Isolation of spoilage microorganisms and evaluation of yeast inhibitory activity in selected traditional beverages in Sokoto State, Nigeria

Traditional beverages that include Kunun aya, Kunun zaki, Zobo, Ginger drink, and Fura are widely consumed in Sokoto State, Nigeria. Their high-water activity, manual handling, and lack of preservatives render them susceptible to microbial spoilage. Saccharomyces cerevisiae has potential as a natural biocontrol agent against spoilage organisms. This study aimed to isolate and identify common spoilage microorganisms in selected traditional beverages and evaluate the inhibitory activity of S. cerevisiae against them. A total of 200 samples (40 per beverage type) were collected from households, market vendors, and small-scale processors in Four (4) selected Local government Areas of Sokoto State. Total bacterial and fungal counts were determined using standard plate count techniques, and isolates were identified phenotypically. Yeast inhibitory activity was assessed via agar well diffusion, co-culture broth assays, cell-free supernatants, and in-matrix challenge tests. Data were analysed using ANOVA (p < 0.05). Bacterial loads ranged from 3.51 to 5.61 log₁₀ CFU/mL, with Fura and Kunun Zaki exhibiting the highest contamination, whereas Zobo exhibited the lowest. Fungal loads ranged from 2.41 to 4.01 log₁₀ CFU/mL, with Fura having the highest levels. Predominant spoilage organisms included Bacillus spp., Staphylococcus aureus, E. coli, Enterobacter spp., Aspergillus niger, and Candida spp. S. cerevisiae significantly inhibited these organisms, producing inhibition zones of 8.5–14.2 mm and reducing bacterial counts by 2.6–3.5 log₁₀ CFU/mL within 48 hours. Fura and Kunun zaki are highly susceptible to microbial contamination, whereas Zobo is more microbiologically stable. S. cerevisiae effectively inhibited spoilage organisms, demonstrating its potential as a natural biocontrol agent to enhance the safety and shelf-life of traditional beverages. Vendors and households should adopt strict hygiene practices during beverage preparation, including cleaning of utensils and containers, to reduce initial microbial loads.