported that, as a general rule, the higher the storage temperature, the shorter the bacterial division.

Studies by Li et al. [12] show that Salmonella and E. coli O157: H7 did not grow in the skin of cantaloupe, honeydew, and watermelon at 4°C, but at 15°C and higher. The proliferation of these bacteria began rapidly. E. coli O157: H7 began to multiply more rapidly than Salmonella at room temperature (23–25°C). Contrary to expectations, despite the different pH of watermelon (pH 5.1–5.6) and melon (pH 6.1–6.6), the same proliferation and growth of bacteria were observed in these two fruits. However, the growth rate of Salmonella and E. coli in honeydew melon was slightly lower than in other types of melons [19].

If the peeled melon is stored for a long time without refrigeration, the risk of germs growing in it increases [19]. Storing melon at 22°C caused severe growth of Salmonella. The number of Salmonella reached 1.3 cfu/g bacteria after 5 h and 0.2 cfu/g in a watermelon after 5 h [19]. In melons that were not refrigerated, the number of Listeria increased at 20°C compared to those refrigerated at 5°C. The researchers concluded that storing melon slices under normal room conditions, even for a limited number of hours, could increase Listeria bacteria [21].

According to scientific studies, washing with water does not significantly reduce the number of germs in melon skin [19]. Washing the cantaloupe melon for 3 minutes did not reduce the number of Salmonella and E. coli [2]. The researchers attributed the large surface area of the melon to the absorption, preservation, and contamination of the melon. To clean the surface of the melon, it is a good way to use a brush. A study by Parnell et al. [15] showed that brushing melon skin for 60 s reduced the number of Salmonella quadruples, and large-skinned melons reduced the number of bacteria by 1.6 times. After the melon was disinfected with 2.5% hydrogen peroxide, the number of microbes was reduced in it, except that Listeria bacteria is still observed in the melon flesh after spraying [19].

4. Conclusion and recommendations

Fruits and vegetables have caused diseases in the most developed countries. In the past, many cases of disease outbreaks have been reported after eating melons, some of which were very serious. For example, 147 people became infected with L. monocytogenes in the United States in 2011 after eating melons, including 33 deaths and a pregnant woman who was unable to give birth as a result of the disease. To reduce diseases, the following orders should be considered along the production chain to consume vegetables, fruits, and especially melon fruits.

During production, use plastic and/or organic mulch to reduce contamination, or place fruits in plastic bags. Another way to reduce contamination is to roll over fruits consistently. This is done by the hands and the hands should be clean, otherwise, it will cause more contamination [10, 21].

Studies show that peeling melon before eating significantly reduces germs [21]. In the United States, Canada, Australia, and New Zealand, the melon is cooled immediately after slicing as a precaution, and discarding melon slices that have been left in normal air for more than 2 h has been ordered [20, 22]. Therefore, observing these measures is recommended.

It is recommended that restaurants, wholesalers, and families cut and consume melon little by little, and melon slices should be consumed in less than 2 h. It is recommended that pregnant women and other vulnerable people, such as young children, adults, and the sick, refrain from eating melon that has been stored outdoors for several hours.

Hygiene measures should be taken when cutting the melon, such as slicing should be done in a wider and clean place with clean hands, and a clean knife and a clean container should be used to prevent contamination of the melon flesh. It is very important to consider home hygiene and personal hygiene because the infection dose of Listeria bacterium is very low (100 colonies). In addition to maintaining good hygiene, it prevents the melon from becoming contaminated with other germs, such as campylobacter, type A jaundice, and norovirus.

To prevent contamination and disease, retailers, restaurants, cafeterias, and others should cut a small amount of melon and consume it in less than 2 h.

It is recommended that the melon husk be eaten immediately or put in the refrigerator immediately. The suitable temperature for the refrigeration of melon cut is 4-6 Degree Celsius as it minimizes the multiplication of germs. Pregnant women and people with weak immune systems, such as children, the elderly, and the sick, should refrain from eating peeled melons that have been left in the room for more than 2 h.

In the field of exports, since the issue of food safety is more important today than food security, producers and exporters must consider hygiene throughout the stages of the supply chain, because competition and continuity in international markets are possible only if the fruits are healthy and free of pathogens and dangerous elements, such as Argentum, lead, and arsenic; also, free of residues of agricultural chemicals. Therefore, exported fruits must comply with the standards of the global quality control organizations, especially the food standards of the Codex Alimentarius Commission, and HACCP.