Post-harvest Losses of Agricultural Produce
Food losses and waste are the result of ineffective functioning of food systems. “Post-harvest losses” in the PHL system refer to the quantitative and qualitative loss of food in various post-harvest operations. “Food loss” is defined too as food available for human consumption, but not consumed. Limiting post-harvest losses (PHL) is a priority area of cooperation between FAO and world development banks.
About 1/3 of the food produced in the world per year for human consumption is lost or wasted. Food losses and waste total approximately $680 billion in industrialized countries and around $310 billion in developing countries. The industrialized and developing countries are wasting approximately comparable amounts of food (670 and 630 million tons, respectively). Usually fruits and vegetables, as well as tubers and roots, have the highest level of losses compared to all food groups. Global quantitative food losses and wastes during the year are around 30% for cereals; 40–50% for root crops and fruit and vegetables; 20% for oilseeds, meat, and dairy products; and 35% for fish. Every year, consumers in rich countries lose almost as much food (over 220 million tons) as the total net food production in sub-Saharan Africa (around 230 million tons). The entire amount of food lost or wasted annually is equivalent to more than half of the world’s annual crop production (about 2.3 billion tons per year). Waste per capita in Europe and North America is 95–115 kg/year, while consumers in sub-Saharan Africa, South Asia, and Southeast Asia throw away only 6–11 kg/year. At a time when the demand for food of a growing population is a major global problem, more than a third of food is lost or wasted in post-harvest agricultural operations. Reducing the waste after harvest, especially in developing countries, can be a sustainable solution to increase food availability, reduce pressure on natural resources, eliminate hunger, and improve farmers’ living conditions. Cereal crops are the basis of food in most developing countries around the world. The maximum losses after harvest are estimated on the basis of calories among all agricultural products. As much as 50–60% of cereal yields can be lost at the storage stage due to the lack of technical possibilities for their proper harvesting and storage. The use of scientific storage methods can reduce these losses by up to 1–2% (Obiedzińska 2017; De Lucia and Assennato 2006). Depending on the volume or region, in which they occur, they generate economic, social, environmental, and health effects. The term “post-harvest losses” in the PHL system refers to the quantitative and qualitative loss of food in various post-harvest operations. This system includes interrelated activities from the time of harvest through crop processing, marketing, and food preparation to the consumer’s final decision about eating or throwing food away (Abass et al. 2014; Abedin et al. 2012; Abraha et al. 2018). Post-harvest losses can also be described as degradation, both in terms of quantity and quality of food, from harvest to consumption. Quantity losses are the loss of product quantity. They are more common in developing countries (Alavi et al. 2012) than in developed ones. At the global level, the amount of lost and wasted food in high-income regions is higher in the further phases of the food chain, and vice versa situation is in low-income regions, where more food is lost and wasted in the start-up phase (Anonymous 2010a, b, 2011; Aulakh et al. 2013). In turn, the quality losses also include those that affect the nutritional composition, calorie content, digestibility, and acceptability of the food product. These losses are generally more common in developed countries (Abass et al. 2014; Alavi et al. 2012). Yield losses occur during the post-harvest treatment of seeds, fruit, or tubers as a result of physiological processes in vegetative and generative organs of plants, uneconomic collection, loading and unloading (e.g., in the process of transporting seeds for purchase), cleaning and calibration, drying, and storage. Satisfying the demand for food for a growing population in the world is becoming a great challenge for humanity. It is expected that by 2050, the population will increase to 9.1 billion people, and about 70% of additional food will be needed for their food (Obiedzińska 2017; De Lucia and Assennato 2006; Kiaya 2014). Progressing urbanization, climate change, and land management for the production of energy crops and other, unrelated to food, deepen these concerns related to the increase in food demand. Post-harvest losses (PHL), however, are a contentious and critical issue (Kitinoja et al. 2011; FAO, LEI 2015; Food and Agriculture Organization of the United Nations 2013, 2014). About one-third of the world’s food (about 1.4 billion tons), estimated at around USD 1 trillion, is lost annually during the post-harvest operations and post-harvest treatments (Food and Agriculture Organization of the United Nations 2016). This “food loss” is defined as food available for human consumption, but not consumed (Aulakh et al. 2013; Buzby et al. 2018). Different solutions and proposals that reduce the post-harvest losses require relatively small investments and can bring high results compared to increasing plant production. Post-harvest losses can generally be classified as loss of weight due to deterioration, loss of quality, loss of nutritional value, loss of viability, and finally commercial loss (Boxall 2001; FAO 2017a). The size of losses after harvest in the food supply chain varies greatly depending on the crop, geographical area, and type of economy. In