Edible indigenous fruits in Zimbabwe: A review on the post-harvest handling, processing, and commercial value

Abstract Indigenous fruits are considered to be part of the diet mostly by people in rural communities of Zimbabwe, but they are still being underutilized. They can be eaten raw or processed into different products dating long back. There are various indigenous food post-harvest handling methods that have been used in Zimbabwean rural communities in order to maintain food security and add variety to their diets. Post-harvest handling of some commonly consumed indigenous fruits has been reported in the literature. Systematic review of literature method was used. Results showed that traditional processing and preservation methods of only 22 indigenous fruits had been documented out of 82 wild fruits. However, the information on post-harvest handling of most indigenous fruits is limited and incomplete. The review aimed to interrogate existing knowledge in literature on post-harvest handling of indigenous fruits in Zimbabwe and identify gaps for further research. This review attempts to contribute to this effort by evaluating existing literature. There is a need for indigenous fruit surveys to be conducted so as to get more information on indigenous fruits.

Patience Nemapare is a PhD student and lecturer at Midlands State University in Zimbabwe. Her key research interests include cereal technology and food fortification, product development, beverages and indigenous plants, and fermentation. The research included in this paper on indigenous fruits in Zimbabwe is part of the sustainable development goals 1 and 2 which aims at alleviating poverty and hunger through enhanced production and export of value added traditional fruits. A review of literature on post-harvest handling of indigenous fruits can help in identification of opportunities to transform local communities in Zimbabwe.
Tendekayi H. Gdaga is the Pro-Vice Chancellor (Academic) and Associate Professor at University of Eswatini in Swaziland. His research interests include food safety, HACCP, public health community surveys, indigenous foods and project evaluations.
Desmond T. Mugadza is a PhD holder and lecturer at Midlands State University in Zimbabwe. His research interests include food safety, microbiology, food security and new food product development.

Terminology
Wild fruits are defined as fruits of wild plants often either exotic/introduced or indigenous/natural, whereas indigenous fruits are defined as those fruits that grow naturally, are culturally accepted as local foods, and previously eaten for generations in that society. In this paper, the words wild and indigenous fruits will be used to interchangeably to mark the inclusion or exclusion of exotic/ introduced fruits in the context.

