Effect of lactic acid bacteria fermentation and tigernut supplementation on the nutritional quality and microbial safety of Kunun zaki beverage

Kunun zaki is a traditional cereal-based fermented beverage widely consumed in West Africa; however, its nutritional quality and microbiological stability are often limited due to spontaneous fermentation. This study investigated the effects of controlled fermentation using defined lactic acid bacteria (LAB; Lactobacillus acidophilus and Lactobacillus plantarum) combined with graded tigernut supplementation (10–40%) on the amino acid composition and microbial quality of sorghum-based kunun zaki beverage. Five formulations were produced: a spontaneously fermented 100% sorghum (control) and four LAB-inoculated sorghum-tigernut blends. Amino acid profiles were determined and microbiological quality was assessed during 72 h of storage. Controlled LAB fermentation significantly improved the essential amino acid profile of kunun zaki, with notable increases in lysine, isoleucine, and valine in tigernut-enriched formulations (p < 0.05), indicating enhanced protein quality. Tigernut supplementation contributed to compositional complementation, further increasing essential amino acid density without disrupting the EAA/NEAA balance. LAB-fermented samples exhibited sustained LAB dominance (>5.5 log10 CFU/mL), absence or minimal detection of coliforms and fungi and improved microbial stability compared with the control during storage. Among the formulations, the 70% sorghum: 30% tigernut blend demonstrated the most balanced nutritional and microbiological profile. These findings demonstrate that integration of defined LAB starter cultures with optimized tigernut inclusion represents an effective biotechnology strategy for enhancing the nutritional value, microbial safety and storage stability of kunun zaki, thereby supporting its development as an improved functional beverage with commercialization potential.