developing countries, the society tries to make the best use of produced food; however, a significant amount of products is usually lost in operations after harvest due to lack of knowledge, inadequate technology for harvesting, harvest technology, transport technology, processing, and/or poor infrastructure. Conversely, in developed countries, the loss of food in the middle stages of the supply chain is relatively low, due to the availability of advanced technologies and more efficient systems of handling and storage of crops. Despite these advantages, a large part of the food is lost at the end of the supply chain, called “food waste.” That food waste can also be defined as rejected food or, alternatively, the intentional use of food not intended for consumption or because of food spoilage (FAO 2017a; Lipinski et al. 2013). In 2010, about 133 billion pounds of food (about 31% of total available food) was wasted only in the USA at the retail and consumer level (FAO, LEI 2015). It was estimated that in terms of cereals, root crops, fruits, and vegetables, these losses account for, respectively, approx. 19%, 20%, and 44% of losses (FAO, LEI 2015; Food and Agriculture Organization of the United Nations 2016). Root plants and vegetables are particularly vulnerable to mechanical damage, both during treatments and during harvesting or technological processes, because the tubers, roots, leaves, and stems of these plants are exposed to mechanical damage, such as bruises, abrasions, intersections, and cracks, which in the vast majority of cases are the result of dynamic loads (Abraha et al. 2018; Zhang et al. 2018). Mechanical properties of root crops are dependent on the turgor. Exceeding the permissible load level results in damages that cause losses resulting from a decrease in the quality of the raw material. The causes of such damage are mechanical injuries that occur primarily in association with harvesting and grading. For example, in potatoes, mechanical damage and the formation of black spots in the tuber parenchyma cause significant economic losses and degradation of quality (Grudzińska and Barbaś 2017). However, due to the calorific value of products, cereals (53%) have the largest share in losses, such as wheat, rice, and maize, and are the most popular edible plants in the world and form the basis of the main food items in most developing countries. Minimizing cereal grain losses along the supply chain can be the only effective resource that can help strengthen food security, fight hunger, reduce agricultural land needed for production, and develop rural areas and improve the living conditions of farmers, especially in Africa and Asia (Food and Agriculture Organization of the United Nations 2016). Only sub-Saharan Africa (SSA) loses grains worth approximately US $4 billion per year (Abass et al. 2014). These losses play a key role in the lives of millions of small agricultural producers, affecting the available quantities of food and the commercial value of goods. In addition to economic and social impacts, post-harvest losses also have an impact on the environment, as the land, water, and energy (the main means of agricultural production) used for the production of lost food are also wasted along with food. Unused food also causes additional CO2 emissions, ultimately affecting the environment. The Food and Agriculture Organization of the United Nations (FAO) estimates a CO2 emission of 3.3 Gton equivalent for food that was produced but not consumed (FAO, LEI 2015). “Traces of blue water” (water consumption during the food life cycle) for wasted food around the world were estimated at about 250 km3 (Food and Agriculture Organization of the United Nations 2013, 2014, 2016). Considering the criticality of PHL reduction in increasing the food security, it is very important to understand the structure and scale of post-harvest losses of agricultural produce around the world, especially in developing countries, as well as to identify their causes and possible solutions. A review of the literature on the state of the storage losses of main cereal crops and main factors leading to these losses and possible solutions is presented. Therefore too the post-harvest losses of agricultural crops in developing countries and the condition and causes of losses during the storage as well as technological interventions aimed at reducing these losses were discussed. The principles of storing seeds of cultivated plants in silos as well as the principles of hermetic storage and its effectiveness for several types of crops are also presented. Losses and waste of food generate many negative effects that can directly or indirectly affect the main pillars of food security: food availability, access to food, food use, and stability of accessibility and access to food over time. Many actions are taken to prevent or minimize these losses and wastage. Wasted food can be used, among others, to redistribute or reuse its components.
Grain Supply Chain
Cereal seeds, when transported from the farmer (farm) to the consumer, must undergo a series of operations, such as preparation for harvesting, harvesting, threshing, cleaning, drying, storage, processing, and transport. During these treatments, yields are lost due to many factors, such as improper handling, inefficient processing equipment, biodegradation caused by microorganisms and insects, etc. (Zorya et al. 2011; Gliński et al. 2014). It is important to understand the supply chain and identify factors at different stages of the harvest that cause food losses. Different stages of the grain supply chain and various types of losses occurring at each stage from field to table were discussed.