Introduction
Ending hunger and malnutrition by 2030 is proving to be a challenge, with an estimate of more than 820 million people without sufficient food worldwide (FAO, 2020). In Southern Africa, most rural people are said to be food insecure and are more prone to chronic malnutrition (Kalaba, Chirwa & Prozesky, 2009). In Zimbabwe, El Nino induced 2015/16 drought left over 4 million people, food insecure, of which 51% of these were women. To curb this, the country adopted the Sustainable Development Goals (SDGs) with goal 1 and 2 advocating the end of poverty and hunger, and achievement of food security and improved nutrition.
Malnutrition exists in two common forms, acute and chronic, with the latter causing irreversible damage. Stunting/hidden hunger is a form of chronic malnutrition that results in poor cognitive ability and poor growth in children under 5 years of age. Stunting is caused by lack of a balanced diet, especially growth-limiting nutrients, such as zinc, iron, vitamin A, vitamin D, and folate. Insufficient duration of breastfeeding and early formula feeding can also increase the risk of stunting (Macheka et al., 2022). Subclinical infections resulting from exposure to contaminated environments and poor hygiene are also associated with stunting due to nutrient malabsorption and reduced ability of the gut to function as a barrier against pathogens (WHO, 2014).
As a consequence, stunting leads to poor economic development in poverty-stricken countries (Weatherspoon et al., 2019). With the global stunting rate in children under 5 years standing at 21.9%, which is above the threshold of 20% set by the WHO to signify a public health concern, sustainable solutions are yet to be found. In Zimbabwe, according to (ZIMVAC, 2019) the stunting rate was at 26.8% for children under 5, translating to 1 in 3 children being chronically malnourished in the population. In addition, the survey showed that at least 57% of women of childbearing age were at risk of micronutrient deficiencies.
Prevention of stunting is a multidisciplinary approach. Various strategies of alleviating chronic malnutrition have so far been employed, including vitamin A and micronutrient supplementation, bio-fortification, probiotic foods, and improved food processing methods (Pridmore & Hill, 2011;Younis et al., 2015). Akinnifesi et al. (2004) recommended that one way of addressing stunting is through consumption of indigenous fruits, which are cheap and locally available.
Fruits are plant-based excellent sources of fiber, essential vitamins, minerals, and antioxidants, such as magnesium, calcium, iron, zinc, vitamin A, D, and folate. which all support growth and development (Nachvak et al., 2020). However, the fruit intake should be supported by water sanitation, disease control, and high protein foods, such as eggs, fish, and chicken liver, and fats and carbohydrates, to attain dietary diversity. Previous studies, for example (E. M. Lee et al., 2012), observed that consumption of meat, fruits, and vegetables in children of normal height was higher than in stunted children. This shows that fruits and vegetables are an essential part of the diet as they provide micronutrients that prevent chronic malnutrition.
Indigenous fruits have always been consumed as a survival strategy to escape hunger in poor households (Kalaba, Chirwa & Prozesky, 2009). According to (Neudeck et al., 2012), some lowincome households rely on indigenous fruits as an alternative to cultivated food for a quarter of all the meals during lean/dry seasons. Indigenous fruits have been underutilized, and yet they are part of the solution in ameliorating stunting.
Information available on traditional use, handling, and marketing of the indigenous fruits is based on commonly consumed fruits and not all fruits found in Zimbabwe (Muok, 2019). Zimbabwe is rich in indigenous fruits of which some have documented traditional handling, preparation, and processing techniques used by the local communities which are incomplete and outdated for example Garcinia livingstonei, Garcinia huillensis, Hexabolis monopetalus etc. Whilst some of the wild fruits such as Ziziphus mauritiana, Strychnos cocculoides, Adansonia digitata, and Parinari curatellifolia have been studied extensively in Zimbabwe by various authors. Most studies that have been done have paid attention to profiling and documenting the types of indigenous fruits, seasonality, and general uses. Little attention has been given to consumption patterns, post-harvest handling, processing, and preservation of most indigenous fruits (Parawira & Muchuweti, 2008). Efforts to document all underutilized edible indigenous fruits in the national food inventory are long overdue and necessary for the development of a food database for sustainable harvesting and post-harvest handling strategies. Information from literature aids in guiding on gaps that need to be exploited in a bid to create a complete database of indigenous fruits. Knowledge on these traditional processes is vital in innovation and use of upgraded modern techniques in value addition and commercialization of indigenous fruits.
Unlike herbs, most indigenous fruits are either consumed directly or processed/preserved for later use. Most of the locally processed fruit products are usually consumed at household level and rarely make their way to the market. However, a few indigenous fruits, such as Baobab and Marula, are now being recognized in South Africa, Malawi, and Zimbabwe and processed for international markets . Traditional harvesting methods employed by rural communities lead to post harvest losses of fruits (Ngadze, 2018). Mechanical damage of the fruits,spoilage, oxidative browning and poor transportation conditions has led to loss of potential income from the sale of harvested fruits apart from not having a ready, defined market (Elago, 2016). Kuyu and Bereka (2020) added that fruit losses can be reduced through upgrading traditional processing and preservation methods using modern methods and equipment. Krishnan et al. (2014) added that common traditional methods for fruit preservation include fermentation, sun drying, and pickling. It is against this background that the review attempts to critique the evidence of post-harvest handling of indigenous fruits that has been documented so far.

Materials & methods
Systematic online literature search using terms and keywords such as ethno-botanical studies on indigenous plants, post-harvest handling of indigenous fruits in Africa, indigenous fruits in Southern Africa and Zimbabwe, and edible wild plants was conducted. Articles with the above keywords were selected and studies based on traditional knowledge and post-harvest handling of wild edible fruits/indigenous fruit. The search engines and databases used were Google, Google Scholar, Flora of Zimbabwe, Useful Tropical Plants, and PlantZ Africa. Textbooks were also reviewed. The inclusion criteria were wild fruits in Africa and Zimbabwe, and the exclusion criteria were wild fruits outside Africa.

