Global literature review - Food and nutrition security

A range of development initiatives have made the case that dried fish is essential to reducing malnutrition among the world's poor. The FAO has promoted sun-dried fish production to tackle food insecurity in Somalia [1], for instance, while nutrition scientists funded by DANIDA have engineered nutrition-dense food supplements that include dried fish, designed for the extremely poor in Cambodia [2] and Kenya [3]. Consumption surveys indicate that traditionally-dried fish already provides a significant proportion of animal protein intake in the Global South, particularly among urban consumers [4]. Small fish - which are typically processed and consumed whole - additionally provide a majority of calcium intake among the poorest, leading to such fish having been described as the "milk of Southeast Asia" [5].

The importance of dried fish to food security in arid regions is evident from historical and archaeological records. In the Sudan, for example, Dirar has argued that dried fish emerged, along with other dried and fermented foods, as "famine" or "survival" foods designed to help overcome food shortages [6]. Similarly, there is evidence that dried fish had a particularly important food security role in the arid Middle East, as a primary food during periods of extreme food scarcity among inland communities, serving also as livestock feed and fertilizer for date trees [7].

A significant applied and “grey” literature exists concerning health, nutrition, and food security. Household surveys and market inventories by FAO, WorldFish, and other international organizations [8] provide a sense of consumption patterns in individual countries or communities, although this information is not necessarily comparable across sites, and fish consumption data tend to be disaggregated by species but not by fish product (fresh, frozen, dried, or fermented). Development-sector technical reports often address improvements to dried fish production as a means to greater food security, with a focus on post-harvest loss reduction [9].

A substantial proportion of nutritional research concerning dried and fermented fish involves either nutrient or microbiological analysis of existing products. Nutrient content analysis has proven useful in demonstrating the nutritional value of dried and fermented fish products, typically by profiling the micronutrients, protein, fatty acids, fibre, ash, and moisture content of products available in local markets [10]. Some studies have tested the effects on nutritional profiles of temperature and other environmental storage conditions [11], methods of fish handling and evisceration [12], degree of fermentation [13], salt concentration [14], or smoking and drying techniques [15], suggesting the possibility of enhancing nutritional quality through processing improvements.

Several research groups have isolated and characterized lactic acid bacteria strains in fermented fish products, supporting the goal of improving production technologies or developing mixed starter cultures for industrial processing of products with optimal sensorial, probiotic, and microbial safety characteristics. Such research has examined products as varied as hentak, a fermented sun-dried powdered fish from India [16]; adjuevan, a condiment produced from spontaneously-fermented fish in Cote d'Ivoire [17]; suan yu, a Chinese fish snack made by mixing fermented then dried fish pieces with spices and corn meal [18]; and ngachin, small fish fermented with boiled rice in Myanmar [19].

Food quality analyses have identified various forms of contamination affecting traditionally produced dried fish. In addition to physical contaminants such as sand [20], dried fish have been found to be contaminated with heavy metals such as lead and mercury [21] or microplastics [22]. A more significant and widespread source of contamination involves hazardous pesticides applied directly to fish by processers and traders to prevent losses due to blowfly and beetle infestation. Although widespread application of controlled or banned toxins such as DDT and dichlorvos has been a recognized problem since the 1980s [23], safe alternatives have yet to be adopted on a wide scale. Hazardous pesticide levels continue to be detected in dried and smoked fish samples from Nigeria [24], India [25], and Bangladesh [26]. A substantial number of microbiological studies of dried and fermented fish products have identified unsafe bacteria or fungi in commercially available products from local markets, occasionally measured in relation to variables such as storage temperature [27], the use of improved technologies such as solar dryers [28], ingredients and processing conditions [29], or starter cultures used in fermentation [30]. The survival of zoonotic parasites in fermented fish products is also a potential concern [31], albeit one that has not received much research attention. Finally, in the case of smoked fish, several studies have measured known genotoxins, notably the carcinogenic polycyclic aromatic hydrocarbons (PAH) that commonly occur in smoked foods, with recent analyses of product samples from Sub-Saharan Africa, Eastern Europe, and Asia finding PAH levels far in excess of limits set in food safety standards [32]. While concern for the creation or better enforcement of food safety standards is an underlying theme of all this research, more stringent testing on its own may be unable to eliminate some sources of food contamination - such as mercury from artisanal mines, an attributed source of dried fish contamination in Ghana [33].

Microbiological and food quality analyses have also been applied in testing a range of new products, which may be designed to achieve better food safety or nutritional parameters than traditional equivalents. Examples of such initiatives include dried fish powder using byproducts from fish processing factories in Ghana, intended to meet the nutritional needs of the extremely poor [34]; fish smoked in kilns rather than on bamboo racks in India [35]; dried fish produced locally in Nigeria using a solar tent dryer, to replace low-quality imported dried fish [36]; or a fish sauce produced in India using a new starter culture that reduces fermentation time and improves nutritional quality [37]. Some researchers have explored the use of new technical methods for accurately identifying fish species used in salted products [38] or rapidly identifying biogenic amines in salted fish samples [39].

Although the pace of research on the dietary impacts of dried fish consumption has slowed, research from previous decades linked regular consumption of salted or smoked fish to various disease risks. In particular, multiple dietary studies from the 1980s and 1990s identified salted fish consumption as a risk factor contributing to the relatively high incidence of nasopharyngeal carcinoma among Cantonese, Malaysian, and other South-East Asian groups [40], though this correlation has more recently been challenged [41]. Other research has suggested a connection between salted fish intake and hypertension [42] and brain cancer risk [43], while fermented fish sauce has been linked to esophageal cancer [44]. Carcinogenic N-nitroso compounds have also been identified in fermented, salted, and dried fish in Thailand and China [45]. Among smoked fish producers, long-term and continuous exposure to smoke can additionally be a source of respiratory disease [46].

Overall, research on food safety and nutritional aspects of dried and fermented fish addresses several long-standing challenges. As early as the 1970s field experiments were being conducted with the use of improved fish-drying methods such as elevated racks [47] or the application of less hazardous pesticides (such as pyrethrins) to control blowfly and beetle infestations during sun-drying of fish [48]. The poor adoption of safe and effective processing technologies indicates a need for greater attention to the socio-economic factors that may limit their uptake.