Maturity moisture content of various crops
Maturity moisture content
Maturity moisture content
Threshing and Cleaning
The purpose of the threshing process is peeling the grain from the panicles. This process is achieved by rubbing, removing the cover, impact, or combination of these activities. This operation can be performed manually (trampling, hacking) using animal force or mechanical threshing. Manual threshing is the most common practice in developing countries. Seed splitting, incomplete separation from the chaff, and cracking of seeds due to excessive impact force are the main causes of threshing losses (Baloch 2010; Shah 2013). Delay in threshing after harvesting results in a significant loss of the quantity and quality of the crop, because the plant is exposed to atmospheric and biotic factors (rodents, birds, and insects) (Gliński et al. 2014; Alavi et al. 2012; Sarkar et al. 2013). Lack of mechanization is the main cause of this delay, which causes significant losses. High accumulation of moisture in crops in the field can even lead to the onset of mold growth in the field. The cleaning process is carried out after threshing to separate whole grains from broken ones and other foreign materials, such as straw, stones, sand, chaff, and weed seeds. Screening is the most common cleaning method in developing countries. Screening is another common method that can be done manually or mechanically. Improperly cleaned grains can increase the insect invasion and mold growth during storage, add undesirable taste and color, and damage processing equipment. A large amount of grain is lost as a leak during this operation, and grain losses during screening can amount to as much as 4% of total production (Bala et al. 2010).
Cereal seeds are usually harvested with high moisture content to minimize losses due to scattering in the field. However, the safe moisture content for a long-term storage of most crops is considered to be below 13% (Banjaw 2017). Even in the case of short-term storage (less than 6 months), the moisture should be less than 15% for most crops. Inadequate drying can lead to mold growth and large losses during storage and grinding. Therefore, drying is an important element of post-harvest work to maintain high crop quality, minimize storage losses, and reduce transport costs (Gliński et al. 2014; Bala et al. 2010). Drying can be done naturally (in the sun or in the shade) or using a mechanical dryer. Natural drying or drying in the sun is a traditional and economical practice of drying the harvested crops and is the most popular method in developing countries. Sometimes, the entire crops without threshing remain in the field only to dry. Solar drying requires a large manpower, is slow, depends on the weather, and causes large losses. Grain lying in the open sun is eaten by birds and insects, as well as contaminated by mixing stones, dust, and other foreign materials. Rain or adverse weather conditions can limit proper drying, and yields are stored in high humidity, which leads to large losses caused by the growth of mold. Approximately 3.5–4.5% of losses are recorded during drying of maize on raised platforms in Zambia and Zimbabwe (Lipinski et al. 2013; Calverley 1996). Some farmers use mats or plastic sieves to sift the grain, which reduces dust pollution and facilitates drying of cereals. Mechanical drying solves some of the limitations of natural drying and offers benefits such as reducing losses, better control over the air temperature. However, the disadvantage is the limitations associated with the high initial and maintenance costs of the dryer and the lack of knowledge about their operation. For this reason, dryers are rarely used by small producers in developing countries (Grudzińska and Barbaś 2017; Alavi et al. 2012).
Storage plays an important role in the food supply chain, and several studies have shown that during this operation, maximum losses will occur (Aulakh et al. 2013; Gliński et al. 2014; Calverley 1996; Majumder et al. 2016). In most places, crops are conducted seasonally, and after harvest, the grain is stored for a short or long period as food reserves and as seeds for the next season. In developing countries such as India, about 50–60% of seeds are stored in traditional structures (e.g., Kanaja, Kothi, Sanduka, clay flower pots, Gummi, and Kacheri) at household and farm level for self-seeding and consumption (Grover and Singh 2013). Local storage structures are made of locally available materials (grass, wood, clay, etc.) and cannot guarantee the crop protection against pests for a long time. Costa (2014) estimates a loss of up to 59.5% in maize grain after storage for 90 days in traditional storage structures (grain/polypropylene bags). The causes of grain storage losses will be discussed in detail later.
Transport is an important operation of the grain supply chain, as the goods have to be transferred from one stage to another, for example, from the field to processing plants, from the field to warehouses, and processing plants to the market. Lack of proper transport infrastructure causes damage to food products through bruising and losses caused by spillage. Losses in transport are relatively low in developed countries due to better road infrastructure and engineering facilities in the field as well as processing equipment that allows fast loading and unloading of vehicles with very little or no damage. At the field level, most crops are transported in combat vehicles or open trolls in South Asian countries. Grains for independent use are usually transported in sacks from field warehouses to processing plants in combat vehicles, bicycles, small motor vehicles, or open trucks. Poor road infrastructure along with improper and poorly maintained means of transport results in large losses and high pollution. Repeated movement of plants is another important reason for high transport losses. In countries such as India and Pakistan, sometimes packaged wheat is loaded and unloaded from vehicles up to ten times before being ground (Gliński et al. 2014; Baloch 2010). During each movement, some of the grains are lost as leaks. In contrast to efficient bulk transport systems in developed countries, the loading and unloading of grains from wagons, trucks, and rails in processing plants take place mainly by hand in developing countries and cause large spills. Low-quality jute bags are often used during transport and even storage, which causes large losses due to leakage of bags. Large amounts (usually 100 kg of grains) in each bag and hooks used to lift these bags cause tears in these bags and large losses (Baloch 2010). Trucks used in developing countries are not completely suitable for transporting cereals and oilseeds. Alavi et al. (2012) reported 2–10% losses only during rice transport in Southeast Asia.
