Moulds and their secondary metabolites associated with the fermentation and storage of two cocoa bean hybrids in Nigeria
Introduction
Globally, cocoa (Theobroma cacao L.) is an important food source in many homes due to the frequent consumption of its processed/finished forms such as biscuits, chocolate, chocolate drinks, cocoa powder and sweets (Sanchez–Hervas et al., 2008). It is a cash crop predominantly cultivated in the West and Central Africa regions where annual optimal temperatures are in the range of 28–32 °C. According to FAOSTAT (2017), Nigeria ranked fourth on the global scale for cocoa production at 328,263 tons; thus, this crop is highly prized as a major export crop to other parts of world. In Nigeria as well as other cocoa-producing countries, harvested cocoa pods are broken open to obtain the beans which are then fermented, dried and stored prior to industrial processing into cocoa-based products or exportation to other countries (Kamphuis, 2009). In these countries, these initial processing steps (fermentation, drying and storage) are often performed under poor conditions that favour fungal contamination and proliferation in the samples due to the relatively poorly developed food processing systems (Copetti et al., 2010; Gutiérrez, 2017; Hatmi et al., 2015). Furthermore, the seasonal production of cocoa makes the storage over a long period (up to six months) essential. In Nigeria, the dried fermented beans are normally stored in wooden baskets or jute bags for a period of one to three months.
Fermentation of cocoa seeds is an absolute requirement for the development of chocolate flavor precursors; however, fungi may threaten the outcome of the process when they proliferate during this production step (Copetti et al., 2014; Hatmi et al., 2015). Several studies have reported fungal and/or mycotoxin contamination of different cocoa products (beans, powder or chocolates) at different stages of processing (farm, fermentation and on shelve/market) in various countries, including Nigeria (Adebayo, 2016; Aroyeun et al., 2007; Aroyeun et al., 2009; Copetti et al., 2010; Copetti et al., 2011; Egbuta et al., 2013; Fapohunda et al., 2018; Hatmi et al., 2015; Naz et al., 2017; Ogundeji and Olufolaji, 2015; Pires et al., 2019; Raters and Matissek, 2005; Sanchez–Hervas et al., 2008). However, the studies from Nigeria mostly included farm, stored or market samples (Adebayo, 2016; Aroyeun et al., 2009; Egbuta et al., 2013; Fapohunda et al., 2018; Ogundeji and Olufolaji, 2015) with limited information on samples during fermentation (Aroyeun et al., 2007). Thus, there is paucity of information on the diversity of fungi and multiple secondary metabolites including mycotoxins that could contaminate cocoa beans during processing/fermentation of cocoa in Nigeria. Furthermore, there is a gap in extensive secondary metabolite profiling of fungal contaminants of cocoa processing globally. Understanding these fungal contaminants and their secondary metabolite patterns using robust analytical techniques such as the liquid chromatography tandem mass spectrometry (LC–MS/MS) may aid the prediction of possible food safety risks to consumers of cocoa and its products. Therefore, this study assessed the fungal profile and fungal metabolite patterns in cocoa beans processed in Nigeria with a view to determine the safety of cocoa beans during fermentation and storage. The potential of the fungi recovered from the beans to produce secondary metabolites in culture media was also examined.
Section snippets
Sampling of cocoa pods
Cocoa pods of two hybrids, F series and T series, were collected between late December 2016 and end of January 2017 from the cocoa plantation of the Cocoa Research Institute of Nigeria, Ibadan. Only fully ripened pods were harvested; physically damaged or diseased pods with lesions were sorted out and discarded. The remaining healthy pods were retained in the open field for no >48 h prior to processing.
Cocoa beans fermentation and storage
Fermentation and storage of the cocoa beans were performed at the facilities of the Cocoa
Moisture, pH and fungal species during cocoa fermentation and storage
The moisture content of the two cocoa hybrids ranged from 8.19% to 18.72%, with significantly (p < 0.05) higher levels in bean samples collected before fermentation (F series: 18.40 ± 0.32; T series: 15.21 ± 0.11) than in sun-dried fermented beans (F series: 8.43 ± 0.24; T series: 8.72 ± 0.12). The moisture content level for cocoa (8%; Guehi et al., 2007; Legrand, 1999) reported to limit fungal invasion was exceeded in the dried samples, suggesting that the drying process was insufficient due
Conclusion
This study assessed the fungal profile and fungal metabolite patterns in cocoa beans processed in Nigeria with a view to determine the safety of cocoa beans during fermentation and storage. The potential of the fungi recovered from the beans to produce secondary metabolites in culture media was also examined. Fungi in the samples were diverse and included toxigenic species such as those capable of producing citrinin – a nephrotoxic compound. Inadequate drying and poor storage of the beans were
Declaration of competing interest
Authors have no conflict to declare.
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