Indigenous fruits and their distribution in Zimbabwe
Indigenous fruits in Sub-Saharan Africa are widely distributed; they are mainly found in Miombo woodlands Dewees et al., 2010;Kadu et al. 2006). Miombo woodlands are a vast region of tropical grasslands, savannas, and shrub lands which are characterized by a canopy cover of 2-7% ( Figure 1) (Campbell, 1987).
Zimbabwe is a land-locked country located in south central Africa between the Zambezi and Limpopo rivers (FAO, 2016). The country is endowed with wild food plants, of which Tredgold (1986) documented about 180. It was estimated that more than 20% of these are edible fruits (Mapfumo & Mtindi, 1996;Ngadze, 2018;Tredgold, 1986). Zimbabwe is endowed with many indigenous fruits which are distributed in different parts of the country. Campbell (1987) noted that, although indigenous fruits are spread out in the five natural regions of Zimbabwe, the largest edible fruit reserves were found in the Julbernardia globiflora (Benth.) Miombo woodlands, which are dominant in ecological regions 3 and 4 (Macheka et al., 2022), focused on the agro-ecological distribution of at least 26 common edible indigenous fruits in Zimbabwe and showed that they are widely distributed in all the provinces regardless of the agro-ecological regions. Table 1 shows a representative, though not complete, list of edible wild fruits found in Zimbabwe. Seventy-seven (77) indigenous fruits in Zimbabwe were reported in literature. Tredgold (1986) documented about 55 indigenous fruits in Zimbabwe. It is important to note that the lower number of indigenous fruits reported by Tredgold (1986) could have been due to the fact that some of the fruits had not been categorized into their different species. Maroyi and Cheikyoussef (2017), from their survey in Zimbabwe's Midlands province, reported about 50 wild fruit species, while other researchers documented an average of 30 wild fruits. Some of the fruits recorded by Tredgold (1986) were not documented by other researchers and vice versa, as it is not a complete or comprehensive listing of all indigenous fruits available in Zimbabwe. Campbell (1987) and Tredgold (1986) carried out surveys in almost every province in the country whilst other researchers focused on single provinces. The differences in types and number of indigenous fruits could have been due to the differences in the study areas. For example, some of the indigenous fruits found in the Midlands province were not found in Mashonaland Central or Matebeleland. Indigenous fruit dominance or abundance is a result of the soil type and climatic conditions, for example mazhanje. (Uapaca kirkiana) is found in mixed communities of Brachystegia Jubernardia woodland vegetation, and its distribution is mainly in dry and semi-dry areas,    especially well-drained escarpments, with low fertility soil (Macheka et al., 2022). Some of the fruits reported by Campbell (1987) and Tredgold (1986) were not commonly found. They could have become extinct over time due to deforestation or the trees were sparsely distributed. As a measure to curb indigenous fruit tree extinction and to promote sustainable use of edible indigenous fruits, various researches have been done in an effort to domesticate the trees through propagation. For instance, trial plantings for Syzigium guineense DC. have been conducted with success using their seeds . Bridgemohan and Isaac (2017) stated that indigenous fruits are harvested, handled, and processed using traditional methods at household level. The type and timing of harvesting indigenous fruits in Africa is dependent on the fruit tree species and maturity of the fruits (Kadzere et al., 2007). For example, Adansonia digitata fruits do not abscise readily when ripe and hence need to be physically dislodged (Ham et al. 2008). Vangueria infausta fruits are also physically dislodged from the tree, otherwise they dry whilst attached to the tree branches if not harvested (Mothapo et al., 2014). The method and time of harvesting usually determine the handling of the fruits. For example, early harvesting requires incubation of the fruits to encourage ripening. This is commonly done for wild loquat fruits and monkey oranges (Ngadze et al., 2017).,