Grinding or processing operations are different for different types of cereals. In the case of rice, the purpose of milling is to remove the husks and bran from rice seeds to provide pure and whole white rice grains intended for human consumption. The operation can be performed manually or using milling machines. Traditionally, in rural areas of developing countries, grinding is done manually by repeated hitting. The grinding efficiency depends largely on the grinding method, the operator’s skills, and the growing conditions before the grinding process. Grinding the seeds containing foreign materials causes a large amount of cracked and broken grains and can also damage the machine. Inadequately maintained grinding machines cause a high amount of broken grains and low grinding efficiency (De Lucia and Assennato 2006). Alavi et al. (2012) reported that grinding losses are greatest during the rice post-harvest operations in five southeastern countries: China, Thailand, Indonesia, Philippines, and Vietnam. The rice milling efficiency in all these five countries is well below the theoretical yield of 71–73%. High humidity and inadequately cleaned forecrops deepen the situation and reduce the yields.
Post-harvest Losses of Cereals in Developing Countries
Rice, wheat, and corn are the main cereal grains in most developing countries. In countries like Bangladesh, rice accounts for over 90% of food produced and about 70% of calorie intake (Abedin et al. 2012). In West Africa, Nigeria is currently the largest producer of rice with an annual production of around 3.3 million tons (Gesellschaft für Internationale Zusammenarbeit 2014). Despite the large production and huge imports of rice each year, a large number of people are undernourished in Nigeria. Similarly, Bangladesh is the fourth largest producer of rice in the world, but it is still a shortage of food and imports more than 1 million tons of rice each year. Reducing grain losses during post-harvest operations can help to meet food demand and reduce the burden on the economy. World Bank report estimated 7–10% of grain loss in post-harvest operations in the field and 4–5% of losses on the market and distribution in India in 1999 (Shah 2013; Ognakossan et al. 2013). Estimates also suggest that these 12–16 million metric tons of grains wasted each year can meet the demand for food for about one-third of India’s poor population (Nagpal and Kumar 2012). However, despite the criticism of this issue, the availability of consistent and reliable data on post-harvest losses remains a challenge. Significant research into loss assessments has been carried out in very important emerging economies such as India, China, and Brazil (FAO 2017a).
Wheat is the basic food for most countries in Europe, Asia, and North America. High losses occur during the post-wheat processing of wheat in developing countries. According to data collected by the American National Academy of Sciences (before 1978), wheat losses in Sudan and Zimbabwe were estimated at 6–19% and 10%, respectively (Basavaraja et al. 2007). Bala et al. (2010) reported that storage losses were the maximum (42%) of all post-harvest losses for wheat in Bangladesh, even considering that the storage period for wheat is relatively short. Total losses in the wheat supply chain from harvest to seller in India were estimated at 4.3%. Operations in the field contributed to the creation of 75.9% of all losses after harvest (Basavaraja et al. 2007).
Corn is an important part of the diet in sub-Saharan Africa (SSA) and the main source (~36%) of daily caloric intake. Pantenius (1988) estimated 0.2–11.8% weight loss as a result of insect invasion in maize after 6 months of storage in traditional granaries in Togo. The Inter-American Institute for Cooperation on Agriculture (IICA), which conducted a survey on post-harvest losses in Latin America and the Caribbean, estimated the losses in various regions from 1.4% to 30%. In almost all regions, the majority of losses was observed in small- and medium-sized farms due to the lack of appropriate harvesting, drying, and storage technologies, as well as the lack of information about good agricultural practices. In Guatemala, due to the lack of storage facilities and high humidity in this region, losses in maize storage were estimated at as much as 40–45% (Gitonga et al. 2015). The insect infection was considered the main cause of the losses. Kaminski and Christiaensen (2014) conducted a study to estimate the post-harvest losses in maize in three SSA countries (Uganda, Tanzania, and Malawi). These losses at the farm level were estimated at 1.4–5.9%. Insects and pests are considered to be the main cause of grain losses during storage. According to Alavi et al. (2012), there is an average of 23% of losses in the maize supply chain in the ASEAN countries (Association of Southeast Asian Nations), with the maximum losses occurring during drying of 9%. Most of the corn is dried along the sides of the road, especially in the Philippines. In Vietnam, large losses occur due to the attack of rodents and fungal diseases during the storage of maize.
