Nutrients and contaminants in processed small indigenous fish species from Ghana : Implications for food and nutrition security

Abstract

The prevalence of malnutrition is increasing globally, along with the need to access nutritious, safe and sustainable foods. Fish are known as a rich source of protein, essential fatty acids and micronutrients, and including small indigenous fish species (SIS) in the diet has been proposed as a strategy towards alleviating malnutrition. SIS are a central part of the diet in Ghana and are commonly preserved by smoking or drying. Still, stunting and micronutrient deficiencies among young children persist. Furthermore, the livelihoods of millions of Ghanaians depend on the small-scale fisheries, from fishers and traders, to processors and market women. Having reliable data on SIS availability and food composition data on nutrients and contaminants in SIS is therefore essential to assess its potential role towards improving food and nutrition security (FNS) in Ghana.

The broad aim of this thesis was to explore how SIS contribute to FNS in Ghana, while specific aims of the study were addressed in three articles: Firstly, we aimed to assess the current challenges and opportunities in the Ghanaian fish value-chain through a literature review, and assess how future strategies can strengthen the role of SIS towards enhancing FNS. Secondly, we aimed to determine the nutritional quality and food safety of six commonly consumed processed SIS from Ghana by analyzing key nutrients, heavy metals, PAHs and microbial contamination. Lastly, we aimed to determine nutrient and contaminant distribution in tissues of smoked European anchovy and assess how exposure potentially affects vulnerable population groups.

Through a narrative literature review, we found that uncertainties in fish availability and access are challenging the sustenance of the millions of Ghanaians involved in the small-scale fisheries value-chain. The synthesized data further indicated that fish utilization is constrained by inadequate young child feeding practices and food safety issues, while seasonality and climate changes are hindering stability.

To assess the nutritional quality and food safety of commonly consumed SIS, samples of smoked European anchovy (Engraulis encrasicolus) bigeye grunt (Brachydeuterus auritus), round sardinella (Sardinella aurita), African moonfish (Selene dorsalis), dried/smoked West African (WA) pygmy herring (Sierrathrissa leonensis) and salt dried tilapia (Tilapia spp.) were collected from fish markets in five different regions in Ghana. Samples of European anchovy were divided into subsamples of whole fish, heads and skin and samples without heads and skin. Using accredited methods, composite samples of SIS were analyzed for nutrients (crude protein and fat, fatty acids, key vitamins, minerals, and trace elements), microbiological quality and contaminants (PAH4 and heavy metals). The marine SIS, tissues of European anchovy and WA pygmy herring had the potential to significantly contribute to the nutrient intakes of essential micronutrients, including Fe, Zn, I, Se, Ca, vitamin D, vitamin B12 and ω-3 polyunsaturated fatty acids (PUFAs), while tilapia was the least nutrient dense. High levels of Fe, Hg, Pb and Cd were detected in certain SIS and tissues and PAH4 in all smoked fish samples reached high concentrations, up to 1,300 μg/kg. In a scenario referencing Ghanaian infants and toddlers (6-23 months), it was determined that consuming smoked SIS will entail potential risk in terms of Cd and PAH-exposure.

In this thesis, we determined that processed SIS contain high levels of nutrients and represent a promising food-based approach to alleviate micronutrient deficiencies in Ghana. However, the current levels of certain heavy metals and PAHs above recommended limits may entail potential consumer risk. Generating data on dietary intakes of SIS, identification of contamination sources and improvement of processing methods are therefore warranted in order to secure safe utilization of SIS in Ghana. Furthermore, the current lack of focus on fish and FNS in scientific literature and legislation highlights the need for fish to be given greater priority, which is essential to secure the sustenance of Ghana’s small-scale fisheries.