Harvesting and post-harvest handling of indigenous fruits
Traditional methods of harvesting employed in Zimbabwe include knocking down of either ripe or unripe fruits, plucking of fruits from branches and/or picking of fallen ripe fruits from the ground (Ngadze et al., 2017). In Malawi, Uapaca kirkiana fruits are harvested by knocking them down from the branches in the middle of the season when they are mature but still firm (Kadzere et al., 2007). As the season progresses, soft and ripe fruits knocked or plucked from the tree would be more susceptible to compression damage (Ntupanyama et al., 2008). Dislodging of the fruits using sticks (Kadzere et al., 2007) or stones accelerates deterioration of fruits by enzymatic oxidation. Ioannou and GhouL (2013) named enzymatic browning as the second-largest cause of quality loss in fruits and vegetables after harvesting. Enzymatic browning in fruits is mainly caused by polyphenol oxidase activity (Ioannou & GhouL, 2013). The enzyme catalyzes two steps: hydroxylation of monophenols to diphenols, which are colorless, and oxidation of the diphenols to quinones, which are colored (Queiroz et al., 2008).
Various methods can be used to reduce fruit damage including collecting onto nets or modifying the ground by using soft vegetative materials (Vossen, 1999). In Zimbabwe, most harvesters collect fallen fruits from the ground as a method of harvesting (Chirwa & Akinnifesi, 2007). These fallen fruits may be ripe or overripe and are susceptible to physical and pest damage.
According to Kadzere et al. (2007) after harvesting, indigenous wild fruits are packed in woven baskets or tins and transported home. Usually, the unripe or firm ones are packed at the bottom whilst the ripe and soft ones are on top. The use of rigid containers such as woven reed baskets and tins for ripe fruits reduces compression and further damage to ripe fruits during transportation. Ripe fruits are usually kept at room temperature in well-ventilated containers such as porous woven baskets and plastic bags.
After harvesting wild fruits, the gatherers in Zimbabwe normally carry them on their heads in buckets/sacks or in ox-drawn carts to their homes, markets or roadside collection points (Ham et al. 2008). Similarly, in Zambia, 14% of interviewed traders indicated that they paid for transport to deliver fresh indigenous fruits to the market, whilst the majority ferried the fruits on their own (Karaan et al., 2006;Ramadhani, 2002). A few collectors protect the fruits from harsh weather conditions such as the sun or rain (Ham et al. 2008). Fruits that go to urban centers go through various handlers and different transport and handling conditions which do not follow a standard protocol as done with exotic fruits . Poor harvesting and handling of fruits in transit leads to discoloration, over ripening and decay.

Storage practices
Unripe fruits are usually stored and ripened by incubating them in a shallow pit in the ground and covering with soil, storing in tightly closed plastic containers or baskets sealed with plastic and mud, or leaving them in loosely closed or open containers/clay pots (Chadzimura, 2016). Burying of unripe fruits is also a common practice in Malawi, Zambia, and Namibia and is used both as a preservation and fruit ripening method (Kadzere et al., 2007). Burying the fruits in the soil reduces the direct effects of the atmospheric conditions thus reducing the shriveling of the fruits (Rampedi & Olivier, 2013). Apart from preserving the fruits, burying unripe fruits is done to reduce competition from other fruit collectors who will be vying for the popular varieties which sell quickly at the market (Ngadze et al., 2017). As a result, fruit collectors tend to harvest fruits before they are ripe so as to secure the product before others. During incubation, ripening is accelerated by the dark and airtight environments that allow for accumulation of ethylene hormone in plants thereby speeding up the ripening process (Barry & Giovannoni, 2007). When ripened, the fruits are taken out and cleaned. Incubated fruits remain fresh for a period of 3-5 days depending on the water content and characteristics of the fruit. Short shelf life remains a major constraint in the traditional handling and utilization of indigenous fruits.
Another storage approach employed by the fruit collectors at the homestead or market is to keep ripe fruits in a cool dry area, such as a shade at ambient temperatures (Kadzere et al., 2004). Rural communities use traditional storage practices as coping strategies to reduce fruit quality losses. Indigenous storage structures are made of locally available raw materials, such as wood, grass, and so on, without any scientific design and no guarantee to protect the fruits against temperature, humidity fluctuations, and insects (Kumar & Kalita, 2017). Fruits are spread under a shade with little or no control over temperature fluctuations which have a detrimental effect on respiration and fruit quality. Temperature and humidity management is important in extending the shelf life of fruits (S. K. Lee & Kader, 2000;Tembo et al., 2008). This is because heat and humidity when combined provide conditions favorable for fungal and bacteria growth (Emongor & Ramagonono, 2019).
Keeping fruits in cool, dry areas aids in reducing temperature build up and sweating, which normally encourage insect infestation (Tembo et al., 2008). By lowering the temperature of the fruits, water loss is reduced, respiration rate is decreased, ethylene production is suppressed, and microbial development is slowed down. However, this requires constant temperature and humidity control which is not possible due to changes in weather.