Storage Losses in Developing Countries
The maximum amount of losses occurs during the storage of crops due to the lack of adequate infrastructure. Losses in storage can be classified into direct losses caused by physical loss of goods and indirect losses resulting from the loss of quality and nutritional value. “Damage” may refer to physical signs of deterioration, for example, to holes in seeds. They mainly affect the quality of grains. “Loss,” on the other hand, is the total destruction of food that can be measured quantitatively (Boxall 2002). The loss of quality also results in the loss of the value of the product and sometimes leads to a total destruction (Aulakh et al. 2013). Degree of crop destruction depends on the economic status of a given person as well as on cultural origin. For example, a farmer who produces for his own needs may eat food to a certain extent, while rich customers may throw away even slightly damaged food. A certain loss occurs in the form of pouring out of leaking sacks. Storage losses are influenced by biotic (insects, pests, rodents, fungi) and abiotic factors (temperature, humidity, precipitation). The water content and temperature are the most important factors affecting the storage duration. Most losses during storage increase rapidly at temperatures of 20–40 °C and relative humidity over 70% (Grudzińska and Barbaś 2017; Abedin et al. 2012). Low relative humidity below 70% limits the growth of mold. In traditional storage infrastructure, temperature fluctuations caused by weather changes cause the accumulation of moisture on the top or bottom of the grain mass, depending on the direction of air convection. This can be avoided by minimizing the temperature difference inside and outside the storage structure. The seeds should be dried to about 13% of the water content before storage to minimize losses. At a humidity of 16% or more, the safe storage period for cereals, e.g., rice, is only a few weeks (Abedin et al. 2012). The quality of grains before storage is another critical factor influencing the storage losses. Mechanical damage during harvesting and threshing can result in seed breakage and bruising. Damage sites can become centers of infection and cause deterioration of stored seeds (Shah 2013; Sarkar et al. 2013). In most developing countries, especially in Africa and South Asia, cereals are usually stored in bulk or in sacks, in simple granaries built of locally available materials (straw, bamboo, clay). Clay containers and pots, side walls (straw), kothis, and plastic containers are typical structures built to store seeds in Asia (Grover and Singh 2013). Gunny sacks and plastic, polyethylene, or polypropylene bags are commonly used for short-term storage, and drums Dole, Berh, Gola, Motka, and steel/plastics are used for long-term storage. Different types of granaries are used in African countries. Smoked storage is just some of the typical structures for storing maize in Togo (Pantenius 1988). In internal methods, corn is stored in flats, in the space between the ceiling and the roof above the cooking place, to receive heat. In Western Africa, cereal and legume seeds are usually stored at home or in the field in jute or polypropylene bags, lifted on platforms, on conical constructions or in baskets (Zhang et al. 2018; Compton et al. 1997). In eastern and southern Africa, farmers use ash from cow dung in small sacks, wooden containers, pits, iron drums encased in mud, and metal containers for storing the grains (Zhang et al. 2018; Wambugu et al. 2009). “Nkokwe” is one of the most commonly used warehouse structures used, e.g., in Malawi and Kenya. It is a kind of cylindrical basket consisting of woven bamboo covered with a conical roof of grass. This construction is erected on stilts (Bradford et al. 2018). Most of the structures are not designed professionally and made of materials available locally and cause damage to stored seeds due to biological, environmental, and other factors.
