Microbial food safety and sustainable resource management in cassava-based processing systems

Cassava (Manihot esculenta Crantz) is one of Mozambique´s main staple crops, crucial for rural food security and livelihoods. However, its traditional processing into cassava roasted flour (rale) and other products generates considerable amount of solid and liquid residues that remain underutilised, while the associated handling practices may compromise food safety.This thesis investigates three interlinked aspects of cassava processing and utilisation: (i) the microbial safety and hygienic quality of rale produced in smallholder processing units; (ii) the potential of cassava residues as feedstocks for microbial lipid and ethanol production; and (iii) the cyanide tolerance of yeasts from cassava-processing environments.Microbial analyses showed that, although occasional microbial contaminants were detected, rale met microbial safety limits, with roasting acting as the key step in reducing both microbial loads and cyanogenic compounds. Enzymatic hydrolysis and yeast fermentation of cassava residues demonstrated efficient conversion of these into microbial lipids and ethanol by Rhodotorula toruloides CBS 14 and Saccharomyces cerevisiae J672, respectively. In parallel, isolates of microbes from cassava effluents, such as Pichia bovicola J709 and Magnusiomyces ingens J711, exhibited notable cyanide tolerance, suggesting potential for biological effluent detoxification.Overall, the study integrates food safety, residue valorisation, and microbial detoxification within cassava processing systems, highlighting the feasibility of combining safe food production with bio-based waste conversion and management. The findings in the work contribute to sustainable cassava bioprocessing strategies and can support Mozambique´s transition towards a circular, residue-driven bioeconomy.