Traditional processing and preservation methods
Different traditional methods of preservation and processing in the Sub-Saharan Africa were reported for only 35 wild fruits. For example, fermentation, drying, salting, cooking, baking, juicing, and roasting. Table 2 shows that the most common traditional methods of processing and/or preserving fruits are sun drying, salting, and fermentation (Asogwa et al., 2017).

Drying
Drying is one of the methods used to increase the shelf life of perishable indigenous fruits when they are in excess (CTA, 2007). According to Asogwa et al. (2017) sun drying is one of the most common methods employed on indigenous fruits. Sun drying is more effective for low to medium moisture fruits such as Vangueria infausta, Berchemia discolor, Diospyros mespiliformis, Ziziphus mauritiana to mention a few. Low moisture fruits dry quickly and effectively unlike high moisture fruits such as Uapaca kirkiana. Drying of indigenous fruits is a common practice employed by Zimbabwean rural households as a preservation and intermediate processing method. Drying fruits prolongs their shelf life with reduced microorganism viability. For example, dried products are used as starting materials for snacks, sweets, instant powders, and porridge . Fruits require drying before grinding them into powderfor example, wild fruits such as masawu (Ziziphus mauritiana) are pounded together with their seeds into a powder which is then mixed with water   Campbell (1987) to make a mahewu like slurry (Ham et al. 2008). Dried V. infausta fruit powders can be soaked, boiled, and mashed to make porridge as the final product (Munodawafa, 2012). (Ngadze et al., 2017) mentioned that people in Bikita alternate sun and fire drying of S. innocua and S. madagascariensis. The use of both sun and fire drying methods reduce the drying times which are usually influenced by the sugar content of the fruits. The water diffuses from the fruit to the sugar solution through osmosis until both solutions are in equilibrium (Kabuo et al., 2014). Increased sugar concentrations serve as a preservative due to the hygroscopic nature of sucrose, which binds together water molecules making them unavailable for microbial spoilage and also adds flavor to the dried fruits (Kabuo et al., 2014). Sugar also provides protection of the fruit membranes from enzymatic or oxidative browning, hence preserving the fruit color. However, high sugar content within the fruit pulp results in longer drying periods since sugars are hygroscopic and bind with water, thus lowering vapor pressure (Muzaffar et al., 2018). This decreases the drying efficiency and hence the need to coat the fruit surfaces with sugar/salt outside the membrane to create a diffusion gradient. Also, compounds such as sugars when in large quantities form a hard, impermeable case on the upper surface of the fruit if the drying temperatures are too high, thus resulting in slow dehydration (Yadav & Singh, 2014).
Traditional drying of fruits is not a controlled process hence determination of final moisture content and desired level of dryness is subjective, it is usually done by physical assessment of the product stickiness using hands to feel the product texture (Ngadze et al., 2017), a method which is not accurate for commercialized products. There is also loss of vitamins, color, flavor, and development of toxins from insect infestation and yeast and mold formation (Belessiotis & Delyannis, 2011). This is attributed to the dependence of sun drying on weather and exposure of the fruits to moisture, dust, insects, and other animals (Bourdoux et al., 2016). However, some of these losses can be prevented by sun drying on raised platforms and for short-time intervals. Sun/fire drying of fruits can be improved through modern drying methods so as to produce value added products of good quality for commercialization. Modern methods ensure the attainment of shelf stable products, with a water content ranging from 18% to 24% which is not viable for the growth of microorganisms (Santos & Silva, 2008). These methods include solar drying, freeze drying, oven drying, and osmotic drying (Ahmed et al., 2013).