Of all biotic factors, pests are considered the most important and cause very large losses in crops (30–40%) (Obiedzińska 2017; Abraha et al. 2018; Kiaya 2014). Maize grain during storage is exposed to various types of losses. Some of them result from improper storage, and some are the result of the settlement, development, and feeding of various storage pests, including harmful mites and insects. These organisms may cause losses, both resulting from the loss of mass of the raw material due to feeding and much more severe quality losses. In Ghana, for example, maize losses due to insects reach 50% (Boxall 2002). According to the economic model of Compton et al. (1997), each percent of insect invasions causes a decrease in the value of maize by 0.6–1% (Compton et al. 1997; Baoua et al. 2014). In Togo, for example, insects and pests are responsible for 80–90% of losses during seed storage. Callosobruchus maculatus (F.) is a common pest, responsible for losses up to 24% in stored seeds in Nigeria (Pantenius 1988). In Cameroon, the losses caused by insects in maize seeds range from 12% to 44% (Tapondjou et al. 2002). Corn grain is inhabited by various species of storage mites, including mold mite and flour mite. Their microscopic bodies, however, are delicate and sensitive to drying out, which is why they gather more often in places of higher humidity, where they intensively feed and reproduce. As a result of life processes, the temperature and humidity of the stored raw material may gradually increase in these places. As a result, its slow deterioration takes place. Feeding mites primarily damage embryos that are the most wetted part of the kernel, and microscopic damages can later result in lower seed sowing values. The mites not only damage and pollute the raw material that settles with their excretions, secretions, louts, and dead individuals. At a very large population, the grain acquires a specific, unpleasant odor. The unfavorable processes resulting from the presence, feeding, and development of mites significantly affect the quality of the raw material (Kumar et al. 2007). The stored corn grain may feed on beetles and storage butterflies, such as larger grain borer, lesser grain borer, Areacersus fasciculatus Deg., mealworm beetle, cornsap beetle, dried-fruit beetle, Carpophilus flavipes, Carpophilus mutilatus, Cryptolestes ferrugineus Steph., cabinet beetle, Trogoderma variabile, sawtoothed grain beetle, red flour beetle, confused flour beetle, Typhaea stercorea, cadelle beetle, Sitophilus zeamais, rice weevil, wheat weevil, Caulophilus oryzae, bread beetle, and even barkflies. The butterflies include almond moth, mill moth, rice moth, weevil moth, and Angoumois grain moth. These insects are larger than mites, more mobile, and less sensitive to unfavorable environmental conditions. Large inter-grain spaces in the stored corn allow the insects to freely penetrate the whole profile of the prism. Like mites, they accumulate more in more humid places, as well as in non-temperate periods. Their presence in a given place and their life processes (breathing) cause locally an increase in the moisture and temperature of the raw material. Mites begin feeding from embryos, as well as broken seeds, and those covered by the fruit and seed shell have been damaged (e.g., mechanically). As a result of feeding insects, large amounts of dust are generated, which falls clogging gradually into the spaces between the grains, as a result of which the free flow of air through the grain prism is limited. The processes of heating and humidifying the grain in the occluded layer are then intensified. There is an intense growth of the bacterial and fungal microflora, which leads to the spoiling of the raw material. Feeding on moldy kernels is easier. The beetles feed on adult insects and larvae. Most species of storage beetles are small. Their bodies usually have from 3 to 5 mm in length, although some are relatively large, because they have from 15 to 25 mm (e.g., mealworm beetle). The larvae of most beetles are also small. Most of the larvae and stages of adult beetles feed on and develop from egg to adult outside the kernels, with the exception of grain weevil. Maize kernels are much larger than other cereals; hence more than one individual can grow in one. From the inside of the corn kernels, eggs develop larvae, pupae, and finally young beetles, with no visible external symptoms. Over time, from the settled kernels through the holes formed as a result of feeding pests, the dust resulting from their intensive feeding begins to pour out. Many harmful species of warehouse beetles spend one or two descendants during the year. Under favorable conditions, with higher humidity of the raw material and at a higher temperature, the number of generations of insects increases. In most species of storage beetles, the damage is caused by both larvae and adults (Boxall 2001; Bereś et al. 2013).
In butterflies, the harmful stage is larvae or caterpillars. They usually stay in the top layer of the raw material. Only in extreme cases, after thoroughly eating the top layer of grain, they go deeper. The places where larvae feed, as well as the kernels they feed on, are stuck with threads of sticky yarn secreted by them (47). In maize, however, Sitophilus zeamais and Prostephanus truncatus are the main pests of grain. On average, 23% of losses in cereals stored for 6 months, mainly due to cereal swine and LGB infections, are recorded in African countries (Boxall 2001; Ognakossan et al. 2013). LGB was established in Central America and was accidentally brought to Africa in the late 1970s (Kimenju and de Groote 2010). It is present in most parts of Africa and is considered the most dangerous pest, because it causes huge damage in a very short time (Markham et al. 1994; Tefera et al. 2011). During storage on the farm, there may be more than 30% of the grain loss of maize due to these pests (Kiaya 2014; Shaaya et al. 1997). In Ghana, 5–10% of the market value loss of corn seeds is due to the invasion of Sitophilus spp. and 15–45% of market value loss – as a result of damage by LGB. Generally, these losses accounted for around 5% of the average household income in this area (Boxall 2001; Magrath et al. 1996, 1997). Abass et al. (2014) reported that after 6 months of maize storage, LGB was responsible for more than half (57%) of storage losses and then losses due to grain weevil (Patel et al. 1993).