Fermentation
Approximately 10% of the wild plants found in Zimbabwe can be fermented into some form of enriched sour porridge, beer or wine at household level (Gadaga et al., 1999). Fermentation is another method used to preserve and process fruits. Fermentation improves the nutritional quality of the fruits and results in release of organic acids which lower the pH thereby preventing the growth of spoilage microorganisms (Motarjemi, 2002). Fermentation also improves digestibility of food by enzyme modifications of primary products through hydrolysis of polysaccharides, proteins, and lipids (Oyewole & Isah, 2012).
Traditional fermentation of fruits, such as S. birrea, H. benguellensis, P. curatellifolia, and U. kirkiana involves spontaneous fermentation of the fruits using natural microbiota found on the fruits (Gadaga et al., 1999). During fermentation, the fruit mash is left to ferment using natural flora in covered containers at room temperature for several days . The use of a mixture of naturally occurring microorganisms from the fruits and environment results in competition for substrates and in some instances the beer/wine may develop off-flavors. Fermentation of the fruit mash anaerobically is achieved by sealing the drums with lids or plastics . In some cases, they cover the drums with damp clay (Gadaga et al., 1999). In terms of handling, traditional processing of fruits involves too much direct contact with the fruits and squeezing juice is normally done by hand (Tredgold, 1986). This requires strict hygiene practices to reduce the risk of product contamination. Although fermented fruit porridges and beverages are popular among rural households, the processes are uncontrolled, and the procedures used are not standard. Improvement of old technologies for fermenting wild fruit beverages and beers like mukumbi from mapfura (marula), munyani, munyii, muremberembe, mutunduru, mukute fruits; mutandabota from matamba and mauyu fruits; mudetemwa from muhacha fruits and mutandavira from mazhanje and kachasu from masawu fruits have the potential to benefit rural communities as it will improve the product, its keeping qualities, and increase revenue. There is an opportunity for improvement and optimization of these technologies for commercialization. The microbiology and biochemistry of traditional fermentation needs to be fully researched in order to improve critical stages in the whole process (Gadaga et al., 1999).

Other processing methods
Other methods of processing indigenous fruits in Zimbabwe performed besides drying include cooking, flavoring, baking, and grinding . Surplus fruits are sun/fire dried and processed later into products such as cereal-fruit enriched porridge, cakes, flavoring agents, bread (chimodho), juices, and fermented beverages such as mutandabota (Gadaga et al., 1999). Brazier (2020) noted that in Zimbabwe fresh fruits such as wild loquats, monkey oranges and mobola plums, to name a few, are usually squeezed mechanically by hand or sieving the pulp through a woven sack to make juices or to use as condiments in soups. Sieving is usually done by hand, and the level of cleaning the woven fruit sacks used for sieving is subjective. There is also the addition of lemon juice as a preservative and addition of sugar depending on consumer preference. The role of lemons is to act as an antioxidant which prevents browning of the juice (Bille et al., 2013). The juice may be boiled as a way of reducing its microbial load. However, this leads to discoloration and loss of antioxidant activity (Marszałek et al., 2016) in (Petruzzi et al., 2017). It also reduces the concentration of heat-sensitive nutrients such as proteins, leaching of watersoluble vitamins such as Vitamin C, and pigments (Renard & Maingonnat, 2012). Boiling fruit juices are also responsible for off-flavor and product color change. The juice is then cooled and stored to be consumed for at least 3 days (Ngadze et al., 2017). Commercially, mild heat treatment methods used for fruit juices employed include pasteurization, high temperature short-time sterilization, and other non-conventional thermal processing methods, such as ohmic and microwave heating (J. Y. Lee et al., 2015) in (Petruzzi et al., 2017).
A high level of strict hygiene is required to prevent contamination of the final product (Parawira & Muchuweti, 2008). The water used for traditional fruit processing is either from boreholes, wells, or rivers depending on their source of water. Water used for traditional processing of fruits is not tested for its microbiological quality, chemistry, and appearance (Wujie & Xujing, 2011), instead they just use the available potable water found in that area regardless of its source. Regardless of the source of water, to ensure microbial safety of juice, traditional processors boil the juice before cooling and packaging it. On the other hand, in commercial fruit processing, water quality is a contributing factor to the final product microbiological quality, and therefore, it is tested together with other raw materials (FAO, 2020). Water is usually treated with chlorine in order to reduce spoilage microbes such as coliforms and E. coli.
Baked products such as cakes and bread can be made from a mixture of indigenous fruit flour and wheat or maize flour. For example B. discolour powder can be mixed with maize meal and kneaded into a dough which is baked into bread (Brazier, 2020). The fruit flour or juice can be used as a major or minor ingredient to add flavor or color to the baked product.
Podded fruits, e.g. mobola plums, are crushed, ground, and used to make (inintele) nut butter which in turn is used to cook vegetables in Hwange district (Brazier, 2020). Some of the nuts such as P. curatellifolia can be roasted, seasoned with salt, and consumed as snacks (Benhura et al., 2013). Nuts have a long shelf life and can last for weeks or months depending on the storage conditions. Traditional processing methods used and hygiene practices employed are subjective depending on the processor hence they are not standardized.