Mycotoxin contamination is another challenge, especially in the case of maize, which makes the food unfit for human consumption or for animal nutrition. A large amount (25–40%) of cereal seeds is contaminated by mycotoxins produced by storage fungi all over the world (Kumar et al. 2007; Rachoń et al. 2016). Mycotoxins cause loss of seed quality and pose a threat in the food chain (Magan and Aldred 2007). Aflatoxins, feminizing, deoxynivalenol, and ochratoxins are the most common and most important mycotoxins, especially in maize (Kimanya et al. 2012; Suleiman and Kurt 2015; Suleiman et al. 2013). Aflatoxins, produced as a secondary metabolite by two species of fungi Aspergillus flavus and A. parasiticus, are considered the most dangerous group of mycotoxins, because they increase the risk of liver cancer and affect the growth in young children (Kimanya et al. 2012). About 4.5 billion people are exposed to aflatoxins in developing countries due to the food contamination (Kumar et al. 2007; Suleiman et al. 2013). High concentrations of aflatoxin can lead to aflatoxicosis, which can cause serious illness and even death (Fox 2013). Penicillium verrucosum (ochratoxin), the main mycotoxin mold commonly found in humid and cool climates (e.g., in Northern Europe), and Aspergillus flavus are most commonly observed in temperate and tropical climate (Magan and Aldred 2007). Mold during storage damages the seeds and also limits their germination. It also worsens the quality of grain with an increased content of fatty acids and a reduced content of starch and sugar. Lipid peroxidation is another phenomenon that causes deterioration of foods, changes taste and smell, and may cause undesirable effects on human health (Kumar et al. 2007). Oilseed species and varieties with a high oil content require special attention during storage, because high levels of moisture cause degradation of vegetable oil and produce fatty acids, which sometimes also causes self-heating of seeds (Fox 2013). In developing countries, even rodents can damage a large part of the crop, while fungi can be the main reason for spoiling seeds when stored in high relative humidity. The use of professional storage structures and proper handling of seeds can reduce storage losses to less than 1% (Costa 2014; Weifen and Zuxun 2003). Losses can be minimized by physically avoiding the penetration of insects and rodents and maintaining the environmental conditions that prevent the growth of microorganisms. Knowing the control points during collection and drying before storage can help to reduce losses during grain storage (Obiedzińska 2017).
Interventions to Reduce Losses
Losses associated with the storage of plant raw materials can be reduced by using efficient storage technology, updating infrastructure and good storage practices. The World Food Programme (WFP), with the help of governments and nongovernmental organizations (NGOs), carried out operation trials in Uganda and Burkina Faso to demonstrate the impact of improved post-harvest management practices and the application of new storage technologies to crop losses after harvest (Costa 2014). Regardless of the period of cultivation or storage, the use of improved practices and new technologies contributes to reducing the food loss by around 98% (Abedin et al. 2012). Losses in traditional storage structures are much higher, because the storage period is longer than that commonly used by farmers in these countries. It is important to understand their usefulness, technical effectiveness, and limitations in order to promote their adaptability among consumers. Technological practices and interventions that can help reduce storage losses are chemical fumigation, natural insecticides, and hermetic storage. In addition to saving losses, the availability of cheap and effective storage structures can motivate farmers to store their cereals and obtain high prices instead of selling just after harvest, when there is a large supply of cereals (Baoua et al. 2014; De Groote et al. 2013). Storage structures as well as technological interventions can significantly reduce losses in warehouses, super- and hypermarkets, and in stores. First of all, it is important to understand that the training of service staff, not only large warehouses but also small store owners, is equally necessary as the distribution of storage technology (European Commission 2016a; Kitinoja 2013; FAO 2017b). With the provision of these technologies, government agencies and organizations must ensure the development of devices providing information and training on the use and maintenance of these technologies, in order to successfully adapt and use them effectively (European Commission 2016b; FAO, LEI 2015; Godfray et al. 2010).
Achieving Food Security, Sustainable Development and Resilience Through the Use of Genetic Diversity and Indigenous Knowledge: SDG2
Genetic diversity preserved by local, native agricultural knowledge and practices is a valuable source of information for improving food security and adaptation to climate change. These practices can significantly increase productivity, income, and resilience in harsh environmental conditions, contributing to the goals set in sustainable development.
There is a need for increased support for innovation and agricultural practices of indigenous peoples to ensure that we do not lose the genetic diversity and knowledge that this population has. The priority should be to preserve and improve the resistance of local plant and animal species through the local community, seed banks, community-managed landscapes, traditional active plant breeding, and market links for traditional products (Swiderska et al. 2016).
Reduction of post-harvest losses (PHL) is a priority area of collaboration between FAO and the African Development Bank (ADB). It was one of three pillars identified by ADB within its African Food Crisis Response (AFCR) of June 2008, in response to the rise of food prices in 2007 and 2008 (Hodge et al. 2011; Anonymous 2011).