Commercial value of indigenous fruits in Zimbabwe
Indigenous fruits are important cash plants for 26%-50% rural communities and dietary supplements, especially during times of famine (Elago 2016;Ham et al. 2008). In Zimbabwe, indigenous fruits have been reported to reduce poverty by at least 33% in households when in season (Chadare et al., 2009;Mithöfer & Waibel, 2003). As a result of the positive impact of indigenous fruits on household income, harvesting of these fruits for marketing purposes is increasing annually (Elago, 2016;Ramadhani, 2002). There are many opportunities for commercialization of many indigenous fruits in Africa, which are yet to be explored. In Zimbabwe, some of the few indigenous fruits that have been commercialized by Bio innovation Zimbabwe are baobab, marula, and sourplum (Murekedzi, 2019). The company exports most of its products to American and European markets, but local sales are low as a result of the negative perception on indigenous fruits. Indigenous fruits are generally regarded as poor man's food and hence have been marginalized and left out even in policy making.
The value chain for indigenous fruits in Zimbabwe has no clear framework in the formal market as compared to exotic fruits. It is not regulated by the country's policies, and therefore, each player dictates his/her own price, method of storage/transportation and packaging (Dubey et al., 2020). The value chain for indigenous fruits includes the fruit collectors, retailers, wholesalers, middlemen, and consumers (Ramadhani, 2002). The fruit collector sells to both the retailer and wholesaler or directly to the customer, whereas the wholesaler sells to the retailer depending on who is the vendor in that particular value chain (Moombe, 2009). The fruit collectors are the first link in the value chain of indigenous fruits (Figure 2). There are no fixed relationships between the fruit suppliers and the retailers or wholesalers as any retailer can buy from any supplier depending on price and fruit availability (Karaan et al., 2006). The transactions are also done using cash, and specifications such as cold chains are not observed. Exotic fruits such as oranges and apples have a cold value chain as they are transferred from the farm to the food processors and major retailers (Elik et al., 2019).
The indigenous fruit market is generally informal and small  and the marketing system of indigenous fruits does not have a clear separation of marketing activities or formal pricing system (Chawafambira et al., 2020). This is because anyone can become a collector, vendor, and a consumer at the same time. Unlike their exotic counterparts, indigenous fruits lack product differentiation at production level as there is no grading, packing, or washing of the collected fruits prior to sale (Chawafambira et al., 2020). The pricing of indigenous fruits is based on the regional location of the market (Kadzere & Jackson, 1997). One of the major informal markets of indigenous fruits is Mbare market in Harare (Karaan et al., 2006).
The commercial value of each type of indigenous fruit is determined by its popularity, supply, demand, and availability. Wholesale traders at the Mbare market buy substantial volumes of indigenous fruits from collectors of an average 1036 × 20-liter containers whilst in the rural markets they buy an average of 15 containers. This may be because of easy accessibility of indigenous fruits in rural areas, hence demand is low. As a result, the commercial value of indigenous fruits in rural areas is less than that in urban areas where the commodity is scarce. The other cause of low commercial value is the mass fruiting season which is short hence resulting in an influx of supply over demand subsequently causing a fall in prices during harvesting periods .
Existing studies revealed that trading of indigenous fruits is a profitable enterprise . Indigenous fruit collection is an efficient labor allocation strategy, and its returns to labor are considerably higher than that of crop production (Mithöfer & Waibel, 2003). Although indigenous fruits are found in the market, they are traded in the informal sector and thus do not appear in national statistics. In a survey conducted in the south of Zimbabwe drier regions wild fruits contribute about 16% of household income (cash and in kind). Sales of about 20 buckets of indigenous fruits such as U. kirkiana accumulated an average gross income of 971ZWD at rate of 1USD = 38ZWD which was equivalent to $25USD (Mithöfer & Waibel, 2003). In some Sub-Saharan Africa countries like Namibia non-timber forest products contribute directly and indirectly to the national economy (Elago & Tjaveondja, 2015). In 2004 it was estimated to be $77 432.37USD. For example, S. cocculoides in Kavango community is used to produce a liquor that is exported to South Africa. In rural setups, the S. cocculoides fruits are sold on the road side at $0.06 to $0.13USD per fruit. Likewise, in Zimbabwe fruits such as U. kirkiana and S. cocculoides are sold on the road sides and local markets. The Collection of U. kirkiana generated $50USD in Zimbabwe and Sclerocarya birrea generated $78 in South Africa . A Southern Africa natural products trade association (Phytotrade, 2005) reported gross revenue of $629 500USD from sale of natural tree products with Sclerocarya birrea fetching $126 420USD, Ximenia caffra $44 120, and Adansonia digitata $22 250.
A survey conducted in Domboshava indicated that harvesting and marketing of fruitsfor example, Uapaca kirkiana, was mostly practiced by women. The range of income generated from Uapaca kirkiana was US$10-260 per annum after post-harvest losses (Chadzimura, 2016). Indigenous fruits marketing and trading are essential for economic development as evidenced by (Karaan et al., 2006). However, the income generated from indigenous fruits varies as there is no standard mechanism for setting market prices. The prices are determined by the quantity of fruit in that season, labor costs, and transport . Lack of a standard unit of measurement is also a contributing factor for the difference in prices of the same fruit, for example, some vendors use cups, plates, tins, and buckets, which makes it difficult to compare the prices (Ramadhani, 2002).