Achieving food security, sustainable development, and resilience through the use of genetic diversity and indigenous knowledge.
Preservation of the genetic diversity of seeds, arable crops, farmed and domesticated animals and their related wild species, grazing, fishery, or forest resources.
Getting more support for the innovations and practices of the natives, so as not to lose the genetic diversity and knowledge they possess, with the same priority for preserving and improving the resistance of local ecotypes and cultivar varieties, through the community, seed banks, community-managed landscapes, active plant breeding, and market links for traditional products.
Increasing the productivity of crop species and animals, especially in marginal areas already affected by climate change, without causing loss of genetic diversity for future generations.
Ensuring sustainable production and implementation of resilient farming practices to help maintain ecosystems, strengthen adaptability to climate change and extreme events, and improve the quality of arable land and undeveloped agricultural soils.
Ensuring sustainable production and implementation of resistant agricultural practices, so as to strengthen the ability to adapt to climate change and extreme events, improve the quality of arable land and undeveloped soils, and help maintain ecosystems.
Risk management and diversification. In developing countries, farmers began to grow different varieties of the same species together, including local varieties, resistant to disease, to reduce the risk of crop failure. For example, hybrid, improved, and traditional varieties of maize and manioc were planted in Kenya, which reduced the yield decrease by about 20%. Domesticated wild trees have also been dominated to mitigate climate change.
Soil and water protection. The use of micro-reservoirs of water, which combine traditional technology of obtaining water (aruna) with modern materials and techniques and ensure the availability of water for irrigation and consumption.
New techniques of organic composting improved soil fertility and moisture, which increased crop yields and improved water use.
Reintroduction of traditional cultivation and fertilization techniques to reduce soil erosion. Restoring traditional intercrop crops to improve soil fertility and its physico-chemical composition.
Aerating the soil by plowing and bringing manure, which allows it to increase its ability to retain water.
Planting trees from the Fabaceae family, able to bind nitrogen from the air, especially in food crops, which improves soil fertility and increases crop production by about 15–20%
Natural pest control. Traditional techniques combining, e.g., organic cultivation of rice or maize with the production of geese, ducks, and fish, which provides natural pest control on the crop plantations.
The post-harvest losses are a serious problem, and their scale is different for different crops, practices, climatic conditions, and the economic situation of a given country. The main limiting factors for PHL are different, as in developed countries, they include education campaigns for consumers, well-targeted taxation, and partnership, both in the private and public sectors, which are responsible for reducing post-harvest losses. The factors that increase the development of LDC are more common education of farmers in the causes of PHL; favorable infrastructure favoring the merging of small holders with markets; more efficient value chains that provide financial incentives at the level of producers; the adoption of common marketing and effective technologies supported by access to microcredit; as well as the public and private sectors sharing investment and risk costs in market-oriented interventions.
In developing countries, wastage and food losses occur mainly at the early stages of the food value chain and can be linked to financial, management, and technical constraints in harvesting techniques as well as storage and cooling equipment. Strengthening the supply chain through the direct support of farmers and investments in infrastructure, transport, as well as in the development of the food and packaging industry can help reduce the amount of food wastes and losses.
In middle- and high-income countries, food is wasted and lost mainly at later stages of the supply chain. There is no coordination between entities in the supply chain as a factor contributing to post-harvest losses. Farmers’ agreements can help to increase the level of these coordination. In addition, raising awareness among industry, retailers, and consumers and finding a beneficial use of food that is currently being thrown away are useful measures to reduce of losses and wastes.
Losses in storage represent the maximum part of all losses after harvest for cereals, oil, and legume plants, in developing countries, and negatively affect farmers’ incomes. Most harvested crops are stored in traditional storage structures, which are currently not sufficient to avoid invading insects, pests, or molds during storage and lead to large losses. Technological interventions and improved storage structures can play a key role in reducing the post-harvest losses and increasing farmers’ incomes. Hermetic storage will allow to reduce these losses. It creates an automatically modified atmosphere with a high concentration of carbon dioxide using hermetic, waterproof bags or construction and significantly reduces insect losses. The use of sealed, hermetic storage structures has led to a reduction in losses during the storage of cereal seeds, leguminous seeds, and oilseeds, maintaining their lifetime and their quality for long storage duration by 98. The integration of food safety, environment, and immunity (SDG2) will allow to develop local, resistant varieties and production strategies, while maintaining a rich genetic diversity. Using local resources, knowledge, and innovations (all free and easily available), it is possible to increase productivity without causing loss of genetic diversity for future adaptation by farmers. Local species and varieties are often more valuable, more nutritious, and more resistant to drought and pests, with greater storage durability than their modern counterparts.
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