Figure 2. Indigenous fruit(s) value chain in Zimbabwe
Apart from price instability, one of the major issues experienced during marketing of indigenous fruits is post-harvest losses. Most fruit harvesters in Zimbabwe experience fruit losses of 50%-70% during marketing (Ramadhani, 2002). This may be due to insufficient market infrastructure and lack of effective storage techniques. Losses of fruits due to harvesting methods, handling, and transportation accounts for 83% of the total fruit loss and it is the most economically important loss. Other sources of loss include the use of inappropriate containers such as sacks instead of baskets (3%), rotting (11%) and excessive heat (3%). Sacks encourage sweating and accumulation of heat in the fruits leading to microbial spoilage and subsequent rotting of the fruits due to minimum aeration. Some wholesalers, especially in Mbare, store fruits in piles of heaps where there is no protection from harsh weather conditions such as high temperatures and rain, thus reducing the quality in turn the commercial value of the fruits . Depending on the popularity and demand of the fruit, some of the fruits such as S. cocculoides are harvested, while unripe and later ripened by traders. This is due to the competition in demand of the fruits hence any delay in harvesting the fruits will result in shortage of the supply (Elago, 2016).

Conclusion
This review was able to critique traditional methods of harvesting, post-harvest handling, and marketing of some of the indigenous fruits in Zimbabwe and how they move along the value chain from the collector to the consumer. Most of the traditional methods employed can be used to produce edible products. However, there is need to upgrade/optimize these methods if commercialization of indigenous fruits is to be successful. A clear framework for processing and marketing of indigenous fruits has to be developed, and indigenous knowledge on processing and preservation for most of the fruits needs to be studied using surveyswhile updating current information on reported ones.